Multi-wavelength characterization of the blazar S5~0716+714 during an unprecedented outburst phase
MAGIC Collaboration, M. L. Ahnen, S. Ansoldi, L. A. Antonelli, C. Arcaro, D. Baack, A. Babić, B. Banerjee, P. Bangale, U. Barres de Almeida, J. A. Barrio, J. Becerra González, W. Bednarek, E. Bernardini, R. Ch. Berse, A. Berti, W. Bhattacharyya, A. Biland, O. Blanch, G. Bonnoli, R. Carosi, A. Carosi, G. Ceribella, A. Chatterjee, S. M. Colak, P. Colin, E. Colombo, J. L. Contreras, J. Cortina, S. Covino, P. Cumani, P. Da Vela, F. Dazzi, A. De Angelis, B. De Lotto, M. Delfino, J. Delgado, F. Di Pierro, A. Domínguez, D. Dominis Prester, D. Dorner, M. Doro, S. Einecke, D. Elsaesser, V. Fallah Ramazani, A. Fernández-Barral, D. Fidalgo, M. V. Fonseca, L. Font, C. Fruck, D. Galindo, S. Gallozzi, R. J. García López, M. Garczarczyk, M. Gaug, P. Giammaria, N. Godinović, D. Gora, D. Guberman, D. Hadasch, A. Hahn, T. Hassan, M. Hayashida, J. Herrera, J. Hose, D. Hrupec, K. Ishio, Y. Konno, H. Kubo, J. Kushida, D. Kuveždić, D. Lelas, E. Lindfors, S. Lombardi, F. Longo, M. López, C. Maggio, P. Majumdar, M. Makariev, G. Maneva, M. Manganaro, K. Mannheim, L. Maraschi, M. Mariotti, M. Martínez, S. Masuda, D. Mazin, K. Mielke, M. Minev, J. M. Miranda, R. Mirzoyan, A. Moralejo, V. Moreno, E. Moretti, T. Nagayoshi, V. Neustroev, A. Niedzwiecki, M. Nievas Rosillo, C. Nigro, K. Nilsson, et al. (90 additional authors not shown)
AAstronomy & Astrophysics manuscript no. main˙02˙07˙2018 c (cid:13)
ESO 2019August 13, 2019
Multi-wavelength characterization of the blazar S5 0716+714 duringan unprecedented outburst phase
MAGIC Collaboration: M. L. Ahnen , S. Ansoldi , , L. A. Antonelli , C. Arcaro , , D. Baack , A. Babi´c ,B. Banerjee , P. Bangale , U. Barres de Almeida , , J. A. Barrio , J. Becerra Gonz´alez , W. Bednarek ,E. Bernardini , , , , R. Ch. Berse , A. Berti , , W. Bhattacharyya , A. Biland , O. Blanch , G. Bonnoli ,R. Carosi , A. Carosi , G. Ceribella , A. Chatterjee , S. M. Colak , P. Colin , E. Colombo , J. L. Contreras ,J. Cortina , S. Covino , P. Cumani , P. Da Vela , F. Dazzi , A. De Angelis , , B. De Lotto , M. Delfino , ,J. Delgado , F. Di Pierro , , A. Dom´ınguez , D. Dominis Prester , D. Dorner , M. Doro , , S. Einecke ,D. Elsaesser , V. Fallah Ramazani , A. Fern´andez-Barral , , , D. Fidalgo , M. V. Fonseca , L. Font , C. Fruck ,D. Galindo , S. Gallozzi , R. J. Garc´ıa L´opez , M. Garczarczyk , M. Gaug , P. Giammaria , N. Godinovi´c ,D. Gora , D. Guberman , D. Hadasch , A. Hahn , T. Hassan , M. Hayashida , J. Herrera , J. Hose , D. Hrupec ,K. Ishio , Y. Konno , H. Kubo , J. Kushida , D. Kuveˇzdi´c , D. Lelas , E. Lindfors (cid:63) , S. Lombardi , F. Longo , ,M. L´opez , C. Maggio , P. Majumdar , M. Makariev , G. Maneva , M. Manganaro (cid:63) , K. Mannheim ,L. Maraschi , M. Mariotti , , M. Mart´ınez , S. Masuda , D. Mazin , , K. Mielke , M. Minev , J. M. Miranda ,R. Mirzoyan , A. Moralejo , V. Moreno , E. Moretti , T. Nagayoshi , V. Neustroev , A. Niedzwiecki , M. NievasRosillo , C. Nigro , K. Nilsson , D. Ninci , K. Nishijima , K. Noda , L. Nogu´es , S. Paiano , , J. Palacio ,D. Paneque , R. Paoletti , J. M. Paredes , G. Pedaletti (cid:63) , M. Peresano , M. Persic , , P. G. Prada Moroni ,E. Prandini , , I. Puljak , J. R. Garcia , I. Reichardt , , W. Rhode , M. Rib´o , J. Rico , C. Righi , A. Rugliancich ,T. Saito , K. Satalecka , T. Schweizer , J. Sitarek , , I. ˇSnidari´c , D. Sobczynska , A. Stamerra , M. Strzys ,T. Suri´c , M. Takahashi , L. Takalo , F. Tavecchio , P. Temnikov , T. Terzi´c , M. Teshima , , N. Torres-Alb`a ,A. Treves , S. Tsujimoto , G. Vanzo , M. Vazquez Acosta , I. Vovk , J. E. Ward , M. Will , D. Zari´c ;from Fermi -LAT Collaboration: D. Bastieri , D. Gasparrini , B. Lott , B. Rani (cid:63) , D. J. Thompson ;MWL Collaborators: I. Agudo , E. Angelakis , G. A. Borman , C. Casadio , , T. S. Grishina , M. Gurwell ,T. Hovatta , , , R. Itoh , E. J¨arvel¨a , , H. Jermak , S. Jorstad , , E. N. Kopatskaya , A. Kraus ,T. P. Krichbaum , N. P. M. Kuin , A. L¨ahteenm¨aki , , V. M. Larionov , , L. V. Larionova , A. Y. Lien ,G. Madejski , A. Marscher , I. Myserlis , W. Max-Moerbeck , S. N. Molina , D. A. Morozova , K. Nalewajko ,T. J. Pearson , V. Ramakrishnan , A. C. S. Readhead , R. A. Reeves , S. S. Savchenko , I. A. Steele ,M. Tornikoski , Yu. V. Troitskaya , I. Troitsky , A. A. Vasilyev , and J. Anton Zensus (A ffi liations can be found after the references) ABSTRACT
Context.
The BL Lac object S5 0716 + Aims.
The comprehensive dataset collected is investigated in order to shed light on the mechanism of the broadband emission.
Methods.
Multi-wavelength light curves have been studied together with the broadband Spectral Energy Distributions (SEDs). The data setcollected spans from radio (E ff elsberg, OVRO, Mets¨ahovi, VLBI, CARMA, IRAM, SMA), UV ( Swift -UVOT), optical photometry and polarimetry(Tuorla, Steward, RINGO3, KANATA, AZT-8 + ST7, Perkins, LX-200), X-ray (
Swift -XRT and
NuSTAR ), high-energy (HE, 0.1 GeV ¡ E ¡ 100 GeV)with
Fermi -LAT to the very-high-energy (VHE, E¿100 GeV) with MAGIC.
Results.
The flaring state of Phase A was detected in all the energy bands, providing for the first time a multi-wavelength sample of simultaneousdata from the radio band to the VHE. In the constructed SED the
Swift -XRT + NuSTAR data constrain the transition between the synchrotronand inverse Compton components very accurately, while the second peak is constrained from 0.1 GeV to 600 GeV by
Fermi + MAGIC data. Thebroadband SED cannot be described with a one-zone synchrotron self-Compton model as it severely underestimates the optical flux in order toreproduce the X-ray to γ -ray data. Instead we use a two-zone model. The electric vector position angle (EVPA) shows an unprecedented fastrotation. An estimation of the redshift of the source by combined HE and VHE data provides a value of z = . ± . stats ± . sys , confirmingthe literature value. Conclusions.
The data show the VHE emission originating in the entrance and exit of a superluminal knot in and out a recollimation shock in theinner jet. A shock-shock interaction in the jet seems responsible for the observed flares and EVPA swing. This scenario is also consistent with theSED modelling.
Key words. galaxies: active – BL Lacertae objects: individual: S5 0716 +
714 – galaxies:jets – gamma-rays:galaxies 1 a r X i v : . [ a s t r o - ph . H E ] J u l . Introduction The blazar S5 0716 +
714 is a BL Lac object characterized byextreme variability in almost all energy bands. Because of thefeatureless optical continuum (Paiano et al., 2017) it is hard toestimate its redshift. Nilsson et al. (2008) claimed a value of z = . ± .
08 based on the photometric detection of the hostgalaxy. Detection of intervening Ly α systems in the ultra-violetspectrum of the source confirms the earlier estimates with a red-shift value z < .
32 (95% confidence) (Danforth et al., 2013).The familiar shape of the Spectral Energy Distribution(SED) of blazars, in which the two bumps are identified assynchrotron and inverse Compton (IC) respectively, is used fortheir classification. In the case of S5 0716 +
714 the first peakof the SED is located between 10 and 10 Hz, leading toa classification as intermediate synchrotron peaked blazar orIBL (Intermediate-peaked BL Lac object) (Giommi et al., 1999;Ackermann et al., 2011).Because of its remarkable variability, S5 0716 +
714 has beenthe subject of many optical monitoring campaigns (Wagneret al., 1996; Montagni et al., 2006; Rani et al., 2011, 2013,2015). Several authors carried out flux variability studies (e.g.Quirrenbach et al., 1991; Wagner et al., 1996) and morpho-logical / kinematic studies at radio frequencies (Antonucci et al.,1986; Witzel et al., 1988; Jorstad et al., 2001; Bach et al., 2005;Rastorgueva et al., 2011). The observed intraday variability atradio wavelengths is likely to be a mixture of intrinsic and exter-nal (due to interstellar scintillation) mechanisms. Wagner et al.(1996) reported a significant correlation between optical – radioflux variations at day-to-day timescales. Rani et al. (2010) re-ported the detection of a ∼ ffi cult taskbecause of the complexity of the flaring activity, which canvary rapidly on a timescale of a few hours to days, while on atimescale of ∼ ∼ ◦ on kiloparsecscales (Antonucci et al., 1986): Britzen et al. (2009) suggest thatthere is an apparent stationarity of jet components relative to thecore. However, recently apparent speeds of ∼
40 c have beenreported (Rastorgueva et al., 2011; Larionov et al., 2013; Listeret al., 2013; Rani et al., 2015). (Britzen et al., 2009; Rastorguevaet al., 2011; Rani et al., 2014) observed non-radial motion andwiggling component trajectories in the inner milliarcsecond jetregion.Observations by
BeppoSAX (Tagliaferri et al., 2003) and
XMM-Newton (Foschini et al., 2006) provide evidence for a con-cave X-ray spectrum in the 0.1 – 10 keV band, a signature of thepresence of both the steep tail of the synchrotron emission andthe rising part of IC spectrum.EGRET on board the
Compton Gamma-ray Observatory(CGRO) detected high-energy (HE, 0.1 GeV ¡ E ¡ 100 GeV) γ -ray emission from S5 0716 +
714 several times from 1991 to1996 (Lin et al., 1995; Hartman et al., 1999). Two strong γ -ray flares in September and October 2007 were detected in thesource with AGILE (Chen et al., 2008) in the HE range. These (cid:63)
Corresponding authors: M. Manganaro, email: [email protected];B. Rani, NPP fellow, email:[email protected]; G. Pedaletti, email:[email protected]; E. Lindfors, email: elilin@utu.fi authors also carried out SED modeling of the source with twosynchrotron self-Compton (SSC) emitting components, repre-sentative of slowly and rapidly variable components, respec-tively.S5 0716 +
714 was first detected in the very-high-energy(VHE, E¿100 GeV) range by MAGIC with 5 . σ significancelevel in November 2007 and then in April 2008 (Anderhub et al.,2009) during an optical flare. At that time MAGIC was work-ing with a single telescope and the energy threshold of the tele-scope for such an high zenith range (47 ◦ < zd < ◦ ) was 400GeV. The analysis of multi-wavelength data suggested a corre-lation between the VHE γ -ray and optical emission. A struc-tured jet model, composed of a fast spine surrounded by a slowermoving layer (Ghisellini et al., 2005; Tavecchio & Ghisellini,2009) better described the data compared to a simple one-zoneSSC model. This source is also among the bright blazars inthe Fermi -LAT (Large Area Telescope) Bright AGN Sample(LBAS) (Abdo et al., 2010) and in the
Fermi third catalog (Aceroet al., 2015) it is among the ones with the highest variability in-dex. The combined GeV – TeV spectrum of the source mightdisplay an absorption-like feature in the 10 – 100 GeV energyrange (Senturk et al., 2013).Apart from the γ -ray / optical connection, which is to be ex-pected in one-zone, single population leptonic models, anotherinteresting feature of the broadband activity was reported in Raniet al. (2013), in which the authors found the γ -ray / optical fluxvariations leading the radio variability by ∼
65 days. An orphanX-ray flare was detected in 2009 by
Swift -XRT but no VHE ob-servations were available to check if there was a counterpart inthe VHE range. The behavior of the source in the past years canbe contextualized in the scenario of a shockwave propagatingalong a helical path in the blazar’s jet (Marscher et al., 2008;Larionov et al., 2013).Recently, more attention was given to the electric vector po-sition angle swings: Rani et al. (2014) found a significant cor-relation between the inner jet outflow orientation and γ -ray fluxvariations, showing how the morphology of the inner jet has astrong connection with the γ -ray flares. Chandra et al. (2015a)studied the rapid variation in the degree of polarization (PD) andin the polarization angle (PA) within the Helical Magnetic FieldModel (HMFM) (Zhang et al., 2014), explaining such featuresas most likely due to reconnections in the emission region of thejet. In the present work, we report the results of a multi-wavelength (MWL) campaign organised to follow an unprece-dented outburst phase of the blazar S5 0716 +
714 during January2015. The source was detected at its historic highest brightnessat optical and IR bands. On January 11, 2015, (MJD 57033)the NIR photometry reported an increase of its flux by a fac-tor of 2.5 in the NIR band in a rather short lapse of 12 days(Carrasco et al., 2015; Chandra et al., 2015b). During the nightof 18 January 2015 (MJD 57040), the source was detected at itshistoric high brightness, with R band magnitude ∼ ff erent bands. Section 4 is devoted to thejet analysis of the object by VLBI. In Section 5 the spectral fit-ting of NuSTAR and
Swift -XRT data are shown. In Section 6 the . L. Ahnen et al.: MWL characterization of S5 0716 +
714 during an unprecedented outburst
VHE spectra obtained by MAGIC and the redshift estimationusing MAGIC and
Fermi -LAT simultaneous data are presented,and in Section 7 the broadband SED for the two phases con-sidered is discussed together with the modeling of the source.Results and Conclusions are given in Section 8.
2. Observations and analysis γ -ray observations MAGIC is a stereoscopic system consisting of two 17 m diam-eter Imaging Atmospheric Cherenkov Telescopes located at theObservatorio del Roque de los Muchachos, on the Canary Islandof La Palma. The current sensitivity for medium-zenith obser-vations (30 ◦ < zd < ◦ ) above 210 GeV is 0 . ± .
04 %of the Crab Nebula’s flux in 50 h (Aleksi´c et al., 2016). On19 January 2015 (MJD 57041), triggered by the high opti-cal state and by high-energy photons detected by
Fermi -LAT,MAGIC started to observe S5 0716 + σ , and it reached a maximum value of 13.2 σ on 26 January(MJD 57048): the flux increased from (4 . ± . × − cm − s − to (8 . ± . × − cm − s − above 150 GeV, which is thehighest level ever detected in the VHE band for this source.The next activity of S5 0716 +
714 in the VHE range was de-tected by MAGIC on 13 February (MJD 57066), this time last-ing four days only, up to the 16 February (MJD 57069). In thepresent work the two multi-wavelength periods of observationsthat include MAGIC data are indicated as Phase A, from 18 to 27January 2015 (MJD 57040 to MJD 57050), and Phase B from 12to 17 February 2015 (MJD 57065 to MJD 57070). We collected17.74 hours of data in the zenith angle range of 40 ◦ < zd < ◦ and the analysis was performed using the standard MAGIC anal-ysis framework MARS (Zanin et al., 2013; Aleksi´c et al., 2016).After the applied quality cuts, the survived events amount to17.46 hours in total. A statistical significance of 18.9 σ wasfound for the full sample after cuts. The significance of the signalwas calculated as in Eq. 17 in Li & Ma (1983). For the MAGICSED, the systematic uncertainty on the flux normalization wasestimated to be 11%, and on the spectral slope ± ∼
125 GeV, measured as the peak ofthe Monte Carlo (MC) energy distribution for a source with thespectral shape of S5 0716 + γ -ray observations The HE γ -ray (0.1–300 GeV) observations for a time periodbetween 1 November 2014 (MJD 56962) and 31 July 2015(MJD 57234) were obtained in a survey mode by the Fermi -LAT (Atwood et al. , 2009). The LAT data were analyzed usingthe standard ScienceTools (software version v10.01.01, pass8)with instrument response function P8R2 SOURCE V6. Photonsin the source event class were selected for the analysis. We an-alyzed a region of interest (ROI) of 10 ◦ in radius centered atthe position of S5 0716 +
714 using a maximum-likelihood algo-rithm (Mattox et al., 1996). We included all 54 sources of the3FGL catalog (Acero et al., 2015) within 20 ◦ of the position ofS5 0716 +
714 in the unbinned likelihood analysis. Model param-eters for sources within 5 ◦ of the ROI are kept free; we kept themodel parameters for the rest fixed to their catalogue values. https: // fermi.gsfc.nasa.gov / ssc / data / analysis / To investigate the source variability at E ¿100 MeV, we gen-erated the daily-binned photon flux and index curves using un-binned likelihood analysis. The daily binned data were com-puted by modeling the spectra by a power-law model (PWL,N(E) = N E − Γ , N : prefactor, and Γ : power law index). We ex-amined the spectral behavior over the whole energy range with aPWL model fitting over equally spaced logarithmic energy binswith Γ kept constant and equal to the value fit over the wholerange. Even if in the Fermi third catalog (Acero et al., 2015) thesource spectrum is described by a log parabola model, for thepresent dedicated analysis the PWL model better fits the data.The upper limits for the light curve are shown as grey trianglesin the second panel from top in Fig. 1 and they were calculatedfor test statistics ¡9.
NuSTAR
The exceptional flare from the object triggered a Target ofOpportunity observation of the object by
NuSTAR . NuSTAR , aNASA Small Explorer satellite sensitive in the hard X-ray bandfeatures two multilayer-coated telescopes, focusing the reflectedX-rays on the pixellated CdZnTe focal plane modules with thehalf-power diameter of an image of a point source of ∼ (cid:48) . Itprovides a bandpass of 3-79 keV with spectral resolution of ∼ NuSTAR
Data Analysis Software (NuSTARDAS) packagev.1.3.1 (via the script nupipeline ), the source data were ex-tracted from a region of 45 (cid:48)(cid:48) radius, centered on the centroid ofX-ray emission, while the background was extracted from a 1 . (cid:48) radius region roughly 5 (cid:48) SW of the source location. Spectra werebinned in order to have at least 30 counts per rebinned channel.We considered the spectral channels corresponding nominally tothe 3-60 keV energy range, where the source was robustly de-tected. The mean net (background-subtracted) count rates were0 . ± .
003 and 0 . ± .
003 cts s − , respectively, for the mod-ules FPMA and FPMB. We found no variability of the sourceas a function of time within the NuSTAR observation, and wesummed the data into one spectral file for each focal plane mod-ule.
Swift -XRT
The multi epochs (35) event-list obtained by the X-ray Telescope(
XRT ) (Burrows et al. , 2004), on-board the
Neil GehrelsSwift satellite in the period 1 January 2015 (MJD 57023.2)to 28 February 2015 (MJD 57081.2) with total exposure timeof ∼ Swift
XRT Instrument Log). They were pro-cessed using the procedure described in Ramazani et al. (2017).All these observations have been performed in photon count-ing (PC) mode, with an average integration time of 1.7 ks each.The equivalent Galactic hydrogen column density is fixed to thevalue of n H = . × cm − (Kalberla et al., 2005). We per-formed spectral fits to all 35 epochs using a simple power lawmodel, with Galactic absorption. This model provides a goodfit, and the 0.3 -10 keV spectral index is 2 . ± .
1. We discussthe Swift observations more extensively in Section 3. We notespecifically that one of the pointings was simultaneous with the
3. L. Ahnen et al.: MWL characterization of S5 0716 +
714 during an unprecedented outburst
NuSTAR observation (at MJD 57045–24 January 2015) and weuse that observation for joint XRT -
NuSTAR spectral fitting inSection 5.
Swift -UVOT
Photometric observations by the
Swift
Ultra-Violet and OpticalTelescope (UVOT) instrument were made in the three UV(uvw2, uvm2, and uvw1) and three optical (u, b, and v) filtersin both imaging and event mode. During the February 2015 ob-servations, good coverage in the UV and u bands exist and inparticular uvm2 data in event mode were obtained in order toresolve short timescale variability in the UV.The UVOT data reduction used the Heasarc Heasoft version6.16 and
Swift
CALDB (September 2013). The event mode datawere typically 800 s long exposures and were binned into shortertime slices, converted into images, then aspect corrected.This analysis allowed the identification of a few observationsfor which the pointing drift was too large, and those were ex-cluded from further analysis. Data taken in image mode weresimilarly validated. The magnitudes were determined from theimages using the UVOTMAGHIST program using the standardcalibration (Poole et al., 2008; Breeveld et al., 2011). The de-tails of the event mode data processing are as follows: GTI ex-tensions were created in the event file for the desired time in-tervals; UVOTATTJUMPCORR was run to improve the attitudefile; COORDINATOR and UVOTSCREEN were used to correctthe event file, which was then processed using UVOTIMAGE sothe individual data could be inspected.
The Tuorla Blazar monitoring program collects blazar opti-cal light curves in the R band from several observatories. Thepresent work shows in particular data from the 1.03 m telescopeat Tuorla Observatory, Finland and the 35 cm telescope at theKVA observatory on La Palma, Canary Islands, Spain. The dataare analyzed with a semi-automatic pipeline using standard pro-cedures (Nilsson et al., 2017)The Boston University (BU) group uses the 1.83 m PerkinsTelescope at Lowell Observatory (Flagsta ff , AZ) to carry outoptical observations of a sample of γ -ray blazars, includingS5 0716 + +
714 is one of the targets regularly monitored by thisprogram, with a time cadence of ∼ ff erentpassbands recorded in the so called ”Red”, ”Green”, and ”Blue”cameras . Here we only present the data from the ”Green” cam-era (the one with the closest wavelength passband to R-band).The RINGO3 data were reduced following the procedure ex-plained in Steele et al. (2017). http: // users.utu.fi / kani / See the RINGO3 specifications at:http: // telescope.livjm.ac.uk / TelInst / Inst / RINGO3 / R-band photometry and polarimetry observations ofS5 0716 +
714 were performed using the HONIR (HiroshimaOptical and Near-InfraRed camera) instrument installed onthe 1.5 m Kanata telescope located at the Higashi-HiroshimaObservatory, Japan (Akitaya et al., 2014). A sequence of pho-topolarimetric observations consisted of successive exposures at4 position angles of a half-wave plate: 0, 45, 22.5 and 67.5 deg.The data were reduced under the standard procedure of CCDphotometry. The aperture photometry was performed using theAPPHOT package in PYRAF , and the di ff erential photometrywith a comparison star taken in the same frame of S5 0716 + = = + = and the 40 cm telescope LX-200in St. Petersburg, both equipped with nearly identical imagingphotometers-polarimeters. Polarimetric observations were per-formed using two Savart plates rotated by 45 ◦ relative to eachother (see Larionov et al., 2008b). Instrumental polarization wasfound via stars located near the object under the assumption thattheir radiation is unpolarized. This is indicated also by the lowlevel of extinction in the direction of S5 0716 +
714 ( A V = . A R = .
067 mag; Schlafly & Finkbeiner 2011).
The 230 GHz (1.33 mm) flux density data were obtained at theSubmillimeter Array (SMA) near the summit of Mauna Kea(Hawaii). S5 0716 +
714 is included in an ongoing monitoringprogram at the SMA to determine the flux densities of compactextragalactic radio sources that can be used as complex gain cal-ibrators at mm wavelengths (Gurwell et al. , 2007). Potentialcalibrators are from time to time observed for 3 to 5 minutes.Data from this program are updated regularly and are availableat the SMA website , while the present analysis was a dedicatedone.The IRAM 30 m millimeter Radiotelescope provided230 GHz (1.3 mm) and 86 GHz (3.5 mm) data that were ob-tained as part of the POLAMI (Polarimetric AGN Monitoringat Millimeter Wavelengths) program, see Agudo et al. (2018a,b)and Thum et al. (2018). The POLAMI data of S5 0716 + γ -ray Active galactic nu-clei with Radio, Millimeter and Optical Telescopes (MARMOT)project . We used 7.5 GHz of bandwidth with a center frequencyof 94 GHz. The integration time on S5 0716 +
714 was 5 minutesfor each observation, which yields a typical rms of 10 −
110 mJy.Absolute flux density calibration was done using nearby obser-vations of Mars. The observational errors are dominated by theabsolute calibration uncertainty, assumed to be 10%. All datawere processed using the Multichannel Image Reconstruction http: // / institute / software hardware / pyraf / http: // craocrimea.ru / ru http: // sma1.sma.hawaii.edu / callist / callist.html http: // polami.iaa.es http: // / marmot /
4. L. Ahnen et al.: MWL characterization of S5 0716 +
714 during an unprecedented outburst
Image Analysis and Display (MIRIAD; Sault, Teuben & Wright,1995).We have analyzed Very Long Baseline Array (VLBA) dataobtained for S5 0716 + , which are contemporaneous with the high energy event inJanuary and February 2015. The data include total and polarizedintensity images at 43 GHz at 9 epochs from November 2014 toAugust 2015. They were reduced using the Astronomical ImageProcessing System (AIPS) and Difmap software packages,in the general manner described by Jorstad et al. (2017, 2005).The total intensity images were modeled by components withcircular Gaussian brightness distributions. This allows us to de-termine the minimum number of components that provides thebest fit between the data and model at each epoch, as well as thefollowing parameters of components: flux density, S , distancefrom the core, r , position angle with respect to the core, Θ , andsize of the component, a (FWHM of the Gaussian). These pa-rameters are given in Table A.1 of Appendix A.The 37 GHz observations were made with the Mets¨ahovi ra-dio telescope. The measurements were made with a 1 GHz-banddual beam receiver centered at 36.8 GHz. The observations areON–ON observations, alternating the source and the sky in eachfeed horn. A typical integration time to obtain one flux densitydata point is between 1200 and 1800 s. Data points with a signal-to-noise ratio ¡ 4 are handled as non-detections. The flux densityscale is set by observations of DR 21. A detailed descriptionof the data reduction and analysis is given in Ter¨asranta et al.(1998). The error estimate in the flux density includes the con-tribution from the measurement rms and the uncertainty of theabsolute calibration.S5 0716 +
714 was observed at 15 GHz as part of a high-cadence γ -ray blazar monitoring program using the OwensValley Radio Observatory (OVRO) 40 m telescope (Richardset al., 2011). The OVRO 40 m uses o ff -axis dual-beam opticsand a cryogenic pseudo-correlation receiver with a 15.0 GHzcenter frequency and 3 GHz bandwidth. The source is alter-nated between the two beams in an ON-ON fashion to removeatmospheric and ground contamination. The fast gain variationsare corrected using a 180 degree phase switch. Calibration isachieved using a temperature-stable diode noise source to re-move receiver gain drifts, and the flux density scale is derivedassuming the value of 3.44 Jy at 15.0 GHz in Baars et al. (1997).The systematic uncertainty of about 5% in the flux density scaleis not included in the error bars. Complete details of the re-duction and calibration procedure are found in Richards et al.(2011).Observations at 2.6, 4.8, 10, and 15 GHz radio bandswere conducted using the E ff elsberg 100 m radio telescope .Measurements for the target source and for the calibrator sourceswere made quasi-simultaneously using the cross-scan methodslewing over the source position, in azimuth and elevation di-rection in order to gain the desired sensitivity. Subsequently, at-mospheric opacity correction, pointing o ff -set correction, gaincorrection, and sensitivity correction were applied to the data.Details of the observations and data reduction are referred toAngelakis et al. (2015).The sources 3C 286, NGC 7027 and 3C 84 have been usedas common calibrators for the instruments listed in this section. / blazars / VLBAproject.html http: // / index.shtml ftp: // ftp.eso.org / scisoft / scisoft4 / sources / difmap / difmap.html http: // / en / e ff elsberg
3. Multi-wavelength light curves
In Fig. 1 we present the multi-wavelength data collected duringthe course of the campaign. A summary of the most importantdates can be found in Table 1. The top panel shows the daily-binned MAGIC light curve: in the VHE band, the no-variabilityhypothesis has been discarded, since the fit for a constant fluxresulted in a χ / n . d . f . = / χ / n . d . f . = / χ / n . d . f . = / χ / n . d . f . = . / ± . . ± . × − cm − s − ; the standard deviation ofthe fit is σ = (2 . ± .
5) days. Phase B peaks on 14 February2015 (MJD 57067.9 ± .
2) with a corresponding flux of (5 . ± . × − cm − s − indicated by the vertical dashed line P4.The standard deviation of the fit is σ = (1 . ± .
3) days. Intra-dayvariability (in shorter time scales with respect to the daily-binnedlight curves) was not detected with MAGIC: the light curve wasfit at di ff erent time intervals down to 5 minutes, but a constantfit was found to be consistent with the data up to the daily scale,where variability is significant.The Fermi -LAT daily-binned light curve is shown in the sec-ond panel from top: the first peak visible in the curve, markedwith the vertical dashed line P1, is the precursor of the wholeflaring activity. After P1, (MJD 57038.5, 16 January 2017),which triggered VHE observations, two other peaks are visiblein Phase A, and the maximum flux reached in HE is (8 . ± . × − cm − s − , 4 times the average flux in HE for the source fromthe Fermi -LAT 3FGL Catalog (Acero et al., 2015). The photonindex for
Fermi -LAT observations stays very close to the average
Fermi -LAT index of the source, indicated in the correspondingpanel of Fig. 1 with the horizontal dashed blue line.The average integral photon X-ray flux (0.3–10 keV) re-ported by
Swift -XRT in Fig. 1, fourth panel from top, is(1 . ± . × − erg cm − s − . The X-ray flux peaking atMJD 57047 (25 January 2015) with F (0 . − = (3 . ± . × − erg cm − s − which is a factor of ∼ . ≤ Γ X ≤ .
56. Thesoftest spectral index was obtained on the night of the highestX-ray and VHE γ -ray flux (MJD 57047–25 January 2015). TheX-ray spectra start hardening smoothly afterwards for the next14 consecutive nights. The X-ray spectra on the nights of VHE γ -ray flares of Phase A and B can be well described by a powerlaw with spectral index of Γ X , MJD = . ± .
06 (reduced χ / n.d.f. = . /
29 ) and Γ X , MJD = . ± .
06 (reduced χ / n.d.f. = . /
26) respectively.From the Tuorla optical monitoring, on 18 January 2015(MJD 57040) the magnitude in the R-band reached a value of ∼ mag ∼ mag = ± mag = ± mag = Swift -UVOT light curves show the same trend, a doublepeaked shape with the second peak coincident with the dashedvertical line P2 in Fig. 1. P2 is in fact identifying a peak not onlyin the VHE light curve, but also in the X-ray, optical, and UVbands. AZT-8 + ST7 light curve can be fit by a Gaussian peak-ing on MJD 57047 (25 January 2015) at a flux of (67 . ± . σ = . ± .
001 days.The
Swift -UVOT light curve can be fit by a Gaussian peaking on
5. L. Ahnen et al.: MWL characterization of S5 0716 +
714 during an unprecedented outburst ] - s - c m - [ F P1 P2 P3
MAGIC >150 GeV ] - s - c m - [ F - · Fermi-LAT 0.1-100 GeV i nde x F e r m i - L A T ] - s - e r g c m - [ F - · SWIFT-XRT 0.3-10 keV [ m Jy ] ( R - band ) n F Tuorla PerkinsAZT-8+ST7 LX-200KanataTuorla PerkinsAZT-8+ST7 LX-200KanataTuorla PerkinsAZT-8+ST7 LX-200KanataTuorla PerkinsAZT-8+ST7 LX-200Kanata [ m Jy ] ( U - V - B - band s ) n F UVOT B UVOT UUVOT W1 UVOT W2UVOT M2 [ Jy ] ( M illi m e t r e ) n F SMA 230GHz IRAM 230 GHzCARMA 90 GHz IRAM 86GHzhovi 37 GHzaMets [ Jy ] ( R ad i o ) n F OVRO 15 GHz Effelsberg 15GHzEffelsberg 10GHz Effelsberg 4.8GHz P o l a r i z a t i on [ % ] Kanata Perkins AZT-8+ST7LX-200 Steward RINGO3 ] (cid:176) EVPA [ Kanata Perkins AZT-8+ST7LX-200 Steward RINGO3
MJD57010 57020 57030 57040 57050 57060 57070
Phase A Phase B
Fig. 1: Multi-wavelength flux and index curves of S5 0716 +
714 during the period from MJD 57010 to MJD 57080 (19 December2014 to 27 February 2015). The shadowed areas indicate Phase A (from 18 to 27 January 2015 – MJD 57040 to MJD 57050) andPhase B (from 12 to 17 February 2015 – MJD 57065 to MJD 57070) high states in the VHE range and the corresponding activity inthe other bands. P1, P2 and P3 (vertical dashed lines) indicate peaks in the HE and VHE emission.MJD 57047 (25 January 2015) at a flux of (50 . ± .
1) mJy. Thestandard deviation of the fit is σ = . ± .
02 days. The activity in the radio band shown in Fig. 1 in Phase Aand Phase B is moderate compared to the other energy bands but
6. L. Ahnen et al.: MWL characterization of S5 0716 +
714 during an unprecedented outburst
Table 1: Summary of important dates
MJD Calendar date Description57038.5 16 January 2015 P1: first peak of the HE emission → trigger VHE observations57040 18 January 2015 start of Phase A57044 /
45 22 /
23 January 2015 1day EVPA rotation of ∼ ◦ ± ± ± Energy [GeV] - - - - ] - s - d N / d E [ T e V c m E - - - - - - - va r F Phase A var
F Phase B var
FMWL SED 26 Jan
Fig. 2: Fractional variability ( F var ) as a function of the energy for Phase A and Phase B. Vertical bars denote 1 σ uncertainties. Ingray a Spectral Energy Distribution of the source is overlayed (a snapshot of 26 January 2015), to make easier to associate the valueof the fractional variability to the corresponding energy band.does not describe a simply quiescent radio state. In the past thesource has gone through many high states in the radio band, forinstance the one described in Rani et al. (2013), Fig. 2, namedR6. During the R6 flare, the highest flux density reported was ∼
10 Jy while in the present one, the highest level of radio fluxdensity at the same frequency (230 GHz) is only 5 Jy. We studyin more detail the possible delay between radio and optical / γ -raybands in Sec. 3.1.As reported in Chandra et al. (2015a), the Phase A flarepresents a double peaked shape in the HE γ -ray and opticalbands. The feature is particularly evident in the R-band. The γ -ray light curve has the first sub-peak (in Fig. 1 corresponding tothe P1 vertical dashed line) located immediately before Phase Aat MJD 57038.5 (16 January 2015). That indicates the optical / γ -ray emission as possible precursors of the VHE activity, whosepeak starts to rise after MJD 57040 (18 January 2015) as indi-cated by the Gaussian fit of the VHE light curve in the top panelof Fig. 1.The Phase B flare is very di ff erent, being clearly visible inthe VHE and X-ray band only. All the other bands are in a quies-cent level, perhaps reproducing the conditions of the X-ray flarein December 2009 in Rani et al. (2013), where VHE data were not available. In that case, the X-ray emission was described byboth synchrotron and inverse Compton mechanisms in a single-zone, one-population leptonic model.The fractional variability F var has been calculated usingequation 10 in Vaughan et al. (2003): F var = (cid:115) S − σ x , (1)which represents the normalized excess variance. S stands forthe standard deviation and σ the mean square error of the fluxmeasurements, while ¯ x indicates the average flux. The uncer-tainty of F var is given by Eq.(2) in Aleksi´c et al. (2015), afterPoutanen et al. (2008). F var was calculated for all the light curvesshown in Fig. 1 and the results are plotted in Fig. 2 for both PhaseA (full black dots) and Phase B (red open circles).To make a direct comparison of the variability determinedfor the various energy bands, we computed F var using only themulti-instrument observations strictly simultaneous to those per-formed by MAGIC.The overall behaviour of the fractional variability shows arising tendency with increasing energy, at least up to the X-ray frequency. Since F var is highly sensitive to the sampling of
7. L. Ahnen et al.: MWL characterization of S5 0716 +
714 during an unprecedented outburst ] - s - c m - [ -r a y ) g F ( - · P1 P2 R4 P3 R5
Fermi-LAT 0.1-100 GeVFermi-LAT 3FGL 0.1-100 GeV [ m Jy ] ( R - band ) n F Tuorla AZT-8+ST7LX-200 KanataTuorla AZT-8+ST7LX-200 KanataTuorla AZT-8+ST7LX-200 Kanata [ m Jy ] ( U - V - B - band s ) n F UVOT B UVOT UUVOT W1 UVOT W2UVOT M2 [ Jy ] ( M illi m e t r e ) n F SMA 230GHz IRAM 230 GHzCARMA 90 GHz IRAM 86GHzhovi 37 GHzaMets [ Jy ] ( R ad i o ) n F OVRO 15 GHz Effelsberg 15GHzEffelsberg 10GHz Effelsberg 4.8GHz
MJD56960 56980 57000 57020 57040 57060 57080 57100 57120 57140
A B
Fig. 3: HE γ -ray, optical and radio activity of S5 0716 +
714 during the period from MJD 56950 to MJD 57150 (20 October 2014to 08 May 2015). The three shadowed areas indicate (from the left side) Phase A (from 18 to 27 January 2015 – MJD 57040 toMJD 57050), an intermediate phase (from 28 January to 11 February 2015 – MJD 57050 to MJD 57064), and Phase B (from 12 to17 February 2015 – MJD 57065 to MJD 57070). Vertical dashed lines mark important dates, as shown in Table 1.the observed data, in the HE and VHE bands where the sam-pling is poorer, the results are a ff ected by very large error bars,making impossible to confirm a general trend of F var for thewhole energy spectrum. The highest fractional variabilities inPhase A occur in the VHE γ -ray band and in the X-ray band,with MAGIC ( F var = ± Swift -XRT ( F var = ± F var = ± F var = ± × − ). When MAGIC detected S5 0716 +
714 for the first time in 2008(Anderhub et al., 2009), the radio band was in a quiescent level.Here we see an increased activity in the low radio frequencies,
8. L. Ahnen et al.: MWL characterization of S5 0716 +
714 during an unprecedented outburst especially in the intermediate period between Phase A and B.This activity could be just an e ff ect of a previous smaller flarein high energy delayed by months as it seems typical for thissource when considering longer periods of observation (Raniet al., 2013, 2014).The present work includes one month of data, from the be-ginning of Phase A to the end of Phase B (MJD 57040 toMJD 57070). To have a better understanding of the radio be-havior of the source we gathered γ -ray, optical and radio datain Fig. 3, for a longer time-period of 8 months centered on 28January 2015 (MJD 57050). VHE emission was not detectedoutside of Phase A and Phase B, but the data from the avail-able instruments in the 8-months time window make it possi-ble to better investigate the radio response and to compare thepresent dataset with the scenarios described in other previousmulti-wavelength flares.In Fig. 3 Phase A and Phase B are still defined by grey shad-owed areas, while the intermediate phase is filled in light red.From Fig. 3, second panel from the bottom, the radio activityin the intermediate zone between Phase A and Phase B (fromMJD 57051 to MJD 57065–29 January to 12 February 2015)could be fit by a Gaussian shape ( χ / n . d . f . = . /
14 and stan-dard deviation of σ = . ± . . ± .
07 Jy, corresponding to MJD 57056 (03 February2015).In the bottom panel of Fig. 3, which shows the radio activityin lower frequencies from the E ff elsberg telescope, a peak couldbe identified by a Gaussian fit of the data ( χ / n . d . f . = . / σ = . ± . . ± .
02 Jy, correspondingto MJD 57057 (04 February 2015). If we consider the dashedvertical line R4 as the position of the radio peak (using the valueof MJD 57056–03 February 2015 retrieved from the Mets¨ahovidata which has a smaller error), we can see a delay with respectto the γ -ray / optical peak P2 of ∼ ∼
65 days or more found in Raniet al. (2014). Another hint of delayed activity, indicated by thedashed vertical line labeled as R5, can be seen in Mets¨ahovidata, with a maximum flux density of 3 . ± .
06 Jy, corre-sponding to MJD 57092 (11 March 2015), fit by a Gaussian with χ / n . d . f . = . /
13 and standard deviation of σ = . ± . ∼
45 days.Based on data from April 2007 to January 2011, a consid-erable delay of the radio, ∼
65 days from the optical / γ flare,was found in Rani et al. (2013). In Rani et al. (2014) using adataset from August 2008 to September 2013, the highest peakin radio flux occurred ∼ ±
32 days after the γ -ray one. Thedelay in the radio emission from the optical / γ ones is support-ing a scenario in which the γ -ray emission is produced upstreamof the core while the radio one has its origin in a shock in thejet, first appearing and evolving in the innermost, ultracompactVLBI core region and subsequently moving downstream the jetat parsec scales with apparent superluminal speeds. Similar re-sults, on a larger sample of blazars, are presented in Fuhrmannet al. (2014). A longer-term study centered on the flaring activityreported here could be interesting for future investigations but isbeyond the scope of the present work. An important feature of Phase A is determined by the very fastchange in the electric vector position angle (EVPA) happeningover the night MJD 57044 (22 January 2015), 4 days after the first peak P1 in the optical band and 2 days before the MAGICpeak P2. This particular feature can be seen in the bottom panelof Fig. 1, as well as in Fig. 4, where the feature is zoomed in thetime range MJD 57043-MJD 57048 (21-26 January 2015).
MJD ] (cid:176) EVPA [ - Kanata AZT-8+ST7Steward RINGO3
Fig. 4: Zoom of the Electric Vector Position Angle rotation ofS5 0716 +
714 during the period from MJD 57043 to MJD 57048(21 to 26 January 2015) in Phase A.The dataset we presented put together EVPA data comingfrom many di ff erent instruments, as shown in the bottom panelof Fig. 1. All the EVPA data collected are in agreement and weretreated as in Larionov et al. (2013): in particular, to solve the ± ◦ ambiguity, we have added / subtracted 180 ◦ each time thatthe subsequent value of EVPA was > ◦ less / more than thepreceding one.In Marscher et al. (2008), a similar behaviour of the EVPAwas reported for BL Lacertae: a radio to γ -ray outburst, accom-panied by a rotation of the EVPA, was observed as the conse-quence of a bright feature moving in the jet. In that case, theEVPA rotation was slower: it rotated steadily by about 240 ◦ overa five-day interval before settling at a value of 195 ◦ .In 2008, when the source was observed in the VHE rangefor the first time (Anderhub et al., 2009), the simultaneous op-tical outburst was accompanied by a ∼ ◦ PA rotation of theelectric vector, as reported in Larionov et al. (2008a). The rota-tion happened with an approximate rate of 60 ◦ per day, so slowerthan in the present case. That rotation was interpreted as a con-sequence of the propagation of polarized emission from a knotspiraling down the jet. Chandra et al. (2015a) investigated thePA rotation swing from Phase A using the data from the StewardObservatory, in the frame of the HMFM (Zhang et al., 2014),suggesting that the fast rotation was due to reconnections in theemission region in the jet.
4. Jets evolution study with very-long-baselineinterferometry
We analyzed the structure of the jet with very-long-baselineinterferometry. Details of the analysis have been presented inSection 2.5.As shown in Fig. 5, the core of the jet is the brightest knot,designated as A
0, which is the southern-most feature of the jet,and assumed to be stationary. The position of the core across
9. L. Ahnen et al.: MWL characterization of S5 0716 +
714 during an unprecedented outburst
Fig. 5: A sequence of total (contours) and polarized (color scale) intensity images of S5 0716 +
714 at 43 GHz, convolved with abeam of 0.24 × at PA = -10 ◦ . The global total intensity peak is 2655 mJy / beam and the global polarized intensity peak is107 mJy / beam; black line segments within each image show the direction of polarization; the black horizontal line indicates theposition of the core, A0. (a) Separation of knots A A A σ uncertainty of the ejection times of K14a and K14b, respec-tively. (b) Light curves of the core A0 (black), stationary feature A ∼ Jy for clarity; vertical blueand red lines indicate time of passage of K14b through A A
1, respectively.
Fig. 6: VLBA-BU-BLAZAR analysis of S5 0716 + A
1, and two movingknots, K14a and K14b. Fig. 6a shows the evolution of the posi-tions of the knots. Note that a stationary feature at a position sim-ilar to that of A ± ± ∼ Φ is Φ K a = (25.4 ± Φ K b = (43.3 ± ±
22 and MJD 56971 ±
30, respectively.Knot K14b is of special interest with respect to the high en-ergy event in January 2015 (MJD 57040-57050): according to itsproper motion of (0.51 ± / yr, K14b passed through A1on MJD 57050 ±
30. This coincides with the high γ -ray state andTeV detection of S5 0716 + A A A ∼ ◦ to ∼ ◦ is detected around the time of the expected pas-sage (see Table A.1). The latter angle is close to the PA of K14b, Θ= (47.5 ± A ± ±
13) days to pass throughthe stationary feature. The latter agrees very well with the dura-tion of 34 days of the elevated γ -ray flux in the Fermi light curveof S5 0716 +
10. L. Ahnen et al.: MWL characterization of S5 0716 +
714 during an unprecedented outburst
5. Spectral fitting of
NuSTAR and
Swift -XRT data
For
NuSTAR data, we performed the spectral fitting with XSPECv12.8.2, with the standard instrumental response matrices ande ff ective area files derived using the ftool nuproducts . We fitthe data for both NuSTAR detectors simultaneously, allowing ano ff set of the normalization factor for module FPMB with respectto module FPMA. Regardless of the adopted models, the nor-malization o ff set was less than 5%. First, we adopted a simplepower-law model modified by the e ff ects of the Galactic absorp-tion, corresponding to a column of 3 . × cm − (Kalberlaet al., 2005). The fit returns the power-law index of 1 . ± . NuSTAR spectrum is more con-cave (i.e., the spectrum gets flatter towards higher energies) thana simple power-law model would imply. In addition, this indexis significantly harder than that inferred from the
Swift -XRT dataalone (which shows the index of ∼ .
75 ), which also suggestsa more complex spectral model.Since the
NuSTAR and
Swift data were nearly strictly con-temporaneous (with a significant overlap) we fit the
NuSTAR and
Swift -XRT data simultaneously, but allowing for the nor-malizations of
Swift and
NuSTAR to fit independently. We at-tempted two more complex models (both with absorption fixedat the Galactic value as above). First, we considered a brokenpower law, with steeper low-energy and harder high-energy in-dices. This is similar to the model considered by Wierzcholska& Siejkowski (2016). The low- and high-energy indices are, re-spectively, 2 . ± .
07 and 1 . ± .
08, the break energy is at5 . + . − . keV, and χ is 351 for 328 PHA channels. We note thatthe break energy in our fit is somewhat lower than that deter-mined by Wierzcholska & Siejkowski (2016), but this is likelydue to a di ff erent choice of bandpass, size of the source extrac-tion region, and precise location of the region of the detectorfrom which the background was subtracted.We also attempted a double power-law representation of thedata, also modified by Galactic absorption as above: here, theresulting spectrum is a sum of two power-law models, and isprobably more physically motivated than a broken power law.The fit returns χ =
352 for 328 PHA bins with a low-energyindex of 2 . ± .
16 and a high-energy index of 1 . ± . −
10 keVflux is (9 . ± . × − erg cm − s − . We note here that themost reasonable interpretation of such a 2-component spectralshape is that we witness a contribution of two separate compo-nents, namely the “tail” of the low-energy component (presum-ably produced by the synchrotron process) and the onset of thehigh energy component (presumably due to the IC process). Weplot the unfolded spectrum of the Swift XRT and NuSTAR dataobserved on 24 January 2015 (MJD 57046) and fit to the two-power-law model in Fig. 7.
6. VHE Differential Energy Spectrum and EBLdeabsorbtion
The VHE γ -rays from distant blazars can interact with theoptical-UV photons from the extragalactic background light(EBL)(Gould & Schreder, 1967; Stecker et al., 1992) via pairproduction, resulting in an attenuation of the intrinsic VHE spec-trum. Finite resolution of the instrument will also modify the in-trinsic spectrum. Unfolding techniques are adopted in the MARScode to unfold the observed spectrum from the instrument re-sponse. The di ff erential spectrum of S5 0716 +
714 is shown in Fig. 7: Unfolded X-ray spectrum of S50716 +
714 derived fromsimultaneous fitting of the contemporaneous
Swift -XRT and
NuSTAR data obtained on 24 January 2015 (MJD 57046). Theadopted model is a sum of two power laws.
Swift -XRT data areplotted in green, while the two
NuSTAR modules are plotted inred and black, respectively. The “valley” between the two mainbroad-band spectral peaks is in the X-ray band.Fig. 8 for a simple unfolding considering instrumental responseonly (hereafter observed spectrum). An unfolding including alsode-absorption from EBL with the Dom´ınguez et al. (2011) model(hereafter the intrinsic spectrum) was also performed, and pa-rameters of the observed and intrinsic spectra are reported inTable 2. The EBL imprint on the γ -ray spectra from distantblazars could be used to constrain the EBL density, under someassumptions on the intrinsic spectrum of the source (see e.g.Ackermann et al., 2012; Abramowski et al., 2013). The di ff er- Energy [GeV]
200 300 400 500 600 700 ] - s - c m - / d E [ T e V f d - - - - - - - MAGIC Phase A, with 11.95 hours totalMAGIC Phase B, with 5.49 hours total
Fig. 8: Unfolded observed di ff erential energetic spectra byMAGIC for Phase A (black full dots) and Phase B (red fullsquares). Parameters for the spectra (including the ones regard-ing the intrinsic EBL deabsorbed spectra with Dom´ınguez et al.(2011) model) are reported in Table 2.ential VHE spectra, observed as well as EBL-corrected using themodel of Dom´ınguez et al. (2011), can be described by a power-law :
11. L. Ahnen et al.: MWL characterization of S5 0716 +
714 during an unprecedented outburst
Table 2: VHE spectrum parameters for a PWL fit f (cm − s − TeV − ) Γ χ / n.d.f. P E (GeV)-Phase A-observed (2 . ± . stat ± . sys ) × − . ± . stat ± . sys . / .
99 127.2-659.1intrinsic (4 . ± . stat ± . sys ) × − . ± . stat ± . sys . / .
64 127.2-659.1- Phase B -observed (7 . ± . stat ± . sys ) × − . ± . stat ± . sys . / .
92 127.2-474.3intrinsic (1 . ± . stat ± . sys ) × − . ± . stat ± . sys . / .
89 127.2-474.3 dFdE = f (cid:18) E
150 GeV (cid:19) − Γ , (2)where the normalization constant f , the spectral index Γ , thegoodness of the fit ( χ / n.d.f. and probability P ), the energy rangeof the fit E are indicated in Table 2 for Phase A and Phase B datarespectively. The simultaneous spectra from MAGIC and
Fermi -LAT wereused to estimate the redshift of the source. We apply the methodpresented in Prandini et al. (2010, 2011) based on the assumptionthat the slope of the VHE spectrum corrected for EBL absorptionshould not be harder than the one measured by
Fermi -LAT atlower energies. The redshift at which the two slopes match, z*,is then used as upper limit estimate of the source distance if thereis no spectroscopic redshift available. If we apply the method tothe data presented here assuming the Franceschini et al. (2008)EBL model, a 2 σ upper limit on the redshift of 0.598 is found.The empirical formula proposed in Prandini et al. (2011) ap-plied to this data gives as most probable value for the redshift z rec = . ± . stat ± . sys , where the first error is relatedto the statistical errors of Fermi -LAT and MAGIC slopes, whilethe second error is the error of the method itself, as estimated inPrandini et al. (2011). This value is in agreement with the onesgiven in literature by Nilsson et al. (2008); Danforth et al. (2013).The value of z = . ± .
08 found in Nilsson et al. (2008)was based on the photometric detection of the host galaxy, whilethe z < .
322 (95% confidence) result reported by Danforthet al. (2013) was obtained by detection of Ly- α systems in theultra-violet spectrum of the source. For the SED modelling (seenext section), we used the redshift value of 0.26 as in Anderhubet al. (2009). This value is within the errorbars of the redshiftdetermined here as well as within other observations (see theIntroduction).
7. Broadband Spectral Energy Distribution
The multi-wavelength SEDs for Phase A and B respectively arepresented in Fig. 9. Archival data from ASDC (ASI ScienceData Center) are shown in grey. When the source was detectedfor the first time in the VHE range (Anderhub et al., 2009) byMAGIC, the only available simultaneous multi-wavelength datawere coming from KVA (optical) and Swift (X-rays) and therewere no constraints on the second bump beyond the MAGICdata. Nevertheless the very soft X-ray spectra belonging to thesynchrotron component, combined with the high VHE γ -ray flux http: // / challenged the simple one-zone SSC model as it would require avery high flux of γ -rays around 10 GeV, higher than has been ob-served from the source with Fermi -LAT or its precursor EGRET.This condition for one-zone persists also for the new data, butnow we actually have simultaneous data in this energy rangefrom
Fermi -LAT and we find that we cannot describe the ob-served broadband SED with the one-zone SSC model during thisflaring period.While a one-zone SSC model can match the observed
Swift -XRT + NuSTAR spectrum as a transition between synchrotronand IC components, and simultaneously the γ -ray data from Fermi -LAT and MAGIC, it tends to under-reproduce the ob-served optical flux. This has been independently verified usingthe BLAZAR code (Moderski et al., 2003).Based on the multiwavelength data in Section 3 and VLBAdata in Section 4, we use two-zone model to describe the SEDin Phase A and Phase B. We use two blobs close to each other torepresent a situation where a superluminal knot (blob 1) is inter-acting a recollimation shock region (blob 2). The Phase A SEDrepresents a snapshot of a time when the knot enters the rec-ollimation shock region and the Phase B SED a time when theknot has exited the recollimation region. We model the two blobswith the framework similar to one presented for flat-spectrumradio quasar PKS 1222 +
216 in Tavecchio et al. (2011), modi-fied for the case of no external seed photons as in Aleksi´c et al.(2014) for PKS 1424 + + γ min , γ b and γ max are the minimum, break and maximumLorentz factors respectively; n and n are the low and high en-ergy slope of the smoothed power law electron energy distribu-tion), magnetic field B , normalization of the electron distribution K , radius of the emission region R and Doppler factor δ .We also use the observed variability behaviour as a guideon how the parameters change between Phase A and Phase B.As discussed in Section 3, Phase A and Phase B have di ff erentvariability behaviours; while Phase A consists of a flare in allbands, in Phase B the activity is constrained to the X-ray andVHE γ -ray bands. To limit the number of free parameters, wefix the larger component (which is representing the recollima-tion shock) to have most of the parameters the same in Phases Aand B. We only change K to a lower value to represent the gen-eral lower state in optical and GeV γ -rays of Phase B. We thenfind parameters for the smaller emission region to describe theobserved SEDs in Phase A and B separately. In both panels ofFig. 9 the ”blob1” component is represented by the red dashedline. The ”blob2” component of the model is represented by theblue dash-dotted line in both panels, and the emission resultingfrom the interaction of two components is reported with a greenline.
12. L. Ahnen et al.: MWL characterization of S5 0716 +
714 during an unprecedented outburst
Energy [GeV] - - -
10 1 ] - s - d N / d E [ T e V c m E - - - - - - MWL SED Phase A
Energy [GeV] - - -
10 1 ] - s - d N / d E [ T e V c m E - - - - - - MWL SED Phase B
Fig. 9: MWL Spectral Energy distributions for Phase A and Phase B. Archival data form ASDC are shown in grey. The two compo-nents (blobs representing a moving emission feature and a recollimation shock, see text) are shown with blue and red dashed lines.The green line is the emission that is a result of interaction between these two blobs and the black solid line the sum of these threecomponents. The red full circles represent the intrinsic (EBL deabsorbed according to (Dom´ınguez et al., 2011)) MAGIC SED usedin the model. For data taken in the radio and optical band the error bars are smaller than the size of the marker.Table 3: Input parameters for the emission models of S5 0716 + γ min γ b γ max n n B (G) K R (cm) δ z -Phase A-”blob1” 100 1 . × × .
95 3 . . . × . ×
25 0 . × . × .
32 4 . .
12 1 . × . ×
25 0 .
26- Phase B -”blob1” 4 × × × . . .
09 9 × . ×
25 0 . × . × .
32 4 . .
12 1 × . ×
25 0 . We report a set of parameters we found to give a reasonabledescription (but see below) of the observed SED in Table 3 forthe both phases. The set of parameters we present is not unique,but the parameters used are within the range typically found forTeV blazars and also for the ones found for PKS 1424 +
240 usingthe similar modelling setup.Even if this simple two-zone model provides a better rep-resentation of the observed data from radio to VHE γ -rays re-spect to a one-zone model, the model line is slightly lower thanthe γ -ray fluxes in the range of 10-100 GeV even though withinthe systematic uncertainties of the data. The data in this energyrange suggests a rather sharp feature, which is impossible to re-produce with this simplistic model we used. In general sharpfeatures require presence of external seed photons such as usede.g. by B¨ottcher et al. (2013) to model the SED of the sourcein a lower state. However, there is no observational evidence forsuch an external seed photon field from optical spectroscopy norfrom the scenario we presented for the flaring behaviour withinthis epoch therefore no such a component was added to the mod-elling.There are also other possible two-zone model setups, suchas a spine-sheath model (Ghisellini et al., 2005), where a slowersheath of the jet surrounds a faster spine. For the previous VHE γ -ray flaring epoch a spine-sheath mode (Ghisellini et al., 2005),was shown to provide a reasonable fit to the SED data (Anderhubet al., 2009; Tavecchio & Ghisellini, 2009). We tested the spine-sheath model for the spectral energy distributions shown here and found acceptable agreement with the SED data. This em-phasizes that SED data alone are not enough to separate di ff erenttwo-zone models, but must be combined with constraints fromVLBA and light curve variability.According to the scenario described above, which is sup-ported by the dedicated VLBI study we performed in Sec. 4,we explain the extremely fast rotation of ∼ ◦ as produced byturbulence in the interaction between a superluminal knot and astationary feature near the core. Being dependent on the orienta-tion of the shock and the magnetic field threading it, EVPA pro-vides a unique tool to understand the acceleration mechanismsand behavior of the shocked plasma. Recent studies on EVPAswings larger than 180 ◦ simultaneous with HE γ -ray emission(Marscher et al., 2008, 2010; Abdo et al., 2010) have been inter-preted as additional evidence for a helical magnetic field struc-ture. The existing models focusing on the description of the syn-chrotron polarization features (e.g. Lyutikov et al., 2005) ap-ply a simple and time-independent power-law electron spectrumnot taking into account possible predictions for the resulting HEemission. Our model, on the other hand, does not include a de-tailed geometry of the magnetic field and the angle-dependentsynchrotron emissivity and polarization. At the moment onlytwo models may represent the SED of blazars together withtheir synchrotron polarization features, including rotations ofthe EVPA: the HMFM (Helical Magnetic Field Model) (Zhanget al., 2014) and the TEMZ (Turbulent, Extreme Multi-Zone)(Marscher, 2014). In the HMFM large polarization angle rota-
13. L. Ahnen et al.: MWL characterization of S5 0716 +
714 during an unprecedented outburst tions by (cid:38) ◦ are explained with the passage of a movingshock through a region with a highly disordered field: the com-pression of the shock orders the field partially, but this order-ing is seen at di ff erent depths as time advances owing to light-travel delays. This leads to an apparent rotation of the polariza-tion of 180 ◦ per shock. In the TEMZ model randomness in themagnetic field direction in di ff erent turbulent cells can cause ob-served rotations in the linear polarization vector, even fast as theone observed in our case. Turbulence in general gives at di ff erenttimes ”clusters” with small EVPA variation, relatively smoothEVPA rotations, step-wise EVPA changes, and random fluctu-ations. The behavior of S5 0716 +
714 in Phase A is consistentwith this scenario.
8. Summary and Conclusions
The BL Lac object S5 0716 +
714 has been studied in a multi-wavelength frame from radio to the VHE γ -ray band. In January2015 an unprecedented outburst of S5 0716 +
714 was registeredin all energy bands, from low frequency radio to VHE, and afteralmost a month another high state was detected by the MAGICand
Swift -XRT instruments only. We divide the data into twophases (Phase A from 18 to 27 January 2015 – MJD 57040to MJD 57050, and Phase B from 12 to 17 February 2015 –MJD 57065 to MJD 57070) that represent very di ff erent charac-teristics, allowing a deep study of the broadband SEDs.The broadband flaring activity period of Phase A coincideswith the passage of a moving feature through a stationary feature(at ∼ >
400 degree swingin the optical EVPA is explained here as the passage of a su-perluminal knot through a stationary feature near the radio core.The VHE emission is then found originating in the entrance andexit of a superluminal knot in and out a recollimation shock inthe inner jet. This suggests that shock-shock interaction in the jetseems to be responsible for the observed flares and EVPA swing.The jet behaviour, studied with VLBA-BU-BLAZAR data,is in agreement with the scenario described in Rani et al. (2015),suggesting a connection between jet kinematics and the observedbroadband flaring activity. More precisely, the γ -ray emission inthe HE and VHE bands is attributed to a shock in the helicaljet downstream of the core, closely followed by an optical andX-ray outburst in the core. The presence of low radio activity,observed during Phase A, was not reported in April 2008, whenMAGIC observed the source in the VHE range for the first time(Anderhub et al., 2009), but it could be a delayed response of aprevious less intense flare, as observed in the past in the samesource, when between optical / γ flares lagged the radio counter-parts almost two months (Rani et al., 2013, 2014).The first peak in the VHE γ -ray emission takes place ∼ ∼
18 daysafter the new knot has been emerged from the VLBA core. Thisis a strong indication that the VHE γ -ray emission is associatedto a component entering and exiting the core region.The broadband SEDs, for the first time including MAGICand Fermi -LAT simultaneous data and the quasi-simultaneous
NuStar data, could not be described by a simple one-zone model.Instead we used a two-zone model, where two spherical blobsare co-spatial and provide seed photons to each other. This mod-elling setup provides an acceptable description of the spectralenergy distributions in Phase A and B, even if it is certainly anover-simplified presentation of the true physical processes takingin place when superluminal knots enter and exit the recollima-tion shock region. Finally we also investigated the redshift of S5 0716 + Fermi -LAT the red-shift was calculated to be z = . ± . stat ± . sys , confirmingthe value present in literature based on the photometric detectionof the host galaxy (Nilsson et al., 2008) and the more recent up-per limit from a direct detection (Danforth et al., 2013).S50716 +
714 is an intermediate BL Lac object, and only ahandful of these sources have been detected in VHE γ -rays. Inalmost all detections of VHE γ -rays, activity in other bands (op-tical and / or HE γ -rays) has been seen, but our very comprehen-sive dataset provided a unique insight on how these VHE γ -rayflares are connected to the activity in the jet.In the end of December 2017 S5 0716 +
714 was flaring againin VHE γ -rays (Mirzoyan et al., 2017). It will be interesting tosee if the recognized patterns will repeat also during this ongoingflaring period. This will be studied in a future paper. Acknowledgements.
We would like to thank the Instituto de Astrof´ısica deCanarias for the excellent working conditions at the Observatorio del Roque delos Muchachos in La Palma. The financial support of the German BMBF andMPG, the Italian INFN and INAF, the Swiss National Fund SNF, the ERDFunder the Spanish MINECO (FPA2015-69818-P, FPA2012-36668, FPA2015-68378-P, FPA2015-69210-C6-2-R, FPA2015-69210-C6-4-R, FPA2015-69210-C6-6-R, AYA2015-71042-P, AYA2016-76012-C3-1-P, ESP2015-71662-C2-2-P, CSD2009-00064), and the Japanese JSPS and MEXT is gratefully ac-knowledged. This work was also supported by the Spanish Centro deExcelencia “Severo Ochoa” SEV-2012-0234 and SEV-2015-0548, and Unidadde Excelencia “Mar´ıa de Maeztu” MDM-2014-0369, by the CroatianScience Foundation (HrZZ) Project IP-2016-06-9782 and the University ofRijeka Project 13.12.1.3.02, by the DFG Collaborative Research CentersSFB823 / C4 and SFB876 / C3, the Polish National Research Centre grant UMO-2016 / / M / ST9 / Fermi
LAT Collaboration acknowledges generous ongoing support from a num-ber of agencies and institutes that have supported both the development andthe operation of the LAT as well as scientific data analysis. These include theNational Aeronautics and Space Administration and the Department of Energyin the United States, the Commissariat `a l’Energie Atomique and the CentreNational de la Recherche Scientifique / Institut National de Physique Nucl´eaireet de Physique des Particules in France, the Agenzia Spaziale Italiana and theIstituto Nazionale di Fisica Nucleare in Italy, the Ministry of Education, Culture,Sports, Science and Technology (MEXT), High Energy Accelerator ResearchOrganization (KEK) and Japan Aerospace Exploration Agency (JAXA) in Japan,and the K. A. Wallenberg Foundation, the Swedish Research Council andthe Swedish National Space Board in Sweden. Additional support for sci-ence analysis during the operations phase is gratefully acknowledged fromthe Istituto Nazionale di Astrofisica in Italy and the Centre National d’ ´EtudesSpatiales in France. This research was supported by an appointment to theNASA Postdoctoral Program at the Goddard Space Flight Center, administeredby Universities Space Research Association through a contract with NASA.Wethank the
Swift team duty scientists and science planners. The Mets¨ahovi teamacknowledges the support from the Academy of Finland to our observingprojects (numbers 212656, 210338, 121148, and others). The VLBA is an in-strument of the Long Baseline Observatory. The Long Baseline Observatory is afacility of the National Science Foundation operated by Associated Universities,Inc. The Submillimeter Array is a joint project between the SmithsonianAstrophysical Observatory and the Academia Sinica Institute of Astronomy andAstrophysics and is funded by the Smithsonian Institution and the AcademiaSinica. The OVRO 40-m monitoring program is supported in part by NASAgrants NNX08AW31G, NNX11A043G and NNX14AQ89G, and NSF grantsAST-0808050 and AST-1109911. The St. Petersburg University team acknowl-edges support from Russian Science Foundation grant 17-12-01029. The BUgroup acknowledges support by NASA under
Fermi
Guest Investigator grantNNX14AQ58G and by NSF under grant AST-1615796. Part of this work wasdone with funding by the UK Space Agency. The VLBA is an instrument ofthe National Radio Astronomy Observatory. The National Radio AstronomyObservatory is a facility of the National Science Foundation operated under co-operative agreement by Associated Universities, Inc. The PRISM (Perkins Re-Imaging SysteM) camera at Lowell Observatory was developed by K. Janeset al. at BU and Lowell Observatory, with funding from the NSF, BU, andLowell Observatory. This paper makes use of data obtained with the 100 mE ff elsberg radio-telescope, which is operated by the Max-Planck-Institut f¨urRadioastronomy (MPIfR) in Bonn (Germany). Part of this work is based onarchival data, software or online services provided by the ASI Science DataCenter (ASDC). PYRAF is a product of the Space Telescope Science Institute,
14. L. Ahnen et al.: MWL characterization of S5 0716 +
714 during an unprecedented outburst which is operated by AURA for NASA. This paper is partly based on obser-vations carried out with the IRAM 30m. IRAM is supported by INSU / CNRS(France), MPG (Germany) and IGN (Spain). IA acknowledges support by aRamon y Cajal grant of the Ministerio de Economia, Industria y Competitividad(MINECO) of Spain. The research at the IAA-CSIC was supported in part by theMINECO through grants AYA2016-80889-P, AYA2013-40825-P, and AYA2010-14844, and by the regional government of Andalucia through grant P09-FQM-4784. The Liverpool Telescope is operated by JMU with financial support fromthe UK-STFC.
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Proc. of the 33th InternationalCosmic Ray Conference (ICRC)
15. L. Ahnen et al.: MWL characterization of S5 0716 +
714 during an unprecedented outburst
Appendix A: Knot parameters for S5 0716+714 (July2014-August 2015)
In Table A.1 the parameters of components from the Section 4are listed. They indicate the flux density, S , the relative RA andDEC with respect to the core, the distance from the core r , theposition angle with respect to the core, Θ , and the size of thecomponent, a (FWHM of the Gaussian) for every knot. Someknots present in Table A.1 do not have any assigned name be-cause they have been seen at 1-2 epochs only. ETH Zurich, CH-8093 Zurich, Switzerland Universit`a di Udine, and INFN Trieste, I-33100 Udine, Italy National Institute for Astrophysics (INAF), I-00136 Rome, Italy Universit`a di Padova Technische Universit¨at Dortmund, D-44221 Dortmund, Germany Croatian MAGIC Consortium: University of Rijeka, 51000 Rijeka,University of Split - FESB, 21000 Split, University of Zagreb -FER, 10000 Zagreb, University of Osijek, 31000 Osijek and RudjerBoskovic Institute, 10000 Zagreb, Croatia. Saha Institute of Nuclear Physics, HBNI, 1 / AF Bidhannagar, SaltLake, Sector-1, Kolkata 700064, India Max-Planck-Institut f¨ur Physik, D-80805 M¨unchen, Germany now at Centro Brasileiro de Pesquisas F´ısicas (CBPF), 22290-180URCA, Rio de Janeiro (RJ), Brasil Unidad de Part´ıculas y Cosmolog´ıa (UPARCOS), UniversidadComplutense, E-28040 Madrid, Spain Inst. de Astrof´ısica de Canarias, E-38200 La Laguna, andUniversidad de La Laguna, Dpto. Astrof´ısica, E-38206 La Laguna,Tenerife, Spain University of Ł´od´z, Department of Astrophysics, PL-90236 Ł´od´z,Poland Deutsches Elektronen-Synchrotron (DESY), D-15738 Zeuthen,Germany Institut de F´ısica d’Altes Energies (IFAE), The Barcelona Instituteof Science and Technology (BIST), E-08193 Bellaterra (Barcelona),Spain Universit`a di Siena and INFN Pisa, I-53100 Siena, Italy Universit¨at W¨urzburg, D-97074 W¨urzburg, Germany Finnish MAGIC Consortium: Tuorla Observatory and FinnishCentre of Astronomy with ESO (FINCA), University of Turku,Vaisalantie 20, FI-21500 Piikki¨o, Astronomy Division, Universityof Oulu, FIN-90014 University of Oulu, Finland Departament de F´ısica, and CERES-IEEC, Universitat Aut´onomade Barcelona, E-08193 Bellaterra, Spain Universitat de Barcelona, ICC, IEEC-UB, E-08028 Barcelona,Spain Japanese MAGIC Consortium: ICRR, The University of Tokyo,277-8582 Chiba, Japan; Department of Physics, Kyoto University, 606-8502 Kyoto, Japan; Tokai University, 259-1292 Kanagawa,Japan; The University of Tokushima, 770-8502 Tokushima, Japan Inst. for Nucl. Research and Nucl. Energy, Bulgarian Academy ofSciences, BG-1784 Sofia, Bulgaria Universit`a di Pisa, and INFN Pisa, I-56126 Pisa, Italy Humboldt University of Berlin, Institut f¨ur Physik D-12489 BerlinGermany also at Dipartimento di Fisica, Universit`a di Trieste, I-34127 Trieste,Italy also at Port d’Informaci´o Cient´ıfica (PIC) E-08193 Bellaterra(Barcelona) Spain also at INAF-Trieste and Dept. of Physics & Astronomy, Universityof Bologna INFN, I-35131 Padova, Italy ASI Science Data Center and INFN, 06123 Perugia, Italy CEN Bordeaux-Gradignan, 33170 Gradignan, France NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA Instituto de Astrofsica de Andaluca (CSIC), Apartado 3004, E-18080 Granada, Spain Max–Planck–Institut f¨ur Radioastronomie, Auf dem H¨ugel, 69, D–53121, Bonn, Germany Crimean Astrophysics Observatory, P / O Nauchny, Crimea, 298409,Russia Astron. Inst., St. Petersburg State University, Russia Harvard-Smithsonian Center for Astrophysics, MA 02138Cambridge, USA Mets¨ahovi Radio Observatory, Aalto University, FI-02540 Kylm¨al¨a Department of Electronics and Nanoengineering, Aalto University,FI-00076 Aalto, Finland Tuorla Observatory, University of Turku, V¨ais¨al¨antie 20, 21500Piikki¨o, Finland Department of Physical Science, Hiroshima University, Higashi-hiroshima, 739-8526, Japan Institute for Astrophysical Research, Boston University, Boston MA02215 Mullard Space Science Lab., UCL, Dorking, RH5 6NT, UK Pulkovo Observatory, St.-Petersburg, Russia Kavli Institute for Particle Astrophysics and Cosmology, StanfordUniversity and SLAC National Accelerator Laboratory, 2575 SandHill Road, Menlo Park, CA 94025 Nicolaus Copernicus Astronomical Center, Polish Academy ofSciences, Bartycka 18, 00-716 Warsaw, Poland Owens Valley Radio Observatory, California Institute ofTechnology, Pasadena, CA 91125, USA CePIA, Astronomy Department, Universidad de Concepcion,Casilla 160-C, Concepcion, Chile Astrophysics Research Institute, Liverpool John Moores University,Brownlow Hill, Liverpool, L3 5RF, UK16. L. Ahnen et al.: MWL characterization of S5 0716 +
714 during an unprecedented outburst
Table A.1: Knot parameters for S5 0716 +
714 (July 2014-August 2015)
Epoch MJD S (Jy) x(mas) y(mas) r (mas) Θ (deg) aa