A luminous and isolated gamma-ray flare from the blazar B2 1215+30
VERITAS Collaboration, A. U. Abeysekara, S. Archambault, A. Archer, W. Benbow, R. Bird, M. Buchovecky, J. H. Buckley, V. Bugaev, K. Byrum, M. Cerruti, X. Chen, L. Ciupik, W. Cui, H. J. Dickinson, J. D. Eisch, M. Errando, A. Falcone, Q. Feng, J. P. Finley, H. Fleischhack, L. Fortson, A. Furniss, G. H. Gillanders, S. Griffin, J. Grube, M. Hutten, N. Hakansson, D. Hanna, J. Holder, T. B. Humensky, C. A. Johnson, P. Kaaret, P. Kar, M. Kertzman, D. Kieda, M. Krause, F. Krennrich, S. Kumar, M. J. Lang, G. Maier, S. McArthur, A. McCann, K. Meagher, P. Moriarty, R. Mukherjee, T. Nguyen, D. Nieto, R. A. Ong, A. N. Otte, N. Park, V. Pelassa, M. Pohl, A. Popkow, E. Pueschel, J. Quinn, K. Ragan, P. T. Reynolds, G. T. Richards, E. Roache, C. Rulten, M. Santander, G. H. Sembroski, K. Shahinyan, D. Staszak, I. Telezhinsky, J. V. Tucci, J. Tyler, S. P. Wakely, O. M. Weiner, A. Weinstein, A. Wilhelm, D. A. Williams, Fermi-LAT Collaboration, S. Fegan, B. Giebels, D. Horan, A. Berdyugin, J. Kuan, E. Lindfors, K. Nilsson, A. Oksanen, H. Prokoph, R. Reinthal, L. Takalo, F. Zefi
aa r X i v : . [ a s t r o - ph . H E ] J a n Draft version January 5, 2017
Preprint typeset using L A TEX style AASTeX6 v. 1.0
A LUMINOUS AND ISOLATED GAMMA-RAY FLARE FROM THE BLAZAR B2 1215+30
A. U. Abeysekara , S. Archambault , A. Archer , W. Benbow , R. Bird , M. Buchovecky , J. H. Buckley ,V. Bugaev , K. Byrum , M. Cerruti , X. Chen , L. Ciupik , W. Cui , H. J. Dickinson , J. D. Eisch ,M. Errando , A. Falcone , Q. Feng , J. P. Finley , H. Fleischhack , L. Fortson , A. Furniss ,G. H. Gillanders , S. Griffin , J. Grube , M. H¨utten , N. H˚akansson , D. Hanna , J. Holder ,T. B. Humensky , C. A. Johnson , P. Kaaret , P. Kar , M. Kertzman , D. Kieda , M. Krause ,F. Krennrich , S. Kumar , M. J. Lang , G. Maier , S. McArthur , A. McCann , K. Meagher , P. Moriarty ,R. Mukherjee , T. Nguyen , D. Nieto , R. A. Ong , A. N. Otte , N. Park , V. Pelassa , M. Pohl ,A. Popkow , E. Pueschel , J. Quinn , K. Ragan , P. T. Reynolds , G. T. Richards , E. Roache , C. Rulten ,M. Santander , G. H. Sembroski , K. Shahinyan , D. Staszak , I. Telezhinsky , J. V. Tucci , J. Tyler ,S. P. Wakely , O. M. Weiner , A. Weinstein , A. Wilhelm & D. A. Williams (VERITAS Collaboration),S. Fegan , B. Giebels & D. Horan ( Fermi -LAT Collaboration), A. Berdyugin , J. Kuan , E. Lindfors , K.Nilsson , A. Oksanen , H. Prokoph , R. Reinthal , L. Takalo & F. Zefi Department of Physics and Astronomy, University of Utah, Salt Lake City, UT 84112, USA Physics Department, McGill University, Montreal, QC H3A 2T8, Canada Department of Physics, Washington University, St. Louis, MO 63130, USA, [email protected] Fred Lawrence Whipple Observatory, Harvard-Smithsonian Center for Astrophysics, Amado, AZ 85645, USA School of Physics, University College Dublin, Belfield, Dublin 4, Ireland Department of Physics and Astronomy, University of California, Los Angeles, CA 90095, USA Argonne National Laboratory, 9700 S. Cass Avenue, Argonne, IL 60439, USA Institute of Physics and Astronomy, University of Potsdam, 14476 Potsdam-Golm, Germany DESY, Platanenallee 6, 15738 Zeuthen, Germany Astronomy Department, Adler Planetarium and Astronomy Museum, Chicago, IL 60605, USA Department of Physics and Astronomy, Purdue University, West Lafayette, IN 47907, USA Department of Physics and Center for Astrophysics, Tsinghua University, Beijing 100084, China. Department of Physics and Astronomy, Iowa State University, Ames, IA 50011, USA Department of Physics and Astronomy, Barnard College, Columbia University, NY 10027, USA, [email protected] Department of Astronomy and Astrophysics, 525 Davey Lab, Pennsylvania State University, University Park, PA 16802, USA School of Physics and Astronomy, University of Minnesota, Minneapolis, MN 55455, USA Department of Physics, California State University - East Bay, Hayward, CA 94542, USA School of Physics, National University of Ireland Galway, University Road, Galway, Ireland Department of Physics and Astronomy and the Bartol Research Institute, University of Delaware, Newark, DE 19716, USA Physics Department, Columbia University, New York, NY 10027, USA Santa Cruz Institute for Particle Physics and Department of Physics, University of California, Santa Cruz, CA 95064, USA Department of Physics and Astronomy, University of Iowa, Van Allen Hall, Iowa City, IA 52242, USA Department of Physics and Astronomy, DePauw University, Greencastle, IN 46135-0037, USA School of Physics and Center for Relativistic Astrophysics, Georgia Institute of Technology, 837 State Street NW, Atlanta, GA 30332-0430 Enrico Fermi Institute, University of Chicago, Chicago, IL 60637, USA Department of Physical Sciences, Cork Institute of Technology, Bishopstown, Cork, Ireland Tuorla Observatory, Department of Physics and Astronomy, University of Turku, Finland Laboratoire Leprince-Ringuet, Ecole polytechnique, CNRS/IN2P3, Universit´e Paris-Saclay, 91128, Palaiseau, France, [email protected],zefi@llr.in2p3.fr Finnish Centre for Astronomy with ESO, University of Turku, Finland Nyrola observatory, Jyvaskylan Sirius ry, Finland Department of Physics and Electrical Engineering, Linnaeus University, 351 95 V¨axj¨o, Sweden
ABSTRACTB2 1215+30 is a BL Lac-type blazar that was first detected at TeV energies by the MAGIC atmo-spheric Cherenkov telescopes, and subsequently confirmed by the VERITAS observatory with data collected between 2009 and 2012. In 2014 February 08, VERITAS detected a large-amplitude flarefrom B2 1215+30 during routine monitoring observations of the blazar 1ES 1218+304, located in thesame field of view. The TeV flux reached 2.4 times the Crab Nebula flux with a variability timescaleof < . Fermi -LAT,
Swift , and the Tuorla observatory revealeda correlated high GeV flux state and no significant optical counterpart to the flare, with a spectralenergy distribution where the gamma-ray luminosity exceeds the synchrotron luminosity. When in-terpreted in the framework of a one-zone leptonic model, the observed emission implies a high degreeof beaming, with Doppler factor δ >
10, and an electron population with spectral index p < . Keywords: galaxies: active — galaxies: nuclei — galaxies: jets — BL Lacertae objects: individual(B2 1215+30 = VER J1217+301) — gamma rays: galaxies INTRODUCTIONExtreme flux variability is one of the defining proper-ties of the blazar class of active galactic nuclei, appear-ing at all wavelengths over a wide range of timescales.Flares with amplitudes up to hundred times the quies-cent flux and variability timescales as short as 3 minuteshave been observed at TeV energies ( E & . . ± . × − cm − s − at E > . Fermi -LAT (GeV energies;0 . . E .
100 GeV), and the Tuorla optical ob-servatory. B2 1215+30 (R.A. = 12 h m s , decl.= +30 ◦ ′ ′′
1, J2000), also known as ON 325 or1ES 1215+303, was first detected at TeV energies byMAGIC (Aleksi´c et al. 2012). At GeV energies it is as-sociated with 3FGL J1217.8+3007 (Acero et al. 2015).There is some uncertainty in the distance to this source,with values of z = 0 .
130 (Akiyama et al. 2003) and z = 0 .
237 (Lanzetta et al. 1993) being quoted for itsspectroscopic redshift. Based on the location of itssynchrotron peak, B2 1215+30 has been either classi-fied as an intermediate (IBL, Nieppola et al. 2006) orhigh-frequency peaked BL Lac (HBL, Ackermann et al.2015).Throughout this paper we assume a Friedmann uni-verse with H = 67 . − Mpc − , Ω m = 0 .
309 andΩ λ = 0 . z = 0 .
130 ( d L = 630 Mpc)for B2 1215+30. Measurement uncertainties are statis-tical only unless indicated otherwise. VERITAS OBSERVATIONSVERITAS (Very Energetic Radiation Imaging Tele-scope Array System) is an array of four imaging at-mospheric Cherenkov telescopes located at the FredLawrence Whipple Observatory in southern Arizona,USA. VERITAS operates by recording Cherenkov lightfrom particle showers initiated by gamma rays in the up-per atmosphere and is sensitive to gamma-ray energiesfrom about 85 GeV to more than 30 TeV (Park 2015).Table 1 summarizes the VERITAS observations andresults on B2 1215+30. Observations were made in“wobble” pointing mode (Fomin, et al. 1994) consider-ing the presence of another TeV source in the field ofview (1ES 1218+304, offset 0 . ◦ from B2 1215+30) asdescribed in Aliu et al. (2013). Data were processed us-ing standard VERITAS analysis pipelines (Acciari et al.2009; Archambault et al. 2013). The energy threshold ofthe analysis is 200 GeV, with a systematic uncertaintyof 20% on the energy estimation.A TeV flare from B2 1215+30 was detected in 2013Feb 07 (MJD 56330, Figure 1) with flux F > . =(5 . ± . stat ± . sys ) × − cm − s − , or 0.24 Crab.The measured gamma-ray spectrum is compatible with apower-law (cid:0) d N/ d E = N · E − Γ (cid:1) with photon index Γ =3 . ± . stat ± . sys , in line with Γ = 3 . ± . . ± . F ( t ) = F (cid:0) − ( t − t ) /t var (cid:1) results in an upper limit on the flux halving time of t var <
52 h at a 90% confidence level (c.l.).A brighter subsequent flare from B2 1215+30 wasobserved on 2014 Feb 08 (MJD 56696, Figure 1) withflux F > . = (5 . ± . stat+4 . sys − . sys ) × − cm − s − ,or 2.4 Crab. The reconstructed energy spectrum iscompatible with a power-law with photon index Γ =3 . ± . stat ± . sys between 0.2 and 2 TeV (Figure 2).The observations targeted 1ES 1218+304 and had amean zenith distance of 27 ◦ , accumulating 45 min oflive-time exposure. On that night, a high-cloud layerat an altitude of 11 . luminous TeV flare from B2 1215+30 Table 1 . Summary of the VERITAS and
Fermi -LAT results from observations of B2 1215+30 in different epochs. TheVERITAS upper limit is computed at 95% c.l. assuming a power-law spectrum with index Γ = 3 . − s − ]VERITAS > . . σ (6 . ± . × − . σ (5 . ± . × − . σ (2 . ± . × − . σ (5 . ± . × − . σ < . × − Fermi -LAT 0.1–500 GeV 2013 Jan 06 – 2013 May 12 (MJD 56298–56424) 28 . σ (6 . ± . × − . σ (1 . ± . × − . σ (4 . ± . × −
200 GeV gamma rays is produced above 11.2 km (see,e.g., Rossi & Greisen 1941). This fraction decreaseswith increasing gamma-ray energy (see, e.g., Weekes2003). If all Cherenkov light emitted above the cloudlayer is lost, VERITAS would underestimate the energyof incoming gamma rays by ∼ t var < . FERMI-LAT OBSERVATIONSThe Large Area Telescope (LAT) is a pair-conversiongamma-ray telescope on board the
Fermi satellite cover-ing energies from about 20 MeV to more than 500 GeV(Atwood et al. 2009). Table 1 summarizes the
Fermi -LAT observations and results on B2 1215+30. Datawere analyzed using the unbinned likelihood analysis inLAT ScienceTools ( v10r0p5 ) with
P8R2 SOURCE V6 in-strument response functions, selecting photons with en-ergy 100 MeV < E <
500 GeV in a circular region of10 ◦ radius centered on the position of B2 1215+30. Theenergy spectrum of B2 1215+30 was modeled with apower law. Further analysis details and standard qual-ity cuts followed Acero et al. (2015). Light curves werederived by dividing the data in bins of one and threedays duration.A clear flux peak is seen coinciding with theVERITAS-detected flare of 2014 Feb 08 (Figure 1), fol-lowed by a rapid decay that constrains the flux halvingtime to t var < . . σ ), go- ing from an averaged Γ GeV = 1 . ± .
04 during the 2014campaign to Γ
GeV = 1 . ± .
09 in the four days of high-est GeV flux (MJD 56693-56696). In 2013, the LAT lightcurve shows no significant flux variability (Figure 1).However, the same TeV to GeV flare amplitude ratioseen in 2014 can be accomodated within the error barsof the 2013 LAT light curve. SWIFT OBSERVATIONSAn observation by the
Swift
Observatory (Ob-sId 00031906012) was carried out one day after theVERITAS-detected flare (Figure 3) with an expo-sure of 1.97 ks. X-ray Telescope (XRT, 0 . −
10 keV,Burrows et al. 2005) data were obtained in photon-counting mode and processed with the xrtpipeline tool (HEASOFT 6.16). The exposure shows a stablesource-count rate of ∼ . − , suggesting negligible pile-up effects.The spectrum was rebinned to have at least 20 countsper bin, ignoring channels with energy below 0.3 keV,and fit using PyXspec v1.0.4 (Arnaud 1996). An ab-sorbed power law with column density N H = 1 . × cm − (Kalberla et al. 2005) and photon index Γ X =2 . ± .
07 gives a good description of the spectral data( P ( χ ) = 0 . F . −
10 keV =(1 . ± . × − erg cm − s − .To analyze the Swift -UVOT data ( E ∼ . uvotsource tool (HEASOFT v6.16), corrected for extinction ac-cording to Roming et al. (2009) using E ( B − V ) fromSchlafly & Finkbeiner (2011), and converted to fluxesfollowing Poole et al. (2008). OPTICAL OBSERVATIONSOptical R-band data were obtained as partof the Tuorla blazar monitoring program ] - s - c m - [ > . T e V F ] - s - c m - [ . - G e V F time [MJD]56300 56320 56340 56360 56380 56400 56420 R - band f l u x [ m Jy ]
246 Tuorla ] - s - c m - [ > . T e V F VERITAS 2014 ] - s - c m - [ . - G e V F R - band f l u x [ m Jy ]
246 Tuorla
Figure 1 . TeV ( top ), GeV ( middle ), and optical ( bottom ) light curves of B2 1215+30 in 2013 ( left panel ) and 2014 ( right panel ).Fluxes are calculated in 1-day bins for VERITAS.
Fermi -LAT fluxes are calculated with 3-day integration bins (blue crosses)and 1-day bins (orange crosses) around the time of the 2014 flare. Down-pointing triangles indicate 95% c.l. upper limits derivedfrom the
Fermi -LAT data for time bins with signal smaller than 2 σ . The yearly-averaged TeV flux in 2011 (8 . × − cm − s − ,Aliu et al. 2013) is shown by a red-dashed line, and a blue-dashed line indicates the average GeV flux from Acero et al. (2015).Statistical errors on the Tuorla optical fluxes are smaller than the data points. (http://users.utu.fi/kani/1m, Takalo et al. 2008).Observations were taken using a 35 cm Celestron tele-scope attached to the KVA 60 cm telescope (La Palma,Canary Islands, Spain) and the 50 cm Searchlight Ob-servatory Network telescope (San Pedro de Atacama,Chile). Data were analyzed using a semi-automaticpipeline developed at the Tuorla Observatory. Thehost galaxy flux of 1.0 mJy (Nilsson et al. 2007) wassubtracted from the observed fluxes, and a correctionfor Galactic extinction was applied using values fromSchlafly & Finkbeiner (2011). The yearly-averagedoptical flux of (3 . ± .
01) mJy in year 2013 is similarto historical values dating back to 2003. In 2014,B2 1215+30 appeared to be in a long-lasting highoptical state, with average flux of (5 . ± .
02) mJy.No significant enhancement of the optical emission wasdetected in coincidence with the two gamma-ray flaresreported in Sections 2 and 3. DISCUSSIONWith the data presented here and in Aliu et al.(2013), VERITAS has published TeV observations ofB2 1215+30 spanning over 50 nights between 2008and 2014, finding no significant deviations from yearly-averaged fluxes other than the flares on 2013 Feb 07and 2014 Feb 08 reported in this paper. These two TeVflares had amplitudes of ∼ ∼
60 times the av-erage quiescent flux from B2 1215+30, with associated http://users.utu.fi/kani/1m/ON 325 jy.html flux halving times of ∼
52 and ∼ . . ± . × − cm − s − . This corresponds to an isotropic lumi-nosity L γ = 1 . × erg s − . To date, only four otherblazars have episodically been observed to emit TeV ra-diation with luminosity exceeding 10 erg s − . For com-parison, the historical TeV blazar Mrk 421 would haveto exhibit a 35 Crab flare to reach the luminosity of theB2 1215+30 outburst reported here.(ii) A non-detection by VERITAS 24 h after the flareindicates a flux halving time t var < . R ) and Doppler factor ( δ ) of thegamma-ray emitting region by Rδ − ≤ c t var / (1 + z ) = 3 . × cm , (1)(iii) The TeV flare was accompanied by a significantGeV flare measured by Fermi -LAT that extended overfour days and displayed some evidence for spectral hard-ening, with Γ
GeV = 1 . ± . luminous TeV flare from B2 1215+30 Swift -BAT (15-50 keV) andMAXI (4-10 keV) on the day of the TeV flare (MJD56696) can be interpreted as a limit on the hard X-ray flux of the order of ν x F ν x . × − erg cm − s − (Krimm et al. 2013; Hiroi et al. 2013). This effectivelylimits the peak synchrotron luminosity to L syn ≤ erg s − . (2)(vi) No change in the 15 GHz radio brightness ofB2 1215+30 was seen in the OVRO light curves in coin-cidence or after the TeV flare. B2 1215+30 is in fact inthe lower third of the OVRO sample in terms of radioflux variability (Richards et al. 2014).(vii)
Swift -XRT data taken 24 h after the flare showedan X-ray flux comparable with historical average values(Aleksi´c et al. 2012; Aliu et al. 2013), although the TeVflux was back to a quiescent level at that point.A lower limit on δ can be derived by estimating therequired Doppler boosting for gamma rays with en-ergy E γ to escape pair production on a co-spatial syn-chrotron photon field with density F ( E ), where E = (cid:0) m e c (cid:1) (1 + z ) − δ E − γ . For photons with E γ ∼ E = 76 eV. Using the expression foroptical depth from Dondi & Ghisellini (1995), imposing τ γγ ≤
1, and estimating F ( E ) from the Swift -XRT andUVOT measurements described in Section 4 results in δ ≥ " σ T d (1 + z ) α hc F ( E ) t var / (4+2 α ) ,δ ≥ . , (3)where σ T is the Thomson cross section and α is the spec-tral index of the synchrotron emission around E . Wenote that the Swift observations were made 24 h after theTeV flare (Figure 3). The lower limit on δ is still valid,however, as long as the density of synchrotron photonswas not lower during the flare than that measured onthe subsequent day.The spectral energy distribution (SED) of B2 1215+30during the flare is shown in Figure 2. TeV emission canbe explained by a fresh injection of relativistic electrons,where the injected perturbation propagates down in en-ergy as the plasma cools, explaining the smaller ampli-tude of the GeV flare and the lack of optical variability http://swift.gsfc.nasa.gov/results/transients/weak/QSOB1215p303/ http://maxi.riken.jp/mxondem/
10 15 20 25Frequency, log (ν/Hz)10 -12 -11 -10 -9 F l u x , ν F ν [ e r g c m − s − ] SSCSSC+ECMJD 56697LAT MJD 56693-6VERITAS MJD 56696
Figure 2 . Broadband SED of B2 1215+30 at differentepochs. Red markers show the state of the source duringthe 2014 Feb 08 flare, including VERITAS (MJD 56696.52),
Fermi -LAT (MJD 56693-56696),
Swift -BAT (MJD 56696),and Tuorla (MJD 56696.72) data. Blue markers show
Swift -XRT and UVOT fluxes and VERITAS 95% c.l. upper limitstaken 24 h after the flare. Gray markers show archival ob-servations from Aliu et al. (2013). The numerical SSC andSSC+EC models described in Section 6 are shown with asolid and a dashed gray line, respectively. Gamma-ray ab-sorption by the extragalactic background light is applied tothe models following Finke et al. (2010). (see, e.g., Giebels et al. 2007). Taking the radio spec-trum from Ant´on et al. (2004) and the R-band flux fromthe Tuorla observatory we derive a radio-to-optical spec-tral index α ro = 0 .
45. If the cooling break in the syn-chrotron SED happens beyond optical frequencies, as as-sumed in Aleksi´c et al. (2012) and Aliu et al. (2013) andtypically observed in BL Lac objects (Tavecchio et al.2010), α ro determines the power-law spectral index ( p )of the emitting electrons (see, e.g., Rybicki & Lightman1979): p = 1 + 2 α ro ≈ . . (4)Beyond the cooling break, the electron distribution hasto extend to Lorentz factors ( γ ) of the order γ max ≈ (1 + z ) δ − m e c > . × ( δ/ − (5)to produce the ∼ corresponding to emitting electron energies at which the ra-diative cooling and escape timescales are equal. (3) to constrain L syn and δ , we derive B ≃ (1 + z ) δ − L L γ c t var ! / , . (cid:0) L syn / erg s − (cid:1) ( δ/ − . (6)The scarcity of multiwavelength coverage simultane-ous with the TeV flare, specially of the synchrotron com-ponent, leaves numerical modeling of the SED under-constrained. However, even if modeling solutions arenot unique, they can be used to understand the levelof kinetic and magnetic jet power required under differ-ent scenarios. We test the feasibility of a SSC scenarioby using the stationary leptonic model of B¨ottcher et al.(2013), fixing the jet viewing angle to δ − for simplicity.Models within the parameter constraints from equa-tions (1–6) reproduce the measured gamma-ray lumi-nosity without overproducing the optical flux measuredby the Tuorla observatory, and keeping L syn . L γ asconstrained by the Swift -BAT non-detection (Figure 2).These solutions would indicate an emitting region wherethe kinetic power of relativistic electrons ( L e ) exceedsthe power carried by the magnetic field ( L B ) by a factorof ∼ δ would imply even higher L e /L B ratios. Giventhe observational uncertainty in the shape of the syn-chrotron emission, we also explore a wider range of elec-tron spectral indices than indicated in equation (4), find-ing that p < . Fermi -LAT.The lack of observable thermal emission fromthe accretion disk and associated emission lines inB2 1215+30 supports an SSC emission scenario. How-ever, the observed Compton dominance ( L γ /L syn &
1) typically points to external Compton models (EC;Dermer & Schlickeiser 1993) to explain the high-energyemission. Assuming an EC scenario, constraints on δ and the distance of the energy dissipation region fromthe black hole ( r diss ) can be derived assuming reasonablelimits on the jet collimation and luminosity of upscat-tered synchrotron photons. Following Nalewajko et al.(2014) results in: δ ( r diss ) < (cid:20) (1 + z ) r diss c t var (cid:21) / , (7) δ ( r diss ) > (cid:20) L γ ζ ( r diss ) L d (cid:21) / (cid:20) (1 + z ) r diss c t var (cid:21) / , (8) E.g., L e = 1 . × erg s − , q e = 1 . δ = γ min = 40, γ max = 10 , B = 0 .
03 G, R = 1 . × cm, η esc = 1, seeB¨ottcher et al. (2013) for parameter definitions not included inthe text. ] - s - c m - [ > . T e V F S w i ft - X R T ] - s - c m - [ . - G e V F R - band f l u x [ m Jy ]
246 Tuorla time - MJD 56696.5 [min]10 20 30 40 50 60020406080
Figure 3 . Same as Figure 1 around the night of 2014 Feb08 (MJD 56696). The top panel insert shows the TeV flux onMJD 56696 in 5-minute bins. A fit of the 5-minute binnedTeV light curve to a constant flux (gray-dashed line) yields P ( χ ) = 4 . × − . A vertical blue-dashed line indicates thetime of the Swift -XRT observation described in Section 4. where the accretion disk luminosity ( L d ) is assumed tobe 4 × erg s − (Ghisellini et al. 2010) and ζ ( r diss )describes the composition of the external radiationfields. Equations (7) and (8) constrain the ( δ, r diss ) pa-rameter space with a marginal solution at δ >
19 and r diss > . × cm that would place the emitting blobbeyond the broad-line region. A numerical EC model (B¨ottcher et al. 2013) with an external photon field de-scribed as blackbody emission with T ext = 10 K typicalof hot dust can reproduce the SED with L e /L B ∼ p . .
3) derived from themultiwavelength SED is usually obtained in semi-analytical calculations of relativistic shock acceleration L e = 5 × erg s − , q e = 1 . δ = γ min = 40, γ max = 10 , B = 0 . R = 10 cm, u ext = 2 × − erg cm − , T ext = 10 K, η esc = 1, see B¨ottcher et al. (2013) for parameter definitions notincluded in the text. luminous TeV flare from B2 1215+30 p ∼ . L e /L B . Fermi -LAT Collaborationacknowledges generous ongoing support from a num-ber of agencies and institutes that have supported boththe development and the operation of the LAT as wellas scientific data analysis. These include the NationalAeronautics and Space Administration and the Depart-ment of Energy in the United States, the Commis-sariat `a l’Energie Atomique and the Centre National dela Recherche Scientifique/Institut National de PhysiqueNucl´eaire et de Physique des Particules in France, theAgenzia Spaziale Italiana and the Istituto Nazionale diFisica Nucleare in Italy, the Ministry of Education, Cul-ture, Sports, Science and Technology (MEXT), the HighEnergy Accelerator Research Organization (KEK) andJapan Aerospace Exploration Agency (JAXA) in Japan,and the K.A. Wallenberg Foundation, the Swedish Re-search Council, and the Swedish National Space Boardin Sweden. Additional support for science analysis dur-ing the operations phase is gratefully acknowledged fromthe Istituto Nazionale di Astrofisica in Italy and theCentre National d’`Etudes Spatiales in France.REFERENCES