MAGIC extragalactic highlights from a MeV perspective
MMem. S.A.It. Vol. 75, 282 c (cid:13) SAIt 2008
Memorie della
MAGIC extragalactic highlights from a MeVperspective
E. Prandini for the MAGIC Collaboration Dipartimento di Fisica e Astronomia G. Galilei, Universit´a degli Studi di Padova, Italy &I.N.F.N. Sez. di Padova e-mail: [email protected]
Abstract.
In the past fifteen years, the way to study TeV gamma-ray emitters changed dras-tically. The detection-based approach aimed at populating the TeV gamma-ray sky evolvedinto a physics-driven one, with the ambitious objective of understanding the mechanismsresponsible for the emission and their environments. The synergic collaboration betweeninstruments operating in di ff erent electromagnetic bands and with di ff erent messengersis therefore crucial. In this talk, I will report highlights on extragalactic physics studiesachieved with the MAGIC telescopes, with special emphasis on the MeV-TeV connection. Key words.
Stars: abundances – Stars: atmospheres – Stars: Population II – Galaxy: glob-ular clusters – Galaxy: abundances – Cosmology: observations
1. Introduction
The study of the most energetic photons fromgalactic and extragalactic emitters, the veryhigh-energy photons (VHE, E >
100 GeV) isone of the most recent disciplines in observa-tional astronomy.The current generation of ImagingAtmospheric Cherenkov Telescopes (IACTs)includes two arrays of telescopes located inthe Northern hemisphere, namely the MajorAtmospheric Gamma-ray Imaging Cherenkov(MAGIC) and the Very Energetic RadiationImaging Telescope Array System (VERITAS),and one array in the Southern hemisphere, theHigh Energy Stereoscopic System (H.E.S.S.).
Since 2004, the MAGIC telescopes observe theNorthern sky from the Canary island of La Palma, at ∼ ∼
60 GeV and afast positioning system, essential in case offast alerts such as gamma-ray bursts (GRBs)and neutrino alerts. The MAGIC science stud-ies are divided into the following working a r X i v : . [ a s t r o - ph . H E ] A ug randini: MAGIC extragalactic highlights 283 Fig. 1.
Map of the sources detected as VHEgamma-ray emitters with the MAGIC tele-scopes. Adapted from http://tevcat2.uchicago.edu .groups: Galactic, Extragalactic, Transient, andFundamental Physics.Due to its location, low energy threshold,and fast repositioning MAGIC is best suitedfor studies involving extragalactic sources andtransient events.
The extragalactic sky at VHE gamma raysis completely dominated by jetted ActiveGalactic Nuclei (AGNs): only three sourcesout of the ∼
80 sources listed in the TeV cat-alog ( http://tevcat2.uchicago.edu ) arenon-AGNs. These sources are the two starburstgalaxies M 82 and NGC 253, and the gammaray burst GRB 190114C.In its first 16 years of operations, theMAGIC telescopes detected significant sig-nals from more than half of the known ex-tragalactic TeV emitters. The 44 extragalac-tic objects detected with MAGIC as of April2019 are illustrated in Fig. 1. In the Figurethe GRB 190114C (ATel ff s. Thestudy of the interplay between VHE gammarays and photons at shorter wavelengths is fun-damental to achieve the physics goal and co-ordinated, broadband observation campaignsare the becoming the standard in the field.Moreover, the connection with other messen-gers, like neutrinos, plays a crucial role andshould be taken into consideration.For this contribution, three highlights wereselected with a special attention on the possibleMeV–TeV connection.
2. Highlight Results
Blazars, jetted-AGNs with a jet pointing to-wards the observer, are divided into two mainclasses depending on the presence or not ofbroad lines in their optical spectrum. BL Lacobjects feature no or very weak emission lineswhile flat spectrum radio quasars (FSRQs) arecharacterized by strong optical lines due to adense cloud region distributed between the jetand the disk. On average, FSRQs are more lu-minous and they are detected up to redshiftabove 2, while known BL Lac objects arefainter and their distance is limited (mostly be-low 1 for gamma-ray detected objects, see forexample the 3LAC catalog (Ackermann et al.2015). In both cases, the spectral energy distri-bution (SED) is dominated by a double peaked,non thermal-emission from the jet.The large majority of AGNs detected byIACTs in the VHE gamma-ray range belongsto the BL Lac class that despite the limited lu-minosity is characterized by an SED shiftedtowards higher energies with respect to theFSRQ case. In FSRQ, the second SED peakusually lies in the MeV to GeV range, makingthem ideal targets for MeV instruments. In par-
84 Prandini: MAGIC extragalactic highlightsSource z Discoverer YearB 0218 +
367 0.944 MAGIC 2014PKS 1441 +
25 0.939 MAGIC 2015TON 599 0.720 MAGIC 20173C 279 0.536 MAGIC 2006S4 0954 +
65* 0.356? MAGIC 2015PKS 1222 +
216 0.432 MAGIC 2010PKS 1510-089 0.361 HESS 2009PKS 0736 +
017 0.189 HESS 2016
Table 1.
List of FSRQs detected by currentgeneration of IACTs. The classification of S40954 +
65, marked with ∗ , is uncertain.ticular, the MeV range is essential for the studyof distant FSRQs, see Sbarrato et al. (2015).Only 8 FSRQs populate the VHE extra-galactic sky. They are listed in Table 1. Dueto the second SED peak frequency, well belowthe VHE range, FSRQs are usually detected byIACTs only at low energies ( ∼
100 GeV) andduring bright flares. The only source detectedat VHE also in its persistent state is PKS 1510-089 (MAGIC Coll. 2018a).Thanks to the good performance at low en-ergies (MAGIC Coll. 2016), FSRQs are idealtargets for MAGIC. Since these objects showfast, day-scale variability at all bands, a quickreaction to alerts is essential and was the keyaspect for many MAGIC discoveries.The main open question adressed withVHE observations is related to the locationof the emitting region in FSRQs, which isstrongly connected to the VHE spectral cut-o ff and to the variability timescale. Accordingto the standard scenario of non-thermal emis-sion from FSRQs, a short, minute-scale, vari-ability implies a strong self-absorption alreadyat few tens of GeV, while a day-scale variabil-ity is compatible with a non-self absortion sce-nario. In MAGIC observations of the sourcePKS 1222 + Neutrino blazar
TXS 0506 +
056 is a gamma-ray emitting blazarlocated at redshift 0.336 (Paiano et al. 2018).This object was only one of the many gamma-ray emitting blazars detected by
Fermi -LAT atgamma rays, at least until the 22nd September2017, when IceCube reported the detectionof a neutrino from a region compatible withthat of TXS 0506 +
056 (GCN / AMON Noticedated 22 September 2017 20:55:13 UTC).The alert was immediately followed by multi-wavelength and multi-messenger observationssummarized in IceCube Coll. et al. (2018). Theanalysis of
Fermi -LAT data collected after thealert and in the precedent years revealed thatTXS 0506 +
650 was in an active gamma-raystate since several months at the moment of thealert. Moreover, the emission reaches the VHEgamma-ray band, as announced by MAGICand confirmed by the VERITAS collaboration.This exceptional event o ffi cially markedthe beginning of the era of extragalactic multi-messenger astronomy with neutrinos. Everymessenger, as well as every band of the electro-magnetic spectrum, carries important informa-tion needed to unveil the main mechanisms atwork in jetted AGNs. As detailed in Ojha et al.(2019), the MeV band (including polarization)is an excellent proxy for photo-hadronic pro-cesses in blazar jets, that are expected to pro-duce neutrino counterparts.Sub-TeV observations are also crucial toprobe the emitting mechanisms, as discussed inMAGIC Coll. (2018b). In that paper, the broad-band SED including MAGIC sub-TeV spectraboth during the quiescent state of the sourceand during its flaring state are interpreted in theframework of a novel one-zone lepto-hadronicmodel. According to this model, electrons andprotons co-accelerated in the jet interact withexternal photons coming from a slow-movingplasma layer surrounding the faster jet spine.Figure 2 illustrates the results of MAGICobservations. In the light curve (upperpanel) two flaring events are highlighted, at randini: MAGIC extragalactic highlights 285 F l u x > G e V [ c m s ] IC-170922AMAGIC60 80 100 200 300 400 500 600Energy [GeV]10 E F [ e r g c m s ] MJD 58029-30MJD 58057Lower state
Fig. 2.
Upper panel: MAGIC light curve above300 GeV starting from the neutrino alert (ver-tical dashed line). Two flaring states were de-tected (green areas). Lower panel: di ff eren-tial energy spectra at VHE as measured byMAGIC during the two flares reported above(MJD 58029-30 and MJD 58057) and duringthe low / quescent state. Figure from MAGICColl. (2018b).MJD 58029-30 and MJD 58057 respectively.The corresponding di ff erential energy spectraare represented in the lower panel (greenpoints), together with the averaged emis-sion obtained from the low state / quiescentnights. Interestingly, the slope of the MAGICspectrum does not show strong evidence forvariability during the di ff erent flux states.Main outcome of the lepto-hadronic modelproposed is that a non-negligible contributionin the SED arises from cascade emission in-duced by protons, most notably in the hardX-ray and VHE gamma-ray bands. The max-imum energy of protons inferred from themodel is consistent with an important contri-bution to the flux of ultra high-energy cosmicrays from protons (and heavier nuclei) acceler-ated in the jet region. Extreme blazars are a sub-class of blazars fea-turing the first SED peak, i.e. the synchrotronpeak, above 10 Hz (Costamante et al. 2001).The second SED peak is therefore possiblyshifted in the sub-TeV range. This at least for a sub-sample of objects, as discussed in Fo ff anoet al. (2019). TeV blazars are interesting tar-gets for MeV observations as their synchrotronpeak could lie in this band (De Angelis et al.2018).The TeV-peaking SED of the extremeblazar 1ES 0229 +
200 attracted a number of in-teresting studies on various subjects. Namely:the study of particle acceleration mechanismsin such extreme objects, e.g. Kaufmann etal. (2011); estimate of new limits on the ex-tragalactic background light (H.E.S.S. Coll.2007; MAGIC Coll. 2019), intergalactic mag-netic field (Vovk et al. 2012), and for axion-like particles (Galanti et al. 2018); test for thehadron beam scenario (Tavecchio et al. 2018);probe for cosmology and ultra-high-energycosmic rays (Tavecchio et al. 2015); study ofLorentz invariance violation (Tavecchio et al.2016). Therefore, the impact of the observationand characterization of these extreme blazarsfor the astrophysical and cosmological com-munity is very broad. The field, however, suf-fers from the still quite limited number of ob-jects belonging to this category.With the aim of increasing the number ofTeV-detected extreme blazars, the MAGIC col-laboration started a multi-year observationalcampaign on several objects. In addition, deepobservation of 1ES 0229 + +
3. Conclusions
In this exciting moment for the high-energy as-trophysical community, with the recent birth of
86 Prandini: MAGIC extragalactic highlightsMAGICSource z detectionTXS 0210 +
515 0.049 Y1ES 2037 +
521 0.053 YPGC 2402248 0.065 YBZB J0809 + +
244 0.104 Hint1ES 1426 +
428 0.129 YRGB J2313 +
147 0.163 N1ES 0927 +
500 0.187 NRBS 0723 0.198 YRBS 0921 0.236 NTXS 0637-128 unknown N
Table 2.
Extreme blazars observed with theMAGIC telescopes from 2010 to 2018 orderedaccording to their distance. [Hz] ν ] s ) [ e r g s c m ν f ( ν
10 E [eV]
10 10 preliminary Fig. 3.
Multi-band SED of 1ES 2037 +
521 dur-ing MAGIC observations in 2016 (red), includ-ing
Swift -UVOT,
Swift -XRT,
Fermi -LAT, andMAGIC data, along with archival data (gray).The black curve represents the SSC model(Asano et al. 2014) fitting the data.multi-messenger extragalactic astronomy withneutrinos, MAGIC has a leading role in thestudy of VHE gamma-ray emissions from ex-tragalactic sources. The photon-neutrino con-nection from blazars, as well as the characteri-zation of the broadband emission from FSRQsand from extreme blazars presented here aresome examples of common interest for the TeVand the MeV communities.
Acknowledgements:
We would like to thank the Instituto de Astrof´ısicade Canarias for the excellent working conditions at the Observatorio delRoque de los Muchachos in La Palma. The financial support of the GermanBMBF and MPG, the Italian INFN and INAF, the Swiss National FundSNF, the ERDF under 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, FPA201790566REDC), the Indian Department ofAtomic Energy, the Japanese JSPS and MEXT and the Bulgarian Ministry ofEducation and Science, National RI Roadmap Project DO1-153 / / C4 and SFB876 / C3, the Polish National Research Centregrant UMO-2016 / / M / ST9 / References
MAGIC Coll. 2017, Astroparticle Physics, 94,29MAGIC Coll. 2016, Astroparticle Physics, 72,76Ackermann, M. et al. 2015, ApJ, 810, 1, 14Sbarrato, T. et al. 2015 MNRAS, 462, 2, 1542MAGIC Coll. et al. 2018a, A&A, 619, A159MAGIC Coll. et al. 2011, ApJL, 730, 1,L8Paiano, S. et al. 2018, ApJL, 854, 2, L32IceCube Coll. et al. 2018, Science, 361, 6398Ojha, R. et al. White paper submitted to theAstro2020 Decadal SurveyMAGIC Coll. et al. 2018b, ApJL, 863, 1, L10Costamante, L., et al. 2001, A&A, 371, 2Fo ffff