
	&nbsp;The detection of Flat Spectrum Radio Quasars (FSRQs) in the Very High Energy (VHE, E&gt;100

	GeV) range is challenging, mainly because of their steep spectra in this energy band. Up to now,

	only five FSRQs are known to be VHE &gamma;-ray emitters, all of them have been detected by the

	MAGIC telescopes, that discovered four of them in the VHE band. The observations in the VHE

	band are crucial to understand their emission, specially to constrain the location of the emitting

	region within the jet due to the absorption from their broad line region (BLR). Typically, FS-

	RQs are detected during high flux states, enhancing the probability of detection with the current

	instruments sensitivities. However, the last observation campaigns performed with the MAGIC

	telescopes show emission during moderate states, thus challenging our understanding of the emis-

	sion mechanisms in FSRQs. In this contribution, we give an overview and present the most recent

	results of the three FSRQs 3C279, PKS1222+21 and PKS1510-089 in a multi-wavelength context

	with special focus on MAGIC and Fermi-LAT simultaneous observations.</div

A. Lähteenmäki

A. Marscher

E. Lindfors

E. Prandini

F. Tavecchio

G. De Caneva

J. Becerra González

J. McEnery

J. Sitarek

K. Satalecka

M. Tornikoski

MAGIC and Fermi-LAT Collaborations

S. Jorstad

T. Hovatta

V. Fallah Ramazani

UTUPub

PoS(ICRC2015)876Flat Spectrum Radio Quasars through the MAGICglassesJ. Becerra González∗1,2,3, E. Lindfors4, E. Prandini5,6, K. Satalecka7, J. Sitarek8, G.De Caneva9, V. Fallah Ramazani4, F. Tavecchio10, J. McEnery1, T. Hovatta11,12, M.Tornikoski11, A. Lähteenmäki11, S. Jorstad13 and A. Marscher13 for the the MAGICand Fermi-LAT Collaborations1 NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA2 Department of Physics and Department of Astronomy, University of Maryland, College Park,MD 20742, USA3 Inst. de Astrofísica de Canarias, E-38200 La Laguna, Tenerife, Spain4 Finnish MAGIC Consortium, Tuorla Observatory, University of Turku and Department ofPhysics, University of Oulu, Finland5 ETH Zurich, CH-8093 Zurich, Switzerland6 ISDC - Science Data Center for Astrophysics, 1290, Versoix (Geneva), Switzerland7 Universidad Complutense, E-28040 Madrid, Spain8 University of Łódź, PL-90236 Łódź, Poland9 Deutsches Elektronen-Synchrotron (DESY), D-15738 Zeuthen, Germany10 INAF National Institute for Astrophysics, I-00136 Rome, Italy11 Aalto University Metsähovi Radio Observatory, Metsähovintie 114, FI-02540 Kylmälä, Finland12 Cahill Center for Astronomy and Astrophysics, California Institute of Technology, Pasadena,CA 91125, USA13 Institute for Astrophysical Research, Boston University, 725 Commonwealth Avenue, Boston,MA 02215, USA; Astronomical InstituteE-mail: josefa.becerra@nasa.govThe detection of Flat Spectrum Radio Quasars (FSRQs) in the Very High Energy (VHE, E>100GeV) range is challenging, mainly because of their steep spectra in this energy band. Up to now,only five FSRQs are known to be VHE γ-ray emitters, all of them have been detected by theMAGIC telescopes, that discovered four of them in the VHE band. The observations in the VHEband are crucial to understand their emission, specially to constrain the location of the emittingregion within the jet due to the absorption from their broad line region (BLR). Typically, FS-RQs are detected during high flux states, enhancing the probability of detection with the currentinstruments sensitivities. However, the last observation campaigns performed with the MAGICtelescopes show emission during moderate states, thus challenging our understanding of the emis-sion mechanisms in FSRQs. In this contribution, we give an overview and present the most recentresults of the three FSRQs 3C279, PKS1222+21 and PKS1510-089 in a multi-wavelength contextwith special focus on MAGIC and Fermi-LAT simultaneous observations.The 34th International Cosmic Ray Conference,30 July- 6 August, 2015The Hague, The Netherlandsc© Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence. http://pos.sissa.it/PoS(ICRC2015)876Flat Spectrum Radio Quasars with MAGIC J. Becerra González1. IntroductionBlazars are active galactic nuclei (AGNs) whose relativistic jets point close to our line of sight,making their emission strongly boosted. They constitute the most numerous source class detectedat high energies, dominating the extragalactic γ-ray sky. Only 65 extragalactic sources have beendetected to date in the VHE band by the Cherenkov telescopes, 59 of them being blazars. Blazarsemit strongly throughout the whole electromagnetic spectrum, and their multi-wavelength (MWL)spectral energy distributions (SEDs) are characterized by two broad peaks. Depending on thefrequency of the peaks and the optical spectral characteristics, blazars are classified as BL Lacobjects and flat spectrum radio quasars (FSRQs). The MWL SED of FSRQs typically peaks atlower energies [1], making the detection of such targets challenging in VHE. Up to now, only 5FSRQs have been detected in the VHE band: 3C 279 [2, 3], PKS 1510-089 [4, 5], PKS 1222+216[6], S3 0218+357 [7] and PKS 1441+25 [9, 10].The emission of blazars at low frequencies is attributed to synchrotron emission from relativis-tic electrons in the jet. The high energy peak origin is still under debate, it can be produced throughinverse Compton scattering within a low frequency photon field (leptonic models) or by hadronicinteractions [14]. The low frequency photon field can have different origins: the synchrotron emis-sion within the jet (Synchrotron self-Compton -SSC- models, [11]) or an external region to the jet,the optical-UV photons from the BLR or the IR photons from the dusty torus (External Comptonmodels, [12], [13]). In FSRQs, typically the high energy peak is much more luminous that the lowenergy one (Compton dominance). In such case, it is hard to explain the high energy emission onlyas SSC, and some additional external seed photons are needed to explain its SED. Strong emissionlines are typically present in the optical spectra from FSRQs, we can infer therefore that there isa strong BLR in this type of blazars, with high density of UV-optical photons. Such UV-opticalphotons can serve as seed for the inverse Compton process to produce high energy photons. How-ever, it can also contribute to the absorption of the γ-rays. If the emitting region of the jet is locatedwithin the BLR, a strong absorption is expected above tens of GeV, in the high energy extremeof the Fermi-LAT energy range. Instead, if the emitting region within the jet is considered to belocated farther away from the central engine, were the IR photons form the torus are dominant asexternal seed for the inverse Compton process, the absorption spectral feature is expected to bedetected above ∼1 TeV. Therefore, VHE observations are crucial to constrain the location of theemitting region in FSRQs together with the Fermi-LAT monitoring.The FSRQs detected in VHE band show different observational characteristics. A brief de-scription of each FSRQ detect in the VHE band up to date can be found below:• 3C 279 (z=0.54) has been detected twice in VHE γ-rays before 2014: MAGIC discovered thesource on February 23, 2006, and then detected it again on January 16, 2007. The flux andspectra of the two observations are comparable within the errors, the 2006 measured integralflux being F(> 150GeV)= (5.15± 0.82stat ± 1.5syst)× 10−10phcm−2 s−1 and spectral indexα = 4.1± 0.7stat ± 0.2syst . In both cases, the significant detection is preceded by a hint ofsignal on 2-3 σ level from the previous night.∗Speaker.2PoS(ICRC2015)876Flat Spectrum Radio Quasars with MAGIC J. Becerra González• PKS 1222+216 (z=0.43) was detected in VHE γ-rays on June 17, 2010 by the MAGICtelescopes. The source had been monitored by the MAGIC telescope since the beginningof May 2010, the data from May 8, 2010 showed a hint of signal at 4.4 σ level [15]. TheMAGIC observations on June 17, 2010 had a duration of only 30 minutes, but even withinthis short observation the flux was significantly variable with the flux doubling time of orderof ∼ 9 minutes [6]. The observed spectral slope is soft with Γ = 3.75 ± 0.29. In 2014,VERITAS reported the detection of a significant signal from this source from several nightsrather than from a single night strong flare [16]. This detection is coincident with the MAGICobservations discussed in this contribution.• PKS 1510-089 (z=0.36) has also been detected twice in VHE γ-rays in two extended periodsfrom March and April 2009 by H.E.S.S. [4] and February-April 2012 by MAGIC [5]. Theflux and spectra of the two observations agree within the errors. The integral flux of the 2012measurement is F(>200GeV)= (3.6±0.9)×10−11phcm−2 s−1. The best-fit power law to theVHE data has a photon index of Γ = 3.8±0.4stat±0.3sys. There is no published upper limitsof the source below these detections and therefore it cannot be concluded if the detected fluxpresents high or quiescent state of the source at VHE γ-rays. Neither of the data sets showstatistically significant variability on daily, weekly or monthly scales. It should be noted,however, that in the Fermi Hard source catalog this source is listed as variable above >10GeV [17].• S3 0218+357 is a gravitationally lensed FSRQ discovered by MAGIC in July 2014 [7] atthe redshift of 0.94. The VHE detection was possible thanks to the gravitational lens effectfrom which we could predict when the delayed emission from the flare would reach the Earthbased on a previous Fermi-LAT flare detection [8].• PKS 1441+25 is the latest FSRQ detected in the VHE band, first discovered by MAGIC [9]and later confirmed also by VERITAS [10]. It is also a very distant blazar located at the samedistance than S3 0218+357, z=0.94. The observations were triggered by the high state andspecially the hard index observed by the Fermi-LAT.S3 0218+357 and PKS 1441+25 are the most distant VHE blazars known to date. Besidesthe study of the intrinsic characteristics of FSRQs, which are poorly known due to the lack ofstatistics, they are also important to test for the first time the EBL models at high redshifts in thisenergy range.As discussed above, due to the steep spectrum of FSRQs in the VHE band, they are typicallydetected while undergoing strong flares. However, in this contribution we will present the resultsfrom the observational campaign in 2013-2014 of the three VHE FSRQs 3C 279, PKS 1510-089and PKS 1222+216. Their detection in the VHE band is not strongly correlated with the high stateof the sources.2. MAGIC data analysis and resultsThe VHE γ-ray observations were performed by the MAGIC telescopes. The MAGIC systemconsists of two 17 m-diameter Imaging Atmospheric Cherenkov Telescopes (IACT) located on the3PoS(ICRC2015)876Flat Spectrum Radio Quasars with MAGIC J. Becerra GonzálezFigure 1: Detection plot for the FSRQs 3C 279, PKS 1222+216 and PKS1510-089 during 2013-2014campaign with the MAGIC telescopes. θ 2 is calculated as the square distance between the reconstructedand nominal position of the source. Black points represent the θ 2 distribution from the source, while thedistribution for background events are denoted by the gray shaded area.Roque de los Muchachos, Canary Island of La Palma (28◦46′N,17◦53′W), at a height of 2200 mabove sea level. The system reaches a sensitivity of (0.66± 0.03)% of the Crab Nebula flux forE>220 GeV in 50 h of observations [19].The VHE observations of the three FSRQs we discuss in this contribution where observedwith the MAGIC telescopes in wobble mode [20], with the source located 0.4◦ from the centre ofthe field of view. The analysis of the data has been performed using the standard MAGIC analysischain [21, 22].The FSRQ 3C279 was observed for 30.5 hours from 2013-12-30 to 2014-05-31 (MJD 56656-56808) with zenith angles from 34 to 50 degrees. As shown in Fig. 1, the source was detected witha confident level of 5.8 σ .The observations on PKS 1222+216 were carried out from 2013-12-30 to 2014-03-25 (MJD56656-56741) at zenith angles from 9 to 46 degrees for a total of 14.46 hours. We detected thesource at 7.0 σ level.PKS 1510-089 was observed with the MAGIC telescopes from 2013-03-15 to 2013-06-05(MJD 56366-56448) and 2014-06-17/18 (MJD 56825/26) for 22.4 hours covering a zenith anglerange from 27 to 45. The plot shown in Fig. 1 reveals a detection of the source at 7.6 σ confidencelevel.The nightly light curve at E>150 GeV does not show hints of variability for any of the threesources presented in this contribution. The flux is compatible with a constant emission during theobserved period.4PoS(ICRC2015)876Flat Spectrum Radio Quasars with MAGIC J. Becerra González3. Multi-wavelength framework and resultsSince blazars emit throughout the whole electromagnetic spectrum and are highly variablesources, they can only be properly studied in a MWL framework. Only part of the large compi-lation of MWL data will be presented in the proceedings, but they will be discussed in the oralcontribution and the forthcoming paper.Thanks to the strong cooperation between the Fermi-LAT and the MAGIC telescopes togetherwith the optical monitoring performed with the KVA telescope by the Tuorla Observatory AGNgroup (http://users.utu.fi/kani/1m/), we have detected the "classical" VHE FSRQs during moderategamma-ray activity and two new VHE FSRQs have been discovered with the MAGIC telescopes.The long-term monitoring of the gamma-ray sky performed by Fermi-LAT above 100 MeV allowsto study in detail the time evolution of the emission from individual sources. This is specially im-portant in the case of FSRQs. As discussed in the previous sections, due to the intrinsic character-istics of FSRQs, the detection of the VHE gamma-rays is very challenging. However, Fermi-LATobservations can trigger ground-based Cherenkov telescopes during active periods of the source.This is particularly relevant when considering the small field of view and short duty cycle of theCherenkov telescopes.In Fig. 2, the gamma-ray light curve of 3C279 above 100 MeV observed with the Fermi-LATand the optical R-band light curve observed with the KVA telescope are shown. The vertical linesdenote the MAGIC observations. The flare around MJD 56750 detected with the LAT is one of thestrongest flare of the source detected with this instrument. Unfortunately, the peak of the emissionwas not well sampled by the MAGIC telescopes due to moon/weather constraints. Nevertheless,the VHE emission is not centered only around the strong flare. Indeed, it is compatible with aconstant flux during the observation period. There is not clear correlation between optical andgamma-rays evolution.In case of PKS 1222+216, as show in Fig. 3, due to observation constraints MAGIC could notobserve the strong flare during the period. As opposite to the case of 3c279, the gamma-ray andoptical seem to be correlated at least during the strong flare. However, the optical flare is delayedwith respect to the gamma-ray.The FSRQ PKS 1510-089 was only detected by MAGIC during the 2013 campaign, therefore,the light curve shown in Fig. 4 is focuses in that period. As in the case of 3c279, no strongcorrelation can be claimed between the optical and gamma-ray light curves. MAGIC observationswere only performed during moderate activity of the source in gamma-rays.Despite the different characteristics of the sources and evolutions with/without gamma-rayand optical correlation, all three sources were detected during moderate gamma-ray activity. Nohint of variability in the MAGIC light curves was found. The only previous detection compatiblewith a constant emission was PKS 1510-089, for the rest of the FSRQs, strong variability has beenpreviously one of the fingerprints of FSRQs detection in the VHE band. However, remarkablyduring the 2013-2014 VHE observation campaign, the detection of the three sources are compatiblewith a constant flux, pointing to the fact that the VHE emission in FSRQs not necessarily need tobe associated with extreme flares.5PoS(ICRC2015)876Flat Spectrum Radio Quasars with MAGIC J. Becerra GonzálezFigure 2: Top: Light curves of the FSRQ 3c279 for energies between 100 MeV and 300 GeV observed withthe Fermi-LAT and calculated in 1 day bins. Bottom: R-band light curve observed with the KVA telescope.The vertical lines denote the MAGIC observations.Figure 3: Top: Light curves of the FSRQ PKS 1222+216 for energies between 100 MeV and 300 GeVobserved with the Fermi-LAT and calculated in 1 day bins. Bottom: R-band light curve observed with theKVA telescope. The vertical lines denote the MAGIC observations.6PoS(ICRC2015)876Flat Spectrum Radio Quasars with MAGIC J. Becerra GonzálezFigure 4: Top: Light curves of the FSRQ PKS 1510-089 (only 2013 data) for energies between 100 MeVand 300 GeV observed with the Fermi-LAT and calculated in 1 day bins. Bottom: R-band light curveobserved with the KVA telescope. The vertical lines denote the MAGIC observations.AcknowledgmentsWe would like to thank the Instituto de Astrofísica de Canarias for the excellent workingconditions at the Observatorio del Roque de los Muchachos in La Palma. The financial supportof the German BMBF and MPG, the Italian INFN and INAF, the Swiss National Fund SNF, theERDF under the Spanish MINECO (FPA2012-39502), and the Japanese JSPS and MEXT is grate-fully acknowledged. This work was also supported by the Centro de Excelencia Severo OchoaSEV-2012-0234, CPAN CSD2007-00042, and MultiDark CSD2009-00064 projects of the SpanishConsolider-Ingenio 2010 programme, by grant 268740 of the Academy of Finland, by the CroatianScience Foundation (HrZZ) Project 09/176 and the University of Rijeka Project 13.12.1.3.02, bythe DFG Collaborative Research Centers SFB823/C4 and SFB876/C3, and by the Polish MNiSzWgrant 745/N-HESS-MAGIC/2010/0.The Fermi-LAT Collaboration acknowledges support for LAT development, operation anddata analysis from NASA and DOE (United States), CEA/Irfu and IN2P3/CNRS (France), ASIand INFN (Italy), MEXT, KEK, and JAXA (Japan), and the K.A. Wallenberg Foundation, theSwedish Research Council and the National Space Board (Sweden). Science analysis support inthe operations phase from INAF (Italy) and CNES (France) is also gratefully acknowledged.7PoS(ICRC2015)876Flat Spectrum Radio Quasars with MAGIC J. Becerra GonzálezReferences[1] G. Fossati et al., A unifying view of the spectral energy distributions of blazars, MNRAS 98, 299, 433[2] J. Albert et al., Very-High-Energy gamma rays from a Distant Quasar: How Transparent Is theUniverse?, Science 08, 320, 1752[3] J. Aleksic̀ et al., MAGIC observations and multiwavelength properties of the quasar 3C279 in 2007and 2009, A&A 11, 530, id.A4[4] A. Abramowski et al., H.E.S.S. discovery of VHE ?-rays from the quasar PKS 1510-089, A&A 13,554, id.A107[5] J. Aleksic̀ et al., MAGIC gamma-ray and multi-frequency observations of flat spectrum radio quasarPKS 1510-089 in early 2012, A&A 14, 569, id.A46[6] J. Aleksic̀ et al., MAGIC Discovery of Very High Energy Emission from the FSRQ PKS 1222+21,ApJL 11, 730, L8[7] R. Mirzoyan, Discovery of Very High Energy Gamma-Ray Emission From Gravitationally LensedBlazar S3 0218+357 With the MAGIC Telescopes, ATel #6349[8] C. C. 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Holder, Detection of Persistent VHE emission from PKS 1222+216 (4C +21.35) with VERITAS,ATel #5981[17] M. Ackermann et al., The First Fermi-LAT Catalog of Sources Above 10 GeV, ApJS 13, 209, id. 34[18] S. Buson, Fermi LAT Detection of a Hard Spectrum Gamma-ray Flare from Gravitationally LensedBlazar S3 0218+357, ATel #6316[19] J. Aleksic̀ et al., The major upgrade of the MAGIC telescopes, Part II: A performance study usingobservations of the Crab Nebula, arXiv:1409.5594[20] V. P. Fomin et al., New methods of atmospheric Cherenkov imaging for gamma-ray astronomy. I. Thefalse source method, ApJ 94, 2, 137[21] A. Moralejo et al., MARS, the MAGIC Analysis and Reconstruction Software, [arXiv:0907.0943][22] S. Lombardi et al., Advanced stereoscopic gamma-ray shower analysis with the MAGIC telescopes[arXiv:1109.6195]8

The 34th International Cosmic Ray Conference

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The 34th International Cosmic Ray Conference

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