B\uf6ttcher, Markus

Bottacini, Eugenio

Collmar, Werner

Gasparrini, Dario

Pian, Elena

English

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Challenges in reconciling observations and theory of the brightest high-energy flare ever of 3C 279

Böttcher, Markus

Archivio istituzionale della ricerca - Università di Padova

PoS(ICRC2017)642Challenges in reconciling observations and theoryof the brightest high-energy flare ever of 3C 279Eugenio Bottacini∗†Dipartimento di Fisica e Astronomia "G. Galilei", Universita di Padova, I-35131 Padova, ItalyW.W. Hansen Experimental Physics Laboratory & Kavli Institute for Particle Astrophysics andCosmology, Stanford University, USAE-mail: eugenio.bottacini@unipd.itMarkus BöttcherCentre for Space Research, North-West University, Potchefstroom 2531, South AfricaElena PianINAF, Istituto di Astrofisica Spaziale e Fisica Cosmica, via P. Gobetti 101, 40129 Bologna, ItalyScuola Normale Superiore, Piazza dei Cavalieri 7, 56122 Pisa ItalyINFN, Sezione di Pisa, Largo Pontecorvo 3, 56127 Pisa, ItalyWerner CollmarMax-Planck-Institut für extraterrestrische Physik, Giessenbach, 85748 Garching, GermanyDario GasparriniAgenzia Spaziale Italiana (ASI) Space Science Data Center, I-00133, Roma, ItalyIstituto Nazionale di Fisica Nucleare, sezione di Perugia, I-06123, Perugia, ItalyRecent high-energy missions have allowed keeping watch over blazars in flaring states, whichprovide deep insights into the engine powered by supermassive black holes. However, havinga quasar caught in a very bright flaring state is not easy requiring long surveys. Therefore, theobservation of such flaring events represents a goldmine for theoretical studies.Such a flaring event was captured by the INTEGRAL mission in June 2015 while performing its (asof today) deepest extragalactic survey when it caught the prominent blazar 3C 279 in its brightestflare ever recorded at gamma-ray energies. The flare was simultaneously recorded by the Fermigamma-ray mission, by the Swift mission, by the INTEGRAL mission and by observations rangingfrom UV, through optical to the near-IR bands. The derived snapshot of this broad spectral energydistribution of the flare has been modeled in the context of a one-zone radiation transfer leptonicand lepto-hadronic models constraining the single emission components. The derived parametersof both models challenge the physical conditions in the jet. However, very recently publishedvery-high-energy (VHE) data at TeV energies are very close to our lepto-hadronic model.35th International Cosmic Ray Conference — ICRC201710–20 July, 2017Bexco, Busan, Korea∗Speaker.†NASA grant NNX13AO84G is acknowledged.c© Copyright owned by the author(s) under the terms of the Creative CommonsAttribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0). http://pos.sissa.it/PoS(ICRC2017)6423C 279, the flare of June 2015 Eugenio Bottacini1. IntroductionThe flat spectrum radio quasar (FSRQ) 3C 279 has gained prominence due to its bright flaringstate detected by the Energetic Gamma Ray Experiment Telescope (EGRET) on board the ComptonGamma-Ray Observatory (CGRO) mission [1]. This blazar, at redshift z=0.5362 [2], was the first(of currently only 5) FSRQs detected by ground-based Atmospheric Cherenkov Telescope facilitiesat very-high-energy (VHE: E > 100 GeV) gamma rays [3, 4]. This makes it an ideal target formultifrequency studies. Such extensive multifrequency campaigns [5] have allowed constrainingimportant single emission components from the source [6].Here we present the results from of the multifrequency campaign that pivots around the detection bythe INTEGRAL mission of the brightest high-energy flare ever displayed by 3C 279 in June 2015.We discuss the challenges faced by the modeling of the SED with a leptonic and a lepto-hadronicmodel shown in our recent work [7] and the implications of recently analyzed TeV data.2. Observations- INTEGRAL – In June 2015 INTEGRAL was performing its deepest extragalactic survey onthe Come sky region. Due to the huge field of view of 29 × 29 deg2 the imager IBIS [8] detectedthe outburst of 3C 279 in only 50 ks allowing us to compute a spectrum at energies above 15 keV.Data analysis is performed with the standard Off-line Scientific Analysis (OSA) software1 providedby the INTEGRAL Science Data Centre.- Swift – During the INTEGRAL monitoring of 3C 279, the source was observed nearly simultane-ously by Swift-XRT in photon counting mode on 2015-06-15 14:27 UTC (obs id: 00035019176),which allows for a detailed spectrum in the energy range 0.6 – 6.0 keV. In agreement with the verytimely analysis by [9], we find the spectrum to be affected by pile-up due to the bright flare and thehard spectrum. After correcting for pile-up the spectral index is Γ=-1.37.The same pointing by Swift led to observations with the UV-Optical Telescope (UVOT) with the Ufilter.- SMARTS – During the INTEGRAL monitoring the blazar 3C 279 was also targeted by the Mod-erate Aperture Research Telescope System (SMARTS) run by Yale University. Observations coverthe optical to near-IR bands B, V , R, J, and K.- FERMI – Also the Large Area Telescope (LAT) on board the Fermi gamma-ray mission capturedthe bright flare of the source. A prompt analysis of this detection [10] allowed for a precise spec-trum and lightcurve of 3C 279.3. Spectral Energy DistributionThe spectral energy distribution (SED) of the sources displays the two broad non-thermal ra-diation components characteristic of blazars (see Figure 1). The low-energy component is due tosynchrotron emission by relativistic electrons (possibly also positrons) in the jet, while the high-energy component can be either due to Compton scattering by the same relativistic electrons (lep-1http://www.isdc.unige.ch/integral/analysis#Software2PoS(ICRC2017)6423C 279, the flare of June 2015 Eugenio Bottacinitonic processes) or due to proton synchrotron radiation and synchrotron emission from secondariesproduced in photo-pion interactions (hadronic processes).To model this boradband SED, we adopt the two approaches: a leptonic and a hadronic model.We use their time-independent homogeneous one-zone jet radiation transfer [11], building upon anearlier work [12].1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022 1023 1024 1025 1026Frequency [Hz]10-1410-1310-1210-1110-1010-910-810-7ν F ν [erg cm−2s−1]Leptonic ModelLepto-Hadronic ModelSynchrotron ComponentEC BLREC DiskSSC componentElectron SynchrotronProton SynchrotronSMARTSSwift-UVOTSwift-XRTINTEGRAL-IBIS/ISGRIFermi-LAT (Paliya 2015)H.E.S.S. (Cerruti 2016)Figure 1: Quasi-simultaneous SED of 3C 279, along with the leptonic (red solid) model and the lepto-hadronic (green solid) model, as described in the text. The different emission components for both modelsas shown too (see legend). The data from the H.E.S.S. collaboration were not included in the modeling.However, they line up surprisingly well with the lepto-hadronic model.4. Discussion and ConclusionsThe SED can be equally well modeled by a leptonic and by a lepto-hadronic model (see Fig-ure 1). However, both models challenge the physical conditions in the jet.The leptonic model indicates that the emission region is dominated by kinetic energy by a factorof ∼ 10 compared to the energy carried in the magnetic field. This may be difficult to realizein a jet in which the magnetic field is the primary source of jet power because one would expectany mechanism converting magnetic-field to particle kinetic energy to cease once equipartition isreached. In the leptonic scenario the emission region is inferred to be well within the broad linereagion (BLR), thus VHE photons would not escape this region unattenuated [13]. Therefore, the3PoS(ICRC2017)6423C 279, the flare of June 2015 Eugenio Bottacinileptonic model predicts that no VHE photons should be detected in this flare, if not originating at adifferent location.On the other hand, our lepto-hadronic SED model allows us to choose parameters close to equipar-tition between the magnetic field and the relativistic proton population. An important issue for thismodel may be the extreme jet power, of the order of the Eddington luminosity of the central blackhole in 3C 279.Because 3C 279 is one of currently only 5 FSRQs detected at VHE, the source is subject to a ToOprogram by H.E.S.S. triggered on the basis of publicly available blazar observations. Here weadapt the data of the 3C 279-flare presented in a very recent analysis by the H.E.S.S. collaboration[14]. The data are shown in Figure 1. These data line up surprisingly well with our lepto-hadronicmodel.References[1] Hartman, R. C., Bertsch, D. L., Fichtel, C. E., et al. 1992, ApJL, 385, L1[2] Marziani, P., Sulentic, J. W., Dultzin-Hacyan, D., Calvani, M., & Moles, M. 1996, ApJS, 104, 37[3] Albert, J., Aliu, E., Anderhub, H., et al., 2008, Science, 320, 1752[4] Mirzoyan, R. 2015, The Astronomer’s Telegram, 7080[5] Collmar, W., Böttcher, M., Krichbaum, T. P., et al. 2010, A&A, 522, A66[6] Pian, E., Urry, C. M., Maraschi, L., et al. 1999, ApJ, 521, 112[7] Bottacini, E., Böttcher, M., Pian, E., & Collmar, W. 2016, ApJ, 832, 17[8] Ubertini, P., Lebrun, F., Di Cocco, G., et al. 2003, A&A, 411, L131[9] Pittori, C., Verrecchia, F., Puccetti, et al. 2015a, The Astronomer’s Telegram, 7639[10] Paliya, V. S. 2015, ApJL, 808, L48[11] Böttcher, M., Reimer, A., Sweeney, K., & Prakash, A. 2013, ApJ, 768, 54[12] Böttcher, M., & Chiang, J. 2002, ApJ, 581, 127[13] Böttcher, M., & Els, P. 2016, ApJ, 821, 102[14] Cerruti, M., Böttcher, M., Chakraborty, N., et al. 2016, arXiv:1610.055234

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Challenges in reconciling observations and theory of the brightest high-energy flare ever of 3C 279

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