THE JUNE 2008 FLARE OF MARKARIAN 421 FROM OPTICAL TO TeV ENERGIES
I. DonnarummaV. VittoriniS. VercelloneE. Del MonteM. FerociF. D’AmmandoL. PaccianiA. ChenM. TavaniA. BulgarelliA. GiulianiF. LongoG. PucellaA. ArganG. BarbielliniF. BoffelliP. A. CaraveoP. W. CattaneoV. CoccoE. CostaG. De ParisG. Di CoccoY. EvangelistaM. FioriniT. FroyslandM. FruttiF. FuschinoM. GalliF. GianottiC. LabantiI. LapshovF. LazzarottoP. LipariM. MarisaldiM. MastropietroS. MereghettiE. MorelliA. MorselliA. PellizzoniF. PerottiP. PicozzaG. PorrovecchioM. PrestM. RapisardaA. RappoldiA. RubiniP. SoffittaM. TrifoglioA. TroisE. VallazzaA. ZambraD. ZanelloC. PittoriP. SantolamazzaF. VerrecchiaP. GiommiS. ColafrancescoL. SalottiM. VillataC. M. RaiteriWen-Ping ChenН. В. ЕфимоваB. JordanT. S. KonstantinovaE. KoptelovaO. M. KurtanidzeV. M. LarionovJ. AgramuntA. C. SadunH. AnderhubL. A. AntonelliP. AntoranzMichael BackesC. BaixerasS. BalestraJ. A. BarrioH. BartkoD. BastieriJ. Becerra GonzálezJ. K. BeckerW. BednarekK. BergerE. BernardiniA. BilandR. K. BöckG. BonnoliP. BordasD. Borla TridonV. Bosch‐RamonT. BretzI. BritvitchMiguel CámaraE. CarmonaA. ChilingarianS. CommichauJ. L. ContrerasJ. CortinaM. T. CostadoS. CovinoV. CurtefF. DazziA. De AngelisE. De Cea del PozoR. de los ReyesB. De LottoMónica MaríaF. De SabataC. Delgado MendezA. DomínguezD. DornerM. DoroD. ElsäesserM. ErrandoD. FerencE. FernándezR. FirpoM. V. FonsecaL. FontN. GalanteR. J. Garcı́a LópezM. GarczarczykM. GaugF. GöebelD. HadaschM. HayashidaA. HerreroD. Höhne-MönchJ. HoseC. C. HsuStefan HuberT. JoglerD. KranichA. La BarberaA. LailleE. LeonardoE. LindforsS. LombardiMarcos LópezE. LorenzP. MajumdarG. ManevaN. MankuzhiyilK. MannheimL. MaraschiM. MariottiM. Martı́nezD. MazinM. MeucciM. MeyerJ. M. MirandaR. MirzoyanJ. MoldónM. MolesA. MoralejoD. NietoK. NilssonJ. NinkovićR. MirzoyanR. PaolettiJ. M. ParedesM. PasanenD. PascoliFelicitas PaussR. PegnaM. A. P. TorresM. PersicL. PeruzzoF. PradaE. PrandiniN. PuchadesA. RaymersW. RhodeM. RibóJ. RicoM. RissiA. RobertS. RügamerA. SaggionT. SaitoM. SalvatiM. Sánchez‐CondeP. SartoriK. SataleckaV. ScalzottoV. ScapinT. SchweizerM. ShaydukK. ShinozakiS. N. ShoreN. SidroA. Sierpowska-BartosikA. SillanpääJ. SitarekD. SobczyńskaF. SpanierA. StamerraL. S. StarkL. O. TakaloF. TavecchioP. TemnikovD. TescaroM. TeshimaM. TluczykontD. F. TorresN. TuriniH. VankovA. VenturiniV. VitaleR. M. WagnerW. WittekV. ZabalzaF. ZandanelR. ZaninJ. ZapateroV. A. AcciariE. AliuT. ArlenM. BeilickeW. BenbowS. M. BradburyJ. H. BuckleyV. BugaevY. ButtK. ByrumA. CannonA. CesariniY. C. ChowL. CiupikP. CoganP. ColinWei CuiM. K. DanielR. DickherberC. DukeT. ErginS. FeganJ. P. FinleyG. FinneganP. FortinA. FurnissD. GallG. H. GillandersR. GuénetteG. GyukJ. GrubeD. HannaJ. HolderD. HoranC. M. HuiT. B. HumenskyAsif ImranP. KaaretN. KarlssonM. KertzmanD. KiedaJ. KildeaA. KonopelkoH. KrawczynskiF. KrennrichM. J. LangS. LeBohecG. MaierA. McCannM. McCutcheonA. MilovanovićP. MoriartyT. NagaiR. A. OngA. N. OtteD. PandelJ. S. PerkinsA. PichelM. PohlK. RaganL. C. ReyesP. T. ReynoldsE. RoacheH. J. RoseM. SchroedterG. H. SembroskiA. W. SmithD. SteeleS. P. SwordyM. TheilingJ. A. TonerL. ValcarcelA. VarlottaS. P. WakelyJ. E. WardT. C. WeekesA. J. WeinsteinD. A. WilliamsStephanie WisselM. WoodB. Zitzer
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We present optical, X-ray, high energy ($\lessapprox 30$ GeV) and very high energy ($\gtrapprox 100$ GeV; VHE) observations of the high-frequency peaked blazar Mrk 421 taken between 2008 May 24 and June 23. A high energy $\gamma$-ray signal was detected by AGILE with \sqrt{TS}=4.5 on June 9--15, with $F(E>100 \mathrm{MeV})= 42^{+14}_{-12}\times 10^{-8}$ photons cm$^{-2}$ s$^{-1}$. This flaring state is brighter than the average flux observed by EGRET by a factor of $\sim$3, but still consistent with the highest EGRET flux. In hard X-rays (20-60 keV) SuperAGILE resolved a 5-day flare (June 9-15) peaking at $\sim$ 55 mCrab. SuperAGILE, RXTE/ASM and Swift/BAT data show a correlated flaring structure between soft and hard X-rays. Hints of the same flaring behavior are also detected in the simultaneous optical data provided by the GASP-WEBT. A Swift/XRT observation near the flaring maximum revealed the highest 2-10 keV flux ever observed from this source, of 2.6 $\times 10^{-9}$ erg cm$^{-2}$ s$^{-1}$ (i.e. > 100 mCrab). A peak synchrotron energy of $\sim$3 keV was derived, higher than typical values of $\sim$0.5-1 keV. VHE observations with MAGIC and VERITAS on June 6-8 show the flux peaking in a bright state, well correlated with the X-rays. This extraordinary set of simultaneous data, covering a twelve-decade spectral range, allowed for a deep analysis of the spectral energy distribution as well as of correlated light curves. The $\gamma$-ray flare can be interpreted within the framework of the synchrotron self-Compton model in terms of a rapid acceleration of leptons in the jet.Keywords:
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We present a maximum‐likelihood method of determining the intrinsic spectral index distribution (ISID) of a population of gamma‐ray emitters which accounts for error in measurement of individual spectral indices, and we apply it to Energetic Gamma‐Ray Experiment Telescope (EGRET) blazars and simulated Gamma‐ray Large Area Space Telescope (GLAST) blazars. We find that the most likely Gaussian ISID for EGRET blazars has a mean of 2.27 and a standard deviation of 0.20. We also test for systematic spectral index hardening associated with blazar variability for which we find no evidence.
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We examine the radio properties of EGRET-detected blazars observed as part of the VLBA Imaging and Polarimetry Survey (VIPS). VIPS has a flux limit roughly an order of magnitude below the MOJAVE survey and most other samples that have been used to study the properties of EGRET blazars. At lower flux levels, radio flux density does not directly correlate with gamma-ray flux density. We do find that the EGRET-detected blazars tend to have higher brightness temperatures, greater core fractions, and possibly larger than average jet opening angles. A weak correlation is also found with jet length and with polarization. All of the well-established trends can be explained by systematically larger Doppler factors in the gamma-ray-loud blazars, consistent with the measurements of higher apparent velocities found in monitoring programs carried out at radio frequencies above 10 GHz.
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The IceCube Collaboration recently reported the observation of a > 290 TeV muon neutrino, IceCube-170922A, coincident with a ~6-month-long γ-ray flare of the blazar TXS 0506+056. The neutrino detection prompted electromagnetic follow-up of the event, and the blazar flare was detected by several instruments, including MAGIC at energies exceeding > 100 GeV. The correlation of the neutrino with the flare of TXS 0506+056 is inconsistent with arising by chance at the 3σ level. An archival search revealed 13 ± 5 further high-energy neutrinos in the direction of TXS 0506+056 during a 6-month period in 2014-2015. These events were not accompanied by a γ-ray flare. Such an accumulation of events is inconsistent with arising from a background fluctuation at the 3.5σ level. Here, recent results on neutrino emission expectations, aimed at interpreting, and motivated by these observations are summarised. The topics briefly reviewed include models of neutrino production in TXS 0506+056 during the 2017 γ-ray flare, during the 2014-2015 period, and expectations of neutrino emission from blazar flares from other sources that occurred in the period 2008-2018 in declinations favourable for detection with IceCube.
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Active Galactic Nuclei (AGNs) show high variability in the γ-ray energy band above 30 MeV on time-scales, in some cases, as short as one day. Up to now, the sparse coverage provided by the EGRET instrument has made it difficult to firmly establish both if and especially how often the transient activity occurs. We report our results on the estimate of the duty–cycle of γ-ray blazars by means of a re-analysis of the EGRET data and their comparison with numerical simulations. We attribute a γ-ray activity index, ψ, to all EGRET blazars, and show that FSRQs dominate the sample with non-zero ψ. We also characterise the blazar activity, including the discovery of a region of consistency between the γ-ray flaring duty–cycle and the recurrence time between flares.
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The blazar 3C 345 is similar to the gamma-ray blazar 3C 279 in many aspects, but EGRET did not detect any gamma-rays from 3C 345. We investigate this issue by comparing 3C 345 with 3C 279 and 3C 273, another strong gamma-ray blazar, in the following aspects: the optical (4400 A) and radio (8 GHz,22 GHz, and 37 GHz) variability amplitude, the optical shortest variability timescale, and the time lags among variations in the four bands. However, we do not find any significant differences between 3C 345 and the other two sources. This suggests that the differences in the gamma-ray properties may result from other reasons.
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We present the results of a new model calculation of the γ-ray background produced by unresolved blazars, using the second EGRET catalogue and taking account of flaring. These results are compared to the preliminary γ-ray background spectrum reported recently by the EGRET team. We find that blazars can account for the entire extragalactic γ-ray background observed by EGRET. In addition the EGRET spectrum shows some evidence of a signature for the blazar background, a concavity in the spectrum first pointed out in our earlier paper. Subject headings: galaxies: active – gamma-rays: theory – quasars: general
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In preparation for GLAST, we have compiled a sample of blazar candidates to increase the pool of well studied AGN from which GLAST counterparts will be drawn. Sources were selected with our Figure of Merit (FoM) ranking; thus, they have radio and X-ray properties very similar to the EGRET blazars. Spectroscopic confirmation of these candidates is in progress, and more than 70% of these objects have been identified as flat spectrum radio quasars and BL Lac objects. We present ~250 new optical blazar identifications based on McDonald Observatory spectroscopy, 224 with redshifts. Of these, 167 are in our FoM-selected set. To motivate the Gamma-ray nature of these objects, we analyzed the current release of the EGRET data for possible point sources at their radio positions. We develop two distinct methods to combine multiple EGRET observations of a sky position into a single detection significance. We report a detection of the signal of the set of blazar candidates in the EGRET data at the > 3 sigma level by both techniques. We predict that the majority of these blazar candidates will be found by GLAST due to its increased sensitivity, duty cycle and resolving power.
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