The flat spectrum radio quasar 3C 279 was observed in an extremely high activity state on June 16, 2015 (MJD 57189). In this paper, we investigate the properties of this flaring episode in the high energy $γ$-ray and optical bands using data from the \emph{Fermi}-LAT, SMARTS, and SPOL observations during the period June 1-30, 2015 (MJD 57174-57203). The highest emission state in the $γ$-ray band detected by the \emph{Fermi}-LAT exhibits a peak flux of $\sim$ 2$\times$10$^{-7}$ erg~cm$^{-2}$~s$^{-1}$ which is more than 25 times the flux level measured in the low activity state of the source. The temporal analysis of the daily \emph{Fermi}-LAT light curve suggests that the giant flaring episode has characteristic rise and decay times less than one day. The optical daily light curves in B, V, R, and J bands also indicate the flaring activity from 3C 279 with flux levels peaking for two days on June 16-17, 2015 (MJD 57189-57190). The discrete correlation function analysis indicates a time lag of 1 day or longer between the $γ$-ray and optical peaks during the flaring episode. The $γ$-ray emission is also observed to show a harder-when-brighter behaviour whereas optical emission exhibits an opposite behaviour. The $γ$-ray emission region during the flare is observed to be very compact and is located close to the base of the jet. The degree of linear polarization in the wavelength range 500-700 nm measured using SPOL during this period is also highly variable with a peak of $\sim$ 30$\%$ one day after the $γ$-ray flare. Near simultaneous $γ$-ray flux points show a linear anti-correlation with the degree of polarization during the period of $γ$-ray flare. The significant drop in the degree of linear polarization suggests a sudden increase in the tangled magnetic field strength in the emission region.
Synchrotron Gamma-Ray Emission Model of the Giant Outburst of Quasar 3C 279 in 2015 June: Fast Reconnection or Stochastic Acceleration with Electromagnetic Cascade?
AGN in Gaia Alerts: from flares to Changing Look Quasars
Sorbonne University & CNRS, Institut d’Astrophysique de Paris (IAP)（索邦大学与法国国家科学研究中心，巴黎天体物理研究所）；Nordic Optical Telescope (NOT)（北欧光学望远镜）；University of Maryland, College Park（马里兰大学帕克分校）；Technical University of Denmark, DTU Space（丹麦技术大学）；University of Warwick（华威大学）；University of Tartu, Tartu Observatory（塔尔图大学）；University of Turku（图尔库大学）；CSIC, Inst. de Astrofisica de Andalucia（西班牙国家研究委员会，安达卢西亚天体物理研究所）；Universita di Bologna（博洛尼亚大学）；Trinity College Dublin（都柏林三一学院）；INAF-Osservatorio Astronomico di Roma（意大利国家天体物理研究所罗马天文台）
The physical scenario responsible for gamma-ray flaring activity and its location for Flat Spectrum Radio Quasars is still debated. The study of the statistical distribution of waiting-times between flares (the time intervals between consecutive activity peaks) can give information on the distribution of flaring times, and constrain the physical mechanism responsible for gamma-ray emission. We adopt here a Scan-Statistic driven clustering method (iSRS) to recognize flaring states within the FERMI-LAT data, and identify the time of activity-peaks. Results: Flares waiting times can be described …
High-energy gamma-ray activity from V404 Cygni detected by AGILE during the 2015 June outburst
AGILE卫星在2015年6月的射电、光学、X射线和软伽马射线频率观测到的爆发期间，探测到了来自X射线双星V404 Cygni的瞬态高能伽马射线发射。该活动由AGILE在50-400 MeV能带观测，时间为2015-06-24 UT 06：00：00至2015-06-26 UT 06：00：00（MJD 57197.25 - 57199.25），探测意义为${\sim}4.3σ$。伽马射线探测，与费米-LAT同期观测一致，与在无线电和硬X射线频率下观察到的明亮耀斑相关，并与511千电子伏线发射的强烈增强相关，可能表明轻子主导的瞬态喷流中的等离子体喷射。这个双星系统的AGILE观测与微类星体的情况是兼容的，在这种情况下，瞬态喷流是负责高能伽马射线发射。
Blazars are known to show flux variations over a range of energies from low energy radio to high energy gamma-rays. Cross-correlation analysis of the optical and $γ$-ray light curves in blazars shows that flux variations are generally correlated in both bands, however, there are exceptions. We explored this optical-GeV connection in four flat spectrum radio quasars (FSRQs) by a systematic investigation of their long term optical and $γ$-ray light curves. On analysis of the four sources, namely 3C 273, 3C 279, PKS 1510$-$089 and CTA 102 we noticed different behaviours between the optical and Ge…
We present a temporal and spectral analysis of the gamma-ray flux from nine of the brightest flat spectrum radio quasars (FSRQs) detected with the Fermi Large Area Telescope (LAT) during its first eight years of operation, with the aim of constraining the location of the emission region. Using the increased photon statistics provided from the two brightest flares of each source, we find evidence of sub-hour variability from B2 1520+31, PKS 1502+106 and PKS 1424-41, with the remaining sources showing variability on timescales of a few hours. These indicate gamma-ray emission from extremely comp…
New Swift monitoring observations of the variable, radio-quiet quasar, PDS 456, are presented. A bright X-ray flare was captured in September 2018, the flux increasing by a factor of 4 and with a doubling time-scale of 2 days. From the light crossing argument, the coronal size is inferred to be about 30 gravitational radii for a black hole mass of $10^{9} {\rm M}_{\odot}$ and the total flare energy exceeds $10^{51}$ erg. A hardening of the X-ray emission accompanied the flare, with the photon index decreasing from $Γ=2.2$ to $Γ=1.7$ and back again. The flare is produced in the X-ray corona, th…
Max Planck Institute for Radio Astronomy（马克斯·普朗克射电天文研究所）；Department of Astronomy, University of Michigan（密歇根大学天文学系）；Special Astrophysical Observatory of the Russian Academy of Sciences（俄罗斯科学院特别天文台）；Instituto de Astrofísica de Andalucía-CSIC（安达卢西亚天体物理学研究所-CSIC）；Department of Physics and Astronomy, Denison University（丹尼森大学物理与天文学系）；Institute for Nuclear Research（核物理研究所）；Lebedev Physical Institute（列别杰夫物理研究所）；Department of Physics and Astronomy, Purdue University（普渡大学物理与天文学系）；CePIA, Astronomy Department, Universidad de Concepción（孔塞普西翁大学天文学系CePIA）；Black Hole Initiative, Harvard University（哈佛大学黑洞倡议）；Moscow Institute of Physics and Technology（莫斯科物理技术学院）
Disk winds and jets are ubiquitous in active galactic nuclei (AGN), and how these two components interact remains an open question. We study the radio properties of a radio-intermediate quasar III Zw 2. We detect two jet knots J1 and J2 on parsec scales, which move at a mildly apparent superluminal speed of $1.35\,c$. Two $γ$-ray flares were detected in III Zw 2 in 2009--2010, corresponding to the primary radio flare in late 2009 and the secondary radio flare in early 2010. The primary 2009 flare was found to be associated with the ejection of J2. The secondary 2010 flare occurred at a distanc…
Determining the location of $γ$-ray emission in blazar jets is a challenging task. Pinpointing the exact location of $γ$-ray production within a relativistic jet can place strong constraints on our understanding of high-energy astrophysics and astroparticle physics. We present a study of the radio- and $γ$-bright flat-spectrum radio quasar (FSRQ) 4C +01.28 (PKS B1055+018) in which we try to pinpoint the emission site of several prominent GeV flares. This source shows prominent high-amplitude broadband variability on time scales ranging from days to years. We combine high-resolution VLBI observ…
Flat spectrum radio quasars (FSRQs) are the most luminous blazars at GeV energies, but only rarely emit detectable fluxes of TeV gamma rays, typically during bright GeV flares. We explore the gamma-ray variability and spectral characteristics of three FSRQs that have been observed at GeV and TeV energies by Fermi-LAT and VERITAS, making use of almost 100 hours of VERITAS observations spread over 10 years: 3C 279, PKS 1222+216, and Ton 599. We explain the GeV flux distributions of the sources in terms of a model derived from a stochastic differential equation describing fluctuations in the magn…
