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Title: MINUTE-TIMESCALE >100 MeV γ -RAY VARIABILITY DURING THE GIANT OUTBURST OF QUASAR 3C 279 OBSERVED BY FERMI -LAT IN 2015 JUNE

Abstract

On 2015 June 16, Fermi -LAT observed a giant outburst from the flat spectrum radio quasar 3C 279 with a peak >100 MeV flux of ∼3.6 × 10{sup −5} photons cm{sup −2} s{sup −1}, averaged over orbital period intervals. It is historically the highest γ -ray flux observed from the source, including past EGRET observations, with the γ -ray isotropic luminosity reaching ∼10{sup 49} erg s{sup −1}. During the outburst, the Fermi spacecraft, which has an orbital period of 95.4 minutes, was operated in a special pointing mode to optimize the exposure for 3C 279. For the first time, significant flux variability at sub-orbital timescales was found in blazar observations by Fermi -LAT. The source flux variability was resolved down to 2-minute binned timescales, with flux doubling times of less than 5 minutes. The observed minute-scale variability suggests a very compact emission region at hundreds of Schwarzschild radii from the central engine in conical jet models. A minimum bulk jet Lorentz factor (Γ) of 35 is necessary to avoid both internal γ -ray absorption and super-Eddington jet power. In the standard external radiation Comptonization scenario, Γ should be at least 50 to avoid overproducing the synchrotron self-Compton component. However, thismore » predicts extremely low magnetization (∼5 × 10{sup −4}). Equipartition requires Γ as high as 120, unless the emitting region is a small fraction of the dissipation region. Alternatively, we consider γ rays originating as synchrotron radiation of γ {sub e} ∼ 1.6 × 10{sup 6} electrons, in a magnetic field B ∼ 1.3 kG, accelerated by strong electric fields E ∼ B in the process of magnetoluminescence. At such short distance scales, one cannot immediately exclude the production of γ -rays in hadronic processes.« less

Authors:
;  [1]; ; ; ; ; ; ;  [2];  [3];  [4];  [5];  [6];  [7]; ;  [8];  [9];  [10];  [11];  [12] more »; « less
  1. Deutsches Elektronen Synchrotron DESY, D-15738 Zeuthen (Germany)
  2. W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305 (United States)
  3. Institute for Cosmic-Ray Research, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba, 277-8582 (Japan)
  4. Istituto Nazionale di Fisica Nucleare, Sezione di Trieste, I-34127 Trieste (Italy)
  5. Istituto Nazionale di Fisica Nucleare, Sezione di Padova, I-35131 Padova (Italy)
  6. NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)
  7. Istituto Nazionale di Fisica Nucleare, Sezione di Pisa, I-56127 Pisa (Italy)
  8. Istituto Nazionale di Fisica Nucleare, Sezione di Bari, I-70126 Bari (Italy)
  9. Istituto Nazionale di Fisica Nucleare, Sezione di Torino, I-10125 Torino (Italy)
  10. Laboratoire Leprince-Ringuet, École polytechnique, CNRS/IN2P3, F-91128 Palaiseau (France)
  11. INAF-Istituto di Astrofisica Spaziale e Fisica Cosmica, I-20133 Milano (Italy)
  12. Agenzia Spaziale Italiana (ASI) Science Data Center, I-00133 Roma (Italy)
Publication Date:
OSTI Identifier:
22654297
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal Letters; Journal Volume: 824; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABSORPTION; ELECTRIC FIELDS; EMISSION; GALAXIES; GAMMA RADIATION; HADRONS; JET MODEL; LUMINOSITY; MAGNETIC FIELDS; MAGNETIZATION; MEV RANGE 100-1000; PHOTONS; QUASARS; SCHWARZSCHILD RADIUS; SPACE VEHICLES; SPECTRA; SYNCHROTRON RADIATION

Citation Formats

Ackermann, M., Buehler, R., Anantua, R., Baldini, L., Blandford, R. D., Bloom, E. D., Bottacini, E., Caliandro, G. A., Cameron, R. A., Asano, K., Barbiellini, G., Bastieri, D., Gonzalez, J. Becerra, Bellazzini, R., Bissaldi, E., Caragiulo, M., Bonino, R., Bruel, P., Caraveo, P. A., Cavazzuti, E., and and others. MINUTE-TIMESCALE >100 MeV γ -RAY VARIABILITY DURING THE GIANT OUTBURST OF QUASAR 3C 279 OBSERVED BY FERMI -LAT IN 2015 JUNE. United States: N. p., 2016. Web. doi:10.3847/2041-8205/824/2/L20.
Ackermann, M., Buehler, R., Anantua, R., Baldini, L., Blandford, R. D., Bloom, E. D., Bottacini, E., Caliandro, G. A., Cameron, R. A., Asano, K., Barbiellini, G., Bastieri, D., Gonzalez, J. Becerra, Bellazzini, R., Bissaldi, E., Caragiulo, M., Bonino, R., Bruel, P., Caraveo, P. A., Cavazzuti, E., & and others. MINUTE-TIMESCALE >100 MeV γ -RAY VARIABILITY DURING THE GIANT OUTBURST OF QUASAR 3C 279 OBSERVED BY FERMI -LAT IN 2015 JUNE. United States. doi:10.3847/2041-8205/824/2/L20.
Ackermann, M., Buehler, R., Anantua, R., Baldini, L., Blandford, R. D., Bloom, E. D., Bottacini, E., Caliandro, G. A., Cameron, R. A., Asano, K., Barbiellini, G., Bastieri, D., Gonzalez, J. Becerra, Bellazzini, R., Bissaldi, E., Caragiulo, M., Bonino, R., Bruel, P., Caraveo, P. A., Cavazzuti, E., and and others. Mon . "MINUTE-TIMESCALE >100 MeV γ -RAY VARIABILITY DURING THE GIANT OUTBURST OF QUASAR 3C 279 OBSERVED BY FERMI -LAT IN 2015 JUNE". United States. doi:10.3847/2041-8205/824/2/L20.
@article{osti_22654297,
title = {MINUTE-TIMESCALE >100 MeV γ -RAY VARIABILITY DURING THE GIANT OUTBURST OF QUASAR 3C 279 OBSERVED BY FERMI -LAT IN 2015 JUNE},
author = {Ackermann, M. and Buehler, R. and Anantua, R. and Baldini, L. and Blandford, R. D. and Bloom, E. D. and Bottacini, E. and Caliandro, G. A. and Cameron, R. A. and Asano, K. and Barbiellini, G. and Bastieri, D. and Gonzalez, J. Becerra and Bellazzini, R. and Bissaldi, E. and Caragiulo, M. and Bonino, R. and Bruel, P. and Caraveo, P. A. and Cavazzuti, E. and and others},
abstractNote = {On 2015 June 16, Fermi -LAT observed a giant outburst from the flat spectrum radio quasar 3C 279 with a peak >100 MeV flux of ∼3.6 × 10{sup −5} photons cm{sup −2} s{sup −1}, averaged over orbital period intervals. It is historically the highest γ -ray flux observed from the source, including past EGRET observations, with the γ -ray isotropic luminosity reaching ∼10{sup 49} erg s{sup −1}. During the outburst, the Fermi spacecraft, which has an orbital period of 95.4 minutes, was operated in a special pointing mode to optimize the exposure for 3C 279. For the first time, significant flux variability at sub-orbital timescales was found in blazar observations by Fermi -LAT. The source flux variability was resolved down to 2-minute binned timescales, with flux doubling times of less than 5 minutes. The observed minute-scale variability suggests a very compact emission region at hundreds of Schwarzschild radii from the central engine in conical jet models. A minimum bulk jet Lorentz factor (Γ) of 35 is necessary to avoid both internal γ -ray absorption and super-Eddington jet power. In the standard external radiation Comptonization scenario, Γ should be at least 50 to avoid overproducing the synchrotron self-Compton component. However, this predicts extremely low magnetization (∼5 × 10{sup −4}). Equipartition requires Γ as high as 120, unless the emitting region is a small fraction of the dissipation region. Alternatively, we consider γ rays originating as synchrotron radiation of γ {sub e} ∼ 1.6 × 10{sup 6} electrons, in a magnetic field B ∼ 1.3 kG, accelerated by strong electric fields E ∼ B in the process of magnetoluminescence. At such short distance scales, one cannot immediately exclude the production of γ -rays in hadronic processes.},
doi = {10.3847/2041-8205/824/2/L20},
journal = {Astrophysical Journal Letters},
number = 2,
volume = 824,
place = {United States},
year = {Mon Jun 20 00:00:00 EDT 2016},
month = {Mon Jun 20 00:00:00 EDT 2016}
}
  • Here we report the results of a multiband observing campaign on the famous blazar 3C 279 conducted during a phase of increased activity from 2013 December to 2014 April, including first observations of it with NuSTAR. The γ-ray emission of the source measured by Fermi-LAT showed multiple distinct flares reaching the highest flux level measured in this object since the beginning of the Fermi mission, with F(E>100 MeV) of 10 -5 photons cm -2 s -1, and with a flux-doubling time scale as short as 2 hr. The γ-ray spectrum during one of the flares was very hard, with an index of Γ γ =1.7±0.1, which is rarely seen in flat-spectrum radio quasars. The lack of concurrent optical variability implies a very high Compton dominance parameter L γ/L syn > 300. Two 1 day NuSTAR observations with accompanying Swift pointings were separated by 2 weeks, probing different levels of source activity. While the 0.5-70 keV X-ray spectrum obtained during the first pointing, and fitted jointly with Swift-XRT is well-described by a simple power law, the second joint observation showed an unusual spectral structure: the spectrum softens by ΔΓ xmore » $$\simeq$$ 0.4 at ~ keV. Modeling the broadband spectral energy distribution during this flare with the standard synchrotron plus inverse-Compton model requires: (1) the location of the γ-ray emitting region is comparable with the broad-line region radius, (2) a very hard electron energy distribution index p $$\simeq$$ 1, (3) total jet power significantly exceeding the accretion-disk luminosity L j/L d ≳ 10, and (4) extremely low jet magnetization with L B/L j ≲ 10 -4. In conclusion, we also find that single-zone models that match the observed γ-ray and optical spectra cannot satisfactorily explain the production of X-ray emission.« less
  • Blazars radiate from radio through gamma-ray frequencies and thereby make ideal targets for multifrequency studies. Such studies allow the properties of the emitting jet to be constrained. 3C 279 is among the most notable blazars and therefore subject to extensive multifrequency campaigns. We report the results of a campaign ranging from near-IR to gamma-ray energies that targeted an outburst of 3C 279 in 2015 June. The campaign pivots around the detection in only 50 ks by INTEGRAL , whose IBIS/ISGRI data pin down the high-energy component of the spectral energy distribution (SED) between Swift -XRT data and Fermi -LAT data. The overallmore » SED from near-IR to gamma rays can be well represented by either a leptonic or a lepto-hadronic radiation transfer model. Even though the data are equally well represented by the two models, their inferred parameters challenge the physical conditions in the jet. In fact, the leptonic model requires parameters with a magnetic field far below equipartition with the relativistic particle energy density. In contrast, equipartition may be achieved with the lepto-hadronic model, although this implies an extreme total jet power close to the Eddington luminosity.« less
  • A large X-ray flare-up of the quasar 3C 279, coinciding with an unusual multifrequency outburst, was detected with X-ray astronomy satellite Ginga. Observations carried out on two occasions indicate that the 2-20 keV flux has increased by a factor of more than 4, from 1.2 to 5.3 micro-Jy at 2 keV, within about a year. During the outburst, the X-ray spectrum became slightly harder than that in the quiet period, the photon index changing from Gamma = 1.70 + or - 0.06 to 1.58 + or -0.03. The X-ray flux varied by 20 percent during the outburst within a periodmore » as short as 45 minutes, which indicates Delta L/Delta t greater than 2 x 10 to the 42nd ergs/sq s for H(0) = 100 km/s mpc and q(0) = 0.5, the largest value ever observed for a quasar. The observed Delta L/Delta t suggests that the X-ray-emitting region is moving with a relativistic velocity toward us. These results suggest that a relativistic jet is being formed. 33 refs.« less
  • Here, we present time-resolved broadband observations of the quasar 3C 279 obtained from multi-wavelength campaigns conducted during the first two years of the Fermi Gamma-ray Space Telescope mission. And, while investigating the previously reported γ-ray/optical flare accompanied by a change in optical polarization, we found that the optical emission appears to be delayed with respect to the γ-ray emission by about 10 days. X-ray observations reveal a pair of "isolated" flares separated by ~90 days, with only weak γ-ray/optical counterparts. The spectral structure measured by Spitzer reveals a synchrotron component peaking in the mid-infrared band with a sharp break atmore » the far-infrared band during the γ-ray flare, while the peak appears in the millimeter (mm)/submillimeter (sub-mm) band in the low state. Selected spectral energy distributions are fitted with leptonic models including Comptonization of external radiation produced in a dusty torus or the broad-line region. Furthermore, by adopting the interpretation of the polarization swing involving propagation of the emitting region along a curved trajectory, we can explain the evolution of the broadband spectra during the γ-ray flaring event by a shift of its location from ~1 pc to ~4 pc from the central black hole. On the other hand, if the γ-ray flare is generated instead at sub-pc distance from the central black hole, the far-infrared break can be explained by synchrotron self-absorption. We also model the low spectral state, dominated by the mm/sub-mm peaking synchrotron component, and suggest that the corresponding inverse-Compton component explains the steady X-ray emission.« less