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Title: High-energy Gamma-Ray Activity from V404 Cygni Detected by AGILE during the 2015 June Outburst

Abstract

The AGILE satellite detected transient high-energy γ -ray emission from the X-ray binary V404 Cygni, during the 2015 June outburst observed in radio, optical, X-ray, and soft γ -ray frequencies. The activity was observed by AGILE in the 50–400 MeV energy band, between 2015 June 24 UT 06:00:00 and 2015 June 26 UT 06:00:00 (MJD 57197.25–57199.25), with a detection significance of ∼4.3 σ . The γ -ray detection, consistent with a contemporaneous observation by Fermi -LAT, is correlated with a bright flare observed at radio and hard X-ray frequencies, and with a strong enhancement of the 511 keV line emission, possibly indicating plasmoid ejections in a lepton-dominated transient jet. The AGILE observations of this binary system are compatible with a microquasar scenario in which transient jets are responsible for the high-energy γ -ray emission.

Authors:
; ;  [1];  [2];  [3]
  1. INAF-IAPS, Via del Fosso del Cavaliere 100, I-00133 Roma (Italy)
  2. ASI Data Center (ASDC), Via del Politecnico snc, I-00133 Roma (Italy)
  3. Special Astrophysical Observatory RAS, Karachaevo-Cherkassian Republic, Nizhnij Arkhyz 36916 (Russian Federation)
Publication Date:
OSTI Identifier:
22663703
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 839; 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; BINARY STARS; BLACK HOLES; COSMIC GAMMA BURSTS; COSMIC GAMMA SOURCES; EMISSION; GAMMA DETECTION; GAMMA RADIATION; HARD X RADIATION; KEV RANGE; LEPTONS; MEV RANGE; PLASMOIDS; SATELLITES; STARS

Citation Formats

Piano, G., Munar-Adrover, P., Tavani, M., Verrecchia, F., and Trushkin, S. A., E-mail: giovanni.piano@iaps.inaf.it. High-energy Gamma-Ray Activity from V404 Cygni Detected by AGILE during the 2015 June Outburst. United States: N. p., 2017. Web. doi:10.3847/1538-4357/AA6796.
Piano, G., Munar-Adrover, P., Tavani, M., Verrecchia, F., & Trushkin, S. A., E-mail: giovanni.piano@iaps.inaf.it. High-energy Gamma-Ray Activity from V404 Cygni Detected by AGILE during the 2015 June Outburst. United States. doi:10.3847/1538-4357/AA6796.
Piano, G., Munar-Adrover, P., Tavani, M., Verrecchia, F., and Trushkin, S. A., E-mail: giovanni.piano@iaps.inaf.it. Thu . "High-energy Gamma-Ray Activity from V404 Cygni Detected by AGILE during the 2015 June Outburst". United States. doi:10.3847/1538-4357/AA6796.
@article{osti_22663703,
title = {High-energy Gamma-Ray Activity from V404 Cygni Detected by AGILE during the 2015 June Outburst},
author = {Piano, G. and Munar-Adrover, P. and Tavani, M. and Verrecchia, F. and Trushkin, S. A., E-mail: giovanni.piano@iaps.inaf.it},
abstractNote = {The AGILE satellite detected transient high-energy γ -ray emission from the X-ray binary V404 Cygni, during the 2015 June outburst observed in radio, optical, X-ray, and soft γ -ray frequencies. The activity was observed by AGILE in the 50–400 MeV energy band, between 2015 June 24 UT 06:00:00 and 2015 June 26 UT 06:00:00 (MJD 57197.25–57199.25), with a detection significance of ∼4.3 σ . The γ -ray detection, consistent with a contemporaneous observation by Fermi -LAT, is correlated with a bright flare observed at radio and hard X-ray frequencies, and with a strong enhancement of the 511 keV line emission, possibly indicating plasmoid ejections in a lepton-dominated transient jet. The AGILE observations of this binary system are compatible with a microquasar scenario in which transient jets are responsible for the high-energy γ -ray emission.},
doi = {10.3847/1538-4357/AA6796},
journal = {Astrophysical Journal},
number = 2,
volume = 839,
place = {United States},
year = {Thu Apr 20 00:00:00 EDT 2017},
month = {Thu Apr 20 00:00:00 EDT 2017}
}
  • In this paper, we report on Fermi/Large Area Telescope observations of the accreting black hole low-mass X-ray binary V404 Cygni during its outburst in 2015 June–July. Detailed analyses reveal a possible excess of γ-ray emission on 2015 26 June, with a very soft spectrum above 100 MeV, at a position consistent with the direction of V404 Cyg (within the 95 per cent confidence region and a chance probability of 4 × 10 -4). This emission cannot be associated with any previously known Fermi source. Its temporal coincidence with the brightest radio and hard X-ray flare in the light curve ofmore » V404 Cyg, at the end of the main active phase of its outburst, strengthens the association with V404 Cyg. If the γ-ray emission is associated with V404 Cyg, the simultaneous detection of 511 keV annihilation emission by INTEGRAL reqires that the high-energy γ-rays originate away from the corona, possibly in a Blandford–Znajek jet. Finally, the data give support to models involving a magnetically arrested disc where a bright γ-ray jet can re-form after the occurrence of a major transient ejection seen in the radio.« less
  • The black hole binary GS 2023+338 exhibited an unprecedently bright outburst in 2015 June. On 2015 June 17, the high energy instruments on board INTEGRAL detected an extremely variable emission during both bright and low luminosity phases, with dramatic variations of the hardness ratio on timescales of approximately seconds. The analysis of the IBIS and SPI data reveals the presence of hard spectra in the brightest phases, compatible with thermal Comptonization with a temperature of kT{sub e} ∼ 40 keV. The seed photon’s temperature is best fit by kT{sub 0} ∼ 7 keV, which is too high to be compatiblemore » with blackbody emission from the disk. This result is consistent with the seed photons being provided by a different source, which we hypothesize to be a synchrotron driven component in the jet. During the brightest phase of flares, the hardness shows a complex pattern of correlation with flux, with the maximum energy released in the range of 40–100 keV. The hard-X-ray variability for E > 50 keV is correlated with flux variations in the softer band, showing that the overall source variability cannot originate entirely from absorption, but at least part of it is due to the central accreting source.« less
  • We report results from a Giant Metrewave Radio Telescope (GMRT) monitoring campaign of the black hole X-ray binary V404 Cygni during its 2015 June outburst. The GMRT observations were carried out at observing frequencies of 1280, 610, 325, and 235 MHz, and extended from June 26.89 UT (a day after the strongest radio/X-ray outburst) to July 12.93 UT. We find the low-frequency radio emission of V404 Cygni to be extremely bright and fast-decaying in the outburst phase, with an inverted spectrum below 1.5 GHz and an intermediate X-ray state. The radio emission settles to a weak, quiescent state ≈11 daysmore » after the outburst, with a flat radio spectrum and a soft X-ray state. Combining the GMRT measurements with flux density estimates from the literature, we identify a spectral turnover in the radio spectrum at ≈1.5 GHz on ≈ June 26.9 UT, indicating the presence of a synchrotron self-absorbed emitting region. We use the measured flux density at the turnover frequency with the assumption of equipartition of energy between the particles and the magnetic field to infer the jet radius (≈4.0 × 10{sup 13} cm), magnetic field (≈0.5 G), minimum total energy (≈7 × 10{sup 39} erg), and transient jet power (≈8 × 10{sup 34} erg s{sup −1}). The relatively low value of the jet power, despite V404 Cygni’s high black hole spin parameter, suggests that the radio jet power does not correlate with the spin parameter.« less
  • In 2015 June, the source V404 Cygni (= GS2023+38) underwent an extraordinary outburst. We present the results obtained during the first revolution dedicated to this target by the INTEGRAL mission and focus on the spectral behavior in the hard X-ray domain, using both SPI and IBIS instruments. The source exhibits extreme variability and reaches fluxes of several tens of Crab. However, the emission between 20 and 650 keV can be understood in terms of two main components, varying on all the observable timescales, similar to what is observed in the persistent black hole system Cyg X-1. The low-energy component (upmore » to ∼200 keV) presents a rather unusual shape, probably due to the intrinsic source variability. Nonetheless, a satisfactory description is obtained with a Comptonization model, if an unusually hot population of seed photons (kT{sub 0} ∼ 7 keV) is introduced. Above this first component, a clear excess extending up to 400–600 keV leads us to investigate a scenario where an additional (cutoff) power law could correspond to the contribution of the jet synchrotron emission, as proposed in Cyg X-1. A search for an annihilation feature did not provide any firm detection, with an upper limit of 2 × 10{sup −4} ph cm{sup −2} s{sup −1} (2σ) for a narrow line centered at 511 keV, on the averaged obtained spectrum.« less
  • We present simultaneous optical and near-infrared (NIR) polarimetric results for the black hole binary V404 Cyg spanning the duration of its seven-day-long optically brightest phase of its 2015 June outburst. The simultaneous R- and K{sub s}-band light curves showed almost the same temporal variation except for the isolated (∼30-minute duration) orphan K{sub s} -band flare observed at MJD 57193.54. We did not find any significant temporal variation of polarization degree (PD) and position angle (PA) in both R and K{sub s} bands throughout our observations, including the duration of the orphan NIR flare. We show that the observed PD andmore » PA are predominantly interstellar in origin by comparing the V404 Cyg polarimetric results with those of the surrounding sources within the 7′ × 7′ field of view. The low intrinsic PD (less than a few percent) implies that the optical and NIR emissions are dominated by either disk or optically thick synchrotron emission, or both. We also present the broadband spectra of V404 Cyg during the orphan NIR flare and a relatively faint and steady state by including quasi-simultaneous Swift /XRT and INTEGRAL fluxes. By adopting a single-zone synchrotron plus inverse-Compton model as widely used in modeling of blazars, we constrained the parameters of a putative jet. Because the jet synchrotron component cannot exceed the Swift /XRT disk/corona flux, the cutoff Lorentz factor in the electron energy distribution is constrained to be <10{sup 2}, suggesting that particle acceleration is less efficient in this microquasar jet outburst compared to active galactic nucleus jets. We also suggest that the loading of the baryon component inside the jet is inevitable based on energetic arguments.« less