$Fermi$ GBM Observations of V404 Cyg During its 2015 Outburst

Abstract

V404 Cygni was discovered in 1989 by the $Ginga$ X-ray satellite during its only previously observed X-ray outburst and soon after confirmed as a black hole binary. On June 15, 2015, the Gamma Ray Burst Monitor (GBM) triggered on a new outburst of V404 Cygni. We present 13 days of GBM observations of this outburst including Earth occultation flux measurements, spectral and temporal analysis. The Earth occultation fluxes reached 30 Crab with detected emission to 100 keV and determined, via hardness ratios, that the source was in a hard state. At high luminosity, spectral analysis between 8 and 300 keV showed that the electron temperature decreased with increasing luminosity. This is expected if the protons and electrons are in thermal equilibrium during an outburst with the electrons cooled by the Compton scattering of softer seed photons from the disk. However, the implied seed photon temperatures are unusually high, suggesting a contribution from another source, such as the jet. No evidence of state transitions is seen during this time period. The temporal analysis reveals power spectra that can be modeled with two or three strong, broad Lorentzians, similar to the power spectra of black hole binaries in their hard state.

References in corpus (5)

• X-ray Properties of Black-Hole Binaries
• Modelling the behaviour of accretion flows in X-ray binaries
• Localization of Gamma-Ray Bursts using the Fermi Gamma-Ray Burst Monitor
• Positron annihilation signatures associated with the outburst of the microquasar V404 Cygni
• The Five Year Fermi/GBM Magnetar Burst Catalog

Cited by in corpus (19)

• The Fourth Fermi-GBM Gamma-Ray Burst Catalog: A Decade of Data
• Evidence for simultaneous jets and disk winds in luminous low-mass X-ray binaries
• The 2015 Decay of the Black Hole X-ray Binary V404 Cygni: Robust Disk-Jet Coupling and a Sharp Transition into Quiescence
• The obscured X-ray binaries V404 Cyg, Cyg X-3, V4641 Sgr, and GRS 1915+105
• A Long Look At MCG-5-23-16 With NuSTAR: I- Relativistic Reflection And Coronal Properties
• SWIFT view of the 2015 outburst of GS 2023+338 (V404 Cyg): complex evolution of spectral and temporal characteristics
• Hard X-ray variability of V404 Cyg during the 2015 outburst
• A Physical Background Model for the Fermi Gamma-ray Burst Monitor
• High-energy gamma-ray activity from V404 Cygni detected by AGILE during the 2015 June outburst
• A challenging view of the 2015 summer V404 Cyg outburst at high energy with INTEGRAL/SPI: The finale
• The nova-like nebular optical spectrum of V404 Cygni at the beginning of the 2015 outburst decay
• Optical and X-ray Correlations During the 2015 Outburst of the Black Hole V404 Cyg
• Simultaneous multiwavelength observations of V404 Cygni during its 2015 June outburst decay strengthen the case for an extremely energetic jet-base
• Rapid Optical Variations Correlated with X-rays in the 2015 Second Outburst of V404 Cygni (GS 2023$+$338)
• The December 2015 re-brightening of V404 Cyg: Variable absorption from the accretion disc outflow
• Fermi Gamma-ray Space Telescope
• Searching for High Energy, Horizon-scale Emissions from Galactic Black Hole Transients during Quiescence
• Rapid spectral transition of the black hole binary V404 Cyg
• Timing Analysis of V404 Cyg during Its Brightest Outburst with INTEGRAL/SPI