Episodic Transient Gamma-Ray Emission from the Microquasar Cygnus X-1

Abstract

Cygnus X-1 is the archetypal black hole (BH) binary system in our Galaxy. We report the main results of an extensive search for transient gamma-ray emission from Cygnus X-1 carried out in the energy range 100 MeV - 3 GeV by the AGILE satellite, during the period 2007 July - 2009 October. The total exposure time is about 300 days, during which the source was in the "hard" X-ray spectral state. We divided the observing intervals in 2 or 4 week periods, and searched for transient and persistent emission. We report an episode of significant transient gamma-ray emission detected on 2009, October 16 in a position compatible with Cygnus X-1 optical position. This episode, occurred during a hard spectral state of Cygnus X-1, shows that a 1-2 day time variable emission above 100 MeV can be produced during hard spectral states, having important theoretical implications for current Comptonization models for Cygnus X-1 and other microquasars. Except for this one short timescale episode, no significant gamma-ray emission was detected by AGILE. By integrating all available data we obtain a 2$\sigma$ upper limit for the total integrated flux of $F_{\gamma ,U.L.}=3\times 10^{-8}\mathrm{phc}{\mathrm{m}}^{-2}{\mathrm{s}}^{-1}$ in the energy range 100 MeV - 3 GeV. We then clearly establish the existence of a spectral cutoff in the energy range 1-100 MeV that applies to the typical hard state outside the flaring period and that confirms the historically known spectral cutoff above 1 MeV.

Accepted for publication by ApJ on the 9th of Feb 2010, 5 pages, 3 figures

References in corpus (27)

• Fermi Large Area Telescope Bright Gamma-ray Source List
• Radiation mechanisms and geometry of Cygnus X-1 in the soft state
• The Two-Phase Pair Corona Model for Active Galactic Nuclei and X-ray Binaries: How to Obtain Exact Solutions
• The AGILE Mission
• Radiative Processes, Spectral States and Variability of Black-Hole Binaries
• Simultaneous X-ray and gamma-ray observations of Cyg X-1 in the hard state by Ginga and OSSE
• The Soft Gamma-Ray Spectral Variability of Cygnus X-1
• Very High Energy Gamma-ray Radiation from the Stellar-mass Black Hole Cygnus X-1
• Long Term Variability of Cyg X-1 I. X-ray spectral-temporal correlations in the hard state
• Discovery of extreme particle acceleration in the microquasar Cygnus X-3
• Understanding the long-term spectral variability of Cygnus X-1 with BATSE and ASM observations
• Controlling the False Discovery Rate in Astrophysical Data Analysis
• Orbital, precessional and flaring variability of Cygnus X-1
• SuperAGILE: the hard X-ray Imager for the AGILE space mission
• Long Term Variability of Cygnus X-1. IV. Spectral Evolution 1999-2004
• A new source detection algorithm using FDR
• Evolutionary constraints on the masses of the components of HDE 226868/Cyg X-1 binary system
• First AGILE Catalog of High Confidence Gamma-Ray Sources
• The broad-band spectrum of Cygnus X-1 measured by INTEGRAL
• RXTE Observation of Cygnus X-1 In Its High State
• Stellar Wind Variations During the X-ray High and Low States of Cygnus X-1
• Bimodal spectral variability of Cygnus X-1 in an intermediate state
• On the interaction of microquasar jets with stellar winds
• An intense state of hard X-ray emission of Cyg X-1 observed by INTEGRAL coincident with TeV measurements
• Observations of giant outbursts from Cygnus X-1
• A model of the TeV flare of Cygnus X-1: electron acceleration and extended pair cascades
• Very high energy gamma-ray production inside the massive binary system Cyg X-1/HDE 226868

Cited by in corpus (51)

• Gamma-ray binaries and related systems
• Polarized Gamma-ray Emission from the Galactic Black Hole Cygnus X-1
• Relativistic Jets in Active Galactic Nuclei und Microquasars
• Long-term monitoring of the high-energy gamma-ray emission from LS I +61° 303 and LS 5039
• High-energy gamma-ray emission from Cyg X-1 measured by Fermi and its theoretical implications
• The MeV spectral tail in Cyg X-1 and optically-thin emission of jets
• Detection of gamma rays of likely jet origin in Cygnus X-1
• Jet contributions to the broad-band spectrum of Cyg X-1 in the hard state
• Magic constraints on Gamma-ray emission from Cygnus X-3
• The Fermi All-sky Variability Analysis: A list of flaring gamma-ray sources and the search for transients in our Galaxy
• Gamma-ray observations of the microquasars Cygnus X-1, Cygnus X-3, GRS 1915+105, and GX 339-4 with the Fermi Large Area Telescope
• Large-scale flow dynamics and radiation in pulsar gamma-ray binaries
• Non-thermal processes around accreting galactic black holes
• BeppoSAX observations of the X-ray pulsar MAXI J1409-619 in low state: discovery of cyclotron resonance features
• Gamma-ray observations of Cygnus X-1 above 100 MeV in the hard and soft states
• 3D simulations of microquasar jets in clumpy stellar winds
• An inhomogeneous lepto-hadronic model for the radiation of relativistic jets. Application to XTE J1118+480
• A magnetic reconnection model for explaining the multi-wavelength emission of the microquasars Cyg X-1 and Cyg X-3
• Lepto-hadronic model for the broadband emission of Cygnus X-1
• AGILE detection of Cygnus X-3 γ-ray active states during the period mid-2009/mid-2010
• VERITAS Observations of the Nova in V407 Cygni
• The effects of the stellar wind and orbital motion on the jets of high-mass microquasars
• The Second AGILE Catalog of Gamma-Ray Sources
• Binaries with the eyes of CTA
• IGR J17354-3255 as a candidate intermediate SFXT possibly associated with the transient MeV AGL J1734-3310
• The doubling of the superorbital period of Cyg X-1
• GeV detection of HESS J0632+057
• Gamma-ray absorption and the origin of the gamma-ray flare in Cygnus X-1
• Discovery of a GeV blazar shining through the Galactic plane
• Gamma rays from clumpy wind-jet interactions in high-mass microquasars
• The missing GeV γ-ray binary: Searching for HESS J0632+057 with Fermi-LAT
• Study of the gamma-ray source 1AGL J2022+4032 in the Cygnus Region
• An updated list of AGILE bright gamma-ray sources and their variability in pointing mode
• Search for very-high-energy gamma-ray emission from the microquasar Cygnus X-1 with the MAGIC telescopes
• High energy gamma-ray emission from compact galactic sources in the context of observations with the next generation Cherenkov Telescope Arrays
• The gamma-ray source AGL J2241+4454 as the possible counterpart of MWC 656
• The jet and arc molecular clouds toward Westerlund 2, RCW 49, and HESS J1023-575; 12CO and 13CO (J=2-1 and J=1-0) observations with NANTEN2 and Mopra Telescope
• Gamma-rays from anisotropic IC e^{\pm} pair cascades in microquasars: Application to Cyg X-3
• Galactic transient sources with the Cherenkov Telescope Array Observatory
• A year-long AGILE observation of Cygnus X-1 in hard spectral state
• Relativistic stellar jets: dynamics and non-thermal radiation
• IGR J17354-3255 as bench test for investigation of gamma-ray emission from Supergiant Fast X-ray Transients
• A Very-High-Energy Gamma-Ray View of the Transient Sky
• Detection of the microquasar V404 Cygni at gamma-rays revisited: short flaring events in quiescence
• AGILE results on relativistic outflows above 100 MeV
• The strange case of HESS J0632+057 and the γ-ray High Mass X-ray Binaries
• VHE observations of binary systems performed with the MAGIC telescopes
• Expected gamma-ray emission from x-ray binaries
• A variability study of the AGILE first catalog of γ-ray sources on 2.3 years of AGILE pointed observations
• Non-Thermal Emission from Galactic Jets
• Extreme Transients in Gamma Rays