Microquasars are accreting black holes or neutron stars in binary systems with associated relativistic jets. Despite their frequent outburst activity, they have never been unambiguously detected emitting high-energy gamma rays. The Fermi Large Area Telescope (LAT) has detected a variable high-energy source coinciding with the position of the x-ray binary and microquasar Cygnus X-3. Its identification with Cygnus X-3 is secured by the detection of its orbital period in gamma rays, as well as the correlation of the LAT flux with radio emission from the relativistic jets of Cygnus X-3. The gamma-ray emission probably originates from within the binary system, opening new areas in which to study the formation of relativistic jets.

https://science.sciencemag.org/content/sci/early/2009/11/26/science.1182174.full.pdf

Modulated High-Energy Gamma-Ray Emission from the Microquasar Cygnus X-3

After initial claims and a long hiatus, it is now established that several binary stars emit high- (0.1–100 GeV) and very high-energy (>100 GeV) gamma rays. A new class has emerged called “gamma-ray binaries”, since most of their radiated power is emitted beyond 1 MeV. Accreting X-ray binaries, novae and a colliding wind binary (η Car) have also been detected—“related systems” that confirm the ubiquity of particle acceleration in astrophysical sources. Do these systems have anything in common? What drives their high-energy emission? How do the processes involved compare to those in other sources of gamma rays: pulsars, active galactic nuclei, supernova remnants? I review the wealth of observational and theoretical work that have followed these detections, with an emphasis on gamma-ray binaries. I present the current evidence that gamma-ray binaries are driven by rotation-powered pulsars. Binaries are laboratories giving access to different vantage points or physical conditions on a regular timescale as the components revolve on their orbit. I explain the basic ingredients that models of gamma-ray binaries use, the challenges that they currently face, and how they can bring insights into the physics of pulsars. I discuss how gamma-ray emission from microquasars provides a window into the connection between accretion–ejection and acceleration, while η Car and novae raise new questions on the physics of these objects—or on the theory of diffusive shock acceleration. Indeed, explaining the gamma-ray emission from binaries strains our theories of high-energy astrophysical processes, by testing them on scales and in environments that were generally not foreseen, and this is how these detections are most valuable.

Gamma-ray binaries and related systems

After initial claims and a long hiatus, it is now established that several binary stars emit high (0.1-100 GeV) and very high energy (>100 GeV) gamma rays. A new class has emerged called 'gamma-ray binaries', since most of their radiated power is emitted beyond 1 MeV. Accreting X-ray binaries, novae and a colliding wind binary (eta Car) have also been detected - 'related systems' that confirm the ubiquity of particle acceleration in astrophysical sources. Do these systems have anything in common ? What drives their high-energy emission ? How do the processes involved compare to those in other sources of gamma rays: pulsars, active galactic nuclei, supernova remnants ? I review the wealth of observational and theoretical work that have followed these detections, with an emphasis on gamma-ray binaries. I present the current evidence that gamma-ray binaries are driven by rotation-powered pulsars. Binaries are laboratories giving access to different vantage points or physical conditions on a regular timescale as the components revolve on their orbit. I explain the basic ingredients that models of gamma-ray binaries use, the challenges that they currently face, and how they can bring insights into the physics of pulsars. I discuss how gamma-ray emission from microquasars provides a window into the connection between accretion--ejection and acceleration, while eta Car and novae raise new questions on the physics of these objects - or on the theory of diffusive shock acceleration. Indeed, explaining the gamma-ray emission from binaries strains our theories of high-energy astrophysical processes, by testing them on scales and in environments that were generally not foreseen, and this is how these detections are most valuable.

The Gamma Ray Observatory (GRO) is currently planned for a launch from the space shuttle in 1990. After the long hiatus in high-energy gamma-ray astronomy since the end of the COS-B mission in 1982, the Soviet missions Granat and Gamma-1 and the NASA mission GRO will resume observations in the energy range from below 100 keV and extending to above 10 GeV. GRO will carry four instruments designed to cover this range of over five decades in photon energy. It is planned to perform a complete sky survey above 1 MeV in the first year of the GRO mission. Data from this survey will be used to study galactic and extragalactic sources of gamma radiation as well as the galactic and extragalactic diffuse emissions. Additionally, measurements of gamma ray bursts will be performed. The angular and spectral resolution of the GRO instruments is significantly improved with respect to previous experiments. The sensitivity for point sources will be better by an order of magnitude, and the location of strong, high energy sources will be determined to about 0.1°–0.2°. After a brief description of the complement of GRO instruments, a detailed discussion of the high-energy telescope EGRET, its design and scientific objectives, is presented in this review.

The project EGRET (Energetic Gamma-Ray Experiment Telescope) on NASA's Gamma-Ray Observatory (GRO)

The COS-B satellite operated from August 1975 until April 1982 during which time an extensive survey of the Galaxy was made in the energy range 50 MeV to 5 Gev. The Caravane Collaboration built the gamma-ray telescope and performed the bulk of the scientific data reduction. Since the data are now available to the Astrophysics community at large, some alternate analyses are now being presented. A summary of the major findings of the mission is given in the context of the multi-disciplinary nature of this meeting. Hopefully, some the myths will be dispelled and some of the facts reinforced.

COS-B: The highlights

COS-B viewed the Cyg X-3 region seven times between November, 1975, and February, 1982; a search for steady gamma-ray emission pulsed at the characteristic 4.8-hour period did not reveal its source. Leiden-MIT balloon experiment observations of Cyg X-3 in May, 1979 show the 4.8-hour modulation with sinusoidal light curve and modulation depth of 0.30, for energies of up to about 140 keV. The strong variability of Cyg X-3 over more than one order of magnitude at energies below 20 keV does not emerge in the data collected at hard X-ray energies.

High-energy gamma-ray and hard X-ray observations of Cyg X-3

The Compton imaging telescope (COMPTEL) on the Gamma Ray Observatory (GRO) is a wide field of view instrument. The coincidence measurement technique in two scintillation detector layers requires specific analysis methods. Straightforward event projection into the sky is impossible. Therefore, detector events are analyzed in a multi-dimensional dataspace using a gamma ray sky hypothesis convolved with the point spread function of the instrument in this dataspace. Background suppression and analysis techniques have important implications on the gamma ray source results for this background limited telescope. The COMPTEL collaboration applies a software system of analysis utilities, organized around a database management system. The use of this system for the assistance of guest investigators at the various collaboration sites and external sites is foreseen and allows different detail levels of cooperation with the COMPTEL institutes, dependent on the type of data to be studied.

/pdf/data-analysis-of-the-comptel-instrument-on-the-nasa-gamma-y9pr8sxdto.pdf

Data analysis of the COMPTEL instrument on the NASA gamma ray observatory

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High-energy gamma-ray and hard X-ray observations of Cyg X-3

Data analysis of the COMPTEL instrument on the NASA gamma ray observatory