2010A&A...518A..12R -
Astronomy and Astrophysics, volume 518, A12-12 (2010/7-2)
Gamma-ray absorption and the origin of the gamma-ray flare in Cygnus X-1.
ROMERO G.E., DEL VALLE M.V. and ORELLANA M.
Abstract (from CDS):
The high-mass microquasar Cyg X-1, the best-established candidate for a stellar-mass black hole in the Galaxy, has been detected in a flaring state at very high energies (VHE), E>200GeV, by the Atmospheric Cherenkov Telescope MAGIC. The flare occurred at orbital phase φ=0.91, where φ=1 is the configuration with the black hole behind the companion high-mass star, when the absorption of gamma-ray photons by photon-photon annihilation with the stellar field is expected to be highest. We aim to set up a model for the high-energy emission and absorption in Cyg X-1 that can explain the nature of the observed gamma-ray flare. We study the gamma-ray opacity due to pair creation along the whole orbit, and for different locations of the emitter. Then we consider a possible mechanism for the production of the VHE emission. We present detailed calculations of the gamma-ray opacity and infer from these calculations the distance from the black hole where the emitting region was located. We suggest that the flare was the result of a jet-clump interaction where the decay products of inelastic p-p collisions dominate the VHE outcome. We are able to reproduce the spectrum of Cyg X-1 during the observed flare under reasonable assumptions. The flare may be the first event of jet-cloud interaction ever detected at such high energies.
Abstract Copyright:
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Journal keyword(s):
X-rays: binaries - gamma-rays: general - radiation mechanisms: non-thermal - stars: winds, outflows
Simbad objects:
5
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