2006/10/11 by Antonella Tarana, Angela Bazzano, Tarana, Antonella +7
Physics and Astronomy · #Astrophysics (astro-ph) #FOS: Physical sciences #astro-ph
paper · pdf · doi:10.48550/arxiv.astro-ph/0610328
4 pages, 3 figures, submitted proceeding of the 6th INTEGRAL Workshop "The Obscured Universe" July 2-8, 2006 Space Research Institute Moscow, Russia
arxiv created 2006/10/11 · arxiv updated 2009/12/01
The 4-200 keV spectral and temporal behaviour of the low mass X-ray binary 4U 1820-30 has been studied with INTEGRAL during 2003-2005. This source as been observed in both the soft (banana) and hard (island) spectral states. A high energy tail above 50 keV in the hard state has been revealed for the first time. This places the source in the category of X-ray bursters showing high-energy emission. The tail can be modeled as a soft power law component, with the photon index of ~ 2.4, on top of thermal Comptonization emission from a plasma with the electron temperature of kTe ~ 6 keV and optical depth of τ~ 4. Alternatively, but at a lower goodness of the fit, the hard-state broad band spectrum can be accounted for by emission from a hybrid, thermal-nonthermal, plasma. During the observations, the source spent most of the time in the soft state, as previously reported and the ≥4 keV spectra can be represented by thermal Comptonization with kTe ~ 3 keV and τ~ 6-7.