Astronomy and Astrophysics – Astrophysics
Scientific paper
2006-08-28
Astrophys.J.654:494-498,2006
Astronomy and Astrophysics
Astrophysics
14 pages, 4 figures, accepted for publication by ApJ
Scientific paper
10.1086/508744
We study the 4-200 keV spectral and temporal behaviour of the low mass X-ray binary 4U 1820-30 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 observed 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 kT_e~6 keV and optical depth of \tau~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 this monitoring the source spent most of the time in the soft state, usual for this source, and the >~4 keV spectra are represented by thermal Comptonization with kT_e~3 keV and \tau~6-7.
Bazzano Angela
Tarana Antonella
Ubertini Pietro
Zdziarski Andrzej A.
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