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SIGMA and XTE observations of the soft X-ray transient XTEJ1755-324

P. Goldoni·M. Vargas·A. Goldwurm·J. Paul·V. Borrel·E. Jourdain·L. Bouchet·J. -P. Roques·M. Revnivtsev·E. Churazov·M. Gilfanov·R. Sunyaev·A. Dyachkov·N. Khavenson·I. Tserenin·N. Kuleshova
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Abstract

We present observations of the X-ray transient XTEJ1755-324 performed during summer 1997 with the XTE satellite and with the SIGMA hard X-ray telescope onboard the GRANAT observatory. The source was first detected in soft X-rays with XTE on July 25 1997 with a rather soft X-ray spectrum and its outburst was monitored in soft X-rays up to November 1997. On September 16 it was first detected in hard X-rays by the French soft gamma ray telescope SIGMA during a Galactic Center observation. The flux was stronger on September 16 and 17 reaching a level of about 110 mCrab in the 40-80 keV energy band. On the same days the photon index of the spectrum was determined to be alpha =-2.3 +/- 0.9 (1 sigma error) while the 40-150 keV luminosity was about 8 x 10^{36} erg/s for a distance of 8.5 kpc. SIGMA and XTE results on this source indicate that this source had an ultrasoft-like state during its main outburst and a harder secondary outburst in September. These characteristics make the source similar to X-Nova Muscae 1991, a well known black hole candidate.

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P. Goldoni, M. Vargas, A. Goldwurm, J. Paul, V. Borrel, E. Jourdain, L. Bouchet, J. -P. Roques, M. Revnivtsev, E. Churazov, M. Gilfanov, R. Sunyaev, A. Dyachkov, N. Khavenson, I. Tserenin, N. Kuleshova. 1998-08-20. SIGMA and XTE observations of the soft X-ray transient XTEJ1755-324. https://doi.org/10.1086/306726

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