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INTEGRAL detection of Hard X-ray emission from XTEJ1720-318

ATel #153; P. Goldoni (SAp/CEA, Saclay), A. Goldwurm (SAp/CEA, Saclay), E. Kuulkers (ESA/ESTEC), A. Parmar (ESA/ESTEC), C. Budtz-Joergensen (DSRI, Copenhagen), G. Palumbo (Universita' degli studi di Bologna), J. P. Roques (CESR, Toulouse), R. Sunyaev (IKI, Moscow;MPA Garching), P. Favre (ISDC, Geneva)
on 24 Apr 2003; 18:02 UT
Credential Certification: Paolo Goldoni (pgoldoni@cea.fr)

Subjects: X-ray, Request for Observations, Binary, Transient

We report the detection of the soft X-Ray transient XTE J1720-318 (ATEL #113, ATEL #115) with the IBIS/ISGRI instrument onboard the INTEGRAL observatory during routine scans of the Galactic Center region and two pointed observations of the source IGRJ1746-3213(=H1743-322), all performed in April. The source started to be active at energies higher than 40 keV around March 30, reached a level of ~25 mCrabs and ~30 mCrabs in the 15-40 and 40-100 keV bands, respectively, on April 6 and 7, and was then detected at approximately the same level between April 15 and 16. On these occasions a positive detection was also recorded at energies between 100 and 200 keV indicating a hard spectrum. On April 15 and 16 its 4-18 keV flux was estimated to be smaller than 20 mCrab with the JEM-X X-ray monitor. During a previous dedicated INTEGRAL observation of XTE J1720-318 on February 28, the source was not detected with IBIS/ISGRI above 40 keV and was only marginally visible between 15 and 40 keV at an estimated flux of 2-4 mCrab. At that time it was observed at a level of ~100 mCrab with ASM/RXTE in soft (2-12 keV) X-ray band. These observations suggest that the source has undergone a transition from a high/soft to a low/hard state, typical of later stages of black hole X-ray transients outbursts, when compact radio jets are often observed. Multiwavelength observations are encouraged.