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New outburst of IGR J17544-2619 detected with INTEGRAL

ATel #252; S. A.Grebenev (IKI, Moscow), J. Rodriguez (CEA, Saclay & ISDC, Versoix), N. J.Westergaard (DSRI, Copenhagen), R. A.Sunyaev (IKI, Moscow & MPA, Garching), T. Oosterbroek (ESA/ESTEC, Noordwijk)
on 18 Mar 2004; 17:52 UT
Distributed as an Instant Email Notice Transients
Credential Certification: S.A.Grebenev (sergei@hea.iki.rssi.ru)

Subjects: Radio, Infra-Red, Optical, X-ray, Binary, Black Hole, Neutron Star, Transient

Referred to by ATel #: 338, 1265, 1266, 1454

A new outburst of the hard X-ray transient IGR J17544-2619 (ATEL #190, #192, #194, IAUC # 8202 ) was detected with INTEGRAL during recent observations dedicated to the Galactic Center Deep Exposure. The source was first detected with IBIS/ISGRI on March 8, 2004 at 08h UTC and remained bright during at least 10 hours. The S/N ratio was equal to 33. The average 17-45 keV flux was about 50 mCrab but the source reached ~160 mCrab at the peak of the outburst (at 11h UTC). The source was very variable with an oscillation-like behaviour on a time scale of 1.5-2 hours. The source spectrum was rather steep. It could be described by a power law with the photon index of about -4 with some evidence for a high energy cutoff. The source was also detected with JEM-X in the 6-30 keV band but only during the short time interval (~25 min) corresponding to the maximum of its hard X-ray brightness. The S/N ratio was ~18. The spectrum was slightly flatter than that in the ISGRI band and could be described with the photon index of about -3. This observation shows that the outburst in September when the source was discovered (ATEL #190, #192) was not an unique event and IGR J17544-2619 is actually a recurrent transient. We encourage persistent monitoring of this source at all wavelengths.