Recent and past activity of the supergiant fast X-ray transient IGR J17544-2619 as seen by INTEGRAL

ATel #1266; E. Kuulkers (ESA/ESAC, Spain), D. Risquez Oneca (LAEFF/INTA, Spain), S. Brandt (DNSC, Denmark), S. Shaw (Southampton, UK/ ISDC, Switzerland),V. Beckmann (ISDC, Switzerland), J. Chenevez (DNSC, Denmark), T. J.-L. Courvoisier (ISDC, Switzerland), A. Domingo (LAEFF/INTA, Spain), K. Ebisawa (ISAS, Japan), P. Jonker (SRON, The Netherlands), P. Kretschmar (ESA/ESAC, Spain), C. Markwardt (GSFC, USA), T. Oosterbroek (ESA/ESTEC, The Netherlands), A. Paizis (INAF-IASF, Italy), C. Sanchez-Fernandez (ESA/ESAC, Spain), R. Wijnands (UvA, The Netherlands)
on 9 Nov 2007; 16:04 UT
Credential Certification: Erik Kuulkers (ekuulker@rssd.esa.int)

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Following the report of the recent activity seen by Swift/BAT (ATel #1265) we note that the supergiant fast X-ray transient IGR J17544-2619 was also active about one and a half month earlier. During our INTEGRAL Galactic Bulge monitoring observations (see ATels #438, #874 and #1005) on UT 2007 Sep 21 04:10-07:52 the source flared on timescales of half an hour, from around the IBIS/ISGRI detection limits of one pointing (about 10 mCrab) up to 36 +/- 5 mCrab (20-60 keV). The average IBIS/ISGRI detection significance over the 12.6 ksec observation is about 14 sigma (20-60 keV). No simultaneous activity was seen from the optical counterpart with the OMC (V-band magnitude stayed near 12.8); the source was not detected by JEM-X with an upper limit of about 20 mCrab (3-20 keV).

Activity prior to this was also seen by Kuulkers et al. (2007, A&A 466, 595) with INTEGRAL on UT 2005, October 15, when IGR J17544-2619 reached a flux of up to about 60 mCrab (IBIS/ISGRI; 20-60 keV). We note that the recent hard X-ray activity of the source, together with that reported in the literature (ATel #190; #192; #252; Walter et al. 2006, A&A 453, 133; Kuulkers et al. 2007), can not be described with a recurrence period of about 165 days suggested by Walter et al. (2006).

The INTEGRAL Galactic Bulge monitoring results (JEM-X and IBIS/ISGRI light curves and mosaic images) are publicly available at http://isdc.unige.ch/Science/BULGE/.