INTEGRAL confirms that XTE J1728-295 = IGR J17285-2922

ATel #2825; M. Turler, C. Ferrigno (ISDC - University of Geneva, Switzerland) E. Kuulkers (ESA/ESAC, Spain), J. Alfonso-Garzon (LAEX-CAB/INTA-CSIC, Spain), V. Beckmann (APC, France), T. Bird (Southampton, UK), S. Brandt, L. Chenevez (DNSC, Denmark), T. Courvoisier (ISDC, Switzerland), A. Domingo (LAEX-CAB/INTA-CSIC, 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 1 Sep 2010; 06:39 UT
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Credential Certification: Nami Mowlavi (Nami.Mowlavi@obs.unige.ch)

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Following the renewed activity of XTE J1728-295 and its probable association with IGR J17285-2922 (ATels #2823, #2824), we searched for a coincident outburst of the source in the data from the on-going INTEGRAL Galactic bulge monitoring program (see ATel #438).

IGR J17285-2922 is detected by IBIS/ISGRI, in the energy range 20-40 keV, on UT 26 Aug 2010 11:28-16:23 (10+/-2 mCrab, with a detection significance of 5 sigma), 26 Aug 23:09 - 27 Aug 02:53 (11+/-2 mCrab, 5 sigma) and 29 Aug 22:53 - 30 Aug 02:37 (12+/-2 mCrab, 6 sigma). Earlier observations on 20 Aug 23:37 - 21 Aug 03:19 do not show any source activity, with a 3-sigma upper limit of 7 mCrab (20-40 keV).

By combining the three observations when the source is detected, we obtain a detection significance of 9.4 and 7.0 sigma in the 20-40 keV and 40-80 keV energy bands, respectively. The average ISGRI spectrum can be well described (reduced chi^2 of 0.8 for 8 degrees of freedom) by a simple power-law of index 2.1+/-0.5 (uncertainty at 68% c.l.) and a 20-80 keV flux of 9.8e-11 erg/s/cm^2. The best-determined position with a 90% confinement radius of 2.8 arcmin (Gros et al., 2003, A&A, L179) is (RA,DEC)=(262.172,-29.325), fully consistent with the location of the Swift/XRT Soft X-ray counterpart (ATel #2824).

IGR J17285-2922 was not detected by JEM-X with a 3-sigma upper limit of about 12 mCrab (3-11 keV). This is consistent with the peak flux of 6.5 mCrab obtained for XTE J1728-295 in the 2-10 keV band with RXTE/PCA (ATel #2823). We note that the hard X-ray activity is confirmed by the Swift/BAT Hard X-ray Transient Monitor (see ATel #904), which evidences enhanced emission around the same time, and at a similar level.

The coincidence of the renewed low-level activity of IGR J17285-2922 in the hard X-rays with the reported X-ray outburst of XTE J1728-295 (ATel #2823) and the positional coincidence with the proposed Soft X-ray counterpart (ATel #2824) strengthen the suggestion that the two sources are actually the same object.

The next INTEGRAL Galactic bulge monitoring observation is foreseen to start at UT 4 Sep 2010 11:26.