XTE J1810-189 measurements by INTEGRAL and Swift

ATel #1430; A. Neronov, V. Beckmann (ISDC), H. Krimm (CRESST/GSFC/USRA), C. B. Markwardt (CRESST/GSFC/UMD), J. Tueller (NASA/GSFC), L. Kuiper (SRON), A. Bazzano, I. Donnarumma, A. De Rosa, M. Fiocchi, L. Natalucci (INAF/IASF-Roma), M. Cadolle-Bel (ESA/ESAC), M. Falanga, A. Goldwurm (CEA/Saclay), J.-C. Leyder (IAG Liege), S. Mereghetti (INAF/IASF-Milano), S. Piraino (IAAT), K. Pottschmidt (CRESST/NASA/UMBC), J. Tomsick (UCB), R. Walter (ISDC), and K. Watanabe (FGCU)
on 17 Mar 2008; 19:02 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Volker Beckmann (Volker.Beckmann@obs.unige.ch)

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During the INTEGRAL Key Programme observations of the Galactic Centre (revolution 661, from 2008-03-12T22:17 to 2008-03-15T00:48), the IBIS/ISGRI telescope detected a hard X-ray transient, IGR J18103-1903, at the position RA = 18 10 23.3, DEC= -19 03 32 (statistical error of 2.0'). The source is detected in the combined data set at 21 sigma in the 20-40 keV band with a rate of 2.9±0.2 cps (about 17 mCrab) for an effective exposure time of 168 ksec, using OSA7 analysis software. IGR J18103-1903 is also detected in the 40-80 keV band with 10 sigma and 12±1 mCrab. Unfortunately, IGR J18103-1903 was too far off-axis to be covered by JEM-X. The position is close (9 arcmin) to XTE J1810-189, a new transient reported by Markwardt & Swank (ATel#1424). Observations with Swift/BAT on 2008-03-16 show a source with 0.005±0.0007 counts/cm**2/sec (22 mCrab; 15-50 keV) at RA = 18 10 25.9, DEC = -19 04 12 (3.0 arcmin error circle), consistent with the IBIS/ISGRI position. Swift/BAT first detected the source at 10 mCrab on 2008-03-10. We therefore suggest that the source seen by Swift/BAT and INTEGRAL IBIS/ISGRI is identical with XTE J1810-189.

The ISGRI spectrum can be represented by a simple power law model with photon index 2.26±0.12 (reduced chi squared 1.28) with a model flux of F(20-200 keV) = 3.8E-10 erg/cm**2/sec. The upper limit on the flux at the source position from public data (2004-2007) is about 0.5 mCrab.

No source was detected by ROSAT within the ISGRI error circle, but two sources by 2MASS as well as IRAS 18073-1904, with a flux of 5.0±0.4 Jy at 12 μm.

Swift pointed observations are in progress in order to further constrain the X-ray position.