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An improvement of the position of IGR J17191-2821

ATEL # 1070; M. Klein-Wolt (University of Amsterdam), D. Maitra (University of Amsterdam), R. Wijnands (University of Amsterdam), J. H. Swank (NASA/GSFC), C. B. Markwardt (CRESST/U.Md./NASA/GSFC), C. Bailyn (Yale University)
on 8 May 2007; 19:55 UT
Password Certification: Marc Klein-Wolt (

Subjects: Optical, X-ray, Binaries, Neutron Stars, Transients

We observed the transient IGR J17191-2821 (Atels #1021,#1022,#1025,#1065,#1068,#1069) again for 1.8 ksec on May 07 (18:30 UTC) with Swift/XRT in the imaging mode (Photon-Counting mode). The source is heavily piled-up but a position could be obtained: (RA, DEC)=(259.81306, -28.29919) (J2000) with an error of ~4 arcsec. This improved position is offset from the original Integral position (Atel #1021) by about 3.8 arcminutes, but is consistent with the variable faint source detected in our Swift/XRT observation taken on March 8 (Atel #1025). The spectrum (excluding the central piled-up region) is best described by a power law with an index of 1.71 +/- 0.07 and an interstellar extinction of 0.57 +/- 0.05 E22 cm^-2, consistent with our May 1th observation (Atel #1065).We estimate the unabsorbed 2-10 keV flux at ~53 mCrab, which clearly indicates the source is decaying during its outburst as already suggested by Markwardt et al. (Atel #1068).

We obtained V, I and H-band images of the field of IGR J17191-2821 using the SMARTS 1.3m telescope and ANDICAM instrument on May 4.295 UT. While both USNO-B1.0 and 2MASS point source catalogs do not have any sources within the 4 arcsec Swift/XRT error circle, two sources were detected [at (RA,DEC) of (259.811453,-28.297926) and (259.812253 -28.297579) with an error of approximately 0.4"] in our images within the error circle, in all three bands. The SMARTS consortium will continue to monitor this field to search for variability in brightness expected from X-ray binaries, in order to confirm the true optical counterpart.

We would like to thank the Swift Team for making these observations possible.

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