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Swift/XRT Observations Confirm that IGR J17091-3624 is in Outburst

ATel #3148; H. A. Krimm (CRESST/GSFC/USRA) and J. A. Kennea (PSU)
on 4 Feb 2011; 18:22 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Hans A. Krimm (Hans.Krimm@nasa.gov)

Subjects: X-ray, Binary, Transient

Referred to by ATel #: 3150, 3159, 3167, 3168, 3225, 3229, 3232, 3913, 4173, 4773

Swift/XRT carried out a 983-s observation starting at 3 Feb 2011 21:29:03 UTC at a pointing location chosen so that both IGR J17091-3624 and IGR J17098-3628 were in the field of view. IGR J17091-3624 is strongly detected in the XRT image in Photon Counting mode, consistent with the proposed identification of the outburst source from the Swift/BAT data (Krimm et al., ATel #3144). There is no detection of any X-ray flux from IGR J17098-3628.

The data are fitted by an absorbed power-law model (Reduced chi2 = 0.76) with the following parameters:

N_H = 1.10 +/- 0.3 x 10^22 cm-2
Gamma = 1.73 +/- 0.29
Flux (0.3-10 keV) = 4.3 +/- 0.5 x 10^-10 erg/s/cm-2

We note that the spectrum was affected by pile up. The source was not detected in the Swift/UVOT, which is consistent with the large absorption.

Further Swift monitoring observations in Windowed Timing mode have been requested.