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Swift/XRT follow-up of the periodic activity of the transient pulsar IGR J19294+1816

ATel #5104; M. Fiocchi (INAF/IAPS Roma, Italy), L. Sidoli (INAF/IASF Milano, Italy), A. J. Bird (Univ. of Southampton, UK), S. P. Drave (Univ. of Southampton, UK), V. Sguera (INAF/IASF Bologna, Italy), on behalf of the INTEGRAL/GPS team.
on 4 Jun 2013; 17:32 UT
Credential Certification: mariateresa fiocchi (mariateresa.fiocchi@iasf-roma.inaf.it)

Subjects: X-ray, Binary, Transient

Hard X-ray emission has been detected from the high mass X-ray binary system IGR J19294+1816 during recent INTEGRAL observations of the Cygnus region of the Galactic Plane (PI: A. Bazzano) performed during revolution 1294 (ATel #5079). Following this renewed activity, two Swift ToO observations were performed starting on 2013 May 28 at 16:11:47 UT and 2013 May 29 at 17:21:11 UT, with exposure times of 787s and 4481s, respectively. The Swift/XRT net count rates of the source are 0.51+/-0.03 c/s and 0.63+/-0.01 c/s in the 1-10 keV energy range. The current outburst corresponds to the ephemeris defined by Corbet & Krimm in ATel #2008, confirming this transient source is once again active during the periastron passage.

The XRT spectra are well described by an absorbed power law model, with the following fit results:

observation #1: a photon index of 0.86+/-0.40, a column density of NH=(3.5+/-1.2)E+22 cm-2 and a 1-10keV unabsorbed flux of (1.0+/-0.1)*10^-10 erg cm-2 s-1 (chi2_red=0.74 for 39 d.o.f.)

observation #2: a photon index of 0.75+/-0.15, a column density of NH=(3.0+/-0.4)E+22 cm-2 and a 1-10keV unabsorbed flux of (1.10+/-0.05)*10^-10 erg cm-2 s-1 (chi2_red=0.88 for 242 d.o.f.)

By comparison with previous Swift observations (ATel #4136), we note an indication that the source is harder when it is brighter. Timing analysis on the barycentered events shows pulsations with a period of p=12.457+/-0.002 s, compatible with the previous XRT measurement (ATel #4136).

Further hard X-ray emission has been detected from IGR J19294+1816 during very recent INTEGRAL Galactic Plane Scanning performed in revolution 1296 (from 2013-05-26 UTC 21:49:40 to 2013-05-27 14:37:18) and 1299 (from 2013-06-03 UTC 01:54:29 to 2013-06-03 16:52:07). IBIS/ISGRI detected this binary system with a flux of 22.0+/-2.5 mCrab (revolution 1296) and 10.5+/-1.5 mCrab (in revolution 1299) in the 18-40 keV energy band, for an exposure of 28 ks and 16 ks, respectively, showing that the outburst has a similar duration and orbital phase to previous outbursts and shows the behavior expected for type I bursts from a Be X-ray binary.

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