A Chandra observation of IGR J17177-3656

ATel #3236; A. Paizis (INAF-IASF Milano), M. Nowak (MIT-CXC), J. Rodriguez (CEA Saclay), M. Del Santo (INAF-IASF Roma), J. Wilms (University of Erlangen-Nuremberg), S. Chaty (CEA Saclay), P. Ubertini (INAF-IASF Roma)
on 25 Mar 2011; 17:50 UT
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Credential Certification: Adamantia Paizis (ada@iasf-milano.inaf.it)

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Following the discovery of IGR J17177-3656 (Frankowski et al. 2011, ATel #3223) on 2011-03-15, we triggered our Chandra HETGS ToO observation, which was executed from 2011-03-22T06:07:15 to 2011-03-22T12:00:48 UT, for a total exposure time of about 20 ksec.

The J2000.0 Chandra position we obtain is
RA: 17 17 42.62
DEC: -36 56 04.5

We estimate our position error to be dominated by a 1 sigma systematic error of 0.6" determined by the absolute accuracy with which the Chandra aspect solution is typically known. Our position is consistent with the INTEGRAL/JEM-X one (about 55" away with respect to their 1.5' quoted error, ATel #3223) but it is not overlapping with the Swift one (about 4.8" away with respect to their 2.1" quoted error, ATel #3226).

The Chandra angular separation from the optical counterpart proposed by Malizia et al. based on the INTEGRAL position (ATel #3224) is about 2', hence we confirm that the association can be ruled out, as already stated by the Swift follow-up of the source; the Chandra separation from the source 2MASS J17174269-3656039 proposed by Zhang et al. based on the Swift position (ATel #3226) is about 1.05", making it an unlikely association given our 0.6" position error.

We have performed a simple phenomenological fit to the grating spectra. The MEG and HEG first order spectra are consistent with an absorbed power-law with a column of approximately N_H=(5.9 +/- 1.5)E22 cm-2 (90% confidence, "tbabs" in XSPEC by Wilms et al., 2000) and Gamma = 1.2 +/- 0.4 (90% confidence). The absorbed 2-10 keV flux is 6.2E-11 ergs cm-2 sec-1 (about 3 mCrab). We confirm that, similarly to what reported by the recent INTEGRAL and Swift observations of the source, the absorption is larger than the Galactic column density and additional absorption intrinsic to the source is detected.

The quoted fit is to be considered as the best fit obtained from the average Chandra spectrum. Spectral variability within the observation as well as slope dependence on the narrow band-pass will be studied in the forthcoming paper.

We thank the INTEGRAL Science Data Center staff (in particular Carlo Ferrigno) and the INTEGRAL Galactic Bulge observations PI (Erik Kuulkers) for their quick and efficient sharing of INTEGRAL results.
We would like to thank also the Chandra team for their rapid response in both scheduling this Target of Opportunity observation and in delivering the data.