Swift/XRT spectrum of the accreting X-ray pulsar IGR J01572-7259

ATel #2252; A. Bodaghee, J. A. Tomsick (SSL, UC Berkeley), J. Rodriguez (CEA Saclay)
on 22 Oct 2009; 15:19 UT
Credential Certification: Arash Bodaghee (bodaghee@ssl.berkeley.edu)

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Re-analysis of a Swift/XRT ToO observation of IGR J01572-7259 in the Magellanic Bridge (=IGR J015712-7259, c.f. Coe et al., 2008, ATel #1882) has enabled us to establish the first soft X-ray spectrum for this 11.6-s X-ray pulsar and suspected high-mass X-ray binary.

Observation-ID 00031313001 was taken on December 20, 2008, for an effective exposure time of 1950 s. The 0.5–7 keV spectrum was fit with a power law including a photoelectric absorption component that assumed either Solar abundances or those described by Wilms et al., 2000. We derived a photon index of 0.9(3) in both cases, and column densities (in units of 10²¹ cm^-2) of 3±2 for the Solar case, and 4_-2⁺³ assuming the abundances of Wilms et al., 2000. This is greater (by a factor of 5–10) than the interstellar absorption expected along the line of sight, which suggests a small amount of intervening material that is local to this source (in addition to material in the Magellanic Bridge). Errors are quoted at 90% confidence. In both fits, the reduced Chi-squared value is 1.0 for 25 degrees of freedom. The unabsorbed flux in the 2–10 keV energy range is 1.2x10^-11 erg/cm²/s (~0.6 mCrab) which translates to 4x10³⁶ erg/s for an assumed distance of 55 kpc.