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Swift/XRT localization of IGR J00569-7226, a likely new Be/X-ray binary

ATel #5553; J. A. Kennea (PSU)
on 6 Nov 2013; 16:57 UT
Credential Certification: Jamie A. Kennea (kennea@astro.psu.edu)

Subjects: X-ray, Transient

Referred to by ATel #: 5557, 5631, 5662, 5925

We report on Swift target-of-opportunity observations of the recently reported transient IGR J00569-7226 (Coe et al., ATEL #5547). Beginning 23:42UT on November 5th, 2013, Swift performed a 1ks observation of the INTEGRAL error circle. In XRT Photon Counting mode data, we detect a previously uncatalogued transient inside the INTEGRAL error circle. Correcting for systematic errors in the astrometry utilizing UVOT attitude correction, we find a position of: RA/Dec(J2000) = 14.25973, -72.43204, equivalent to:

RA(J2000) = 00h 57m 02.34s
Dec(J2000) = -72d 25m 55.34s

with an estimated uncertainty of 2.6 arc-seconds radius (90% confidence).

The massive star NGC 330-070, which was reported by the VLT-FLAMES survey (Evans et al., 2006, A&A, 456, 623) to be a Be star of type B0.5e, lies 0.6 arc-seconds from the center of the Swift/XRT error circle, and therefore is consistent with being the optical counterpart of IGR J00569-7226. We therefore conclude that IGR J00569-7226 is likely a newly discovered Be/X-ray binary, associated with a star in the SMC globular cluster NGC 330.

The XRT spectrum is hard, well fit by a power-law model with photon index = 0.9 +/- 0.2 and an absorption column density of 2.5 +/- 2.0 x 1021 cm2 . The flux, corrected for absorption, is ~1.2 x 10-10 erg cm-2 s-1 (0.5 - 10 keV). Assuming a standard SMC 61 kpc distance, this corresponds to a flux of ~5.5 x 1037 erg/s (0.5 - 10 keV).

Examination of the combined archival data on this field, ~19ks of Swift/XRT Photon Counting mode data, shows no previous detection of IGR J00569-7226 with an estimated 3-sigma upper limit of 7 x 10-14 erg/s/cm^2, constraining the pre-outburst flux to be <3 x 1034 erg/s (0.5-10 keV). Therefore the outburst flux from IGR J00569-7226 is greater than 3 orders of magnitude brighter than the quiescent level, consistent with a Be/X-ray binary nature.