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Chandra localisation of IGR J17361-4441 in the globular cluster NGC 6388

ATel #3627; D. Pooley (Sam Houston State U., Eureka Scientific), J. Homan (MIT), C. O. Heinke, G. R. Sivakoff (U. Alberta), D. Altamirano (U. Amsterdam), J. E. Maxwell, H. Cohn, and P. Lugger (Indiana U.)
on 3 Sep 2011; 16:10 UT
Credential Certification: dave pooley (dave@mit.edu)

Subjects: X-ray, Globular Cluster, Transient

Referred to by ATel #: 3958

We report on a 2.5 ks Chandra observation of IGR J17361-4441 (ATel #3565, #3566, #3595, #3617) that began on 2011-08-29 at 12:53 UT. The observation was taken with the ACIS S3 chip in half-chip subarray imaging mode. We use the CIAO tool wavdetect on a 0.5-6 keV image to determine the locations of the transient and several other sources in the globular cluster.

The transient is located at RA = 17h36m17.418s, Dec = -44:44:05.98 (J2000) with a wavdetect error circle of 0.04" radius.

We detect four additional four sources in the cluster that are easily matched to sources detected in a 45 ks Chandra observation in 2005 (Maxwell et al., in prep). The agreement between the two frames is excellent, with the average offsets of these four sources being less than 0.1" in both RA and Dec. Maxwell et al. measure the cluster center in the 2005 Chandra frame to be RA = 17h36m17.175s, Dec = -44:44:06.77.

IGR J17361-4441 is located ~2.7" away from the cluster center and is therefore unlikely to be an intermediate mass black hole, as suggested in ATel #3595. Its location is not consistent with any detected source in the prior Chandra observation, permitting an upper limit on its quiescent luminosity of ~10^31 ergs/s.

We attempted to model the Chandra spectrum, but pileup effects prevented a reliable fit.

Initial timing analyses, including tests for secular variations and periodic signals in the 5-645 mHz range, revealed no significant intra-observation variability.

We thank Harvey Tananbaum and the entire Chandra staff for their help in executing this observation.