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XMM-Newton Observation of IGR J18538-0102 and an Optical/IR Candidate

ATEL # 2445; J. P. Halpern, E. V. Gotthelf
on 18 Feb 2010; 7:40 UT
Password Certification: Jules Halpern (

Subjects: Infra-Red, Optical, X-ray, Gamma Ray, Request for Observations

We observed the X-ray counterpart of IGR J18538-0102 (Stephen et al., ATel #2441) in a pointed observation with XMM-Newton on 2004 October 8. This apparently steady source (in an 8 ks exposure) can be fitted with a power-law model of photon index 1.7+/-0.1, NH = (1.5+/-0.2)e22 cm-2, and unabsorbed 1-10 keV flux 5.6e-12 erg cm-2 s-1. Its coordinates 18h53m48.50s, -01d02'30.0" (J2000), with 90% confidence error radius of 3.2", coincide with an object in the 2MASS Point Source Catalog at 18h53m48.48s, -01d02'29.6" of magnitudes H=14.00+/-0.05 and K=12.50+/-0.05. On 2006 June 29, we obtained a 60 s uncalibrated exposure in the I-band on the 2.4m Hiltner telescope of the MDM Observatory under partly cloudy conditions, that shows a faint object at 18h53m48.49s, -01d02'29.2", consistent with the XMM-Newton and 2MASS coordinates. As argued previously, IGR J18538-0102 is unlikely to be a compact object in the supernova remnant G32.1-0.9. Deeper images and red or near-IR spectra of our candidate are desired to ascertain its nature. We have already obtained optical spectra that rule out a brighter star in the X-ray error circle.

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