GRO J1744-28: Swift XRT confirmation of outburst
ATel #5845; J. A. Kennea (PSU), C. Kouveliotou (MSFC), G. Younes (MSFC/USRA)
on 3 Feb 2014; 01:53 UT
Credential Certification: Jamie A. Kennea (kennea@astro.psu.edu)
Subjects: X-ray, Transient
We report on a Swift target-of-opportunity observation of GRO J1744-28, suggested recently to be in outburst by the detection of enhanced X-ray emission in the region by MAXI and the Swift Burst Alert Monitor (Negoro et al., ATEL #5790). Swift began observations starting 14:04UT on February 2nd, 2014, we report on 1.2ks of Photon Counting (PC) mode data. We find a bright, piled-up source in the field of view. Utilizing UVOT to correct for astrometric errors and fitting a piled-up PSF in order to obtain an accurate localization, using the methods described by Evans et al. (2007, A&A, 469, 379) and Evans et al. (2009, MNRAS 397, 1177), we find a position of RA/Dec(J000) = 266.13801, -28.74077, which is equivalent to:
RA(J2000) = 17h 44m 33.12s,
Dec(J2000) = -28d 44' 26.8'',
with an error radius of 2.2 arc-seconds (90% confidence). This position lies 0.5 arc-seconds from the position of GRO J1744-28 reported by Liu et al (2007, A&A, 469, 807), confirming the that the latest outburst is indeed from GRO J1744-28.
Although the PC mode data are highly piled-up, we extracted a pile-up corrected spectrum, and find that it is well fit by an absorbed power-law model, with N_H = 4.7 +/- 1.5 x 10^22 cm-2, and photon index = 0.6 +/- 0.4. The 0.5-10 keV flux is 7 +/- 1 x 10-9 erg/s/cm2, corrected for absorption this is ~1 x 10-8 erg/s/cm2 (0.5 - 10 keV). In the short observation the source shows no significant variability, although observations in Windowed Timing (WT) mode will be needed to measure short term variability.
This work made use of data supplied by the UK Swift Science Data Centre at the University of Leicester.