MAXI J1647-227: Swift/XRT localization of the new X-ray transient

ATel #4178; J. A. Kennea (PSU), P. A. Evans (U Leicester), H. A. Krimm (CRESST/GSFC/USRA), P. Romano, V. Mangano (INAF-IASFPA), P. Curran (CEA-Saclay), K. Yamaoka (AGU) and H. Negoro (Nihon U.)
on 16 Jun 2012; 01:09 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Jamie A. Kennea (kennea@astro.psu.edu)

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At 20:20 UT on June 15, 2012 Swift took a 2 ks target of opportunity observation of the error circle of MAXI J1647-227 (Negoro et al., ATEL #4175). We utilized a 4-point tiling observation (500s exposure per tile) with XRT in Photon Counting (PC) mode, in order to completely image the MAXI error circle. In one of those tiles, Swift/XRT detected a bright previously uncatalogued X-ray source at the following location: RA/Dec(J2000) = 252.05134, -23.01534, which is equivalent to:

RA(J2000) = 16h 48m 12.32s
Dec(J2000) = -23d 00’ 55.2’’

with an estimated uncertainty of 2.4 arc-seconds radius (90% confidence). This position lies 17 arc-minutes from the center of the MAXI error circle reported in ATEL #4175, well within the MAXI error circle and therefore consistent with the XRT detected point source being MAXI J1647-227.

The source is bright and piled up with an estimated count rate of ~20 XRT count/s (corrected for pile-up). The PC mode spectrum, after pile-up correction, can be fitted by an absorbed power-law model, with the following parameters: N_H = 4.3 +/ 1.5 x 10²¹ cm^-2, photon index = 1.5 +/- 0.3. The 0.3-10 keV flux is 1.1 +/- 0.2 x 10^-9 erg/s/cm², uncorrected for absorption.

Analysis of these data was performed utilizing the methods described by Evans et al. (2009, MNRAS, 397, 1177) and Evans et al. (2007, A&A, 469, 379). This work made use of data supplied by the UK Swift Science Data Centre at the University of Leicester.