MAXI J1543-564: Swift/XRT localization

ATel #3331; 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 9 May 2011; 04:03 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Jamie A. Kennea (kennea@astro.psu.edu)

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At 18:19 UT on May 8th, 2011, Swift began a 1 ks long target of opportunity observation of the error circle of MAXI J1543-564 (Negoro et al., ATEL #3330), a newly found X-ray transient near the galactic plane discovered by MAXI. Utilizing 1 ks of Photon Counting mode data, and correcting for the astrometric errors utilizing Swift/UVOT data using the method described by Evans et al. (2009, MNRAS, 2009, 397, 1177) and Goad et al. (2008, A&A, 476, 1401), we find a bright, uncatalogued X-ray source at the following location, RA/Dec (J2000) = 235.82283, -56.41358, which is equivalent to:

RA(J2000) = 15^h 43^m 17.48^s
Dec(J2000) = -56^o 24' 48.9''

with an estimated uncertainty of 1.8 arc-seconds radius (90% containment). This position lies inside the reported MAXI error circle, 1.2 arc-minutes from the center of the MAXI error circle (Negoro et al., ATEL #3330). This position does not match any catalogued X-ray source. The closest catalogued object to MAXI J1543-564 is 2MASS 15431782-5624467, which has a magnitude of J=15.3, and although this lies outside of the 90% confidence XRT error circle, 3.5 arc-seconds from the Swift/XRT position.

The spectrum of the source can be well described by an absorbed power-law fit, with a measured photon index of 1.45 +/- 0.20, and absorption of N_H = 0.9 x 10²² cm^-2, compared to the expected Galactic absorption in that direction of ~1.5 x 10²² cm^-2. The measured flux is 4.4 +/- 0.5 x 10^-10 erg/s/cm² (0.3-10 keV), or ~6.3 x 10^-10 erg/s/cm² (0.3-10 keV) corrected for absorption. During the 1ks observation the source flux remains consistent with a constant value.