MAXI J1421-613: Swift XRT localization and confirmation of the new X-ray transient
ATel #5751; J. A. Kennea (PSU), H. A. Krimm (CRESST/GSFC/USRA), P. A. Evans (U Leicester), P. Romano (INAF-IASF PA), V. Mangano (PSU), P. Curran (Curtin), K. Yamaoka (Nagoya U) and H. Negoro (Nihon U.)
on 10 Jan 2014; 04:07 UT
Credential Certification: Jamie A. Kennea (kennea@astro.psu.edu)
Subjects: X-ray, Transient
At 19:35 UT on January 9th, 2014, Swift began a target-of-opportunity observation of MAXI J1421-613, a newly discovered soft X-ray transient (Morooka et al, ATEL #5750). In order to cover the MAXI error ellipse, we observed using a 7-point tiling configuration, with 500s exposure per tile. We detect a previously uncatalogued X-ray point source in a region covered by two of the pointings, at the following UVOT enhanced location: RA/Dec(J2000) = 215.40838, -61.60693, which is equivalent to:
RA(J2000) = 14h 21m 38.01s,
Dec(J2000) = -61d 36' 24.9'',
with an estimated uncertainty of 2.2 arc-seconds radius (90% confidence). This source lies 15.7 arc-minutes from the center of the MAXI error ellipse, and is therefore consistent with being MAXI J1421-613. In optical/IR catalogs the only object consistent with the XRT location is G313.4386-00.5893 in the GLIMPSE catalog, which lies 2.1 arc-seconds from the center of the error circle.
The XRT spectrum of MAXI J1421-613 is relatively soft, and well fit by a power-law with photon index = 2.7 +/- 0.4, and N_H = 5 +/- 1 x 1022 cm-2. The observed flux is 1.2 x 10-9 erg/s/cm2 (0.5-10 keV), although we note that the source is bright (~15 XRT count s-1) and therefore piled up in Photon Counting mode. Windowed Timing mode data will be requested to better characterize the X-ray spectrum. During the short observation, the source appears to be at a constant brightness.
The BAT Transient Monitor (Krimm et al., 2013, ApJS, 209, 14) does not detect MAXI J1421-613, likely due to the soft spectrum. A UVOT observation obtained with the u filter did not yield a detection of any new point source at the location of the X-ray transient, although we note that there is likely high extinction, making optical detection unlikely.
This work is supported by the Swift Guest Investigator Program.