NICER observed the new transient Swift J005139.2-721704 located in the Small Magellanic Cloud (SMC), and discovered on 2018 Nov. 9 (ATel #12209). The source position identified using Swift XRT as RA=00:51:39.2 and DEC=-72:17:03.6 (with an uncertainty of 1.4″, ATel #12209).
We obtained 8.6 ksec of NICER data between 2018 November 14 at 22:11:16 UTC and 2018 November 15 at 15:36:13 UTC. The average NICER count rate is 22.4 c/s (5.4 mCrab) in the 0.5-8 keV range (after background subtraction of ~0.5 c/s in that range).
The spectrum can be described by an absorbed blackbody+powerlaw model in 0.5-8.0 keV range, with chi2=1.2 (399 d.o.f.), and with best fit parameters NH = (0.56±0.04) ×1022cm-2, kT = 0.120±0.005 keV and a powerlaw photon index Gamma = 1.07±0.03 (all uncertainties are at the 90% confidence level). The flux in that energy range is 1.1×10-10erg s-1cm-2, which corresponds to a luminosity (corrected for absorption) of LX ~7×1037erg s-1, assuming a distance of 60 kpc to the SMC.
A timing analysis on these initial NICER exposures finds no sign of short period coherent pulsations. However, we find significant variability (~30% fractional amplitude) on a timescale of ~600-650 seconds. The current NICER snapshots are too short for a definitive conclusion on a periodicity on such timescale, and additional observations are needed to decipher the nature of this variability. We encourage follow-up observations with other facilities. The short-term schedule of additional NICER observations is as follows:
Start Time-----------------End Time-------------Exposure (in seconds)
2018-319T22:49:20 2018-319T23:20:20 1860
2018-320T06:32:20 2018-320T07:04:40 1940
2018-320T14:15:20 2018-320T14:48:40 2000
2018-320T15:48:00 2018-320T16:21:20 2000
2018-320T21:58:20 2018-320T22:32:20 2040
2018-320T23:31:00 2018-321T00:05:00 2040
2018-321T07:14:00 2018-321T07:49:00 2100
2018-321T08:46:40 2018-321T09:21:40 2100
2018-321T13:24:20 2018-321T14:00:00 2140
NICER is a 0.2-12 keV X-ray telescope operating on the International Space Station. The NICER mission and portions of the NICER science team activities are funded by NASA.
|Publication date||15 Nov 2018|
|Publication status||Published - 15 Nov 2018|
|Series||The Astronomer's telegram|
- Neutron Star