A new X-ray transient in SDSS J143359.16+400636.0

ATel #13464; Murray Brightman (Caltech)
on 10 Feb 2020; 22:57 UT
Credential Certification: Murray Brightman (murray@srl.caltech.edu)

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We report a new X-ray source detected in the Swift/XRT observation of PTF13ast. The position of the source is at RA=218.4957 deg, Dec=40.1093 deg (=14:33:58.96, +40:06:33.5), with an error radius of 3.5" (90% confidence). The source was first detected in obsID 00032818012 on 2020-02-05 and continues to be detected at similar count rates in daily observations since then. Previous observations of the source in 2013 and 2016 with Swift/XRT did not show the source, and the upper limits on the count rate are two orders of magnitude below that currently observed. The position of the source is ~6' from PTF13ast and therefore not related. The galaxy SDSS J143359.16+400636.0 is within the error radius of the source, which has a photometric redshift of 0.109+/-0.036 from SDSS. The 0.3--10 keV flux as measured by XRT is 5x10^-12 erg cm^-2 s^-1, which corresponds to a luminosity of 2x10^44 erg s^-1 at z=0.1. This quasar-like luminosity suggests a supermassive black hole origin of the transient, but the lack of a transient in the optical or UV as seen by Swift/UVOT does not support this. The X-ray spectrum of the source as measured by XRT is consistent with a power-law with Gamma=2.7+/-0.4 with no evidence of absorption. The relatively constant flux of the source since it was first detected argue against a flare from a foreground star. We therefore encourage followup observations at all wavelengths to determine the nature of this source.