A nuclear X-ray transient in NGC 7793 at 3.8 Mpc
ATel #15632; Murray Brightman (Caltech)
on 26 Sep 2022; 22:38 UT
Credential Certification: Murray Brightman (murray@srl.caltech.edu)
Subjects: X-ray, Request for Observations, AGN, Black Hole, Neutron Star, Transient, Tidal Disruption Event
We report on the detection of an X-ray transient serendipitously discovered in a Swift/XRT observation of NGC7793P13 (obsID 00031791173) on 2022-09-25. The source has a position of RA=359.45788, Dec=-32.59104 (=23 57 49.89, 32 35 27.8) with an error radius 3.0'' (90% confidence) and a 0.3--10 keV count rate of 0.052+/-0.008 cts/s. The source position is consistent with the nucleus of NGC 7793 at 3.8 Mpc.
The XRT spectrum is not well constrained, nevertheless it can be described by an absorbed power-law model with NH<3x10^21 cm^-2 and Gamma=1.5^+0.8_-0.4. The observed 0.3--10 keV flux is 2.2x10^-12 erg/cm^2/s, which corresponds to a luminosity of 3.8x10^39 erg/s assuming a distance of 3.8 Mpc to NGC 7793. Previous to this detection, NGC 7793 was observed with Swift on 2022-09-11 when the source was not detected, however a Chandra source with a flux 3 orders of magnitude lower than seen has been reported at the position of the Swift/XRT source. While this appears to be a nuclear transient, the luminosity does not preclude a transient ULX. Further observations with other X-ray observatories are encouraged to determine the nature of this source.
