Follow-up observations of the X-ray transient in the nuclear region of NGC 7793 with Swift, NuSTAR and Chandra imply a ULX nature of the source
ATel #15737; Murray Brightman (Caltech)
on 2 Nov 2022; 19:54 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Murray Brightman (murray@srl.caltech.edu)
Subjects: X-ray, Black Hole, Neutron Star, Transient
Referred to by ATel #: 15744
We report on follow up observations of the transient X-ray source serendipitously detected by Swift/XRT on 2022-09-25 in the nuclear region of NGC 7793 reported in ATel #15632.
Continued Swift/XRT observations showed the source declining monotonically in count rate by a factor of ~3 in the ~30 days since detection.
NuSTAR observed the source on 2022-10-07 (obsID 90801526002) for 50 ks with a count rate of 5x10^-3 counts/s in the 3--10 keV band in each FPM. A joint spectral fit with the Swift/XRT data reveal a spectral turnover at 1.3^+0.5_-0.2 keV typical of an ultraluminous X-ray source.
Finally, Chandra observed the source on 2022-10-27 (obsID 27481) for 10 ks with a count rate of 2.6x10^-2 counts/s in the 0.5--8 keV band in ACIS-S. The improved position afforded by Chandra's spatial resolution is RA=359.45787 deg, Dec-32.591155 deg (=23:57:49.9, -32:35:28.2), with an uncertainty of 0.6 arcsec. These coordinates have a small but significant offset from the nucleus of NGC 7793 which confirms what NuSTAR suggested, that this is likely a new transient ultraluminous X-ray source.
We would like to thank Brad Cenko and the Swift team, Fiona Harrison and the NuSTAR SOC and Patrick Slane and the CXC for approving and carrying out these observations.
