Further Swift observations of the TDE candidate Swift J023017.0+283603
ATel #15461; P. A. Evans (U. Leicester), A. A. Breeveld (MSSL/UCL), S. R. Oates (U. Birmingham)
on 23 Jun 2022; 16:43 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Phil Evans (pae9@star.le.ac.uk)
Subjects: Ultra-Violet, X-ray, Transient, Tidal Disruption Event
Swift-XRT has reobserved the candidate Tidal Disruption Event Swift J023017.0+283603 (ATEL #15454) for 4 ks on 2022 June 22, between 16:07 UT and 19:25 UT. Using these new data we derive an enhanced position (using UVOT data to correct the astrometry) of RA,Dec = 37.57140, 28.60124 degrees, which is equivalent to
RA (J2000) = 02h 30m 17.14s
Dec(J2000) = +28d 36m 04.5s
with an uncertainty of 2.7" (radius, 90% confidence). This is 0.25" away from 2MASX J02301709+2836050, which has a photometric redshift of 0.03997 (NED / 2MPZ catalogue: Bilicki et al., 2014, ApJS, 210, 9).
We have fitted the X-ray spectrum with a diskbb model in xspec, with a Galactic absorber with NH = 1.12 x 10^21 cm^-2 (Willingale et al., 2013) and a second absorber at z=0.03997. The best-fitting inner disk temperature is 121 (+13,-25) eV, with an intrinsic column density of <1.1 x 10^21 cm^-2. The 0.3-10 keV fitted flux is (7.5 +/- 1.2) x 10^-13 erg cm^-2 s. Assuming a redshift of 0.03997 = 174 Mpc, this corresponds to L = (2.8 +/- 0.4) x 10^42 erg s^-1. These parameters are consistent with expected TDE properties.
The two observations taken so far are too close in time to assess variability, although future observations are scheduled. Swift has observed this location 11 times prior to the transient detection; the most recent of these observations occurred on 2022 January 08, and showed no X-rays near the source location in 900 s of exposure, thus we can constrain the outburst start time to between January 8th and June 22nd (of 2022).
Unfortunately, in about half of the previous observations, the location of Swift J023017.0+283603 was outside the UVOT field of view, with the most recent UVOT observation covering the source being on 2021 December 24. The host galaxy is clearly visible in all UVOT filters, but shows no evidence for an increase in brightness since 2021 December 24 and 2022 June 22.
