AstroNote 2022-237

We report follow-up observations of the Fast Blue Optical Transient (FBOT) AT2022tsd with the Chandra X-ray Observatory (CXO). We acquired a third epoch of CXO observations of AT2022tsd on November 4th 2022 (~58 days since discovery, observer frame) with the ACIS-S instrument for a total exposure of 18.8 ks (OBS ID: 26643, Proposal 24500280 PI: D. Matthews). At the redshift of AT2022tsd (z=0.256, Schulze+ AstroNote #2022-199) this corresponds to ~46 days rest frame. The results from our first and second epochs of monitoring were reported in Matthews+ (AstroNotes #2022-218 and #2022-229). 

We detect significant X-ray emission from the location of AT2022tsd, and infer an absorbed flux of 1.2e-13 (3 sigma confidence between 8.5e-14 and 1.7e-12) erg/s/cm^2 (0.3-10 keV) for a power law spectral model with a photon index of 1.68 (3 sigma confidence between 1.35 and 2.01). The Galactic neutral hydrogen column density along the line of sight to the transient is 1.08E+21 cm^-2 (Kalberla+ 2005). At a distance of d~1.3 Gpc this corresponds to a luminosity of 2.4e+43 erg/s (0.3-10 keV, corrected for Galactic absorption only, 3 sigma confidence between 1.7e+43 and 3.4e+43 erg/s). Our previous CXO epoch at ~40 days rest-frame indicated Lx = 6.9e+43 erg/s (3 sigma confidence between 5.5e+43 and 9.1e+43 erg/s). We conclude that the X-ray emission from AT2022tsd is time variable, thus supporting the association of this X-ray emission with the transient.

Further observations are planned.

We thank the entire CXO team for carrying out these observations.