AstroNote 2022-229

We report follow-up observations of the Fast Blue Optical Transient (FBOT) AT2022tsd with the Chandra X-ray Observatory (CXO). We acquired a second epoch of CXO observations of AT2022tsd on October 27th 2022 (~50 days since discovery, observer frame) with the ACIS-S instrument for a total exposure of 19.8 ks (OBS ID: 26641, Proposal 24500280 PI: D. Matthews). At the redshift of AT2022tsd (z=0.256) this corresponds to ~40 days rest frame. The results from our first epoch of monitoring were reported in Matthews+ (AstroNote #2022-218). 

We detect significant X-ray emission from the location of AT2022tsd, and infer an absorbed flux of 3.4e-13 (3 sigma confidence between 2.7e-13 and 4.5e-13) erg/s/cm^2 (0.3-10 keV) for a power law spectral model with a photon index of 1.95 (3 sigma confidence between 1.44 and 2.47).  The Galactic neutral hydrogen column density along the line of sight to the transient is 1.08E+21 cm^-2 (Kalberla+ 2005). At a redshift of z=0.256 (d~1.3 Gpc, Schulze+ AstroNote #2022-199) this corresponds to a luminosity of 6.9e+43 erg/s (0.3-10 keV, corrected for Galactic absorption only, 3 sigma confidence between 5.5e+43 and 9.1e+43 erg/s). Our first CXO epoch at 32 days rest-frame indicated Lx = 4.75e+43 erg/s (3 sigma confidence between 3.6e+43 and 6.1e+43 erg/s). We thus find no evidence for fading of the X-ray emission in this time interval at the 3 sigma confidence level. At this epoch AT2020tsd is the most luminous X-ray counterpart to an FBOT to date.

Further observations are planned.

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