Redshifts of Candidate Host Galaxies of Four Fast X-ray Transients Using VLT/MUSE

Fast X-ray transients (FXTs) are X-ray flares lasting minutes to hours. Multi-wavelength counterparts to these FXTs have been proven hard to find. As a result distance measurements are through indirect methods such as host galaxy identification. The three main models proposed for FXTs; supernova shock breakout emission (SN SBO), binary neutron star (BNS) mergers and tidal dirsuption events (TDEs) of an intermediate mass black hole (IMBH) disrupting a white dwarf (WD), have a different associated L_X, peak. Therefore obtaining the distance to FXTs will be a powerful probe to investigate the nature of these FXTs. We use VLT/MUSE observations of a sample of FXTs to report the redshift of between 13 and 22 galaxies per FXT and use these redshifts to calculate the distance, L_X, peak and the projected offsets. We find L_X, peak>10^44 erg s^-1 if we assume any of the sources with a redshift measurement is the true host galaxy of the corresponding FXT. For XRT 100831 we find a very faint galaxy within the 1σ uncertainty region with a chance alignment probability of 0.04. For XRT 060207 we find a candidate host galaxy at z = 0.939 with a low chance alignment probability. However, we also report the detection of a late-type star within the 3σ uncertainty region with a similar chance alignment probability. For the remaining FXTs we find no sources within their 3σ uncertainty regions. We rule out a SN SBO nature for all FXTs based on L_X, peak and the projected offsets. For XRT 100831 we conclude the detected galaxy within the 1σ uncertainty position is likely to be the host galaxy of this FXT. From the available information, we are not able to determine if XRT 060207 originated from the galaxy found within 1σ of the FXT position or was due to a flare from the late-type star detected within the 3σ uncertainty region.