We report for a larger collaboration that: we observed the galaxy SDSS J134856.75+263946.7 that lies at a distance of ~4.5" from the position of the fast X-ray transient XRT210423 (Lin et al., ATel #14599) with the VLT/X-shooter spectrograph on May 16, 2021. We obtained exposures of 2x735 sec in the UVB arm, 2x 680 sec in the VIS arm, and 4x300 sec in the NIR arm of the spectrograph, using slit widths of 1.3"/1.2"/1.2", respectively.
We confirm the detection of faint emission at a wavelength ~9355 AA reported by Andreoni et al. ATel #14641. Those authors associate this emission with the [OII] doublet obtaining a redshift of z=1.5105. In addition to the emission at 9355 AA, we detect the [OIII] line at 12563 AA (restframe wavelength 5007 AA) and Halpha at 16465 AA (restframe wavelength 6562 AA) in the NIR arm, confirming the redshift of z=1.5105.
At the evaluated redshift the 4.5" angular separation between the fast X-ray transient and the galaxy corresponds to an offset of approximately 39 kpc. The peak X-ray flux reported by Lin et al. ATel #14599 translates to a peak X-ray luminosity of 5.8E45 erg/s. Therefore, the galaxy SDSS J134856.75+263946.7 can be the host galaxy of the fast X-ray transient. In addition, the transient can potentially be an off-axis short GRB / binary neutron star merger. This matches well with the properties of XT2 (Xue et al. 2019, Nature, 568, 198).
| Catalog | Name | Reported RA | Reported DEC | Reported Obj-Type | Reported Redshift | Host Name | Host Redshift | Remarks | TNS RA | TNS DEC | TNS Obj-Type | TNS Redshift |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Other | XRT210423 | 13:48:56.460 | +26:39:44.30 |