LEIA detected a fast X-ray transient LXT 230815A on August 15, 2023. The source position is R.A. = 249.474 deg, DEC = -46.412 deg (J2000) with an uncertainty of
3 arcmin (radius, 90% C.L. statistical and systematic). The source was firstly detected by LEIA at 2023-08-15T11:08:53 with a flux of ~3.0e-11 erg/s/cm2 in 0.5-4.0 keV, and the flux dropped undetected in the next orbit one and half hour later. There is no known X-ray source within the error circle of the LEIA position.
We performed a target of opportunity observation with the Swift/XRT following the LEIA detection. The XRT observation started at 18:47:00 UT on August 16, 2023, with an exposure time of 559 s in Photon Counting mode. An X-ray source is detected within the position error circle of the LEIA source with a signal-to-noise (S/N) ratio of 3.8. The XRT ground-calculated position of this source is R.A. = 249.425 deg, Dec = -46.402 deg (J2000), with an uncertainty of 5.7 arcsec (radius, 90% C.L. statistical and systematic). Its estimated 0.5-4.0 keV flux is 3.9e-13 erg/s/cm2. The source is uncatalogued in the previous Swift Galactic Plane Survey (ATel #5200), which covered
this position. We tend to suggest that this XRT source is possibly associated with LXT 230815A. In this case, its flux dropped by two orders of magnitude in 31 hours when compared with that in the LEIA observation. We note that both the LEIA and XRT spectra, though with poor S/N, hint at a low absorption column density. An origin of stellar flare cannot be ruled out.
Follow-up observations are encouraged to identify this new transient.
We thank the Neil Gehrels Swift Observatory team for making the ToO observation possible.
The preliminary results have been posted at Astronomer's Telegram as ATel 16195. Click here for more EP/LEIA Astronomer's Telegrams.