Chandra detection of a fast X-ray transient
ATel #14599; Dacheng Lin (Northeastern University), Jimmy A. Irwin (University of Alabama), Edo Berger (CfA)
on 4 May 2021; 19:55 UT
Credential Certification: Dacheng Lin (dacheng.lin@gmail.com)
Subjects: Radio, Millimeter, Infra-Red, Optical, X-ray, Gamma Ray, Request for Observations, Gamma-Ray Burst, Gravitational Waves, Neutron Star, Transient, Magnetar
We report Chandra serendipitous detection of a fast X-ray transient (FXT) in a calibration observation of Abell 1795 on 2021 April 23 (therefore the FXT can be named as XRT 210423). The source position is RA=13:48:56.46, Decl.=+26:39:44.3, with a 95% positional uncertainty of 1.0 arcsec. After a fast rise (within a few tens of seconds), it maintained at a plateau lasting 4.1 ks at a flux of 4e-13 erg/s/cm^2, followed by a steep decay of t^(-3.6). The FXT was not detected in previous Chandra observations around the field (totaling 2.2 Ms), with a 3\sigma$ upper limit on the long-term persistent flux of 9e-16 erg/s/cm^2. No known GRB was associated with this FXT (K. Hurley. D. Svinkin, A. Ridnaia, D. Frederiks, private communication). The closest nearby galaxy is 4 arcsec away based on the CFHT optical and UKIDSS IR images.
The properties of this FXT are thus very similar to those of CDF-S XT2, which was recently argued to be powered by a newborn magnetar in a binary neutron star merger (Xue et al. 2019, Nature, 568, 198). If it is the case, its kilonova might be still detectable in IR for at least another week.
We encourage multiwavelength follow-up (from radio to X-ray) of this special FXT to search for the kilonova, afterglow from an off-axis jet, and the host galaxy.
