Swift XRT and UVOT Upper Limits of FRB 20250316A
ATel #17101; Y. J. Yang, A. Aryan, T.-W. Chen (NCU), A. K. H. Kong (NTHU), T. Hashimoto (NCHU), R. Jin (NTTU)
on 22 Mar 2025; 16:32 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Amar Aryan (amararyan941@gmail.com)
Subjects: Optical, X-ray, Fast Radio Burst
We report a pointed Swift observation (requested by Tohuvavohu) of the field of FRB 20250316A (ATel #17081, #17082, #17084, #17086, #17090, #17091, #17095, #17100). The observation was conducted on 2025-03-16 at 21:10:00 UTC, 12.6 hours after the first detection (Ng et al., ATel #17081), with a total exposure time of approximately 5 ks.
No significant X-ray source was detected by XRT within the refined CHIME-KKO localization region (Leung et al., ATel #17086). Using the method described by Kraft et al. (1991), we estimated a 90% confidence level (CL) upper limit for the count rate at 0.00046073 c/s. Assuming a photon index of 2 and NH = 1.43E+20 cm^-2 along the line of sight to the position (at z=0.0067; Connor, ATel #17091), WebPIMMS predicts an unabsorbed flux of 1.300E-14 ergs cm^-2 s^-1 in the 0.5 - 10 keV band, which is consistent with the flux level of EP J120944.2+585060 (Sun et al., ATel #17100).
No uncataloged optical counterpart consistent with the CHIME-KKO location was detected in the UVOT observation, with a total exposure of 154.29 seconds using the WHITE filter. A 3-sigma upper limit magnitude of >22.13 (AB system) was obtained.
We thank the Swift team for scheduling the observation.
