TITLE: GCN CIRCULAR NUMBER: 31966 SUBJECT: GRB 220426A: Swift-XRT and UVOT observations DATE: 22/04/28 17:31:31 GMT FROM: Valerio D'Elia at ASDC V. D’Elia (ASI-SSDC & INAF-OAR) and M. H. Siegel (PSU) report on behalf of the Swift team: Swift has performed follow-up observations of the Fermi/GBM-detected burst GRB 220426A (GCN Circ. 31950, 31955), which was also detected by Swift/BAT-GUANO (GCN Circ. 31954), Konus-Wind (GCN Circ. 31959), INTEGRAL/SPI-ACS, and HEND/Mars-Odyssey (GCN Circ. 31958). The XRT observations consist of three tiles of 1 ks each, to cover the GRB error region. The data were acquired between 45 and 47 hours after the burst and are entirely in PC mode. One bright, uncatalogued X-ray source has been detected: Source 1: RA (J2000.0): 22h 32m 34.33s Dec (J2000.0): -22° 57′ 01.0″ Error: 3.7 arcsec (radius, 90% conf.) Count-rate: (1.4 +/- 0.5)e-2 ct s^-1 Distance: 3.2 arcmin from the IPN position Flux: (4.1 +/- 1.4)e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV) Nevertheless, we note that at the XRT position the RASS PSPC 3 sigma upper limit is 0.05 cts/s (XRT equivalent count-rate). The UVOT took images of 616s each on the three XRT tiles with the white filter 160-170 ks after the trigger. We identify one source at 1.9” from the XRT coordinates of Source 1, with a white magnitude of 18.01. The UVOT position is: RA (J2000) = 22:32:34.39 = 338.14330 (deg.) Dec (J2000) = -22:57:02.7 = 22.95074 (deg.) with an estimated uncertainty of 0.5 arc sec. (radius, 90% confidence). However, we note that this is a known source in the DSS and is therefore unlikely to be the afterglow. No other sources are detected to a limiting magnitude in the white filter of 20.8. More Swift observations are planned in the next days to assess for variability The results of the XRT-team automatic analysis of the XRT observations, including a position-specific upper limit calculator, are available at https://www.swift.ac.uk/xrt_products/TILED_GRB00104/. This circular is an official product of the Swift team.