GCN Circular 31966
Subject
GRB 220426A: Swift-XRT and UVOT observations
Event
Date
2022-04-28T17:31:31Z (4 years ago)
From
Valerio D'Elia at ASDC <valerio.delia@ssdc.asi.it>
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/<https://eur02.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.swift.ac.uk%2Fxrt_products%2FTILED_GRB00104%2F&data=05%7C01%7Cvalerio.delia%40ssdc.asi.it%7Cbbf1b046abbf47f102b008da29348927%7Ccbfc58d4e60f468d8fe490676de085f7%7C0%7C0%7C637867602862749464%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=rivAVi0hBq7OV9vDQ4K1Xb1mbfcuxK9etLjffE3p1UI%3D&reserved=0>.
This circular is an official product of the Swift team.