Swift/XRT observations of GRB 221017A

ATel #15702; Amar Deo Chandra (IISER Kolkata)
on 20 Oct 2022; 08:53 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Amar Deo Chandra (amar.deo.chandra@gmail.com)

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The MAXI/GSC nova alert system triggered on a bright uncatalogued X-ray transient source at 2022-10-17T05:39:31 UT (GCN #32777). The inferred location of the transient from MAXI/GSC observations was RA/Dec(J2000) = (116.859, 39.409) = (07:47:26, +39:24:32) with a statistical 90% C.L. elliptical error region with long and short radii of 0.45 deg and 0.4 deg, respectively (GCN #32777). The averaged X-ray flux obtained from MAXI/GSC observations was 109 +- 30 mCrab (1-sigma error) in the 4.0-10.0 keV energy band (GCN #32777). Global MASTER-Net follow-up optical observations from the MASTER-OAFA robotic telescope set an upper limit of up to 17.2 mag on the transient source (GCN #32779). MAXI GRB221017 was also detected by INTEGRAL (SPI-ACS), Konus-Wind, and Mars-Odyssey (HEND) observations (GCN #32787). The location of the source was triangulated using INTEGRAL (SPI-ACS), Konus-Wind, and Mars-Odyssey (HEND) observations to obtain a preliminary 3-sigma error box which reduced the area of the MAXI/GSC error box (GCN #32787).

Swift/XRT observations of GRB 221017A were performed in Photon Counting (PC) mode (ObsID: 00021529002) between 2022-10-19 12:19:02 UT and 2022-10-19 20:23:59 UT, for a net exposure time of about 1.9 ks. Swift/XRT follow-up observations of GRB 221017A could not be scheduled earlier owing to Swift Moon observing constraint until 2022-10-19 morning hours. Two uncatalogued X-ray sources 6.8' and 8.0' away from the MAXI position have been detected in preliminary analysis of Swift/XRT observations at the following locations:

Source 1
RA (J2000.0): 116.8816 = 07:47:31.58
Dec (J2000.0): 39.3449 = +39:20:41.5
Error: 10.7" (radius, 90% confidence)
Avg. XRT count-rate: 5.4(+2.6,-2.0)x10^(-3) cts/s
Distance: 6.8' from the MAXI position

Source 2
RA (J2000.0): 116.9220 = 07:47:41.27
Dec (J2000.0): 39.2614 = +39:15:41.2
Error: 10.0" (radius, 90% confidence)
Avg. XRT count-rate: 3.3(+2.1,-1.5)x10^(-3) cts/s
Distance: 8.0' from the MAXI position

The uncatalogued X-ray sources lie within the MAXI/GSC localization error box (GCN #32777) and towards the periphery of the IPN triangulation map (GCN #32787). The inferred locations of the uncatalogued X-ray sources superposed on the MAXI/GSC error box and IPN triangulation map are available at the link. However, confirmation is required whether any of these uncatalogued X-ray sources are related to GRB 221017A.

We thank the Swift Team and Observatory Duty Scientists who made these observations possible.