GRB 251023B: Swift observation summary

This is a confirmed GRB (GRB 251023B), the afterglow is source 1 -- please see the GRB results at https://www.swift.ac.uk/xrt_products/03000150 for updated analysis

Mission:	Einstein Probe/WXT
Einstein Probe RA:	73.496°
Einstein Probe Dec:	+12.661°
Einstein Probe Err:	3.1 arcmin
T0:	2025-10-23 08:48:47 UT
Galactic:	187.01° -19.02°
Galactic N_H:	1.45× 10²¹ cm^-2

Sun distance:	135.31°
Sun angle:	8.95 [hr](West of Sun)
Moon distance:	152.38°
Visibility of this field.

Data analysed so far:

ObsID: 03000150001 with 1.8 ks exposure.

About tiled field analysis.

So far 1 fields have been scheduled for observations. Data are available and processed for 1 of these.

3000150 — 1.8 ks of cleaned data taken between 2025-10-23 10:38:49 and 2025-10-23 15:30:45

Details of afterglow candidates

1 sources were found which matches the afterglow criteria.

#	RA (J2000)	Dec (J2000)	Err₉₀¹	Detection Flag²	Rank³	Dist from Einstein Probe/WXT pos	Exposure	Notes	Vizier
1 [details]	04h 54m 00.52s73.50216°	+12° 39′ 28.9″12.65803°	2.8′′ ^*	Good	1 (T)	0.4′	1.8 ks	The source is fading with 3.4-σ significance. The source is 3.9-σ above the RASS limit.
Mean XRT rate: 0.138 (±0.010) ct s^-1 Peak XRT rate: 0.22 (±0.05) ct s^-1 RASS PSPC 3-σ upper limit: 0.03 ct s^-1 (PSPC count-rate) Mean XRT rate converted to PSPC: 0.160 (±0.012) ct s^-1 Peak XRT rate converted to PSPC: 0.26 (±0.06) ct s^-1 Mean XRT flux: 5.4 (±0.4) ×10^-12 erg cm^-1s^-1 Peak XRT flux: 8.6 (±1.9) ×10^-12 erg cm^-1s^-1 Products: Light curve \| Spectrum \| Enhanced position

¹ Radius, 90% confidence.
² Indicates how likely the source is to be real. See the LSXPS documentation.
³ T=Transient Source, O=Outbursting known source, U=Uncatalogued X-ray source, K=Known X-ray source.
^* The position was enhanced using astrometry derived from the Swift UVOT.
^† The position was astrometrically corrected using the XRT sources and the 2MASS catalogue.

Find an upper limit.

Sources found so far

So far 2 sources have been found in the XRT data. 1 sources match catalogued sources.

#	RA (J2000)	Dec (J2000)	Err₉₀¹	Detection Flag²	Rank³	Dist from Einstein Probe/WXT pos	Exposure	Notes
1 [details]	04h 54m 00.52s73.50216°	+12° 39′ 28.9″12.65803°	2.8′′ ^*	Good	1 (T)	0.4′	1.8 ks	The source is fading with 3.4-σ significance. The source is 3.9-σ above the RASS limit.
Mean XRT rate: 0.138 (±0.010) ct s^-1 Peak XRT rate: 0.22 (±0.05) ct s^-1 RASS PSPC 3-σ upper limit: 0.03 ct s^-1 (PSPC count-rate) Mean XRT rate converted to PSPC: 0.160 (±0.012) ct s^-1 Peak XRT rate converted to PSPC: 0.26 (±0.06) ct s^-1 Mean XRT flux: 5.4 (±0.4) ×10^-12 erg cm^-1s^-1 Peak XRT flux: 8.6 (±1.9) ×10^-12 erg cm^-1s^-1 Products: Light curve \| Spectrum \| Enhanced position
2 [details]	04h 54m 10.51s73.54378°	+12° 46′ 16.5″12.77124°	5.4′′	Good	3 (U)	7.2′	1.8 ks	Matches SIMBAD source: UCAC4 514-009025, 2.6″ away.
Mean XRT rate: 6.5 (+2.8, -2.2) ×10^-3 ct s^-1 Peak XRT rate: 6.5 (+2.8, -2.2) ×10^-3 ct s^-1 RASS PSPC 3-σ upper limit: 0.03 ct s^-1 (PSPC count-rate) Mean XRT rate converted to PSPC: 0.012 (+0.005, -0.004) ×10^-2 ct s^-1 Peak XRT rate converted to PSPC: 0.012 (+0.005, -0.004) ×10^-2 ct s^-1 Mean XRT flux: 1.3 (+0.6, -0.4) ×10^-13 erg cm^-1s^-1 Peak XRT flux: 1.3 (+0.6, -0.4) ×10^-13 erg cm^-1s^-1 Products: Light curve \| Spectrum

Image

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Exposure map

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FITS exposure map.