sb25101602
GCN Circular 42311
Subject
sb25101602: Swift-XRT counterpart detection
Date
2025-10-16T20:00:35Z (4 days ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
P.A. Evans (U. Leicester), J.A. Kennea (PSU), E. Ambrosi (INAF-IASFPA) , A.P.
Beardmore (U. Leicester), M.G. Bernardini (INAF-OAB), R. Brivio (INAF-OAB), D.N.
Burrows (PSU), S. Campana (INAF-OAB), M. Capalbi (INAF-OAR), A. D'Ai (INAF-IASFPA),
P. D'Avanzo (INAF-OAB), V. D'Elia (SSDC & INAF-OAR), S. Dichiara (PSU), M. Ferro
(INAF-OAB), A. Melandri (INAF-OAR), J.P. Osborne (U. Leicester), K.L. Page (U.
Leicester), M. Perri (SSDC & INAF-OAR), C. Salvaggio (INAF-OAB), T. Sbarrato
(INAF-OAB), B. Sbarufatti (INAF-OAB), M.A. Williams (PSU) report on behalf of the
Swift-XRT team:
Swift-XRT has performed follow-up observations of the SVOM/ECLAIRs-detected
GRB251016A (sb25101602), collecting 749 s of Photon Counting (PC) mode data between
T0+6.6 ks and T0+7.4 ks after the trigger. A likely counterpart has been found. The
details of this source are:
Source 1 (SWIFT J174512.5-393337):
==================================
RA (J2000.0): 266.3024 = 17 45 12.58
Dec (J2000.0): -39.5606 = -39 33 38.2
Error: 4.6 (arcsec, radius, 90% confidence).
Detect flag: GOOD
Distance: 4.5 arcmin from the SVOM/ECLAIRs position.
Mean rate: 0.057 +/- 0.011 ct s^-1
Mean flux: (3.41 +/- 0.64)e-12 erg cm^-2 s^-1
Peak rate: 0.072 +/- 0.019 ct s^-1
Peak flux: (4.4 +/- 1.1)e-12 erg cm^-2 s^-1
ECF: 6.02e-11 erg cm^-2 ct^-1
assuming NH=7.85e+21 cm^-2, gamma=1.55
determined from a spectral fit.
XMM UL: 6.5e-13 erg cm^-2 s^-1, (0.3-10 keV)
so the source is 3.2-sigma above this 3-sigma upper limit.
The source may be fading, at the 1.1-sigma level.
There are 2 2MASS objects within the source's 3-sigma error radius.
We have detected a total of 9 sources. These have been automatically classified as
follows:
* 1 likely counterpart
* 0 candidate counterparts
* 8 uncatalogued X-ray sources
* 0 known X-ray sources
Uncatalogued X-ray sources
--------------------------
Source 2 (SWIFT J174439.5-394550):
==================================
RA (J2000.0): 266.1646 = 17 44 39.50
Dec (J2000.0): -39.7642 = -39 45 51.1
Error: 6.1 (arcsec, radius, 90% confidence).
Detect flag: POOR
Distance: 11.4 arcmin from the SVOM/ECLAIRs position.
Mean rate: 0.0300 [+0.0096, -0.0079] ct s^-1
Mean flux: (1.29 [+0.41, -0.34])e-12 erg cm^-2 s^-1
Peak rate: 0.0300 [+0.0096, -0.0079] ct s^-1
Peak flux: (1.29 [+0.41, -0.34])e-12 erg cm^-2 s^-1
XMM UL: 7.9e-13 erg cm^-2 s^-1, (0.3-10 keV)
so the source is not above this 3-sigma upper limit.
There is no evidence for fading.
There are 5 2MASS objects within the source's 3-sigma error radius.
Source 3 (SWIFT J174431.8-393913):
==================================
RA (J2000.0): 266.1326 = 17 44 31.82
Dec (J2000.0): -39.6537 = -39 39 13.3
Error: 5.9 (arcsec, radius, 90% confidence).
Detect flag: POOR
Distance: 5.7 arcmin from the SVOM/ECLAIRs position.
Mean rate: (-1.0 +/- -1.0)e0 ct s^-1
Mean flux: (-4.3 +/- -4.3)e-11 erg cm^-2 s^-1
Peak rate: 0.0123 [+0.0069, -0.0053] ct s^-1
Peak flux: (5.3 [+2.9, -2.3])e-13 erg cm^-2 s^-1
XMM UL: 1.3e-12 erg cm^-2 s^-1, (0.3-10 keV)
so the source is not above this 3-sigma upper limit.
There is no evidence for fading.
There are 5 2MASS objects within the source's 3-sigma error radius.
Source 4 (SWIFT J174456.1-392739):
==================================
RA (J2000.0): 266.2340 = 17 44 56.16
Dec (J2000.0): -39.4609 = -39 27 39.2
Error: 14.0 (arcsec, radius, 90% confidence).
Detect flag: POOR
Distance: 7.1 arcmin from the SVOM/ECLAIRs position.
Mean rate: (-1.0 +/- -1.0)e0 ct s^-1
Mean flux: (-3.5 +/- -3.5)e-9 erg cm^-2 s^-1
Peak rate: (6.3 [+5.6, -4.0])e-3 ct s^-1
Peak flux: (2.2 [+1.9, -1.4])e-11 erg cm^-2 s^-1
ECF: 3.48e-09 erg cm^-2 ct^-1
assuming NH=3.52e+22 cm^-2, gamma=5.05
determined from a spectral fit.
XMM UL: 1.0e-12 erg cm^-2 s^-1, (0.3-10 keV)
so the source is 1.3-sigma above this 3-sigma upper limit.
There is no evidence for fading.
There are 34 2MASS objects within the source's 3-sigma error radius.
Source 5 (SWIFT J174354.6-392827):
==================================
RA (J2000.0): 265.9777 = 17 43 54.65
Dec (J2000.0): -39.4743 = -39 28 27.5
Error: 9.8 (arcsec, radius, 90% confidence).
Detect flag: POOR
Distance: 12.2 arcmin from the SVOM/ECLAIRs position.
Mean rate: 0.0128 [+0.0066, -0.0050] ct s^-1
Mean flux: (5.5 [+2.8, -2.1])e-13 erg cm^-2 s^-1
Peak rate: 0.0128 [+0.0066, -0.0050] ct s^-1
Peak flux: (5.5 [+2.8, -2.1])e-13 erg cm^-2 s^-1
XMM UL: 7.2e-13 erg cm^-2 s^-1, (0.3-10 keV)
so the source is not above this 3-sigma upper limit.
There is no evidence for fading.
There are 22 2MASS objects within the source's 3-sigma error radius.
Source 6 (SWIFT J174500.5-394402):
==================================
RA (J2000.0): 266.2523 = 17 45 00.55
Dec (J2000.0): -39.7341 = -39 44 02.8
Error: 11.1 (arcsec, radius, 90% confidence).
Detect flag: POOR
Distance: 9.7 arcmin from the SVOM/ECLAIRs position.
Mean rate: 0.0156 [+0.0070, -0.0055] ct s^-1
Mean flux: (6.7 [+3.0, -2.4])e-13 erg cm^-2 s^-1
Peak rate: 0.0156 [+0.0070, -0.0055] ct s^-1
Peak flux: (6.7 [+3.0, -2.4])e-13 erg cm^-2 s^-1
XMM UL: 1.3e-12 erg cm^-2 s^-1, (0.3-10 keV)
so the source is not above this 3-sigma upper limit.
There is no evidence for fading.
There are 18 2MASS objects within the source's 3-sigma error radius.
Source 7 (SWIFT J174411.2-392428):
==================================
RA (J2000.0): 266.0470 = 17 44 11.28
Dec (J2000.0): -39.4079 = -39 24 28.4
Error: 13.9 (arcsec, radius, 90% confidence).
Detect flag: POOR
Distance: 12.5 arcmin from the SVOM/ECLAIRs position.
Mean rate: 0.0167 [+0.0073, -0.0057] ct s^-1
Mean flux: (7.2 [+3.2, -2.4])e-13 erg cm^-2 s^-1
Peak rate: 0.0167 [+0.0073, -0.0057] ct s^-1
Peak flux: (7.2 [+3.2, -2.4])e-13 erg cm^-2 s^-1
XMM UL: 1.1e-12 erg cm^-2 s^-1, (0.3-10 keV)
so the source is not above this 3-sigma upper limit.
There is no evidence for fading.
A SIMBAD object `OGLE BLG-DSCT-13120' is 43.9" away.
There are 33 2MASS objects within the source's 3-sigma error radius.
Source 8 (SWIFT J174427.1-393500):
==================================
RA (J2000.0): 266.1131 = 17 44 27.14
Dec (J2000.0): -39.5835 = -39 35 00.6
Error: 11.9 (arcsec, radius, 90% confidence).
Detect flag: POOR
Distance: 4.3 arcmin from the SVOM/ECLAIRs position.
Mean rate: (-1.0 +/- -1.0)e0 ct s^-1
Mean flux: (-4.3 +/- -4.3)e-11 erg cm^-2 s^-1
Peak rate: (8.7 [+6.1, -4.5])e-3 ct s^-1
Peak flux: (3.7 [+2.6, -1.9])e-13 erg cm^-2 s^-1
XMM UL: 6.6e-13 erg cm^-2 s^-1, (0.3-10 keV)
so the source is not above this 3-sigma upper limit.
There is no evidence for fading.
There are 28 2MASS objects within the source's 3-sigma error radius.
Source 9 (SWIFT J174502.9-392734):
==================================
RA (J2000.0): 266.2622 = 17 45 02.93
Dec (J2000.0): -39.4596 = -39 27 34.6
Error: 8.8 (arcsec, radius, 90% confidence).
Detect flag: POOR
Distance: 7.5 arcmin from the SVOM/ECLAIRs position.
Mean rate: (-1.0 +/- -1.0)e0 ct s^-1
Mean flux: (-4.3 +/- -4.3)e-11 erg cm^-2 s^-1
Peak rate: (8.9 [+6.4, -4.7])e-3 ct s^-1
Peak flux: (3.8 [+2.7, -2.0])e-13 erg cm^-2 s^-1
XMM UL: 7.1e-13 erg cm^-2 s^-1, (0.3-10 keV)
so the source is not above this 3-sigma upper limit.
There is no evidence for fading.
There are 11 2MASS objects within the source's 3-sigma error radius.
All fluxes are 0.3-10 keV, observed. For all flux conversions and comparisons with
catalogues and upper limits from other missions, we assumed a power-law spectrum
with NH=3x10^20 cm^-2 and photon index (Gamma)=1.7 unless otherwise stated.
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/SVOM/SVOM_FIELD00042.
This circular is an official product of the Swift-XRT team.