Gamma-ray Burst 251016A

(All information courtesy of the instrument teams.)

Previous IAU Circulars

none

Results of Observations

GCN Circular #42308
S. Basa, S. Boissier (LAM), O. Godet, S. Guillot (IRAP), D. Turpin (CEA)
At 2025-10-16T14:59:20 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 251016A (SVOM burst-id sb25101602).
The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network.
The burst was only detected by the Count-Rate Trigger (CRT), which produced a sequence of 5 alerts. CRT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 8.16 in the [8-120] keV energy band over a time window of 0.60 seconds starting at 2025-10-16T14:59:19.
The localization of the best alert is R.A., Dec. 266.207, -39.577 degrees:
```
R.A. (J2000) = 17h44m49.58s
Dec. (J2000) = -39d34m35.95s
```
with a 90% confidence level (C.L.) radius of 9.64 arcmin (including systematic error of 2 arcmin added in quadrature).
The SVOM/ECLAIRs light curve showed a single and narrow peak.
This burst also triggered SVOM/GRM at 2025-10-16T14:59:19 on a timescale of 0.10 seconds with an SNR of 37.30.
This burst seems to have been detected by Fermi, but with a declination of about 10 degrees offset.
The satellite did not slew due to Sun constraint. No X-ray observation could be performed by SVOM/MXT for the time being. No optical observation could be performed by SVOM/VT for the time being.
The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. SVOM/ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. SVOM/GRM was developed by the Institute of High Energy Physics (IHEP) of CAS. SVOM/MXT was developed jointly by CNES, CEA-IRFU, CNRS-IJCLab, University of Leicester, MPE.
The Burst Advocate (BA) on shift for this alert is Stephane Basa: stephane.basa@lam.fr. Please contact the BA by email if you require additional information.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 16 Oct 25 17:08:41 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     3000141,   Seg_Num: 1
POINT_RA:        266.196d {+17h 44m 47s} (J2000)
POINT_DEC:       -39.572d {-39d 34' 17"} (J2000)
ROLL:            268.517d
IMG_START_DATE:  20964 TJD;   289 DOY;   25/10/16
IMG_START_TIME:  61346.26 SOD {17:02:26.26} UT,   9902.5 [sec] since BAT Trigger Time
FILTER:          3, V
EXPOSURE_ID:     782326982
X_OFFSET:        723 [pixels]
Y_OFFSET:        872 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       883
Y_GRB_POS:       1032
BINNING_INDEX:   1
IM_URL:          sw03000141001msuni96339.fits
SUN_POSTN:       201.83d {+13h 27m 20s}   -9.16d {-09d 09' 27"}
SUN_DIST:         64.83 [deg]   Sun_angle= -4.3 [hr] (East of Sun)
MOON_POSTN:      152.27d {+10h 09m 04s}  +13.21d {+13d 12' 39"}
MOON_DIST:       117.08 [deg]
MOON_ILLUM:      21 [%]
GAL_COORDS:      350.81, -5.38 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      266.95,-16.17 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Image.  
COMMENTS:        This Notice is generated as a result of an uploaded TOO on an old GRB -- this is not a newly detected burst.  
COMMENTS:        And the IMG_START_DATE/TIME fields are the current epoch -- not the original detection.  
COMMENTS:        The GRB Position came from the Window Position in the Mode Command.  
COMMENTS:        The image has 2x2 binning (compression).

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 16 Oct 25 17:08:57 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     3000141,   Seg_Num: 1
POINT_RA:        266.196d {+17h 44m 47s} (J2000)
POINT_DEC:       -39.572d {-39d 34' 17"} (J2000)
ROLL:            268.517d
IMG_START_DATE:  20964 TJD;   289 DOY;   25/10/16
IMG_START_TIME:  61346.26 SOD {17:02:26.26} UT,   9902.5 [sec] since BAT Trigger Time
FILTER:          3, V
EXPOSURE_ID:     782326982
X_OFFSET:        723 [pixels]
Y_OFFSET:        872 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       883
Y_GRB_POS:       1032
BINNING_INDEX:   1
IM_URL:          sw03000141001msuni96339.fits
SUN_POSTN:       201.83d {+13h 27m 20s}   -9.16d {-09d 09' 27"}
SUN_DIST:         64.83 [deg]   Sun_angle= -4.3 [hr] (East of Sun)
MOON_POSTN:      152.27d {+10h 09m 05s}  +13.21d {+13d 12' 36"}
MOON_DIST:       117.08 [deg]
MOON_ILLUM:      21 [%]
GAL_COORDS:      350.81, -5.38 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      266.95,-16.17 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Processed Image.  
COMMENTS:        This Notice is generated as a result of an uploaded TOO on an old GRB -- this is not a newly detected burst.  
COMMENTS:        And the IMG_START_DATE/TIME fields are the current epoch -- not the original detection.  
COMMENTS:        The GRB Position came from the Window Position in the Mode Command.  
COMMENTS:        The image has 2x2 binning (compression).  
COMMENTS:        All 4 attachments are included.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 16 Oct 25 17:10:14 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     3000141,   Seg_Num: 1
POINT_RA:        266.196d {+17h 44m 47s} (J2000)
POINT_DEC:       -39.572d {-39d 34' 17"} (J2000)
POINT_ROLL:      268.517d
IMG_START_DATE:  20964 TJD;   289 DOY;   25/10/16
IMG_START_TIME:  61602.17 SOD {17:06:42.17} UT,   10158.4 [sec] since BAT Trigger Time
FILTER:          4, UVM2
BKG_MEAN:        0.090
N_STARS:         34
X_OFFSET:        164 [pixels]
Y_OFFSET:        313 [pixels]
X_MAX:           1603 [pixels]
Y_MAX:           1752 [pixels]
DET_THRESH:      4
PHOTO_THRESH:    2
SL_URL:          sw03000141001msufc96558.fits
SUN_POSTN:       201.84d {+13h 27m 20s}   -9.16d {-09d 09' 29"}
SUN_DIST:         64.83 [deg]   Sun_angle= -4.3 [hr] (East of Sun)
MOON_POSTN:      152.28d {+10h 09m 07s}  +13.20d {+13d 12' 18"}
MOON_DIST:       117.07 [deg]
MOON_ILLUM:      21 [%]
GAL_COORDS:      350.81, -5.38 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      266.95,-16.17 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Processed Source List.  
COMMENTS:        This Notice is generated as a result of an uploaded TOO on an old GRB -- this is not a newly detected burst.  
COMMENTS:        And the IMG_START_DATE/TIME fields are the current epoch -- not the original detection.  
COMMENTS:        All 4 attachments are included.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 16 Oct 25 17:10:34 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     3000141,   Seg_Num: 1
POINT_RA:        266.196d {+17h 44m 47s} (J2000)
POINT_DEC:       -39.572d {-39d 34' 17"} (J2000)
ROLL:            268.517d
IMG_START_DATE:  20964 TJD;   289 DOY;   25/10/16
IMG_START_TIME:  61602.17 SOD {17:06:42.17} UT,   10158.4 [sec] since BAT Trigger Time
FILTER:          4, UVM2
EXPOSURE_ID:     782327238
X_OFFSET:        723 [pixels]
Y_OFFSET:        872 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       883
Y_GRB_POS:       1032
BINNING_INDEX:   1
IM_URL:          sw03000141001msuni96595.fits
SUN_POSTN:       201.84d {+13h 27m 20s}   -9.16d {-09d 09' 29"}
SUN_DIST:         64.83 [deg]   Sun_angle= -4.3 [hr] (East of Sun)
MOON_POSTN:      152.28d {+10h 09m 08s}  +13.20d {+13d 12' 13"}
MOON_DIST:       117.07 [deg]
MOON_ILLUM:      21 [%]
GAL_COORDS:      350.81, -5.38 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      266.95,-16.17 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Image.  
COMMENTS:        This Notice is generated as a result of an uploaded TOO on an old GRB -- this is not a newly detected burst.  
COMMENTS:        And the IMG_START_DATE/TIME fields are the current epoch -- not the original detection.  
COMMENTS:        The GRB Position came from the Window Position in the Mode Command.  
COMMENTS:        The image has 2x2 binning (compression).

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 16 Oct 25 17:10:49 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     3000141,   Seg_Num: 1
POINT_RA:        266.196d {+17h 44m 47s} (J2000)
POINT_DEC:       -39.572d {-39d 34' 17"} (J2000)
ROLL:            268.517d
IMG_START_DATE:  20964 TJD;   289 DOY;   25/10/16
IMG_START_TIME:  61602.17 SOD {17:06:42.17} UT,   10158.4 [sec] since BAT Trigger Time
FILTER:          4, UVM2
EXPOSURE_ID:     782327238
X_OFFSET:        723 [pixels]
Y_OFFSET:        872 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       883
Y_GRB_POS:       1032
BINNING_INDEX:   1
IM_URL:          sw03000141001msuni96595.fits
SUN_POSTN:       201.84d {+13h 27m 21s}   -9.16d {-09d 09' 29"}
SUN_DIST:         64.83 [deg]   Sun_angle= -4.3 [hr] (East of Sun)
MOON_POSTN:      152.28d {+10h 09m 08s}  +13.20d {+13d 12' 10"}
MOON_DIST:       117.07 [deg]
MOON_ILLUM:      21 [%]
GAL_COORDS:      350.81, -5.38 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      266.95,-16.17 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Processed Image.  
COMMENTS:        This Notice is generated as a result of an uploaded TOO on an old GRB -- this is not a newly detected burst.  
COMMENTS:        And the IMG_START_DATE/TIME fields are the current epoch -- not the original detection.  
COMMENTS:        The GRB Position came from the Window Position in the Mode Command.  
COMMENTS:        The image has 2x2 binning (compression).  
COMMENTS:        If you have elected to receive attachments:  
COMMENTS:        The uvot_catalog_image.fits.gz file does not exist; skipping the attachment.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 16 Oct 25 17:09:55 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     3000141,   Seg_Num: 1
POINT_RA:        266.196d {+17h 44m 47s} (J2000)
POINT_DEC:       -39.572d {-39d 34' 17"} (J2000)
POINT_ROLL:      268.517d
IMG_START_DATE:  20964 TJD;   289 DOY;   25/10/16
IMG_START_TIME:  61602.17 SOD {17:06:42.17} UT,   10158.4 [sec] since BAT Trigger Time
FILTER:          4, UVM2
BKG_MEAN:        0.090
N_STARS:         34
X_OFFSET:        164 [pixels]
Y_OFFSET:        313 [pixels]
X_MAX:           1603 [pixels]
Y_MAX:           1752 [pixels]
DET_THRESH:      4
PHOTO_THRESH:    2
SL_URL:          sw03000141001msufc96558.fits
SUN_POSTN:       201.83d {+13h 27m 20s}   -9.16d {-09d 09' 28"}
SUN_DIST:         64.83 [deg]   Sun_angle= -4.3 [hr] (East of Sun)
MOON_POSTN:      152.28d {+10h 09m 07s}  +13.21d {+13d 12' 22"}
MOON_DIST:       117.07 [deg]
MOON_ILLUM:      21 [%]
GAL_COORDS:      350.81, -5.38 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      266.95,-16.17 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.  
COMMENTS:        This Notice is generated as a result of an uploaded TOO on an old GRB -- this is not a newly detected burst.  
COMMENTS:        And the IMG_START_DATE/TIME fields are the current epoch -- not the original detection.

GCN Circular #42309
The Fermi GBM team reports the detection of a likely SHORT GRB
"At 14:59:19.76 UT on 16 October 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251016A (trigger 782319564/251016625).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 268.93, Dec = -48.82 (J2000 degrees, equivalent to J2000 17h 55m, -48d 49'), with a statistical uncertainty of 3.55 degrees.
The angle from the Fermi LAT boresight is 33 degrees.
The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251016625/quicklook/glg_skymap_all_bn251016625.png
The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251016625/quicklook/glg_healpix_all_bn251016625.fit
The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251016625/quicklook/glg_lc_medres34_bn251016625.gif"
GCN Circular #42310
V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory)
MASTER-SAAO robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa (South African Astronomical Observatory) started inspect of the Fermi GRB 251016A ( Fermi GBM team, GCN 42309) errorbox 9753 sec after notice time and 9784 sec after trigger time at 2025-10-16 17:42:24 UT, with upper limit up to 16.8 mag. Observations started at twilight. The observations began at zenith distance = 38 deg. The sun altitude is -11.4 deg.
The galactic latitude b = -12 deg., longitude l = 344 deg.
Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3016116
We obtain a following upper limits.
```
Tmid-T0  |      Date Time      |          Site       |             Coord (J2000)          |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________

    9814 | 2025-10-16 17:42:24 |         MASTER-SAAO | (17h 41m 59.48s , -48d 04m 09.1s) |   C |    60 | 14.4 |        
    9814 | 2025-10-16 17:42:24 |         MASTER-SAAO | (17h 44m 44.95s , -48d 19m 26.1s) |   C |    60 | 16.5 |        
    9909 | 2025-10-16 17:43:58 |         MASTER-SAAO | (17h 39m 01.22s , -50d 11m 14.5s) |   C |    60 | 16.8 |        
    9909 | 2025-10-16 17:43:58 |         MASTER-SAAO | (17h 36m 07.40s , -49d 55m 40.2s) |   C |    60 | 15.2 |        
   10004 | 2025-10-16 17:45:33 |         MASTER-SAAO | (17h 48m 32.79s , -46d 10m 37.6s) |   C |    60 | 14.6 |        
   10004 | 2025-10-16 17:45:33 |         MASTER-SAAO | (17h 51m 12.71s , -46d 25m 54.6s) |   C |    60 | 16.6 |        
```
Filter C is a clear (unfiltred) band.
The observation and reduction will continue. The message may be cited.

GCN Circular #42311
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.

GCN Circular #42313
R. Woolf, C.C. Cheung, M. Kerr, J.E. Grove (NRL), A. Goldstein (USRA), C.A. Wilson-Hodge, D. Kocevski (MSFC), and M.S. Briggs (UAH) report:
The Glowbug gamma-ray telescope [1,2,3], operating on the International Space Station, reports the detection of GRB 251016A, which was also detected by SVOM/ECLAIRs (GCN 42308), Fermi/GBM (GCN 42309), and CALET (Trigger 1444661491).
Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2025-10-16 14:59:18.560 with a duration of 0.64 s and a total significance of about 76 sigma. The light curve comprises a single peak.
The analysis results presented here are preliminary and use a response function that lacks a detailed characterization of the surrounding passive structure of the ISS.
Glowbug is a NASA-funded technology demonstrator for sensitive, low-cost gamma-ray transient telescopes developed, built, and operated by the U.S. Naval Research Laboratory (NRL) with support from the University of Alabama in Huntsville, USRA, and NASA MSFC. It was launched on 2023 March 15 aboard the Department of Defense Space Test Program’s STP-H9 to the ISS, and operated until 2024 April when it was put in safe storage on orbit. Glowbug was removed from storage and resumed operation on 2025 September 12.
```
[1] Grove, J.E. et al. 2020, Proc. Yamada Conf. LXXI, arXiv:2009.11959
[2] Woolf, R.S. et al. 2022, Proc. SPIE, 12181, id. 121811O
[3] Woolf, R.S. et al. 2024, Proc. SPIE, 13151, id. 1315108
```
Distribution Statement A: Approved for public release. Distribution is unlimited.
GCN Circular #42314
I. Perez-Garcia, E. Fernandez-Garcia, M.D. Caballero-Garcia, R. Sanchez-Ramirez, S.-Y. Wu, S. Guziy and A. J. Castro-Tirado (IAA-CSIC, Granada), P. J. Meintjes and H. J. van Heerden (UFS, South Africa), A. Martin-Carrillo and L. Hanlon (UCD, Ireland), M. Gritsevich (Univ. of Helsinki), M. Jelinek (ASU-CAS), A. Kumar (ARIES) and C. J. Perez del Pulgar (UMA, Malaga), on behalf of a larger collaboration, report:
Following the detection of GRB 251016A by Fermi/GBM (Smith et al., GCN 42309) and SVOM/ECLAIRs (Basa et al., GCN 42308), the BOOTES-6/DPRT 0.6m robotic telescope at Boyden Observatory in Maselspoort (South Africa) responded to this event starting on Oct 16, 17:35 UT (~ 2.6 h after trigger) with 60s images. No new source is detected within the Swift/XRT X-ray afterglow Source 1 position (Evans et al., GCN 42311) up to magnitude 17.14 using Gaia DR3 Gmag magnitude as reference on our first image. Further images were gathered and using ATLAS REFCAT2 as reference (Tonry et al. 2018) we get an upper limit of:
```
| UT  mid exposure    | Mag limit | Filter | Exp time (sec) |
| ------------------- | --------- | ------ | -------------- |
| 2025-10-16 18:05:07 | 19.3      | clear  | 60x7           |
| 2025-10-16 18:37:07 | 17.6      | Z      | 60x4           |
| 2025-10-16 18:43:02 | 19.1      | g      | 60x4           |
| 2025-10-16 19:05:30 | 18.7      | r      | 60x3           |
| 2025-10-16 19:10:38 | 18.3      | i      | 60x4           |
```
We thank the staff at Boyden Observatory for their excellent support.
GCN Circular #42321
Y. Kawakubo , A. Yoshida, T. Sakamoto, S. Sugita (AGU), K. Yamaoka (Nagoya U), S. Nakahira (JAXA), Y. Asaoka (ICRR), S. Torii, Y. Akaike, K. Kobayashi (Waseda U), Y. Shimizu, T. Tamura (Kanagawa U), N. Cannady (GSFC/UMBC), M. L. Cherry (LSU), S. Ricciarini (U of Florence), P. S. Marrocchesi (U of Siena), and the CALET collaboration:
The short GRB 251016A (SVOM detection: Basa et al., GCN Circ. 42308; Fermi GBM Final Localization: Fermi GBM team, GCN Circ. 42309; Glowbug gamma-ray detection: Woolf et al., GCN Circ. 42313) triggered the CALET Gamma-ray Burst Monitor (CGBM) at 14:59:19.37 UTC on 16 October 2025 (https://cgbm.calet.jp/cgbm_trigger/flight/1444661491/index.html). The burst signal was seen by all CGBM detectors.
The burst light curve shows a short pulse that starts at T+0.32 sec, peaks at T+0.51 sec, and ends at T+0.69 sec. The T90 and T50 durations measured by the SGM data are 0.29 +/- 0.05 sec and 0.10+/- 0.03 sec (40-1000 keV), respectively.
The ground-processed light curve is available at
https://cgbm.calet.jp/cgbm_trigger/ground/1444661491/
The CALET data used in this analysis are provided by the Waseda CALET Operation Center located at Waseda University.
GCN Circular #42327
A. Goyal (IITB), A. Arya (IITB), S. Salunke (IUCAA), M. Tembhurnikar (IUCAA), Harsha K. H. (IUCAA), G. Waratkar (Caltech/IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration:
Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of a short-duration GRB 251016A which was also detected by SVOM/ECLAIRs (Basa et al., GCN Circ. 42308), Fermi GBM (Fermi GBM Team, GCN Circ. 42309), Glowbug (Woolf et al., GCN Circ. 42313) and CALET GBM (Kawakubo et al., GCN Circ. 42321).
The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2025-10-16 14:59:16.90 UTC. The measured peak count rate associated with the burst is 1142 (+782, -64) counts/s above the background in the combined data of all four quadrants, with a total of 140 (+39, -30) counts. The local mean background count rate was 264 (+14, -45) counts/s. Using cumulative rates, we measure a T90 of 0.31 (+0.04, -0.08) s.
The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2025-10-16 14:59:16.68 UTC. The measured peak count rate associated with the burst is 1099 (+76, -82) counts/s above the background in the combined data of all quadrants, with a total of 1056 (+117, -126) counts. The local mean background count rate was 1232 (+9, -10) counts/s. Due to the intrinsic 1 s binning of veto data, we cannot reliably estimate a T90 from it.
CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project.
CZTI GRB detections are reported regularly on the payload site at: http://astrosat.iucaa.in/czti/?q=grb

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 17 Oct 25 20:45:38 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     3000141,   Seg_Num: 3
POINT_RA:        266.215d {+17h 44m 52s} (J2000)
POINT_DEC:       -39.580d {-39d 34' 48"} (J2000)
ROLL:            268.905d
IMG_START_DATE:  20965 TJD;   290 DOY;   25/10/17
IMG_START_TIME:  74068.59 SOD {20:34:28.59} UT,   42824.0 [sec] since BAT Trigger Time
FILTER:          9, B
EXPOSURE_ID:     782426105
X_OFFSET:        846 [pixels]
Y_OFFSET:        875 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       1006
Y_GRB_POS:       1035
BINNING_INDEX:   1
IM_URL:          sw03000141003msuni42860.fits
SUN_POSTN:       202.91d {+13h 31m 38s}   -9.58d {-09d 34' 39"}
SUN_DIST:         63.76 [deg]   Sun_angle= -4.3 [hr] (East of Sun)
MOON_POSTN:      165.38d {+11h 01m 31s}   +6.64d {+06d 38' 21"}
MOON_DIST:       102.91 [deg]
MOON_ILLUM:      12 [%]
GAL_COORDS:      350.81, -5.40 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      266.96,-16.18 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Image.  
COMMENTS:        This Notice is generated as a result of an uploaded TOO on an old GRB -- this is not a newly detected burst.  
COMMENTS:        And the IMG_START_DATE/TIME fields are the current epoch -- not the original detection.  
COMMENTS:        The GRB Position came from the Window Position in the Mode Command.  
COMMENTS:        The image has 2x2 binning (compression).

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 17 Oct 25 20:45:51 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     3000141,   Seg_Num: 3
POINT_RA:        266.215d {+17h 44m 52s} (J2000)
POINT_DEC:       -39.580d {-39d 34' 48"} (J2000)
ROLL:            268.905d
IMG_START_DATE:  20965 TJD;   290 DOY;   25/10/17
IMG_START_TIME:  74068.59 SOD {20:34:28.59} UT,   42824.0 [sec] since BAT Trigger Time
FILTER:          9, B
EXPOSURE_ID:     782426105
X_OFFSET:        846 [pixels]
Y_OFFSET:        875 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       1006
Y_GRB_POS:       1035
BINNING_INDEX:   1
IM_URL:          sw03000141003msuni42860.fits
SUN_POSTN:       202.91d {+13h 31m 38s}   -9.58d {-09d 34' 39"}
SUN_DIST:         63.76 [deg]   Sun_angle= -4.3 [hr] (East of Sun)
MOON_POSTN:      165.38d {+11h 01m 31s}   +6.64d {+06d 38' 18"}
MOON_DIST:       102.91 [deg]
MOON_ILLUM:      12 [%]
GAL_COORDS:      350.81, -5.40 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      266.96,-16.18 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Processed Image.  
COMMENTS:        This Notice is generated as a result of an uploaded TOO on an old GRB -- this is not a newly detected burst.  
COMMENTS:        And the IMG_START_DATE/TIME fields are the current epoch -- not the original detection.  
COMMENTS:        The GRB Position came from the Window Position in the Mode Command.  
COMMENTS:        The image has 2x2 binning (compression).  
COMMENTS:        All 4 attachments are included.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 17 Oct 25 21:28:49 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     3000141,   Seg_Num: 3
POINT_RA:        266.215d {+17h 44m 52s} (J2000)
POINT_DEC:       -39.580d {-39d 34' 48"} (J2000)
POINT_ROLL:      268.905d
IMG_START_DATE:  20965 TJD;   290 DOY;   25/10/17
IMG_START_TIME:  74636.42 SOD {20:43:56.42} UT,   43391.8 [sec] since BAT Trigger Time
FILTER:          9, B
BKG_MEAN:        4.960
N_STARS:         190
X_OFFSET:        527 [pixels]
Y_OFFSET:        556 [pixels]
X_MAX:           1486 [pixels]
Y_MAX:           1515 [pixels]
DET_THRESH:      19
PHOTO_THRESH:    11
SL_URL:          sw03000141003msufc43391.fits
SUN_POSTN:       202.94d {+13h 31m 45s}   -9.59d {-09d 35' 18"}
SUN_DIST:         63.74 [deg]   Sun_angle= -4.2 [hr] (East of Sun)
MOON_POSTN:      165.71d {+11h 02m 50s}   +6.46d {+06d 27' 50"}
MOON_DIST:       102.55 [deg]
MOON_ILLUM:      12 [%]
GAL_COORDS:      350.81, -5.40 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      266.96,-16.18 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.  
COMMENTS:        This Notice is generated as a result of an uploaded TOO on an old GRB -- this is not a newly detected burst.  
COMMENTS:        And the IMG_START_DATE/TIME fields are the current epoch -- not the original detection.  
COMMENTS:        The Pointing RA,Dec,Roll values came from the 1st SrcList Notice.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 17 Oct 25 21:29:05 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     3000141,   Seg_Num: 3
POINT_RA:        266.215d {+17h 44m 52s} (J2000)
POINT_DEC:       -39.580d {-39d 34' 48"} (J2000)
POINT_ROLL:      268.905d
IMG_START_DATE:  20965 TJD;   290 DOY;   25/10/17
IMG_START_TIME:  74636.42 SOD {20:43:56.42} UT,   43391.8 [sec] since BAT Trigger Time
FILTER:          9, B
BKG_MEAN:        4.960
N_STARS:         190
X_OFFSET:        527 [pixels]
Y_OFFSET:        556 [pixels]
X_MAX:           1486 [pixels]
Y_MAX:           1515 [pixels]
DET_THRESH:      19
PHOTO_THRESH:    11
SL_URL:          sw03000141003msufc43391.fits
SUN_POSTN:       202.94d {+13h 31m 45s}   -9.59d {-09d 35' 18"}
SUN_DIST:         63.74 [deg]   Sun_angle= -4.2 [hr] (East of Sun)
MOON_POSTN:      165.71d {+11h 02m 51s}   +6.46d {+06d 27' 46"}
MOON_DIST:       102.55 [deg]
MOON_ILLUM:      12 [%]
GAL_COORDS:      350.81, -5.40 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      266.96,-16.18 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Processed Source List.  
COMMENTS:        This Notice is generated as a result of an uploaded TOO on an old GRB -- this is not a newly detected burst.  
COMMENTS:        And the IMG_START_DATE/TIME fields are the current epoch -- not the original detection.  
COMMENTS:        All 4 attachments are included.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 17 Oct 25 21:30:18 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     3000141,   Seg_Num: 3
POINT_RA:        266.215d {+17h 44m 52s} (J2000)
POINT_DEC:       -39.580d {-39d 34' 48"} (J2000)
ROLL:            268.905d
IMG_START_DATE:  20965 TJD;   290 DOY;   25/10/17
IMG_START_TIME:  74636.42 SOD {20:43:56.42} UT,   43391.8 [sec] since BAT Trigger Time
FILTER:          9, B
EXPOSURE_ID:     782426672
X_OFFSET:        846 [pixels]
Y_OFFSET:        875 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       1006
Y_GRB_POS:       1035
BINNING_INDEX:   1
IM_URL:          sw03000141003msuni43428.fits
SUN_POSTN:       202.94d {+13h 31m 45s}   -9.59d {-09d 35' 19"}
SUN_DIST:         63.73 [deg]   Sun_angle= -4.2 [hr] (East of Sun)
MOON_POSTN:      165.72d {+11h 02m 53s}   +6.46d {+06d 27' 29"}
MOON_DIST:       102.54 [deg]
MOON_ILLUM:      12 [%]
GAL_COORDS:      350.81, -5.40 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      266.96,-16.18 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Image.  
COMMENTS:        This Notice is generated as a result of an uploaded TOO on an old GRB -- this is not a newly detected burst.  
COMMENTS:        And the IMG_START_DATE/TIME fields are the current epoch -- not the original detection.  
COMMENTS:        The Pointing RA,Dec,Roll values came from the 1st Image Notice.  
COMMENTS:        The GRB Position came from the Window Position in the Mode Command.  
COMMENTS:        The image has 2x2 binning (compression).

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 17 Oct 25 21:30:33 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     3000141,   Seg_Num: 3
POINT_RA:        266.215d {+17h 44m 52s} (J2000)
POINT_DEC:       -39.580d {-39d 34' 48"} (J2000)
ROLL:            268.905d
IMG_START_DATE:  20965 TJD;   290 DOY;   25/10/17
IMG_START_TIME:  74636.42 SOD {20:43:56.42} UT,   43391.8 [sec] since BAT Trigger Time
FILTER:          9, B
EXPOSURE_ID:     782426672
X_OFFSET:        846 [pixels]
Y_OFFSET:        875 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       1006
Y_GRB_POS:       1035
BINNING_INDEX:   1
IM_URL:          sw03000141003msuni43428.fits
SUN_POSTN:       202.94d {+13h 31m 45s}   -9.59d {-09d 35' 20"}
SUN_DIST:         63.73 [deg]   Sun_angle= -4.2 [hr] (East of Sun)
MOON_POSTN:      165.72d {+11h 02m 54s}   +6.46d {+06d 27' 25"}
MOON_DIST:       102.53 [deg]
MOON_ILLUM:      12 [%]
GAL_COORDS:      350.81, -5.40 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      266.96,-16.18 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Processed Image.  
COMMENTS:        This Notice is generated as a result of an uploaded TOO on an old GRB -- this is not a newly detected burst.  
COMMENTS:        And the IMG_START_DATE/TIME fields are the current epoch -- not the original detection.  
COMMENTS:        The GRB Position came from the Window Position in the Mode Command.  
COMMENTS:        The image has 2x2 binning (compression).  
COMMENTS:        All 4 attachments are included.

GCN Circular #42349
Roberto Ricci (U Rome), Niccolo Passaleva ( U Rome) and Eleonora Troja (U Rome) report:
We observed the field of the short duration GRB 251016A detected by SVOM/ECLAIRs (Basa et al., GCN 42308), FERMI-GBM (Fermi GBM team, GCN 42309), CALET-GBM (Kawakubo et al., GCN 42321), Glowbug (Woolf et al., GCN 42313) and Astro Sat CZTI (Arya et al., GCN 42327) with the FORS2 imager on the ESO VLT UT1 (Antu). Observations started on Oct 16th, 2025 at 23:45 UT (~9 hours after the SVOM trigger) and were carried out in the I_BESS filter with an average airmass of ~1.3.
The GRB lies within a very crowded region at low Galactic latitude. Several optical sources are detected within the localization of Swift/XRT Source #1 (Evans et al., GCN 42311). Objects brighter than 24 AB mag have counterparts in the GAIA DR3 catalogue (Babusiaux et al., 2023), however several fainter (>24 AB mag) sources remain unmatched.
Further observations are planned to determine variability.
We thank the staff at the VLT for the rapid execution of these observations.
GCN Circular #42354
S.P.R. Shilling (Lancaster U.) reports on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 251016A, detected by SVOM/ECLAIRs (Basa et al., GCN Circ. 42308) and Fermi/GBM (Fermi GBM team, GCN Circ. 42309), 6.66 ks after the SVOM/ECLAIRs trigger.
A source is detected in the optical by the Swift/UVOT at a position that is consistent with the likely X-ray counterpart detected by the Swift/XRT (Source 1: Evans et al., GCN Circ. 42311).
Preliminary detections and upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the images are:
```
Filter         T_start(ks)   T_stop(ks)      Exp(s)            Mag

u	       6.66	     12.6	     491.7	       19.13 +/- 0.26
b	       6.91	     12.7	     296.0	       18.70 +/- 0.18
v	       7.42	     7.67	     245.8	       17.52 +/- 0.15
w1	       12.1	     12.4	     245.8	       >18.93
w2	       7.17	     7.42	     245.8	       >19.05
m2	       7.68	     7.85	     168.3	       >18.66
```
The magnitudes reported here are not corrected for Galactic extinction.
GCN Circular #42356
P. D'Avanzo (INAF-OAB), M.G. Bernardini (INAF-OAB), E. Ambrosi (INAF-IASFPA) , S. Lanava (PSU), S. Dichiara (PSU), J.A. Kennea (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team:
Swift-XRT has performed follow-up observations of GRB 251016A. We searched for X-ray sources in 3.5 ks of Photon Counting (PC) mode data. The total exposure at the position of the afterglow (see below) is 5.6 ks, obtained between T0+6.6 ks and T0+107.3 ks.
Thirty-two uncatalogued X-ray sources are detected, of which one ("Source 1") is fading with >3-sigma significance, and is therefore likely the GRB afterglow. Using 1190 s of PC mode data and 2 UVOT images, we find an enhanced XRT position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 266.30279, -39.56008 which is equivalent to:
```
RA (J2000): 17h 45m 12.67s
Dec(J2000): -39d 33' 36.3"
```
with an uncertainty of 3.2 arcsec (radius, 90% confidence).
The light curve can be modelled with a power-law decay with a decay index of alpha=4.53 (+0.08, -3.08).
A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.4 (+1.0, -0.6). The best-fitting absorption column is 4.8 (+8.8, -0.9) x 10^21 cm^-2, consistent with the Galactic value of 3.9 x 10^21 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 6.4 x 10^-11 (8.0 x 10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
```
Total column:	     4.8 (+8.8, -0.9) x 10^21 cm^-2
Galactic foreground: 3.9 x 10^21 cm^-2
Excess significance: <1.6 sigma
Photon index:	     1.4 (+1.0, -0.6)
```
The results of the XRT-team automatic analysis are available at https://www.swift.ac.uk/xrt_products/03000141. The results of the full analysis of the XRT observations are available at https://www.swift.ac.uk/SVOM/SVOM_FIELD00042.
This circular is an official product of the Swift-XRT team.
GCN Circular #42359
Xue-Yuan Zao, Chen-Wei Wang, Zheng-Hang Yu, Cheng-Kui Li, Shao-Lin Xiong, and Chao Zheng report on behalf of the Insight-HXMT team:
At 2025-10-16T14:59:19.750 (T0), Insight-HXMT/HE detected the short burst GRB 251016A, which is also detected by SVOM/ECLAIRs (Basa et al., GCN 42308), FERMI-GBM (Fermi GBM team, GCN 42309), CALET-GBM (Kawakubo et al., GCN 42321), Glowbug (Woolf et al., GCN 42313) and Astro Sat CZTI (Arya et al., GCN 42327).
The Insight-HXMT/HE light curve mainly consists of a single pulse with a T90 of 0.34 +/-0.06 s. The total counts from this burst is 2297 counts.
The HXMT/HE light curve can be found here: https://www.bursthub.cn//admin/static/hxmtgrb251016A.png
All measurements above are made with the CsI detectors operating in the regular mode with the energy range of about 30-1000 keV (deposited energy). Only gamma-rays with energy greater than about 200 keV can penetrate the spacecraft and leave signals in the CsI detectors installed inside of the telescope.
Insight-HXMT is the first Chinese space X-ray telescope, which was funded jointly by the China National Space Administration (CNSA) and the Chinese Academy of Sciences (CAS). More information about it could be found at: http://www.hxmt.org.
GCN Circular #42365
Jacob Smith (UAH) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team:
"At 14:59:19.76 UT on 16 October 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251016A (trigger 782319564/251016625), which is was detected by SVOM/ECLAIRs (Basa et al., GCN 42308), CALET-GBM (Kawakubo et al., GCN 42321), Glowbug (Woolf et al., GCN 42313) and Astro Sat CZTI (Arya et al., GCN 42327). The Fermi GBM on-ground location is consistent with the SVOM/ECLAIRs position.
The angle from the Fermi LAT boresight is 42 degrees.
The GBM light curve consists of a single emission episode with a duration (T90) of about 0.32 s (50-300 keV). The time-averaged spectrum from T0-0.1 to T0+0.4 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.83 +/- 0.04 and the cutoff energy, parameterized as Epeak, is 1317 +/- 145 keV.
The event fluence (10-1000 keV) in this time interval is (3 +/- 0.08)E-06 erg/cm^2. The 64-ms peak photon flux measured starting from T0+0.13 s in the 10-1000 keV band is 34 +/- 2 ph/s/cm^2.
The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog: https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html
For Fermi GBM data and info, please visit the official Fermi GBM Support Page: https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/"
GCN Circular #42374
M. Brunet, O. Godet, S. Guillot (IRAP), B. Hubert (CEA), S.Basa, S.Boissier (LAM)
Using the event-by-event data downloaded through the X-band ground station, we report further analysis of ECLAIRs observations of GRB 251016A (SVOM burst-id sb2525101602, GCN 42308) detected at T0 = 2025-10-16T14:59:20, which was also detected by SVOM/GRM, Fermi/GBM (GCN 42309), CALET/GBM (GCN 42321), Glowbug (GCN 42313), AstroSat/CZTI (GCN 42327) and HXMT/HE (GCN 42359).
The burst that triggered ECLAIRs consists of a single short peak, with a duration of T90 = 0.69 +0.09/-0.19 s in the 4-120 keV energy band.
The time-averaged spectrum from the peak (T0-0.4 s to T0+0.4 s) in the 5-120 keV energy range is well fitted by a power-law model with a photon index of 1.00 +/-0.16, which is consistent with the results found by Smith at al. 2025 (GCN 42365). With this model, the total 4-120 keV fluence is (3.01 +0.27/-0.94) e-07 erg/cm^2 .
All the quoted errors are at the 68% confidence level.
The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. The SVOM/ECLAIRs point of contact for this burst is: Marius Brunet (IRAP) (marius.brunet at irap.omp.eu).
GCN Circular #42473
V. Panteleeva, D. Frederiks, A. Lysenko, A. Ridnaia, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report:
The short-duration GRB 251016A (SVOM/ECLAIRs detection: Basa et al., GCN 42308; Brunet et al., GCN 42374; Fermi-GBM detection: The Fermi GBM team, GCN 42309; Smith and Meegan, GCN 42365; Glowbug detection: Woolf et al., GCN 42313; CALET-GBM detection: Kawakubo et al., GCN 42321; AstroSat-CZTI detection: Arya et al., GCN 42327; Insight-HXMT/HE detection: Zao et al., GCN 42359) triggered Konus-Wind at T0=53956.564 s UT (14:59:16.564).
The burst light curve shows a single pulse which starts at ~T0-0.2 s and has a total duration of ~0.5 s. The emission is seen up to ~3 MeV.
The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB251016_T53956/
As observed by Konus-Wind, the burst had the total fluence of 6.32(-0.91,+1.04)x10^-6 erg/cm2, and the 16-ms peak flux, measured from T0+0.018 s, of 2.46(-0.52,+0.58)x10^-5 erg/cm2/s (both in the 20 keV - 10 MeV energy range).
The time-averaged spectrum of the burst (measured from T0 to T0+0.256 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -0.44(-0.20,+0.35), the high energy photon index beta = -2.14(-0.72,+0.34), the peak energy Ep = 825(-282,+293) keV (chi2 = 30/25 dof).
All the quoted errors are at the 68% confidence level. All the quoted values are preliminary.
GCN Circular #42601
Daniel Shy (a), C.C. Cheung (a), Bernard Phlips (a), Michael Streicher (b), James Mason (b), Douglas M. Groves (b), Feng Zhang (b), and Willy Kaye (b)
(a) U.S. Naval Research Laboratory, 4555 Overlook Ave SW, Washington, DC 20375 (b) H3D, Inc., 812 Avis Dr., Ann Arbor, MI 48108, USA
The cadmium zinc TElluride Radiation Imager (TERI) gamma-ray telescope [1], operating on the International Space Station, reports the detection of GRB 251016A, which was also detected by SVOM/ECLAIRs (GCN 42308, 42374), Fermi/GBM (GCN 42309, 42365), Glowbug (GCN 42313), CALET (GCN 42321), AstroSat/CZTI (GCN 42327), Insight-HXMT/HE (GCN 42359), and Konus-Wind (GCN 42473).
Using 1 Hz binning, at 2025-10-16T14:59:20.0 we observe a single peak with an excess count rate of roughly 34 counts per second (cps) above the 32 cps baseline rate observed in nearby off-source intervals.
The analysis results presented here are preliminary and currently lack a detailed response function.
TERI is an Office of Naval Research funded technology demonstrator for large-volume pixelated CdZnTe detectors developed, built, and operated by the U.S. Naval Research Laboratory (NRL) in conjunction with H3D, Inc. The pixelated CdZnTe detectors have an energy range of 40 keV to 3 MeV per pixel. It was launched on 2025 April 21 aboard the Department of Defense Space Test Program’s STP-H10 to the ISS. On the ISS, it is located on the SOX external payload facility on the Columbus module. Analysis of TERI data at NRL is supported under contract with NASA as correlative science for the Fermi Gamma-ray Space Telescope.
[1] Shy, Daniel, et al. "Development of the cadmium zinc TElluride Radiation Imager." Journal of Astronomical Telescopes, Instruments, and Systems 10.4 (2024): 044009-044009 (arXiv:2408.04559).
Distribution Statement A: Approved for public release. Distribution is unlimited.

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Jochen Greiner, last update: 06-Nov-2025 [Disclaimer]