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GRB 251022A

GCN Circular 42427

Subject
GRB 251022A: KAIT optical observations
Date
2025-10-24T18:47:18Z (2 days ago)
From
Weikang Zheng at UC Berkeley <weikang@berkeley.edu>
Via
email
WeiKang Zheng (UCB) and Alexei V. Filippenko (UCB) report on

behalf of the KAIT GRB team:


The 0.76-m Katzman Automatic Imaging Telescope (KAIT), located at

Lick Observatory, observed the field of GRB 251022A (Fermi GBM

Team, GCN 42380; Di Lalla et al., GCN 42384; DeLaunay et al.,

GCN 42409; Mukherjee et al., GCN 42410) starting at ~0.46d and

again at ~1.39d after the burst. A set of clear (roughly R)

filter images were obtained. We detected the optical afterglow

(O’Neill et al. GCN 42386; Becerra et al. GCN 42394; Lipunov

et al. GCN 42395; Mandarakas et al. GCN 42397; Mohan et al. GCN

42413; Méndez et al., GCN 42423) in our coadd images. We estimate

the afterglow to be 19.2 +/- 0.2 and 21.6 +/- 0.3 mag (Vega) at a

mid time of ~0.47d and ~1.40d respectively.

GCN Circular 42423

Subject
GRB 251022A: COLIBRÍ Further Multi-frequency Optical Observations
Date
2025-10-24T15:05:07Z (2 days ago)
From
Rosa Leticia Becerra Godínez at Instituto de Astronomía, UNAM <rbecerra@astro.unam.mx>
Via
Web form
Enrique Moreno Méndez (UNAM), Nikos Mandarakas (LAM), Alan M. Watson (UNAM), Rosa L. Becerra (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM):

We reobserved the field of the Fermi GRB 251022A (Fermi GBM Team, GCN Circ. 42380; Di Lalla et al., GCN Circ. 42384) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2025-10-24 07:25 to 08:30 UTC (from 32.8 to 33.9 hours after the trigger) and obtained 10 minutes of exposure in each of the g, r, i, and z filters and 20 minutes of exposure in the y filter.

The data were reduced and coadded with the COLIBRÍ pipeline and analysed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction.

In our second epoch, we still detect the optical counterpart firstly reported by GOTO (O’Neill et al. GCN Circ. 42386) and subsequently followed-up by DDOTI (Becerra et al. GCN Circ. 42394), MASTER (Lipunov et al. GCN Circ. 42395), COLIBRÍ (Mandarakas et al. GCN Circ. 42397), and GROWTH (Mohan et al. GCN Circ. 42413) at preliminary magnitudes and upper limits of:

g = 22.52 +/- 0.23

r = 22.05 +/- 0.20

i = 21.99 +/- 0.31

z = 21.95 +/- 0.65

y > 20.7 (3-sigma)

Compared with the values reported in our first epoch (Mandarakas et al. GCN Circ. 42397), we estimate a temporal decay index of ~-2, consistent with a jet break. 

Our detection in g suggests that this is not a high-redshift GRB, but instead has z < 3.

We thank the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and the COLIBRÍ and DDRAGO engineering teams.

COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico.

GCN Circular 42417

Subject
GRB 251022A: Swift-XRT detection of GOTO25iym
Date
2025-10-24T08:12:16Z (2 days ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
D.N. Burrows (PSU), S. Lanava (PSU), S. Dichiara (PSU), J.P. Osborne
(U. Leicester), K.L. Page (U. Leicester), M. Capalbi (INAF-OAR), M.
Perri (SSDC & INAF-OAR), V. D'Elia (SSDC & INAF-OAR) and P.A. Evans (U.
Leicester) reports on behalf of the Swift-XRT team:

Swift-XRT has performed follow-up observations of the
Fermi/LAT-detected burst GRB 251022A in a series of observations tiled
on the sky.  The total exposure time is  4.6 ks, distributed over 4
tiles; the maximum exposure at a single sky location in the tiling was
2.5 ks. The data were collected between T0+26.7 ks and T0+71.7 ks, and
are entirely in Photon Counting (PC) mode. 

Seven uncatalogued X-ray sources have been detected, however none of
them is above the RASS limit or shows definitive signs of fading in the
X-rays. 

Source 4 is 2.6 arcsec from the reported optical transient GOTO25iym
(O'Neill et al., GCN Circ. 42386) and thus is likely the counterpart to
that transient and the GRB afterglow, though we cannot at present
confirm fading in X-rays. The details of this source are:

Source 4:
  RA (J2000.0):  65.4968  =  04h 21m 59.23s
  Dec (J2000.0): -18.9188  =  -18d 55' 07.8"
  Error: 4.8 arcsec (radius, 90% conf.)
  Count-rate: 0.0110 [+0.0026, -0.0025] ct s^-1   
  Distance: 1463 arcsec from Fermi/LAT position.
  Flux: (2.96 [+0.71, -0.67])e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV)

The other 6 uncatalogued sources detected are enumerated below:

Source 1:
  RA (J2000.0):  65.0135  =  04h 20m 03.25s
  Dec (J2000.0): -19.3306  =  -19d 19' 50.1"
  Error: 6.3 arcsec (radius, 90% conf. [Enhanced position])
  Count-rate: 0.0173 [+0.0061, -0.0050] ct s^-1   
  Distance: 1247 arcsec from Fermi/LAT position.
  Flux: (3.5 [+1.2, -1.0])e-12 erg cm^-2 s^-1 (observed, 0.3-10 keV)

Source 2:
  RA (J2000.0):  65.0984  =  04h 20m 23.62s
  Dec (J2000.0): -19.2625  =  -19d 15' 45.2"
  Error: 5.4 arcsec (radius, 90% conf.)
  Count-rate: 0.0115 [+0.0046, -0.0037] ct s^-1   
  Distance: 971 arcsec from Fermi/LAT position.
  Flux: (4.4 [+1.8, -1.4])e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV)

Source 5:
  RA (J2000.0):  65.3796  =  04h 21m 31.10s
  Dec (J2000.0): -18.9857  =  -18d 59' 08.4"
  Error: 6.0 arcsec (radius, 90% conf.)
  Count-rate: (7.7 [+2.6, -2.1])e-3 ct s^-1   
  Distance: 1167 arcsec from Fermi/LAT position.
  Flux: (2.17 [+0.72, -0.60])e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV)

Source 6:
  RA (J2000.0):  65.5456  =  04h 22m 10.93s
  Dec (J2000.0): -19.1086  =  -19d 06' 30.8"
  Error: 6.5 arcsec (radius, 90% conf.)
  Count-rate: (6.0 [+2.5, -2.0])e-3 ct s^-1   
  Distance: 917 arcsec from Fermi/LAT position.
  Flux: (9.1 [+3.9, -3.0])e-14 erg cm^-2 s^-1 (observed, 0.3-10 keV)

Source 8:
  RA (J2000.0):  65.4382  =  04h 21m 45.16s
  Dec (J2000.0): -19.0268  =  -19d 01' 36.6"
  Error: 7.8 arcsec (radius, 90% conf.)
  Count-rate: (3.2 [+1.8, -1.3])e-3 ct s^-1   
  Distance: 1038 arcsec from Fermi/LAT position.
  Flux: (6.8 [+3.9, -2.8])e-14 erg cm^-2 s^-1 (observed, 0.3-10 keV)

Source 9:
  RA (J2000.0):  65.3956  =  04h 21m 34.95s
  Dec (J2000.0): -19.0576  =  -19d 03' 27.4"
  Error: 6.3 arcsec (radius, 90% conf.)
  Count-rate: (3.6 [+2.1, -1.5])e-3 ct s^-1   
  Distance: 910 arcsec from Fermi/LAT position.
  Flux: (1.15 [+0.65, -0.48])e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV)

Two catalogued sources were also detected.

The results of the XRT-team automatic analysis of the tiled XRT
observations, including a position-specific upper limit calculator, are
available at https://www.swift.ac.uk/xrt_products/TILED_GRB00139.

This circular is an official product of the Swift-XRT team.

GCN Circular 42413

Subject
GRB 251022A: GROWTH-India Telescope optical observations
Date
2025-10-24T01:01:59Z (3 days ago)
From
V. Swain at IIT Bombay <vishwajeet.s@iitb.ac.in>
Via
Web form

T. Mohan, V. Swain, A.P. Saikia, V. Bhalerao (IITB), G.C. Anupama, S. Barway (IIA) and K. Angail (IAO) report on behalf of the GIT team:

We observed the field of Fermi GRB 251022A (Fermi GBM team, GCN 42380

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), with 0.7m GROWTH-India Telescope (GIT). We started the observation at 2025-10-23 22:25:05 UT, i.e., 23.85 hours after the Fermi trigger. Multiple exposures were obtained in the r'-band, and we clearly detect the optical counterpart in the stacked image. The photometry result follows as:

MJD (mid)tmid - t0 (hours)FilterExposure (s)Magnitude (AB)
60971.9447424.1r'5 x 36020.89 +- 0.12

The measurement is calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected for Galactic extinction.

Our magnitude is consistent with other optical observations (O’Neill et al., GCN 42386

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; Becerra et al., GCN 42394; Lipunov et al., GCN 42395; Mandarakas et al., GCN 42397).

The GROWTH India Telescope (GIT; Kumar et al. 2022) is a 70-cm telescope with a 0.7-degree field of view, set up by the Indian Institute of Astrophysics (IIA) and the Indian Institute of Technology Bombay (IITB) with funding from DST-SERB and IUSSTF. It is located at the Indian Astronomical Observatory (Hanle), operated by IIA. We acknowledge funding by the IITB alumni batch of 1994, which partially supports the operations of the telescope. Telescope technical details are available at https://sites.google.com/view/growthindia/.

GCN Circular 42410

Subject
GRB 251022A: Fermi GBM Observation
Date
2025-10-23T22:45:23Z (3 days ago)
From
oindabimukherjee@gmail.com
Via
Web form
O. Mukherjee (USRA) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:

"At 22:34:15.26 UT on 22 October 2025, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 251022A (trigger 782865260/251022940)
which was also detected by Fermi-LAT ( N. Di Lalla et al. 2025, GCN 42384), 
MASTER OT (V. Lipunov et al. 2025, GCN 42395),
and Swift/BAT-GUANO (James DeLaunay et al. 2025, GCN 42409).
The Fermi GBM on-ground location is consistent with the Fermi-LAT position.

The angle from the Fermi LAT boresight is 36.5 degrees.

The GBM light curve consists of multiple emission episodes with a duration (T90)
of about 99.6 s (50-300 keV). The time-averaged spectrum
from T0-1 to T0+107.5 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -0.88 +/- 0.04 and the cutoff energy,
parameterized as Epeak, is 154 +/- 5 keV.

The event fluence (10-1000 keV) in this time interval is
(2.16 +/- 0.05)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+100 s in the 10-1000 keV band is 12.4 +/- 0.3 ph/s/cm^2.

A Band function fits the spectrum equally well
with Epeak= 138 +/- 7 keV, alpha = -0.8 +/- 0.05 and beta = -2.6 +/- 0.2.

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 42409

Subject
GRB 251022A: Swift/BAT-GUANO localization skymap of a burst
Date
2025-10-23T20:18:12Z (3 days ago)
From
Jimmy DeLaunay at Penn State <delauj2@gmail.com>
Via
Web form

James DeLaunay (PSU), Samuele Ronchini (GSSI), Aaron Tohuvavohu (Caltech), Jamie A. Kennea (PSU), Tyler Parsotan (NASA GSFC), Maia Williams (Northwestern) report:

Swift/BAT did not localize GRB 251022A onboard (T0: 2025-10-22T22:34:45.26 UTC, Fermi Trig 782865260)

The Fermi notice, distributed in near real-time, triggered the Swift Mission Operations Center operated Gamma-ray Urgent Archiver for Novel Opportunities (GUANO; Tohuvavohu et al. 2020, ApJ, 900, 1).

Upon trigger by this notice, GUANO sent a command to the Swift Burst Alert Telescope (BAT) to save 200 seconds of BAT event-mode data from [-50,+150] seconds around the time of the burst. All the requested event mode data was delivered to the ground.

The BAT likelihood search, NITRATES (DeLaunay + Tohuvavohu 2022, ApJ, 941, 169), performed on the temporal window [T0-20 s, T0+50 s], detects the burst with a sqrt(TS) of 26.2 in a 2.048 s analysis time bin, starting at T0 + 32.560 s. The main peak was outside the typical search window of [T0-20 s, T0+20 s], so we expanded it in this case.

Using the NITRATES analysis, parameter estimation was performed to obtain the localization of this burst in the form of a HEALPIX Multi-Order Coverage (MOC) skymap. This localization accounts for both statistical and systematic errors. More details in the creation and calibration of these maps will soon be published (DeLaunay et al. 2025. in prep)

The 90% credible area is 2,100 deg2 and the 50% credible area is 380 deg2. The integrated probability inside the coded field of view is <1%.

The NITRATES skymap is consistent with the Fermi localization reported in the final position notice (GCN 42380

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). The combined Fermi/GBM+NITRATES 90% credible area is 111 deg2 and the 50% credible area is 29 deg2.

The NITRATES and combined Fermi/GBM+NITRATES skymaps are consistent with the Fermi/LAT (GCN 42384

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) and optical afterglow positions (GOTO GCN 42386, DDOTI GCN 42394, MASTER GCN 42395).

A plot of the probability skymap can be viewed here:

skymap_plot

The probability skymap and joint skymap files can be downloaded from the links here

skymap_fits_file

joint_skymap_fits_file

Instructions on how to read and manipulate this map can be found here:

https://guano.swift.psu.edu/documentation

More details about this burst can be found on the trigger report page here:

https://guano.swift.psu.edu/trigger_report?id=782865321

GUANO is a fully autonomous, extremely low latency, spacecraft commanding pipeline designed for targeted recovery of BAT event mode data around the times of compelling astrophysical events to enable more sensitive GRB searches.

A live reporting of Swift/BAT event data recovered by GUANO can be found at: https://www.swift.psu.edu/guano/

GCN Circular 42397

Subject
GRB 251022A: COLIBRÍ optical observations
Date
2025-10-23T14:12:44Z (3 days ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
Nikos Mandarakas (LAM), Ramandeep Gill (UNAM), Jean-Grégoire Ducoin (CPPM), Alan M. Watson (UNAM), Noémie Globus (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU) , Damien Dornic (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM):

We imaged the field of the Fermi GRB 251022A (Di Lalla et al., GCN Circ. 42384) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2025-10-23 06:12:44 to 07:32:34 UTC (from 7.64 to 8.97 hours after the trigger) and obtained 16 and 3 minutes of exposure in the r and z filters respectively.

The data were reduced and coadded with the COLIBRÍ pipeline and analysed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction.

We detected the optical counterpart reported by O’Neill et al. (GCN Circ. 42386), Becerra et al. (GCN Circ. 42394), and Lipunov et al. (GCN Circ. 42395) at preliminary magnitudes of:

r = 18.97 +/- 0.01
z = 18.54 +/- 0.04

Further observations are planned.

We thank the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and the COLIBRÍ and DDRAGO engineering teams.

COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico.

GCN Circular 42395

Subject
GRB 251022A: MASTER OT detection
Date
2025-10-23T12:43:30Z (3 days ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
Via
email
V. Lipunov, I.Panchenko, A.Kuznetsov, O.Gress,  G.Antipov, P.Balanutsa, E.Gorbovskoy,
K.Zhirkov,  N.Tiurina, A.Sankovich, Ya.Kechin, A.Chasovnikov, V.Topolev, D.Vlasenko, V.Senik, D.Vlasenko, V.Shumkov, K.Vetrov, Yu. Tselik, M.Shilova(Lomonosov MSU, SAI, Moscow),
R.Podesta, C.Francile,  F. Podesta, E. Gonzalez (OAFA, San Juan Uni.,Argentina);
D.Buckley (SAAO, South Africa),
N.Budnev (ISU, Irkutsk),
A.Sosnovskij (CrAO RAS),
A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory),
A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity),
V.M.Pillet, R.Rebolo Lopez (The Instituto de Astrofisica de Canarias, Spain),
L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez,J.Martinez,A.R.Corella,L.H.Rodriguez (INAOE, Guillermo Haro Astrophysic Observatory, Mexico)

MASTER Global Robotic Net [1-4] started Fermi GRB 251022A (GCNC 42380,
Ttrigger=2025-10-22 22:34:15.26 ,GBM_notice=2025-10-22 22:43:43,
LAT_notice=2025-10-23 03:04:17UT, LAT_center=04 21 31.18 -19 18 35.6 +-0.32deg (Di Lalla et al. GCN 42384)
at MASTER-SAAO and MASTER-OAFA (Lipunov et al. GCNC 42381) 13s after LAT_notice_time (16215s after trigger time)

There is MASTER OT J042159.34-185510.4 since 2025-10-23 03:04:54UT with unfiltered m_OT=18.0. This OT can be on MASTER very wide field images at earlier images in MASTER-Tunka, that started GBM error-filed observations in alert mode, the reduction will be continued.

This OT was discovered by  GOTO (O'Neill et al. GCNC 42386) and also observed by DDOTI (Becerra et al. GCNC 42394)

We analyzed SWIFT XRT candidates (Evans et al. GCNC42382, https://www.swift.ac.uk/xrt_products/TILED_GRB00139/ )
The first one ( 04h 20m 03.25s 	-19° 19′ 50.1″) coincides with QSO (UV/GALEX, xray/eROSITA detection) in 2.8" from center of SWIFT error-box.

The second one (04 20 23.62 -19 15 45.2) coincides with second QSO (see VIZIER for full information) in 2.5" from the center of Swift error-box.

Both has complicated light curves without significant details at 23 oct 2025.

Observation and reduction will be continued.


[1] Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L
[2] Lipunov et al. 2022, Universe, Vol. 8(5), id.271
[3] Lipunov et a. 2019, ARep, vol.63, 293
[4] Lipunov V., Kornilov V., Gorbovskoy E., Tiurina N., Kuznetsov A.
 2023,  Astronomical Robotic Networks and Operative Multichanel Astrophysics,Lomonosov MSU PRESS, 591pp.
http://www.pereplet.ru/lipunov/625.html#625

GCN Circular 42394

Subject
GRB 251022A: DDOTI Optical Detection
Date
2025-10-23T11:09:52Z (3 days ago)
From
Rosa Leticia Becerra Godínez at Instituto de Astronomía, UNAM <rbecerra@astro.unam.mx>
Via
Web form
Rosa L. Becerra (U Roma), Simone Dichiara (Penn State University), Eleonora Troja (U Roma), Alan M. Watson (UNAM), Camila Angulo Valdez (UNAM), Sahil Atri (U Roma), Nat Butler (ASU), Tsvetelina Dimitrova (ASU), Alexander Kutyrev (GSFC/UMD), William H. Lee (UNAM), Océlotl López (UNAM) and Margarita Pereyra (UNAM) report:

We observed the field of GRB 251022A detected by Fermi/GBM (Fermi GBM Team, GCN Circ. 42380) and Fermi/LAT (Di Lalla et al., GCN Circ. 42384) with the DDOTI/OAN wide-field imager at the Observatorio Astronómico Nacional on Sierra San Pedro Mártir (http://ddoti.astroscu.unam.mx) on the night of 2025-10-23 UTC. 

DDOTI covered the entire Fermi/GBM error region from 07:00 UTC to 10:16 UTC (from T+8.4 h to T+ 11.7 h after the trigger), obtaining a total exposure of 80 minutes, alternating with other scientific programs.

Comparing our observations to the USNO-B1 and Pan-STARRS PS1 DR2 catalogues, our system automatically identified the fading nature of the optical candidate previously reported by GOTO (O’Neill et al., GCN Circ. 42386) with a preliminary AB magnitude of:

w = 19.45 +/- 0.04.
  
Further observations and analysis are on going. 

This value is not corrected for the Galactic extinction.

We thank the staff of the Observatorio Astronómico Nacional on the Sierra of San Pedro Mártir.

GCN Circular 42386

Subject
GRB 251022A: GOTO optical counterpart detection
Date
2025-10-23T08:26:52Z (3 days ago)
Edited On
2025-10-23T22:18:17Z (3 days ago)
From
d.s.oneill@bham.ac.uk
Edited By
Vidushi Sharma at NASA GSFC/UMBC <vidushi.sharma@nasa.gov> on behalf of d.s.oneill@bham.ac.uk
Via
Web form
D. O’Neill, M. Wortley, B. P. Gompertz, R. Starling K. Ackley, M. Dyer, J. Lyman, K. Ulaczyk, D. Steeghs, D. Galloway, V. Dhillon, P. O'Brien, G. Ramsay, K. Noysena, R. Kotak, R. Breton, J. Casares, L. Nuttall, B. Godson, T. Killestein, A. Kumar, M. Pursiainen report on behalf of GOTO collaboration:

We report on observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) in response to GRB 251022A (Fermi GBM team, GCN 42380; Di Lalla et al. GCN 42384). Targeted observations were performed beginning at 2025-10-23 00:58:21 UT, (+2.4h post trigger) and continued through to 2025-10-23 05:04:03 UT (+6.5h post trigger). 161 images were taken, across 10 unique pointings, covering 219.8 square degrees within the 90% localisation contour. ~89.9% of the total 2D localisation probability was covered, with an average 5-sigma depth of 20.5 mag. Each observation consisted of 4x90s exposures in the GOTO L-band (400-700 nm). Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations of the same pointings.

We detect a new optical source, GOTO25iym, with coordinates:
RA,DEC (J2000) = 65.497023, -18.9195 | 04:21:59.29, -18:55:10.19

This position lies on the 92% contour of the Fermi/GBM localisation and is offset by 0.41 degrees from the Fermi/LAT position (90% statistical uncertainty: 0.32 deg; Di Lalla et al., GCN 42384).
The source was initially detected with AB magnitude L = 18.21 ± 0.03 mag (+2.4h), before fading to L = 18.82 ± 0.06 mag (+4.67h). We find no evidence of this source prior to the GRB trigger time in the previous GOTO observation taken at 2025-10-22 14:20:35 UT (8.23h pre-trigger) down to a 5-sigma depth of L > 19.54 AB mag.

Despite the mild inconsistency with the Fermi/LAT position, which may be explained by the unaccounted-for systematic uncertainty, the power-law decay seen across three epochs combined with the recent deeper non-detection at the position pre-GRB strongly suggest that GOTO25iym is the afterglow of GRB 251022A.

Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and are not corrected for Galactic extinction.

GOTO (https://goto-observatory.org) is a network of telescopes that is principally funded by the STFC and operated at the Roque de los Muchachos Observatory on La Palma, Spain, and Siding Spring Observatory in NSW, Australia, on behalf of a consortium including the University of Warwick, Monash University, Armagh Observatory & Planetarium, the University of Leicester, the University of Sheffield, the National Astronomical Research Institute of Thailand (NARIT), the University of Turku, the University of Portsmouth, the University of Manchester and the Instituto de Astrofisica de Canarias (IAC).

GCN Circular 42384

Subject
GRB 251022A: Fermi-LAT detection
Date
2025-10-23T07:29:47Z (3 days ago)
From
Elisabetta Bissaldi at Politecnico and INFN Bari <elisabetta.bissaldi@ba.infn.it>
Via
Web form
N. Di Lalla (Stanford Univ.), D. Kocevski (NASA/MSFC), N. Omodei (Stanford Univ.), S. Cutini (INFN Perugia) A. Holzmann Airasca (UniTrento and INFN Bari), F. Longo (University and INFN, Trieste) and E. Bissaldi (Politecnico and INFN Bari) report on behalf of the Fermi-LAT Collaboration:


On October 22, 2025, Fermi-LAT detected high-energy emission from GRB 251022A, which was also detected by Fermi-GBM (trigger 782865260 / 251022940, GCN 42380). The best LAT on-ground location is found to be:

RA, Dec = 65.38, -19.31 (J2000)

with an error radius of 0.32 deg (90 % containment, statistical error only). This was 36 deg from the LAT boresight at the time of the GBM trigger (T0 = 22:34:15.26 UT).

The data from the Fermi-LAT shows a significant increase in the event rate that is spatially and temporally correlated with the GBM emission with high significance. The photon flux above 100 MeV in the time interval 0 - 300 s after the GBM trigger is (5.4 ± 2.0) E-6 ph/cm2/s. The estimated photon index above 100 MeV is -2.5 ± 0.5. The highest-energy photon is a 2 GeV event which is observed ~ 71 seconds after the GBM trigger.

A Swift ToO has been approved for this burst.

The Fermi-LAT point of contact for this burst is Sara Cutini (sara.cutini@pg.infn.it).


The Fermi-LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden.

GCN Circular 42382

Subject
GRB 251022A: Tiled Swift observations
Date
2025-10-23T05:56:57Z (3 days ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email

P. A. Evans (U. Leicester) reports on behalf of the Swift team:

Swift has initiated a series of observations, tiled on the sky, of the
Fermi/LAT GRB 251022A. Automated analysis of the XRT data will
be presented online at https://www.swift.ac.uk/xrt_products/TILED_GRB00139

Any uncatalogued X-ray sources detected in this analysis will be
reported on this website and via GCN COUNTERPART notices. The probability of finding
serendipitous sources, unrelated to the Fermi/LAT event is high: any X-ray source
considered to be a probable afterglow candidate will be reported via a GCN Circular
after manual consideration.

Details of the XRT automated analysis methods are detailed in Evans et
al. (2007, A&A, 469, 379; 2009, MNRAS, 397, 1177 and 2014, ApJS, 210, 8).

This circular is an official product of the Swift-XRT team.

GCN Circular 42381

Subject
LAT GRB251022A: Global MASTER-Net observations report
Date
2025-10-23T03:11:21Z (4 days ago)
Edited On
2025-10-23T22:16:23Z (3 days ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
Edited By
Vidushi Sharma at NASA GSFC/UMBC <vidushi.sharma@nasa.gov> on behalf of Vladimir Lipunov at Lomonosov Moscow State University <lipunov@sai.msu.ru>
Via
email
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) was pointed to the LAT GRB251022.94 (trigger No 782865260,04h 21m 31.18s , -19d 18m 35.6s, R=0.32) errorbox  13 sec after notice time and 16215 sec after trigger time at 2025-10-23 03:04:30 UT, with upper limit up to  17.2 mag. Observations started at twilight.  The observations began at zenith distance = 32 deg. The sun  altitude  is -10.1 deg. 

The galactic latitude b = -41 deg., longitude l = 216 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=3021522

We obtain a following upper limits.  

Tmid-T0  |      Date Time      |          Site       |             Coord (J2000)          |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________

   16245 | 2025-10-23 03:04:30 |         MASTER-SAAO | (04h 21m 02.62s , -19d 31m 07.4s) |   C |    60 | 17.2 |        
   16245 | 2025-10-23 03:04:30 |         MASTER-SAAO | (04h 19m 05.26s , -19d 15m 42.2s) |  P\ |    60 | 16.7 |        
   16324 | 2025-10-23 03:05:49 |         MASTER-SAAO | (04h 21m 02.39s , -19d 31m 03.5s) |   C |    60 | 16.7 |        
   16324 | 2025-10-23 03:05:49 |         MASTER-SAAO | (04h 19m 05.05s , -19d 15m 37.8s) |  P\ |    60 | 16.6 |        
   16404 | 2025-10-23 03:07:08 |         MASTER-SAAO | (04h 19m 04.85s , -19d 15m 33.5s) |  P\ |    60 | 16.6 |        
Filter C is a clear (unfiltred) band. 


The observation and reduction will continue. 
The message may be cited.

GCN Circular 42380

Subject
GRB 251022A: Fermi GBM Final Real-time Localization
Date
2025-10-22T22:44:50Z (4 days ago)
From
Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply@GIOC.nsstc.nasa.gov>
Via
email
The Fermi GBM team reports the detection of a likely LONG GRB

At 22:34:15 UT on 22 Oct 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251022A (trigger 782865260.264246 / 251022940).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 74.5, Dec = -22.7 (J2000 degrees, equivalent to J2000 04h 58m, -22d 41'), with a statistical uncertainty of 1.9 degrees.

The angle from the Fermi LAT boresight is 29.0 degrees.

The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251022940/quicklook/glg_skymap_all_bn251022940.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/bn251022940/quicklook/glg_healpix_all_bn251022940.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251022940/quicklook/glg_lc_medres34_bn251022940.gif
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