GRB 250925A
GCN Circular 42514
Subject
GRB 250925A: VZLUSAT-2 detection
Date
2025-10-29T16:38:52Z (10 months ago)
From
Marianna Dafčíková at Masaryk University <500025@mail.muni.cz>
Via
Web form
M. Dafcikova, J. Ripa (Masaryk U.), A. Pal (Konkoly Observatory), N. Werner (Masaryk U.), M. Ohno (Hiroshima U.), L. Meszaros, B. Csak (Konkoly Observatory), H. Takahashi (Hiroshima U.), F. Munz , M. Topinka, F. Hroch, N. Husarikova, J.-P. Breuer (Masaryk U.), J. Hudec, J. Kapus, M. Frajt, M. Rezenov (Spacemanic s.r.o), R. Laszlo (Needronix), G. Galgoczi (Wigner Research Center/Eotvos U.), N. Uchida (ISAS/JAXA), T. Enoto (Kyoto U.), Zs. Frei (Eotvos U.), Y. Fukazawa, K. Hirose, H. Matake (Hiroshima U.), S. Hisadomi (Nagoya U.), Y. Ichinohe (Rikkyo U.), L. L. Kiss (Konkoly Observatory), T. Mizuno (Hiroshima U.), K. Nakazawa (Nagoya U.), H. Odaka (Univ of Tokyo), K. Torigoe (Hiroshima U.), P. Svoboda, V. Daniel, J. Dudas, M. Junas, J. Gromes (VZLU), I. Vertat (FEL ZCU) -- the VZLUSAT-2/GRB payload collaboration.
The long-duration GRB 250925A (Swift/BAT detection: GCN 41985) was detected by the GRB detector on board of the VZLUSAT-2 3U CubeSat (https://www.vzlusat2.cz/en/).
The data acquisition was performed by the GRB detector unit no. 0. The detection was confirmed at the peak time 2025-09-25 17:04:21 UTC. The T90 duration is 22 s and the significance during T90 reaches 6.6 sigma.
The light curve obtained by VZLUSAT-2 is available here:
https://vzlusat2.konkoly.hu/static/share/GRB250925A_GCN_VZLUSAT2.pdf
All VZLUSAT-2 detections are listed at: https://monoceros.physics.muni.cz/hea/VZLUSAT-2/
The GRB detectors on VZLUSAT-2 are a demonstration payload for a future CubeSat constellation (Werner et al. Proc. SPIE 2018). Two GRB modules of VZLUSAT-2 are placed in a perpendicular manner and each consists of a 75 x 75 x 5 mm3 CsI scintillator read out by a SiPM array, covering the energy range from ~30 keV to ~1000 keV. VZLUSAT-2 was launched on 2022 January 13 from Cape Canaveral.
GCN Circular 42030
Subject
GRB 250925A: MAO/AZT-22 optical observations
Date
2025-09-30T08:51:39Z (a year ago)
From
Yodgor Rajabov at UBAI <rajabov@astrin.uz>
Via
Web form
Y. Rajabov, O. Burkhonov, B.Abidkhanov, S. Ehgamberdiev, Y. Tillayev (UBAI), T. Boyqobilov, A. Shaymanov (Maidanak Observatory/UBAI) report on behalf of UBAI team.
We observed the field of GRB 250925A detected by Swift (Dichiara et. al, GCN 41985), at z=3.899 (Castro-Tirado et. al, GCN 41997), with the AZT-22 1.5m telescope of the Maidanak Observatory (MAO) starting on 2025-09-25 at 19:13:36 UT, i.e. ~2.18 hours since trigger. In total we obtained 6x300 s exposures in the R-band using 4kx4k CCD SNUCAM camera (Im et al., 2010).
The optical afterglow initially detected by NOT/ORM (Corcoran et. al, GCN 41990) and also observed (Saikia et. al, GCN 41986; Pavoni & Moretti et. al, GCN 41989; Bochenek & Perley, GCN 41991; Masi et. al, GCN 41992; Mendez et. al, GCN 41995; Castro-Tirado et. al, GCN 41997; Liu et. al, GCN 41998; Ochi et. al, GCN 41999; Xin et. al., GCN 42002; Rakotondrainibe et. al, GCN 42004; Pankov et. al, GCN 42005; Pankov et. al, GCN 42025 ) is detected in our stacked frames.
Preliminary photometry is as follows:
Date UTstart Exptime t-T0 Filter OT Err. UL Site/Telescope
(nxs) (mid, days)
2025-09-25 19:13:36 6x300 0.10011 R 21.74 0.17 21.82 MAO/AZT-22
All the data have been reduced by a single data processing pipeline, STDPipe (Karpov et al., 2022).
Images obtained in Johnson Cousins filters were calibrated using the Gaia DR3 Synphot catalog.
The data has not corrected for the Galactic extinction.
Maidanak astronomical observatory (MAO) is an observational facility of the Ulugh Beg Astronomical
Institute (UBAI), Uzbekistan Academy of Sciences (http://maidanak.uz/).
GCN Circular 42025
Subject
GRB 250925A: Mondy I-band optical observations
Date
2025-09-29T13:09:19Z (a year ago)
From
Nicolai Pankov at HSE, IKI RAS <colinsergesen@gmail.com>
Via
Web form
N. Pankov (HSE, IKI), A. Pozanenko (IKI), E. Klunko (ISTP) report on behalf of GRB-IKI-FuN:
We observed the field of GRB 250925A detected by Swift (Dichiara et. al, GCN 41985), at z=3.899 (Castro-Tirado et. al, GCN 41997), with the AZT-33IK 1.5m telescope of the Sayan Solar Observatory (Mondy) starting on 2025-09-27 at 14:45 UT, i.e. ~1.93 days since trigger. In total we obtained 45x120 s exposures in the I-band using CMOS photometer. The optical afterglow initially detected by NOT/ORM (Corcoran et. al, GCN 41990) and also observed by (Saikia et. al, GCN 41986; Pavoni & Moretti et. al, GCN 41989; Bochenek & Perley, GCN 41991; Masi et. al, GCN 41992; Mendez et. al, GCN 41995; Castro-Tirado et. al, GCN 41997; Liu et. al, GCN 41998; Ochi et. al, GCN 41999; Xin et. al., GCN 42002; Rakotondrainibe et. al, GCN 42004; Pankov et. al, GCN 42005) is not visible in the stacked image. Preliminary photometry and observation properties are presented below:
Date UTstart Exptime t-T0 Filter OT Err. UL FWHM
(nxs) (mid, days) (3sigma) (")
2025-09-27 14:45:07 45x120 1.93451 I n/d n/d 22.3 1.6
The photometry was calibrated against nearby USNO-B1.0 stars (I-mags) and not corrected for the Galactic extinction.
GCN Circular 42017
Subject
GRB 250925A: Swift-XRT refined Analysis
Date
2025-09-27T18:53:06Z (a year ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
A. Melandri (INAF-OAR), 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), T. Sbarrato (INAF-OAB), P. D'Avanzo
(INAF-OAB) and P.A. Evans report on behalf of the Swift-XRT team:
We have analysed 7.8 ks of XRT data for GRB 250925A, from 3.7 ks to
172.4 ks after the trigger. The data are entirely in Photon Counting
(PC) mode. Using 4854 s of PC mode data and 10 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 = 341.21377, +46.55568
which is equivalent to:
RA (J2000): 22h 44m 51.31s
Dec(J2000): +46d 33' 20.5"
with an uncertainty of 2.0 arcsec (radius, 90% confidence).
The light curve can be modelled with a power-law decay with a decay
index of alpha=0.60 (+/-0.11).
A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.04 (+0.18, -0.17). The
best-fitting absorption column is 3.1 (+0.7, -0.5) x 10^21 cm^-2,
consistent with the Galactic value of 2.6 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 3.7 x 10^-11 (5.7 x
10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
Total column: 3.1 (+0.7, -0.5) x 10^21 cm^-2
Galactic foreground: 2.6 x 10^21 cm^-2
Excess significance: <1.6 sigma
Photon index: 2.04 (+0.18, -0.17)
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/01352124.
This circular is an official product of the Swift-XRT team.
GCN Circular 42007
Subject
GRB 250925A: Swift/UVOT Upper Limits
Date
2025-09-26T16:33:59Z (a year ago)
From
noelklin@umbc.edu
Via
Web form
N. J. Klingler (NASA-GSFC/UMBC/CRESST II) reports on behalf of the
Swift-UVOT team:
Swift-UVOT has performed follow-up observations of the Swift-BAT-detected burst GRB 250925A (Dichiara et al. GCN 41985), collecting 6.0 ks of observations between T0+3.74 ks and T0+16.74 ks. No source was detected in the UVOT data at the position of the optical source detected by the Nordic Optical Telescope (NOT) reported by Corcoran et al. (GCN 41990; RA, Dec = 22 44 51.31, +46 33 21.3), which is also consistent with the enhanced position of the X-ray source detected by Swift-XRT reported by Page et al. (GCN 41988; RA, Dec = 22 44 51.30, +46 33 20.6).
3-sigma upper limits (AB) using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) are:
Filter T_start(s) T_stop(s) Exp(s) Mag
white 4150.3 4350.1 199.80 >21.55
white 9527.3 10434.5 907.20 >22.41
B 3945.3 5554.0 1608.70 >21.16
U 3739.8 3939.6 199.80 >20.48
U 5175.9 5375.7 199.80 >20.52
V 4560.9 4760.7 199.80 >19.94
V 15320.0 16227.1 907.10 >20.81
W1 4971.0 5170.7 199.70 >20.10
W2 4356.1 4555.9 199.80 >20.10
W2 10440.9 11158.4 717.50 >21.02
M2 4765.8 4965.6 199.80 >19.99
M2 16232.4 16737.3 504.90 >20.67
The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.254 in the direction of the burst (Schlegel et al. 1998).
GCN Circular 42006
Subject
GRB 250925A: Swift-BAT refined analysis
Date
2025-09-26T15:51:01Z (a year ago)
From
Hans Krimm at NSF/NASA-GSFC <hkrimm@nsf.gov>
Via
email
S. D. Barthelmy (GSFC), S. Dichiara (PSU), R. Gupta (GSFC),
H. A. Krimm (NSF), S. Laha (GSFC/UMBC), A. Y. Lien (U Tampa),
C. B. Markwardt (GSFC), M. J. Moss (GSFC), D. M. Palmer (LANL),
T. Parsotan (GSFC), D. Sadaula (GSFC/UMBC), T. Sakamoto (AGU)
(i.e. the Swift-BAT team):
Using the data set from T-240 to T+962 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 250925A (trigger #1352124)
(Dichiara, et al., GCN Circ. 41985). The BAT ground-calculated position is
RA, Dec = 341.207, 46.549 deg which is
RA(J2000) = 22h 44m 49.7s
Dec(J2000) = +46d 32' 57.0"
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 76%.
The mask-weighted light curve shows a broad, multi-peaked structure starting at ~T-25 sec and decaying to background by T+50 sec. T90 (15-350 keV) is 64.51 +- 6.59 sec (estimated error including systematics).
The time-averaged spectrum from T-23.52 to T+64.42 sec is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
1.87 +- 0.09. The fluence in the 15-150 keV band is 2.7 +- 0.1 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+0.19 sec in the 15-150 keV band
is 1.2 +- 0.2 ph/cm2/sec. All the quoted errors are at the 90% confidence
level.
The results of the batgrbproduct analysis are available at
https://swift.gsfc.nasa.gov/results/batgrbcat/BAT_refined_circular/1352124
GCN Circular 42005
Subject
GRB 250925A: Mondy and AbAO optical observations
Date
2025-09-26T15:27:34Z (a year ago)
Edited On
2025-09-29T13:35:15Z (a year ago)
From
Nicolai Pankov at HSE, IKI RAS <colinsergesen@gmail.com>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of Nicolai Pankov at HSE, IKI RAS <colinsergesen@gmail.com>
Via
Web form
N. Pankov (HSE, IKI), A. Pozanenko (IKI), E. Klunko (ISTP), R. Ya. Inasaridze (AbAO) report on behalf of GRB-IKI-FuN:
We observed the field of GRB 250925A detected by Swift (Dichiara et. al, GCN 41985) at z=3.899 (Castro-Tirado et. al, GCN 41997) with the AZT-33IK 1.5m telescope of the Sayan Solar Observatory (Mondy) and the AS-32 0.7m telescope of the Abastumani Observatory (AbAO). The observations started at AbAO on 2025-09-25 at 19:24 UT, i.e. ~0.097 days (~2.3 hr) since trigger. In total we obtained 30x120 s exposures with AZT-33IK, and 85x60 s exposures with AS-32. The optical afterglow initially detected by NOT/ORM (Corcoran et. al, GCN 41990) and also observed by (Saikia et. al, GCN 41986; Pavoni & Moretti et. al, GCN 41989; Bochenek & Perley, GCN 41991; Masi et. al, GCN 41992; Mendez et. al, GCN 41995; Castro-Tirado et. al, GCN 41997; Liu et. al, GCN 41998; Ochi et. al, GCN 41999; Xin et. al., GCN 42002; Rakotondrainibe et. al, GCN 42004) is clearly visible in the stacked images from Mondy. Preliminary photometry is as follows:
Date UTstart Exptime t-T0 Filter OT Err. UL Site/Telescope
(nxs) (mid, days) (3sigma)
2025-09-25 19:24:44 79x60 0.12486 R n/d n/d 21.0 AbAO/AS-32
2025-09-25 20:00:15 6x120 0.12626 R 21.47 0.19 22.3 Mondy/AZT-33IK
2025-09-25 20:12:15 6x120 0.13460 R 21.26 0.15 22.2 Mondy/AZT-33IK
2025-09-25 20:24:16 6x120 0.14294 R 21.32 0.18 22.3 Mondy/AZT-33IK
2025-09-25 20:36:16 6x120 0.15128 R 21.26 0.14 22.3 Mondy/AZT-33IK
2025-09-25 20:48:16 6x120 0.15962 R 21.79 0.24 22.3 Mondy/AZT-33IK
The photometry was calibrated against nearby USNO-B1.0 stars (R2-mags) and not corrected for the Galactic extinction. Using all available r-data we estimate a temporal slope of alpha = -1.17 +/- 0.05.
GCN Circular 42004
Subject
GRB 250925A: COLIBRÍ photometric redshift
Date
2025-09-26T15:11:23Z (a year ago)
From
Ny Avo Rakotondrainibe at LAM <nyavo.rakotobe@gmail.com>
Via
Web form
N. A. Rakotondrainibe (LAM), Enrique Moreno Méndez (UNAM), Alan M. Watson (UNAM), Benjamin Schneider (LAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (OCA), Rosa L. Becerra (U Roma), 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), Fredd Sánchez Álvarez (UNAM), and Antonio de Ugarte Postigo (LAM):
COLIBRÍ performed follow-up observations of the Swift GRB 250925A (Dichiara et al., GCN Circ. 41985, Moreno Méndez et al., GCN Circ. 41995) from 2025-09-26 04:47 to 06:46 UTC (from 11.7 to 13.7 hours after the trigger) and obtained 16/16 minutes of exposure in the g/y filters. We report a detection in the y-filter, with a magnitude of y = 20.64 +/- 0.13 mag and a non-detection of the burst in the g-filter with a 3-sigma upper limit of g > 23.75 mag. The photometry was performed using STDWeb/STDPipe (Karpov 2025), was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction.
After correcting for the Galactic foreground extinction corresponding to a reddening of E(B-V) = 0.212 mag (Schlafly & Finkbeiner 2011) and fitting a power-law model to the grizy-bands using the LMC extinction curve, we derive a photometric redshift of z = 4.20+0.34-0.52 (1-sigma c.l.), according to the g- and r-band dropouts with g-r > 0.68 mag and r-i ~ 1.45 mag. Our result is consistent with the GTC/OSIRIS+ redshift of z=3.899 (Castro-Tirado et al., GCN Circular 41997).
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 42002
Subject
GRB 250925A: SVOM/GWAC-F60A upper limit
Date
2025-09-26T13:10:46Z (a year ago)
From
Liping Xin at NAOC, SVOM <xlp@nao.cas.cn>
Via
Web form
L. P. Xin, X. H. Han, J. Wang, P. P. Zhang, W. L. Dong, H. L. Li, C. WU, Y. L. Qiu, X .M. Lu, R. S. Zhang, Y. Xu, L. Huang, H. B. Cai, Y. J. Xiao, L. Lan, W. J. Xie, Z. H. Yao, J. Y. Wei(NAOC), X. G. Wang, E. W. Liang(GXU) report on behalf of the SVOM follow-up team:
We observed the field of GRB 250925A (Dichiara et al., GCN 41985) with the GWAC-F60A at Xinglong Observatory, China. F60A started observing at 2025-09-25T17:05:15 UTC, about 49 sec after the burst.
After the image stacking with the exposure time 9*20sec, we do not detected the optical counterpart at the location (Corcoran et al., GCN 41990, Bochenek et al., GCN 41991, Masi et al., GCN 41992,Méndez et al., GCN 41995, Castro-Tirado et al., GCN 41997, Liu et al., GCN 41998) within the XRT error box (Page et al., GCN 41988). The upper limit of R~17.0 mag for GWAC-F60A at mid time of 132 seconds after burst.
GCN Circular 42001
Subject
GRB 250925A/EP250925a: EP-WXT detection
Date
2025-09-26T13:07:12Z (a year ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
H. Zhou, D. F. Hu (PMO, CAS), Z. H. Yang, Q. C. Zhao (IHEP, CAS), Y. L. Wang (NAO, CAS; ICE, CSIC-IEEC) and C. C. Jin (NAO, CAS) on behalf of the Einstein Probe (EP) team:
We report on the detection of a fast X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP250925a. This transient was found in the ground-processed data, and consistent with GRB250925A in terms of time and space (Dichiara et al., GCN 41985). The start time of EP250925a is around 2025-09-25T17:03:22 UTC. The ground-porcessed WXT location of GRB 250925A is R.A. = 341.205 deg, DEC = 46.564 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic), which is consistent with the localization reported by other groups (Dichiara et al., GCN 41985; Page et al., GCN 41988; Corcoran et al., GCN 41990; Bochenek et al., GCN 41991; Masi et al., GCN 41992; Méndez et al., GCN 41995; Castro-Tirado et al., GCN 41997; Liu et al., GCN 41998).
The analysis of the WXT data shows that the event lasted for about 200 seconds with a peak flux of 1.5 x 10^-8 erg/s/cm^2. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 2.58 x 10^21 cm^-2 and a photon index of 1.18 +/- 0.18. The derived average unabsorbed 0.5-4 keV flux is (5.1 +/- 0.5) x 10^-9 erg/s/cm^2.
Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics).
GCN Circular 41999
Subject
GRB 250925A : MITSuME Akeno optical upper limits
Date
2025-09-26T11:39:31Z (a year ago)
From
ochi.a.21f9@m.isct.ac.jp
Via
Web form
A. Ochi, Y. Kubo, I. Takahashi, R. Kato, H. Hagio, M. Sasada, H. Seki, S. Joshima, Y. Yatsu and N. Kawai (Science Tokyo) report on behalf of the MITSuME collaboration:
We observed the field of GRB 250925A detected by Swift/BAT (Dichiara et al. GCN 41985) with the optical three-color (g', Rc, and Ic) CCD cameras attached to the MITSuME 50-cm telescope Akeno.
The observation started at 2025-09-25 17:05:14 UT (48 seconds after the Swift/BAT trigger). We stacked the images with good conditions. We did not detect any obvious point sources at the position reported by Saikia et al., GCN 41986, Pavoni et al., GCN 41989, Corcoran et al., GCN41990, Bochenek et al., GCN41991, Gianluca et al., GCN41992, Enrique et al., GCN41995, Castro-Tirado et al., GCN41997. We obtained the 5-sigma limits of the stacked images as follows:
T0+[s] | MID-UT | T-EXP[sec] | 5-sigma limits
------------------------------------------------------------------------------------------------
633 | 2025-09-25 17:15:00 | 600 | g'>18.2, Rc>18.1, Ic>17.6
------------------------------------------------------------------------------------------------
T0+ : Elapsed time after the trigger
T-EXP: Total Exposure time
We used the PS1 catalog for flux calibration. The catalog magnitudes in PS1 g, r and i bands were converted to our g', Rc and Ic band magnitudes following Tonry et al. (2012), Table 6. The magnitudes are expressed in the AB system. The images were processed in real-time through the MITSuME GPU reduction pipeline (Niwano et al. 2021, PASJ; https://github.com/MNiwano/Eclaire).
GCN Circular 41998
Subject
GRB 250925A: JinShan optical observations
Date
2025-09-26T09:44:45Z (a year ago)
Edited On
2025-09-26T15:43:53Z (a year ago)
From
liuxing@nao.cas.cn
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of liuxing@nao.cas.cn
Via
Web form
GRB 250925A: JinShan optical observations
X. Liu (NAOC), S.Y. Fu (HUST) S.Q. Jiang, J. An, Z.P. Zhu, D. Xu (NAOC), A.D. Zhu, L. Lei (HUST), J.Z. Liu (XAO) report on behalf of a large collaboration:
We observed the field of GRB 250925A detected by Swift/BAT (Dichiara, GCN 41985), using the 100cm-A (100A) and 100cm-C telescope (100C) of the JinShan project, located at Altay, Xinjiang, China. The 100A observation automatically started at 17:05:21.07 UT on 2025-09-25, i.e., 54.57 seconds after the BAT trigger, and the 100C observation started one hour later. A series of frames were obtained in the Sloan r- and z- bands.
The reported optical afterglow (Corcoran et al., GCN41990; Bochenek et al., GCN 41991; Masi et al., GCN 41992; Méndez et al., GCN 41995; Méndez et al., GCN 41995) was detected in our stacked 100C images in both r- and z- bands. Preliminary photometric results are as follows:
T-mid (hr) | Filter | Exposure | Mag
2.05 | z | 24x180s | 20.26 +/- 0.15
3.02 | r | 8x200s | 22.10 +/- 0.20
calibrated with nearby Pan-STARRS1 DR2 stars without the Galactic extinction correction.
We acknowledge the excellent support from T.Q. Chen and J.F. Zhang for enabling these observations.
GCN Circular 41997
Subject
GRB 250925A: 1.5m OSN optical detection and redshift with the 10.4m GTC/OSIRIS+
Date
2025-09-26T09:41:57Z (a year ago)
From
Alberto Castro-Tirado at Inst.de Astro. de Andalucia <ajct@iaa.es>
Via
email
A. J. Castro-Tirado, A. Sota, R. Sanchez-Ramirez, S. Guziy, M.D. Caballero-Garcia, S.-Y. Wu and I. Perez-Garcia (IAA-CSIC), D. Garcia-Alvarez (GTC, IAC), A. Perez-Romero (GTC), A. Cabrera-Lavers (IAC, GTC), S. B. Pandey (ARIES), M. Gritsevich (Univ. of Helsinki), Y.-D. Hu (GXI), A. Nicuesa Guelbenzu (Tautenburg Obs.), L. Piro (INAF/IAPS) and B.-B. Zhang (NJU), on behalf of a larger collaboration, report:
Following the detection of GRB 250925A by Swift (Dichiara et al. GCNC 41985) we conducted optical follow-up observations with the 1.5m OSN at Observatorio de Sierra Nevada (Granada), starting on Sep 25 at 21:47 UT. At the position of the X-ray afterglow (Page et al. GCNC 41988), we detect the optical afterglow (with I = 19.7 +/- 0.1) previously discovered at the NOT (Corcoran et al. (GCNC 41990) and also reported by means of other ground-based telescopes (Bochenek et al. GCNC 41991, Masi et al. GCNC 41992, Moreno Mendez et al. GCNC 41995).
Additional observations were conducted with the 10.4m GTC telescope, at the Spanish Roque de los Muchachos Observatory, on the island of La Palma, equipped with the OSIRIS+ instrument. The spectroscopic observations consisted of 900s exposures using grisms R1000B and R2500I, with a joint spectral coverage between 3,600 and 10,000 A. The observations started on Sep 25, 21:57 UT (i.e. 4.9 h after the burst trigger).
We detect a strong DLA at ~6000 A, among a plethora of metal absorption lines, that we interpret as coming from NV, SiII, SiII*, OI, CII, SiIV, CIV, FeII, FeII*, AlII, AlII, NiII, MgII, MgI at z=3.899, consistent with the COLIBRI photometry as suggested (Moreno Mendez et al. GCNC 41995). The detection of fine structure features confirms the association of this absorption system to GRB 250925A.
GCN Circular 41995
Subject
GRB 250925A: COLIBRÍ optical photometry of the afterglow
Date
2025-09-26T05:52:29Z (a year ago)
From
enriquemm@astro.unam.mx
Via
Web form
Enrique Moreno Méndez (UNAM), N. A. Rakotondrainibe (LAM), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (OCA), Rosa L. Becerra (U Roma), 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), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM), and Antonio de Ugarte Postigo (LAM):
We imaged the field of the Swift GRB 250925A (Dichiara et al., GCN Circ. 41985) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2025-09-26 02:45 to 04:30 UTC (from 9.7 to 11.4 hours after the trigger) and obtained 32/32/64 minutes of exposure in the r/i/z filters.
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 source reported by Corcoran et al. (GCN Circ. 41990) at preliminary magnitudes of:
r = 23.07 +/- 0.18
i = 21.62 +/- 0.07
z = 21.02 +/- 0.06
The source has faded, confirming that it is the afterglow. Compared to the early observations reported by Corcoran et al., we derive a temporal index of about -0.9 in z.
The very red r-i color is suggestive of a GRB at a moderately high redshift with a break in r.
Further observations are ongoing.
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 41992
Subject
GRB 250925A: Optical Observations via Virtual Telescope Project, Italy
Date
2025-09-26T00:08:38Z (a year ago)
From
Gianluca Masi at Virtual Telescope Project <gianluca@bellatrixobservatory.org>
Via
Web form
Gianluca Masi, Virtual Telescope Project (Italy), reports:
We attempted to observe the optical counterpart (Dichiara et al., GCN 41985) of GRB 250925A with the 14” robotic unit available at the Virtual Telescope Project facility in Manciano, Italy, equipped with a KAF-3200E based CCD camera, its QE peaking (90%) in the red part of the spectrum.
We collected 9, 300-second unfiltered exposures, then we averaged them. The central time of the resulting stack was 25 Sept., 23:27 UTC, that is about 6.38 hours after the burst.
We detected a faint object at the following position (J2000.0):
RA: 22 44 51.32
Decl.: +46 33 20.7
R= 21.5 (assuming R-mags from Gaia DR2 for the reference stars).
This position is consistent with Corcoran et al., GCN 41990 and Bochenek et al., GCN 41991
GCN Circular 41991
Subject
GRB250925A: Liverpool Telescope optical observations
Date
2025-09-25T21:46:51Z (a year ago)
From
A. Bochenek at Liverpool John Moores University <a.m.bochenek@2023.ljmu.ac.uk>
Via
Web form
A. Bochenek and D. A. Perley (LJMU) report:
We observed the field of GRB250925a detected by Swift (Dichiara et al., GCN 41915) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 5x100s exposures in the SDSS i’ filter starting at 2025-09-25 20:59:51 UT, approximately 3.92 hours after the trigger.
We report a detection in the stacked image at the position of the candidate optical counterpart (Corcoran et al., GCN 41990), inside the XRT error field (Page et al., GCN 41988). The magnitude of the candidate afterglow is i = 20.78 ± 0.03. The photometry was calibrated using nearby PanSTARRS secondary standards and was not corrected for extinction.
GCN Circular 41990
Subject
GRB 250925A: NOT optical afterglow candidate
Date
2025-09-25T21:19:47Z (a year ago)
From
Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani@nbi.ku.dk>
Via
Web form
G. Corcoran (UCD), L. Cotter (UCD), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), A. de Ugarte Postigo (LAM), B. Schneider (LAM), K. Valeckas (NOT and NBI), report on behalf of a larger collaboration:
We observed the field of GRB 250925A (Dichiara et al., GCN 41985) using the Nordic Optical Telescope (NOT) equipped with the ALFOSC imager. Observations started on 2025 Sep 25.847 UT (3.254 hr after trigger) and consisted of 3x300 s and 5x200 s in each of the SDSS r and z bands.
Within the UVOT-enhanced XRT position (Page et al., GCN 41988), we detect an object which is not seen in Pan-STARRS archival imaging of this field. Its coordinates are:
RA(J2000) = 22:44:51.31
Dec(J2000) = +46:33:21.3
with an estimated error of 0.3”. Calibrated against nearby objects from Pan-STARRS, we measure AB magnitudes (not corrected for Galactic extinction):
r = 21.99 +- 0.10 (3.30 hr after the trigger)
z = 19.96 +- 0.05 (3.69 hr after the trigger)
We note that this is a rather red r-z color, even considering the non-negligible but still modest Galactic extinction A_V ~ 0.75 mag along this line of sight (Schlafly & Finkbeiner 2011; doi:10.1088/0004-637X/737/2/103). This might indicate either an intrinsic spectral slope, or unaccounted extinction in our Galaxy or in the GRB host.
GCN Circular 41989
Subject
GRB 250925A: Leavitt Observatory optical upper limit
Date
2025-09-25T21:19:01Z (a year ago)
From
leavittob@gmail.com
Via
Web form
E. Pavoni, L. Moretti (Leavitt Observatory, Italy)
Members of:
GRB/UAI - Gamma Ray Burst Section of Unione Astrofili Italiani
ATA - Associazione Tuscolana di Astronomia
In a large collaboration with:
M.G. Dainotti (National Astronomical Observatory of Japan), Y. Niino (Tokyo University, Institute of Astronomy), K. Kalinowski (Aarhus University, Department of Physics and Astronomy), report:
We observed the field of GRB 250925A detected by Swift (Dichiara et al., GCN 41985), using our Ritchey-Chrétien telescope (D=250 mm, F/D=8).
The observations began approximately 128 minutes after the trigger, stacking a set of CCD images of 180 seconds each, with good weather conditions. All images were processed by a single data processing pipeline based on astropy package (Astropy Collaboration et al., 2022ApJ...935..167A).
No credible candidate was detected in our stacked frame within the Swift error circle.
We derived the following upper limit:
| Mid-Time (UTC) | Filter | Exp. Time | Upper limit (3-sigma) |
| ------------------- | ------ | ----------- | ----------------------|
| 2025-09-25T19:42:51 | CR | 20x180 sec | 20.49 |
CR magnitude is unfiltered with R zero point.
The photometry was calibrated with the Pan-STARRS cat. (R-mags obtained via Lupton 2005 transformations). Not corrected for the Galactic extinction.
This upper limit is consistent with the report by GROWTH-India Telescope (Saikia et al., GCN 41986).
This message may be cited.
Reference:
https://leavittobservatory.altervista.org
GCN Circular 41988
Subject
GRB 250925A: Enhanced Swift-XRT position
Date
2025-09-25T20:39:16Z (a year ago)
From
K.L. Page at U Leicester <klp5@leicester.ac.uk>
Via
email
K.L Page, P.A. Evans and M.R. Goad (U. Leicester) report on behalf of the
Swift-XRT team:
Using 1810 s of XRT Photon Counting mode data and 4 UVOT images, we find
an astrometrically corrected X-ray position (using the XRT-UVOT alignment
and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec =
341.21375, 46.55573 which is equivalent to:
RA (J2000): 22 44 51.30
Dec (J2000): +46 33 20.6
with an uncertainty of 2.3 arcsec (radius, 90% confidence).
This position may be improved as more data are received. The latest
position can be viewed at http://www.swift.ac.uk/xrt_positions. Position
enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans
et al. (2009, MNRAS, 397, 1177).
This circular is an official product of the Swift-XRT team
GCN Circular 41986
Subject
GRB 250925A: GROWTH-India Telescope Upper Limits
Date
2025-09-25T19:01:36Z (a year ago)
From
V. Swain at IIT Bombay <vishwajeet.s@iitb.ac.in>
Via
Web form
A.P. Saikia, S. Patil, Y. Wagh, T. Mohan, V. Swain, 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 Swift GRB 250925A (Dichiara et al., GCN 41985), with 0.7m GROWTH-India Telescope (GIT). We started the observation at 2025-09-25 17:17:09 UT, i.e., 13 minutes after the GRB trigger. We obtained multiple exposures in g', r', and i' bands. We did not detect the source in our images within the Swift-BAT localization region. The photometric upper limits are as follow:
| MJD (mid) | Filter | tmid-t0 (min) | Exposure Time (sec) | Upper limit (AB) |
| ------------ | ------ | ------------ | ------------------- | ---------------- |
| 60943.727303 | g' | 22.88 | 300 | 20.5 |
| 60943.753831 | r' | 61.08 | 300 | 20.4 |
| 60943.730914 | i' | 28.08 | 300 | 19.5 |
The measurement is calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected for Galactic extinction.
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 41985
Subject
GRB 250925A: Swift detection of a burst
Date
2025-09-25T17:19:22Z (a year ago)
From
David Palmer at LANL <palmer@lanl.gov>
Via
email
S. Dichiara (PSU), R. Gupta (NASA GSFC),
N. J. Klingler (GSFC/UMBC/CRESSTII), S. Lanava (PSU),
K. L. Page (U Leicester), D. M. Palmer (LANL) and M. H. Siegel (PSU)
report on behalf of the Neil Gehrels Swift Observatory Team:
At 17:04:26 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 250925A (trigger=1352124). Swift could not immediately
slew to the burst due to an observing constraint.
The BAT on-board calculated location is
RA, Dec 341.201, +46.574 which is
RA(J2000) = 22h 44m 48s
Dec(J2000) = +46d 34' 25"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve is only available until
T+8s, but this shows a complex peak of at least 20 s duration.
The peak count rate was ~1400 counts/sec (15-350 keV), at ~1 sec
after the trigger.
Due to an observing constraint, Swift will not slew at this time. XRT and UVOT
data will be obtained later.
Burst Advocate for this burst is S. Dichiara (sbd5667 AT psu.edu).
Please contact the BA by email if you require additional information
regarding Swift followup of this burst. In extremely urgent cases, after
trying the Burst Advocate, you can contact the Swift PI by phone (see
Swift TOO web site for information: http://www.swift.psu.edu/)
GCN Circular 41984
Subject
Swift GRB 250925A: Global MASTER-Net observations report
Date
2025-09-25T17:14:34Z (a year ago)
Edited On
2025-09-29T13:35:34Z (a year ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@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-Tunka robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Applied Physics Institute, Irkutsk State University) was pointed to the Swift GRB250925.71 (trigger No 1352124,22h 44m 48.24s , +46d 34m 26.4s, R=0.05) errorbox 16 sec after notice time and 59 sec after trigger time at 2025-09-25 17:05:26 UT, with upper limit up to 12.9 mag. The observations began at zenith distance = 16 deg. The sun altitude is -40.0 deg.
The galactic latitude b = -11 deg., longitude l = 102 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=2999810
We obtain a following upper limits.
Tmid-T0 | Site |Filt.| Expt. | Limit| Comment
_________|_____________________|_____|_______|______|________
65 | MASTER-Tunka | P- | 10 | 12.9 |
65 | MASTER- | C | 10 | 16.6 |
Filter C is a clear (unfiltred) band.
The observation and reduction will continue.
The message may be cited.