EP251230a, GRB 251230A
GCN Circular 43301
Subject
GRB 251230A / EP251230a: GECAM-B detection
Date
2026-01-02T13:08:59Z (2 days ago)
From
guohx@ihep.ac.cn
Via
Web form
Hao-Xuan Guo, Chen-Wei Wang, Zheng-Hang Yu, Shao-Lin Xiong (IHEP) report on behalf of GECAM team:
GECAM-B was triggered in-flight by GRB 251230A / EP251230a at 2025-12-30T01:21:44.050 UTC (denoted as T0), which is also detected by Swift (Lanava et al., GCN #43252), EP-WXT (Li et al., GCN #43255 and Wang et al., GCN #43272) and Insight-HXMT/HE (Guo et al., GCN #43299).
According to the GECAM-B light curve in about 70-6000 keV, this burst mainly consists of multi-pulses with a duration (T90) of 71.2 +4.6/-8.2 s.
The GECAM-B light curve can be found here:
https://www.bursthub.cn//admin/static/gecambgrb251230A.png
Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission originally consists of two micro-satellites (GECAM-A and GECAM-B) launched in Dec. 2020. As the third member of GECAM constellation, GECAM-C was launched onboard SATech-01 experimental satellite in July 2022. GECAM mission is funded by the Chinese Academy of Sciences (CAS).
GCN Circular 43299
Subject
GRB 251230A / EP251230a: Insight-HXMT/HE detection
Date
2026-01-02T12:17:17Z (2 days ago)
From
guohx@ihep.ac.cn
Via
Web form
Hao-Xuan Guo, Chen-Wei Wang, Cheng-Kui Li, Shao-Lin Xiong, and Chao Zheng (IHEP) report on behalf of the Insight-HXMT team:
At 2025-12-30T01:22:22.000 (T0), Insight-HXMT/HE detected a burst, GRB 251230A / EP251230a, which is also detected by Swift (Lanava et al., GCN #43252) and EP-WXT (Li et al., GCN #43255 and Wang et al., GCN #43272).
The Insight-HXMT/HE light curve mainly consists of multiple pulses with T90 of 54.4 +11.6/-8.4 s. The 1s peak rate, measured from T0-0.70 s, is 797 cnts/sec. Insight-HXMT/HE detected a total of 10,311 counts from this burst.
The Insight-HXMT /HE light curve can be found here:
https://www.bursthub.cn//admin/static/hxmtgrb251230A.png
All measurements above are made with the CsI detectors of Insight-HXMT/HE operating in the Low-Gain mode with the energy range of about 300-3000 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 43282
Subject
GRB 251230A / EP251230a: SVOM/VT optical continued observations and upper limit
Date
2025-12-31T17:00:53Z (3 days ago)
From
Yinuo Ma <mayn@bao.ac.cn>
Via
Web form
Y. N. Ma, L. P. Xin, Y. L. Qiu, C. Wu, H. L. Li, Z. H. Yao, X. H. Han, Y. Xu, J. Wang, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA), J. X. Cao (GXU), W. L. Zhang (PMO) report on behalf of the SVOM/VT team.
SVOM/VT conducted continued observations of GRB 251230A / EP251230a detected by Swift/BAT and EP/WXT (Lanava et al., GCN 43252; Wang et al., GCN 43259; Osborne et al., GCN 43263; Wang et al., GCN 43272; Sbarrato et al., GCN 43275). The magnitudes of the optical afterglow (Li et al., GCN 43255; Lipunov et al., GCN 43256; Busmann et al., GCN 43258; Masi, GCN 43260; Ghosh et al., GCN 43262; Ma et al., GCN 43265; Starling et al., GCN 43267; He et al., GCN 43269; Tak et al., GCN 43270; Breeveld et al., GCN 43271; Gupta et al., GCN 43277; Sankar.K et al., GCN 43279; He et al., GCN 43280; Antier et al., GCN 43281) are:
mid time (h) | exposure time (s) | band | mag (AB)
-------------|-------------------|------|----------
16.51 | 37*50 | VT_B | 23.0+-0.3
29.48 | 41*50 | VT_B | >23.4
16.51 | 37*50 | VT_R | 22.5+-0.2
29.46 | 39*50 | VT_R | >23.1
Our photometry was not corrected for Galactic extinction. Further analysis is ongoing.
The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Centre for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS.
Happy New Year to everyone ! ! !
GCN Circular 43281
Subject
GRB 251230A: GRANDMA/TAROT Early Detection
Date
2025-12-31T14:25:21Z (3 days ago)
From
Dalya Akl at New York University Abu Dhabi <dka2010@nyu.edu>
Via
Web form
S. Antier (IJCLAB), A. Klotz (IRAP), D. Akl (NYUAD), C. Limonta (OCA), A. Dupin (OCA), Q. André (OCA), M. Coughlin (UNM), R. Strausbaugh (EIU), Z. Maksut (NU), E. Abdikamalov (NU), P. Hello (IJCLAB), S. Karpov (FZU), M. Pillas (IAP), C. Douzet (IJCLAB), Z. Wang (BNU), N. Kochiashvili (AbAO), A. Iskandar (XAO) on behalf of GRANDMA:
We observed the field of the fast X-ray transient GRB 251230A/EP251230a (Lanava et al., GCN 43252; Wang et al., GCN 43259; Osborne et al., GCN 43263; Wang et al., GCN 43272; Sbarrato et al., GCN 43275) using TAROT/TCA with no filter. The observations started at 01:22:07 UTC on the 30th of December 2025, 36s post Swift trigger time, and lasted for 3 hours.
We detected the optical afterglow candidate in the first (earliest) measurement with TAROT/TCA (60s exposure time), and we measured on 2025-12-30 01:23:19, r = 13.1 +/- 0.05 mag, after color correction. The data were reduced by a single data processing pipeline, STDPipe (Karpov et al., 2022), using the PS1 catalogue for reference.
Part of the light curve is public here on Skyportal/ICARE (https://skyportal-icare.ijclab.in2p3.fr) and also accessible in the public-report group of Skyportal: https://skyportal-icare.ijclab.in2p3.fr/public/sources/GRB-251230_012141/version/b0d22ea59d7dca3f28dc30442ec03598
We use the SkyPortal application (skyportal.io) to monitor our observational campaign (Coughlin et al. 2023).
The results are consistent with other measurements reported.
GRANDMA is a worldwide telescope network (grandma.ijclab.in2p3.fr) devoted to the observation of transients in the context of multi-messenger astrophysics (Antier et al. 2020 MNRAS 497, 5518). Kilonova-Catcher (KNC) is the citizen science program of GRANDMA (http://kilonovacatcher.in2p3.fr/).
GCN Circular 43280
Subject
GRB 251230A / EP251230a: further NOT optical observations revealing shallower decay or possible rebrightening
Date
2025-12-31T12:31:28Z (4 days ago)
From
luca.izzo@inaf.it
Via
Web form
L. He (NAOC), L. Izzo (INAF/OACN and DARK/NBI), A. Martin-Carrillo (UCD), A. Saccardi (CEA/Irfu), K. Valeckas (NOT & NBI) report on behalf of a larger collaboration:
We observed the optical counterpart (Lanava et al., GCN 43252; Li et al., GCN 43255; Busmann et al., GCN 43258; Masi, GCN 43260; Ghosh et al., GCN 43262; Ma et al., GCN 43265; Starling et al., GCN 43267; He et al., GCN 43269; Breeveld et al., GCN 43271; Sankar et al., GCN 43279) of GRB 251230A / EP251230a (Lanava et al., GCN 43252; Wang et al., GCN 43259; Osborne et al., GCN 43263), using the Nordic Optical Telescope (NOT), equipped with the ALFOSC camera. A series of 10 x 150s exposures was taken in the i band starting on 2025 Dec 31 at 04:46:27 (1.14 days after the Swift trigger).
The afterglow is detected in the final stacked images with an AB magnitude of i = 22.93 +/- 0.09 mag, at a mid-time of 1.15 days after the trigger. Our photometry was calibrated using nearby stars from the Pan-STARRS catalog and is not corrected for Galactic extinction.
This new epoch suggests that the fading of the optical afterglow has slowed down considerably from the decay index reported by He et al. GCN 43269. We note that, based on the colour measured in our earlier epoch, the r-band upper limit reported by Sankar et al. GCN 43279 suggests a possible rebrightening.
Happy New Year to everyone!!!
GCN Circular 43279
Subject
GRB 251230A/EP251230a: Optical upper limit with Kinder observations
Date
2025-12-31T10:29:09Z (4 days ago)
From
Janet Chen at National Central University <janetstars@gmail.com>
Via
Web form
A. Sankar.K, A. Aryan, T.-W. Chen, C.-S. Lin (all NCU), A. K. H. Kong (NTHU), J. H. Gillanders, S. J. Smartt (both Oxford), Y. J. Yang (NYUAD), Y.-H. Lee, M.-H. Lee, Y.-C. Pan, C.-C. Ngeow, C.-H. Lai, W.-J. Hou, H.-Y. Hsiao, H.-C. Lin, J.-K. Guo (all NCU), S. Yang, Z. N. Wang, L. L. Fan, G. H. Sun (all HNAS), H.-W. Lin (UMich), H. F. Stevance, S. Srivastav, L. Rhodes (all Oxford), M. Nicholl, M. Fulton, T. Moore, K. W. Smith, C. Angus, A. Aamer (all QUB), A. Schultz and M. Huber (both IfA, Hawaii) report:
We observed the field of the fast X-ray transient GRB 251230A/EP251230a (Lanava et al., GCN#43252; Wang et al., GCN#43259; Osborne et al., GCN#43263; Wang et al., GCN#43272; Sbarrato et al., GCN#43275) using the 40cm SLT at Lulin Observatory in Taiwan as part of the Kinder collaboration (Chen & Yang et al., 2025, ApJ, 983, 86, doi:10.3847/1538-4357/adb428). The first SLT epoch of observations started at 18:17 UTC on the 30th of December 2025 (MJD 61039.762), 16.91 hr after the Swift/BAT trigger.
We utilized the astroalign (Beroiz et al., 2020, A&C, 32, 100384) and astropy (Astropy Collaboration et al., 2022, ApJ, 935, 167) packages to align and stack the individual frames. In the stacked frame, we did not detect the proposed optical counterpart candidate (Li et al., GCN#43255; Busmann et al., GCN#43258; Masi et al., GCN#43260; Ghosh et al., GCN#43262; Ma et al., GCN#43265; Breeveld et al., GCN#43271), which has a tentative redshift upper limit of z < 2.2 (He et al., GCN#43269).
Moreover, we utilized AutoPhOT to perform the PSF photometry. The details of the observations and the measured 3-sigma upper limit (in the AB system) are as follows:
Telescope | Filter | MJD (start) | t-t0 (hr) | Exposure (s) | Magnitude | avg. Seeing | med. Airmass
SLT | r | 61039.762 | 16.91 | 300 * 24 | >22.5 | 2".10 | 1.17
Utilizing the rigorous Lulin Observatory optical follow-up of the Einstein-Probe-discovered FXTs within the first year of the mission's operation, we investigated the possible connection between FXTs and GRBs, as reported in Aryan et al. (2025), ApJS, 281, 20. Our upper limits are the deepest and latest among those reported (Starling et al., GCN#43267; Tak et al., GCN#43270).
The presented upper limit is calibrated using the field stars from the PanSTARRs DR2 and is not corrected for the expected Galactic foreground extinction of A_r = 0.05 mag in the direction of the transient (Schlafly & Finkbeiner, 2011). The methodology, details on the Lulin observatory telescopes, and a compilation of our optical follow-up campaign for FXTs discovered within the first year of operation of the Einstein-Probe mission are presented in Aryan et al., 2025, ApJS, 281, 20, doi:10.3847/1538-4365/adfc69.
GCN Circular 43277
Subject
GRB 251230A: 1.3m DFOT optical upper limit
Date
2025-12-31T09:38:27Z (4 days ago)
From
ANSHIKA GUPTA at ARIES <anshika05180@gmail.com>
Via
Web form
Anshika Gupta, Kuntal Misra, Pankaj Pawar, Dhruv Jain, Debalina Kar (ARIES) report:
We observed the field of GRB 251230A detected by Swift (Lanava et al. 2025, GCN 43252) with the 1.3m Devasthal Fast Optical Telescope (DFOT), located at the Devasthal Observatory of the Aryabhatta Research Institute of Observational Sciences (ARIES), India. The observations began on 2025-12-30 at 21:36:37 UT, ~ 20.24 hours after the Swift trigger. We have taken multiple frames with an exposure time of 300s in the R filter. We stacked the images after the alignment. We could not detect the optical emission in our stacked image within the error box of Swift/UVOT (Breeveld et al. 2025, GCN 43271). We obtain the following 3-sigma upper limit in the stacked image:
Date Start_UT T_start-T0 (hour) Filter Exp time (s) Magnitude
===============================================================
2025-12-30 21:36:37 ~20.24 R 300s*6 >22.3
The non-detection of the burst is consistent with Li et al. 2025, (GCN 43255); Lipunov et al. 2025, (GCN 43256); Busmann et al. 2025, (GCN 43258); Masi et al. 2025, (GCN 43260); Ghosh et al. 2025, (GCN 43262); Ma et al. 2025, (GCN 43265); Starling et al. 2025, (GCN 43267); He et al. 2025, (GCN 43269); Breeveld et al. 2025, (GCN 43271).
The magnitude is not corrected for the Galactic extinction in the direction of the burst. Photometric calibration is performed using the standard stars from the USNO-B1.0 catalogue.
GCN Circular 43275
Subject
GRB 251230A: Swift-XRT refined Analysis
Date
2025-12-31T01:48:14Z (4 days ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
T. Sbarrato (INAF-OAB), P. D'Avanzo (INAF-OAB), M.G. Bernardini
(INAF-OAB), D.N. Burrows (PSU), S. Lanava (PSU), S. Dichiara (PSU),
J.P. Osborne (U. Leicester), K.L. Page (U. Leicester) and P.A. Evans
report on behalf of the Swift-XRT team:
We have analysed 5.6 ks of XRT data for GRB 251230A, from 92 s to 50.9
ks after the trigger. The data comprise 329 s in Windowed Timing (WT)
mode (the first 6 s were taken while Swift was slewing) with the
remainder in Photon Counting (PC) mode.
The light curve can be modelled with a series of power-law decays. The
initial decay index is alpha=7.1 (+/-0.5). At T+129 s the decay
flattens to an alpha of 0.2 (+0.3, -1.1) before breaking again at T+194
s to a final decay with index alpha=1.51 (+/-0.05).
A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.80 (+/-0.06). The
best-fitting absorption column is 4.4 (+1.3, -1.2) x 10^20 cm^-2, in
excess of the Galactic value of 1.9 x 10^20 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 1.82 (+/-0.14) and a
best-fitting absorption column of 5.7 (+3.6, -3.2) x 10^20 cm^-2. The
counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum is 3.6 x 10^-11 (4.1 x 10^-11) erg cm^-2
count^-1.
A summary of the PC-mode spectrum is thus:
Total column: 5.7 (+3.6, -3.2) x 10^20 cm^-2
Galactic foreground: 1.9 x 10^20 cm^-2
Excess significance: 2.0 sigma
Photon index: 1.82 (+/-0.14)
If the light curve continues to decay with a power-law decay index of
1.51, the count rate at T+24 hours will be 2.3 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 8.4 x
10^-14 (9.4 x 10^-14) erg cm^-2 s^-1.
The results of the XRT-team automatic analysis are available at
https://www.swift.ac.uk/xrt_products/01429020.
This circular is an official product of the Swift-XRT team.
GCN Circular 43272
Subject
EP251230a / GRB 251230A: refined analysis of the EP-WXT and EP-FXT observations
Date
2025-12-30T14:21:51Z (4 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
B.T. Wang (YNAO, CAS), J.P. Chen (SYSU), D. Zhu, K.J. Zhang (YNU), and Z.X. Ling (NAO, CAS) on behalf of the Einstein Probe (EP) team:
The fast X-ray transient EP251230a triggered the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Wang et al., GCN 43259) and Swift/BAT as GRB 251230A (Lanava et al., GCN 43252, Osborne et al., GCN 43263), and was followed by several optical telescopes (Li et al., GCN 43255, Lipunov et al., GCN 43256, Busmann et al., GCN 43258, Masi et al., GCN 43260; Ghosh et al., GCN 43262; Ma et al., GCN 43265, Starling et al., GCN 43267, He et al., GCN 43269, Tak et al., GCN 43270, Breeveld et al., GCN 43271). The refined analysis of the WXT data shows that the event started at T0=2025-12-30T01:21:31 (UTC) and lasted for 72 s with a single pulse. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a Galactic hydrogen column density of 1.21(-0.48/+0.59) x 10^22 cm^-2 and a photon index of 2.16 (-0.82/+0.89). The derived average unabsorbed 0.5-4 keV flux is 6.56 (-2.40, +2.80) x 10^(-9) erg/s/cm^2.
The autonomous observation by the Follow-up X-ray Telescope (FXT) on board EP was performed at 2025-12-30T01:24:36 (UTC), about 3 minutes after T0. The exposure time of this observation is 1859 s. The on-ground analysis shows that an uncatalogued source was detected at R.A., Dec. = 179.8974, 11.4382 deg (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic). The average FXT 0.5-10 keV spectrum can be fitted with an absorbed power law with a fixed Galactic equivalent hydrogen column density of 2.0 x 10^20 cm^-2 and a photon index of 1.83 (-0.04/+0.04). The derived average unabsorbed 0.5-10 keV flux is 4.02 (-0.13/+0.13) x 10^(-11) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters.
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 43271
Subject
GRB 251230A: Swift/UVOT detection
Date
2025-12-30T13:45:04Z (5 days ago)
From
Alice Breeveld at MSSL-UCL <a.breeveld@ucl.ac.uk>
Via
email
A.A. Breeveld (UCL-MSSL), N.P.M. Kuin (UCL-MSSL), S. Lanava (PSU) and M. De Pasquale (U. Messina) report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 251230A 76s after the BAT trigger (Lanava et al., GCN Circ. 43252).
A bright, fading source consistent with the enhanced XRT position (Osborne et al., GCN Circ. 43263) and optical detections (Lanava et al., GCN 43252; Li et al., GCN 43255; Busmann et al., GCN 43258; Masi et al., GCN 43260; Ghosh et al., GCN 43262; Ma et al., GCN 43265, He et al., GCN 43269) is detected in the initial UVOT exposures in the white, v, b, u and uvw1 filters.
The burst is also detected in the UV grism and, while there is some contamination from other zeroth orders, we obtain a tentative redshift of z=1.73.
The preliminary UVOT position is:
RA (J2000) = 11:59:35.41 = 179.89756 (deg.)
Dec (J2000) = +11:26:19.2 = 11.43867 (deg.)
with an estimated uncertainty of 0.42 arc sec. (radius, 90% confidence).
Preliminary detections using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the finding chart (FC) and other early settled exposures are:
Filter T_start(s) T_stop(s) Exp(s) Mag
white_FC 76 226 147 13.61 ± 0.03
white 868 1017 286 15.63 ± 0.02
v 619 638 19 14.69 ± 0.07
b 545 564 20 14.78 ± 0.05
u_FC 288 538 246 13.77 ± 0.02
uvw1 668 687 19 15.2 ± 0.1
uvm2 643 1775 136 >18.8
uvw2 594 614 19 >17.7
The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.024 in the direction of the burst (Schlegel et al. 1998).
GCN Circular 43270
Subject
GRB251230A: 7DT optical upper limits
Date
2025-12-30T13:38:44Z (5 days ago)
From
Donggeun Tak <donggeun.tak@gmail.com>
Via
Web form
Donggeun Tak (SNU ARC/SNU), Myungshin Im (SNU ARC/SNU), YoungPyo Hong (SNU ARC/SNU), Hyeonho Choi (SNU ARC/SNU), Donghwan Hyun (SNU ARC/SNU), Gregory S.H. Paek (IfA, SNU ARC/SNU), Seo-Won Chang (SNU ARC/SNU), and Ji Hoon Kim (SNU ARC/SNU) report on behalf of the 7 Dimensional Telescope (7DT) team:
We report optical follow-up observations of GRB251230A (GCN 43252; GCN 43263), conducted with the 7-Dimensional Telescope (7DT), located in Chile.
The 7DT follow-up began at 06:52:54 UTC on 2025-12-30, corresponding to T0 + 5.5 hours, pointing to a region covering the target localization provided by Swift (GCN 43252) at RA, DEC = 179.89760 deg, 11.43870 deg.
Initial observations were made with 12 units in 20 medium-band filters as well as g-, r-, and i-band filters (23 filters in total).
The following table summarizes the derived 5-sigma upper limits:
Filter Mag Mag_err Exposure Date Time
----------------------------------------------------------------------------------------------------
g >20.04 N/A 300s 2025-12-30T06:49:06.000
r >19.42 N/A 300s 2025-12-30T06:54:28.333
i >18.34 N/A 300s 2025-12-30T06:49:04.000
m400 >18.32 N/A 300s 2025-12-30T06:54:34.667
m425 >18.89 N/A 300s 2025-12-30T06:54:20.000
m450 >18.95 N/A 300s 2025-12-30T06:49:02.667
m475 >19.00 N/A 300s 2025-12-30T06:54:26.000
m500 >19.04 N/A 300s 2025-12-30T06:49:10.667
m525 >18.93 N/A 300s 2025-12-30T06:54:29.000
m550 >18.60 N/A 300s 2025-12-30T06:54:34.000
m575 >18.79 N/A 300s 2025-12-30T06:49:09.667
m600 >18.60 N/A 300s 2025-12-30T06:49:08.667
m625 >18.21 N/A 300s 2025-12-30T06:54:42.667
m650 >18.25 N/A 300s 2025-12-30T06:49:03.000
m675 >18.28 N/A 300s 2025-12-30T06:54:38.333
m700 >18.16 N/A 300s 2025-12-30T06:49:07.000
m725 >17.72 N/A 300s 2025-12-30T06:54:36.333
m750 >17.56 N/A 600s 2025-12-30T06:51:49.833
m775 >17.04 N/A 300s 2025-12-30T06:54:24.667
m800 >16.81 N/A 300s 2025-12-30T06:49:05.667
m825 >16.65 N/A 300s 2025-12-30T06:54:29.667
m850 >16.44 N/A 300s 2025-12-30T06:48:59.000
m875 >15.91 N/A 300s 2025-12-30T06:49:08.000
----------------------------------------------------------------------------------------------------
No significant transient event was identified in the preliminary result. Preliminary analysis yields 5σ limiting magnitudes in the range of 15.91–20.04 mag depending on sky brightness and airmass.
Photometric flux calibration was performed using synthetic photometry based on the Gaia DR3 XP catalog (Gaia Collaboration et al. 2022) within the AB magnitude system. Note that no extinction correction has been applied.
The 7-Dimensional Telescope (7DT), located in Chile and comprising 20 wide-field telescopes equipped with 40 medium-bandwidth (~25nm) filters, aims to detect optical counterparts of GW sources and conduct the 7-Dimensional Sky Survey (7DS) of the Southern Hemisphere. Further information about the 7DT is available at https://7ds.snu.ac.kr/ and http://gwuniverse.snu.ac.kr/.
GCN Circular 43269
Subject
GRB 251230A / EP251230a: NOT observations and spectroscopic redshift upper limit z < 2.2
Date
2025-12-30T13:23:01Z (5 days ago)
From
Antonio Martin-Carrillo at UCD,Space Science Group <antonio.martin-carrillo@ucd.ie>
Via
Web form
L. He (NAOC), L. Izzo (INAF/OACN and DARK/NBI), A. Martin-Carrillo (UCD), A. Saccardi (CEA/Irfu), J. An (NAOC), G. Corcoran (UCD), D. B. Malesani (DAWN/NBI and Radboud), A. Kadela (NOT & NBI) report on behalf of a larger collaboration:
We observed the optical counterpart (Lanava et al., GCN 43252; Li et al., GCN 43255; Busmann et al., GCN 43258; Masi, GCN 43260; Ghosh et al., GCN 43262; Ma et al., GCN 43265) of GRB 251230A / EP251230a (Lanava et al., GCN 43252; Wang et al., GCN 43259; Osborne et al., GCN 43263), using the Nordic Optical Telescope (NOT), equipped with the ALFOSC camera and spectrograph.
We obtained three exposures of 300 s in the r-band starting on 2025 Dec 30 at 06:30:20 UT (5.144 hr after the Swift trigger). The afterglow is clearly detected with an AB magnitude of r = 20.75 +/- 0.02 mag, calibrated against nearby stars from the Pan-STARRS catalogue and not corrected for Galactic extinction. Compared to previous measurements, our photometry suggests rapid optical decay with power-law index ~1.95.
A sequence of 4 spectra of 1200 s each was acquired, covering the wavelength range 3700-9600 AA. In a preliminary reduction of the spectra, we detect a continuum over the entire covered wavelength range. From detection in the blue down to ~3900 AA, and the lack of hydrogen absorption, we set a redshift upper limit z < 2.2. We do not identify clear metal absorption features.
Further analysis is ongoing.
GCN Circular 43267
Subject
GRB 251230A: GOTO optical upper limit
Date
2025-12-30T11:26:15Z (5 days ago)
From
Rhaana Starling at U of Leicester <rlcs1@leicester.ac.uk>
Via
Web form
R. Starling, A. Kumar, G. Ramsay, D. O’Neill, B. P. Gompertz, K. Ackley, M. J. Dyer, J. Lyman, K. Ulaczyk, S. Belkin, B. Godson, D. Steeghs, D. K. Galloway, V. Dhillon, P. O'Brien, K. Noysena, R. Kotak, R. P. Breton, L. K. Nuttall, and J. Casares report on behalf of the GOTO collaboration:
We report on observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) that serendipitously covered the field of GRB 251230A detected by Swift (Lanava et al., GCN 43252; Osborne et al., GCN 43263) and likely coincident with an Einstein Probe trigger (Wang et al., GCN 43259). Two sets of observations were performed by GOTO-North at 2025-12-30 06:01:45 UT and 2025-12-30 06:16:08 UT. Each observation consisted of 4x45 s exposures in the GOTO L-band (400-700 nm). Images were processed using the GOTO pipeline.
We do not detect the optical counterpart (Lanava et al., GCN 43252; Li et al., GCN 43255; Busmann et al., GCN 43258; Masi et al., GCN 43260; Ghosh et al., GCN 43262; Ma et al., GCN 43265) down to 3-sigma limiting magnitudes of L >20.8 (AB) and L >20.6 (AB) at 4.7 hours and 4.9 hours post-trigger, respectively.
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, the University of Birmingham and the Instituto de Astrofisica de Canarias (IAC).
GCN Circular 43265
Subject
GRB 251230A / EP251230a: SVOM/VT optical observation
Date
2025-12-30T09:58:05Z (5 days ago)
From
Yinuo Ma <mayn@bao.ac.cn>
Via
Web form
Y. N. Ma, L. P. Xin, Y. L. Qiu, C. Wu, H. L. Li, Z. H. Yao, X. H. Han, Y. Xu, J. Wang, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA), J. X. Cao (GXU), W. L. Zhang (PMO) report on behalf of the SVOM/VT team.
SVOM/VT performed a Target of Opportunity observation of GRB 251230A / EP251230a detected by Swift/BAT and EP/WXT (Lanava et al., GCN 43252; Wang et al., GCN 43259; Osborne et al., GCN 43263). SVOM/VT began observing the field at 2025-12-30T03:13:20 UTC, 1.861 hours after the trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
With X-band data available, the optical counterpart (Li et al., GCN 43255; Busmann et al., GCN 43258; Masi, GCN 43260; Ghosh et al., GCN 43262) was clearly detected in both VT_B and VT_R bands. The magnitudes are:
mid time (s) | exposure time (s) | band | mag (AB) | mag err
-------------|-------------------|------|----------|--------
6874 | 50 | VT_B | 19.11 | 0.04
8174 | 50 | VT_B | 19.53 | 0.05
6874 | 50 | VT_R | 18.57 | 0.03
8174 | 50 | VT_R | 19.07 | 0.05
Our photometry was not corrected for Galactic extinction.
The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS.
GCN Circular 43263
Subject
GRB 251230A: Enhanced Swift-XRT position
Date
2025-12-30T08:02:58Z (5 days ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
J.P. Osborne, A.P. Beardmore, P.A. Evans and M.R. Goad (U. Leicester)
report on behalf of the Swift-XRT team.
Using 1379 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 251230A, 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 = 179.89737, +11.43831 which is equivalent
to:
RA (J2000): 11h 59m 35.37s
Dec (J2000): +11d 26' 17.9"
with an uncertainty of 2.2 arcsec (radius, 90% confidence).
This position may be improved as more data are received. The latest
position can be viewed at https://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 was automatically generated, and is an official product of the
Swift-XRT team.
GCN Circular 43262
Subject
GRB 251230A: Early optical counterpart detection by LCO.
Date
2025-12-30T05:52:21Z (5 days ago)
From
ankur ghosh at CAPP, University of Johannesburg <ghosh.ankur1994@gmail.com>
Via
Web form
Ankur Ghosh, Soebur Razzaque (CAPP, University of Johannesburg), Rahul Gupta (NASA GSFC), Alexander Moskvitin, Yulia Sotnikova (SAO RAS), Naveen Dukiya (ARIES) on behalf of a larger collaboration.
We observed the field of the GRB 251230A triggered by Swift (Lanava et al., GCN 43252) in B, V, and r filter of the 1-m Sinistro telescope and 0.4-m SCICAM QHY600 at the Las Cumbres Observatory Global Telescope (LCOGT) node located at South African Astronomical Observatory (SAAO). The 1-m Sinistro telescope is equipped with a 4K x 4K CCD (FOV: 26 x 26 arcmin, scale: 0.39 arcsec/pixel) and the 0.4 m SCICAM QHY600 is equipped with 9576 x 6388 pixel CCD (FOV: 1.9 x 1.2 degrees, scale: 0.74 arcsec/pixel). Observations began on October 13, 2025, starting from 0.84 hours after the GRB trigger. Further observations are still ongoing.
We clearly detect the optical transient (OT) reported by GCNs (Lanava et al., GCN 43252, Li et al., GCN 43255, Masi et al., GCN 43260).
-----------------------------------------------------------------------------------------------------
|Date| |JDstart| |t-T0 (hours)| |Exp (sec)| |Filter| |Magnitude|
-----------------------------------------------------------------------------------------------------
2025-12-30 2461039.59159 0.84 1 x 300 r r = 17.20 +/- 0.01
2025-12-30 2461039.60333 1.12 2 x 300 r r = 17.64 +/- 0.11
-----------------------------------------------------------------------------------------------------
The field was calibrated against nearby APASS stars, with magnitudes converted using Lupton (2005) equations, and has not been corrected for Galactic extinction.
GCN Circular 43260
Subject
GRB 251230A: Optical Observations via Virtual Telescope Project, Italy
Date
2025-12-30T03:16:13Z (5 days 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 of GRB 251230A (Lanava et al., GCN 43252) with the 17” robotic unit available at the Virtual Telescope Project facility in Manciano, Italy, equipped with a KAF-6303E based CCD camera, its QE peaking (68%) in the red part of the spectrum.
We collected four, 120-second unfiltered exposures, then we averaged them. The central time of the resulting stack was 30 Dec., 02:58:46 UTC, that is about 1.6 hours after the burst.
We detected a bright object at the following position (J2000.0):
R.A.: 11 59 35.38
Decl.: + 11 26 18.5
mean residuals < 0.1” on both axes
R= 18.4 (assuming R-mags from Gaia DR2 for the reference stars).
This position is consistent with Lanava et al. (GCN 43252), Li et al. (GCN 43255) and Busmann et al. (GCN 43258).
GCN Circular 43259
Subject
EP251230a / GRB 251230A: Einstein Probe detection of an X-ray transient
Date
2025-12-30T02:47:03Z (5 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
B.T. Wang (YNAO, CAS), J. P. Chen (SYSU), D. Zhu, K. J. Zhang (YNU),and Z. X. Ling (NAO, CAS) on behalf of the Einstein Probe (EP) team:
We report on the detection of an X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP251230a. The transient triggered EP-WXT (ID: 01709250693) at 2025-12-30T01:22:21 (UTC). The WXT position of the source is R.A. = 179.881 deg, DEC = 11.427 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic).
A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed automatically. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 179.8996 deg, DEC = 11.4361 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic). No significant X-ray source is detected within the 20 arcsec radius of the EP-FXT position. The position of FXT is 10.1 arcsec from Swift/XRT detection of GRB 251230A (Lanava et al., GCN 43252), and 11.6 arcsec from its optical counterpart (Li et al., GCN 43255).
Further information will be updated when the telemetry data is received.
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 43258
Subject
GRB 251230A/EP#01709250693 (likely EP251230a): FTW optical and NIR observations
Date
2025-12-30T02:22:30Z (5 days ago)
From
Malte Busmann at Ludwig-Maximilians-Universität München <m.busmann@physik.lmu.de>
Via
Web form
Malte Busmann (LMU), Xander J. Hall (CMU), Brendan O'Connor (CMU), Daniel Gruen (LMU), and Antonella Palmese (CMU) report:
We observed the counterpart of Swift GRB 251230A (Lanava et al. GCN 43252, Li et al. GCN 43255) which is spacially and temporally consistent with EP trigger 01709250693 (likely EP251230a) with the Three Channel Imager (3KK) at the Fraunhofer Telescope at Wendelstein Observatory (FTW) in the r, i, and J-band simultaneously for 2 x 180 s starting at 2025-12-30T01:50:41 UT (28.3 minutes after the trigger). We detect the counterpart in all bands and measure an r-band magnitude of
r = 16.30 +/- 0.05 AB mag.
The magnitude is calibrated against the PS1 catalog and not corrected for Galactic extinction.
We thank Christoph Ries from the Wendelstein Observatory for the rapid response in obtaining these observations.
GCN Circular 43256
Subject
Swift GRB 251230A: Global MASTER-Net observations report
Date
2025-12-30T02:03:04Z (5 days ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.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 [1] located in South Africa (South African Astronomical Observatory) was pointed to the Swift GRB 251230A ( S. Lanava et al., GCN 43252) errorbox 1907 sec after notice time and 1930 sec after trigger time at 2025-12-30 01:53:52 UT, with upper limit up to 19.7 mag. The observations began at zenith distance = 53 deg. The sun altitude is -18.1 deg.
The galactic latitude b = 70 deg., longitude l = 265 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=3090261
We obtain a following upper limits.
Tmid-T0 | Site |Filt.| Expt. | Limit| Comment
_________|_____________________|_____|_______|______|________
2021 | MASTER-SAAO | C | 180 | 19.7 |
2021 | MASTER-SAAO | C | 180 | 14.4 |
Filter C is a clear (unfiltred) band.
The observation and reduction will continue.
The message may be cited.
[1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp.
http : // www.pereplet.ru/lipunov/625.html
GCN Circular 43255
Subject
The EP-WXT trigger 01709250693/GRB 251230A: Las Cumbres detection of the optical counterpart
Date
2025-12-30T02:02:19Z (5 days ago)
Edited On
2025-12-30T03:17:33Z (5 days ago)
From
Wenxiong Li at NAOC <liwenxiong1992@gmail.com>
Edited By
Vidushi Sharma at NASA GSFC/UMBC <vidushi.sharma@nasa.gov> on behalf of Wenxiong Li at NAOC <liwenxiong1992@gmail.com>
Via
Web form
Wenxiong Li, Runduo Liang (NAOC), Iair Arcavi (TAU), Ido Keinan (TAU), David Sand (U of Arizona)
We observed the position of EP-WXT trigger 01709250693/GRB 251230A with a Las Cumbres 1m telescope at Sutherland Observatory, South Africa, 9 mins after the Einstein Probe WXT trigger. We took 2x300s exposures in the broad optical w band.
We find an uncataloged source at RA=179.8972, Dec=11.4383 within the EP-WXT error circle and measure the following preliminary photometry calibrated to the r band:
MJD 61039.063 Mag 15.1
The position of the counterpart is consistent with that reported by Lanava et al. (GCN 43252).
GCN Circular 43252
Subject
GRB 251230A: Swift detection of a burst with a bright optical counterpart
Date
2025-12-30T01:48:56Z (5 days ago)
From
Simone Dichiara at Pennsylvania State University <sbd5667@psu.edu>
Via
email
S. Lanava (PSU), S. Dichiara (PSU) and R. Gupta (NASA GSFC) report on
behalf of the Neil Gehrels Swift Observatory Team:
At 01:21:41 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 251230A (trigger=1429020). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 179.894, +11.415 which is
RA(J2000) = 11h 59m 35s
Dec(J2000) = +11d 24' 55"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve showed a multiple-peaked
structure with a duration of about 80 sec. The peak count rate
was ~5000 counts/sec (15-350 keV), at ~30 sec after the trigger.
The XRT began observing the field at 01:22:49.3 UT, 68.1 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
fading, uncatalogued X-ray source with an enhanced position: RA, Dec
179.89781, 11.43828 which is equivalent to:
RA(J2000) = 11h 59m 35.47s
Dec(J2000) = +11d 26' 17.8"
with an uncertainty of 1.9 arcseconds (radius, 90% containment). This
location is 84 arcseconds from the BAT onboard position, within the BAT
error circle. This position may be improved as more data are received;
the latest position is available at https://www.swift.ac.uk/sper.
A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density in excess of the Galactic value (1.88 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 4.4
(+1.47/-1.34) x 10^21 cm^-2 (90% confidence).
The initial flux in the 2.5 s image was 4.73e-09 erg cm^-2 s^-1 (0.2-10
keV).
UVOT took a finding chart exposure of 150 seconds with the White filter
starting 76 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
RA(J2000) = 11:59:35.42 = 179.89760
DEC(J2000) = +11:26:19.3 = 11.43870
with a 90%-confidence error radius of about 0.74 arc sec. This position is 4.7
arc sec. from the center of the XRT error circle. The estimated magnitude is
13.74 with a 1-sigma error of about 0.14. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.024.
Burst Advocate for this burst is S. Lanava (sml7284 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/)