GRB 251205A
GCN Circular 43044
Subject
GRB 251205A: J-band detection with WINTER
Date
2025-12-09T02:23:58Z (7 hours ago)
From
Geoffrey Mo at Caltech / Carnegie Observatories <gmo@mit.edu>
Via
Web form
Geoffrey Mo (Caltech/Carnegie), Tomas Ahumada (NOIRLab), Benjamin Schneider (LAM), Viraj Karambelkar (Columbia), Robert Stein (UMD), Danielle Frostig (CfA), Nathan Lourie (MIT), Robert Simcoe (MIT), and Mansi Kasliwal (Caltech) report:
We observed the field of GRB 251205A (Lanava et al., GCN 43005; Beardmore et al., GCN 43007; Dichiara et al., GCN 43017; Krimm et al., GCN 43018) in the near-infrared J band with the Palomar 1-m telescope, equipped with the 1.2-square degree WINTER camera (Lourie et al. 2020, Frostig et al. 2024).
Observations began at 2025-12-06T10:27:54 UTC in the J band (~10.8 hours after the GRB trigger), consisting of 15 x 120 s exposures.The images were processed using the WINTER data reduction pipeline implemented with mirar (https://github.com/winter-telescope/mirar, https://doi.org/10.5281/zenodo.13352565).
We detect a source at the optical counterpart location (Lipunov et al., GCN 43004; Lanava et al., GCN 43005; Lipunov et al., GCN 43006; de Ugarte Postigo et al., GCN 43008; Malesani et al., GCN 43009; O’Neill et al., GCN 43010; Mandarakas et al., GCN 43011; Pankov et al., GCN 43012; Bochenek et al., GCN 43015; Klinger et al., GCN 43016; Patil et al., GCN 43019; Pérez-Fournon et al., GCN 43020; Bochenek et al., GCN 43024; Busmann et al., GCN 43026; Hagio et al., GCN 43029; Bochenek et al., GCN 43038), with magnitude J = 17.9 ± 0.1 mag (AB).
WINTER (Wide-field INfrared Transient ExploreR) is a partnership between MIT and Caltech, housed at Palomar Observatory, and funded by NSF MRI, NSF AAG, the David and Lucile Packard Foundation, and the MIT Kavli Institute for Astrophysics and Space Research.
GCN Circular 43038
Subject
GRB 251205A: Liverpool Telescope further optical follow-up observations
Date
2025-12-08T21:58:15Z (11 hours ago)
From
A. Bochenek at Liverpool John Moores University <a.m.bochenek@2023.ljmu.ac.uk>
Via
Web form
A. Bochenek, D. A. Perley (LJMU), report:
We observed the field of GRB 251205A (Lanava et al., GCN 43005) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 4x100s exposures in the SDSS i and r filters starting at 2025-12-08 05:21:03 UT, approximately 2.24 days after trigger.
We report detections in the stacked images of both filters, at the position first reported by Lanava et al., GCN 43005:
MJD (mid) T_mid-T_0 Filter Mag. (AB)
61017.22543 53.8 h i 21.02 ± 0.19
61017.23156 53.9 h r 21.14 ± 0.26
The photometry was obtained using nearby PanSTARRS secondary standards and was not corrected for extinction. The photometry is consistent with late-time optical measurements by Mandarakas et al., GCN 43011; Pérez-Fournon et al., GCN 43020; Bochenek & Perley, GCN 43024; and Hagio et al., GCN 43029.
GCN Circular 43029
Subject
GRB 251205A : MITSuME Akeno optical afterglow candidate detection
Date
2025-12-08T10:54:40Z (a day ago)
From
hagio.h.ffca@m.isct.ac.jp
Via
Web form
H. Hagio, Y. Kubo, I. Takahashi, M. Sasada, H. Seki, A. Ochi, R. Kato, S. Joshima, Y. Yatsu and N. Kawai (Science Tokyo) report on behalf of the MITSuME collaboration:
We observed the field of GRB 251205A detected by Swift (Lanava et al., GCN 43005) with the optical three-color (g', Rc, and Ic) CCD cameras attached to the MITSuME 50-cm telescope Akeno.
The observation started at 2025-12-06 16:56:58 UT (16.3 hr after the trigger). We stacked the images taken under good conditions. We detected a point source in the Rc- and Ic-band images at a position of the reported optical candidate (Lipunov et al., GCN 43004; Lanava et al., GCN 43005; Lipunov et al., GCN 43006; Malesani et al., GCN 43009; O'Neill et al., GCN 43010; Mandarakas et al., GCN 43011; Pankov et al., GCN 43012; Bochenek et al., GCN 43015; Klingler et al., GCN 43016; Patil et al., GCN 43019; Pérez-Fournon et al., GCN 43020; Bochenek et al., GCN 43024; Busmann et al., GCN 43026 ). Our photometric results can be contaminated by the flux from the nearby galaxy. Here we report the preliminary magnitudes of the source as follows.
T0+[sec] | MID-UT | T-EXP[sec] | magnitudes
---------------------------------------------------------------------------------------------------------------
68759 | 2025-12-06 18:45:46 | 4860 | Rc=19.1+/-0.2, Ic=18.8+/-0.2
---------------------------------------------------------------------------------------------------------------
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 43026
Subject
GRB 251205A: FTW optical and NIR observations
Date
2025-12-07T23:06:48Z (a day ago)
From
Malte Busmann at Ludwig-Maximilians-Universität München <m.busmann@physik.lmu.de>
Via
Web form
Malte Busmann (LMU), Xander J. Hall (CMU), Jule Augustin (LMU), Brendan O’Connor (CMU), Daniel Gruen (LMU), and Antonella Palmese (CMU) report:
We observed the counterpart of GRB 251205A (Lavana et al. GCN 43005) with the Three Channel Imager (3KK) at the Fraunhofer Telescope at Wendelstein Observatory (FTW) in the r, i, z, J, and Ks bands. We detect the counterpart across all bands.
| Start Time | t - t0 (days) | Filter | Exposures | Magnitude (AB) |
|---|---|---|---|---|
| 2025-12-06T03:25:42 | 0.157 | r' | 5 x 150 s + 5 x 180 s | 18.09 +/- 0.05 |
| 2025-12-06T03:25:42 | 0.157 | i' | 5 x 150 s | 18.10 +/- 0.05 |
| 2025-12-06T03:41:46 | 0.168 | z' | 5 x 180 s | 17.74 +/- 0.05 |
| 2025-12-06T03:42:00 | 0.168 | J | 5 x 180 s | 17.46 +/- 0.05 |
| 2025-12-06T03:25:55 | 0.157 | Ks | 10 x 60 s | 17.13 +/- 0.05 |
These measurements are consistent with the magnitudes reported by Lavana et al. (GCN 43005), Lipunov et al. (GCN 43006), Malesani et al. (GCN 43009), O’Neill et al. (GCN 43010), Mandarakas et al. (GCN 43011), Bochenek & Perley (GCN 43015), Klinger et al. (GCN 43016), Patil et al. (GCN 43019), Pérez-Fournon et al. (GCN 43020), and Bochenek et al. (GCN 13024).
The r, i, and z-band magnitudes are calibrated against the PS1 catalog, and the J and Ks-band magnitudes are calibrated with the 2MASS Catalog. All magnitudes are provided in the AB system and are not corrected for Galactic extinction.
We thank Michael Schmidt from the Wendelstein Observatory for obtaining these observations.
GCN Circular 43024
Subject
GRB 251205A: Liverpool Telescope further optical follow-up observations
Date
2025-12-07T16:36:22Z (2 days ago)
From
A. Bochenek at Liverpool John Moores University <a.m.bochenek@2023.ljmu.ac.uk>
Via
Web form
A. Bochenek, D. A. Perley (LJMU), report:
We observed the field of GRB 251205A (Lanava et al., GCN 43005) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 4x100s exposures the SDSS i and r filters starting at 2025-12-07 04:57:54 UT, approximately 29.3 hours after trigger.
Some exposures were affected by telescope wobble or poor seeing and had to be discarded before stacking. We report detections in both filters, at the position first reported by Lanava et al., GCN 43005:
MJD (mid) T_mid-T_0 Filter Mag. (AB)
61016.21035 29.4 h i 19.57 ± 0.06
61016.21529 29.5 h r 19.72 ± 0.07
The photometry is consistent with measurements by Lanava et al. GCN 43005; Lipunov et al. GCN 43006; de Ugarte Postigo et al. GCN 43008; Malesani et al. GCN 43009; O’Neill et al., GCN 43010; Mandarakas et al. GCN 43011; Pankov et al., GCN 43012; Bochenek and Perley, GCN 43015; Klingler et al., GCN 43016; Patil et al., GCN 43019; and Pérez-Fournon et al., GCN 43020. The photometry was obtained using nearby PanSTARRS secondary standards and was not corrected for extinction.
GCN Circular 43020
Subject
GRB 251205A: ZTF and ATLAS optical afterglow detections
Date
2025-12-07T09:28:50Z (2 days ago)
From
Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf@iac.es>
Via
Web form
I. Pérez-Fournon (IAC and ULL), J. Basurto Merino, P.G. Berdayes, A. Caballero-Almagro, A. Cerón, M. Contreras, F. Díaz-Segado, T. Ferrer-Laviña, B. Gandolfi, V. Ghiraldo, J. Hernández Fung, L. Juliá-Maroto, E. Lekaroz-Urriza, M. Manzano García, E. Mejía-Martínez, J. Prieto Polo, M. Pulido-Torres, M. Quintana-Ansaldo, A. Schenone-Zanuzzi, A. Selezneva, T. Tundidor Rodríguez, E. Urquijo-Rodríguez (all ULL) and M. Abdul-Masih (IAC and ULL).
We report on ZTF and ATLAS detections of the optical afterglow of the Swift GRB 251205A (Lanava et al., GCN Circ. 43005; Beardmore et al., GCN Circ. 43007; Dichiara et al., GCN Circ. 43017; and Krimm et al., GCN Circ. 43018) at a spectroscopic redshift of z = 1.100 (de Ugarte Postigo et al., GCN Circ. 43008).
Both ZTF and ATLAS detected the optical afterglow of GRB 251205A during standard observations of these time-domain surveys. ZTF first detected this transient (ZTF25acgbeof) on 2025-12-06 at 12:16:12 UT at a ZTF g-band magnitude of g-ZTF = 19.168 +/- 0.169. It was reported to the Transient Name Server by Rehemtulla et al. (AT 2025afws, TNS Astronomical Transient Report No. 279483).
Using the ATLAS forced-photometry server (Shingles et al. 2021, Transient Name Server AstroNote 2021-7), we find three ATLAS detections, as reported in the following table of ZTF and ATLAS photometry:
MJD mag (AB) error survey filter
61015.511250 19.168 0.169 ZTF g
61015.543854 18.788 0.105 ZTF r
61015.625035 19.062 0.279 ATLAS orange
61015.628805 19.225 0.321 ATLAS orange
61015.646040 18.889 0.229 ATLAS orange
These ZTF and ATLAS detections are consistent with other reported UV and optical detections: Lanava et al. (GCN Circ. 43005), Lipunov et al. (GCN Circ. 43006), de Ugarte Postigo et al. (GCN Circ. 43008), Malesani et al. (GCN Circ. 43009), O'Neill et al. (GCN Circ. 43010), Mandarakas et al. (GCN Circ. 43011), Pankov et al. (GCN Circ. 43012), Bochenek and Perley (GCN Circ. 43015), Klingler et al. (GCN Circ. 43016), and Patil et al. (GCN Circ. 43019).
The ZTF coordinates of ZTF25acgbeof / AT 2025afws are RA (J2000) = 13:21:05.324, Dec (J2000) = 29:55:43.64, consistent within the errors with the optical and X-ray positions of the GRB 251205A afterglow reported by Lanava et al. (GCN Circ. 43005), Lipunov et al. (GCN Circ. 43006), Beardmore et al. (GCN Circ. 43007), de Ugarte Postigo et al. (GCN Circ. 43008), and Klingler et al. (GCN Circ. 43016).
This work made use of the Astro-COLIBRI platform (P. Reichherzer et al. 2021, ApJS, 256, 5).
GCN Circular 43019
Subject
GRB 251205A: GROWTH-India Telescope optical observations
Date
2025-12-07T08:44:48Z (2 days ago)
From
V. Swain at IIT Bombay <vishwajeet.s@iitb.ac.in>
Via
Web form
S. Patil, A.P. Saikia, V. Swain, V. Vijaykumar, T. Mohan, 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 251205A (Lanava et al., GCN Circ. 43005), with 0.7m GROWTH-India Telescope (GIT). We started the observation at 2025-12-05T23:46:13 UT, i.e., 6.43 minutes after the Swift BAT trigger. We obtained multiple exposures in r' filter. We detected the optical afterglow in our stacked image of r' filter at position reported by Swift UVOT (Lanava et al., GCN Circ. 43005). The photometry results are as follow:
| MJD (mid) | Filter | t-t0 (in minutes) | Total Exposure Time (sec) | Magnitude (AB) |
|---|---|---|---|---|
| 61014.99251157 | r' | 9.43 | 360 | 16.84 +/- 0.06 |
| 61015.00966435 | r' | 34.13 | 360 | 17.02 +/- 0.06 |
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 (Lipunov et al., GCN 43004, de Ugarte Postigo et al., GCN 43008, Malesani et al. GCN 43009, O'Neill et al. 43010, Mandarakas et al. GCN 43011, Pankov et al. 43012, Bochenek et al. 43015, Klingler et al. 43016, ).
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 43018
Subject
GRB 251205A: Swift-BAT refined analysis
Date
2025-12-07T04:06:20Z (2 days ago)
From
Amy <yarleen@gmail.com>
Via
email
H. A. Krimm (NSF), S. D. Barthelmy (GSFC), R. Gupta (GSFC), S. Laha
(GSFC/UMBC), S. Lanava (PSU), 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-239 to T+963 sec from the recent telemetry
downlink, we report further analysis of BAT GRB 251205A (trigger #1420873)
(Lanava et al., GCN Circ. 43005). The BAT ground-calculated position is
RA, Dec = 200.260, 29.906 deg which is
RA(J2000) = 13h 21m 02.5s
Dec(J2000) = +29d 54' 21.2"
with an uncertainty of 2.1 arcmin, (radius, sys+stat, 90% containment). The
partial coding was 45%.
The mask-weighted light curve shows a weak pulse that starts at ~T0 and
peaks at ~T+9 s. The main pulse ends at ~T+40s, followed by a weak tail
emission that lasts till ~T+140 s. T90 (15-350 keV) is 128.00 +- 65.97 sec
(estimated error including systematics).
The time-averaged spectrum from T+0.94 to T+144.94 sec is best fit by a
simple power-law model. The power law index of the time-averaged spectrum
is 1.67 +- 0.27. The fluence in the 15-150 keV band is 1.1 +- 0.2 x 10^-06
erg/cm2. The 1-sec peak photon flux measured from T+8.44 sec in the 15-150
keV band is 0.5 +- 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/1420873
GCN Circular 43017
Subject
GRB 251205A: Swift-XRT refined Analysis
Date
2025-12-07T03:50:01Z (2 days ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
S. Dichiara (PSU), J.A. Kennea (PSU), D.N. Burrows (PSU), K.L. Page (U.
Leicester), A.P. Beardmore (U. Leicester), C. Salvaggio (INAF-OAB), M.
Ferro (INAF-OAB), R. Brivio (INAF-OAB) and P.A. Evans report on behalf
of the Swift-XRT team:
We have analysed 6.3 ks of XRT data for GRB 251205A, from 129 s to 94.1
ks after the trigger. The data comprise 352 s in Windowed Timing (WT)
mode (the first 9 s were taken while Swift was slewing) with the
remainder in Photon Counting (PC) mode.
The late-time light curve (from T0+9.7 ks) can be modelled with a
power-law decay with a decay index of alpha=0.77 (+0.12, -0.11).
A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.14 (+/-0.06). The
best-fitting absorption column is 5.6 (+1.3, -1.2) x 10^20 cm^-2, in
excess of the Galactic value of 1.2 x 10^20 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 1.95 (+0.16, -0.15)
and a best-fitting absorption column of 3.8 (+3.5, -2.6) x 10^20 cm^-2.
The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum is 3.4 x 10^-11 (3.7 x 10^-11) erg cm^-2
count^-1.
A summary of the PC-mode spectrum is thus:
Total column: 3.8 (+3.5, -2.6) x 10^20 cm^-2
Galactic foreground: 1.2 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index: 1.95 (+0.16, -0.15)
The results of the XRT-team automatic analysis are available at
https://www.swift.ac.uk/xrt_products/01420873.
This circular is an official product of the Swift-XRT team.
GCN Circular 43016
Subject
GRB 251205A: Swift/UVOT Detection
Date
2025-12-06T18:47:19Z (3 days ago)
From
N. Klingler at NASA-GSFC/UMBC/CRESST II <noelklingler@gmail.com>
Via
Web form
N. Klingler (NASA-GSFC / UMBC / CRESST II) and Sophia Lanava (PSU) report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 251205A 149 s after the BAT trigger (Lanava et al., GCN Circ. 43005). A source consistent with the XRT position (RA, Dec = 13h 21m 05.26s, +29d 55' 44.2"; Beardmore et al., GCN Circ. 43007) is detected in the initial UVOT exposures.
The preliminary UVOT position is:
RA (J2000) = 13:21:05.34 = 200.27223 (deg.)
Dec (J2000) = +29:55:44.0 = 29.92890 (deg.)
with an estimated uncertainty of 0.43 arc sec. (radius, 90% confidence).
Preliminary detections using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are:
Filter T_start(s) T_stop(s) Mag
white 148.9 298.7 17.61 +/- 0.06
white 586.8 606.5 16.96 +/- 0.09
white 759.1 869.1 16.89 +/- 0.08
white 16513.5 17308.6 17.77 +/- 0.05
b 562.4 582.2 17.32 +/- 0.17
b 734.9 754.7 17.29 +/- 0.18
b 15601.3 16508.4 18.18 +/- 0.05
u 306.8 556.6 16.65 +/- 0.06
u 710.3 730.0 16.57 +/- 0.16
u 22323.1 22838.7 17.51 +/- 0.06
v 636.4 656.2 17.10 +/- 0.27
v 808.6 828.4 16.92 +/- 0.24
v 10660.9 11393.6 18.45 +/- 0.10
uvw1 685.8 705.5 16.18 +/- 0.18
uvw1 21416.9 22316.6 17.83 +/- 0.07
uvw2 9754.6 10654.4 18.44 +/- 0.10
The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.014 in the direction of the burst (Schlegel et al. 1998).
GCN Circular 43015
Subject
GRB 251205A: Liverpool Telescope optical follow-up observations
Date
2025-12-06T18:26:59Z (3 days ago)
From
A. Bochenek at Liverpool John Moores University <a.m.bochenek@2023.ljmu.ac.uk>
Via
Web form
A. Bochenek, D. A. Perley (LJMU), report:
We observed the field of GRB 251205A (Lanava et al., GCN 43005) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 4x100s exposures the SDSS i and r filters starting at 2025-12-06 05:37:14 UT, approximately 5.95 hours after trigger.
Some exposures were affected by telescope movement and had to be discarded. We report detections in both filters, at the position first reported by Lanava et al. GCN 43005:
MJD (mid) T_mid-T_0 Filter Mag. (AB)
61015.23465 5.97 h i 17.93 ± 0.05
61015.24283 6.16 h r 18.06 ± 0.03
The photometry is consistent with measurements by Lanava et al. GCN43005; Lipunov et al. GCN 43006; de Ugarte Postigo et al. GCN 43008; Malesani et al. GCN 43009; O’Neill et al., GCN 43010; Mandarakas et al. GCN 43011 and Pankov et al., GCN 43012. The photometry was obtained using nearby PanSTARRS secondary standards and was not corrected for extinction.
GCN Circular 43012
Subject
GRB 251205A: Zeiss-1000 Koshka observatory optical observations
Date
2025-12-06T14:44:43Z (3 days ago)
From
Alexei Pozanenko at IKI, Moscow <grb.alex@gmail.com>
Via
email
N. Pankov (HSE,IKI), A. Novichonok (Petrozavodsk State University,
KIAM), S. Schmalz (KIAM), A. Volnova (IKI), A. Pozanenko (IKI) report
on behalf of IKI GRB-FuN:
We observed the optical afterglow of GRB 251205A (Lanava et al., GCN
43005; Lipunov et al., GCN 43006; de Ugarte Postigo et al., GCN 43008;
Malesani et al., GCN 43009; O'Neill et al., GCN 43010) using the
Zeiss-1000 telescope at Koshka observatory (INASAN). The observations
started/ended on 2025-12-06 (UT) 00:57:28/04:07:07. Preliminary
photometry of the initial stacked image is the following
Date UT start t-T0 Exp. Filter OT Err. UL(3sigma)
(mid, days) (s)
2025-12-06 00:57:28 0.05747 10*90 R 17.92 0.06 20.5
The photometry is based on nearby USNO-B1.0 stars and not corrected
for Galaxy extinction.
GCN Circular 43011
Subject
GRB 251205A: COLIBRÍ optical observations
Date
2025-12-06T12:07:07Z (3 days ago)
From
nikos.mandarakas@lam.fr
Via
Web form
Nikos Mandarakas (LAM), Margarita Pereyra (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), 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), Enrique Moreno Méndez (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM):
We imaged the field of the Swift GRB 251205A (S. Lanava et al., GCN Circ. 43005) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2025-12-06 10:04:31
to 10:47:46 UTC (from 10.41 to 11.13 hours after the trigger) and obtained 32 minutes of simultaneous exposure in the r and 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 counterpart S. Lanava et al. (GCN Circ. 43005); V. M. Lipunov et al. (GCN Circ. 43006); A. de Ugarte Postigo et al. (GCN Circ. 43008); D. B. Malesani et al. (GCN Circ. 43009) and D. O’Neill et al. (GCN Circ. 43010), at a preliminary magnitude of:
r = 18.26 +/- 0.03
z = 17.97 +/- 0.02
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 43010
Subject
GRB 251205A: GOTO optical afterglow detection
Date
2025-12-06T11:03:38Z (3 days ago)
From
d.s.oneill@bham.ac.uk
Via
Web form
D. O'Neill, G. Ramsay, A. Kumar, B. Gompertz, R. Starling, K. Ackley, M. J. Dyer, J. Lyman, K. Ulaczyk, S. Belkin, D. Steeghs, D. K. Galloway, V. Dhillon, P. O'Brien,, K. Noysena, R. Kotak, R. P. Breton, L. K. Nuttall, D. Pollacco, J. Casares Vel'azquez, T. Killestein, B. Godson on behalf of GOTO collaboration:
We report on optical observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) in response to the GRB 251205A.
Serendipitous observations from the all-sky survey covered the position of the counterpart (Malesani et al., GCN 43009; Lanava et al., GCN 43005; Lipunov et al., GCN 43006; de Ugarte Postigo et al., GCN 43008) at 2025-12-06 06:12:01 UT, (+6.5h post trigger). Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations. The counterpart was detected in the GOTO L-band (400-700nm) mag = 18.16 ± 0.12 (AB).
Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and 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 43009
Subject
GRB 251205A: NOT optical observations
Date
2025-12-06T09:45:00Z (3 days ago)
Edited On
2025-12-06T23:59:42Z (2 days ago)
From
Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani@nbi.ku.dk>
Edited By
Vidushi Sharma at NASA GSFC/UMBC <vidushi.sharma@nasa.gov> on behalf of Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani@nbi.ku.dk>
Via
Web form
D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), Z.P. Zhu (NAOC), A. K. Aris-Kiss (Helsinki), N. Routamo (Helsinki), M. Korp-Lagg (Aalto University), S. Wedemeyer (Oslo), S. Armas Perez (NOT) report on behalf of a larger collaboration:
We observed the optical afterglow of GRB 251205A (Lanava et al., GCN 43005; Lipunov et al., GCN 43006; de Ugarte Postigo et al., GCN 43008) using the Nordic Optical Telescope (NOT) equipped with the StanCam camera. Observations started on 2025-12-06 at 05:25:33 UT (5.75 hr after the trigger). Five 150 s observations were taken using the StanCam “interference i” filter.
The optical afterglow is well detected in single images. At a mean time of 5.90 hr after the trigger, we measure a magnitude
i = 17.93 +- 0.03.
This magnitude is in the AB system and is not corrected for Galactic extinction. We note that, due to the small field-of-view of StanCam, only one star from the Pan-STARRS catalog could be used for photometric calibration. Considering that the StanCam i filter is (slightly) different from the Pan-STARRS one, an extra systematic error of 0.1 mag should be conservatively added to the photometric error budget.
GCN Circular 43008
Subject
GRB 251205A: GTC/OSIRIS+ redshift z = 1.100
Date
2025-12-06T09:08:39Z (3 days ago)
From
Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani@nbi.ku.dk>
Via
Web form
A. de Ugarte Postigo (LAM), S. Geier (GTC), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), C. C. Thoene (AbAO), L. Izzo (INAF/OACN and DARK/NBI), J. F. Agui Fernandez (CAHA), M. A. Aloy (UV), J. P. U. Fynbo (DAWN/NBI), L. Galbany (IEEC-CSIC), G. Lombardi (GTC), N. A. Rakotondrainibe (LAM), B. Schneider (LAM), N. R. Tanvir (Univ. Leicester), D. Perez Valladares (GTC) report:
We observed the optical counterpart of GRB 251205A (Lanava et al., GCN 43005; Lipunov et al., GCN 43006) using the Gran Telescopio Canarias (GTC) equipped with the OSIRIS+ instrument.
In the 30-s acquisition image (beginning on 2025-12-06 at 05:21:34 UT, that is 5.68 hr after trigger), the optical afterglow is well detected with a magnitude i = 17.78 +- 0.03 AB, calibrated against nearby Pan-STARRS objects, and not corrected for Galactic extinction. We also report the following, improved coordinates (0.3" accuracy):
RA(J2000) = 13:21:05.32
Dec(J2000) = +29:55:43.6
A total of 4 spectra by 900 s were secured, starting on 2025-12-06 at 05:31:22 UT (5.86 hr after trigger), using grism R1000B. Continuum is detected over the range 3750-7750 AA. A number of absorption features are detected, which we interpret as due to Fe II 2344, 2383, 2586, 2600, Mg II 2796, 2803, and Mg I 2852, all at a common redshift z = 1.100, which we suggest to be the redshift of GRB 251205A.
Given the redshift value measured in absorption, it is thus unlikely that the GRB is associated with the nearby, bright galaxy with photometric redshift z = 0.25 noted by Lipunov et al. (GCN 43006).
GCN Circular 43007
Subject
GRB 251205A: Enhanced Swift-XRT position
Date
2025-12-06T03:12:58Z (3 days ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
A.P. Beardmore, P.A. Evans, M.R. Goad and J.P. Osborne (U. Leicester)
report on behalf of the Swift-XRT team.
Using 366 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 251205A, 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 = 200.27190, +29.92894 which is equivalent
to:
RA (J2000): 13h 21m 05.26s
Dec (J2000): +29d 55' 44.2"
with an uncertainty of 2.4 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 43006
Subject
Swift GRB 251205A : MASTER OT detection with host galaxy
Date
2025-12-06T01:42:41Z (3 days ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
Via
email
V.M. Lipunov (Lomonosov MSU), V.Senik, E.Gorbovskoy, A.Kuznetsov, I.Panchenko,
G.Antipov, P.Balanutsa, K.Zhirkov, N. Tiurina, Ya.Kechin,A.Chasovnikov, D.Vlasenko, Yu.Tselik(Lomonosov MSU, SAI, Moscow),
O.A.Gress, N.M.Budnev, O.Ershova (Irkutsk State University),
R. Podesta, C.Francile, F. Podesta, E. Gonzalez (OAFA, San JuanUni.,Argentina);
D.Buckley (SAAO),
A. Sosnovskij (CrAO RAS),
A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory),
A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity),
L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino, J.Martinez, A.R.Corella,
L.H.Rodriguez (INAOE, Guillermo Haro Astrophysic Observatory, Mexico)
V.M.Pillet, R.Rebolo Lopez (The Instituto de Astrofisica de Canarias,Spain)
MASTER-Kislovodsk robotic telescope of MASTER Global Robotic Net (Lipunov et al. [1-4], http://observ.pereplet.ru ),
started Swift GRB 251205A (Lanava et al GCN 43005)
error-box observations in alert mode (PP filters) 19s after notice time at at 2025-12-05 23:41:19 UT, Lipunov et al. GCN 43004
MASTER auto-detection system found optical counterpart
MASTER OT J132105.37+295545.8 , first publishied by Swift (GCN 43005)
with unfiltered m_OT~18.1m
We have also prompt wide-field cameras images, the reduction will be later.
There is host(possible) galaxy in 4.36" from GRB counterpart with z_phot=0.25470(Cavuoti et al. 2014)
Real time updated cover map and OT position are available here:
https://master.sai.msu.ru/site/master2/observ.php?id=3062088
Observation and reduction will continue.
[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 43005
Subject
GRB 251205A: Swift detection of a burst with an optical afterglow
Date
2025-12-06T00:02:39Z (3 days ago)
From
David Palmer at LANL <palmer@lanl.gov>
Via
email
S. Lanava (PSU), S. Dichiara (PSU), C. Gronwall (PSU),
R. Gupta (NASA GSFC), N. P. M. Kuin (UCL-MSSL), A. Y. Lien (U Tampa),
D. M. Palmer (LANL) and M. H. Siegel (PSU) report on behalf of the
Neil Gehrels Swift Observatory Team:
At 23:39:47 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 251205A (trigger=1420873). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 200.243, +29.962 which is
RA(J2000) = 13h 20m 58s
Dec(J2000) = +29d 57' 45"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve showed a complex
structure with a duration of about 30 sec. The peak count rate
was ~500 counts/sec (15-350 keV), at ~0 sec after the trigger.
The XRT began observing the field at 23:42:07.0 UT, 139.8 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 200.2707, 29.9296 which is equivalent to:
RA(J2000) = 13h 21m 4.97s
Dec(J2000) = +29d 55' 46.6"
with an uncertainty of 5.3 arcseconds (radius, 90% containment). This
location is 145 arcseconds from the BAT onboard position, within the
BAT error circle. No event data are yet available to determine the
column density using X-ray spectroscopy.
The initial flux in the 2.5 s image was 1.44e-09 erg cm^-2 s^-1 (0.2-10
keV).
UVOT took a finding chart exposure of 150 seconds with the White filter
starting 148 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
RA(J2000) = 13:21:05.34 = 200.27223
DEC(J2000) = +29:55:44.0 = 29.92888
with a 90%-confidence error radius of about 0.75 arc sec. This position is 5.4
arc sec. from the center of the XRT error circle. The estimated magnitude is
17.54 with a 1-sigma error of about 0.14. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.014.
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/)
GCN Circular 43004
Subject
Swift GRB251205A: Global MASTER-Net observations report
Date
2025-12-05T23:48:53Z (3 days ago)
Edited On
2025-12-06T01:53:46Z (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-Kislovodsk robotic telescope [1] located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) was pointed to the Swift GRB251205.99 (trigger No 1420873,13h 20m 58.42s , +29d 57m 45.0s, R=0.05) errorbox 19 sec after notice time and 92 sec after trigger time at 2025-12-05 23:41:19 UT, with upper limit up to 17.0 mag. The observations began at zenith distance = 68 deg. The sun altitude is -51.1 deg.
The galactic latitude b = 83 deg., longitude l = 55 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=3062088
We obtain a following upper limits.
Tmid-T0 | Site |Filt.| Expt. | Limit| Comment
_________|_____________________|_____|_______|______|________
103 | MASTER-Kislovodsk | P- | 20 | 16.6 |
103 | MASTER-Kislovodsk | P| | 20 | 16.5 |
131 | MASTER-Kislovodsk | P- | 20 | 16.3 |
131 | MASTER-Kislovodsk | P| | 20 | 16.5 |
164 | MASTER-Kislovodsk | P- | 30 | 16.8 |
164 | MASTER-Kislovodsk | P| | 30 | 16.8 |
208 | MASTER-Kislovodsk | P- | 40 | 16.8 |
208 | MASTER-Kislovodsk | P| | 40 | 16.8 |
261 | MASTER-Kislovodsk | P- | 50 | 17.0 |
261 | MASTER-Kislovodsk | P| | 50 | 17.0 |
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