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GRB 250101A

GCN Circular 39604

Subject
GRB250101A: Radio upper limits from VLA observations
Date
2025-03-06T15:57:17Z (6 months ago)
From
Arvind Balasubramanian <arvind6895@gmail.com>
Via
Web form
A. Balasubramanian (IIA), A.P. Saikia (IITB), V. Swain (IITB), G.C. Anupama (IIA), S. Barway (IIA), V. Bhalerao (IITB) report

We observed the field of the gamma ray burst GRB250101A (Page et al. GCN 38752, Li et al. GCN 38753, Mohan et al. GCN 38754, Zhu et al. GCN 38755, Budnev et al. GCN 38756, Wu et al. GCN 38758, Odeh et al. GCN 38763, Balasubramanian et al. GCN 39307) with the Jansky Very Large Array (VLA) under the DDT 24B-529 (PI: A. Balasubramanian) on 13th February 2025 in S Band (3 GHz) for about 1.5 hours starting at 02:06 hours UTC.

We do not detect any significant radio emission at the position of the optical counterpart (Li et al. GCN 38753). We used 3C47 for the flux calibration and J0238+1636 for complex gain and phase calibration. The CASA calibration and imagining pipeline (version 6.5.4.9) was used for data calibration and imaging. We compute a 3-sigma upper limit of ~805 uJy at 3 GHz. Further analysis is in progress.

We thank the TAC and operations team of VLA for making these observations possible. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.

GCN Circular 39307

Subject
GRB250101A: Radio upper limits from GMRT observations
Date
2025-02-13T03:05:42Z (7 months ago)
From
Arvind Balasubramanian <arvind6895@gmail.com>
Via
Web form
A. Balasubramanian (IIA), A.P. Saikia (IITB), V. Swain (IITB), G.C. Anupama (IIA), S. Barway (IIA), V. Bhalerao (IITB) report

We observed the field of the gamma ray burst GRB250101A (Page et al. GCN 38752, Li et al. GCN 38753, Mohan et al. GCN 38754, Zhu et al. GCN 38755, Budnev et al. GCN 38756, Wu et al. GCN 38758, Odeh et al. GCN 38763) with the Giant Metrewave Radio Telescope (GMRT) under the DDT (PI: A. Balasubramanian, ddtC419) on 8th February 2025 in band 5 (1.3 GHz) for about 2 hours starting at 13:30 hours UTC.

We do not detect any significant radio emission at the position of the optical counterpart (Li et al. GCN 38753). We used 3C48 for the flux calibration and J0238+166 for complex gain and phase calibration. The CASA calibration and imagining CAPTURE-CASA6 pipline was used for data calibration and imaging. We compute a 3-sigma upper limit of ~150 uJy at 1.3 GHz. 

We thank the GMRT Time Allocation Committee for accepting our DDT proposal and GMRT staff that made these observations possible. GMRT is run by the National Centre for Radio Astrophysics of the Tata Institute of Fundamental Research.

GCN Circular 38956

Subject
GRB 250101A: Calapai Observatory, Massa S. Giorgio (Messina), optical observations and rebrightening.
Date
2025-01-15T17:13:17Z (8 months ago)
From
Giovanni Calapai at Calapai Astronomical Observatory, Massa S. Giorgio, Messina, Italy <giovannicalapai@tiscali.it>
Via
Web form
Giovanni Calapai at Calapai Astronomical Observatory, Massa S. Giorgio, (Messina) Italy 
Member of: GRB/UAI Gamma Ray Burst Section of Unione Astrofili Italiani. 

Report:

We observed the field of GRB 250101A (Swift trigger 1278305, Page et al., GCN 38752) with the 11 inches Schmidt-Cassegrain (Celestron 11) telescope F/D=6,3. 
  
The observations were started at 2025-01-01 18:30 UT (approximately 5.08 hours after burst) stacking a set of unfiltered CCD image. The observations were carried out with clear skies and good visibility conditions. 

The OT was detected at the following position:

RA    (J2000.0)  02h 28m 16.62s   +/- 0,03
Decl. (J2000.0) +19° 11' 37.4"    +/- 0,40

Preliminary photometry was obtained using nearby PanSTARRS stars as follows: 

Observation   Mid-Time    T-T0 (hr)      Exposure        Filter      Mag.      Err.
2025-01-01  19:12:46 UT     5.79          5x600s          CR        19.71    +/-0.13

An optical rebrightening was observed as follows:

Observation   Mid-Time    T-T0 (hr)      Exposure        Filter      Mag.      Err.
2025-01-01  20:31:39 UT     7.11          90x60s          CR        19.63    +/-0.09
2025-01-01  22:04:47 UT     8.66          90x60s          CR        19.75    +/-0.08

Magnitude was calibrated with the nearby PanSTARRS stars converted using Lupton (2005) equations. 
No correction for galactic dust extinction was applied.

Our observations are consistent with other already reported Li et al. (GCN 38753), Mohan et al. (GCN 38754), Zhu et al. (GCN 38755); Budnev et al. (GCN 38756), Wu et al. (GCN 38758), Moskvitin and Spiridonova (GCN 38762), Odeh and Guessoum (GCN 38763), Hu et al. (GCN 38764), Moskvitin et al. (GCN 38765), D'Avino and Izzo (GCN 38768), Escudero-Coca et al (GCN 38769), Leonini et al. (GCN 38771), Zhang et al. (GCN 38774), Siegel and Page (GCN 38775), Komesh et al. (GCN 38777), Ghosh et al. (GCN 38779), Moskvitin et al. (GCN 38780), Komesh et al. (GCN 38790), and Bochenek and Perley (GCN 38798), Lapido et al. 2025 (GCN 38810), Anshika Gupta et al. (GCN  38818), M. Ferro et al. (GCN 38831), Jia-Qi Lin et al. (GCN 38837), Pankov et. al. (GCN 38869), Pankov et. al. (GCN 38890), Pankov et. al. (GCN 38926).

The message may be cited.

GCN Circular 38926

Subject
GRB 250101A: Terskol Zeiss-2000 optical observations
Date
2025-01-14T06:25:40Z (8 months ago)
From
Nicolai Pankov at HSE, IKI RAS <colinsergesen@gmail.com>
Via
Web form
E. Mazaeva (IKI), N. Pankov (HSE, IKI), A. Pozanenko (IKI), N. Kapitanov (INASAN), A. Moskvitin (SAO RAS) report on behalf of the IKI-GRB-FuN collaboration:

We performed optical observations of the field of GRB 250101A (Page et. al, GCN 38752; Li et. al, GCN 38753; Mohan et. al, GCN 38754; Zhu et. al, GCN 38755; Budnev et. al, GCN 38756; Wu et. al, GCN 38758; Zhu et. al, GCN 38759; Goad et. al, GCN 38761; Moskvitin et. al, GCN 38762; Odeh et. al, GCN 38763; Hu et. al, GCN 38764; Moskvitin et. al, GCN 38765; D'Avino et. al, GCN 38768; Escudero-Coca et. al, GCN 38769; Leonini et. al, GCN 38771; Dichiara et. al, GCN 38773; Zhang et. al, GCN 38774; Siegel, GCN 38775; Li et. al, GCN 38776; Komesh et. al, GCN 38777; Ghosh et. al, GCN 38779; Moskvitin et al., GCN 38780; Krimm et. al, GCN 38782; Komesh et. al, GCN 38790; Méndez-Lapido et. al, GCN 38810; Gupta et. al, GCN 38818; Ferro et. al, GCN 38831; Lin et. al, GCN 38837; Pankov et. al., GCN 38869; Pankov et. al, GCN 38890) in the R filter with the 2-meter Zeiss-2000 telescope of the Terskol observatory starting on 2025-01-01 17:27 UT, i.e. ~4.8 hours since trigger. The preliminary photometry of the optical afterglow is as follows:

Date       UT start  t-T0         Exp.    Filter   OT     Err.  UL(3sigma)
                     (mid, days)  (s)
2025-01-01 17:27:31  0.19926      38*120  R        20.11  0.04  22.4
2025-01-01 21:37:20  0.35498      30*60   R        19.40  0.05  21.5
2025-01-02 14:57:45  1.07870      57*30   R        22.13  0.33  22.1
2025-01-02 21:44:44  1.35811      39*30   R        21.93  0.28  22.1
2025-01-03 18:02:09  2.22881      90*60   R        n/d    n/d   22.7

The photometry is based on nearby stars from the PS1 catalog (Lupton 2005 transformations). No correction has been made for the Galactic extinction. The obtained results confirm the re-brightening visible in other observations (Moskvitin et. al, GCN 38765; Pankov et. al, GCN 38890).

GCN Circular 38890

Subject
GRB 250101A: CMO RC-500 optical observations
Date
2025-01-10T12:36:46Z (8 months ago)
From
Nicolai Pankov at HSE, IKI RAS <colinsergesen@gmail.com>
Via
Web form
N. Pankov (HSE, IKI RAS), A. Pozanenko (IKI RAS), A. Tarasenkov (INASAN), A. Moskvitin (SAO RAS) 
report on behalf of a larger collaboration:

We performed optical observations of the field of GRB 250101A (Page et. al, GCN 38752; Li et. al, GCN 38753; Mohan et. al, GCN 38754; Zhu et. al, GCN 38755; Budnev et. al, GCN 38756; Wu et. al, GCN 38758; Zhu et. al, GCN 38759; Goad et. al, GCN 38761; Moskvitin et. al, GCN 38762; Odeh et. al, GCN 38763; Hu et. al, GCN 38764; Moskvitin et. al, GCN 38765; D'Avino et. al, GCN 38768; Escudero-Coca et. al, GCN 38769; Leonini et. al, GCN 38771; Dichiara et. al, GCN 38773; Zhang et. al, GCN 38774; Siegel, GCN 38775; Li et. al, GCN 38776; Komesh et. al, GCN 38777; Ghosh et. al, GCN 38779; Moskvitin et al., GCN 38780; Krimm et. al, GCN 38782; Komesh et. al, GCN 38790; Méndez-Lapido et. al, GCN 38810; Gupta et. al, GCN 38818; Ferro et. al, GCN 38831; Lin et. al, GCN 38837; Pankov et. al., GCN 38869) in the R filter with the 0.5-meter RC-500 telescope located at the Caucasus Mountain Observatory (CMO). The observations began on 2025-01-01 14:40:56 UT, i.e. ~1.28 hours since trigger. The preliminary light curve of the optical afterglow is available at http://grb.rssi.ru/GRB250101A/GRB250101A_RC50_KGO.png. After a typical power-law decay, the afterglow light curve demonstrates a re-brightening occurring at ~5 hr since burst, initially reported by Moskvitin et. al, GCN 38765.

GCN Circular 38869

Subject
GRB 250101A: Terskol K-800 optical observations
Date
2025-01-09T12:38:39Z (8 months ago)
From
Nicolai Pankov at HSE, IKI RAS <colinsergesen@gmail.com>
Via
Web form
N. Pankov (HSE, IKI RAS), A. Pozanenko (IKI RAS), V. Agletdinov (KIAM), A. Moskvitin (SAO RAS) 
report on behalf of a larger collaboration:

We performed optical observations of the field of GRB 250101A (Page et. al, GCN 38752; Li et. al, GCN 38753; Mohan et. al, GCN 38754; Zhu et. al, GCN 38755; Budnev et. al, GCN 38756; Wu et. al, GCN 38758; Zhu et. al, GCN 38759; Goad et. al, GCN 38761; Moskvitin et. al, GCN 38762; Odeh et. al, GCN 38763; Hu et. al, GCN 38764; Moskvitin et. al, GCN 38765; D'Avino et. al, GCN 38768; Escudero-Coca et. al, GCN 38769; Leonini et. al, GCN 38771; Dichiara et. al, GCN 38773; Zhang et. al, GCN 38774; Siegel, GCN 38775; Li et. al, GCN 38776; Komesh et. al, GCN 38777; Ghosh et. al, GCN 38779; Moskvitin et al., GCN 38780; Krimm et. al, GCN 38782; Komesh et. al, GCN 38790; Méndez-Lapido et. al, GCN 38810; Gupta et. al, GCN 38818; Ferro et. al, GCN 38831; Lin et. al, GCN 38837) in the clear light with the 0.8-meter K-800 telescope of the Terskol observatory of INASAN. The observations began on 2025-01-01 18:09:54 UT, i.e. ~0.2 days since trigger. The preliminary photometry of the optical afterglow in the combined image of 160*30 sec is as follows:

Date       UT start  t-T0         Exp.    Filter   OT     Err.  UL(3sigma)
                     (mid, days)  (s)
2025-01-01 18:09:54  0.22713      160*30  Clear    20.03  0.18  21.5

The photometry is based on nearby stars of PS1 catalog (Lupton transformations) and not corrected for the Galactic extinction.

GCN Circular 38837

Subject
GRB 250101A: J band upper limit by SYSU 80cm telescope
Date
2025-01-07T06:20:55Z (8 months ago)
From
Jiaqi Lin <islinjiaqi@gmail.com>
Via
Web form
Jia-Qi Lin, Jin-Ji Li, Zhong-Nan Dong, Si-Yuan Zhu, Wei-Sen Huang, Pu Lin, Hao-Nan Yang, Yan Yu, Hao-Ran Zhang, Pak-Hin Thomas Tam, Bin Ma (Sun Yat-sen University) report on behalf of the SYSU 80cm telescope team:

We observed the field of GRB 250101A (Page et al., GCN 38752), using the Sun Yat-sen University 80cm telescope, with 158 × 20 s exposures in J band. Our observations began at 2025-1-1 15:18:18 UTC, 1.92 hours after the BAT trigger. 

We did not detect any counterpart in the stacked images at the position of the optical afterglow (Li et al., GCN 38753; Mohan et al., GCN 38754; Zhu et al., GCN 38755; Budnev et al., GCN 38756; Wu et al., GCN 38758; Odeh et al., GCN Circular 38763), down to a 5-sigma depth of J ~ 18.0 Vega magnitudes.

GCN Circular 38831

Subject
GRB 250101A: REM optical/NIR counterpart detection
Date
2025-01-06T15:58:24Z (8 months ago)
From
Matteo Ferro at INAF-OAB <matteo.ferro@inaf.it>
Via
Web form
M. Ferro, R.Brivio, P. D’Avanzo, S. Covino, D. Fugazza (INAF-OAB) report on behalf of the REM team:

We observed the field of GRB 250101A, detected by Swift (Page et al., GCN 38752) with the REM 60cm robotic telescope located at the ESO observatory of La Silla (Chile). The observations were carried in the g, r, i, z, J, H, K bands, starting on 2025 January 02 at 00:47:33 UT (i.e. 11.4 hours after the Swift trigger), and lasting for about 1 hour.
From preliminary photometry we detect the counterpart in the optical and NIR images at the position of the optical afterglow (e.g., Page et al., GCN 38752; Li et al., GCN 38753; Mohan et al., GCN 38754; Zhu et al., GCN 38755; Wu et al., GCN 38758), in agreement with the rebrightening reported by Moskvitin et al., GCN 38765, with the following magnitudes:

r = 19.3 +- 0.1 (AB; calibrated against the PanSTARRS catalogue)
at a mid-time of t - t0 = 11.9 hr after the trigger,

H = 17.2 +- 0.2 (Vega; calibrated against the 2MASS catalogue) 
at a mid-time of t - t0 = 11.9 hr after the trigger.

GCN Circular 38818

Subject
GRB 250101A: 1.3m DFOT optical afterglow detection
Date
2025-01-04T06:50:02Z (8 months ago)
From
ANSHIKA GUPTA at ARIES <anshika05180@gmail.com>
Via
Web form
Anshika Gupta, Amit K. Ror, Mamta, Kuntal Misra, and Shashi B. Pandey (ARIES) report:

We observed the field of GRB 250101A detected by Swift-BAT (GCN 38752) 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 were started on 2025-01-01 at 17:14:04 UT, i.e., ~ 3.85 hours after the Swift-BAT trigger. We have taken multiple frames with an exposure time of 300 s in the R filter. We stacked the images after the alignment. We clearly detected optical afterglow in our stacked image within the error box of the enhanced Swift-XRT position by Goad et al. 2025 (GCN 38761). We obtained the following preliminary magnitude in the stacked image:


Date Start_UT T_start-T0 (hour) Filter  Exp time (s)  magnitude

==================================================================

2025-01-01 17:14:04   ~3.85 hour   R     300*12      19.955+-0.003


Our detection is consistent with Page et al. 2025 (GCN  38752); Li et al. 2025 (GCN 38753); Mohan et al. 2025(GCN 38754); Zhu et al. 2025 (GCN 38755); Budnev et al. 2025 (GCN 38756); SVOM/C-GFT team 2025 (GCN 38758); Zhu et al. 2025 (GCN 38759); Moskvitin et al. 2025(GCN 38762, GCN 38765); Odeh et al. 2025 (GCN 38763); Hu et al. 2025 (GCN 39764); D'Avino et al. 2025(GCN 38768); Coca et al. 2025 (GCN 38769); Leonini et al. 2025(GCN 38771); Zhang et al. 2025 (GCN 38774); Siegel et al. 2025 (GCN 38775); Komesh et al. 2025 (GCN 38777); Ghosh et al. 2025 (GCN 38779); Moskvitin et al. 2025 (GCN 38780); Komesh et al. 2025 (GCN 38790); Bochenek et al. 2025 (GCN 38798); Lapido et al. 2025 (GCN 38810). 

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 catalog. This circular may be cited.

GCN Circular 38810

Subject
GRB 250101A: further LCOGT optical afterglow observations
Date
2025-01-04T01:15:20Z (8 months ago)
From
Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf@iac.es>
Via
Web form
C. Méndez-Lapido, B. Armas-Chinea, F. Dobrindt, P. Escudero-Coca, G. Fernández-Rodríguez, Á. García Lozano, A. Huertas Ferrer, I. Ortega-Casas, M. Torreiro Martínez, G. Villa (ULL), S.R. Berlanas, F. Poidevin, and I. Pérez-Fournon (IAC and ULL)


We report on further optical imaging of the field of GRB 250101A, discovered by Swift BAT (Page et al., GCN #38752), with one of the two Las Cumbres Observatory global telescope network (LCOGT) 40-cm telescopes located at the LCOGT node at the Cerro Tololo Inter-American Observatory (CTIO, Chile).
The observation, a single 600-sec exposure in the SDSS r' filter, started on 2025-01-02 01:24:03 UT, i.e. ~ 12.02 hr after the Swift BAT trigger. We detect the optical afterglow at a position consistent with the Swift UVOT position reported by Page et al. (GCN #38752). We measure a magnitude of r' = 20.12 +/- 0.18 calibrated against PanSTARRS DR1 stars and not corrected for Galactic extinction.

This result is consistent with other reports: Li et al. (GCN 38753), Mohan et al. (GCN 38754), Zhu et al. (GCN 38755); Budnev et al. (GCN 38756), Wu et al. (GCN 38758), Moskvitin and Spiridonova (GCN 38762), Odeh and Guessoum (GCN 38763), Hu et al. (GCN 38764), Moskvitin et al. (GCN 38765), D'Avino and Izzo (GCN 38768), Escudero-Coca et al (GCN 38769), Leonini et al. (GCN 38771), Zhang et al. (GCN 38774), Siegel and Page (GCN 38775), Komesh et al. (GCN 38777), Ghosh et al. (GCN 38779), Moskvitin et al. (GCN 38780), Komesh et al. (GCN 38790), and Bochenek and Perley (GCN 38798). 

The spectroscopic redshift has been measured by Zhu et al., z = 2.49 (GCN 38759) and Li et al., z ~ 2.481 (GCN 38776).

These results are based on observations made with the Las Cumbres Observatory’s education network 
telescopes that were upgraded through generous support from the Gordon and Betty Moore Foundation 
and are part of a course on Astrophysical Techniques of the Master in Astrophysics of the Universidad 
de La Laguna, Tenerife, Spain (LCOGT observing programme IAC2024B-010, ULL-ASTRO-MASTER).

GCN Circular 38798

Subject
GRB 250101a: Liverpool Telescope optical follow-up
Date
2025-01-03T16:31:30Z (8 months 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 GRB250101a (Page et. al., GCN 38752) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 6x200s exposures in the SDSS r’ filter starting at 2025-01-02 23:03:59 UT, approximately 1.4 days after the trigger. Three of the images had to be discarded due to autoguider issues.

We report a faint detection in the stacked images of r = 22.8 ± 0.2 mag, at a position consistent with the Swift/UVOT position (Page et. al., GCN 38752). The photometry was obtained using nearby PanSTARRS standards and was not corrected for extinction. The object continues to decline after re-brightening (Moskvitin et al., GCN 38765, Escudero-Coca et al., GCN 38769, Leonini et al., GCN 38771), consistent with the observations reported by Ghosh et al., GCN 38779 and Moskvitin et al., GCN 38780.

GCN Circular 38790

Subject
GRB 250101A: NUTTelA-TAO / BSTI Optical Limits
Date
2025-01-03T12:16:34Z (8 months ago)
From
Toktarkhan Komesh at Nazarbayev University <toktarkhan.komesh@nu.edu.kz>
Via
Web form
T. Komesh (NU), Z. Maksut (NU), Z. Abdullayev (NU), B. Grossan (UCB, NU), D. Berdikhan (NU), M. Krugov (FAI) and E. Abdikamalov (NU) report on behalf of the Energetic Cosmos Laboratory:

The Nazarbayev University Transient Telescope at Assy-Turgen Astrophysical Observatory (NUTTelA-TAO) observed the field of GRB 250101A at 14:00:32 UT on 2025-01-02, 24.8 hours after the BAT trigger. Observations were made in clear conditions. No source consistent with the XRT (P.A. Evans et al., GCN 38708; T. Komesh et al., GCN 38777) was detected. We report the following results:

t-t0(h) UL g' 	UL r' 	exposure_time (s)
-----------------------------------------
24.8 	21.0 	20.8 	300

t is the middle time, t0 is the BAT trigger time, t-t0 is given in hours. UL gives the 5 sigma upper limit sensitivity in magnitudes, for images of the given exposure time. Calibration was done with 4 Pan-STARRS catalog stars on our images. No color or other corrections were applied to the values above.

-----------------------------------------------
NU = Nazarbayev University, Astana, Kazakhstan
UCB = University of California, Berkeley, USA
FAI = Fesenkov Astrophysical Institute, Kazakhstan

This research has been funded by the Science Committee of the Ministry of Science and Higher Education of the Republic of Kazakhstan (Grant No. AP26103591). The NUTTelA-TAO Team acknowledges the support of the staff of the Assy-Turgen Astrophysical Observatory, Almaty, Kazakhstan, and the Fesenkov Astrophysical Institute, Almaty, Kazkhstan.

GCN Circular 38782

Subject
GRB 250101A: Swift-BAT refined analysis
Date
2025-01-02T21:38:42Z (8 months ago)
From
Amy <yarleen@gmail.com>
Via
email
H. A. Krimm (NSF), S. D. Barthelmy (GSFC), R. Gupta (GSFC), S. Laha
(GSFC/UMBC), A. Y. Lien (U Tampa), C. B. Markwardt (GSFC), M. J. Moss
(GSFC), D. M. Palmer (LANL), K. L. Page (U Leicester), 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+800 sec from the recent telemetry
downlink, we report further analysis of BAT GRB 250101A (trigger #1278305)
(Page et al., GCN Circ. 38752).

The BAT ground-calculated position is
RA, Dec = 37.057, 19.181 deg which is
   RA(J2000)  =  02h 28m 13.7s
   Dec(J2000) = +19d 10' 50.5"
with an uncertainty of 1.9 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 47%.

The mask-weighted light curve shows a weak pulse that starts at ~T0, peaks
at ~T+1 s, and ends at ~T+35 s. T90 (15-350 keV) is 34.19 +- 7.71 sec
(estimated error including systematics).

The time-averaged spectrum from T-0.22 to T+36.50 sec is best fit by a
simple power-law model.  The power law index of the time-averaged spectrum
is 2.12 +- 0.24.  The fluence in the 15-150 keV band is 6.3 +- 1.0 x 10^-07
erg/cm2. The 1-sec peak photon flux measured from T+0.95 sec in the 15-150
keV band is 0.8 +- 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/1278305/

GCN Circular 38780

Subject
GRB 250101A: further SAO RAS optical observations
Date
2025-01-02T18:41:47Z (8 months ago)
From
Moskvitin Alexander at SAO RAS <mosk@sao.ru>
Via
Web form
A. S. Moskvitin and O. I. Spiridonova, Yu. V. Sotnikova (SAO RAS), 
A. Ghosh, S. Razzaque (CAPP, University of Johannesburg) and 
A. S. Pozanenko (IKI RAS) report on behalf of the GRB follow-up team.

We observed the field of Swift GRB 250101A (Page et al., GCN 38752) 
with the 1-m telescope of SAO RAS, Zeiss-1000 + CCD-photometer
on January 2, 15:20:13--18:06:55 UT (t_mid - T0 = 1.1394 days).
We obtained 19 x 300 sec. images in Rc band.

The OT (Page et al., GCN 38752; Li et al., GCN 38753, GCN 38776; 
Mohan et al., GCN 38754; Zhu et al., GCN 38755, GCN 38759; 
Budnev et al., GCN 38756; Wu et al., GCN 38758; Moskvitin et al., 
GCN 38762, GCN 38765; Odeh and Guessoum, GCN 38763; Hu et al., 
GCN 38764; D'Avino and Izzo, GCN 38768; Escudero-Coca et al., 
GCN 38769; Leonini et al., GCN 38771; Zhang et al., GCN 38774; 
Siegel and Page, GCN 38775;  Komesh et al., GCN 38777; Ghosh et al.,
GCN 38779) is clearly detected in our stacked image 
with the brightness of R = 21.86 +/- 0.06, calibrated against 
nearby PS1 stars (magnitudes were converted with the Lupton 2005 
equations) and not corrected for the MW extinction.

GCN Circular 38779

Subject
GRB 250101A: LCO optical counterpart detection
Date
2025-01-02T16:56:31Z (8 months 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 250101A triggered by Swift (Page et. al., GCN 38752) in B, V  filter of  the 1-meter Sinistro telescope at the Las Cumbres Observatory Global Telescope (LCOGT) node located at McDonald Observatory. The 1-m Sinistro telescope is equipped with a 4K x 4K CCD (FOV: 26 x 26 arcmin, scale: 0.39 arcsec/pixel).
Observations began on January 02, 2025, starting from 14.48 hours after the GRB trigger.

We clearly detect the optical transient (OT) reported by GCNs (Li et al., GCN 38753; Mohan et al., GCN 38754; Zhu et al., GCN 38755; Budnev et al., GCN 38756; Wu et al., GCN 38758; Moskvitin et al., GCN 38762; Odeh et al., GCN 38763, Hu et al., GCN 38764; D'Avino et al., GCN 38768; Escudero-Coca et al., GCN 38769, Coca et al., Zhang wt al., GCN 38774, Komesh et al., GCN 38777) in our B, V band image. 

|Date|		|UTstart|	|t-T0 (hours)|	|Exp (sec)|	|Filter|	|Magnitude| 
---------------------------------------------------------------------------------------------------      
2025-01-02	03:51:30.528	14.48		1 x 900 	V		V = 20.61 +/- 0.04
2025-01-02	06:19:33.312	16.95		2 x 1200	B		B = 21.82 +/- 0.03

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 38777

Subject
GRB 250101A NUTTelA-TAO / BSTI Early Measurements
Date
2025-01-02T12:04:47Z (8 months ago)
Edited On
2025-01-05T04:52:29Z (8 months ago)
From
Toktarkhan Komesh at Nazarbayev University <toktarkhan.komesh@nu.edu.kz>
Edited By
Vidushi Sharma at NASA GSFC/UMBC <vidushi.sharma@nasa.gov> on behalf of Toktarkhan Komesh at Nazarbayev University <toktarkhan.komesh@nu.edu.kz>
Via
Web form
T. Komesh (NU), Z. Abdullayev (NU), Z. Maksut (NU), B. Grossan (UCB, NU), D. Berdikhan (NU), M. Krugov (FAI) and E. Abdikamalov (NU) report on behalf of the Energetic Cosmos Laboratory:

The Nazarbayev University Transient Telescope at Assy-Turgen Astrophysical Observatory (NUTTelA-TAO) pointed at GRB 250101A on receipt of an automated GCN / BAT position alert, observing in Sloan g' and r' bands, with the Burst Simultaneous Three-Channel Imager (BSTI; Grossan, Kumar & Smoot 2019, JHEA, 32, 14).

We started observations at 13:24:00 UT on 2025-01-01, 70 s after the BAT trigger. Observations were made in partly cloudy conditions. A new and changing source consistent with the XRT position (M.R. Goad et al., GCN 38761) was detected. Note that these observations provide essentially full-time coverage, simultaneous in two bands. We report the following photometric values for the optical transient: 

tc-t0(s)    g'(mag) err   r'(mag) err  exposure_time (s)
--------------------------------------------------------------
100     18.66  0.07     18.20  0.07     57
166     17.64  0.12     17.24  0.12     15
181     17.51  0.10     16.98  0.14     15
196     17.11  0.09     16.87  0.12     15
211     17.34  0.13     16.90  0.09     15
226     17.37  0.12     16.77  0.12     15
241     17.31  0.09     16.65  0.06     15
256     17.30  0.11     16.79  0.06     15
271     17.43  0.09     16.85  0.10     15
286     17.37  0.11     16.89  0.08     15
301     17.50  0.16     17.02  0.08     15
316     17.68  0.20     17.01  0.08     15
331     17.52  0.15     17.01  0.10     15
346     17.67  0.11     17.08  0.09     15
361     17.60  0.11     17.13  0.09     15
376     17.62  0.15     16.95  0.13     15
391     17.96  0.14     16.91  0.08     15
406     17.61  0.15     17.39  0.13     15
421     17.81  0.13     17.23  0.12     15
436     17.46  0.13     17.41  0.12     15
451     18.10  0.15     17.41  0.11     15
466     17.78  0.17     17.30  0.11     15
481     17.81  0.13     17.29  0.10     15
496     17.70  0.15     17.36  0.15     15
511     17.92  0.13     17.45  0.11     15
526     17.68  0.12     17.46  0.12     15
541     18.30  0.19     17.53  0.13     15
556     17.86  0.18     17.34  0.13     15
571     17.96  0.14     17.31  0.14     15
586     17.66  0.16     17.43  0.11     15
601     18.16  0.17     17.82  0.14     15
616     17.90  0.15     17.72  0.16     15
631     17.85  0.13     17.23  0.11     15
653     18.12  0.12     17.58  0.10     30
683     18.06  0.10     17.47  0.07     30
713     18.05  0.10     17.54  0.09     30
743     18.01  0.10     17.46  0.08     30
864     18.20  0.05     17.54  0.04     60
924     18.17  0.07     17.67  0.06     60
984     18.21  0.06     17.67  0.04     60
1044    18.26  0.06     17.77  0.04     60
1104    18.37  0.07     17.81  0.05     60
1164    18.33  0.06     17.81  0.05     60
1224    18.46  0.07     17.82  0.05     60
1284    18.48  0.07     17.91  0.05     60
1344    18.56  0.07     17.84  0.05     60
1404    18.43  0.06     18.04  0.05     60
1464    18.43  0.07     18.15  0.06     60
1524    18.63  0.07     18.12  0.06     60
1584    18.66  0.08     18.19  0.07     60
1644    18.73  0.08     18.26  0.07     60
1704    18.70  0.08     18.18  0.06     60
1764    18.66  0.08     18.23  0.06     60
1824    18.81  0.08     18.38  0.08     60
1884    18.82  0.08     18.39  0.07     60
1944    19.01  0.10     18.27  0.07     60
2004    18.83  0.10     18.43  0.08     60
2064    18.87  0.09     18.33  0.07     60
2124    18.75  0.08     18.34  0.07     60
2184    18.99  0.10     18.46  0.08     60
2244    18.97  0.10     18.49  0.08     60
2304    18.90  0.09     18.48  0.09     60
2364    19.21  0.12     18.45  0.08     60
2424    19.01  0.10     18.43  0.07     60
2484    18.95  0.10     18.64  0.09     60
2544    19.10  0.10     18.64  0.09     60
2604    18.98  0.10     18.77  0.10     60
2664    19.12  0.11     18.76  0.10     60
2724    18.93  0.10     18.78  0.10     60
2784    19.23  0.12     18.85  0.11     60
2844    19.18  0.12     18.78  0.11     60
2904    19.43  0.15     18.59  0.09     60
2964    19.15  0.12     18.92  0.12     60
3024    19.23  0.13     18.72  0.11     60
3084    19.19  0.13     18.65  0.11     60
3144    19.30  0.15     18.87  0.13     60
3204    19.18  0.13     19.07  0.16     60
3294    19.42  0.13     18.86  0.10     120
3414    19.38  0.13     18.70  0.09     120
3534    19.41  0.08     19.05  0.14     120
3654    19.38  0.15     18.96  0.14     120
3774    19.37  0.17     19.00  0.16     120
4166    19.65  0.11     18.89  0.08     360
4526    19.82  0.19     19.17  0.13     360

tc-t0 = trigger time minus image center time. Calibration was done with 5 bright Pan-STARRS catalog stars on our images. A light curve of the optical transient is presented in Figure 1: https://ecl.nu.edu.kz/research/observations/gamma-ray-bursts/grb250101a

Our results are in agreement with those reported in previously published circulars (Li et al., GCN 38753; Mohan et al., GCN 38754; Wu et al., GCN 38758; Escudero-Coca et al., GCN 38769; Zhang et al., 38744).

We caution the reader that these are preliminary results, without color or other corrections, and will likely change in small measure. Please also note that times are approximate.


----------------------------------
NU = Nazarbayev University, Astana, Kazakhstan
UCB = University of California, Berkeley, USA
FAI = Fesenkov Astrophysical Institute, Kazakhstan

This research has been funded by the Science Committee of the Ministry of Science and Higher Education of the Republic of Kazakhstan (Grant No. AP26103591). The NUTTelA-TAO Team acknowledges the support of the staff of the Assy-Turgen Astrophysical Observatory, Almaty, Kazakhstan, and the Fesenkov Astrophysical Institute, Almaty, Kazkhstan.

GCN Circular 38776

Subject
GRB 250101A: GMG spectroscopic redshift at z ~ 2.481
Date
2025-01-02T10:05:57Z (8 months ago)
From
Rui-Zhi Li at Yunnan Observatories, CAS <liruizhi@ynao.ac.cn>
Via
email
R.-Z. Li, B.-T. Wang, F.-F. Song, J. Mao, S.-S. Li, H. Lin and J.-M. Bai (YNAO, CAS) report:

We observed the optical counterpart of GRB 250101A (Page et al., GCN 38752; Li et al., GCN 38753; Mohan et al., GCN 38754; Zhu et al., GCN 38755; Budnev et al., GCN 38756; Wu et al., GCN 38758; Moskvitin and Spiridonova, GCN 38762; Odeh and Guessoum, GCN 38763; Hu et al., GCN 38764; Moskvitin et al., GCN 38765; D’Avino and Izzo, GCN 38768; Escudero-Coca et al., GCN 38769; Leonini et al., GCN 38771). The observation was conducted using the GMG-2.4m telescope with Grism #14, which provides a wavelength coverage of 3600–7460 AA. A single 1800s spectrum was obtained, with exposure beginning at 14:24:54.5 UT on 2025-01-01, about 1.03 hours after the Swift trigger.

The Ly-alpha absorption feature at ~ 4250 AA is evident. Despite the low signal-to-noise ratio of the spectrum, we identified multiple metal absorption lines: Si II at 1303 AA, C II at 1335 AA, Si IV at 1394 AA, Si IV at 1403 AA, C IV at 1549 AA, Al II at 1671 AA, Al III at 1855 AA, and Al III at 1863 AA. These metal absorption features consistently indicate a redshift of z ~ 2.481, which is consistent with the Xinglong-2.16m result (Zhu et al., GCN 38759).

We acknowledge the staff at the Lijiang Observatory for conducting the observation.

GCN Circular 38775

Subject
GRB 250101A: Swift/UVOT Detection
Date
2025-01-02T07:11:25Z (8 months ago)
From
Mike Siegel at PSU/Swift MOC <mhs18@psu.edu>
Via
Web form
M. H. Siegel (PSU) and K. L. Page (U. Leicester)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 250101A
133s after the BAT trigger (Page et al., GCN Circ. 38752).
A fading source consistent with the XRT position (Goad et al., GCN Circ. 37761)
and the previously reported optical source, since confirmed by
multiple observations (Li et al., GCN Circ. 38753; Mohan et al., GCN
Circ. 38754; Zhu et al., GCN Circ., 38755; Wu et al., GCN Circ 38578;
Moskvitin & Spiridonova, GCN Circ. 38762; Odeh et al., GCN Circ 38763;
Hu et al., GCN Circ. 38764; D'Avino & L. Izzo, GCN Circ. 38768;
Escudero-Coca, GCN Circ. 38769; Leonini et al., GCN Circ. 38771)
is detected in the initial UVOT exposures.

The preliminary UVOT position is:
    RA  (J2000) =  02:28:16.47 =  37.06864 (deg.)
    Dec (J2000) = +19:11:39.6  =  19.19433 (deg.)
with an estimated uncertainty of 0.43 arc sec. (radius, 90% confidence).

Preliminary detections and 3-sigma upper limits 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)      Exp(s)           Mag

white              133          283          147         18.03 +/- 0.05
v                  620          813           39         18.10 +/- 0.28
b                  546          738           39         18.66 +/- 0.21
u                  291          540          246         17.93 +/- 0.08
w1                 670         5019          235        >19.8
m2                4614         4814          197        >19.1
w2                 596         4404          216        >18.9

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.164 in the direction of the burst
(Schlegel et al. 1998).

We note that the lack of detection in the NUV bands for this bright burst would
be consistent with the redshift of z=2.49 reported by Zhu et al. (GCN Circ. 38759).

GCN Circular 38774

Subject
GRB 250101A: 1.6m Mephisto multi-band optical followup
Date
2025-01-02T05:41:08Z (8 months ago)
From
Brajesh Kumar at SWIFAR, YNU <brajesh@ynu.edu.cn>
Via
Web form
Jinghua Zhang, Guowang Du, Yangwei Zhang, Xufeng Zhu, Fanchuan Kong, Chenxi Shang,Yuan Fang, Xinlei Chen, Xingzhu Zou, Yu Pan, Brajesh Kumar, Yuanpei, Yang, Xiangkun Liu, Xiaowei Liu (all SWIFAR, YNU) report on behalf of the Mephisto Team:

We performed simultaneous multi-band photometric observations of GRB 250101A detected by Swift/BAT (Page et. al., GCN 38752) with the 1.6m Multi-channel Photometric Survey Telescope (Mephisto) of Yunnan University located at Lijiang Observatory. The observations were initiated at 13:26:07 UTC 2025-01-01 (i.e., 197 s after the Swift/BAT trigger) and continuously followed-up for several hours. Multiple frames were obtained in uvgriz bands. The optical counterpart is clearly detected in all bands. The photometry of the initial frames is the following:

UT start            band  Exp   Mag(AB)
2025/01/01T13:26:07  u   180s   18.66 +/- 0.04 	
2025/01/01T13:26:08  g    50s   17.07 +/- 0.01	 
2025/01/01T13:26:08  i    79s   16.30 +/- 0.01	
2025/01/01T13:30:02  v   180s   18.59 +/- 0.03 	
2025/01/01T13:30:04  r    50s   17.30 +/- 0.02	 
2025/01/01T13:30:04  z    79s   16.73 +/- 0.05	

Our results are consistent with the previously reported circulars (Li et al., GCN 38753; Mohan et al., GCN 38754; Zhu et al., GCN 38755; Budnev et al., GCN 38756; Wu et al., GCN 38758; Moskvitin et al., GCN 38762; Odeh et al., GCN 38763, Hu et al., GCN 38764; D'Avino et al., GCN 38768; Escudero-Coca et al., GCN 38769). Further analysis of the additional images is ongoing.

--------------------------------------------------------------------------
Mephisto (Multi-channel Photometric Survey Telescope) is a 1.6m wide-field multi-channel telescope, the first of its type in the world, capable of imaging the same field of view in three optical bands simultaneously. It provides real-time, high-quality colors of stellar objects. The on-site telescope assemblage and commissioning were carried out in September 2022. The first light in all three channels was achieved on 2023 December 21. 
--------------------------------------------------------------------------

GCN Circular 38773

Subject
GRB 250101A: Swift-XRT refined Analysis
Date
2025-01-02T02:14:48Z (8 months ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
S. Dichiara (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U.
Leicester), A. D'Ai (INAF-IASFPA), A. Melandri (INAF-OAR), T. Sbarrato
(INAF-OAB), J.A. Kennea (PSU), D.N. Burrows (PSU) and P.A. Evans report
on behalf of the Swift-XRT team:

We have analysed 6.8 ks of XRT data for GRB 250101A, from 110 s to 39.2
ks after the  BAT trigger. The data comprise 10 s in Windowed Timing
(WT) mode (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=2.8 (+/-0.7). At T+249 s  the decay
flattens to an alpha of 0.06 (+0.29, -0.74) before breaking again at
T+909 s to a final decay with index alpha=0.79 (+0.13, -0.09).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.02 (+0.18, -0.17). The
best-fitting absorption column is  1.7 (+1.3, -1.1) x 10^22 cm^-2, at a
redshift of 2.49, in addition to the Galactic value of 1.4 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 3.6 x
10^-11 (5.1 x 10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Galactic foreground: 1.4 x 10^21 cm^-2
Intrinsic column:    1.7 (+1.3, -1.1) x 10^22 cm^-2 at z=2.49
Photon index:	     2.02 (+0.18, -0.17)

If the light curve continues to decay with a power-law decay index of
0.79, the count rate at T+24 hours will be 0.018 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 6.4 x
10^-13 (9.1 x 10^-13) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/01278305.

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

GCN Circular 38771

Subject
GRB 250101A: Montarrenti Observatory optical observations and rebrightening
Date
2025-01-02T01:29:17Z (8 months ago)
From
Simone Leonini at Montarrenti Observatory (Siena, Italy) <s.leonini@iol.it>
Via
Web form
S. Leonini, M. Conti, P. Rosi, L.M. Tinjaca Ramirez (Montarrenti Observatory, Siena, Italy, part of UAI/SSV-GRB section), M.G. Dainotti (National Astronomical Observatory of Japan), Y. Niino (Tokyo University, Institute of Astronomy) and K. Kalinowski (Aarhus University, Department of Physics and Astronomy) report:

We observed the field of GRB 250101A (Swift trigger 1278305, Page et al., GCN 38752) with the automated and remoted 0.53m Ritchey-Chretien telescope at Montarrenti Observatory (Siena, Italy, IAU code C88).
  
The observations were started at 2025-01-01 18:03:48 UT (approximately 4.66 hours after burst) stacking a set of Rc-band CCD images. Observations were performed under thin cloud cover in the second part of the night. 

The OT was detected at the following position:

RA    (J2000.0)  02h 28m 16.56s  +/-0.05 
Decl. (J2000.0) +19° 11' 39.82"  +/-0.14

Preliminary photometry was obtained using nearby PanSTARRS stars as follows: 

Observation Mid-Time  	T-T0 (hr)       Exposure        Filter      Mag.       Err.
2025-01-01  18:18:09 UT   4.92	   	 40x40s		  Rc       20.09     +/-0.09
2025-01-01  18:47:18 UT   5.40           43x40s   	  Rc       20.09     +/-0.10

An optical rebrightening was observed as follows:

Observation Mid-Time  	T-T0 (hr)       Exposure        Filter      Mag.       Err.
2025-01-01  19:45:22 UT   6.37	    	 36x40s	  	  Rc       19.63     +/-0.08

Magnitude was calibrated with the nearby PanSTARRS stars converted using Lupton (2005) equations. No correction for galactic dust extinction was applied.

Our observations are consistent with other already reported (Li et al., GCN 38753; Mohan et al., GCN 38754; Zhu et al., GCN 38755; Budnev et al., GCN 38756; Wu et al., GCN 38758; Moskvitin et al., GCN 38762; Odeh et al., GCN 38763, Hu et al., GCN 38764; D'Avino et al., GCN 38768; Escudero-Coca et al., GCN 38769), included those of the optical brightening (Moskvitin et al., GCN 38765).

GCN Circular 38769

Subject
GRB 250101A: LCOGT optical afterglow detection
Date
2025-01-02T00:15:46Z (8 months ago)
From
Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf@iac.es>
Via
Web form
P. Escudero-Coca, B. Armas-Chinea, F. Dobrindt, G. Fernández-Rodríguez, Á. García Lozano, A. Huertas Ferrer, C. Méndez-Lapido, I. Ortega-Casas, M. Torreiro Martínez, G. Villa (ULL), S.R. Berlanas, F. Poidevin, and I. Pérez-Fournon (IAC and ULL)

We report on optical imaging of the field of GRB 250101A, discovered by Swift BAT (Page et al., GCN #38752), with the Las Cumbres Observatory global telescope network (LCOGT) 40-cm telescope located at the LCOGT node at Sutherland Observatory (South Africa). The observation, a single 600-sec exposure in the SDSS r' filter, started on 2025-01-01 19:56:30 UT, i.e. ~ 6.56 hr after the Swift BAT trigger. We detect the optical afterglow at a position consistent with the Swift UVOT position reported by Page et al. (GCN #38752). We measure a magnitude of r' = 19.96 +/- 0.16 calibrated against PanSTARRS DR1 stars and not corrected for Galactic extinction.

This result is consistent with other reports: Li et al., GCN 38753; Mohan et al., GCN 38754; Zhu et al., GCN 38755; Budnev et al., GCN 38756; Wu et al., GCN 38758; Moskvitin and Spiridonova, GCN 38762;
Odeh and Guessoum, GCN 38763; Hu et al., GCN 38764; and D'Avino and Izzo, GCN 38768.

A rebrightening in the optical has been reported by Moskvitin et al. (GCN 38765).

The spectroscopic redshift of z = 2.49 has been obtained by Zhu et al. (GCN 38759).

These results are based on observations made with the Las Cumbres Observatory’s education network 
telescopes that were upgraded through generous support from the Gordon and Betty Moore Foundation 
and are part of a course on Astrophysical Techniques of the Master in Astrophysics of the Universidad 
de La Laguna, Tenerife, Spain (LCOGT observing programme IAC2024B-010, ULL-ASTRO-MASTER).

GCN Circular 38768

Subject
GRB 250101A: OASDG optical observations
Date
2025-01-01T23:37:38Z (8 months ago)
From
luca.izzo@inaf.it
Via
Web form
L. D'Avino (OASDG/AstroCampania), and L. Izzo (INAF-OACn and DARK/NBI) report:

We observed the field of GRB 250101A (Page et al., GCN #38752) using the 0.5-m T1 telescope of the Osservatorio Astronomico S. Di Giacomo, located in Agerola, Italy. Our observations started on 2025 January 1 at 16:57 UT, approximately 3.6 hours after the GRB trigger. We acquired a series of 8x300 s frames in the Rc and Ic filters.

In the stacked images, we clearly detect the optical counterpart initially identified by Swift-UVOT (Page et al., GCN #38752) and reported by several other telescopes (Li et al., GCN #38753; Mohan et al., GCN #38754; Zhu et al., GCN #38755; Budnev et al., GCN #38756; Wu et al., GCN #38758; Zhu et al., GCN #38759; Moskvitin et al., GCN #38762, GCN #38765; Odeh & Guessoum, GCN #38763; Hu et al., GCN #38764). We measure a preliminary magnitude of Rc = 20.00 +/- 0.07 mag (AB), calibrated against nearby stars from the Pan-STARRS catalog, appropriately transformed to Rc and Ic magnitudes.

GCN Circular 38765

Subject
GRB 250101A: SAO RAS observations of optical brightening
Date
2025-01-01T22:57:03Z (8 months ago)
From
Moskvitin Alexander at SAO RAS <mosk@sao.ru>
Via
Web form
A. S. Moskvitin, O. I. Spiridonova (SAO RAS) and 
A. S. Pozanenko (IKI RAS) report on behalf of the GRB follow-up team.
 
We continued follow-up observations of GRB 250101A OT (Page et al., 
GCN 38752; Li et al., GCN 38753; Mohan et al., GCN 38754; Zhu et al., 
GCN 38755, GCN 38759; Budnev et al., GCN 38756; Wu et al., GCN 38758; 
Odeh and Guessoum, GCN 38763; Hu et al., GCN 38764) 
with the 1-m telescope of SAO RAS, Zeiss-1000 + CCD-photometer.

After a steady decline in the afterglow light curve between 3.2 and 5.5
hours (see GCN 38762), we clearly observe an increase in the brightness 
of OT of R= 19.08 +/- 0.02 at 8.24 hours after the trigger.

We encourage further observations of GRB 250101A.

GCN Circular 38764

Subject
GRB 250101A: BOOTES-4/MET optical afterglow detection
Date
2025-01-01T22:09:03Z (8 months ago)
From
Alberto Castro-Tirado at Inst.de Astro. de Andalucia <ajct@iaa.es>
Via
email
Y.-D. Hu (INAF-OAB, Brera), E. Fernandez-Garcia, I. Perez-Garcia, M. D. Caballero-Garcia, G. Garcia-Segura, S. Guziy, R. Sanchez-Ramirez,  S.-Y. Wu and A. J. Castro-Tirado (IAA-CSIC, Granada), C. Perez del Pulgar, A. Castellon, I. M. Carrasco (Univ. de Malaga), M. Gritsevich (Univ. of Helsinki) and D. R. Xiong, J. M. Bai, Y. F. Fan, C. J. Wang, Y. X. Xin, X. H. Zhao, J. R. Mao, B. K. Lun, K. Ye (Yunnan Observatories/CAS, Kunming) on behalf of a larger collaboration, report:

Following the detection of GRB 250101A by Swift (Page et al. GCNC 38752), the 0.6m BOOTES-4/MET robotic telescope at Lijiang Astronomical Observatory (China) automatically responded to this burst starting on Jan. 1, 13:26:58 UT (~248 s after trigger). Series of images in clear filter were gathered and the optical afterglow was detected within the enhanced Swift/XRT position (Goad et al. GCNC 38761), for which we measure a magnitude of 17.7 +- 0.3 on the first 5 s exposure image, which is consistent with the reported detections by UVOT (Page et al. GCNC 38752), GMG (Li et al. GCNC 38753), GIT (Mohan et al. GCNC 38754), Nanshan (Zhu et al. GCNC 38755), MASTER (Lipnov et al. GCNC 38756), C-GFT (Wu et al. GCNC 38758), Xinglong-2.16m (Zhu et al. GCNC 38759), SAO (Moskvitin et al. GCNC 38762) and AKO (Odeh et al. GCNC 38763). Further analysis of the additional images is ongoing.

We thank the staff at Lijiang observatory for their excellent support.

GCN Circular 38763

Subject
GRB 250101A: AKO Optical Afterglow Detection
Date
2025-01-01T19:23:00Z (8 months ago)
From
Mohammad Odeh at Al Khatim Observatory M44 <mshodeh@gmail.com>
Via
email
Mohammad Odeh (Al-Khatim Observatory, AKO, operated by the International
Astronomical Center in Abu Dhabi, UAE), and Nidhal Guessoum (American
University of Sharjah, UAE), report:

We observed the field of GRB 250101A (Page et al., GCN 38752) using our
0.36m f/7.7 robotic telescope. The observation session began on 01 January
2025 at 15:52 UT and continued until 17:25 UT, with a midpoint at 16:40 UT,
approximately 3.3 hours after the trigger.

 

The weather conditions during the observation were partly cloudy. We
obtained multiple 180-second exposures using the Ic filter. The optical
afterglow was barely detected at:

R.A. (J2000): 02:28:16.5

Dec. (J2000): +19:11:40.1

 

Our detection is consistent with the results of (Page et al., GCN 38752; Li
et al., GCN 38753; Mohan et al., GCN 38754; Zhu et al., GCN 38755; Budnev et
al., GCN 38756; Wu et al., GCN 38758).

 

The following observation was calculated using Atlas catalogue as a
reference:

----------------------------------------------------------------------------
-

ObsTime (mid), Exposure (sec), Filter, Mag

----------------------------------------------------------------------------
-

2025-01-01T16:39:55Z, 25 x 180s (stacked), Ic, 17.8 +/- 0.9

----------------------------------------------------------------------------
-

The magnitude is not corrected for galactic extinction.

GCN Circular 38762

Subject
GRB 250101A: SAO RAS optical observations
Date
2025-01-01T19:20:35Z (8 months ago)
From
Moskvitin Alexander at SAO RAS <mosk@sao.ru>
Via
Web form
A. S. Moskvitin and O. I. Spiridonova (SAO RAS), 
report on behalf of the GRB follow-up team.

We observed the field of Swift GRB 250101A (Page et al., GCN 38752) 
with the 1-m telescope of SAO RAS, Zeiss-1000 + CCD-photometer. 
On January 1, 16:18:20--16:51:10 UT (t_mid - T0 = 3.1986 hours)
we obtained first set of 6 x 300 sec. images in Rc band. 
At 18:43:29--18:59:33 UT (t_mid - T0 = 5.4781 hours) 
we obtained second set of data, 3 x 300 sec. images in Rc band.

The OT (Page et. al., GCN 38752; Li et al., GCN 38753; Mohan et al., 
GCN 38754; Zhu et al., GCN 38755, GCN 38759; Budnev et al., GCN 38756;
WU et al., GCN 38758) is clearly detected in our stacked frames 
with the brightness of R = 19.76 +/- 0.01 (t_mid - T0 = 3.1986 hours)
and R = 19.84 +/- 0.02 (5.4781 hours), calibrated against nearby PS1 
stars (magnitudes were converted with the Lupton 2005 equations 
and not corrected for the MW extinction).

Observations are ongoing.

GCN Circular 38761

Subject
GRB 250101A: Enhanced Swift-XRT position
Date
2025-01-01T17:53:29Z (8 months ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
M.R. Goad, J.P. Osborne, A.P. Beardmore and P.A. Evans (U. Leicester) 
report on behalf of the Swift-XRT team.

Using 631 s of XRT Photon Counting mode data and 2 UVOT
images for GRB 250101A, 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 = 37.06921, +19.19403 which is equivalent
to:

RA (J2000): 02h 28m 16.61s
Dec (J2000): +19d 11' 38.5"

with an uncertainty of 2.8 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 was automatically generated, and is an official product of the
Swift-XRT team.

GCN Circular 38759

Subject
GRB 250101A: Xinglong-2.16m spectroscopic redshift
Date
2025-01-01T16:33:10Z (8 months ago)
From
Dong Xu at NAOC/CAS <dxu@nao.cas.cn>
Via
Web form
Z.P. Zhu, S.Y. Fu, X. Liu, S.Q. Jiang, J. An, D. Xu (NAOC) report on behalf of a large collaboration:

We carried out spectroscopy of the optical counterpart (e.g., Page et. al., GCN 38752; Li et al., GCN 38753; Mohan et al., GCN 38754; Zhu et al., GCN 38755) of GRB 250101A detected by Swift/BAT (Page et. al., GCN 38752), using the 2.16-m telescope located at Xinglong, Hebei, China. Our spectra cover the wavelength range 3800 - 9000 AA, and consist of 3 exposures of 1800 s each. 

The whole spectrum has a fairly low S/N, but absorption features are evident. From the detection of a Lya absorption feature at ~ 4240 AA and multiple absorption features, which interpreted as being due to Si II, O I, C IV, Fe II, and Cr II, we infer a common redshift of z = 2.49. We conclude this is the likely redshift of the burst.

We acknowledge the expert support from the Xinglong-2.16m staff, in particular Yu Zhang, Junjun Jia, and Jie Zheng.

GCN Circular 38758

Subject
GRB 250101A: SVOM/C-GFT early optical observations
Date
2025-01-01T16:31:19Z (8 months ago)
From
Chao Wu at NAOC <cwu@nao.cas.cn>
Via
Web form
SVOM/C-GFT team: Chao WU (NAOC), Zhe Kang (CHO), Liping Xin(NAOC), Xuhui Han(NAOC), Pinpin Zhang (NAOC), Xiaomeng Lu (NAOC), Zhenwei Li (CHO), You Lv (CHO), Ruosong Zhang (NAOC), Yujie Xiao(NAOC)

SVOM JSWG: Jian-Yan Wei (NAOC), Bertrand Cordier (CEA), Shuang-Nan Zhang (IHEP), Stéphane Basa (LAM), Arnaud Claret (CEA), Zi-Gao Dai (USTC), Frédéric Daigne (IAP), Jin-Song Deng (NAOC),Olivier Godet (IRAP),  Andrea Goldwurm (APC), Diego Götz (CEA), Xu-Hui Han (NAOC), Cyril Lachaud (APC), En-Wei Liang (GXU), Yu-Lei Qiu (NAOC), Susanna Vergani (Obs.Paris), Jing Wang (NAOC), Chao Wu (NAOC), Li-Ping Xin (NAOC),  Shao-Lin Xiong (IHEP), Bing Zhang (UNLV)


We observed the field of GRB 250101A detected by Swift/BAT (Page et al., GCN 38752) on 2025-01-01T13:24:07 UT, ~ 77s after the trigger with C-GFT in the commissioning phase. A series of g, r and i band images were obtained with exposure time of 10s. The optical counterpart (Page et al. GCN 38752, Li et al. GCN 38753, Mohan et al. GCN 38754, Zhu et al. GCN 38755, Budnev et al., GCN 38756 ) was clearly detected in band g,r and i. The results are,

(T-T0)_mid(s)      mag     mag_err  band
-------------------------------------
82          18.38    +/- 0.26  i
172         17.37    +/- 0.08  g
262         16.83    +/- 0.05  r

The photometry was calibrated with nearby PS1 star. Observations will be continued.

We thank the observation assistant Guangsheng Zhang at Jilin observatory for their excellent support.


Chinese Ground Follow-up Telescope of SVOM mission is located at Jilin, Changchun Observatory, National Astronomical Observatories, CAS. It has FOV of 1.28 deg x 1.28 deg with a 4k*4k CMOS detector mounted on the primary focus of 1.2-meter-aperure telescope.

GCN Circular 38756

Subject
GRB 250101A: MASTER earlier OT observations with SOSS emission features
Date
2025-01-01T15:23:19Z (8 months ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
Via
email

N.Budnev (ISU, V.Lipunov, (Lomonosov MSU), O.Gress (ISU), I.Panchenko, A.Kuznetsov,
P.Balanutsa, K.Zhirkov, V.Topolev, A.Chasovnikov, N.Tiurina, Ya.Kechin, G.Antipov, E.Gorbovskoy, D.Vlasenko, A.Sankovich, V.Senik (Lomonosov MSU),
A.Sosnovskij (CrAO RAS),
D.Buckley (SAAO),
R.Rebolo (The Instituto de Astrofisica de Canarias),
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 Alvarez, J.Martinez,A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory),

MASTER Global robotic net (http://observ.pereplet.ru Lipunov et al.,2010,Advances in Astronomy,2010,30L)
started observation (Lipunov et al. GCN 38751) of Swift GRB 240101A(Page et al. GCN 38752)
 35 sec after notice time (86 sec after trigger time) at 2025-01-01 13:24:16 UT
at MASTER-Tunka, see limits map https://master.sai.msu.ru/site/master2/observ.php?id=2730214 .

There is MASTER OT J022816.52+191139.9 , discovered by Swift (GCN 38752) since 1st image.

We see Smooth Optical Self-similar Emission of this Gamma-Ray Burst
(SOSS-emission, Lipunov et al. 2017, ApJ, 845, id9 https://ui.adsabs.harvard.edu/abs/2017ApJ...845...52L/abstract )

Observations and reduction will be continued.

GCN Circular 38755

Subject
GRB 250101A: Nanshan/HMT optical observations
Date
2025-01-01T14:55:10Z (8 months ago)
From
Dong Xu at NAOC/CAS <dxu@nao.cas.cn>
Via
Web form
Z.P. Zhu, S.Y. Fu, X. Liu, S.Q. Jiang, J. An, D. Xu (NAOC), X. Gao (Urumqi No.1 Senior High School), J.Z. Liu (XAO) report on behalf of a large collaboration:

We observed the optical counterpart of GRB 250101A detected by Swift/BAT (Page et. al., GCN 38752), using the HMT-0.5m telescope located at Nanshan, Xinjiang, China. Observations started at 13:24:51 UT on 2025-01-01, i.e., 121 s after the Swift/BAT trigger, and a series of unfiltered frames with different exposures were obtained.

The optical counterpart (e.g., Page et. al., GCN 38752; Li et al., GCN 38753; Mohan et al., GCN 38754) is clearly detected in the individual frames, and the lightcurve shows an initial rise and then a continuous decay. We measured  G ~ 18.3 mag at 30 mins post-burst, calibrated with GAIA-DR3 and not corrected for Galactic extinction. 

Observations are still ongoing.

GCN Circular 38754

Subject
GRB 250101A : GIT optical detection
Date
2025-01-01T14:35:06Z (8 months ago)
From
V. Swain at IIT Bombay <vishwajeet.s@iitb.ac.in>
Via
Web form

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

We observed the field of Swift GRB 250101A (Page et. al., GCN 38752

Loading...
 
 
) with 0.7m GROWTH-India Telescope (GIT) in r' filter. We started the observation at 2025-01-01 13:55:28 UT, i.e., 32.6 mins after the Swift Bat trigger. The source is detected at UVOT position and photometry result follows as:

JD (mid)t-t0 (mins)FilterExposure (s)Mag (AB)
2460677.08018534.6r'24018.36 +/- 0.08

More broadband observations are ongoing. Our result is consistent with GMG Optical Observation (Li et. al., GCN 38753

Loading...
 
 
) 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 38753

Subject
GRB 250101A: GMG Optical Observation
Date
2025-01-01T14:19:34Z (8 months ago)
Edited On
2025-01-02T02:02:08Z (8 months ago)
From
Rui-Zhi Li at Yunnan Observatories, CAS <liruizhi@ynao.ac.cn>
Edited By
Vidushi Sharma at NASA GSFC/UMBC <vidushi.sharma@nasa.gov> on behalf of Rui-Zhi Li at Yunnan Observatories, CAS <liruizhi@ynao.ac.cn>
Via
Web form
R.-Z. Li, B.-T. Wang, F.-F. Song, J. Mao, H. Lin and J.-M. Bai (YNAO, CAS) report:

We observed the field of GRB 250101A (Page et al., GCN 38752, T0 at 2025-01-01T13:22:50) using the GMG-2.4m telescope at the Lijiang Observatory. The observation began at 2025-01-01T14:00:24, about 0.63 hours after the trigger.

The optical counterpart of GRB 250101A, not visible in the Pan-STARRS1 r-band image, was clearly detected at the coordinates (J2000):
RA  =  02 28 16.50
DEC = +19 11 39.4
, with a positional uncertainty of 0.5" or better. The position is consistent with UVOT position (GCN 38752).

The preliminary analysis results are shown as follows:
+----------------+------------+----------+--------------+----------------+
|  Tmid-T0 [hr]  |  Exp. [s]  |  Filter  |     Mag      |  5-sigma U.L.  |
+================+============+==========+==============+================+
|      0.71      |    600     |    r     | 18.64 ± 0.01 |      22.2      |
+----------------+------------+----------+--------------+----------------+ 
The given magnitudes are derived based on calibration against Pan-STARRS1 field stars, and are not corrected for the expected Galactic foreground extinction, corresponding to a reddening of E(B-V) = 0.1408 mag in the direction of the optical counterpart (Schlafly & Finkbeiner 2011).

GCN Circular 38752

Subject
GRB 250101A: Swift detection of a burst with an optical counterpart
Date
2025-01-01T13:39:49Z (8 months ago)
From
K.L. Page at U Leicester <klp5@leicester.ac.uk>
Via
email
K. L. Page (U Leicester), R. Gupta (NASA GSFC), H. A. Krimm (NSF),
A. Y. Lien (U Tampa) and M. H. Siegel (PSU) report on behalf of the
Neil Gehrels Swift Observatory Team:

At 13:22:50 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 250101A (trigger=1278305).  Swift slewed immediately to the burst.
The BAT on-board calculated location is 
RA, Dec 37.061, +19.154 which is 
   RA(J2000) = 02h 28m 15s
   Dec(J2000) = +19d 09' 14"
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 25 sec.  The peak count rate
was ~400 counts/sec (15-350 keV), at ~0 sec after the trigger.

The XRT began observing the field at 13:24:57.4 UT, 127.4 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source located at RA, Dec 37.06963, 19.19521 which is equivalent
to:
   RA(J2000)  = 02h 28m 16.71s
   Dec(J2000) = +19d 11' 42.8"
with an uncertainty of 3.9 arcseconds (radius, 90% containment). This
location is 151 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.  We cannot determine whether the source
is fading at the present time. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of 1.44
x 10^21 cm^-2 (Willingale et al. 2013).

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 132 seconds after the BAT trigger. There is a candidate afterglow in
the list of sources generated on-board at
  RA(J2000)  =	02:28:16.50 =  37.06873
  DEC(J2000) = +19:11:39.9  =  19.19442
with a 90%-confidence error radius of about 1.10 arc sec. This position is 3.8
arc sec. from the center of the XRT error circle. The estimated magnitude is
18.30. No correction has been made for the expected extinction corresponding to
E(B-V) of 0.164.

Burst Advocate for this burst is K. L. Page (klp5 AT leicester.ac.uk).
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/)
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Contact GCN directly.
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