- GCN Circular #39752
Donghua Zhao, Yinuo Ma, Wenjin XIE(NAOC), Li Zhang (IHEP), F. Robinet (IJCLab), Liping Xin (NAOC)
on behalf of the SVOM mission team.
At 2025-03-17T02:12:08 UTC (Tb) SVOM/ECLAIRs triggered on the gamma-ray burst GRB 250317A (SVOM burst-id sb25031701). The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network.
The burst was detected both by the Count-Rate Trigger (CRT) and the Image Trigger (IMT), which produced a sequence of 13 alerts. CRT provided the alert with the best signal-to-noise-ratio (SNR) of 14.27 in the [5-8] keV energy band over a time window of 40.96 seconds starting at Tb.
The light curve showed a broad peak structure with a T90 duration of about 145.67 (-0.16 +0.16).
The localization of the best alert is R.A., Dec 211.665, 40.056 degrees (J2000) with a 90% C.L. radius of 5.75 arcmin (including systematic error of 2 arcmin added in quadrature).
SVOM slewed to the burst.
MXT began observing the field at 2025-03-17T02:14:36 UTC, 148 seconds after Tb. Using onboard processed data we found a bright and rapidly fainting uncatalogued X-ray source located at R.A., Dec 211.648, 40.057 degrees:
RA (J2000) = 14h06m35s
DEC (J2000) = 40d03m23s
with a 90% C.L. radius of 25 arcseconds.
This location is 48 arcseconds away from the ECLAIRs onboard position.
VT began to observe the field after the slew. No uncatalogued sources were detected within MXT errors compared to DESI catalog based on the VHF sequences. The 3 sigma limit magnitude is about VT_R~21 mag (AB) at about 10 minutes after the trigger. More analysis will be performed after receiving the X band data later.
The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe.
The Burst Advocate (BA) on shift for this burst is Donghua Zhao (zhaodh@bao.ac.cn).
Please contact the BA by email if you require additional information regarding the SVOM follow-up of this burst.
- GCN Circular #39753
Donghua Zhao, Yinuo Ma, Wenjin XIE(NAOC), Li Zhang (IHEP), F. Robinet (IJCLab), Liping Xin (NAOC)
on behalf of the SVOM mission team.
At 2025-03-17T02:12:08 UTC (Tb) SVOM/ECLAIRs triggered on the gamma-ray burst GRB 250317B (SVOM burst-id sb25031701). The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network.
The burst was detected both by the Count-Rate Trigger (CRT) and the Image Trigger (IMT), which produced a sequence of 13 alerts. CRT provided the alert with the best signal-to-noise-ratio (SNR) of 14.27 in the [5-8] keV energy band over a time window of 40.96 seconds starting at Tb.
The light curve showed a broad peak structure with a T90 duration of about 145.67 (-0.16 +0.16).
The localization of the best alert is R.A., Dec 211.665, 40.056 degrees (J2000) with a 90% C.L. radius of 5.75 arcmin (including systematic error of 2 arcmin added in quadrature).
SVOM slewed to the burst.
MXT began observing the field at 2025-03-17T02:14:36 UTC, 148 seconds after Tb. Using onboard processed data we found a bright and rapidly fainting uncatalogued X-ray source located at R.A., Dec 211.648, 40.057 degrees:
RA (J2000) = 14h06m35s
DEC (J2000) = 40d03m23s
with a 90% C.L. radius of 25 arcseconds.
This location is 48 arcseconds away from the ECLAIRs onboard position.
VT began to observe the field after the slew. No uncatalogued sources were detected within MXT errors compared to DESI catalog based on the VHF sequences. The 3 sigma limit magnitude is about VT_R~21 mag (AB) at about 10 minutes after the trigger. More analysis will be performed after receiving the X band data later.
The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe.
The Burst Advocate (BA) on shift for this burst is Donghua Zhao (zhaodh@bao.ac.cn).
Please contact the BA by email if you require additional information regarding the SVOM follow-up of this burst.
We apologize for any confusion and inconvenience caused by this mistake.
- GCN Circular #39754
Alan M. Watson (UNAM), Sarah Antier (OCA/IJCLAB), Jean-Luc Atteia (IRAP), Jean-Grégoire Ducoin (CPPM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Dalya Akl (AUS), Camila Angulo (UNAM), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Francis Fortin (IRAP), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Antonio de Ugarte Postigo (LAM), Benjamin Schneider (LAM) and C. Wu (NAOC) report:
We imaged the field of the SVOM/ECLAIRs GRB 250317B (Zhao et al. GCN Circ. 39752, Zhao et el. GCN Circ. 39753) with the OGSE test camera imager on the COLIBRÍ (SVOM/F-GFT) telescope at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir in Mexico.
We observed from 2025-03-17 04:21 to 04:56 UTC (2.15 to 2.73 hours after the trigger) and obtained 23 minutes of exposure in the r filter at high airmass. The data were coadded with custom software and analyzed in STDWeb/STDPipe (Karpov 2024), with photometric calibration against Pan-STARRS DR1 and image subtraction against Pan-STARRS DR2. Our photometry is in the AB system and is not corrected for Galactic extinction.
We detect an uncatalogued source at RA = 211.64367 degrees and Dec = 40.07953 degrees (J2000) with a magnitude of
r = 18.18 +/- 0.03
The source is observed to fade in later observations and is not present in Legacy Survey DR10, which strongly suggests it is the afterglow of the GRB.
This source is 81 arcsec from the MXT position reported by Zhao et al. (GCN Circ. 39752) and significantly beyond the reported 25 arcsec 90% confidence radius.
Further observations are planned.
We acknowledge excellent support from the staff of the Observatorio Astronómico Nacional.
- GCN Circular #39755
J. T. Palmerio (CEA) reports on behalf of the SVOM/VT team:
After the trigger by SVOM/ECLAIRs at 2025-03-17T02:12:08 UTC (Tb), SVOM performed an automatic slew on the burst. SVOM/VT began observing the field at 2025-03-17T02:18:21, 362 seconds after the SVOM trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
An uncatalogued source is detected within the error box of SVOM/ECLAIRs (Zhao et al. GCN 39753) using the VT VHF pipeline at ra=211.643617, dec=40.079524 (J2000), corresponding to:
RA (J2000) = 14h06m34.5s
Dec (J2000) = +40:04:46.3s
with an uncertainty of 0.5 arcsec.
consistent with the optical afterglow reported by Watson et al. (GCN 39754)
The source is detected in both VT_R and VT_B and was fading between the third and fourth VT observing sequences (starting at 5574 and 8474 seconds after the trigger respectively), the magnitudes are given below:
date-obs | exposure time (s) | mag(AB) | mag err | band
2025-03-17T03:45:13 | 6x50 | 17.48 | 0.02 | VT_R
2025-03-17T04:33:33 | 5x50 | 17.82 | 0.01 | VT_R
2025-03-17T03:45:13 | 6x50 | 18.89 | 0.01 | VT_B
2025-03-17T04:33:33 | 5x50 | 18.97 | 0.02 | VT_B
The source was undetected in the first two sequences (starting at 362 and 512 seconds after the trigger, respectively) and is outside the reported SVOM/MXT position.
The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe.
- GCN Circular #39756
D. Götz (CEA), F. Robinet (IJCLab), H. Goto (CEA), C. Plasse (CEA), P. Maggi (ObAS), M. Moita (CEA), C. van Hove (IJCLab) on behalf of the MXT team report:
We performed further analysis of the GRB 250317B (Zhao et al., GCN 39753) MXT X-ray data, using promptly downloaded photons through the VHF band. We can improve the X-ray afterglow position. The new J2000 coordinates are
R.A. = 14h 06m 32s
Dec. = +40d 05mm 02ss
with a 90% c.l. error radius of 48 arc seconds, including systematics.
This position supersedes the one reported in GCN 39753, which was affected by early satellite instability after the slew.
We note that this position is consistent with the SVOM/F-GFT (COLIBRÍ) position (Watson et al. GCN 39754) and the VT one (Palmeiro et al. GCN 39755).
The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. MXT has been developed by CNES in collaboration with CEA, IJCLab, University of Leicester and MPE.
- GCN Circular #39757
I. Pérez-Fournon, F. Poidevin (IAC and ULL), D. Cano-Morales, I. Correa-Plasencia, and A.E. Hernández-Díaz (ULL)
We report Las Cumbres Observatory Global Telescope network (LCOGT) observations of the field of GRB
250317B, discovered by SVOM/ECLAIRs (Zhao et al., GCN circ. 39752 and GCN circ. 39753) and SVOM/MXT
(Zhao et al., GCN circ. 39752 and GCN circ. 39753; and Götz et al., GCN circ. 39756). We observed the field of GRB 250317B with one of the two LCOGT 1-m telescopes, equipped with Sinistro cameras, located at the LCOGT node at McDonald Observatory (Texas). We obtained a 300-sec exposure in the SDSS r' filter starting at 2025-03-17 07:26:01 UT, about 5.23 hours after the SVOM trigger. An uncatalogued source is clearly detected at the position of the optical afterglow detected by SVOM/F-GFT (COLIBRÍ) (Watson et al., GCN circ. 39754) and SVOM/VT (Palmerio et al., GCN circ. 39755).
We measure the following AB magnitude, calibrated against Pan-STARRS DR2 stars and not corrected for Galactic extinction:
Time (UT, mid term) | mag | error | filter |
----------------------------------------------
2025-03-17T07:28:31 19.27 0.05 r'
This work makes use of observations from the Las Cumbres Observatory global telescope network (LCOGT observing programme IAC2025A-009, SGLF).
- GCN Circular #39759
Ankur Ghosh, Soebur Razzaque (CAPP, University of Johannesburg), Alexander Moskvitin, Yulia Sotnikova (SAO RAS), Naveen Dukiya (ARIES), Rahul Gupta (NASA GSFC) on behalf of a larger collaboration.
We observed the field of the GRB 250317B triggered by SVOM/ECLAIRs (Zhao et al., GCN circ. 39752 and GCN circ. 39753) and SVOM/MXT(Zhao et al., GCN circ. 39752 and GCN circ. 39753; and Götz et al., GCN circ. 39756) in r filter of the 0.4-m SCICAM QHY600 at the Las Cumbres Observatory Global Telescope (LCOGT) node located at Haleakala Observatory, Hawai . The 0.4 m SCICAM QHY600 is equipped with 9576 x 6388 pixel CCD (FOV: 1.9 x 1.2 degrees, scale: 0.74 arcsec/pixel) but we only used the FOV of 30 x 30 arcmin for our observation.
Observations began on March 17, 2025, starting 6.46 hours after the GRB trigger.
We clearly detect the optical transient (OT) reported by GCNs (Watson et al., GCN circ. 39754, Palmerio et al., GCN circ. 39755, Pérez-Fournon et al., GCN 39757) in our r band image.
|Date| |UTstart| |t-T0 (hours)| |Exp (sec)| |Filter| |Magnitude|
--------------------------------------------------------------------------------------------------
2025-03-17 08:39:27.93 6.46 2 x 300 r r = 19.48 +/- 0.11
The field was calibrated against nearby APASS stars, with magnitudes converted using Lupton (2005) equations, and has not been corrected for Galactic extinction.
- GCN Circular #39763
A. Melandri (INAF-OAR), V. D'Elia (SSDC & INAF-OAR), E. Ambrosi, A. D'Ai (INAF-IASFPA) , J.A. Kennea (PSU) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team:
Swift-XRT has performed follow-up observations of the SVOM/ECLAIRs GRB 250317B (Zhao et al., GCN circ. 39752 and GCN circ. 39753) and SVOM/MXT (Götz et al., GCN circ. 39756), collecting 1.7 ks of Photon Counting (PC) mode data between T0+10.0 ks and T0+12.9 ks (SVOM burst-id sb25031701).
One uncatalogued X-ray source has been detected within the estimated 3-sigma SVOM/MXT error region (Götz et al., GCN circ. 39756), consistent with the optical counterpart (Watson et al., GCN 39754). The source is fading with 3.0-σ significance. Details of this source are given below:
Source 1:
RA (J2000.0): 211.6427 = 14:06:34.3
Dec (J2000.0): +40.0796 = +40:04:46.7
Error: 3.0 arcsec (radius, 90% conf. [Enhanced position])
Count-rate: 0.19 (±0.04) ct s-1
Flux: 3.7 (±0.4) ×10-12 erg cm-2 s-1 (observed, 0.3-10 keV)
The results of the XRT-team automatic analysis of the XRT observations, including a position-specific upper limit calculator, are available at https://www.swift.ac.uk/SVOM/SVOM_FIELD00003/.
This circular is an official product of the Swift-XRT team.
- GCN Circular #39764
M. Ferro, R. Brivio, S. Covino, P. D'Avanzo, D. Fugazza (INAF-OAB) report on behalf of the REM team:
We observed the field of the SVOM GRB 250317B (Zhao et al., GCN 39752 & GCN 39753; Götz et al. GCN 39756) with the REM 60 cm robotic telescope located at the ESO observatory of La Silla (Chile). The observations were carried in the g, r, i, z, J, H, and K bands, started on 2025 March 17 at 03:44:41 UT (i.e. 1.54 hr after the burst), and lasted for about 3 hours.
From preliminary inspection, we detected the NIR counterpart at the position of the reported optical afterglow (Watson et al., GCN circ. 39754; Palmerio et al., GCN circ. 39755; Pérez-Fournon et al., GCN 39757; Ghosh et al., GCN 39759), with the following magnitude:
H = 15.5+-0.3 (Vega; calibrated against the 2MASS catalogue),
at a mid-time of 1.62 hours after the trigger.
The afterglow is not detected in our r-band observations down to the following 3sigma limit:
r > 18.0 (AB; calibrated against the Pan-STARRS catalogue),
at a mid-time of 3.05 hours after the trigger.
- GCN Circular #39767
B. Schneider (LAM), C. Adami (LAM/Pytheas/AMU), E. Le Floc'h (CEA/Irfu), A. Ugarte Postigo (LAM), M. Dennefeld (IAP/CNRS/Sorbonne U.) and D. Turpin (CEA/Irfu) report on behalf of a larger collaboration:
We observed the field of the GRB 250317B (Zhao et al., GCN 39753) using the T193cm telescope at the Observatoire de Haute-Provence (France) equipped with the MISTRAL spectro-imager. We obtained 9 exposures (8x360 s and 1x300 s) in the r-band starting at 21:56:41 UT on 2025-03-17 (19.74 hours after the trigger). In the stacked image, we clearly detected the optical counterpart reported by Watson et al., GCN 39754; Palmerio et al., GCN 39755; Pérez-Fournon et al., GCN 39757; Ghosh et al., GCN 39759 and Ferro et al., GCN 39764.
The preliminary magnitude derived for that source is:
r = 21.87 +/- 0.08 mag (AB)
The photometric calibration was performed using nearby stars from the PanSTARRS catalog and the magnitudes are not corrected for Galactic extinction.
We acknowledge the excellent support from the Observatoire de Haute-Provence and in particular Jean Balcaen et Andres Carmona for the MISTRAL observations.
- GCN Circular #39769
C. C. Thoene (AbAO), A. de Ugarte Postigo (LAM), D. B. Malesani (DAWN/NBI and Radboud Univ.), J. F. Agui Fernandez (CAHA), N. A. Rakotondrainibe (LAM), A. Martin-Carrillo (UCD), N. R. Tanvir (Univ. Leicester), L. Izzo (INAF/OACn and DARK/NBI), J. P. U. Fynbo (DAWN/NBI), S. Geier (GTC), G. Lombardi (GTC), Antonio García (GTC), Daniel González (GTC), and Antonio Cabrera-Lavers (GTC) report:
We obtained spectroscopy of the afterglow of the SVOM-detected GRB 250317B (Zhao et al. GCN 39752, Watson et al. GCN 39754, Götz et al. GCN 39756, Pérez-Fournon et al. GCN 39757, Melandri et al. GCN 39763, Ferro et al. GCN 39764, Schneider et al. GCN 39767). Our observations consisted of 4x1200s exposures with grism R1000B, covering the range between 3600 and 7880 AA with a resolving power of around 600 at a mean epoch 2025-03-18T00:16:22 UT (22.07 hr after the burst).
In the acquisition image, obtained 21.328 hr after the burst, the afterglow is detected at a magnitude of r_AB=21.72 +/- 0.05, indicating a slight rebrightening with respect to the OHP observation (Schneider et al. GCN 39767) obtained 1.6 hr earlier. Further monitoring of this behaviour is encouraged.
The spectrum shows continuum above 4000 AA, with features consistent with at least two low-column density Lyman systems at redshifts of z=3.442 and 3.447 (or a dynamic separation of 1500 km/s), likely corresponding to the same galaxy or system. There are tentative detections of SiII, SiII*, OI, SiIV, CIV, FeII and AlII a those same redshifts, which we identify as corresponding to the GRB.
Additionally, we identify two intervening absorbers, one at z=3.196 with absorptions in several Lyman lines, SII and SiII, and a second one at z=1.029 showing the MgII doublet.
- GCN Circular #39770
Z. P. Zhu (NAOC), D. B. Malesani (DAWN/NBI and Radboud Univ.), B. Schneider (LAM), A. Martin-Carrillo (UCD), A. Henderson de la Fuente (NOT), report on behalf of a larger collaboration:
We observed the field of the GRB 250317B (Zhao et al., GCN 39753) using the ALFOSC camera mounted on the Nordic Optical Telescope (NOT). We obtained 2 exposures of 300 s each in the SDSS-r band starting at 22:43:24 UT on 2025-03-17 (20.56 hr after the trigger).
The optical counterpart reported by Watson et al. (GCN 39754), Palmerio et al. (GCN 39755), Pérez-Fournon et al. (GCN 39757), Ghosh et al. (GCN 39759), Ferro et al. (GCN 39764) and Schneider et al. (GCN 39767) is well detected in the stacked image, with a preliminary magnitude of r = 21.7 +/- 0.1 mag (AB). The photometric calibration was performed using nearby stars from the Pan-STARRS catalog and the magnitude is not corrected for Galactic extinction.
We note that the measured magnitude is consistent with those reported by Schneider et al. (GCN 39767), obtained ~1 hr before our observation, and Thoene et al. (GCN 39769), obtained about 0.6 hr after our observation, suggesting a possible optical plateau or rebrightening episode.
Further observations are planned and encouraged to monitor the evolution of the optical afterglow.
- GCN Circular #39772
N. Pankov (HSE, IKI), E. Klunko (ISTP), A. Pozanenko (IKI) report on behalf of IKI-GRB-FuN:
We performed optical observations of the field of GRB 250317B (Zhao et. al, GCN 39753; Götz et. al, GCN 39756; Melandri et. al, GCN 39763) in the R filter with the 1.5-meter AZT-33IK telescope of the Sayan Solar Observatory (Mondy). The observations started on (UT) 2025-03-17 15:41:49, i.e. about 0.58 days since trigger. The optical afterglow (Watson et. al, GCN 39754; Pérez-Fournon et. al, GCN 39757; Ghosh et. al, GCN 39759; Ferro et. al, GCN 39764; Schneider et. al, GCN 39767; Zhu et. al, GCN 39770) is clearly visible in the stacked image. The preliminary photometry is as follows:
Date UT start t-T0 Exp. Filter OT Err UL(3sigma)
(mid, days) (s)
2025-03-17 15:41:49 0.58173 28*120 R 20.94 0.06 23.3
The photometry is based on nearby stars from the USNO-B1.0 catalog (R2 magnitudes) and has not been corrected for the Galactic extinction. Using a simple power law fit to the observed data in the r and R filters, we estimate the light curve decay index to be about -1.5.
- GCN Circular #39774
L. Moretti, E. Pavoni (Leavitt Observatory, Italy)
Members of:
GRB/UAI - Gamma Ray Burst Section of Unione Astrofili Italiani
ATA - Associazione Tuscolana di Astronomia
In a large collaboration with:
M.G. Dainotti (National Astronomical Observatory of Japan),
Y. Niino (Tokyo University, Institute of Astronomy),
K. Kalinowski (Aarhus University, Department of Physics and Astronomy),
report:
We observed the field of the GRB 250317B triggered by SVOM/ECLAIRs (Zhao et al., GCN 39752 and GCN 39753) and SVOM/MXT (Zhao et al., GCN 39752 and GCN 39753; and Götz et al., GCN 39756) with our RC telescope (D=250 mm, F/D=8) of Leavitt Observatory, Manciano, Italy.
The observations started approximately 19 hours after the SVOM/ECLAIRs trigger time, with good weather conditions, stacking a set of unfiltered FITS frames. Images were processed using the astropy package (Astropy Collaboration et al., 2022ApJ...935..167A).
In the stacked frame, we did not found any optical uncatalogued object within the SVOM error circle.
Mid-Time (UTC) Limit (clear filter) Error
2025-03-17T21:18:03 >20.0 +/- 0.1
Magnitudes were estimated with the BP-band of Gaia DR3 catalogue (*) and are not corrected for galactic dust extinction.
The message may be cited.
Reference:
https://leavittobservatory.altervista.org
(*) https://gea.esac.esa.int/archive/documentation/GEDR3/Data_processing/chap_cu5pho/cu5pho_sec_photSystem/cu5pho_ssec_photRelations.html
- GCN Circular #39777
B. Schneider (LAM), C. Adami (LAM/Pytheas/AMU), E. Le Floc'h (CEA/Irfu), A. Ugarte Postigo (LAM), M. Dennefeld (IAP/CNRS/Sorbonne U.) and D. Turpin (CEA/Irfu) report on behalf of the MISTRAL-GRB collaboration:
We performed additional observations of the optical counterpart of GRB 250317B (Zhao et al., GCN 39753; Watson et al., GCN 39754; Palmerio et al., GCN 39755; Pérez-Fournon et al., GCN 39757; Ghosh et al., GCN 39759, Ferro et al., GCN 39764, Schneider et al., GCN 39767; Thöne et al., GCN 39769; Zhu et al., GCN 39770; Pankov et al., GCN 39772; Moretti et al., GCN 39774) using the T193cm telescope at Observatoire de Haute-Provence (France) equipped with the MISTRAL spectro-imager. We obtained 1 exposure of 600s and 5 exposures of 720s in the r-band starting at 19:22 UT on 2025-03-18 (1.84 days after the trigger). In the final stacked image, the afterglow is marginally detected, at a level much fainter than the phase of rebrightening reported earlier by Thöne et al. (GCN 39769) and Zhu et al. (GCN 39770).
The preliminary magnitude derived for the source is :
r = 23.5 +/- 0.4 mag (AB)
The photometric calibration was performed using nearby stars from the PanSTARRS catalog and the magnitudes are not corrected for Galactic extinction.
We acknowledge the excellent support from the Observatoire de Haute-Provence and in particular Jean Balcaen et Andres Carmona for the MISTRAL observations.
- GCN Circular #39784
Jean-Luc Atteia (IRAP), Sarah Antier (OCA/IJCLAB), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Dalya Akl (AUS), Camila Angulo (UNAM), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU), Francis Fortin (IRAP), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Antonio de Ugarte Postigo (LAM), Benjamin Schneider (LAM) report:
We imaged the field of the SVOM/ECLAIRs GRB 250317B (Zhao et al. GCN Circ. 39752, Zhao et al. GCN Circ. 39753) with the DDRAGO imager on the COLIBRÍ (SVOM/F-GFT) telescope at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir in Mexico.
We observed from 2025-03-19 06:32 to 11:00 UTC and obtained 200 minutes of exposure in the r filter at a mean observing time To+54.5h. The data were coadded with custom software and analyzed with STDpipe (Karpov 2024) with photometric calibration against Pan-STARRS DR1. Our photometry is in the AB system and is not corrected for Galactic extinction.
We detect the optical afterglow (Watson et al. GCN Circ. 39754, Pérez-Fournon et al. GCN Circ. 39757, Ghosh et al. GCN Circ. 39759, Ferro et al. GCN Circ. 39764, Schneider et al. GCN Circ. 39767, Schneider et al. GCN Circ. 39767, Thoene et al. GCN Circ. 39769, Zhu et al. GCN Circ. 39770, Zhu et al. GCN Circ. 39770, Pankov et al. GCN Circ. 39772, Moretti
et al. GCN Circ. 39774, Schneider et al. GCN Circ. 39777) with a magnitude of
r = 23.95 +/- 0.25
This confirms the break of the optical light-curve pointed by Schneider et al. in GCN Circ. 39777.
We acknowledge excellent support from the staff of the Observatorio Astronómico Nacional.
- GCN Circular #39790
N. Pankov (HSE, IKI), E. Klunko (ISTP), A. Pozanenko (IKI) report on behalf of IKI-GRB-FuN:
We performed optical observations of the field of GRB 250317B (Zhao et. al, GCN 39753; Götz et. al, GCN 39756; Melandri et. al, GCN 39763) at the redshift of z=3.44 (Thoene et. al, GCN 39769) in the R filter with the 1.5-meter AZT-33IK telescope of the Sayan Solar Observatory (Mondy). The observations started on 2025-03-18 at 18:45:47 (UT), i.e. about 1.72 days since trigger. The optical afterglow (Watson et. al, GCN 39754; Pérez-Fournon et. al, GCN 39757; Ghosh et. al, GCN 39759; Ferro et. al, GCN 39764; Schneider et. al, GCN 39767; Thoene et. al, GCN 39769; Zhu et. al, GCN 39770; Pankov et. al, GCN 39772; Moretti & Pavoni, GCN 39774; Schneider et. al, GCN 39777; Atteia et. al, GCN 39784) is not detected. The preliminary photometry is as follows:
Date UT start t-T0 Exp. Filter OT Err UL(3sigma)
(mid, days) (s)
2025-03-18 18:45:47 1.72130 45*120 R n/d n/d 22.9
2025-03-19 18:02:14 2.70077 59*120 R n/d n/d 23.3
Ref. stars from SDSS-DR12
RA Dec R R_err
211.6590 +40.0703 16.451 0.029
211.5997 +40.0619 18.859 0.055
The photometry is based on nearby stars (see the list above) from the SDSS-DR12 catalog (R magnitudes were obtained using Lupton 2005 transformations) and has not been corrected for the Galactic extinction.
Previous IAU Circulars 