GRB 250617B
GCN Circular 40760
Subject
GRB 250617B: Swift detection of a burst with an optical counterpart
Date
2025-06-17T21:24:27Z (7 days ago)
From
David Palmer at LANL <palmer@lanl.gov>
Via
email
K. L. Page (U Leicester), R. Gupta (NASA GSFC), A. Y. Lien (U Tampa),
M. J. Moss (GSFC), D. M. Palmer (LANL), T. Sakamoto (AGU),
M. H. Siegel (PSU) and M. A. Williams (PSU) report on behalf of the
Neil Gehrels Swift Observatory Team:
At 21:01:50.11 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 250617B (trigger=1325580). Swift did not slew immediately to the burst.
The BAT on-board calculated location is RA, Dec 332.902, +32.727 which is
RA(J2000) = 22h 11m 37s
Dec(J2000) = +32d 43' 38"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The currently available BAT light curve
showed a complex structure with a duration of at least 10 sec.
However, the light curve data from ~T+8 s to ~T+100 s is unavailable
in the immediate data downlink. The peak count rate was ~900 counts/sec
(15-350 keV), at ~0 sec after the trigger.
The XRT began observing the field at 21:15:03.4 UT, 793.4 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source with an enhanced position: RA, Dec 332.89735, 32.73270
which is equivalent to:
RA(J2000) = 22h 11m 35.36s
Dec(J2000) = +32d 43' 57.7"
with an uncertainty of 1.9 arcseconds (radius, 90% containment). This
location is 24 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 in excess of the Galactic value (9.66 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 5.7
(+4.15/-3.46) x 10^21 cm^-2 (90% confidence).
UVOT took a finding chart exposure of 150 seconds with the White filter
starting 796 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
RA(J2000) = 22:11:35.25 = 332.89686
DEC(J2000) = +32:43:56.9 = 32.73247
with a 90%-confidence error radius of about 0.62 arc sec. This position is 1.9
arc sec. from the center of the XRT error circle. The estimated magnitude is
18.17 with a 1-sigma error of about 0.15. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.087.
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/)
GCN Circular 40761
Subject
GRB 250617B: SAO RAS optical observations
Date
2025-06-17T22:54:57Z (7 days ago)
From
Alexander Moskvitin at SAO RAS <mosk@sao.ru>
Via
Web form
A. Moskvitin, O. Spiridonova, Yu. Sotnikova (SAO RAS),
A. Ghosh, S. Razzaque (CAPP, University of Johannesburg)
We observed the field of the GRB 250617B (Page et al., GCN 40760)
with SAO RAS 1-m telescope Zeiss-1000 equipped with CCD-photometer.
We obtained series of 60, 120 and 300 sec. exposures in Rc band
and also one BVIc series. Observations started on 21:28:06 UT,
since 26 minutes after the trigger.
The OT (Page et al., GCN 40760) is clearly visible in individual images
with the brightness of R = 18.31 +/- 0.04 (t_mid - T0 = 0.5444 hours)
and R = 18.66 +/- 0.04 (t_mid - T0 = 0.7635 hours).
This preliminary photometry is calibrated against R2 magnitudes
of following nearby USNO-B1 stars and not corrected for the Galaxy
extinction.
R.A. Dec. (2000) R2
22:11:38.4 +32:43:48.4 14.880
22:11:19.9 +32:44:17.5 15.280
22:11:41.0 +32:40:41.2 15.070
22:11:45.2 +32:42:19.8 14.690
Observations are ongoing.
GCN Circular 40762
Subject
GRB 250617B: Ondrejov D50 optical afterglow detection
Date
2025-06-17T22:55:14Z (7 days ago)
From
Martin Jelinek at Astro.Inst-AVCR,Ondrejov <martin.jelinek@asu.cas.cz>
Via
email
M. Jelinek, J. Strobl, F. Novotny, A. Malenakova and R. Hudec (ASU CAS Ondrejov) report:
We observed the position of the Swift-detected GRB 250617B (Page et al. GCN 40760) with the D50 telescope of the Astronomical Institute Ondrejov, near Prague, Czech Republic. Our observation started at 21:29:35 UT, i.e. 27.8 min after the initial trigger and was performed without filter.
We detect the optical afterglow (Page et al. GCN 40760) in a combined image with exp. mean time ~37.3 min after trigger (exposed 21:29:35-21:39:35 UT). The AB magnitude of the object at this frame is R = 18.64 +/- 0.27.
We can confirm a decaying nature of the object with a temporal decay index of alpha = 0.85 ± 0.13.
GCN Circular 40763
Subject
GRB 250617B: Fermi GBM Final Localization
Date
2025-06-18T00:14:26Z (7 days ago)
From
sumanbala2210@gmail.com
Via
Web form
The Fermi GBM team reports the detection of a likely LONG GRB
"At 21:01:28.19 UT on 17 June 2025, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 250617B (trigger 771886893/250617876).
It is also detected by Swift-BAT/XRT (Page et al. 2025, GCN 40760)
The Fermi GBM on-ground location is consistent with the Swift-XRT position.
The angle from the Fermi LAT boresight is 91 degrees.
The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250617876/quicklook/glg_skymap_all_bn250617876.png
The HEALPix FITS file, including the estimated localization systematic, can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250617876/quicklook/glg_healpix_all_bn250617876.fit
The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250617876/quicklook/glg_lc_medres34_bn250617876.gif"
GCN Circular 40766
Subject
GRB 250617B: Fermi GBM Observation
Date
2025-06-18T04:32:42Z (7 days ago)
From
sumanbala2210@gmail.com
Via
Web form
S. Bala (USRA) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:
"At 21:01:28.19 UT on 17 June 2025, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 250617B (trigger 771886893/250617876).
which was also detected by Swift BAT (Page et al. 2025, GCN 40760).
The Fermi GBM on-ground location is consistent with the Swift BAT position.
The angle from the Fermi LAT boresight is 91 degrees.
The GBM light curve consists of two distinct emission episodes with a duration (T90)
of about 32 s (50-300 keV). The time-averaged spectrum
from T0-4.6 to T0+32.3 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -1.2 +/- 0.1 and the cutoff energy,
parameterized as Epeak, is 40 +/- 2 keV.
The event fluence (10-1000 keV) in this time interval is
(3.4 +/- 0.1)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+23 s in the 10-1000 keV band is 6.9 +/- 0.3 ph/s/cm^2.
The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog:
https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html
For Fermi GBM data and info, please visit the official Fermi GBM Support Page:
https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/"
GCN Circular 40767
Subject
GRB 250617B: Enhanced Swift-XRT position
Date
2025-06-18T04:53:33Z (7 days ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
J.P. Osborne, A.P. Beardmore, P.A. Evans and M.R. Goad (U. Leicester)
report on behalf of the Swift-XRT team.
Using 1717 s of XRT Photon Counting mode data and 2 UVOT
images for GRB 250617B, 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 = 332.89670, +32.73250 which is equivalent
to:
RA (J2000): 22h 11m 35.21s
Dec (J2000): +32d 43' 57.0"
with an uncertainty of 2.3 arcsec (radius, 90% confidence).
This position may be improved as more data are received. The latest
position can be viewed at http://www.swift.ac.uk/xrt_positions. Position
enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans
et al. (2009, MNRAS, 397, 1177).
This circular was automatically generated, and is an official product of the
Swift-XRT team.
GCN Circular 40768
Subject
GRB 250617B: GOTO optical upper limit
Date
2025-06-18T06:29:28Z (6 days ago)
From
Amit Kumar at Royal Holloway - UoL/ U of Warwick, UK <amitkundu515@gmail.com>
Via
Web form
A. Kumar, B. P. Gompertz, G. Ramsay, R. Starling, K. Ackley, M. J. Dyer, J. Lyman, K. Ulaczyk, D. O'Neill, B. Godson, D. Steeghs, D. K. Galloway, V. Dhillon, P. O'Brien, K. Noysena, R. Kotak, R. P. Breton, L. K. Nuttall, and J. Casares report on behalf of the GOTO collaboration:
We report on optical observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022; Dyer et al. 2024) in response to the Swift/BAT and Fermi/GBM detected GRB 250617B (Page et al., GCN 40760; Fermi GBM Team, GCN 40763). Targeted observations were performed by GOTO-North at 2025-06-18T01:03:23 (4.03 hours after the trigger). The observation consisted of 4x90s exposures in the GOTO L-band (400-700 nm).
Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations.
We do not detect the optical afterglow of GRB 250617B (Page et al., GCN 40760; Moskvitin et al., 40761; Jelinek et al., 40762) down to a 3-sigma limiting magnitude of L > 20.3 AB mag.
Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and are not corrected for Galactic extinction.
GOTO (https://goto-observatory.org) is a network of telescopes that is principally funded by the STFC and operated at the Roque de los Muchachos Observatory on La Palma, Spain, and Siding Spring Observatory in NSW, Australia, on behalf of a consortium including the University of Warwick, Monash University, Armagh Observatory & Planetarium, the University of Leicester, the University of Sheffield, the National Astronomical Research Institute of Thailand (NARIT), the University of Turku, the University of Portsmouth, the University of Manchester and the Instituto de Astrofisica de Canarias (IAC).
GCN Circular 40769
Subject
Swift GRB 250617B: Global MASTER-Net observations report
Date
2025-06-18T06:36:55Z (6 days ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
Via
email
V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko,
G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU),
O.Gress, N.Budnev (ISU),
C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA),
A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory),
A.Sosnovskij (CrAO),
A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity),
D.Buckley (SAAO),
R.Rebolo (The Instituto de Astrofisica de Canarias),
L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez,
A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory)
MASTER-OAFA robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Argentina (OAFA observatory of San Juan National University) was pointed to the Swift GRB 250617B ( K. L. Page et al., GCN 40760) errorbox 30652 sec after notice time and 30775 sec after trigger time at 2025-06-18 05:34:46 UT, with upper limit up to 18.6 mag. The observations began at zenith distance = 80 deg. The sun altitude is -74.8 deg.
The galactic latitude b = -19 deg., longitude l = 89 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=2906362
We obtain a following upper limits.
Tmid-T0 | Site |Filt.| Expt. | Limit| Comment
_________|_____________________|_____|_______|______|________
30866 | MASTER-OAFA | C | 180 | 17.3 |
31415 | MASTER-OAFA | C | 60 | 17.4 |
31495 | MASTER-OAFA | C | 60 | 17.7 |
32132 | MASTER-OAFA | C | 180 | 18.2 |
32767 | MASTER-OAFA | C | 60 | 18.1 |
32845 | MASTER-OAFA | C | 60 | 18.1 |
33417 | MASTER-OAFA | C | 180 | 18.6 |
Filter C is a clear (unfiltred) band.
The observation and reduction will continue.
The message may be cited.
GCN Circular 40771
Subject
GRB 250617B: NUTTelA-TAO early time optical observations
Date
2025-06-18T08:09:56Z (6 days ago)
From
Bruce Grossan at LBNL/UCB SSL <Bruce_Grossan@lbl.gov>
Via
Web form
B. Grossan (UCB, NU) , T. Komesh (NU), Z. Maksut (NU), D. Berdikhan
(NU), M. Krugov (FAI), G. F. Smoot (HKUST, UCB, NU), 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
250617B 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 find a fading
OT consistent with the position given in Palmer, 2025 (GCN 40760).
We received the alert and started observations at UT 2025-06-17
21:02:48 (58 seconds between GRB trigger time and notice
receipt/response time). Stabilized images commenced at 21:03:10, 80 s
after trigger. Observations were made under good conditions for more than
1300 s. The early measurements were sufficiently bright that they are
visible in our short frames with no co-addition. Below, we give a
selection of these measurements(irregular sampling due to changes in
exposure time, camera mode,etc.) Note that these data provide
essentially full-time coverage, nearly simultaneous in both bands. We
report the following results:
----------------------------------------------------------------------------
g' tstart(*) tm-ttrig(s) g' err r' err exposure_time (s)
------------ ---------- ----- ------ ------ ----- -----------------
21:03:10.4 80.5 15.29 0.06 14.75 0.09 3.0
21:03:40.4 110.5 15.54 0.10 14.90 0.10 3.0
21:04:46 176 16.12 0.09 15.69 0.04 30.0
21:09:46 476 17.40 0.10 17.02 0.07 30.0
21:15:45 835 17.87 0.12 17.67 0.08 60.0
21:18:45 1015 18.36 0.12 17.81 0.09 60.0
21:23:45 1315 UL18.72 18.00 0.11 60.0
(*) Times for r' are about 1.8 s before times for g'; times are UT
June 17.
"tm-ttrig" gives the mid time of the exposure minus the trigger
time. The Sloan filter g', err, r', err are given in magnitudes. UL
denotes no detection; 5 sigma upper limit only. Conditions at later
times than given in the table showed a significant deterioriation in
stability and sensitivity and so are omitted.
-----------------------------------------------------
Because of the very good, quite early, time coverage thus far, we
encourage observers capable of longer-term observations (12 hours+) to
attempt additional g',r' (and other filters) coverage.
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. We welcome
requests for additional data and collaboration.
----------------------------------
NU = Nazarbayev University, Nur-Sultan, Kazakhstan
UCB = University of California, Berkeley, USA
HKUST = Hong Kong University of Science and Technology
FAI = Fesenkov Astrophysical Institute, Kazakhstan
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 40772
Subject
GRB 250617B: SVOM/VT optical observation
Date
2025-06-18T08:16:40Z (6 days ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
Y.N. Ma, L. P. Xin, Y. L. Qiu, C. Wu, H. L. Li, Z. H. Yao, X. H. Han, Y. Xu, J. Wang, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA), Z. Q. Wang (GXU), W. K. Zheng (UCB), Y. F. Liang (PMO) report on behalf of the SVOM/VT team.
SVOM/VT performed a Target of Opportunity observation of GRB 250617B detected by Swift-BAT（Page et al., GCN 40760; Osborne et al., GCN 40767) and Fermi-GBM (Bala et al., GCN 40766). The observation began at 2025-06-18T01:18:40 UTC, 4.281 hours after the trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
The afterglow (Page et al., GCN 40760; Moskvitin et al., GCN 40761; Jelinek et al., GCN 40762) is detected using VT X-band data, at R.A., Dec 332.89675, 32.73242 degrees:
RA (J2000) = 22:11:35.22
Dec (J2000) = +32:43:56.72
with an uncertainty of 0.5 arcsec.
The magnitudes in both channels are:
date-obs (UT) | exposure time (s) | band | mag (AB) | mag err
-----------------------|-------------------|------|----------|--------
2025-06-18T02:24:34.50 | 70 | VT_B | 21.10 | 0.12
2025-06-18T02:24:34.50 | 70 | VT_R | 20.11 | 0.08
Our photometry was not corrected for Galactic extinction.
The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Centre for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS.
GCN Circular 40773
Subject
GRB 250617B: Swift-XRT refined Analysis
Date
2025-06-18T08:23:52Z (6 days ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
M.A. Williams (PSU), S. Dichiara (PSU), J.P. Osborne (U. Leicester),
K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), E. Ambrosi
(INAF-IASFPA) , M. Capalbi (INAF-OAR), M. Perri (SSDC & INAF-OAR), J.A.
Kennea (PSU) and P.A. Evans report on behalf of the Swift-XRT team:
We have analysed 6.3 ks of XRT data for GRB 250617B, from 779 s to 31.0
ks after the trigger. The data comprise 7 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 power-law decay with a decay
index of alpha=0.90 (+/-0.06).
A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.16 (+0.19, -0.18). The
best-fitting absorption column is 1.9 (+0.6, -0.5) x 10^21 cm^-2, in
excess of the Galactic value of 9.7 x 10^20 cm^-2 (Willingale et al.
2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum is 3.3 x 10^-11 (4.8 x 10^-11) erg
cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
Total column: 1.9 (+0.6, -0.5) x 10^21 cm^-2
Galactic foreground: 9.7 x 10^20 cm^-2
Excess significance: 3.0 sigma
Photon index: 2.16 (+0.19, -0.18)
If the light curve continues to decay with a power-law decay index of
0.90, the count rate at T+24 hours will be 0.025 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 8.3 x
10^-13 (1.2 x 10^-12) erg cm^-2 s^-1.
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/01325580.
This circular is an official product of the Swift-XRT team.
GCN Circular 40774
Subject
GRB 250617B: NOT NIR observations of the afterglow
Date
2025-06-18T09:27:29Z (6 days ago)
From
Antonio Martin-Carrillo at UCD,Space Science Group <antonio.martin-carrillo@ucd.ie>
Via
Web form
B. Schneider (LAM), X. Liu (NAOC), A. de Ugarte Postigo (LAM), A. Martin-Carrillo (UCD), D. B. Malesani (DAWN/NBI and Radboud), B. P. Gompertz (U. Birmingham), A. A. Djupvik (NOT), S. Bijavara Seshashayana (NOT and Malmo Univ.), report on behalf of a larger collaboration:
We observed the field of GRB 250617B detected by Swift (Page et al., GCN 40760) and Fermi (Fermi GBM team, GCN 40763; Bala & Meegan, GCN 40766), using the NOTCam camera mounted on the Nordic Optical Telescope (NOT). We obtained 20x60 s exposures in the J-band starting at 01:02 UT on 2025-05-18 (~4 hr after the Swift trigger).
The optical counterpart reported by Page et al. (GCN 40760), Moskvitin et al. (GCN 40761), Jelinek et al. (GCN 40762), Grossan et al. (GCN 40771), and Ma et al. (GCN 40772) is well detected in our stacked image with a preliminary magnitude:
J = 19.08 +/- 0.10 (Vega), at mid time 4.24 hr after trigger.
The photometric calibration was performed using nearby stars from the 2MASS catalog and the magnitude is not corrected for Galactic extinction.
GCN Circular 40775
Subject
GRB 250617B: COLIBRÍ optical observations
Date
2025-06-18T10:25:49Z (6 days ago)
From
Sarah Antier at OCA <sarah.antier@oca.eu>
Via
Web form
Sarah Antier (OCA/IJCLAB), Diego López-Cámara (UNAM), Jean-Grégoire Ducoin (CPPM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Fredd Alvarez (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (AUS), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU) , Damien Dornic (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM):
We imaged the field of the GRB 250617B (Page et al., GCN 40760; Fermi GBM Team, GCN 40763) using the DDRAGO wide-field imager on the COLIBRÍ telescope. We observed from 2025-06-18 08:09:20 to now UTC (started 11.12 hours after the trigger) and obtained a series of 1 min exposure images in the i filter.
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/SkyMapper catalog, is in the AB system, and is not corrected for Galactic extinction.
We detected the optical counterpart Page et al., GCN Circ. 40760 (also reported by Moskvitin et al. (GCN 40761), Jelinek et al. (GCN 40762), Grossan et al. (GCN 40771), and Ma et al. (GCN 40772)), at a preliminary magnitude using a 6-min stack image at the beginning of the observations:
i = 21.17 +/- 0.16
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 40776
Subject
GRB 250617B: VLT/X-shooter spectroscopic redshift z = 1.396
Date
2025-06-18T10:49:27Z (6 days ago)
From
Antonio Martin-Carrillo at UCD,Space Science Group <antonio.martin-carrillo@ucd.ie>
Via
Web form
G. Corcoran (UCD), M. Garnichey (LUX-Paris Obs.), B. Schneider (LAM), A. Martin-Carrillo (UCD), D. B. Malesani (DAWN/NBI and Radboud), A. Saccardi (CEA/Irfu), S. D. Vergani (LUX-Paris Obs.), report on behalf of a larger collaboration:
We observed the field of GRB 250617B detected by Swift (Page et al., GCN 40760) and Fermi (Fermi GBM team, GCN 40763; Bala & Meegan, GCN 40766), using the ESO VLT UT3 (Melipal) with the X-shooter. Our spectra cover the wavelength range 3000-25000 AA, and consist of 4 exposures of 900 s each. The observation mid time was 2025 Jun 18.375 UT (11.96 hr after the GRB).
In images taken with the acquisition camera, we clearly detect in the g, r, and z bands the optical counterpart reported by Page et al. (GCN 40760), Moskvitin et al. (GCN 40761), Jelinek et al. (GCN 40762), Grossan et al. (GCN 40771), Ma et al. (GCN 40772), Schneider et al. (GCN 40774) and Antier et al. (GCN 40775). We measure a preliminary magnitude:
r = 21.30 +/- 0.04 (AB) at mid time 11.21 hr after trigger.
The photometric calibration was performed using nearby stars from the Pan-STARRS catalog and the magnitude is not corrected for Galactic extinction.
In a preliminary reduction of the spectra, we detect a continuum over the entire covered wavelength range. From the detection of multiple absorption lines, which we interpret as Mg II doublet (2796, 2804) and Fe II, we infer a redshift of z = 1.396. At a consistent redshift, we also detect emission lines due to [O II] doublet and H-alpha from the GRB host galaxy.
We acknowledge excellent support from the ESO observing staff in Paranal.
GCN Circular 40777
Subject
GRB 250617B: Kilonova-Catcher optical afterglow detection
Date
2025-06-18T11:19:22Z (6 days ago)
From
Damien Turpin at CEA-Saclay <dturpin-astro@hotmail.com>
Via
Web form
D. Turpin (CEA-Saclay/Irfu), M. Freeberg (KNC), C. Andrade(UMN), M. Pillas (ULiege), M. Tanasan (NARIT), S. Antier (OCA/IJCLAB) on behalf of the GRANDMA/Kilonova-Catcher collaboration:
We observed the field of GRB 250617B (Page et al., GCN 40760) detected by Swift/BAT with the GRANDMA citizen science project Kilonova-catcher (KNC). Our observations were performed with the TEC160FL telescope operated by M. Freeberg starting from T_GRB+10hr.
In our stacked frames, subtracted from the PanSTARRS DR2 template image, we marginally detect the optical afterglow at the position reported by Swift/UVOT (Page et al., GCN 40760), SAO RAS (Moskvitin et al., GCN 40761), Ondrejov D50 (Jelinek et al., GCN 40762), NUTTelA-TAO (Grossan et al., GCN 40771), SVOM/VT (Mat et al., GCN 40772), NOT (Schneider et al., GCN 40774), COLIBRÍ (Antier et al., GCN 40775) and VLT/X-shooter (Corcoran et al., GCN 40776)
We report our follow-up results in the table below:
+---------------+-------------+--------------+----------------+--------------+
| Tmid-TGRB (hr)| Exp (s) | Filter | Magnitude | Instrument |
+===============+=============+==============+================+==============+
| 10.8 | 18 x 300s | r (AB) | 20.85 +/- 0.29 | TEC160FL |
+---------------+-------------+--------------+----------------+--------------+
All the data have been reduced by a single data processing pipeline, STDPipe (Karpov et al., 2022). Images obtained with the sloan images were calibrated using the PanSTARRS DR1 catalog.
We use the SkyPortal application (skyportal.io) to monitor our observational campaign (Coughlin et al. 2023).
GRANDMA is a worldwide telescope network (grandma.ijclab.in2p3.fr) devoted to the observation of transients in the context of multi-messenger astrophysics (Antier et al. 2020 MNRAS 497, 5518). Kilonova-Catcher (KNC) is the citizen science program of GRANDMA (http://kilonovacatcher.in2p3.fr/).
GCN Circular 40778
Subject
GRB 250617B: Swift/UVOT Detection
Date
2025-06-18T13:09:34Z (6 days 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 250617B 797 s after the BAT trigger (Page et al., GCN Circ. 40760). A source consistent with the XRT position (Osborne et al., GCN Circ
40767) is detected in the initial UVOT exposures. The lack of detection in the uvw2 and uvm2 filters would be consistent with the redshift reported by Corcoran et al. (GCN Circ. 40776).
The preliminary UVOT position is:
RA (J2000) = 22:11:35.25 = 332.89686 (deg.)
Dec (J2000) = +32:43:57.1 = 32.73253 (deg.)
with an estimated uncertainty of 0.44 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 797 946 147 18.18 +/- 0.05
v 1130 2528 172 18.72 +/- 0.19
b 1229 1596 58 18.91 +/- 0.18
u 1204 1397 39 18.10 +/- 0.19
w1 1179 2408 156 19.32 +/- 0.28
m2 1155 2384 117 >18.3
w2 1106 2507 175 >19.2
The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.087 in the direction of the burst
(Schlegel et al. 1998).
GCN Circular 40783
Subject
GRB 250617B: Assy AZT-20 Optical Observations
Date
2025-06-19T14:26:12Z (5 days ago)
From
Nicolai Pankov at HSE, IKI RAS <colinsergesen@gmail.com>
Via
Web form
N. Pankov (HSE, IKI), V. Kim (FAI), A. Pozanenko (IKI), M. Krugov (FAI) report on behalf of IKI-GRB-FuN:
We performed optical observations of the field of GRB 250617B (Page et. al, GCN 40760; The Fermi GBM team, GCN 40763) using the 1.5-meter AZT-20 of the Assy-Turgen Observatory. The observations were conducted starting on 2025-06-18 at 18:02:27 UT, i.e. ~0.87 days since the Swift trigger. The series of 53*60 sec images was taken in the r'-filter. We detect the optical afterglow (Page et. al, GCN 40760, Moskvitin et. al, GCN 40761, Jelinek et. al, GCN 40762; Kumar et. al, GCN 40768; Lipunov et. al, GCN 40769; Grossan et. al, GCN 40771; Ma et. al, GCN 40772; Schneider et. al, GCN 40774; Antier et. al, GCN 40775; Corcoran et. al, GCN 40776; Turpin et. al, GCN 40777; Siegel & Page, GCN 40778). The preliminary photometry is given below:
Date UT start t-T0 Exp. Filter OT Err. UL
(mid, days) (n*s) (3sigma)
2025-06-18 18:02:27 0.87577 53*60 r' 21.58 0.04 22.5
The photometry has calibrated using nearby stars from PS1 (at the same coordinates as USNO-B1.0 stars given in Moskvitin et. al, GCN 40761) and has not corrected for the Galactic extinction.
GCN Circular 40789
Subject
GRB 250617B: Nickel telescope optical observations
Date
2025-06-20T00:49:40Z (5 days ago)
From
Weikang Zheng at UC Berkeley <weikang@berkeley.edu>
Via
email
Eli Gendreau-Distler, Gracelynn Jost, William Wu, WeiKang Zheng and
Alex Filippenko (UC Berkeley) report on behalf of the KAIT GRB team:
We observed the field of GRB 250617B (Page et. al, GCN 40760; The
Fermi GBM team, GCN 40763) with the 1-m Nickel telescope located at
Lick observatory, California. Observations were performed in R band
with 600s x 5 exposure time started at 09:46 UT on June 18. We
clearly detected the optical afterglow (Page et. al, GCN 40760,
Moskvitin et. al, GCN 40761, Jelinek et. al, GCN 40762; Kumar et. al,
GCN 40768; Lipunov et. al, GCN 40769; Grossan et. al, GCN 40771;
Ma et. al, GCN 40772; Schneider et. al, GCN 40774; Antier et. al,
GCN 40775; Corcoran et. al, GCN 40776; Turpin et. al, GCN 40777;
Siegel & Page, GCN 40778; Pankov et al., GCN 40783) in our coadd image
with 21.4 +/- 0.1 mag at a mid time of 13.10 hours after the burst.
GCN Circular 40804
Subject
GRB 250617B: Calapai Observatory, Massa S. Giorgio (Messina), optical observation.
Date
2025-06-21T21:08:57Z (3 days 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 250617B detected by Swift/BAT (Page et al. GCN 40760) with the 11 inches Schmidt-Cassegrain (Celestron 11) telescope F/D=6,3.
The observations were started at 2025-06-17 23:10:55 UT (approximately 2.15 hours after burst) stacking a two consecutive sets of unfiltered CCD image. The observations were carried out with visibility disturbed by passing clouds.
The OT was detected at the following position:
RA (J2000.0) 22h 11m 35.21s +/- 0.02
Decl. (J2000.0) +32° 43' 57.6" +/- 1.1
The results of our photometry are:
Observation Mid-Time T-T0 (hr) Exposure Filter Mag. S/N Mag. err.
2025-06-18 00:05:21 UT 3.06 90x60s CR 19.24 9.1 +/-0.17
2025-06-18 01:47:28 UT 4.76 88x60s CR 20.75 3.4 +/-0.30
Given the low S/N for the OT of second set, we cannot completely rule out it being due to background fluctuation.
Along the span of our observations and within our uncertainties, the afterglow evolves in agreement with a power-law decay index of ~0.89.
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 Moskvitin et al. (GCN 40761); Jelinek et al. (GCN 40762); Kumar et al. (GCN 40768); Lipunov et al. (GCN 40769); Grossan et al. (GCN 40771); Ma et al. (GCN 40772); Williams et al. (GCN 40773); Schneider et al. (GCN 40774); Antier et al. (GCN 40775); Corcoran et al. (GCN 40776); Turpin et al. (GCN 40777); Siegel et al. (GCN 40778); Pankov et al. (GCN 40783); Gendreau-Distler et al. (GCN 40789).
The message may be cited.
GCN Circular 40812
Subject
GRB 250617B: Swift-BAT refined analysis
Date
2025-06-23T11:39:14Z (a day ago)
From
Takanori Sakamoto at AGU <tsakamoto@phys.aoyama.ac.jp>
Via
Web form
S. Laha (GSFC/UMBC), S. D. Barthelmy (GSFC), R. Gupta (GSFC),
H. A. Krimm (NSF), A. Y. Lien (U Tampa), C. B. Markwardt (GSFC),
M. J. Moss (GSFC), K. L. Page (U Leicester), 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-273 to T+962 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 250617B (trigger #1325580)
(Page, et al., GCN Circ. 40760). The BAT ground-calculated position is
RA, Dec = 332.883, 32.721 deg which is
RA(J2000) = 22h 11m 31.8s
Dec(J2000) = +32d 43' 14.5"
with an uncertainty of 1.9 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 10%.
The mask-weighted light curve shows two peaks. The emission starts at
T-30 sec, peaks at T+1 sec, and ends at T+18 sec.
T90 (15-350 keV) is 36.5 +- 6.9 sec (estimated error including systematics).
The time-averaged spectrum from T-29.32 to T+14.30 sec is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
2.13 +- 0.22. The fluence in the 15-150 keV band is 2.3 +- 0.3 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+0.19 sec in the 15-150 keV band
is 2.9 +- 0.8 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/1325580