Gamma-ray Burst 250407A

(All information courtesy of the instrument teams.)

Previous IAU Circulars

none

Results of Observations

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Mon 07 Apr 25 15:48:24 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      48
TRIGGER_NUM:     765733706
GRB_RA:          113.733d {+07h 34m 56s} (J2000),
                 114.170d {+07h 36m 41s} (current),
                 112.868d {+07h 31m 28s} (1950)
GRB_DEC:         +41.317d {+41d 19' 00"} (J2000),
                 +41.260d {+41d 15' 35"} (current),
                 +41.427d {+41d 25' 37"} (1950)
GRB_ERROR:       3.35 [deg radius, statistical plus systematic]
GRB_INTEN:       8143 [cnts/sec]
DATA_SIGNIF:     114.90 [sigma]
INTEG_TIME:      0.512 [sec]
GRB_DATE:        20772 TJD;    97 DOY;   25/04/07
GRB_TIME:        56901.07 SOD {15:48:21.07} UT
GRB_PHI:         302.00 [deg]
GRB_THETA:       120.00 [deg]
DATA_TIME_SCALE: 0.5120 [sec]
HARD_RATIO:      0.12
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:      95%  GRB
2nd_MOST_LIKELY:   3%  Distant Particles
DETECTORS:       0,0,0, 0,1,1, 0,0,0, 0,0,0, 0,0,
SUN_POSTN:        16.68d {+01h 06m 43s}   +7.09d {+07d 05' 26"}
SUN_DIST:         90.91 [deg]   Sun_angle= -6.5 [hr] (East of Sun)
MOON_POSTN:      142.18d {+09h 28m 42s}  +18.42d {+18d 25' 00"}
MOON_DIST:        33.06 [deg]
MOON_ILLUM:      75 [%]
GAL_COORDS:      177.59, 25.29 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      108.69, 19.41 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250407659/quicklook/glg_lc_medres34_bn250407659.gif
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 277.28,4.55 [deg].  
COMMENTS:        The LC_URL file will not be created until ~15 min after the trigger.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Mon 07 Apr 25 15:48:39 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      59
TRIGGER_NUM:     765733706
GRB_RA:          106.870d {+07h 07m 29s} (J2000),
                 107.308d {+07h 09m 14s} (current),
                 106.002d {+07h 04m 00s} (1950)
GRB_DEC:         +40.400d {+40d 23' 60"} (J2000),
                 +40.359d {+40d 21' 31"} (current),
                 +40.479d {+40d 28' 44"} (1950)
GRB_ERROR:       1.00 [deg radius, statistical only]
DATA_SIGNIF:     280.20 [sigma]
DATA_INTERVAL:   2.048 [sec]
GRB_DATE:        20772 TJD;    97 DOY;   25/04/07
GRB_TIME:        56901.07 SOD {15:48:21.07} UT
GRB_PHI:         304.00 [deg]
GRB_THETA:       115.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   4173 (Gnd S/W Version number)
SUN_POSTN:        16.68d {+01h 06m 43s}   +7.09d {+07d 05' 26"}
SUN_DIST:         85.89 [deg]   Sun_angle= -6.0 [hr] (East of Sun)
MOON_POSTN:      142.18d {+09h 28m 43s}  +18.42d {+18d 24' 57"}
MOON_DIST:        37.08 [deg]
MOON_ILLUM:      75 [%]
GAL_COORDS:      176.90, 20.06 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      103.42, 17.74 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250407659/quicklook/glg_lc_medres34_bn250407659.gif
POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_765733706.fits
COMMENTS:        Fermi-GBM Ground-calculated Coordinates.  
COMMENTS:        Bright hard burst in the GBM.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        The LC_URL file will not be created/available until ~15 min after the trigger.  
COMMENTS:        The POS_MAP_URL file will not be created/available until ~1.5 min after the notice.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Mon 07 Apr 25 15:49:07 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      0
TRIGGER_NUM:     765733706
GRB_RA:          106.810d {+07h 07m 14s} (J2000),
                 107.248d {+07h 08m 59s} (current),
                 105.943d {+07h 03m 46s} (1950)
GRB_DEC:         +40.290d {+40d 17' 24"} (J2000),
                 +40.249d {+40d 14' 56"} (current),
                 +40.368d {+40d 22' 07"} (1950)
GRB_ERROR:       1.00 [deg radius, statistical only]
DATA_SIGNIF:     129.20 [sigma]
DATA_INTERVAL:   4.096 [sec]
GRB_DATE:        20772 TJD;    97 DOY;   25/04/07
GRB_TIME:        56901.07 SOD {15:48:21.07} UT
GRB_PHI:         304.00 [deg]
GRB_THETA:       115.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   41731 (Gnd S/W Version number)
SUN_POSTN:        16.68d {+01h 06m 43s}   +7.09d {+07d 05' 26"}
SUN_DIST:         85.86 [deg]   Sun_angle= -6.0 [hr] (East of Sun)
MOON_POSTN:      142.18d {+09h 28m 44s}  +18.41d {+18d 24' 52"}
MOON_DIST:        37.08 [deg]
MOON_ILLUM:      75 [%]
GAL_COORDS:      177.00, 19.98 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      103.38, 17.63 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250407659/quicklook/glg_lc_medres34_bn250407659.gif
POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_765733706.fits
COMMENTS:        Fermi-GBM Ground-calculated Coordinates.  
COMMENTS:        Bright hard burst in the GBM.  
COMMENTS:        This is likely a Long GRB.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        The LC_URL file will not be created/available until ~15 min after the trigger.  
COMMENTS:        The POS_MAP_URL file will not be created/available until ~1.5 min after the notice.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Mon 07 Apr 25 15:57:48 UT
NOTICE_TYPE:     Fermi-GBM Final Position
RECORD_NUM:      0
TRIGGER_NUM:     765733706
GRB_RA:          110.330d {+07h 21m 19s} (J2000),
                 110.772d {+07h 23m 05s} (current),
                 109.454d {+07h 17m 49s} (1950)
GRB_DEC:         +41.980d {+41d 58' 48"} (J2000),
                 +41.931d {+41d 55' 50"} (current),
                 +42.075d {+42d 04' 29"} (1950)
GRB_ERROR:       1.00 [deg radius, statistical only]
GRB_DATE:        20772 TJD;    97 DOY;   25/04/07
GRB_TIME:        56901.07 SOD {15:48:21.07} UT
GRB_PHI:         304.00 [deg]
GRB_THETA:       118.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   41731 (Gnd S/W Version number)
SUN_POSTN:        16.68d {+01h 06m 44s}   +7.09d {+07d 05' 35"}
SUN_DIST:         88.29 [deg]   Sun_angle= -6.3 [hr] (East of Sun)
MOON_POSTN:      142.26d {+09h 29m 01s}  +18.39d {+18d 23' 07"}
MOON_DIST:        35.63 [deg]
MOON_ILLUM:      75 [%]
GAL_COORDS:      176.14, 23.02 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      105.92, 19.66 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250407659/quicklook/glg_lc_medres34_bn250407659.gif
LOC_URL:         http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250407659/quicklook/glg_locplot_all_bn250407659.png
COMMENTS:        Fermi-GBM Final Position.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        The LC_URL file should be available by the time this FINAL notice is produced.  
COMMENTS:        This notice was generated completely by automated pipeline processing.  
COMMENTS:        Bright hard burst in the GBM.  
COMMENTS:        This is likely a Long GRB.

GCN Circular #40104
The Fermi GBM team reports the detection of a likely LONG GRB
At 15:48:21 UT on 7 Apr 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250407A (trigger 765733706.065626 / 250407659).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 110.3, Dec = 42.0 (J2000 degrees, equivalent to J2000 07h 21m, 42d 00'), with a statistical uncertainty of 1.0 degrees.
The angle from the Fermi LAT boresight is 118.0 degrees.
The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250407659/quicklook/glg_skymap_all_bn250407659.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/bn250407659/quicklook/glg_healpix_all_bn250407659.fit
The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250407659/quicklook/glg_lc_medres34_bn250407659.gif
GCN Circular #40105
T. Preis (University of Innsbruck) & J. Greiner (MPE Garching) report:
The public trigdat data of the Fermi Gamma-ray Burst Monitor (GBM) trigger 765733706 at 15:48:21 on 07 April 2025 were automatically fitted for spectrum and sky location with BALROG (Burgess et al. 2018, MNRAS 476, 1427; Berlato et al. 2019, ApJ 873, 60).
The best-fit position is:
```
RA(2000.0) = 111.6 deg
Decl.(2000.0) = 36.5 deg
```
The 1 sigma statistical error radius is 3.5 deg. We estimate an additional systematic error of 2 deg.
Further details are available at: https://grb.mpe.mpg.de/grb/GRB250407659/
The Healpix map can be downloaded from: https://grb.mpe.mpg.de/grb/GRB250407659/healpix
The location parameters are available as JSON at: https://grb.mpe.mpg.de/grb/GRB250407659/json
GCN Circular #40110
S. Molkov, A. Tkachenko, I. Mereminskiy, A. Semena, A. Lutovinov, I. Lapshov, V. Arefiev, A. Shtykovskiy and D. Karasev on behalf of the ART-XC team (IKI Moscow) report:
During the ongoing all sky survey the Mikhail Pavlinsky ART-XC telescope passed through the localization area of GRB250407A (GCN 40104, GCN 40105) and detected a new X-ray source with coordinates: (RA,Dec)=(110.7564,36.7979) J2000; the 1 sigma statistical error radius is 20 arcsec. The source was in the FoV of the ART-XC telescope during ~20 seconds with a central time of 2025-04-07T17:08:20 UTC (on-board time), approximately 90 minutes after the burst had been detected by GBM (GCN 40104).
The mean flux during the transition was about 1.4e-10 ergs/s/cm2 in the 4-12 keV energy band. We expect that it's an afterglow detection of GRB 250407A.
Urgent Swift/XRT follow-up observation was requested to obtain precise localization.
GCN Circular #40111
P. A. Evans (U. Leicester) reports on behalf of the Swift team:
Swift has initiated a ToO observation of the Fermi/GBM-detected event GRB 250407A. Automated analysis of the XRT data will be presented online at https://www.swift.ac.uk/ToO_GRBs/00021826 Any uncatalogued X-ray sources detected in this analysis will be reported on this website and via GCN COUNTERPART notices. These are not necessarily related to the Fermi/GBM event. Any X-ray source considered to be a probable afterglow candidate will be reported via a GCN Circular after manual consideration.
Details of the XRT automated analysis methods are detailed in Evans et al. (2007, A&A, 469, 379; 2009, MNRAS, 397, 1177 and 2014, ApJS, 210, 8).
This circular is an official product of the Swift-XRT team.

GCN Circular #40112
V.Lipunov, E.Gorbovskoy, N.Tiurina, P.Balanutsa, , D.Vlasenko, I.Panchenko, A.Kuznetsov, G.Antipov, A.Sankovich, A.Sosnovskij, Yu.Tselik, M.Gulyaev, 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. 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-Tunka robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Applied Physics Institute, Irkutsk State University) started inspect of the Fermi GRB 250407A ( Fermi GBM team, GCN 40104) errorbox 27 sec after notice time and 46 sec after trigger time at 2025-04-07 15:49:07 UT, with upper limit up to 17.7 mag. The observations began at zenith distance = 42 deg. The sun altitude is -29.6 deg.
MASTER-Kislovodsk robotic telescope located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) started inspect of the Fermi GRB 250407A errorbox 4363 sec after notice time and 4383 sec after trigger time at 2025-04-07 17:01:24 UT, with upper limit up to 16.1 mag. Observations started at twilight. The observations began at zenith distance = 19 deg. The sun altitude is -14.4 deg.
The galactic latitude b = 24 deg., longitude l = 176 deg.
Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2835912
We obtain a following upper limits.

Tmid-T0  |      Date Time      |          Site       |             Coord (J2000)          |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________

      52 | 2025-04-07 15:49:07 |        MASTER-Tunka | (07h 31m 43.27s , +43d 36m 20.3s) |   C |    10 | 16.5 |        
     594 | 2025-04-07 15:58:06 |        MASTER-Tunka | (07h 18m 01.14s , +44d 15m 13.8s) |   C |    15 | 16.8 |        
     609 | 2025-04-07 15:58:06 |        MASTER-Tunka | (07h 18m 01.11s , +44d 15m 13.8s) |   C |    45 | 17.3 |  Coadd 
     612 | 2025-04-07 15:58:25 |        MASTER-Tunka | (07h 18m 01.10s , +44d 15m 13.6s) |   C |    15 | 16.8 |        
     631 | 2025-04-07 15:58:43 |        MASTER-Tunka | (07h 18m 01.05s , +44d 15m 13.2s) |   C |    15 | 16.9 |        
     650 | 2025-04-07 15:59:02 |        MASTER-Tunka | (07h 18m 00.98s , +44d 15m 12.7s) |   C |    15 | 16.8 |        
     665 | 2025-04-07 15:59:02 |        MASTER-Tunka | (07h 18m 00.96s , +44d 15m 12.7s) |   C |    45 | 17.5 |  Coadd 
     668 | 2025-04-07 15:59:21 |        MASTER-Tunka | (07h 18m 00.92s , +44d 15m 12.2s) |   C |    15 | 16.9 |        
     687 | 2025-04-07 15:59:40 |        MASTER-Tunka | (07h 18m 00.86s , +44d 15m 11.4s) |   C |    15 | 17.1 |        
     706 | 2025-04-07 15:59:58 |        MASTER-Tunka | (07h 18m 00.82s , +44d 15m 10.8s) |   C |    15 | 17.0 |        
     721 | 2025-04-07 15:59:58 |        MASTER-Tunka | (07h 18m 00.81s , +44d 15m 10.7s) |   C |    45 | 17.5 |  Coadd 
     724 | 2025-04-07 16:00:17 |        MASTER-Tunka | (07h 18m 00.77s , +44d 15m 10.6s) |   C |    15 | 16.9 |        
     742 | 2025-04-07 16:00:35 |        MASTER-Tunka | (07h 18m 00.71s , +44d 15m 10.3s) |   C |    15 | 16.9 |        
     761 | 2025-04-07 16:00:54 |        MASTER-Tunka | (07h 18m 00.68s , +44d 15m 10.0s) |   C |    15 | 17.0 |        
     776 | 2025-04-07 16:00:54 |        MASTER-Tunka | (07h 18m 00.65s , +44d 15m 09.9s) |   C |    45 | 17.4 |  Coadd 
     779 | 2025-04-07 16:01:12 |        MASTER-Tunka | (07h 18m 00.61s , +44d 15m 09.7s) |   C |    15 | 16.9 |        
     799 | 2025-04-07 16:01:31 |        MASTER-Tunka | (07h 18m 00.55s , +44d 15m 09.2s) |   C |    15 | 16.6 |        
     817 | 2025-04-07 16:01:50 |        MASTER-Tunka | (07h 18m 00.46s , +44d 15m 08.1s) |   C |    15 | 16.4 |        
     832 | 2025-04-07 16:01:50 |        MASTER-Tunka | (07h 18m 00.45s , +44d 15m 08.0s) |   C |    45 | 16.6 |  Coadd 
     835 | 2025-04-07 16:02:08 |        MASTER-Tunka | (07h 18m 00.45s , +44d 15m 07.8s) |   C |    15 | 16.3 |        
     854 | 2025-04-07 16:02:27 |        MASTER-Tunka | (07h 18m 00.39s , +44d 15m 07.6s) |   C |    15 | 16.2 |        
     870 | 2025-04-07 16:02:45 |        MASTER-Tunka | (07h 18m 00.33s , +44d 15m 07.3s) |   C |    10 | 15.9 |        
     880 | 2025-04-07 16:02:45 |        MASTER-Tunka | (07h 18m 00.32s , +44d 15m 07.3s) |   C |    30 | 16.6 |  Coadd 
     883 | 2025-04-07 16:02:58 |        MASTER-Tunka | (07h 18m 00.28s , +44d 15m 07.0s) |   C |    10 | 16.0 |        
     896 | 2025-04-07 16:03:12 |        MASTER-Tunka | (07h 18m 00.22s , +44d 15m 07.0s) |   C |    10 | 16.2 |        
     910 | 2025-04-07 16:03:25 |        MASTER-Tunka | (07h 18m 00.20s , +44d 15m 06.6s) |   C |    10 | 16.2 |        
     920 | 2025-04-07 16:03:25 |        MASTER-Tunka | (07h 18m 00.20s , +44d 15m 06.6s) |   C |    30 | 16.5 |  Coadd 
     924 | 2025-04-07 16:03:39 |        MASTER-Tunka | (07h 18m 00.21s , +44d 15m 07.0s) |   C |    10 | 16.2 |        
     937 | 2025-04-07 16:03:53 |        MASTER-Tunka | (07h 18m 00.17s , +44d 15m 06.7s) |   C |    10 | 16.2 |        
     951 | 2025-04-07 16:04:06 |        MASTER-Tunka | (07h 18m 00.16s , +44d 15m 06.5s) |   C |    10 | 16.2 |        
     961 | 2025-04-07 16:04:06 |        MASTER-Tunka | (07h 18m 00.15s , +44d 15m 06.5s) |   C |    30 | 16.8 |  Coadd 
     964 | 2025-04-07 16:04:20 |        MASTER-Tunka | (07h 18m 00.11s , +44d 15m 06.2s) |   C |    10 | 16.3 |        
     978 | 2025-04-07 16:04:33 |        MASTER-Tunka | (07h 18m 00.08s , +44d 15m 05.8s) |   C |    10 | 16.4 |        
     992 | 2025-04-07 16:04:47 |        MASTER-Tunka | (07h 18m 00.06s , +44d 15m 05.5s) |   C |    10 | 16.5 |        
    1002 | 2025-04-07 16:04:47 |        MASTER-Tunka | (07h 18m 00.06s , +44d 15m 05.4s) |   C |    30 | 16.9 |  Coadd 
    1005 | 2025-04-07 16:05:01 |        MASTER-Tunka | (07h 18m 00.03s , +44d 15m 05.1s) |   C |    10 | 16.5 |        
    1019 | 2025-04-07 16:05:14 |        MASTER-Tunka | (07h 17m 59.92s , +44d 15m 04.5s) |   C |    10 | 16.3 |        
    1032 | 2025-04-07 16:05:28 |        MASTER-Tunka | (07h 17m 59.88s , +44d 15m 04.1s) |   C |    10 | 16.2 |        
    1042 | 2025-04-07 16:05:28 |        MASTER-Tunka | (07h 17m 59.88s , +44d 15m 04.0s) |   C |    30 | 16.6 |  Coadd 
    1046 | 2025-04-07 16:05:42 |        MASTER-Tunka | (07h 17m 59.83s , +44d 15m 03.8s) |   C |    10 | 16.1 |        
    1060 | 2025-04-07 16:05:56 |        MASTER-Tunka | (07h 17m 59.82s , +44d 15m 03.7s) |   C |    10 | 16.1 |        
    1074 | 2025-04-07 16:06:09 |        MASTER-Tunka | (07h 17m 59.75s , +44d 15m 03.5s) |   C |    10 | 16.1 |        
    1084 | 2025-04-07 16:06:09 |        MASTER-Tunka | (07h 17m 59.75s , +44d 15m 03.6s) |   C |    30 | 16.6 |  Coadd 
    1087 | 2025-04-07 16:06:23 |        MASTER-Tunka | (07h 17m 59.74s , +44d 15m 03.4s) |   C |    10 | 16.2 |        
    1101 | 2025-04-07 16:06:37 |        MASTER-Tunka | (07h 17m 59.68s , +44d 15m 03.0s) |   C |    10 | 16.2 |        
    1115 | 2025-04-07 16:06:50 |        MASTER-Tunka | (07h 17m 59.64s , +44d 15m 03.1s) |   C |    10 | 16.4 |        
    1125 | 2025-04-07 16:06:50 |        MASTER-Tunka | (07h 17m 59.64s , +44d 15m 03.1s) |   C |    30 | 17.0 |  Coadd 
    1128 | 2025-04-07 16:07:04 |        MASTER-Tunka | (07h 17m 59.60s , +44d 15m 02.5s) |   C |    10 | 16.5 |        
    1142 | 2025-04-07 16:07:17 |        MASTER-Tunka | (07h 17m 59.60s , +44d 15m 01.8s) |   C |    10 | 16.7 |        
    1156 | 2025-04-07 16:07:31 |        MASTER-Tunka | (07h 17m 59.57s , +44d 15m 02.0s) |   C |    10 | 16.7 |        
    1166 | 2025-04-07 16:07:31 |        MASTER-Tunka | (07h 17m 59.57s , +44d 15m 01.9s) |   C |    30 | 17.3 |  Coadd 
    1169 | 2025-04-07 16:07:45 |        MASTER-Tunka | (07h 17m 59.54s , +44d 15m 02.1s) |   C |    10 | 16.8 |        
    1183 | 2025-04-07 16:07:58 |        MASTER-Tunka | (07h 17m 59.49s , +44d 15m 01.4s) |   C |    10 | 16.8 |        
    1199 | 2025-04-07 16:08:12 |        MASTER-Tunka | (07h 17m 59.47s , +44d 15m 01.1s) |   C |    15 | 16.8 |        
    1214 | 2025-04-07 16:08:12 |        MASTER-Tunka | (07h 17m 59.45s , +44d 15m 01.1s) |   C |    45 | 17.4 |  Coadd 
    1218 | 2025-04-07 16:08:30 |        MASTER-Tunka | (07h 17m 59.40s , +44d 15m 00.9s) |   C |    15 | 16.7 |        
    1237 | 2025-04-07 16:08:49 |        MASTER-Tunka | (07h 17m 59.37s , +44d 15m 00.1s) |   C |    15 | 16.9 |        
    1255 | 2025-04-07 16:09:08 |        MASTER-Tunka | (07h 17m 59.35s , +44d 15m 00.0s) |   C |    15 | 17.0 |        
    1270 | 2025-04-07 16:09:08 |        MASTER-Tunka | (07h 17m 59.35s , +44d 15m 00.1s) |   C |    45 | 17.6 |  Coadd 
    1274 | 2025-04-07 16:09:27 |        MASTER-Tunka | (07h 17m 59.31s , +44d 14m 59.5s) |   C |    15 | 17.2 |        
    1293 | 2025-04-07 16:09:46 |        MASTER-Tunka | (07h 17m 59.25s , +44d 14m 59.2s) |   C |    15 | 17.2 |        
    1312 | 2025-04-07 16:10:04 |        MASTER-Tunka | (07h 17m 59.17s , +44d 14m 58.5s) |   C |    15 | 17.0 |        
    1327 | 2025-04-07 16:10:04 |        MASTER-Tunka | (07h 17m 59.16s , +44d 14m 58.3s) |   C |    45 | 17.5 |  Coadd 
    1330 | 2025-04-07 16:10:22 |        MASTER-Tunka | (07h 17m 59.11s , +44d 14m 58.2s) |   C |    15 | 16.9 |        
    1349 | 2025-04-07 16:10:41 |        MASTER-Tunka | (07h 17m 59.07s , +44d 14m 58.1s) |   C |    15 | 17.1 |        
    1367 | 2025-04-07 16:11:00 |        MASTER-Tunka | (07h 17m 59.06s , +44d 14m 57.8s) |   C |    15 | 17.1 |        
    1382 | 2025-04-07 16:11:00 |        MASTER-Tunka | (07h 17m 59.03s , +44d 14m 57.5s) |   C |    45 | 17.6 |  Coadd 
    1386 | 2025-04-07 16:11:19 |        MASTER-Tunka | (07h 17m 58.96s , +44d 14m 56.9s) |   C |    15 | 17.0 |        
    1405 | 2025-04-07 16:11:37 |        MASTER-Tunka | (07h 17m 58.88s , +44d 14m 56.5s) |   C |    15 | 16.9 |        
    1423 | 2025-04-07 16:11:56 |        MASTER-Tunka | (07h 17m 58.84s , +44d 14m 56.1s) |   C |    15 | 17.0 |        
    1438 | 2025-04-07 16:11:56 |        MASTER-Tunka | (07h 17m 58.82s , +44d 14m 55.9s) |   C |    45 | 17.7 |  Coadd 
    1442 | 2025-04-07 16:12:14 |        MASTER-Tunka | (07h 17m 58.77s , +44d 14m 55.3s) |   C |    15 | 17.1 |        
    1460 | 2025-04-07 16:12:33 |        MASTER-Tunka | (07h 17m 58.72s , +44d 14m 55.3s) |   C |    15 | 17.0 |        
    1479 | 2025-04-07 16:12:52 |        MASTER-Tunka | (07h 17m 58.66s , +44d 14m 55.3s) |   C |    15 | 17.1 |        
    1494 | 2025-04-07 16:12:52 |        MASTER-Tunka | (07h 17m 58.65s , +44d 14m 55.2s) |   C |    45 | 17.6 |  Coadd 
    1498 | 2025-04-07 16:13:10 |        MASTER-Tunka | (07h 17m 58.60s , +44d 14m 54.3s) |   C |    15 | 17.0 |        
    1516 | 2025-04-07 16:13:29 |        MASTER-Tunka | (07h 17m 58.58s , +44d 14m 54.0s) |   C |    15 | 17.0 |        
    4413 | 2025-04-07 17:01:24 |   MASTER-Kislovodsk | (07h 15m 35.87s , +39d 19m 33.6s) |   C |    60 | 16.1 |        
    5084 | 2025-04-07 17:12:35 |   MASTER-Kislovodsk | (07h 15m 35.05s , +39d 18m 41.9s) |   C |    60 | 15.1 |        
   18929 | 2025-04-07 21:03:19 |   MASTER-Kislovodsk | (07h 24m 40.96s , +39d 08m 54.1s) |   C |    60 | 16.1 |        
   18925 | 2025-04-07 21:03:31 |        MASTER-Tunka | (07h 21m 45.98s , +43d 01m 33.5s) |   C |    30 | 16.1 |        
   18955 | 2025-04-07 21:03:31 |        MASTER-Tunka | (07h 21m 45.98s , +43d 01m 33.5s) |   C |    90 | 16.8 |  Coadd 
   18968 | 2025-04-07 21:04:14 |        MASTER-Tunka | (07h 21m 45.94s , +43d 02m 33.2s) |   C |    30 | 16.2 |        
   19010 | 2025-04-07 21:04:56 |        MASTER-Tunka | (07h 21m 51.95s , +43d 01m 32.7s) |   C |    30 | 16.4 |        
   19054 | 2025-04-07 21:05:40 |        MASTER-Tunka | (07h 21m 47.61s , +43d 00m 31.0s) |   C |    30 | 16.5 |        
   19096 | 2025-04-07 21:06:22 |        MASTER-Tunka | (07h 21m 53.31s , +43d 00m 50.5s) |   C |    30 | 16.6 |        
   19139 | 2025-04-07 21:07:05 |        MASTER-Tunka | (07h 21m 49.60s , +43d 02m 03.7s) |   C |    30 | 16.6 |        
   19178 | 2025-04-07 21:07:29 |   MASTER-Kislovodsk | (07h 27m 46.98s , +41d 04m 05.2s) |   C |    60 | 15.7 |        
   19183 | 2025-04-07 21:07:48 |        MASTER-Tunka | (07h 21m 49.75s , +43d 00m 42.4s) |   C |    30 | 16.7 |        
   19213 | 2025-04-07 21:07:48 |        MASTER-Tunka | (07h 21m 49.74s , +43d 00m 41.9s) |   C |    90 | 17.4 |  Coadd 
   19226 | 2025-04-07 21:08:32 |        MASTER-Tunka | (07h 21m 52.80s , +43d 02m 00.8s) |   C |    30 | 16.8 |        
   19268 | 2025-04-07 21:09:14 |        MASTER-Tunka | (07h 21m 47.32s , +43d 01m 19.8s) |   C |    30 | 16.8 |        
   19311 | 2025-04-07 21:09:57 |        MASTER-Tunka | (07h 21m 46.61s , +43d 02m 19.8s) |   C |    30 | 16.7 |        
   19341 | 2025-04-07 21:09:57 |        MASTER-Tunka | (07h 21m 46.59s , +43d 02m 18.6s) |   C |    90 | 17.3 |  Coadd 
   19344 | 2025-04-07 21:10:15 |   MASTER-Kislovodsk | (07h 20m 26.44s , +42d 57m 56.8s) |   C |    60 | 15.8 |        
   19354 | 2025-04-07 21:10:39 |        MASTER-Tunka | (07h 21m 52.13s , +43d 01m 19.1s) |   C |    30 | 16.7 |        
   19398 | 2025-04-07 21:11:23 |        MASTER-Tunka | (07h 21m 46.69s , +43d 00m 15.8s) |   C |    30 | 16.6 |        
   19442 | 2025-04-07 21:12:07 |        MASTER-Tunka | (07h 28m 37.53s , +42d 02m 35.3s) |   C |    30 | 16.3 |        
   19484 | 2025-04-07 21:12:50 |        MASTER-Tunka | (07h 28m 33.74s , +42d 03m 44.2s) |   C |    30 | 16.3 |        
   19527 | 2025-04-07 21:13:32 |        MASTER-Tunka | (07h 28m 33.85s , +42d 02m 30.1s) |   C |    30 | 16.3 |        
   19571 | 2025-04-07 21:14:17 |        MASTER-Tunka | (07h 28m 36.60s , +42d 03m 41.2s) |   C |    30 | 16.2 |        
   19615 | 2025-04-07 21:15:00 |        MASTER-Tunka | (07h 28m 30.97s , +42d 02m 58.7s) |   C |    30 | 16.1 |        
   19659 | 2025-04-07 21:15:45 |        MASTER-Tunka | (07h 28m 30.38s , +42d 03m 55.9s) |   C |    30 | 16.1 |        
   19704 | 2025-04-07 21:16:30 |        MASTER-Tunka | (07h 21m 53.18s , +43d 00m 59.4s) |   C |    30 | 16.2 |        
   19743 | 2025-04-07 21:17:13 |        MASTER-Tunka | (07h 21m 48.54s , +42d 59m 58.8s) |   C |    20 | 16.1 |        
   19774 | 2025-04-07 21:17:45 |        MASTER-Tunka | (07h 21m 52.74s , +43d 00m 00.0s) |   C |    20 | 16.1 |        
   19809 | 2025-04-07 21:18:20 |        MASTER-Tunka | (07h 21m 50.55s , +43d 01m 39.6s) |   C |    20 | 16.2 |        
   19842 | 2025-04-07 21:18:52 |        MASTER-Tunka | (07h 21m 50.60s , +43d 00m 24.5s) |   C |    20 | 16.0 |        
   19875 | 2025-04-07 21:19:25 |        MASTER-Tunka | (07h 21m 54.02s , +43d 01m 40.6s) |   C |    20 | 15.9 |        
   19907 | 2025-04-07 21:20:00 |        MASTER-Tunka | (07h 21m 47.61s , +43d 00m 52.3s) |   C |    15 | 15.8 |        
   19935 | 2025-04-07 21:20:27 |        MASTER-Tunka | (07h 21m 47.97s , +43d 01m 51.2s) |   C |    15 | 15.6 |        
   19964 | 2025-04-07 21:20:57 |        MASTER-Tunka | (07h 21m 53.90s , +43d 00m 50.1s) |   C |    15 | 15.6 |        
   19988 | 2025-04-07 21:21:24 |        MASTER-Tunka | (07h 21m 47.26s , +42d 59m 49.2s) |   C |    10 | 15.6 |

Filter C is a clear (unfiltred) band.
The observation and reduction will continue. The message may be cited.

GCN Circular #40113
S. Dichiara (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), M. Perri (SSDC & INAF-OAR), V. D'Elia (SSDC & INAF-OAR), B. Sbarufatti (INAF-OAB), D.N. Burrows (PSU), M. A. Williams (PSU) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team:
Swift-XRT has performed follow-up observations of the Fermi/GBM-detected burst GRB 250407A (GCN circ. 40104, GCN circ. 40105). We searched for X-ray sources in 293 s of Photon Counting (PC) mode data. The total exposure at the position of the afterglow (see below) is 293 s, obtained between T0+18.8 ks and T0+19.1 ks.
An uncatalogued X-ray source is detected within the estimated 3-sigma Fermi/GBM error region (29 arcsec) and is above the RASS 3-sigma upper limit at this position, and is therefore likely the GRB afterglow. Using 293 s of PC mode data and 1 UVOT image, we find an enhanced XRT position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 110.75876, +36.79827 which is equivalent to:
```
RA (J2000): 07h 23m 02.10s
Dec(J2000): +36d 47' 53.8"
```
with an uncertainty of 2.8 arcsec (radius, 90% confidence). This position is 6.9 arcsec from the SRG/ART-XC position reported by Molkov et al (GCN circ. 40110). We note that the source has faded since the SRG/ART-XC observation.
A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.8 (+0.4, -0.3). The best-fitting absorption column is 3.0 (+1.7, -1.4) x 10^21 cm^-2, in excess of the Galactic value of 7.0 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 4.3 x 10^-11 (5.8 x 10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
```
Total column:	     3.0 (+1.7, -1.4) x 10^21 cm^-2
Galactic foreground: 7.0 x 10^20 cm^-2
Excess significance: 2.8 sigma
Photon index:	     1.8 (+0.4, -0.3)
```
The results of the XRT-team automatic analysis of the likely afterglow are at https://www.swift.ac.uk/ToO_GRBs/00021826/Source1.php. The results of the full analysis of the XRT observations are available at https://www.swift.ac.uk/ToO_GRBs/00021826.
This circular is an official product of the Swift-XRT team.
GCN Circular #40114
O. Mukherjee (USRA) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team:
"At 15:48:21.07 UT on 07 April 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250407A (trigger 765733706/250407659). The afterglow was detected by ART-XC (Molkov et al. 2025, GCN 40110) and Swift-XRT (Dichiara et al. 2025, GCN 40113).
The Fermi GBM Final Localization (GCN 40104) is consistent with the ART-XC and Swift-XRT positions.
The angle from the Fermi LAT boresight is 116 degrees.
The GBM light curve consists of a single-peak emission episode with a duration (T90) of about 6.3 s (50-300 keV). The time-averaged spectrum from T0+0.6 to T0+5.1 s is best fit by a Band function with Epeak = 470 +/- 20 keV, alpha = -0.18 +/- 0.03, and beta = -2.08 +/- 0.03.
The event fluence (10-1000 keV) in this time interval is (2.65 +/- 0.03)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+0.77 s in the 10-1000 keV band is 62.4 +/- 0.7 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 #40116
WeiKang Zheng and Alexei V. Filippenko (UC Berkeley) report on
behalf of the KAIT GRB team:
The 0.76-m Katzman Automatic Imaging Telescope (KAIT), located at
Lick Observatory, observed the field of GRB 250407A (GBM team,
GCN 40104; Preis et al., GCN 40105; Mukherjee et al., GCN 40114)
around the X-ray afterglow location (Molkov et al., GCN 40110;
Dichiara et al., GCN 40113) starting at 04:17, Apr. 08 UT, about
12.48 hours after the burst. A set of clear (roughly R) filter
images were obtained. Within the XRT afterglow (Dichiara et al.,
GCN 40113) error circle, we detected an uncataloged optical
afterglow candidate at J2000 position of (error ~0.5"):
RA: 07:23:02.11
Dec: +36:47:54.97
We estimate the clear band magnitude to be ~20.1 +/- 0.3 mag (Vega)
at 12.48 hours after the burst. Further observations are encouraged.
GCN Circular #40117
Jean-Grégoire Ducoin (CPPM), Camila Angulo (UNAM), Stéphane Basa (UAR Pytheas), Rosa L. Becerra (U Roma), William H. Lee (UNAM), Dalya Akl (AUS), Sarah Antier (OCA), Jean-Luc Atteia (IRAP), 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), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM) report:
We imaged the field of GRB 250407A (Fermi GBM team, GCN Circ. 40104; Preis et al., GCN Circ. 40105) with the DDRAGO wide-field imager on the COLIBRÍ telescope at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir in Mexico on the night of 2025-04-08 UTC.
We observed from 03:01 to 03:53 UTC (11.21 to 12.09 hours after the trigger) and obtained 20 minutes of exposure in the i filter. The data were coadded with the COLIBRÍ pipeline and analysed in STDWeb/STDPipe (Karpov 2025), with photometric calibration against Pan-STARRS DR1. Our photometry is in the AB system and is not corrected for Galactic extinction.
At the position reported previously by SRG/ART-XC (Molkov et al. GCN Circ. 40110) and Swift/XRT (Evans et al., GCN Circ. 40113), we detect a source with a magnitude of
i = 19.96 +/- 0.03,
consistent with the value reported by Zheng et al. (GCN Circ. 40116). In this position, there is a previously identified source (ID: 152151107588088917) in the Pan-STARRS catalog with a PSF magnitude of i = 22.99 +/- 0.14. We propose that this is the host galaxy of GRB 250407A.
Further observations are planned.
We warmly thank the COLIBRÍ and DDRAGO engineering teams and the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir.
GCN Circular #40119
T. C. Zheng, D. F. Hu (PMO, CAS), X. Mao, W. X. Wang, W. D. Zhang (NAO, CAS) report on behalf of the Einstein Probe team:
We report on the detection of the X-ray afterglow of GRB 250407A by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission. In an observation starting at 2025-04-07T17:11:31.158 (UTC), WXT detected an uncatalogued X-ray source at a position R.A. = 110.767 deg, DEC = 36.800 deg (J2000) with an uncertainty of 2.7 arcmin (radius, 90% C.L. statistical and systematic). This source is only 25 arcsec away from the X-ray afterglow of GRB 250407A that was detected by Swift/XRT (GCN 40113). The WXT observation started about 83 minutes after the trigger of GRB 250407A by Fermi/GBM (GCN 40104). The temporal and spatial coincidence suggests that WXT likely detected the X-ray afterglow of GRB 250407A.
The observation lasted for 422 seconds, during which no significant variation was observed. The time-averaged spectrum can be fitted with an absorbed powerlaw model, with a photon index of 1.5(-0.7/+0.8), while nH is fixed at the Galactic value of 7.1 x 10^20 cm^-2. The unabsorbed 0.5-4 keV flux is estimated to be 2.0 (-0.7/+1.2) x 10^-10 erg/s/cm^2. The uncertainties are quoted at the 90% confidence level for the above spectral parameters.
Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics).
GCN Circular #40120
SVOM/GRM team: Chen-Wei Wang, Yue Huang, Shi-Jie Zheng, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP)
SVOM/ECLAIRs team: Marius Brunet, Jean-Luc Atteia, Hui Yang (IRAP), Maria-Grazia Bernardini (INAF-OAB), Stéphane Schanne (CEA),
Report on behalf of the SVOM team:
SVOM/GRM was triggered in-flight by GRB 250407A (SVOM trigger reference: sb25040701) at 2025-04-07T15:48:13.000 (T0). This burst was also detected by Fermi/GBM (Fermi GBM Team, GCN 40104).
With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of multi-pulses with a T90 of 11.1 +0.2/-0.3 s in the 15-5000 keV band.
The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb250407A.png
In addition, ECLAIRs onboard trigger also detected a very significant increase of the count-rates at the time of the burst, but the detector plane image is not correlated with the mask pattern. This confirmed that the position of this burst, which is determined by Swift/XRT (GCN 40113, RA: 110.75876 deg, DEC: 36.79827 deg, Error: 2.8 arcsec), located at about 45.6 degrees from the SVOM optical axis, and was just outside the ECLAIRs field of view.
With this localization, the time-averaged spectrum from T0 to T0+18 s is best fitted by Band function. The alpha is -0.90 +/- 0.01, beta is -2.27 +/- 0.09 and the cutoff energy, parameterized as Epeak, is 569 +/- 27 keV. The event fluence (10-1000 keV) in this time interval is (1.08 +/- 0.01)E-04 erg/cm^2. Thus GRB 250407A is consistent with Type II GRBs in the 'Amati' relation diagram, as shown at: https://www.bursthub.cn//admin/static/grb250407A_amati.png
The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS.
The SVOM/GRM point of contact for this burst is: Chen-Wei Wang (IHEP) (cwwang@ihep.ac.cn)
GCN Circular #40121
D. Frederiks, A.Lysenko, A. Ridnaia, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report:
The long-duration GRB 250407A ( Fermi-GBM detection: The Fermi GBM team, GCN 40104; Mukherjee & Meegan, GCN 40114; SVOM/GRM observation: Wang et al., GCN 20120) triggered Konus-Wind (KW) at T0=56895.249 s UT (15:48:15.249). The burst afterglow was detected and localized by SRG/ART-XC (Molkov et al. 2025, GCN 40110) and Swift-XRT (Dichiara et al. 2025, GCN 40113).
The burst light curve shows a bright pulse which starts at ~T0-6 s and has a total duration of ~20 s. A weaker emission can be traced at least to ~T0+50 s. The emission in the main pulse is seen up to ~15 MeV.
The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB250407_T56895/
As observed by Konus-Wind, the burst had a fluence of (1.57 ± 0.04)x10^-4 erg/cm^2 and a 64-ms peak energy flux, measured from T0 + 5.292 s, of (1.41 ± 0.05)x10^-4 erg/cm^2/s (both in the 20 keV - 10 MeV energy range).
The time-integrated spectrum (measured from T0 to T0+15.616 s) is best fit in the 20 keV - 15 MeV range by a GRB (Band) function with the following model parameters: the low-energy photon index alpha = -1.02 (-0.03,+0.03), the high energy photon index beta = -2.27 (-0.07,+0.06), the peak energy Ep = 648 (-44,+46) keV, chi2 = 162/97 dof.
The spectrum near the peak count rate (measured from T0+5.888 s to T0+7.424 s) is best fit in the 20 keV - 15 MeV range by a GRB (Band) function with the following model parameters: the low-energy photon index alpha = -0.76 (-0.06,+0.07), the high energy photon index beta = -2.38 (-0.14,+0.11), the peak energy Ep = 833 (-99,+106) keV, chi2 = 78/65 dof.
All the quoted errors are estimated at the 68% confidence level. All the presented results are preliminary.
GCN Circular #40125
I. Pérez-Fournon, F. Poidevin (IAC and ULL), D. Cano-Morales, A.E. Hernández-Díaz, I. Correa-Plasencia (ULL), and A. López-Oramas (IAC and ULL)
Following the detection by Fermi GBM of the bright and likely long Gamma-Ray Burst GRB 250407A (Fermi GBM team, GCN circ. 40104; Preis and Greiner, GCN circ. 40105; and Mukherjee et al., GCN circ. 40114) and the associated X-ray afterglow by SRG/ART-XC (Molkov et al., GCN circ. 40110), we observed the field with the two Las Cumbres Observatory Global Telescope network (LCOGT) 1-m telescopes, equipped with Sinistro cameras, located at the LCOGT node at Teide Observatory (Tenerife, Spain) in the SDSS g, r, and i filters. The observations started at 2025-04-07 21:06:04 UTC, about 5.29 hours after the Fermi trigger. We detect the optical afterglow in the r and i filters, but not in the g filter, at the position reported by Zheng and Filippenko (GCN circ. 40116) and Ducoin et al. (GCN circ. 40117), that is consistent within the errors with the SRG/ART-XC (Molkov et al., GCN circ. 40110), Swift-XRT (Dichiara et al., GCN circ. 40113) and EP-WXT (Zheng et al., GCN circ. 40119) X-ray afterglow positions. GRB 250407A has also been detected by SVOM/GRM (Wang et al., GCN circ. 40120) and Konus-Wind (Frederiks et al., GCN circ. 40121).
A fading of the optical brightness between our LCOGT observations and those of KAIT (Zheng and Filippenko, GCN circ. 40116) and COLIBRÍ/DDRAGO (Ducoin et al., GCN circ. 40117) is detected. We measure the following preliminary r and i magnitudes and limiting (5-sigma) g-band magnitude, calibrated against Pan-STARRS DR2 stars, that are not corrected for Galactic extinction:
```
Date       |  UT start |  mag  | error | filter | exposure time (sec)  | limiting magnitude (5 sigma)
------------------------------------------------------------------------------------------------------
2025-04-07   21:06:04    19.67    0.11      r            300                        -----
2025-04-07   21:10:26    -----    ----      g            180                        20.45
2025-04-07   22:01:01    19.92    0.20      r            180                        -----
2025-04-07   22:15:32    19.53    0.19      i            180                        -----
```
This work makes use of observations from the Las Cumbres Observatory global telescope network (LCOGT observing programme IAC2025A-009, SGLF).
GCN Circular #40127
A.S. Kozyrev, D.V. Golovin, M.L. Litvak, I.G. Mitrofanov, and A.B. Sanin on behalf of the MGNS/BepiColombo team,
D. Svinkin, D. Frederiks, A. Lysenko, A. Ridnaia, and T. Cline on behalf of the Konus-Wind team,
A. Goldstein, M. S. Briggs, C. Wilson-Hodge, and E. Burns on behalf of the Fermi GBM team, report:
The very bright, long-duration GRB 250407A (Fermi-GBM detection: The Fermi GBM team, GCN 40104; Mukherjee and Meegan, GCN 40114; BALROG localization: Preis et al., GCN 40105; SVOM-GRM detection: Wang et al., GCN 40120; Konus-Wind detection: Ferderiks et al., GCN 40121) was detected by Fermi (GBM trigger 765733706), Konus-Wind, and BepiColombo (MGNS) at about 56901 s UT (15:48:21).
We have triangulated it to a preliminary, 3 sigma error box whose coordinates are:
```
 ---------------------------------------------
  RA(2000), deg                 Dec(2000), deg
 ---------------------------------------------
 Center:
  110.410 (07h 21m 38s) +35.618 (+35d 37' 06")
 Corners:
  111.023 (07h 24m 05s) +37.563 (+37d 33' 48")
  111.028 (07h 24m 07s) +37.670 (+37d 40' 12")
  109.794 (07h 19m 10s) +33.403 (+33d 24' 09")
  109.787 (07h 19m 09s) +33.265 (+33d 15' 53")
 ---------------------------------------------
```
The error box area is 364 sq. arcmin, and its maximum dimension is 4.52 deg (the minimum one is 1.4 arcmin). The Sun distance was 89 deg.
This localization may be improved.
The IPN localization is consistent with, but reduces the area of, the Fermi-GBM final (GCN 40104) and BALROG (GCN 40105) localizations.
The X-ray transient detected by SRG-ART-XC (GCN 40110) and Swift-XRT (GCN 40113) is inside the box, which further strengthen the interpretation of the transient as the burst afterglow.
A triangulation map is posted at http://www.ioffe.ru/LEA/GRBs/GRB250407_T56895/IPN
GCN Circular #40133
N. Pankov (HSE, IKI), A. Pozanenko (IKI), E. Klunko (ISTP), R. Ya. Inasaridze (AbAO) report on behalf of IKI-GRB-FuN:
We observed the field of GRB 250407A detected by Fermi (the Fermi GBM team, GCN 40104; Preis & Greiner, GCN 40105; Mukherjee & Meegan, GCN 40114), SRG (Molkov et. al, GCN 40110), Swift (Evans, GCN 40111; Dichiara et. al, GCN 40113), EP (Zheng et. al, GCN 40119), Konus-Wind (Frederiks et. al, GCN 40121) with the 1.5-meter AZT-33IK telescope of the Sayan Solar Observatory (Mondy), and the 0.7-meter AS-32 telescope of the Abastumani Astrophysical Observatory (AbAO). The R-band observations began on 2025-04-08 at 18:01:15 UT, i.e. ~1.12 days since trigger at AbAO. The optical counterpart (Zheng & Fillipenko, GCN 40116; Ducoin et. al, GCN 40117; Pérez-Fournon et. al, GCN 40125) is marginally detected in the stacked image taken with AZT-33IK. The preliminary photometry is as follows:
```
Date       UTstart  Exptime     t-T0     Filter OT   Err  UL      Telescope
                      (s)   (mid, days)                  (3sigma)
2025-04-08 18:01:15 89*60    1.12319       R    n/d  n/d 17.5     AS-32
2025-04-09 14:42:55 34*120   1.97818       R    21.0 0.3 21.2     AZT-33IK
```
Ref. stars USNO-B1.0
```
RA Dec R2mag
110.81407 36.79950 15.86
110.78017 36.81867 14.55
```
The photometry is based on nearby USNO-B1.0 stars (R2 magnitudes) and has not been corrected for the Galactic extinction.
GCN Circular #40135
Asia deGraw, Gracelynn Jost, WeiKang Zheng and Alexei V. Filippenko
(UC Berkeley) report on behalf of the KAIT GRB team:
The 0.76-m Katzman Automatic Imaging Telescope (KAIT), located at
Lick Observatory, continued the observation of GRB 250407A optical
afterglow (Zheng et al., GCN 40116; Ducoin et. al, GCN 40117;
Pérez-Fournon et. al, GCN 40125; Pankov et al., GCN 40133) at
03:35 UT, Apr. 09, namely ~1.55 days after burst. A set of clear
(roughly R) filter images were obtained. Compared to our earlier
observations (Zheng et al., GCN 40116), the reported afterglow had
faded to ~20.8 +/- 0.3 mag (Vega) measured in our coadd image.
Additional R band images with 600sx5 exposure were obtained with the
1-m Nickel telescopes located at Lick observatory, starting at ~1.55
days after burst. We measure the brightness of R ~ 21.0 +/- 0.2 mag
(Vega), similar to the R band magnitude reported by Pankov et al.
(GCN 40133) at a slightly later epoch (1.98 days), suggesting that
this might be the host galaxy of GRB 250407A as suggested by Ducoin
et. al, GCN 40117).
GCN Circular #40175
B. Schneider (LAM), D. B. Malesani (DAWN/NBI and Radboud), A. de Ugarte Postigo (LAM), A. Martin-Carrillo (UCD), J. F. Agui Fernandez (CAHA), M. A. Aloy (UV), J. P. U. Fynbo (DAWN/NBI), L. Galbany (IEEC-CSIC), S. Geier (GTC), L. Izzo (INAF/OACN and DARK/NBI), G. Lombardi (GTC), N. A. Rakotondrainibe (LAM), N. R. Tanvir (Univ. Leicester), C. C. Thoene (AbAO), A. Perez (GTC) and R. Scarpa (GTC), report:
We observed the optical afterglow of the GRB 250407A (Fermi GBM team, GCN 40104; Preis & Greiner, GCN 40105; Mukherjee & Meegan, GCN 40114; Molkov et al., GCN 40110; Dichiara et al., GCN 40113; Ducoin et al., GCN 40117; Zheng et al., GCN 40119; Wang et al., GCN 40120; Frederiks et al., GCN 40121; Williams et al., GCN 40123; Pérez-Fournon et al., GCN 40125; Kozyrev et al., GCN 40127; Pankov et al., GCN 40133; deGraw et al., GCN 40135) using the 10.4 m GTC located at the Roque de los Muchachos Observatory in the island of La Palma (Spain) equipped with the OSIRIS+ instrument.
In a 60 s acquisition image in the r-band, starting on 2025-04-17 at 21:27:11 UT (10.24 after the Fermi trigger), an object is detected at the position of the optical afterglow (Zheng & Filippenko, GCN 40116), with a magnitude r = 22.48 +/- 0.06 (AB, calibrated against nearby Pan-STARRS objects). At a consistent location, the Legacy Survey also reveals a source, the likely GRB host galaxy, with a somehow fainter magnitude r = 22.65. In our observation the target flux is thus likely dominated by the host, possibly with some transient contribution.
Our spectroscopic observations started on 2025-04-17 at 21:32:03 UT (10.24 days after the Fermi trigger) and consisted of 3x900 s exposures with grism R1000R, covering the range between 5100 and 10,000 AA.
In a preliminary reduction of the spectra, we clearly detect a continuum over the entire covered range. From the detection of multiple absorption features, including Fe II, Mg II, and Mg I, we infer a redshift of z = 1.36. At a consistent redshift, an emission line is also detected, which we interpret as the [O II] doublet from the host galaxy.
We thus conclude that GRB 250407A is at redshift z = 1.36.
GCN Circular #40177
D. Frederiks, A.Lysenko, A. Ridnaia, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report:
Assuming the spectrum and the observer-frame energetics of the very bright GRB 250407A (GCN 40104) measured by Konus-Wind (GCN 40121); the redshift z=1.36 (Schneider et al., GCNs 40175); and a standard cosmology with H_0 = 67.3 km/s/Mpc, Omega_M = 0.315, and Omega_Lambda = 0.685 (Planck Collaboration, 2014); we estimate the burst isotropic energy release E_iso to (7.86 ± 0.20)x10^53 erg, the isotropic peak luminosity L_iso to (1.66 ± 0.06)x10^54 erg/s, the rest-frame peak energy of the time-integrated spectrum Ep,i,z to (1530 ± 110) keV, and the rest-frame peak energy at the peak of the emission Ep,p,z to (1970 ± 250) keV.
With the obtained estimates, GRB 250407A is among 10 most luminous (and 50 most energetic) GRBs detected by Konus-Wind. The burst is consistent with 68% prediction bands for both 'Amati' and 'Yonetoku' relations derived for the sample of >300 long KW GRBs with known redshifts (Tsvetkova et al., 2017; Tsvetkova et al., 2021), see http://www.ioffe.ru/LEA/GRBs/GRB250407_T56895/GRB250407A_rest_frame.pdf
All the quoted errors are estimated at the 68% confidence level. All the presented results are preliminary.
GCN Circular #40237
M. Dafcikova, J. Ripa (Masaryk U.), A. Pal (Konkoly Observatory), N. Werner (Masaryk U.), M. Ohno, H. Takahashi (Hiroshima U.), L. Meszaros, B. Csak (Konkoly Observatory), N. Husarikova, F. Munz , M. Topinka, M. Duriskova, M. Kolar, L. Szakszonova, J.-P. Breuer, F. Hroch (Masaryk U.), T. Urbanec, M. Kasal, A. Povalac (Brno U. of Technology), J. Hudec, J. Kapus, M. Frajt (Spacemanic s.r.o), R. Laszlo, M. Koleda (Needronix s.r.o), M. Smelko, P. Hanak, P. Lipovsky (Technical U. of Kosice), G. Galgoczi (Wigner Research Center/Eotvos U.), Y. Uchida, H. Poon, H. Matake (Hiroshima U.), N. Uchida (ISAS/JAXA), T. Bozoki (Eotvos U.), G. Dalya (Eotvos U.), T. Enoto (Kyoto U.), Zs. Frei (Eotvos U.), G. Friss (Eotvos U.), Y. Fukazawa, K. Hirose (Hiroshima U.), S. Hisadomi (Nagoya U.), Y. Ichinohe (Rikkyo U.), K. Kapas (Eotvos U.), L. L. Kiss (Konkoly Observatory), T. Mizuno (Hiroshima U.), K. Nakazawa (Nagoya U.), H. Odaka (Univ of Tokyo), J. Takatsy (Eotvos U.), K. Torigoe (Hiroshima U.), N. Kogiso, M. Yoneyama (Osaka Metropolitan U.), M. Moritaki (U. Tokyo), T. Kano (U. Michigan) -- the GRBAlpha collaboration.
The long-duration GRB 250407A (Fermi/GBM detection: GCN 40104; SVOM/GRM detection: GCN 40120; Wind/Konus detection: GCN 40121) was observed by the GRBAlpha 1U CubeSat (Pal et al. 2023, A&A, 677, 40; https://ui.adsabs.harvard.edu/abs/2023A%26A...677A..40P/abstract).
The detection was confirmed at the peak time 2025-04-07 15:48:21.6 UTC. The T90 duration measured by GRBAlpha is 2.0 s and the overall significance during T90 reaches 42 sigma. We note that GRBAlpha was passing through the van Allen radiation belt at the time of this burst and thus experienced a higher background.
The light curve obtained by GRBAlpha is available here: https://grbalpha.konkoly.hu/static/share/GRB250407A_GCN.pdf
All GRBAlpha detections are listed at: https://monoceros.physics.muni.cz/hea/GRBAlpha/ GRBAlpha, launched on 2021 March 22, is a demonstration mission for a future CubeSat constellation (Werner et al. Proc. SPIE 2018). The detector of GRBAlpha consists of a 75 x 75 x 5 mm3 CsI scintillator read out by a SiPM array, covering the energy range from ~50 keV to ~1000 keV. To increase the duty cycle and the downlink rate, the upgrade of the on-board data acquisition software stack is in progress. The ground segment is also supported by the radio amateur community and it takes advantage of the SatNOGS network for increased data downlink volume.
GCN Circular #40326
M. Dafcikova, J. Ripa (Masaryk U.), A. Pal (Konkoly Observatory), N. Werner (Masaryk U.), M. Ohno (Hiroshima U.), L. Meszaros, B. Csak (Konkoly Observatory), H. Takahashi (Hiroshima U.), F. Munz , M. Topinka, F. Hroch, N. Husarikova, J.-P. Breuer (Masaryk U.), J. Hudec, J. Kapus, M. Frajt, M. Rezenov (Spacemanic s.r.o), R. Laszlo (Needronix), G. Galgoczi (Wigner Research Center/Eotvos U.), N. Uchida (ISAS/JAXA), T. Enoto (Kyoto U.), Zs. Frei (Eotvos U.), Y. Fukazawa, K. Hirose, H. Matake (Hiroshima U.), S. Hisadomi (Nagoya U.), Y. Ichinohe (Rikkyo U.), L. L. Kiss (Konkoly Observatory), T. Mizuno (Hiroshima U.), K. Nakazawa (Nagoya U.), H. Odaka (Univ of Tokyo), K. Torigoe (Hiroshima U.), P. Svoboda, V. Daniel, J. Dudas, M. Junas, J. Gromes (VZLU), I. Vertat (FEL ZCU) -- the VZLUSAT-2/GRB payload collaboration.
The long-duration GRB 250210A (Fermi/GBM detection: GCN 40104; SVOM/GRM detection: GCN 40120; Wind/Konus detection: GCN 40121; GRBAlpha detection: GCN 40237) was detected by the GRB detectors on board of the VZLUSAT-2 3U CubeSat (https://www.vzlusat2.cz/en/).
The data acquisition was performed by the GRB detector units no. 0 and no. 1. The detection was confirmed at the peak time 2025-04-07 15:48:20 UTC. The T90 duration is 9 s and the significance during T90 reaches 72 sigma (66 sigma) for detector unit no. 0 (no. 1).
The light curve obtained by VZLUSAT-2 is available here: https://vzlusat2.konkoly.hu/static/share/GRB250407A_GCN_VZLUSAT2.pdf
All VZLUSAT-2 detections are listed at: https://monoceros.physics.muni.cz/hea/VZLUSAT-2/ The GRB detectors on VZLUSAT-2 are a demonstration payload for a future CubeSat constellation (Werner et al. Proc. SPIE 2018). Two GRB modules of VZLUSAT-2 are placed in a perpendicular manner and each consists of a 75 x 75 x 5 mm3 CsI scintillator read out by a SiPM array, covering the energy range from ~30 keV to ~1000 keV. VZLUSAT-2 was launched on 2022 January 13 from Cape Canaveral.

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Jochen Greiner, last update: 02-May-2025 [Disclaimer]