TITLE: GCN CIRCULAR
NUMBER: 40206
SUBJECT: GRB 250419A: Optical Observations via Virtual Telescope Project
DATE: 25/04/22 13:17:41 GMT
FROM: Gianluca Masi at Virtual Telescope Project <gianluca(a)bellatrixobservatory.org>
Gianluca Masi, Virtual Telescope Project (Italy), reports:
We observed the field of GRB 250419A (Wang et al., GCN 40168) with the 14” robotic unit available at the Virtual Telescope Project facility in Manciano, Italy, equipped with a KAF-3200E based CCD camera.
We collected 3, 300-second unfiltered exposures, then we averaged them. The central time of the resulting stack was 19 April, 21:07 UTC, that is about 18.6 hours after the burst.
We clearly detect the optical counterpart of GRB 250419A.
The position of the source is RA: 13 29 37.26; Decl.: +07 02 28.0 (J2000.0, mean residuals of 0.05”, reference stars from GaiaDR2) and the magnitude was estimated to be 19.3 (SNR=12, assuming R mags for the reference stars from GaiaDR2).
The image is available here:
https://www.virtualtelescope.eu/2025/04/22/grb-250419a-detection-of-the-opt…
View this GCN Circular online at https://gcn.nasa.gov/circulars/40206.
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TITLE: GCN CIRCULAR
NUMBER: 40205
SUBJECT: EP250421a: REM optical upper limit
DATE: 25/04/22 09:22:46 GMT
FROM: Riccardo Brivio at INAF-OAB <riccardo.brivio(a)inaf.it>
R. Brivio, M. Ferro, D. Fugazza, P. D'Avanzo, S. Covino (INAF-OAB) report on behalf of the REM team:
We observed the field of EP250421a (Zhao et al., GCN 40198) 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, and z bands, started on 2025 April 21 at 23:08:27 UT (i.e. 6.9 hr after the burst), and lasted for about 1 hour.
From preliminary inspection, we do not detect any counterpart at the position of the optical afterglow (Lee et al., GCN. 40192; Fu et al., GCN 40193; Liu et al., GCN 40197) down to the following 3sigma limit:
r > 20.6 (AB; calibrated against the Pan-STARRS catalogue),
at a mid-time of 7.4 hours after the trigger.
View this GCN Circular online at https://gcn.nasa.gov/circulars/40205.
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TITLE: GCN CIRCULAR
NUMBER: 40204
SUBJECT: EP250421a: Swift/XRT counterpart detection
DATE: 25/04/22 09:04:31 GMT
FROM: Chiara Salvaggio at INAF OABrera <chiara.salvaggio(a)inaf.it>
C. Salvaggio (INAF-OAB), T. Sbarrato (INAF-OAB), R. Brivio (INAF-OAB), M.
Ferro (INAF-OAB), K. Page (U. Leicester), D. Malesani (DAWN/NBI and
Radboud) and P.A. Evans (U. Leicester) report on behalf the Swift-XRT team:
Swift/XRT has performed follow-up observations of EP-WXT detected transient
EP250421a (trigger 01709135179, Zhao et al. GCN 40198).
We searched for X-ray sources in 1.8 ks of Photon Counting (PC) mode data,
from T0+5.8 ks to T0+11.7 ks after the EP-WXT trigger.
We found an uncatalogued X-ray source within the estimated 3-sigma EP-WXT
error region. Using 1772 s of XRT PC mode data and 2 UVOT images, we find
an enhanced XRT position: RA, Dec = 172.420,-24.67568 which is equivalent
to:
RA (J2000): 11h 29m 40.80s
Dec (J2000): -24° 40' 32.4"
with an uncertainty of 2.7 arcsec (radius, 90% confidence).
This position is 35 arcsec from the EP-WXT position, and consistent with
the X-ray counterpart found in EP/FXT data (Zhao et al., GCN 40198) and
with the optical counterpart reported by Lee et al. (GCN 40192), Fu et al.
(GCN 40193), Liu et al. (GCN 40197).
The source has a mean count rate of 0.272 ct/s and shows signs of fading at
2.8 sigma significance.
The results of the XRT-team automatic analysis are available at
https://www.swift.ac.uk/EP/EP_FIELD00035/
This circular is an official product of the Swift-XRT team.
View this GCN Circular online at https://gcn.nasa.gov/circulars/40204.
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TITLE: GCN CIRCULAR
NUMBER: 40203
SUBJECT: EP250421A: COLIBRÍ Optical Upper Limit
DATE: 25/04/22 08:13:37 GMT
FROM: Rosa L. Becerra at Tor Vergata, Roma <rosa.becerra(a)roma2.infn.it>
Rosa L. Becerra (U Roma), Camila Angulo (UNAM), Francis Fortin (IRAP), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Sarah Antier (OCA/IJCLAB), Dalya Akl (AUS), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Ramandeep Gill (UNAM), 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) and Benjamin Schneider (LAM) report:
We imaged the field of EP250421A (Zhao et al., GCN Circ. 40198) 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 2025-04-22 UTC.
We observed from 2025-04-22 04:54 to 06:03 UTC (T+12.6 to T+13.8 hours after the trigger) and obtained 50 minutes of exposure in total in the r filter. Our observations were performed under regular weather conditions. 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 of the optical counterpart (Lee et al., GCN Circ. 40192; Fu et al., GCN Circ. 40193; Liu et al., GCN Circ. 40197), we obtained an upper limit (5-sgima) of:
r > 23.44
We warmly thank the COLIBRÍ and DDRAGO engineering teams and the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir.
View this GCN Circular online at https://gcn.nasa.gov/circulars/40203.
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TITLE: GCN CIRCULAR
NUMBER: 40202
SUBJECT: GRB 250419A: Mondy Continued Optical Observations
DATE: 25/04/22 07:27:22 GMT
FROM: Nicolai Pankov at HSE, IKI RAS <colinsergesen(a)gmail.com>
N. Pankov (HSE, IKI), A. Pozanenko (IKI), E. Klunko (ISTP) report on behalf of IKI-GRB-FuN:
We continued observations of the field of GRB 250419A (Wang et al., GCN 40168; Page et al., GCN 40111; Page et al., GCN 40176) at the redshift of z = 0.845 (Thakur et al., GCN 40174) with the 1.5-meter AZT-33IK telescope of the Sayan Solar Observatory (Mondy). The R-band observations began on 2025-04-20 at 15:54:03 UT, i.e. ~1.58 days since trigger. The optical counterpart (López et al., GCN 40169; Xin et al., GCN 40170; Zheng et al., GCN 40171; Kumar et al., GCN 40172; Thakur et al., GCN 40174; Lipunov et al., GCN 40179; Odeh et al., GCN 40180; Perley & Bochenek, GCN 40181; Pankov et al., GCN 40182; Pérez-Fournon et al., GCN 40183; Kuin, GCN 40185; Wu et al., GCN 40186; Xie et al., GCN 40187; Jiang et al., GCN 40188; Ghosh et al., GCN 40189; Bochenek & Perley, GCN 40190) is detected in the stacked image. The preliminary photometry is as follows:
Date UTstart Exptime t-T0 Filter OT Err UL
(s) (mid, days) (3sigma)
2025-04-20 15:54:03 45*120 1.58995 R 20.00 0.06 22.6
The photometry is based on nearby USNO-B1.0 stars (R2 magnitudes, provided in Pankov et al., GCN 40182) and has not been corrected for the Galactic extinction.
View this GCN Circular online at https://gcn.nasa.gov/circulars/40202.
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TITLE: GCN CIRCULAR
NUMBER: 40201
SUBJECT: Fermi GRB 250421A: Global MASTER-Net observations report
DATE: 25/04/22 06:17:02 GMT
FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru>
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-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) started inspect of the Fermi GRB 250421A ( Fermi GBM team, GCN 40191) errorbox 67295 sec after notice time and 67337 sec after trigger time at 2025-04-22 05:20:48 UT, with upper limit up to 18.9 mag. The observations began at zenith distance = 33 deg. The sun altitude is -68.2 deg.
The galactic latitude b = -9 deg., longitude l = 328 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=2848837
We obtain a following upper limits.
Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________
67368 | 2025-04-22 05:20:48 | MASTER-OAFA | (16h 29m 49.10s , -59d 22m 10.8s) | C | 60 | 18.4 |
67601 | 2025-04-22 05:24:42 | MASTER-OAFA | (16h 25m 54.95s , -61d 15m 16.6s) | C | 60 | 18.4 |
67790 | 2025-04-22 05:28:01 | MASTER-OAFA | (16h 37m 54.84s , -62d 00m 16.5s) | C | 40 | 17.4 |
67800 | 2025-04-22 05:28:01 | MASTER-OAFA | (16h 57m 07.49s , -61d 33m 46.3s) | C | 60 | 18.9 |
68001 | 2025-04-22 05:31:22 | MASTER-OAFA | (16h 29m 45.37s , -59d 21m 53.7s) | C | 60 | 18.3 |
68194 | 2025-04-22 05:34:44 | MASTER-OAFA | (16h 41m 10.93s , -60d 04m 07.5s) | C | 40 | 17.2 |
Filter C is a clear (unfiltred) band.
The observation and reduction will continue.
The message may be cited.
View this GCN Circular online at https://gcn.nasa.gov/circulars/40201.
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TITLE: GCN CIRCULAR
NUMBER: 40200
SUBJECT: EP250421a: Global MASTER-Net observations report
DATE: 25/04/22 05:36:49 GMT
FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru>
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-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 EP250421a ( EP Team et al., GCN 40198) errorbox 2313 sec after notice time and 46767 sec after trigger time at 2025-04-22 05:15:55 UT, with upper limit up to 20.0 mag. The observations began at zenith distance = 43 deg. The sun altitude is -68.7 deg.
The galactic latitude b = 35 deg., longitude l = 281 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=2849886
We obtain a following upper limits.
Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________
46798 | 2025-04-22 05:15:55 | MASTER-OAFA | (11h 29m 43.36s , -24d 18m 41.7s) | C | 60 | 20.0 |
Filter C is a clear (unfiltred) band.
The observation and reduction will continue.
The message may be cited.
View this GCN Circular online at https://gcn.nasa.gov/circulars/40200.
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TITLE: GCN CIRCULAR
NUMBER: 40199
SUBJECT: GRB 250421B: AstroSat CZTI detection of a bright long burst
DATE: 25/04/22 05:05:30 GMT
FROM: Gaurav Waratkar at IIT Bombay <gauravwaratkar(a)iitb.ac.in>
M. Tembhurnikar (IUCAA), G. Waratkar (IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration:
Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of a bright long-duration GRB 250421B.
The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2025-04-21 21:59:57.50 UTC. The measured peak count rate associated with the burst is 586 (+45, -49) counts/s above the background in the combined data of three quadrants (out of four), with a total of 3514 (+233, -248) counts. The local mean background count rate was 209 (+3, -4) counts/s. Using cumulative rates, we measure a T90 of 17 (+1, -1) s.
The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2025-04-21 21:59:57.06 UTC. The measured peak count rate associated with the burst is 1713 (+87, -96) counts/s above the background in the combined data of all quadrants, with a total of 9802 (+468, -504) counts. The local mean background count rate was 1168 (+7, -8) counts/s. We measure a T90 of 17 (+1, -1) s from the cumulative Veto light curve.
CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project.
CZTI GRB detections are reported regularly on the payload site at:
http://astrosat.iucaa.in/czti/?q=grb
View this GCN Circular online at https://gcn.nasa.gov/circulars/40199.
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TITLE: GCN CIRCULAR
NUMBER: 40198
SUBJECT: EP250421a: Einstein Probe detection of an X-ray transient
DATE: 25/04/22 04:36:14 GMT
FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn>
G. Y. Zhao (SYSU), C. Zhou (HUST), R.-Z. Li (YNAO, CAS), W. Chen, Z. X. Ling (NAO, CAS) on behalf of the Einstein Probe (EP) team:
We report on the detection of an X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP250421a. The transient triggered EP-WXT (ID: 01709135179) at 2025-04-21T16:16:28 (UTC) and WXT detected a rise of about 70 s. The WXT position of the source is R.A. = 172.4130 deg, DEC = -24.6830 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic).
A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed automatically about 245 s after the EP/WXT trigger. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 172.4201 deg, DEC = -24.6758 deg (J2000) with an uncertainty of 10 arcsec in radius (90% C.L. statistical and systematic).
The WXT spectrum can be fitted by an absorbed power law model with a photon index of 2.91(+2.76, -1.72) and an absorbing column density of 4.1e21 cm^-2. The unabsorbed 0.5-4 keV flux is about 1.3 (+14.7,-0.81) e-9 erg/cm^2/s.
The FXT spectrum can be fitted by an absorbed power law model with a photon index of 2.11 (+0.15, -0.14) and an absorbing column density of 8.3e20 cm^-2. The unabsorbed 0.5-10 keV flux is about 1.39 (+0.07, -1.39) e-11 erg/cm^2/s.
The contact TA of EP250421a is Chang Zhou. Please contact her via email d202180110(a)hust.edu.cn if needed.
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).
View this GCN Circular online at https://gcn.nasa.gov/circulars/40198.
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TITLE: GCN CIRCULAR
NUMBER: 40197
SUBJECT: EP250421a: Mephisto optical counterpart confirmation
DATE: 25/04/22 04:28:53 GMT
FROM: liuxk(a)ynu.edu.cn
Xiangkun Liu, Xinlei Chen, Yi Zhang, Runnan Jiang, Brajesh Kumar, Guowang Du, Yuan Fang, Jinghua Zhang, Xingzhu Zou, Yu Pan, Yuanpei Yang, Xiaowei Liu (all SWIFAR, YNU) report on behalf of the Mephisto Team:
The field of EP250421a (EP-WXT trigger ID: 01709135179) was observed with the 1.6m Multi-channel Photometric Survey Telescope (Mephisto) of Yunnan University located at Lijiang Observatory. Simultaneous uvgriz band photometric observations were conducted starting from 16:26:55 2025-04-21 UT (~5 mins after the trigger) and 7 frames with 45s exposure time for ugi bands and 6 frames with 45s exposure times for vrz bands were taken, followed by another 2 frames with 300s exposure time for all ugi/vrz bands. We detected an optical transient candidate (Lee et al., GCN 40192; Fu et al., GCN 40193) in the stacked riz band images in both sets of observations but no detection in uvg bands. In our priliminary photometry there is clear indication of the decay of the source as listed below.
Start_Time(UT) | Band | Exp(s) | Mag/LimMag (AB)
---------------------------|--------|---------|------------
2025-04-21T16:26:55 | u | 45*7 | >21.15
2025-04-21T16:38:05 | v | 45*6 | >21.39
2025-04-21T16:26:55 | g | 45*7 | >22.02
2025-04-21T16:38:05 | r | 45*6 | 20.47 +/- 0.10
2025-04-21T16:26:55 | i | 45*7 | 19.07 +/- 0.07
2025-04-21T16:38:05 | z | 45*6 | 18.62 +/- 0.13
Start_Time(UT) | Band | Exp(s) | Mag/LimMag (AB)
---------------------------|--------|---------|------------
2025-04-21T17:12:15 | u | 300*2 | >21.41
2025-04-21T16:59:53 | v | 300*2 | >21.64
2025-04-21T17:12:15 | g | 300*2 | >22.27
2025-04-21T16:59:53 | r | 300*2 | 21.21 +/- 0.16
2025-04-21T17:12:15 | i | 300*2 | 20.28 +/- 0.12
2025-04-21T16:59:53 | z | 300*2 | 19.15 +/- 0.14
-------------------------------------------------------------------------------------------------
Mephisto (Multi-channel Photometric Survey Telescope) is a 1.6-m wide-field multi-channel telescope, the first of its type in the world, capable of imaging the same field of view in three optical bands simultaneously. It provides real-time, high-quality colors of stellar objects. The on-site telescope assemblage and commissioning were carried out in September 2022. The first light in all three channels was achieved on 2023 December 21.
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