GRB 250507A

This is a duplicate submission of GCN 40413
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 .

WeiKang Zheng (UCB), Xuhui Han (NAOC), Pinpin Zhang (NAOC) and

Alexei V. Filippenko (UCB) 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 SVOM GRB 250507A (Wang

et al., GCN 40374
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 ) starting at 06:37:30, May 07 UT, 165 seconds

after the burst. Observations were performed in 3 x 3 tiling mode,

and a set of clear (roughly R) filter images were obtained.

Preliminary analysis do not reveal any new optical counterpart

candidate within the X-ray afterglow error circles (Maggi et al.,

GCN 40381
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 ; Zhang et al., GCN 40385
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 ; Osborne et al., GCN 40389
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 ),

neither in single image, nor in the co-add images. We estimate

the limiting magnitude of our coadd image to be ~20.0 mag at a

mid-time of 15.0 minutes after the burst, consistent with the

upper limit reported by other groups (Ducoin et al., GCN 40376
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 ;

Xin et al., GCN 40379
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 ; Brivio et al., GCN 40380
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 )

J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A.P. Beardmore
(U. Leicester), P. D'Avanzo (INAF-OAB), M.G. Bernardini (INAF-OAB), E.
Ambrosi  (INAF-IASFPA) , M. A. Williams (PSU), S. Dichiara (PSU), J.A.
Kennea (PSU) and P.A. Evans (U. Leicester) reports on behalf of the
Swift-XRT team:

We have analysed 1.8 ks of XRT data for GRB 250507A, from 7.4 ks to
12.5 ks after the  SVOM/ECLAIRs trigger. The data are entirely in
Photon Counting (PC) mode.  We detect an uncatalogued X-ray source
within the SVOM/ECLAIRs 90% C.L. error region (GCN #40374
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 ) at RA, Dec =
183.06416, -23.5888 which is equivalent to:

RA (J2000): 12h 12m 15.40s
Dec (J2000): -23d 35' 19.6"

with an uncertainty of 4.2 arcsec (radius, 90% confidence). This
position is 15.6 arcsec from the SVOM/MXT position (GCN #40381
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 ) and 2.5
arcsec from the source detected by EP-FXT (GCN #40385
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 ).

The source has a mean count rate of 2.6e-02 ct/sec and a flux of       
1.11 (+0.21, -0.20) × 10^-12 erg cm^-2 s^-1 (0.3-10 keV); we cannot
determine at the present time whether it is fading. However, the
decrease in flux compared to the SVOM/MXT observation suggests this
source is the afterglow. 

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00019769.

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

M. H. Zhang, H. Sun (NAO, CAS), Y. J. Zhang (THU), W. Yuan (NAO, CAS) on behalf of the Einstein Probe (EP) team:

EP-FXT performed a follow-up observation of GRB 250507A at 2025-05-07T07:33:50 (UTC), about 1 hour after the SVOM/ECLAIRs trigger (Wang et al., GCN # 40374). 
An uncatalogued X-ray source (EPF_J121215.7−233519) was detected within the ECLAIRs error circle, and is potentially associated with GRB 250507A.

Preliminary analysis of this source was automatically conducted, with the following results:
RA (J2000): 183.0647 deg
Dec (J2000): -23.5883 deg
Flux: 4.91 x 10^-13 erg/cm^2/s (observed, 0.5-10 keV)
Flux_error: 1.54 x 10^-13 erg/cm^2/s (1 sigma)

The position uncertainty of the above source is about 10 arcsec in radius (90% C.L. statistical and systematic). 

We note that this source is spacially consistent with the one reported by SVOM/MXT (Maggi et al., GCN # 40381). The flux measured by EP-FXT shows a rapid decline of more than two orders of magnitude compared to the MXT measurements over a timescale of approximately 50 minutes, consistent with the rapid decay reported previously.


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). 

P. Maggi (ObAS), D. Götz (CEA), H. Goto (Kanazawa University/CEA), M. Moita (CEA), C. Plasse (CEA), F. Robinet (IJCLab), C. Van Hove (IJCLab) report of behalf of the SVOM/MXT Team:

GRB 250507A (Wang et al. GCN 40374
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 ) was observed by SVOM/MXT after an automatic SVOM slew, starting at T0 = 2025-05-07T06:40:59.951 (374s after trigger time Tb). MXT observed during the first orbit for 2.1 ks effective exposure.

Using the full X-band dataset, we measure a complex light curve with two flares of 150 to 200s duration, followed by a rapid decay with a temporal index of -4.1+/-0.2 at times t+T0>400s. The source is no longer detected at t+T0>1200s and hence we restricted the analysis below to the first 20 min of data.

The X-ray source located at R.A., Dec  183.066, -23.5928 degrees:
R.A. (J2000) = 12h12m15.8s
Dec. (J2000) = -23d35m34.12s
with a 90% C.L. radius of 37 arcseconds (including 35 arcseconds systematic error added in quadrature)

The spectrum is modelled with an absorbed power law. Using the average spectrum of the first 1200s of MXT data, the absorption column NH is 5.2 +/-0.5 x 1e22 /cm2 (90% C.L. uncertainties) and a rather soft photon index of 3.6 +/- 0.2. The time-averaged observed flux is 4.5 x 1e-10 ergs/cm^2/s but the count rate varies by a factor 100 between peak at t+T0=160s and t+T0=1200s.

Follow-up observations at other wavelengths are encouraged.

The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. MXT was developed jointly by CEA, CNES, University of Leicester, IJCLab and MPE.

The SVOM point of contact for this burst is:z iqi.wang@st.gxu.edu.cn.
Please contact the BA by email if you require additional information regarding the SVOM follow-up of this burst.

R. Brivio, M. Ferro, P. D'Avanzo, S. Covino, D. Fugazza (INAF-OAB), M. De Pasquale (Univ. of Messina) report on behalf of the REM team:

We observed the field of GRB 250507A detected by SVOM/ECLAIRs (Wang et al., GCN 40374
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 ) with the REM 60 cm robotic telescope located at the ESO observatory of La Silla (Chile). The observations were carried in the g, r, i, z, J, H, and K bands, started on 2025 May 07 at 06:45:31 UT (i.e. about 11 minutes after the burst), and lasted for about 2 hours.

From preliminary inspection, we do not detect any possible counterpart inside the SVOM/MXT error circle down to the following 3sigma limits:

r > 19.3 (AB; calibrated against the Pan-STARRS catalogue),
at a mid-time of 33 minutes after the trigger;

H > 16.0 (Vega; calibrated against the 2MASS catalogue),
at a mid-time of 32 minutes after the trigger.

L. P. Xin, Y. L. Qiu, H. L. Li, C. Wu, Z. H. Yao, Y. N. Ma, 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. T. Palmerio (CEA), Z. Q. Wang (GXU), Y. F. Liang (PMO), W. K. Zheng (UCB) report on behalf of the SVOM/VT instrument team.

After the trigger by SVOM/ECLAIRs at 2025-05-07T06:34:45 UT (SVOM burst-id sb25050703), SVOM performed an automatic slew on the burst. SVOM/VT began observing the field at 260 seconds after the SVOM trigger in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. 

With the downlinked X band data, no any uncataloged sources are detected in single or stacked imags within the errorbox of Eclairs or MXT (Wang et al., GCN 40374
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 ), compared to the Legacy survey. 

The 3 sigma upper limits are derived below:

Mid_time  |   Exposure time  |  Band  |   Upper limit (AB)
550 sec   |  10*50 sec       |  VT_B  |   22.8
550 sec   |  10*50 sec       |  VT_R  |   22.7
1225 sec  |  38*50 sec       |  VT_B  |   23.2
1225 sec  |  38*50 sec       |  VT_R  |   23.1

This results are consistent with the report (J.-G. Ducoin et al. GCN 40376
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 ).

Given the bright X-ray counterpart (Wang et al., GCN 40374
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 ), and the deep optical upper limit at the early phase of the burst, near infrared observations are encouraged to investigate the nature of the burst.

The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe.

Jean-Grégoire Ducoin (CPPM), Alan M. Watson (UNAM), Fredd Alvarez (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (AUS), Sarah Antier (OCA), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU) , Damien Dornic (CPPM), Francis Fortin (IRAP), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM), Z. Wang (GXU) and Y. Liang (PMO): 

We imaged the field of the SVOM GRB 250507A (Wang et al., GCN 40374
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 ) using the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2025-05-07 06:36:04 to 07:34:42  UTC (from 79 to 3597 seconds after the trigger) and obtained 2560 seconds of exposure in the i filter.

The data were reduced and coadded with the COLIBRÍ pipeline and analyzed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog and is not corrected for Galactic extinction.

In the stacked image, we do not detect any new source at the MXT source position (Wang et al., GCN 40374
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 ) down to the following 5-sigma limit (AB):

i > 22.3 mag

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.

Z. Wang (GXU), Y. Liang (PMO), H. Yang, O. Godet (IRAP), P. Maggi (ObAS), D. Götz (CEA), L Xin (NAOC)

report on behalf of the SVOM mission team:

SVOM/ECLAIRs triggered on the gamma-ray burst GRB 250507A (SVOM burst-id sb25050703) starting at 2025-05-07T06:34:45.17 UTC (Tb).

The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network.

The burst was detected by the Count-Rate Trigger (CRT) and Image Trigger (IMT). A sequence of 10 alerts was produced. IMT provided the alert with the best signal-to-noise-ratio (SNR) of 10.65 in the 8-120 keV energy band over a time window of 40.96 seconds starting at Tb.

The localization of the best alert is R.A., Dec. 182.990, -23.615 degrees:
R.A. (J2000) = 12h11m57.6s
Dec. (J2000) = -23h36m54s
with a 90% confidence level (C.L.) radius of 7.5 arcmin (including systematic error of 2 arcmin added in quadrature).

SVOM slewed to the burst.

MXT began observing the field after the slew, starting at 2025-05-07T06:41:02 i.e. 377 s after Tb. Using onboard processed data we found an uncatalogued X-ray source located at R.A., Dec  183.074, -23.598 degrees:
R.A. (J2000) = 12h12m17.76s
Dec. (J2000) = -23d35m52.8s
with a 90% C.L. radius of 30 arcseconds (including 25 arcseconds systematic error added in quadrature).
This location is 4.7’ from the ECLAIRs onboard position. This position may be improved as more data is received.

VT began observing the field after the slew. The analysis of the recorded images will be published in a future circular gathering information on the follow-up of the SVOM optical instruments.

The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe.

The Burst Advocate (BA) on shift for this burst is Ziqi Wang: ziqi.wang@st.gxu.edu.cn.
Please contact the BA by email if you require additional information regarding the SVOM follow-up of this burst.