EP260131a
GCN Circular 43626
Subject
EP260131a: VLA detection
Date
2026-02-06T20:32:30Z (9 months ago)
From
Genevieve Schroeder at Cornell University <genevieveschroeder@u.northwestern.edu>
Via
Web form
Genevieve Schroeder (Cornell), Anna Ho (Cornell), Daniel Perley (LJMU) report:
We observed the position of EP260131a (Ding et al., GCN 43574, Wu et al. GCN 43583), with the Karl G. Jansky Very Large Array (VLA) under program 26A-488 (PI: Ho) beginning on 2026 February 3 at 06:37 UT (3.15 days post discovery) at a mean frequency of 10 GHz. Based on preliminary analysis, we detect a ~40 uJy (~6 sigma) radio source at the position of EP260131a.
At the assumed redshift of EP260131a of z = 0.937 (Schneider et al., GCN 43582), the VLA observation corresponds to a 10 GHz luminosity of ~1e30 erg/s/Hz. This is consistent with, but on the lower end of, a typical GRB radio afterglow (Chandra & Frail 2012, ApJ, 746, 156).
Additional followup is planned.
We thank the VLA staff for quickly approving and executing these observations.
GCN Circular 43594
Subject
EP260131a: Liverpool Telescope optical upper limits
Date
2026-02-01T19:40:28Z (9 months ago)
From
A. Bochenek at Liverpool John Moores University <a.m.bochenek@2023.ljmu.ac.uk>
Via
Web form
A. Bochenek, D. A. Perley (LJMU), report:
We observed the field of EP 260131a (Ding et al., GCN 43574, Wu et al. GCN 43583) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 8x150s exposures in SDSS r filter and 10x120s in SDSS z, starting at 2026-01-31 23:25:26 UT, approximately 19.9 hours after trigger.
One z-band exposure had to be discarded due to telescope movement. We report non-detections in the stacked images in both filters at the position of the counterpart first reported by Li et al. GCN 43577 and Álvarez et al., GCN 43578, with 3-sigma upper limits being r > 22.05 and z > 21.90 mag.
The photometry was obtained using nearby PanSTARRS secondary standards and was not corrected for extinction.
GCN Circular 43593
Subject
EP260131a: COLIBRÍ further observations
Date
2026-02-01T17:30:24Z (9 months ago)
From
globus@astro.unam.mx
Via
Web form
Benjamin Schneider (LAM), William H. Lee (UNAM), Alan M. Watson (UNAM), Noémie Globus (UNAM), Stéphane Basa (UAR Pytheas), Edilberto Aguilar-Ruiz (UNAM), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Jean-Luc Atteia (IRAP), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Asuka Kuwata (UNAM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), and Antonio de Ugarte Postigo (LAM) report:
We imaged the field of the EP260131a (Ding et al., GCN Circ. 43574; Wu et al, GCN Circ 43583) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-02-01 06:33 to 12:16 UTC (from 27.04 to 32.74 hours after the trigger) and obtained, respectively, 160 minutes of exposure in the r and z filters.
The data were reduced and coadded with the COLIBRÍ ASU pipeline and analyzed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction.
The candidate optical counterpart reported by Li et al. (GCN Circ. 43577), Sánchez Álvarez et al (GCN Circ. 43578), Malesani et al. (GCN Circ 43581), Schneider et al. (GCN Circ. 43582), Schneider et al. (GCN Circ 43584), Mu el al. (GCN Circ 43588), and Yao et al. (GCN CIrc. 43589) is clearly detected in our data, with a preliminary magnitude of r ~ 22. We find that the optical counterpart fades with an average temporal power-law index of ~ -0.5.
We encourage further observations.
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 43589
Subject
EP260131a: SVOM/VT optical observation
Date
2026-02-01T08:04:28Z (9 months ago)
From
zhyao@bao.ac.cn
Via
Web form
Z. H. Yao, C. Wu, L. P. Xin, H. L. Li, Y. N. Ma, Y. L. Qiu, X. H. Han, Y. Xu, J. Wang, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. R. Xu, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA) and S. D. Vergani (LUX-Paris Obs.) report on behalf of the SVOM/VT team.
SVOM/VT performed a Target of Opportunity observation of EP260131a detected by EP/WXT (Ding et al., GCN 43574). SVOM/VT began observing the field at 2026-01-31T17:47:46.506 UTC, ~14.3 h after T0, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
With X-band data available, the optical counterpart (Li et al., GCN 43577; Álvarez et al., GCN 43578; Malesani et al., GCN 43581; Schneider et al., GCN 43582; Schneider et al., GCN 43584; Mu el al., GCN 43588) was detected in both VT_B and VT_R band within EP/WXT's (Ding et al., GCN 43574) and EP/FXT's (Wu et al., GCN 43583) error box. The position of this target is R.A., Dec. = 149.902458, -3.307450 degrees, corresponding to:
R.A. (J2000) = 09:59:36.59
Dec. (J2000) = -03:18:26.82
with an uncertainty of 0.5 arcsec.
The photometric measurements are as follows:
mid time (h) | exposure time (s) | band | mag (AB)
--------------|-------------------|------|-------------
15.50 | 40*70 | VT_B | 22.38+/-0.05
15.31 | 41*70 | VT_R | 21.70+/-0.03
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 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. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS.
GCN Circular 43588
Subject
EP260131a: Xinglong optical upper limit
Date
2026-02-01T04:16:49Z (9 months ago)
From
Xinglong Observatory at National Astronomical Observatories (NAOC), Chinese Academy of Sciences (CAS) <xinglong@nao.cas.cn>
Via
Web form
Haiyang-Mu (NAOC),Junjie-Jin (NAOC), Feng-Xiao (NAOC), Pengliang-Du (NAOC),
Zhou-Fan (NAOC), Hong-Wu (NAOC) report:
Following the detection of EP260131a by EP-WXT (GCN Circular 43574,GCN Circular 43577,GCN Circular 43578), we observed the field of EP260131a using the 2.16-m
telescope at Xinglong Observatory, NAOC. We obtained 300s r-band frames with a
median time of (2026-01-31 16:25:55(UT)) 13 hr after the EP trigger.
No uncatalogued optical transient is detected in the stacked images within the 3 arcmin
EP/WXT error circle (GCN Circular 43574,GCN Circular 43578), down to 5-sigma limiting magnitudes of r ~ 19.1(not good day with thin cloud and bad seeing), calibrated with Pan-STARRS sources in the field. Also there is no apparent brightening for the catalogued sources within the error circle. Based on the location of the report(GCN Circular 43574,GCN Circular 43578), the target was not observed.
GCN Circular 43584
Subject
EP260131a: COLIBRÍ observations of slow optical fading
Date
2026-01-31T15:00:38Z (9 months ago)
From
Alan Watson at UNAM <alan@astro.unam.mx>
Via
Web form
Benjamin Schneider (LAM), Alan M. Watson (UNAM), Fredd Sánchez Álvarez (UNAM), Jean-Luc Atteia (IRAP), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Edilberto Aguilar-Ruiz (UNAM), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Asuka Kuwata (UNAM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), and Antonio de Ugarte Postigo (LAM) report:
We imaged the field of the EP260131a (Ding et al., GCN Circ. 43574; Wu et al, GCN CIrc 43583) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-01-31 04:40 to 11:52 UTC (from 1.14 to 8.35 hours after the trigger) and obtained, respectively, 127, 191, and 320 minutes of exposure in the g, r, and z filters.
The data were reduced, coadded, calibrated, and analyzed with the COLIBRÍ ASU pipeline. The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction.
The candidate optical counterpart reported by Li et al. (GCN Circ. 43577), Sánchez Álvarez et al (GCN Circ. 43578), Malesani et al. (GCN Circ 43581), and Schneider et al. (GCN Circ. 43582) is clearly detected in our data. It fades slowly from r ≈ 21.1 to r ≈ 21.4 and z ≈ 20.8 to z ≈ 21.2 during our observations with an apparent average temporal power-law index of -0.16 +/- 0.07.
We observe that the g-r color is 0.14 +/- 0.06, consistent with the detection by Schneider et al. (GCN Circ. 43582) down to the atmospheric cutoff.
We encourage further observations, especially over the next 24 hours.
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 43583
Subject
EP260131a: refined analysis of the EP-WXT and autonomous EP-FXT observations
Date
2026-01-31T13:33:19Z (9 months ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
Q. Y. Wu (NAO, CAS), T. Wu , H. C. Ding (AHNU) , H. Sun (NAO,CAS) on behalf of the Einstein Probe (EP) team:
The fast X-ray transient EP260131a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Ding et al., GCN 43574). The refined analysis of the WXT data shows that the event started at T0=2026-01-31T03:28:00.15 (UTC), and lasted for approximately 340 seconds, after which the observation was interrupted due to Earth occultation. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 3.36 × 10^20 cm^-2, an intrinsic hydrogen column density of 5 (-3/+3) × 10^21 cm^-2, and a photon index of 1.9 (-0.8/+0.9). The derived average unabsorbed 0.5-4 keV flux is 6.3 (-1.5/+3.6) × 10^(-10) erg/s/cm^2.
The Follow-up X-ray Telescope (FXT) on board EP autonomously observed this source a few minutes after the on board trigger. The source was initially occulated the Earth and entered the FXT field of view since 2026-01-31T04:14:01 (UTC, T0+2.7 ks). The effective exposure time of the observation is around 3 ks. On-ground analysis of the FXT data found an uncatalogued source at R.A. = 149.9017, DEC = -3.3074 (J2000) with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic), which is consistent with the WXT position and also the optical counterpart (Li et al., GCN 43577; Álvarez et al., GCN 43578; Malesani et al., GCN 43581; Schneider et al., GCN 43582). The average 0.5-10 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 3.36 × 10^20 cm^-2, an intrinsic hydrogen column density of 1.5 (-1.1/+1.3) × 10^21 cm^-2, and a photon index of 2.2 (-0.4/+0.4). The derived average unabsorbed 0.5-10 keV flux is 4.4 (-0.6/+0.6) × 10^(-13) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters.
Further FXT follow-up observations have been arranged.
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 43582
Subject
EP260131a: VLT/X-shooter spectroscopic redshift z = 0.937
Date
2026-01-31T12:24:23Z (9 months ago)
Edited On
2026-02-02T14:28:18Z (9 months ago)
From
Benjamin Schneider at MIT <bschn@mit.edu>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani@nbi.ku.dk>
Via
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B. Schneider (LAM), A. Saccardi (CEA/Irfu), J. An (NAOC), D. Xu (NAOC), D. B. Malesani (DAWN/NBI and Radboud), V. D'Elia (ASI-SSDC), S. D. Vergani (LUX-Paris Obs.), N. Habeeb (U. Leicester), N. R. Tanvir (U. Leicester), A. L. Thakur (INAF-IAPS) report on behalf of the Stargate collaboration:
We observed the optical counterpart (Li et al., GCN 43577; Sánchez Álvarez et al., GCN 43578, Malesani et al, GCN 43581) of EP260131a (Ding et al., GCN 43574) using the ESO/VLT UT3 (Melipal) equipped with the X-shooter spectrograph. Our spectra cover the wavelength range 3000-21000 AA and consist of 4 exposures of 1200 s each. Observations started on 2026 January 31 at 07:30:09 UT (3.98 hr after the burst).
In a stacked image of 3x60 s secured in the r-band (3.79 after trigger), we measure r = 21.20 +/- 0.04 (AB), calibrated against nearby stars from Pan-STARRS.
In a preliminary reduction of the spectra, we detect a continuum over the entire wavelength range. From detection in the blue down to 3090 AA, and the lack of hydrogen absorption, we set a redshift upper limit z < 1.54. Furthermore, we detect multiple absorption lines, which we interpret as Al II, Mn II, Fe II, Mg II doublet, and Ca II at a common redshift of z = 0.937.
The non-detection of fine-structure transitions at z = 0.937 does not allow us to firmly associate this redshift with the GRB, however, the absence of unidentified features at higher redshift and the good S/N over the full continuum, support z = 0.937 as the most likely redshift.
We acknowledge the excellent support of the ESO observing staff in Paranal, in particular Elisa Garro. The analysis of this spectrum was carried out with the help of the zHunter tool (https://doi.org/10.5281/zenodo.15189495).
GCN Circular 43581
Subject
EP260131a: NOT early detection of the counterpart in "rapid response mode"
Date
2026-01-31T09:00:08Z (9 months ago)
From
Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani@nbi.ku.dk>
Via
Web form
D. B. Malesani (DAWN/NBI and Radboud), J. N. D. van Dalen (Radboud), J. A. Quirola-Vasquez (Radboud), P. G. Jonker (Radboud), K. Valeckas (NOT) report on behalf of a larger collaboration:
We observed the field of the fast X-ray transient EP260131a (Ding et al., GCN 43574) using the Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. Observations were triggered using the recently implemented automatic “Rapid Response Mode” and obtained in the SDSS r and z bands, consisting of 5x180 s and 9x150 s exposures, respectively, starting on 2026-01-31 at 04:56:50 UTC (~2.5 min after the GCN Notice, or 52 min after the WXT trigger).
We detect the counterpart reported by Li et al. (GCN 43577) and Sánchez Álvarez et al. (GCN 43578). In our first frame (mid time 53.5 min after trigger), we measure r' = 21.18 +- 0.10 (AB) and from a stacked z-band image we measure z' = 20.75 +- 0.06 at time 75.2 min after the WXT trigger.
The above magnitudes are calibrated against nearby stars from the Pan-STARRS catalog and are not corrected for Galactic extinction.
GCN Circular 43578
Subject
EP260131a: COLIBRÍ optical observations of the counterpart
Date
2026-01-31T05:53:41Z (9 months ago)
From
Alan Watson at UNAM <alan@astro.unam.mx>
Via
Web form
Fredd Sánchez Álvarez (UNAM), Alan M. Watson (UNAM), Benjamin Schneider (LAM), Noémie Globus (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Asuka Kuwata (UNAM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), and Antonio de Ugarte Postigo (LAM) report:
We imaged the field of the EP260131a (Ding et al., GCN Circ. 43574) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-01-31 04:40 to 05:32 UTC (from 1.14 to 2.02 hours after the trigger) and obtained 39 minutes of simultaneous exposure in the r and z filters.
The data were reduced, coadded, calibrated, and analyzed with the COLIBRÍ ASU pipeline. The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction.
In the stacked image, detect the candidate optical counterpart reported by Li et al. (GCN Circ. 43577) at preliminary magnitudes of:
r = 21.05 +/- 0.08,
z = 20.69 +/- 0.09.
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 43577
Subject
EP260131a: Las Cumbres detection of an optical counterpart
Date
2026-01-31T05:12:32Z (9 months ago)
From
Wenxiong Li at NAOC <liwenxiong1992@gmail.com>
Via
Web form
Wenxiong Li, Runduo Liang (NAOC), Iair Arcavi (TAU), Ido Keinan (TAU), David Sand (U of Arizona)
We observed the position of EP260131a with a Las Cumbres 1m telescope at Cerro Tololo Inter-American Observatory, Chile, ~1 hour after the Einstein Probe WXT trigger. We took 2x300s exposures in the broad optical w band.
We find a uncataloged source at RA=149.9025, Dec=-3.3073 within the EP-FXT error circle and measure the following preliminary photometry calibrated to the r band:
MJD 61071.183 Mag 20.9
Additional followup is encouraged.
GCN Circular 43574
Subject
EP260131a: Einstein Probe detection of an X-ray transient
Date
2026-01-31T04:36:37Z (9 months ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
H. C. Ding, T. Wu (AHNU), Q. Y. Wu, H. Sun (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 EP260131a. The transient triggered EP-WXT (ID: 01709254172) at 2026-01-31T03:31:25 (UTC). The WXT position of the source is R.A. = 149.921 deg, DEC = -3.291 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. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 149.9027 deg, DEC = -3.3094 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic).
Further information will be updated when the telemetry data is received.
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).