EP260128a, GRB 260128A
GCN Circular 43592
Subject
Konus-Wind detection of GRB 260128A / EP260128a
Date
2026-02-01T16:47:41Z (a month ago)
From
Dmitry Frederiks at Ioffe Institute <fred@mail.ioffe.ru>
Via
email
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 260128A/EP260128a
(Einstein Probe detection: Zhow et al., GCN 43549;
Fermi-GBM Sub-Threshold Detection: Ravasio et al., GCN 43556)
was detected by Konus-Wind (KW) in the waiting mode
at T0=T0(KW)~23:40:00 UTC.
A Bayesian block analysis of the KW data in the 20-1500 keV
band reveals a >10 sigma count rate increase in the interval
from ~T0-101 s to ~T0+61 s.
The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB260128A/
The time-integrated spectrum of the burst (measured from from
~T0-101 s to ~T0+61 s) is best described in the 20 - 1500 keV
range by a power law with exponential cutoff (CPL) model
with alpha = -0.93 ± 0.99 and Ep = (103 ± 16) keV.
The spectrum near the peak count rate (measured from ~T0-4 s to T0+14 s)
is best described by a CPL model with alpha = -1.26 ± 0.30 and Ep = (178 ± 31) keV.
The total burst fluence is (6.12 ± 2.89)x10^-6 erg/cm^2,
and the 2.944 s peak energy flux, measured from T0+2.082 s,
is (1.57 ± 0.44)x10^-7 erg/cm^2 (both in the 20 - 1500 keV energy range).
All the quoted errors are estimated at the 68% confidence level.
All the presented results are preliminary.
GCN Circular 43572
Subject
EP260128a / GRB 260128A: COLIBRÍ optical upper limit
Date
2026-01-30T15:46:49Z (a month ago)
From
Jean-Luc Atteia at IRAP <jean-luc.atteia@irap.omp.eu>
Via
Web form
Jean-Luc Atteia (IRAP), Enrique Moreno Méndez (UNAM), Alan M. Watson (UNAM), 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), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM) report:
We imaged the field of the X-ray transient EP260128a / GRB 260128a (Zhou et al., GCN Circ. 43549, Ravasio et al., GCN Circ. 43556) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-01-30 04:48 to 10:12 UTC (from 29.14 to 35.53 hours after the trigger) and obtained 238 minutes of simultaneous exposure in the i 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 images, we do not detect any new source at the Liverpool Telescope proposed candidate position (Eyles-Ferris et al., GCN Circ. 43553) nor at the NOT proposed candidate position (He et al., GCN Circ. 43555), down to the following 3-sigma limits:
i > 23.6
z > 23.1
These upper limits are consistent with the one reported by Malesani et al. (GCN Circ. 43570).
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 43570
Subject
EP260128a / GRB 260128A: NOT and TNG optical and NIR upper limits
Date
2026-01-30T14:23:44Z (a month 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. An (NAOC), G. Corcoran (UCD), P. D’Avanzo (INAF/OAB), M. De Pasquale (U. Messina), L.B. He (NAOC), A. Martin-Carrillo (UCD), A. Melandri (INAF/OAR), D. Xu (NAOC), W. Boschin (TNG), V. Lorenzi (TNG), H. Lucio Medeiros (TNG), T. Pursimo (NOT), report on behalf of a larger collaboration:
We observed the optical counterpart (He et al., GCN 43555) of the high-energy transient EP260128a / GRB 260128A (Zhou et al., GCN 43549; Ravasio et al., GCN 43556) in both the optical and infrared. Optical observations were carried out at the Nordic Optical Telescope (NOT) equipped with the ALFOSC camera, for a total of 14x200 s in the SDSS z filter. NIR observations were carried out at the Telescopio Nazionale Galileo (TNG) equipped with the NICS camera, for a total of 40x60 s in the J filter.
The afterglow (He et al., GCN 43555) is not detected in any of our stacked images. We report 3-sigma limiting magnitudes:
z > 23.2, mean epoch 2026 Jan 29.961 UT (23.39 hr after the EP trigger);
J > 22.0, mean epoch 2026 Jan 29.939 UT (22.88 hr after the EP trigger).
The above magnitudes are in the AB system, are calibrated against nearby objects from the Pan-STARRS (z) and VHS (J) catalogs, and are not corrected for Galactic extinction.
GCN Circular 43565
Subject
EP260128a: J band upper limit by SYSU 80cm infrared telescope
Date
2026-01-30T04:42:48Z (a month ago)
From
linp@mail2.sysu.edu.cn
Via
Web form
Pu Lin, Jin-Ji Li, Hao-Nan Yang, Zhong-Nan Dong, Yan Yu, Jia-Qi Lin, Wei-Sen Huang, Chun Chen, Duo-Le Cao, P H Thomas Tam, Rong-Feng Shen, Bin Ma (Sun Yat-sen University) report on behalf of the SYSU 80cm infrared telescope team:
We observed the field of EP260128a (Zhou et al., GCN 43549) using the Sun Yat-sen University 80cm infrared telescope with 167 x 20 s exposures in J band. The calculated position is RA = 128.32533 deg, DEC = -10.27565 deg J2000, from EP/FXT observation (Zhou et al., GCN 43554). Our observations began at 2026-1-29 20:00:00 UTC, 20.33 hours after the EP trigger.
We do not detect any counterpart at the position of the optical afterglow (H. L. Li et al., GCN 43551, J. A. Quirola-Vasquez et al., GCN 43552, R. A. J. Eyles-Ferris et al., GCN 43553, L.B. He et al., GCN 43555), down to a 5-sigma depth of J~ 18.5 Vega magnitudes.
The SYSU 80cm infrared telescope is operated and managed by the Department of Astronomy, Sun Yat-sen University.
GCN Circular 43556
Subject
GRB 260128A / EP260128a: Fermi-GBM Sub-Threshold Detection
Date
2026-01-29T14:50:07Z (a month ago)
From
mariaedvige.ravasio@ru.nl
Via
Web form
M. E. Ravasio (ICE-CSIC and Radboud Univ.), P.G. Jonker (Radboud Univ.)
and
E. Burns (LSU), C. Malacaria (INAF-OAR) report on behalf of the Fermi-GBM Team:
Fermi-GBM had full spatial and temporal coverage of the transient EP260128a detected by EP-WXT (H. Zhou et al., GCN 43549; H. Zhou et al., GCN 43554). There was no Fermi-GBM onboard trigger around the refined EP starting time at T0 = 2026-01-28T23:38:19 UTC (H. Zhou et al., GCN 43554).
The GBM Targeted Search [1], the most sensitive, coherent search for GRB-like signals, was run in the time interval [-50;+500] s from T0, seeking signals between 64 ms and 32.768 s in duration. A transient was found, with the most significant signal at T0+145 s on a 16 s timescale, with a false alarm rate of 1.1e-05 Hz, although there is significant evidence of an earlier start of the emission. The light curve is multi-peaked, and a significant signal is also found at T0+70 s with FAR of 6.5e-05 Hz. The localisation is consistent with the EP one, with a spatial association probability of 99.3%. Among the three spectral templates tested, the transient was best-fit with a “normal” spectral template (Band function with Epeak = 230 keV, alpha = -1.0, beta = -2.3) for a GRB.
[1] Goldstein et al. 2019 arXiv:1903.12597
GCN Circular 43555
Subject
EP260128a: NOT optical counterpart candidate
Date
2026-01-29T11:54:22Z (a month ago)
From
L. B. He at NAOC <helb@bao.ac.cn>
Via
Web form
L.B. He, J. An, X. Liu, S.Q. Jiang, Z.P. Zhu, D. Xu (NAOC), S.Y. Fu (HUST), J.P.U. Fynbo (DAWN/NBI), N. Pyykkinen (NOT) report on behalf of a large collaboration:
We observed the field of EP260128a (Zhou et al., GCN 43549) using the 2.56-m Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. Observations started at 00:13:10 UT on 2026-01-29, i.e., 33.18 minutes after the EP trigger, and we obtained 9 x 90 s frames in the Sloan r-band and 9 x 100 s frames in the Sloan z- band.
The stacked r- and z- band images have 3-sigma depth of r ~ 24.1 and z ~ 23.5, calibrated with nearby Pan-STARRS1 DR2 stars and not corrected for Galactic extinction.
A new optical source is detected in the stacked z-band image within the EP/FXT error circle (Zhou et al., GCN 43554) at coordinates
RA = 08:33:18.08 (128.32533)
DEC = -10:16:32.3 (-10.27565)
to ~ 4.2-sigma and we measured z = 23.07 +/- 0.26 (AB) at 1.004 hrs post-trigger. This source is not present in the z-band Legacy Survey DR11 early image v2, which is a bit deeper than the z-band NOT image.
This source is also not present in the stacked r-band NOT image, as well as the r-band Legacy Survey image that is deeper than the NOT image.
Considering the r-band non-detection and the z-band (weak) detection for the NOT candidate, EP260128a might be a high-redshift (i.e., z > ~5) event.
We also note that the counterpart candidate by Liverpool Telescope (Eyles-Ferris et al., GCN 43553) is not present in neither r-band nor z-band stacked NOT image.
Further optical and near-infrared follow-ups are encouraged.
GCN Circular 43554
Subject
EP260128a: refined analysis of the EP-WXT and autonomous EP-FXT observations
Date
2026-01-29T10:01:54Z (a month ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
H. Zhou (PMO, CAS), T. Wu, H.-C. Ding (AHNU), Z.-X. Ling (NAO, CAS) on behalf of the Einstein Probe (EP) team:
The fast X-ray transient EP260128a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Zhou et al., GCN 43549). The refined analysis of the WXT data shows that the event started at T0=2026-01-28T 23:38:19(UTC), and lasted for approximately 100 seconds, after which the WXT light curve was interrupted due to the autonomous follow-up observation. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 5.84×10^20 cm^-2 and a photon index of 0.05 +/- 0.73. The derived average unabsorbed 0.5-4 keV flux is 6.98(-4.40/+11.93)×10^(-9) erg/s/cm^2.
The Follow-up X-ray Telescope (FXT) on board EP observed this source autonomously at 2026-01-28T23:43:01(UTC, T0+282 s). The exposure time of this observation is 2102s. On-ground analysis of the FXT data found an uncatalogued source at R.A. = 128.3253, DEC = -10.2750 (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic), which is consistent with the WXT position. The average 0.5-10 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 5.84×10^20 cm^-2 and a photon index of 1.99 +/-0.06. The derived average unabsorbed 0.5-10 keV flux is (2.76 +/- 0.15)×10^(-11) erg/s/cm^2. The best-fitted FXT spectra show no additional absorption is required.
Further FXT follow-up observations have been arranged.
Although a faint counterpart of EP260128a has been reported (Lipunov et al., GCN 43550; Quirola-Vasquez et al., GCN 43552; Eyles-Ferris et al., GCN 43553), further multi-band follow-up observations are encouraged to explore the nature of EP260128a.
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 43553
Subject
EP260128a: Liverpool Telescope optical observations and possible counterpart
Date
2026-01-29T09:33:37Z (a month ago)
From
Rob Eyles-Ferris at U of Leicester <raje1@leicester.ac.uk>
Via
Web form
R. A. J. Eyles-Ferris and R. L. C. Starling (Leicester) report on behalf of a larger collaboration:
We observed the field of EP260128a (Zhou et al., GCN 43549) with the 2m Liverpool Telescope on La Palma using the IO:O instrument. We obtained 6x150s exposures in each of the SDSS r’ and SDSS g’ filters starting at 2026-01-28 23:56:39 UT, approximately 16.6 minutes after the X-ray detection.
We performed image subtraction on the stacked images using reference images from Pan-STARRS and Legacy DR11 and also compared the stacked and reference images manually. In the r’ stack and within the EP/FXT localisation, we tentatively identify a low significance source at a position
RA 08:33:18.17 (128.32569 deg)
Dec -10:16:19.3 (-10.27202 deg)
The source is detected to ~2.6-sigma and we measure r’ = 22.92 +/- 0.38. The source is not visible in the g’ stack (started ~18 minutes later).
We derive 3-sigma upper limits for our stacked images of r’ > 22.8 and g’ > 22.5 with AB photometry calibrated to Pan-STARRS and not corrected for Galactic extinction.
GCN Circular 43552
Subject
EP260128a: LCO optical upper limits
Date
2026-01-29T07:47:19Z (a month ago)
From
Jonathan Quirola at Radboud University <jaquirola1990@gmail.com>
Via
Web form
J. A. Quirola-Vasquez (Radboud), J. N. D. van Dalen (Radboud), J. Chacón(PUC), A. Martin-Carrillo (UCD), P. G. Jonker (Radboud), A. J. Levan (Radboud), D. B. Malesani (DAWN/NBI and Radboud), and F. E. Bauer (SSI and UTA) report on behalf of a larger collaboration:
We observed the field of the fast X-ray transient EP260128a (Zhou et al., GCN 43549) using an LCO 1m telescope located at the Cerro Tololo Inter-American Observatory (Chile) equipped with the SINISTRO instrument. A series of 6x300 s exposures was taken in each of the SDSS-r filter, starting on 2026-01-29 at 02:05:48 UT (2.43 hr after the trigger).
No new source is detected within or at the border of the EP/FXT uncertainty region (Zhou et al., GCN 43549) compared to Legacy DR11. From the stacked images, we obtain the following 3-sigma upper limits:
r > 22.5
These upper limits are in AB magnitudes, calibrated using nearby stars from the Pan-STARRS catalog, and are not corrected for Galactic extinction.
GCN Circular 43550
Subject
EP260128a: Global MASTER-Net observations report
Date
2026-01-29T06:54:20Z (a month ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
Via
email
V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko,
G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU),
O.Gress, N.Budnev (ISU),
C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA),
A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory),
A.Sosnovskij (CrAO),
A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity),
D.Buckley (SAAO),
R.Rebolo (The Instituto de Astrofisica de Canarias),
L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez,
A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory)
MASTER-OAFA robotic telescope [1] located in Argentina (OAFA observatory of San Juan National University) was pointed to the EP260128a ( EP Team et al., GCN 43549) errorbox 9549 sec after notice time and 17258 sec after trigger time at 2026-01-29 04:27:37 UT, with upper limit up to 19.9 mag. The observations began at zenith distance = 21 deg. The sun altitude is -40.7 deg.
The galactic latitude b = 18 deg., longitude l = 235 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=3117956
We obtain a following upper limits.
Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________
17289 | 2026-01-29 04:27:37 | MASTER-OAFA | (08h 29m 07.40s , -10d 15m 51.1s) | C | 60 | 18.7 |
17364 | 2026-01-29 04:28:53 | MASTER-OAFA | (08h 29m 12.43s , -10d 16m 52.4s) | C | 60 | 13.8 |
25520 | 2026-01-29 06:44:48 | MASTER-OAFA | (08h 33m 35.30s , -09d 55m 35.4s) | C | 60 | 19.9 |
25597 | 2026-01-29 06:46:06 | MASTER-OAFA | (08h 33m 42.32s , -09d 56m 34.0s) | C | 60 | 19.9 |
Filter C is a clear (unfiltred) band.
The observation and reduction will continue.
The message may be cited.
[1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp.
http : // www.pereplet.ru/lipunov/625.html
GCN Circular 43549
Subject
EP260128a: Einstein Probe detection of an X-ray transient
Date
2026-01-29T01:47:47Z (a month ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
H. Zhou (PMO, CAS), T. Wu, H.-C. Ding (AHNU), 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 EP260128a. The transient triggered EP-WXT (ID: 01709253190) at 2026-01-28T23:39:59 (UTC). The WXT position of the source is R.A. = 128.303 deg, DEC = -10.281 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. = 128.3233 deg, DEC = -10.2767 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).