Gamma-ray Burst 260227A = EP260227a

(All information courtesy of the instrument teams.)

Previous IAU Circulars

none

Results of Observations

GCN Circular #43867
R. A. J. Eyles-Ferris (Leicester), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), J. N. D. van Dalen (Radboud), J. Chacón (PUC), report on behalf of a larger collaboration:
We observed the field of the EP/WXT trigger 01709258681 (likely EP260227a) using the Sinistro instrument on the 1-m telescope in Sutherland (South Africa), part of the LCO network. Six 300 s observations were secured in the SDSS r band, with mean time 2026 Feb 27.945 UT (2.47 hr after the WXT trigger).
Comparison of our images with archival templates from the Legacy Survey reveals a new object at coordinates (J2000):
```
RA = 14:52:19.94
Dec = -11:24:23.9
```
Photometry yields r = 20.18 +/- 0.04 (AB) calibrated against nearby stars from the Pan-STARRS catalog, and not corrected for Galactic extinction.
We suggest this is the optical counterpart of the EP/WXT trigger 01709258681.
GCN Circular #43868
Wenxiong Li (NAOC), Iair Arcavi (TAU), Ido Keinan (TAU), Runduo Liang (NAOC), David Sand (U of Arizona)
We observed the position of the EP-WXT trigger 01709258681 (EP260227a?) with a Las Cumbres 1m telescope at Siding Spring Observatory 2.6 hours after the Einstein Probe WXT trigger and again 4 hours after the trigger. We took 2x300s exposures in each visit in the broad optical w band. We find a rapidly fading source consistent with the position reported by Eyles-Ferris et al. (GCN 43867) and measure the following preliminary photometry calibrated to the r band:
```
Epoch 1: MJD 61098.954 Mag 20.28 ± 0.09
Epoch 2: MJD 61099.011 Mag 21.08 ± 0.10
```
GCN Circular #43869
Y. Wang (PMO), H. C. Ding, T, Wu, Y. J. Yi (BNU), W. F. Wen (SZTU), Z. X. Ling(NAOC) 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 EP260227a. The transient triggered EP-WXT (ID: 01709258681) at 2026-02-27T20:12:29 (UTC). The WXT position of the source is R.A. = 223.101 deg, DEC = -11.408 deg (J2000) with an uncertainty of 2.586 arcmin in radius (90% C.L. statistical and systematic). The refined analysis of the WXT data shows that the event started at T0=2026-02-27T19:58:52 (UTC), and lasted for approximately 250 seconds. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 9.3×10^20 cm^-2 and a photon index of 0.8 (-0.6/+0.6). The derived average unabsorbed 0.5-4 keV flux is 4.1 (-1.3/+1.7) × 10^(-10) erg/s/cm^2.
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. = 223.1002 deg, DEC = -11.386 deg (J2000) with an uncertainty of 10 arcsec in radius (90% C.L. statistical and systematic). The average 0.5-10 keV spectrum can be fitted with an absorbed power law with a Galactic hydrogen column density of 1.8 (-0.1/+0.1) × 10^21 cm^-2, and a photon index of 1.5 (-0.3/+0.3). The derived average unabsorbed 0.5-10 keV flux is 8.3 (-0.9/+1.2) ×10^(-12) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. The optical counterpart was reported by Eyles-Ferris et al. (GCN 43867) and Li et al. (GCN 43868).
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 #43870
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-SAAO robotic telescope [1] located in South Africa (South African Astronomical Observatory) was pointed to the EP260227a ( EP Team et al., GCN 43869) errorbox 14883 sec after trigger time at 2026-02-28 00:20:32 UT, with upper limit up to 21.0 mag. The observations began at zenith distance = 42 deg. The sun altitude is -44.5 deg.
The galactic latitude b = 41 deg., longitude l = 345 deg.
Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3160292
We obtain a following upper limits.

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

   14913 | 2026-02-28 00:20:32 |         MASTER-SAAO | (14h 50m 11.27s , -11d 34m 27.7s) |   C |    60 | 19.3 |        
   14973 | 2026-02-28 00:20:32 |         MASTER-SAAO | (14h 50m 11.26s , -11d 34m 27.7s) |   C |   180 | 19.8 |        
   15093 | 2026-02-28 00:20:32 |         MASTER-SAAO | (14h 50m 11.26s , -11d 34m 27.7s) |   C |   420 | 20.1 |        
   15693 | 2026-02-28 00:20:32 |         MASTER-SAAO | (14h 50m 11.26s , -11d 34m 27.7s) |   C |  1620 | 21.0 |        
   14913 | 2026-02-28 00:20:32 |         MASTER-SAAO | (14h 48m 18.09s , -11d 18m 45.9s) |   C |    60 | 19.2 |        
   14973 | 2026-02-28 00:20:32 |         MASTER-SAAO | (14h 48m 18.09s , -11d 18m 45.9s) |   C |   180 | 19.8 |        
   15093 | 2026-02-28 00:20:32 |         MASTER-SAAO | (14h 48m 18.09s , -11d 18m 46.0s) |   C |   420 | 20.0 |        
   15693 | 2026-02-28 00:20:32 |         MASTER-SAAO | (14h 48m 17.70s , -11d 18m 51.8s) |   C |  1620 | 20.7 |        
   15005 | 2026-02-28 00:22:04 |         MASTER-SAAO | (14h 50m 17.85s , -11d 34m 01.7s) |   C |    60 | 19.3 |        
   15005 | 2026-02-28 00:22:04 |         MASTER-SAAO | (14h 48m 24.61s , -11d 18m 21.0s) |   C |    60 | 19.2 |        
   15097 | 2026-02-28 00:23:36 |         MASTER-SAAO | (14h 50m 14.69s , -11d 32m 38.3s) |   C |    60 | 19.3 |        
   15097 | 2026-02-28 00:23:36 |         MASTER-SAAO | (14h 48m 21.41s , -11d 16m 58.1s) |   C |    60 | 19.2 |        
   15688 | 2026-02-28 00:32:56 |         MASTER-SAAO | (14h 50m 10.29s , -11d 34m 21.4s) |   C |   120 | 19.7 |        
   15688 | 2026-02-28 00:32:56 |         MASTER-SAAO | (14h 48m 17.24s , -11d 18m 39.5s) |   C |   120 | 19.6 |        
   15840 | 2026-02-28 00:35:28 |         MASTER-SAAO | (14h 50m 16.17s , -11d 34m 15.7s) |   C |   120 | 19.7 |        
   15840 | 2026-02-28 00:35:28 |         MASTER-SAAO | (14h 48m 23.05s , -11d 18m 34.8s) |   C |   120 | 19.6 |        
   15991 | 2026-02-28 00:38:00 |         MASTER-SAAO | (14h 50m 14.08s , -11d 32m 35.0s) |   C |   120 | 19.8 |        
   16111 | 2026-02-28 00:38:00 |         MASTER-SAAO | (14h 50m 14.08s , -11d 32m 35.0s) |   C |   360 | 20.2 |        
   15991 | 2026-02-28 00:38:00 |         MASTER-SAAO | (14h 48m 20.90s , -11d 16m 54.7s) |   C |   120 | 19.7 |        
   16111 | 2026-02-28 00:38:00 |         MASTER-SAAO | (14h 48m 20.90s , -11d 16m 54.7s) |   C |   360 | 20.1 |        
   16144 | 2026-02-28 00:40:32 |         MASTER-SAAO | (14h 50m 14.08s , -11d 33m 59.3s) |   C |   120 | 19.8 |        
   16144 | 2026-02-28 00:40:32 |         MASTER-SAAO | (14h 48m 20.83s , -11d 18m 19.0s) |   C |   120 | 19.6 |        
   16296 | 2026-02-28 00:43:04 |         MASTER-SAAO | (14h 50m 18.07s , -11d 32m 38.9s) |   C |   120 | 19.8 |        
   16296 | 2026-02-28 00:43:04 |         MASTER-SAAO | (14h 48m 24.76s , -11d 16m 58.8s) |   C |   120 | 19.7 |        
   16448 | 2026-02-28 00:45:36 |         MASTER-SAAO | (14h 50m 11.21s , -11d 33m 12.8s) |   C |   120 | 19.8 |        
   16688 | 2026-02-28 00:45:36 |         MASTER-SAAO | (14h 50m 11.21s , -11d 33m 12.8s) |   C |   600 | 20.2 |        
   16448 | 2026-02-28 00:45:36 |         MASTER-SAAO | (14h 48m 17.86s , -11d 17m 32.5s) |   C |   120 | 19.7 |        
   16688 | 2026-02-28 00:45:36 |         MASTER-SAAO | (14h 48m 17.86s , -11d 17m 32.4s) |   C |   600 | 20.2 |        
   16600 | 2026-02-28 00:48:08 |         MASTER-SAAO | (14h 50m 10.14s , -11d 32m 11.3s) |   C |   120 | 19.8 |        
   16600 | 2026-02-28 00:48:08 |         MASTER-SAAO | (14h 48m 16.73s , -11d 16m 31.1s) |   C |   120 | 19.7 |        
   16752 | 2026-02-28 00:50:41 |         MASTER-SAAO | (14h 50m 17.32s , -11d 33m 09.5s) |   C |   120 | 19.8 |        
   17112 | 2026-02-28 00:50:41 |         MASTER-SAAO | (14h 50m 17.32s , -11d 33m 09.5s) |   C |   840 | 20.2 |        
   16752 | 2026-02-28 00:50:41 |         MASTER-SAAO | (14h 48m 23.83s , -11d 17m 29.0s) |   C |   120 | 19.8 |        
   17112 | 2026-02-28 00:50:41 |         MASTER-SAAO | (14h 48m 23.83s , -11d 17m 29.0s) |   C |   840 | 20.2 |        
   16904 | 2026-02-28 00:53:13 |         MASTER-SAAO | (14h 50m 11.91s , -11d 34m 07.5s) |   C |   120 | 19.8 |        
   16904 | 2026-02-28 00:53:13 |         MASTER-SAAO | (14h 48m 18.35s , -11d 18m 26.9s) |   C |   120 | 19.8 |        
   17056 | 2026-02-28 00:55:45 |         MASTER-SAAO | (14h 50m 17.31s , -11d 34m 04.1s) |   C |   120 | 19.8 |        
   17176 | 2026-02-28 00:55:45 |         MASTER-SAAO | (14h 50m 17.31s , -11d 34m 04.1s) |   C |   360 | 20.2 |        
   17056 | 2026-02-28 00:55:45 |         MASTER-SAAO | (14h 48m 23.70s , -11d 18m 23.5s) |   C |   120 | 19.8 |        
   17176 | 2026-02-28 00:55:45 |         MASTER-SAAO | (14h 48m 23.70s , -11d 18m 23.5s) |   C |   360 | 20.1 |        
   17208 | 2026-02-28 00:58:17 |         MASTER-SAAO | (14h 50m 14.06s , -11d 32m 19.1s) |   C |   120 | 19.8 |        
   17208 | 2026-02-28 00:58:17 |         MASTER-SAAO | (14h 48m 20.45s , -11d 16m 38.4s) |   C |   120 | 19.8 |        
   17360 | 2026-02-28 01:00:49 |         MASTER-SAAO | (14h 50m 14.01s , -11d 33m 49.8s) |   C |   120 | 19.8 |        
   17360 | 2026-02-28 01:00:49 |         MASTER-SAAO | (14h 48m 20.41s , -11d 18m 08.7s) |   C |   120 | 19.8 |        
   17512 | 2026-02-28 01:03:21 |         MASTER-SAAO | (14h 50m 17.60s , -11d 32m 08.9s) |   C |   120 | 19.8 |        
   17632 | 2026-02-28 01:03:21 |         MASTER-SAAO | (14h 50m 17.60s , -11d 32m 08.9s) |   C |   360 | 20.2 |        
   17512 | 2026-02-28 01:03:21 |         MASTER-SAAO | (14h 48m 24.04s , -11d 16m 28.0s) |   C |   120 | 19.8 |        
   17632 | 2026-02-28 01:03:21 |         MASTER-SAAO | (14h 48m 24.05s , -11d 16m 27.9s) |   C |   360 | 20.2 |        
   17664 | 2026-02-28 01:05:53 |         MASTER-SAAO | (14h 50m 10.38s , -11d 32m 57.2s) |   C |   120 | 19.9 |        
   17664 | 2026-02-28 01:05:53 |         MASTER-SAAO | (14h 48m 16.83s , -11d 17m 15.8s) |   C |   120 | 19.8 |        
   17816 | 2026-02-28 01:08:25 |         MASTER-SAAO | (14h 48m 18.27s , -11d 16m 14.0s) |   C |   120 | 19.9 |        
   17816 | 2026-02-28 01:08:25 |         MASTER-SAAO | (14h 50m 11.81s , -11d 31m 55.4s) |   C |   120 | 19.8 |        
   17968 | 2026-02-28 01:10:57 |         MASTER-SAAO | (14h 48m 22.89s , -11d 17m 11.4s) |   C |   120 | 19.9 |        
   18208 | 2026-02-28 01:10:57 |         MASTER-SAAO | (14h 48m 22.89s , -11d 17m 11.4s) |   C |   600 | 20.2 |        
   17968 | 2026-02-28 01:10:57 |         MASTER-SAAO | (14h 50m 16.48s , -11d 32m 53.2s) |   C |   120 | 19.8 |        
   18208 | 2026-02-28 01:10:57 |         MASTER-SAAO | (14h 50m 16.48s , -11d 32m 53.1s) |   C |   600 | 20.3 |        
   18121 | 2026-02-28 01:13:29 |         MASTER-SAAO | (14h 48m 16.38s , -11d 18m 08.8s) |   C |   120 | 19.9 |        
   18121 | 2026-02-28 01:13:29 |         MASTER-SAAO | (14h 50m 10.00s , -11d 33m 50.7s) |   C |   120 | 19.9 |        
   18273 | 2026-02-28 01:16:01 |         MASTER-SAAO | (14h 48m 23.93s , -11d 17m 39.4s) |   C |   120 | 19.8 |        
   18273 | 2026-02-28 01:16:01 |         MASTER-SAAO | (14h 50m 17.58s , -11d 33m 21.1s) |   C |   120 | 19.8 |

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 #43873
S.Y. Fu (HUST), L.B. He, Z.P. Zhu, J. An, X. Liu, S.Q. Jiang, D. Xu (NAOC), J. P. U. Fynbo (DAWN/NBI), A. L. Bouquin (NOT) report on behalf of a large collaboration:
We observed the field of EP260227a (Wang et al., GCN 43869) using the 2.56-m Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. The observations started at 02:20:46 UT, 2026-02-28, i.e. 6.14 hrs after the trigger, and we obtained 3x120 s frames each in Sloan g', r' and i' bands.
The previously reported optical counterpart (Eyles-Ferris et al., GCN 43867; Li et al., GCN 43868) was detected in our stacked frames with the following AB magnitudes:
```
| t-mid (hrs) | filter |      mag     |
| ----------- |--------| ------------ |
|    6.21     |   g'   | 21.40 ± 0.20 |
|    6.33     |   r'   | 21.50 ± 0.20 |
|    6.46     |   i    | 21.37 ± 0.12 |
```
calibrated using nearby Pan-STARRS1 dr2 catalog, and not corrected for Galactic extinction.
GCN Circular #43874
Nikos Mandarakas (LAM), Camila Angulo (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), 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), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), 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 EP260227a (Wang et al., GCN Circ. 43869) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-02-28 07:51:00 to 08:49:14 UTC (from 11.64 to 12.61 hours after the trigger) and obtained 44 minutes of simultaneous exposure in the r and z filters.
The data were reduced, coadded, calibrated, and analysed 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.
We detected the optical counterpart reported by Eyles-Ferris et al. (GCN 43867), Li et al. (GCN 43868), Fu et al. (GCN 43873), at a preliminary magnitude of:
```
 r =  21.4644 +/- 0.0680
 z =  20.8905 +/- 0.0745 
```
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 #43875
R. A. J. Eyles-Ferris and N. R. Tanvir (Leicester) report on behalf of a larger collaboration:
We observed the field of EP260227a (Wang et al., GCN 43869) with the 2m Liverpool Telescope on La Palma using the IO:O instrument. We obtained 6x150s exposures in each of the SDSS g’ r’ i’ z’ filters starting at 2026-02-28 04:25:03 UT, approximately 8.21 hours after the X-ray detection.
We detect the optical counterpart (Eyles-Ferris et al., GCN 43867; Li et al., GCN 43868; Fu et al., GCN 43873; Mandarakas et al., GCN 43874) in the r’, i’ and z’ bands. We measure the following magnitudes calibrated to Pan-STARRS and not corrected for Galactic extinction.
```
| t_mid (hours) | Filter |   AB magnitude   |
| ------------- | ------ | ---------------- |
|      8.35     |   g’   | >22.28 (3-sigma) |
|      8.63     |   i’   |  21.12 +/- 0.08  |
|      8.92     |   r’   |  21.61 +/- 0.22  |
|      9.21     |   z’   |  20.74 +/- 0.11  |
```
Compared to the photometry tabulated by Fu et al. (GCN 43873) and Mandarakas et al. (GCN 43874), our observations suggest the source has not faded significantly between these three epochs.
GCN Circular #43876
D. B. Malesani (DAWN/NBI and Radboud), P. G. Jonker (Radboud), A. Martin-Carrillo (UCD), R. A. J. Eyles-Ferris (Leicester), J. van Dalen (Radboud), D. Mata-Sanchez (IAC and ULL), A. de Ugarte Postigo (LAM), N. Castro Rodríguez (GTC), A. L. Cabrera Lavers (GTC) report on behalf of a larger collaboration:
We observed the optical counterpart (Eyles-Ferris et al., GCN 43867; Li et al., GCN 43868; Fu et al., GCN 43873; Mandarakas et al., GCN 43874; Eyles-Ferris & Tanvir, GCN 43875) of EP260227a (Wang et al., GCN 43869) using the Gran Telescopio Canarias (GTC) equipped with the OSIRIS+ spectrograph. Our observations consisted of 4 exposures of 900 s each, using grism R1000B which covers the wavelength range 3670 - 7700 Å. The observation start time was 2026-02-28 at 03:16 UT (~7.1 hr after the trigger).
In the acquisition magnitude, we measure r = 21.55 +/- 0.07 AB at mid time 6.89 hr after trigger (consistent with the NOT measurement; Fu et al., GCN 43873). This value is calibrated against nearby objects from the Pan-STARRS catalog and not corrected for Galactic extinction.
A faint trace is detected down to ~4000 Å, with an apparent spectral break around 4500 Å which is interpreted as due to H I and the onset of the Lyman forest. A few weak, narrow features, due to Si II 1259, Si II 1304, C II 1334, C IV 1548/1550, allow us to measure a redshift z = 2.714.
GCN Circular #43877
R. A. J. Eyles-Ferris (Leicester), S. Littlefair (Sheffield), V. Dhillon (Sheffield), I. Pelisoli (Warwick), J. van Dalen (Radboud), P. G. Jonker (Radboud), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), D. Mata-Sanchez (IAC and ULL), report on behalf of a larger collaboration:
We observed the position of the fast X-ray transient EP260227a (Wang et al., GCN 43869) with the 2.4m Thai National Telescope equipped with the ULTRASPEC instrument. Observations were conducted in the KG5 wideband filter which approximately covers the wavebands of the SDSS ugr filters (https://tinyurl.com/kg5filter; Hardy et al. 2017). The total exposure time was 62 minutes with a mid time of 2026-02-27 22:28:00 UT (2.52 hr after trigger).
We clearly detect the optical counterpart (Eyles-Ferris et al., GCN 43867; Li et al., GCN 43868; Fu et al., GCN 43873; Mandarakas et al., GCN 43874; Eyles-Ferris & Tanvir, GCN 43875; Malesani et al., GCN 43876) at a magnitude m_KG5 = 23.57 +/- 0.07 (AB) calibrated to Pan-STARRS and not corrected for Galactic extinction. The faint magnitude compared to other photometry is likely attributable to the peak response of the adopted filter in the blue and the red colour of the source, broadly consistent with the DLA suggested by Malesani et al (GCN 43876).
GCN Circular #43879
R. Strausbaugh (Eastern Illinois University), A. Cucchiara (NASA) report on behalf of a larger collaboration:
We observed the EP260227a field (Wang et al., GCN 43869) with the LCOGT 1-meter Sinistro instrument at the Cerro Tololo Interamerican Observatory, Chile site, on February 28, from 05:39 to 06:00 UT (corresponding to 9.28 to 9.63 hours after the trigger time) with the SDSS r and i filters.
We performed a series of 3x200s exposures in i-band and r-band. We marginally detect an uncatalogued sources in both bands, consistent with other optical detections (Eyles-Ferris et al., GCN 43867; Li et al., GCN 43868; Fu et al., GCN 43873; Mandarakas et al., GCN 43874; Eyles-Ferris et al., GCN 43875; Malesani et al., GCN 43876).
The following magnitudes are calculated using the PanSTARRS catalog as reference:
```
r = 20.78 +/- 0.58
i = 21.47 +/- 0.52
```
These magnitudes are not corrected for galactic extinction.
GCN Circular #43880
A. Bochenek, D. A. Perley (LJMU) report:
We observed the field of EP260227a (Wang et al., GCN 43869) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 5x120s exposures in SDSS r and i filters and 3x100s + 2x120s in SDSS z, starting at 2026-02-28 02:54:00 UT, approximately 6.69 hours after trigger.
We report detections in stacked images in all filters at the position first reported by Eyles-Ferris et al. (GCN 43867) and Li et al. (GCN 43868).
```
MJD (mid)      T_mid-T_0      Filter      Mag. (AB)
61099.12483	6.79 h         r        21.31 ± 0.19
61099.13319	6.99 h         i        21.10 ± 0.12
61099.14035	7.16 h         z        20.71 ± 0.11
```
Our results are consistent with the slower fading of the optical counterpart as reported by and Eyles-Ferris et al. (GCN 43875), comparing to the observations of Fu et al. (GCN 43873), Mandarakas et al. (GCN 43874) and Eyles-Ferris et al. (GCN 43875).
The photometry was obtained using nearby PanSTARRS secondary standards and was not corrected for extinction.
GCN Circular #43881
Julius Gassert (LMU/CMU), Malte Busmann (LMU), Christoph Ries (LMU), Xander J. Hall (CMU), Brendan O’Connor (CMU), Daniel Gruen (LMU), and Antonella Palmese (CMU) report:
We observed the optical counterpart (Eyles-Ferris et al., GCN 43867; Li et al., GCN 43868; Fu et al., GCN 43873; Mandarakas et al., GCN 43874; Eyles-Ferris & Tanvir, GCN 43875; Malesani et al., GCN 43876; Eyles-Ferris et al., GCN 43877; Strausbaugh et al, GCN 43879, Bochenek et al. GCN 43880) of EP 20260227a (Wang et al., GCN 43869) with the Three Channel Imager (3KK) at the Fraunhofer Telescope at Wendelstein Observatory (FTW) in the r, i, and J bands for 19x 180s, starting at 2026-02-28T04:21:12 (0.34 days after the trigger). We detect the counterpart in all bands and measure an r-band magnitude of
r = 21.69 +/- 0.10 AB mag
The magnitude is calibrated against the PS1 catalog and not corrected for Galactic extinction.
GCN Circular #43884
Anshika Gupta, Dhruv Jain, Pankaj Pawar, Debalina Kar, and Kuntal Misra (ARIES) report:
We observed the field of EP260227A detected by Einstein Probe WXT (Wang et al., GCN 43869) with the 3.6m Devasthal Optical Telescope (DOT), located at the Devasthal Observatory of the Aryabhatta Research Institute of Observational Sciences (ARIES), India. The observations were started on 2026-02-28 at 21:17:26 UT, i.e., ~25.08 hours after the EP/WXT trigger. We have taken multiple frames with an exposure time of 300s in the R filter. We stacked the images after the alignment. We detect an optical counterpart in our stacked image at the position given by the Eyles-Ferris et al. (GCN 43867). We obtain the following preliminary magnitude in the stacked image:
```
Date Start_UT T_start-T0 (hours) Filter  Exp time (s)  Magnitude
==================================================================
2026-02-28  21:17:26  ~25.08   R     300s*24    22.92 +/-0.06
```
Our detection is consistent with Eyles-Ferris et al. (GCN 43867); Li et al. (GCN 43868); Lipunov et al. (GCN 43870); Fu et al.(GCN 43873); Mandarakas et al. (GCN 43874); Eyles-Ferris and N. R. Tanvir et al. (GCN 43875); Malesani et al. (GCN 43876); Eyles-Ferris et al. (GCN 43877); Strausbaugh et al. (GCN 43879); Bochenek et al. (GCN 43880); Gassert et al. (GCN 43881).
The magnitude is not corrected for the Galactic extinction in the direction of the burst. Photometric calibration is performed using the standard stars from the USNO-B1.0 catalog.
GCN Circular #43887
Y. N. Ma, Z. H. Yao, H. L. Li, Y. L. Qiu, C. Wu, L. P. Xin, 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) report on behalf of the SVOM/VT team.
SVOM/VT performed a Target of Opportunity observation of EP260227a detected by EP/WXT (Wang et al., GCN 43869). SVOM/VT began observing the field at 2026-02-28T07:20:51 UTC, 11.14 hours after the trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
With X-band data available, the optical counterpart (Eyles-Ferris et al., GCN 43867; Li et al., GCN 43868; Fu et al., GCN 43873; Mandarakas et al., GCN 43874; Eyles-Ferris & Tanvir, GCN 43875; Malesani et al., GCN 43876; Eyles-Ferris et al., GCN 43877; Strausbaugh & Cucchiara, GCN 43879; Bochenek & Perley, GCN 43880; Gassert et al., GCN 43881; Gupta et al., GCN 43884) was detected in both VT_B and VT_R bands. The magnitudes are:
```
mid time (h) | exposure time (s) | band | mag (AB) 
-------------|-------------------|------|--------------
    11.362   |      38*50        | VT_B |  21.9+-0.1
    11.313   |      31*50        | VT_R |  21.3+-0.1 
```
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 #43888
R. A. J. Eyles-Ferris (Leicester), A. Martin-Carrillo (UCD), P. G. Jonker (Radboud), and J. Chacón (PUC) report on behalf of a larger collaboration:
We observed the optical counterpart of the fast X-ray transient EP260227a (Wang et al., GCN 43869) with an LCO 1m telescope located at the Cerro Tololo Inter-American Observatory (Chile) equipped with the SINISTRO instrument. We obtained nine 300 s exposures in the r band from 2026-03-01 07:52:01 to 2026-03-01 08:43:10 UT (t_mid = 36.09 hr).
In our stacked image, we clearly detect the optical counterpart (Eyles-Ferris et al., GCN 43867; Li et al., GCN 43868; Fu et al, GCN 43873; Mandarakas et al., GCN 43874; Eyles-Ferris and Tanvir et al., GCN 43875; Malesani et al., GCN 43876; Eyles-Ferris et al., GCN 43877; Strausbaugh et al., GCN 43879; Bochenek et al., GCN 43880; Gassert et al., GCN 43881; Gupta et al., GCN 43884; Ma et al., GCN 43887). We measure an AB magnitude of r = 22.82 +/- 0.28 calibrated to Pan-STARRS and not corrected for Galactic extinction.
Our observations suggest there is no significant evolution since the observations of Gupta et al. (GCN 43884) ~12 hr earlier.
GCN Circular #43891
Shiyan Zhong, Hongguang Li, Qinhao Shao, Yuan Fang, Jian Cui, Guowang Du, Yu Pan, Xingzhu Zou, Xinlei Chen, Brajesh Kumar, Jianghua Zhang, Edoardo P. Lagioia, Yuanpei Yang, Xiangkun Liu, Xiaowei Liu (SWIFAR, YNU) report on behalf of the Mephisto Team:
The field of EP260227a (Wang et al., GCN 43869) was observed with the 1.6-meter Multi-channel Photometric Survey Telescope (Mephisto) of Yunnan University located at Lijiang Observatory. The simultaneous observations in Mephisto u/g/i bands were started from 2026-02-27T20:20:38 (~8 minutes after the trigger). The field was again simultaneously observed in v/r/z bands (starting from 2026-02-27T20:23:47). We detected a source at the position reported by Eyles-Ferris et. al. (GCN 43867) and other groups Li et al., (GCN 43868); Fu et al, (GCN 43873); Mandarakas et al., (GCN 43874); Eyles-Ferris and Tanvir et al., (GCN 43875); Malesani et al., (GCN 43876); Eyles-Ferris et al., (GCN 43877); Strausbaugh et al., (GCN 43879); Bochenek et al., (GCN 43880); Gassert et al., (GCN 43881); Gupta et al., (GCN 43884); Ma et al., (GCN 43887) and Eyles-Ferris et al., (GCN 43888). The preliminary photometry results (without extinction correction) are listed below:
```
Start_Time (UT)     | Band | Exp(s) | Mag/LimMag(AB)
--------------------|------|--------|--------------------
2026-02-27T20:20:38 | u    | 45     |  >20.86 (3-sigma)  
2026-02-27T20:20:38 | g    | 45     |   20.58 +/- 0.32
2026-02-27T20:20:38 | i    | 45     |   19.92 +/- 0.18
--------------------|------|--------|--------------------
2026-02-27T20:23:47 | v    | 45     |  >20.80 (3-sigma)
2026-02-27T20:23:47 | r    | 45     |   20.13 +/- 0.25
2026-02-27T20:23:47 | z    | 45     |  >20.28 (3-sigma)
```
-------------------------------------------------------------------------------------------------
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 Mephisto mosaic cameras were installed in October 2025. The first light was achieved in all three channels on 10 October 2025, and these are currently in the commissioning phase. Here, we note that the current data processing pipeline is still at a preliminary stage, with flux calibration precision in each band at the level of about 5% or even higher.
-------------------------------------------------------------------------------------------------
GCN Circular #43894
A. Volnova (IKI), A. Pozanenko (IKI), E. Klunko (ISTP), N. Pankov (IKI) report on behalf of IKI-GRB-FuN:
We observed the field of the fast X-ray transient EP260227a (Wang et al., GCN 43869) with the AZT-33IK 1.5m telescope of the Mondy observatory starting on 2026-02-28 (UT) 20:55:14 and taking several 90-seconds frames in the R band. The optical counterpart (Eyles-Ferris et al., GCNs 43867, 43877, 43888; Li et al., GCN 43868; Fu et al., GCN 43873; Mandarakas et al., GCN 43874; Eyles-Ferris and Tanvir, GCN 43875; Malesani et al., GCN 43876; Strausbaugh et al., GCN 43879; Bochenek et al., GCN 43880; Gassert et al., GCN 43881; Gupta et al., GCN 43884; Ma et al., GCN 43887; Zhong et al., GCN 43891) is barely detected in the stacked frame. Preliminary photometry and observational details are the following:
```
Date        UT start  t-T0      Exp.    Filter Obj.   S/N  UL(3 sigma)
                     (mid,days) (n*s)                      (3sigma)
2026-02-28  20:55:14  1.05053   40*90   R      21.8   2.5   21.5
```
The photometry is based on several nearby stars from the USNO-B1 catalogue (R2 magnitudes) and is not corrected for the Galactic extinction.
GCN Circular #43905
R. A. J. Eyles-Ferris (Leicester), J. Quirola-Vasquez (Radboud), G. Corcoran (UCD), A. Martin-Carrillo (UCD), P. G. Jonker (Radboud), , A. J. Levan (Radboud), D. B. Malesani (DAWN/NBI and Radboud) report on behalf of a larger collaboration:
We observed the optical counterpart of the fast X-ray transient EP260227a (Wang et al., GCN 43869) with the Gemini-South telescope equipped with the GMOS-S instrument, obtained 12x60 s exposures in the r band starting at 2026-03-03 05:52:34 UT (t_mid = 81.9 hr).
In our stacked image, we detect a faint source coincident with the optical counterpart (Eyles-Ferris et al., GCN 43867; Li et al., GCN 43868; Fu et al, GCN 43873; Mandarakas et al., GCN 43874; Eyles-Ferris and Tanvir et al., GCN 43875; Malesani et al., GCN 43876; Eyles-Ferris et al., GCN 43877; Strausbaugh et al., GCN 43879; Bochenek et al., GCN 43880; Gassert et al., GCN 43881; Gupta et al., GCN 43884; Ma et al., GCN 43887; Eyles-Ferris et al., GCN 43888; Zhong et al., GCN 43891; Volnova et al., GCN 43894). In our preliminary photometry, we measure an AB magnitude of r = 24.80 +/- 0.33 calibrated to Pan-STARRS and not corrected for Galactic extinction. It is unclear at this stage whether this is continued transient emission or the underlying host galaxy.

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Jochen Greiner, last update: 03-Mar-2026 [Disclaimer]