GRB 260228A

A. Saccardi (CEA/Irfu), Y. Julakanti (Univ. Leicester), D. Turpin (CEA/Irfu), J.-L. Atteia (IRAP), D. B. Malesani (DAWN/NBI and Radboud), Y. H. Cheng (SWIFAR, YNU), R. A. J. Eyles-Ferris (Univ. Leicester) report on behalf of the SVOM and Einstein Probe teams:

We performed a second observation at the location of the SVOM/ECLAIRs GRB 260228A (Julakanti et al., GCN 43882
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 ) with the Follow-up X-ray Telescope (FXT) on board the Einstein Probe (EP) mission. The observation started on 2026-03-04 at 19:25:58 UT (3.94 days after the trigger) with a total exposure time of ~6000 s.

All six sources detected by EP/FXT during the first visit (Cheng et al., GCN 43900
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 ) are detected in the second epoch data set. The brightest of them (EPF_J155124.0+262035; error radius of 10 arcsec) has faded by a factor of ~10, down to a flux of (1.92 +/- 0.47) x 10^-13 erg/s/cm^-2 (0.5-10 keV; 1-sigma uncertainty).

The fading behavior of this X-ray source confirms it as the afterglow of GRB 260228A.

The early deep optical limits measured by SVOM/VT (Li et al., GCN 43886
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 ), compared to the bright X-ray flux (Cheng et al., GCN 43900
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 ), suggest that this could be a dark GRB.

We encourage multi-wavelength follow-up observation of this source.

​​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).

M. G. Bernardini (INAF-OAB, LUPM), M. Brunet, J.-L. Atteia, O. Godet (IRAP), W. J. Xie (NAOC), Y. Julakanti, R. A. J. Eyles-Ferries (Leicester Univ.) report on behalf of the SVOM/ECLAIRs team:

Using the event-by-event data downloaded through the X-band ground station, we report further analysis of ECLAIRs observations of GRB 260228A (SVOM burst-id 26022802).

The burst that triggered ECLAIRs onboard (GCN 43882
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 ) consists of a double-peaked pulse with a duration of T90 = (18.3 -4.0/+16.0) s in the 4-120 keV energy band. Since the GRB is observed mainly below 20 keV, we also computed the duration in the 4-20 keV energy band: T90 = (22.9 -4.2/+9.4) s.

The time-averaged spectrum from T0+7 s to T0+31 s (T0 = 2026-02-28T20:55:34.620) in the energy range 5-120 keV is best fitted by a broken power-law model with alpha_1 = (-1.33 -0.43/+0.34), alpha_2 = (-2.83 -0.33/+0.37) and E_break = (9.6 -0.9/+1.2) keV. With this model, the total 4-120 keV fluence is (4.27 -2.6/+0.2)E-7 erg/cm^2. 

All the quoted errors are at the 68% confidence level.

With these parameters, the Eiso ranges from 1.6E49 erg assuming z=0.1 to 8.6E52 erg at z=10. The location of GRB 260228A in the Amati plane for different redshifts is available here: https://drive.google.com/file/d/1FfPqOo6kSt6L5QR-DGjUvxdrTwvSlPfT/view?usp=sharing

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. ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC.

The SVOM/ECLAIRs point of contact for this burst is: Maria Grazia Bernardini (INAF-OAB, LUPM) (maria.bernardini at inaf.it)

Y.H.Cheng, D.Zhu, K.J.Zhang (SWIFAR, YNU), H.C.Ding, T.Wu (AHNU), C.C.Jin (NAOC) on behalf of the Einstein Probe (EP) team:

EP-FXT performed a follow-up observation of the SVOM/ECLAIRs-detected burst GRB 260228A (SVOM/sb26022802; Julakanti et al., GCN 43882
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 ) starting at 2026-02-28T22:50:15 UTC, approximately 5 minutes after the SVOM trigger, with a total exposure time of 5527 s. Six uncataloged sources are detected within the ECLAIRs error circle. Preliminary analysis on these sources is automatically conducted, and the details are listed as follows. 

EPF_J155124.0+262035
RA (J2000): 237.8501
Dec (J2000): 26.3431
Flux: 2.1373 x 10^-12 erg/s/cm2 (observed, 0.5-10 keV)
Flux_err: 1.6673 x 10^-13 erg/s/cm2 (1 sigma)

EPF_J155105.1+261820
RA (J2000): 237.7711
Dec (J2000): 26.3055
Flux: 9.6351 x 10^-14 erg/s/cm2 (observed, 0.5-10 keV)
Flux_err: 1.891 x 10^-14 erg/s/cm2 (1 sigma)

EPF_J155123.9+261238
RA (J2000): 237.8498
Dec (J2000): 26.2105
Flux: 7.077 x 10^-14 erg/s/cm2 (observed, 0.5-10 keV)
Flux_err: 1.6973 x 10^-14 erg/s/cm2 (1 sigma)

EPF_J155130.8+261248
RA (J2000): 237.8781
Dec (J2000): 26.2134
Flux: 1.231 x 10^-13 erg/s/cm2 (observed, 0.5-10 keV)
Flux_err: 2.1478 x 10^-14 erg/s/cm2 (1 sigma)


EPF_J155140.7+261349
RA (J2000): 237.9195
Dec (J2000): 26.2303
Flux: 1.5723 x 10^-13 erg/s/cm2 (observed, 0.5-10 keV)
Flux_err: 3.1532 x 10^-14 erg/s/cm2 (1 sigma)

EPF_J155148.8+262150
RA (J2000): 237.9533
Dec (J2000): 26.3640
Flux: 1.0194 x 10^-13 erg/s/cm2 (observed, 0.5-10 keV)
Flux_err: 2.9166 x 10^-14 erg/s/cm2 (1 sigma)


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).

S. Guziy (IAA-CSIC), Y.-D. Hu (GXU), M.D. Caballero-García, M. Gritsevich, I. Pérez-García, R. Sánchez-Ramírez, S-Y. Wu (IAA-CSIC), G. García-Segura (UNAM), M. Blazek, I. Vico (CAHA) and A.J. Castro-Tirado (IAA-CSIC), on behalf of a larger collaboration, report:

Following the detection of GRB 260228A by SVOM/ECLAIRs (Julakanti et al., GCNC 43882), we triggered the 2.2 m CAHA telescope (+ CAFOS) at the Calar Alto Observatory (Almería, Spain). Images were obtained starting on Mar. 1 at 03:34 UT (i.e., ~6.7 hours after the trigger) in the Sloan griz bands covering the entire error region. In the co-added images (60 × 6 s), no optical transient is detected down to limiting magnitudes of 22.1 mag (r') and 21.0 (i'). This non-detection is consistent with the reports from SVOM/VT (Li et al., GCNC 43886) and SVOM/COLIBRÍ (Mandarakas et al. GCNC 43892).

We thank the staff at Calar Alto Observatory for their excellent support.

Nikos Mandarakas (LAM), Margarita Pereyra (UNAM), Nathaniel R. Butler (ASU), Rosa L. Becerra (UNAM), Alan M. Watson (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), 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), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM), Yashaswi Julakanti (U. Leicester), Rob Eyles-Ferris(U. Leicester) report:

We imaged the field of the SVOM GRB 260228A (Julakanti et al., GCN Circ. 43882
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 ) using the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2026-03-01 07:28 to 11:52 UTC (from 10.55 to 14.96 hours after the trigger) and obtained 120 minutes of exposure in the r filter and 129 minutes of exposure in the z filter.

The data were reduced, coadded, calibrated, and analysed with the COLIBRÍ ASU pipeline. The photometry was calibrated using nearby stars from the Pan-STARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction.

In the stacked image, comparing to Pan-STARRS and Legacy Survey (Dey et al. 2019) images, we do not detect any new source within the ECLAIRs uncertainty region (Julakanti et al., GCN Circ. 43882
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 ) down to the following 5-sigma limits:

r > 23.3 
z > 22.5

This upper limit is consistent with the one reported by Li et al. (GCN Circ. 43886
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 ).

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.

H. L. Li, Z. H. Yao, C. Wu, Y. N. Ma, Y. L. Qiu, L. P. Xin, X. H. Han, J. Wang, Y. Xu, 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/Irfu), A. Li (BNU), Z. M. Wang (BNU), Y. Julakanti (Univ. Leicester) and R. Eyles-Ferris (Univ. Leicester) report on behalf of the SVOM/VT team.

SVOM/VT performed an observation with automatic slew to the field of GRB 260228A triggered by SVOM/ECLAIRs (sb26022802, Julakanti et al., GCN 43882
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 ). The observation started at 2026-02-28T21:50:40 UTC, i.e., about 55 minutes post trigger in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously. 

No uncatalogued sources were detected within the ECLAIRs error box (Julakanti et al., GCN 43882
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 ), compared to the Legacy Survey catalog. The 3 sigma upper limits are derived as follows:

Mid time   | Band | Exposure Time | 3 sigma upper limit
1.155 hour   VT_B     35*50 sec      > 23.3 mag    
1.169 hour   VT_R     34*50 sec      > 23.0 mag

More detailed analysis is still ongoing. 

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.

Y. Julakanti, R. Eyles-Ferris (Univ. Leicester), S. Schanne (CEA/IRFU), H. Yang (IRAP), M.-G. Bernardini (INAF-OAB, LUPM) report on behalf of the SVOM mission team:

At 2026-02-28T20:55:55 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 260228A (SVOM burst-id sb26022802).

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

The burst was only detected by the Image Trigger (IMT), which produced a sequence of 7 alerts. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 10.64 in the 5-20 keV energy band over a time window of 40.96 seconds starting at 2026-02-28T20:55:34 (Tb).

The localization of the best alert is R.A., Dec. 237.8312, 26.3060 degrees:
R.A. (J2000) = 15h51m19.50s
Dec. (J2000) = 26d18m21.48s
 with a 90% confidence level (C.L.) radius of 7.51 arcmin (including systematic error of 2 arcmin added in quadrature).

The SVOM/ECLAIRs light curve showed a single broad peak structure in the Energy bands 5-8 and 8-20 keV only. The T90 duration computed in 5-120 keV is (16.6 -3.5/+7.2) s.

SVOM slewed to the burst.

No X-ray observation could be performed by SVOM/MXT for the time being because of Earth occultation.

No optical observation could be performed by SVOM/VT for the time being.

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. SVOM/ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. SVOM/GRM was developed by the Institute of High Energy Physics (IHEP) of CAS. SVOM/MXT was developed jointly by CNES, CEA-IRFU, CNRS-IJCLab, University of Leicester, MPE.

The Burst Advocate (BA) on shift for this alert is Yashaswi Julakanti: skyj1@leicester.ac.uk.
Please contact the BA by email if you require additional information.