EP260116a
GCN Circular 43491
Subject
EP260116a: COLIBRÍ further observations
Date
2026-01-21T19:38:30Z (11 days ago)
Edited On
2026-01-21T20:14:00Z (11 days ago)
From
Alan Watson at UNAM <alan@astro.unam.mx>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of Alan Watson at UNAM <alan@astro.unam.mx>
Via
Web form
Alan M. Watson (UNAM), 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), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM) report:
We observed the field of EP260116a (Wang et al., GCN Circ. 43424) with the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope from 2026-01-21 03:47 to 07:39 UTC (from 123.6 to 127.5 hours after the trigger) and obtained 99 and 171 minutes of exposure in the r and z filters, respectively. The observing conditions were good.
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 source we have previously reported (Butler et al., GCN Circ 43459; Watson et al., GCN Circ 43480) is clearly detected with preliminary magnitudes of
r = 23.09 +/- 0.06,
z = 23.10 +/- 0.13.
Considering all of our data, the rebrightening we tentatively reported (Watson et al., GCN Circ 43480) is not confirmed and the data seem to be best explained by a simple flattening.
We also note that while this source is within the WXT error regions, it is not within the FXT error region (Wang et al., GCN Circ. 43424). We do not consider it to be associated with EP 260116a.
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 43480
Subject
EP260116a: COLIBRÍ observations of a tentative optical rebrightening
Date
2026-01-20T18:36:58Z (12 days ago)
From
Alan Watson at UNAM <alan@astro.unam.mx>
Via
Web form
Alan M. Watson (UNAM), Noémie Globus (UNAM), Nathaniel R. Butler (ASU), Antonio de Ugarte Postigo (LAM) 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), 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 Benjamin Schneider (LAM) report:
We observed the field of EP260116a (Wang et al., GCN Circ. 43424) with the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope from 2026-01-20 03:54 to 08:25 UTC (from 99.7 to 104.3 hours after the trigger) and obtained 142 and 198 minutes of exposure in the r and z filters, respectively. Conditions were poor with variable transparency.
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.
Compared to our observations on the previous night (Butler et al., GCN Circ 43459), we measure an apparent rebrightening of
Delta r = -0.17 +/- 0.11
Delta z = -0.30 +/- 0.21
Individually, these apparent rebrightenings are only at the level of about 1.5 sigma. However, together they point to a possibly more significant result, minimally that the decay seen previously appears to have slowed.
Further observations are planned and encouraged.
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 43459
Subject
EP260116a: COLIBRÍ detection of a fading optical source
Date
2026-01-19T21:20:37Z (13 days ago)
Edited On
2026-01-20T18:19:41Z (12 days ago)
From
Alan Watson at UNAM <alan@astro.unam.mx>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of Alan Watson at UNAM <alan@astro.unam.mx>
Via
Web form
Nathaniel R. Butler (ASU), Noémie Globus (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), Rosa L. Becerra (UNAM), 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), Benjamin Schneider (LAM), and Antonio de Ugarte Postigo (LAM) report:
We observed the field of EP260116a (Wang et al., GCN Circ. 43424) obtained with the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope on the nights of 2026 January 17, 18, and 19 UTC at median times of 30.8, 52.4, and 78.7 hours after the trigger and obtained 80, 96, and 128 minutes, respectively, 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.
We reported preliminary results from the first night in Magnani et al. (GCN Circ. 43436). In contrast to our initial analysis, a refined reprocessing and the subsequent follow up observations have revealed a fading optical source located within the EP/WXT error region (Wang et al., GCN Circ. 43424) at the coordinates RA = 07:35:14.14, Dec = +06:20:14.3 (J2000).
At the last epoch, we measure preliminary magnitudes of
r = 23.22 +/- 0.06,
z = 22.81 +/- 0.14.
Including these observations together with the two earlier epochs, we model the temporal evolution of the source flux with a power-law decay. We find Flux_r = t^(−0.33 +/- 0.12) and Flux_z = t^(-0.53 +/- 0.23).
The source therefore exhibits a slow but consistent decay, which is statistically significant and supports its interpretation as the fading optical counterpart of EP 260116a.
No existing source is visible at this position in the PS1 images.
Further observations are planned.
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 43436
Subject
EP 260116a: COLIBRÍ optical upper limit
Date
2026-01-17T10:52:27Z (16 days ago)
From
Francesco at Aix-Marseille Université, CPPM/CNRS <francesco.magnani.work@gmail.com>
Via
Web form
Francesco Magnani (CPPM), Leonardo García García (UNAM), Stéphane Basa (UAR Pytheas), Jean-Luc Atteia (IRAP), William H. Lee (UNAM), Alan M. Watson (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), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Asuka Kuwata (UNAM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM):
We imaged the field of the EP 260116a (C. Wang at al., GCN Circ. 43424) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-01-17 06:05:01 to 07:29:06 UTC (from 29.9 to 31.3 hours after the trigger) and obtained 64 minutes of simultaneous exposure in the r, z filters.
The data were reduced and coadded with the COLIBRÍ pipeline and analysed 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.
In the stacked image, we do not detect any new optical source at the EP/WXT error region (C. Wang et al., GCN Circ. 43424) down to the following 3-sigma limit:
r > 23.52
z > 22.44
This upper limit is consistent with the one reported by Junjie-Jin et al. (GCN Circ. 43425), V. Lipunov et al. (GCN Circ. 43427), A. Gupta et al. (GCN Circ. 43430), and A. Bochenek et al. (GCN Circ. 43432).
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 43432
Subject
EP260116a: Liverpool Telescope upper limits
Date
2026-01-16T23:35:52Z (16 days ago)
From
A. Bochenek at Liverpool John Moores University <a.m.bochenek@2023.ljmu.ac.uk>
Via
Web form
A. Bochenek and D. A. Perley (LJMU) report:
We observed the field of the fast X-ray transient EP260116a (Wang et al., GCN 43424) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 5x100s exposures in the SDSS r and i filters starting at 2026-01-16 21:52:40 UT, approximately 21.7 hours post trigger.
Two exposures taken in i-band had to be discarded due to poor seeing. We performed image subtraction of the stacked images of remaining exposures in each filter against Pan-STARRS using PSF matching with the help of PSFEx. We do not detect any new objects within the EP/WXT error region of the transient (Wang et al., GCN 43424). The 3-sigma limiting magnitude on the stacked images is r > 22.5 mag and i > 21.9 mag.
GCN Circular 43430
Subject
EP260116A: 1.3m DFOT optical upper limit
Date
2026-01-16T21:53:31Z (16 days ago)
From
ANSHIKA GUPTA at ARIES <anshika05180@gmail.com>
Via
Web form
Anshika Gupta, Kuntal Misra, Tarak Chand, Debalina Kar, Dhruv Jain, and Pankaj Pawar (ARIES) report:
We observed the field of EP260116A detected by EP/WXT (EP Team, GCN 43424) with the 1.3m Devasthal Fast Optical Telescope (DFOT), located at the Devasthal Observatory of the Aryabhatta Research Institute of Observational Sciences (ARIES), India. The observations began on 2026-01-16 at 19:01:13 UT, i.e., ~18.87 hours after the EP trigger. We have taken multiple frames with an exposure time of 300s in the R filter. We stacked the images after the alignment. No uncatalogued source is detected in our stacked image within the EP/WXT error box (EP Team, GCN 43424). We obtain the following 3-sigma upper limit in the stacked image:
Date Start_UT T_start-T0 (hour) Filter Exp time (s) Magnitude
===============================================================
2026-01-16 19:01:13 ~18.87 R 300s*12 >23.0
The non-detection of the burst is consistent with Junjie-Jin et al. 2026 (GCN 43425); Lipunov et al. 2026 (GCN 43427).
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 catalogue.
GCN Circular 43427
Subject
EP260116a: Global MASTER-Net observations report
Date
2026-01-16T17:09:27Z (16 days 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-Tunka robotic telescope [1] located in Russia (Applied Physics Institute, Irkutsk State University) was pointed to the EP260116a ( EP Team et al., GCN 43424) errorbox 16387 sec after notice time and 59243 sec after trigger time at 2026-01-16 16:36:14 UT, with upper limit up to 19.6 mag. The observations began at zenith distance = 44 deg. The sun altitude is -58.9 deg.
The galactic latitude b = 13 deg., longitude l = 213 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=3104022
We obtain a following upper limits.
Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________
59273 | 2026-01-16 16:36:14 | MASTER-Tunka | (07h 33m 54.24s , +06d 54m 24.5s) | C | 60 | 18.3 |
59273 | 2026-01-16 16:36:14 | MASTER-Tunka | (07h 34m 21.60s , +06d 48m 07.1s) | C | 60 | 18.8 |
59333 | 2026-01-16 16:36:14 | MASTER-Tunka | (07h 34m 21.60s , +06d 48m 07.2s) | C | 180 | 19.5 | Coadd
59351 | 2026-01-16 16:37:32 | MASTER-Tunka | (07h 34m 00.18s , +06d 53m 22.7s) | C | 60 | 18.3 |
59351 | 2026-01-16 16:37:32 | MASTER-Tunka | (07h 34m 27.46s , +06d 47m 05.3s) | C | 60 | 18.8 |
59425 | 2026-01-16 16:38:45 | MASTER-Tunka | (07h 33m 55.76s , +06d 52m 20.0s) | C | 60 | 18.5 |
59425 | 2026-01-16 16:38:45 | MASTER-Tunka | (07h 34m 23.07s , +06d 46m 03.1s) | C | 60 | 18.8 |
59499 | 2026-01-16 16:39:59 | MASTER-Tunka | (07h 34m 01.62s , +06d 52m 23.8s) | C | 60 | 18.5 |
59499 | 2026-01-16 16:39:59 | MASTER-Tunka | (07h 34m 28.91s , +06d 46m 06.5s) | C | 60 | 19.0 |
59559 | 2026-01-16 16:39:59 | MASTER-Tunka | (07h 34m 28.91s , +06d 46m 06.5s) | C | 180 | 19.6 | Coadd
59572 | 2026-01-16 16:41:13 | MASTER-Tunka | (07h 33m 57.80s , +06d 54m 14.6s) | C | 60 | 18.5 |
59572 | 2026-01-16 16:41:13 | MASTER-Tunka | (07h 34m 25.14s , +06d 47m 57.4s) | C | 60 | 19.0 |
59647 | 2026-01-16 16:42:27 | MASTER-Tunka | (07h 33m 57.89s , +06d 52m 28.8s) | C | 60 | 18.5 |
59647 | 2026-01-16 16:42:27 | MASTER-Tunka | (07h 34m 25.22s , +06d 46m 11.7s) | C | 60 | 19.0 |
59721 | 2026-01-16 16:43:41 | MASTER-Tunka | (07h 34m 01.50s , +06d 53m 59.9s) | C | 60 | 18.6 |
59721 | 2026-01-16 16:43:41 | MASTER-Tunka | (07h 34m 28.85s , +06d 47m 42.9s) | C | 60 | 19.0 |
59795 | 2026-01-16 16:44:56 | MASTER-Tunka | (07h 33m 55.46s , +06d 53m 09.1s) | C | 60 | 18.4 |
59795 | 2026-01-16 16:44:56 | MASTER-Tunka | (07h 34m 22.81s , +06d 46m 52.3s) | C | 60 | 18.9 |
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 43425
Subject
EP260116a: Xinglong optical upper limit
Date
2026-01-16T16:49:09Z (16 days ago)
From
Xinglong Observatory at National Astronomical Observatories (NAOC), Chinese Academy of Sciences (CAS) <xinglong@nao.cas.cn>
Via
Web form
Junjie-Jin (NAOC), Haiyang-Mu (NAOC), Sen-Liu (NAOC), Pengliang-Du (NAOC),
Zhou-Fan (NAOC), Hong-Wu (NAOC) report:
Following the detection of EP260116a by EP-WXT (GCN Circular 43424), we observed the field of EP260116a using the 2.16-m
telescope at Xinglong Observatory, NAOC. We obtained 3x300s clear-band frames with a
median time of 2026-01-16T15:26:52 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 43424), down to 5-sigma limiting magnitudes of N ~
20.8, calibrated with Pan-STARRS sources in the field. Also there is no apparent brightening
for the catalogued sources within the error circle.
GCN Circular 43424
Subject
EP260116a: Einstein Probe detection of an X-ray transient
Date
2026-01-16T12:01:43Z (17 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
C. Wang, Z. X. Li, G. L. Huang, J. Y. Cao (IHEP), Y. H. Jiang (NJU), 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 EP260116a. A significant outburst is observed in the WXT light curve. The transient triggered EP-WXT (ID: 01709251336) at 2026-01-16T00:08:51 (UTC). The WXT position of the source is R.A. = 113.768 deg, DEC = 6.329 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic).
The average WXT 0.5 - 4 keV spectrum can be fitted with an absorbed power law with a hydrogen column density of 7.65 x 10^20 cm^-2 and a photon index of 1.77. The derived average unabsorbed 0.5-4 keV flux is 7.16 x 10^-11 erg/s/cm^2.
A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed automatically with a 24-minute delay, starting at 2026-01-16 00:32:38 (UTC), by which time the outburst had already ended. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 113.7617 deg, DEC = 6.3244 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic).
The average FXT 0.5 - 10.0 keV spectra can also be fitted with an absorbed power law with the same hydrogen column density and a photon index of 1.98. The derived average unabsorbed 0.5-10.0 keV flux is 9.52 x 10^-14 erg/s/cm^2.
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).