EP261105a
GCN Circular 46172
Subject
EP261105a: PRIME near-infrared upper limit
Date
2026-11-06T14:40:17Z (8 hours ago)
From
N. Passaleva at Sapienza University of Rome <niccolo.passaleva@uniroma1.it>
Via
Web form
N. Passaleva (U Rome), J. Durbak (UMD), O. Guiffreda (UMD), M. El Kabir (U Rome), E. Troja (U Rome), A. S. Kutyrev (NASA/GSFC), S. B. Cenko (NASA/GSFC)
We observed the field of EP261105a detected by Einstein Probe (Guo et al., GCN 46155; Guo et al. 46168) in H and Y filters with PRIME. Observations started ~12h after the trigger.
At the position of the candidate optical afterglow reported by SVOM/VT (Ma et al., GCN 46160) we do not detect any new source down to H>20.3 AB (3-sigma), calibrated Using Two Micron All Sky Survey (2MASS) nearby stars and not corrected for galactic extinction.
PRIME is a 1.8m telescope with 1.56 square degree FOV (0.5 arcsec/pixel) located in Sutherland, South Africa at the South African Astronomical Observatory (SAAO) (Kutyrev et al. 2023, Yama et al. 2023, Durbak et al. 2024).
We thank the Osaka University observers at PRIME and the staff at SAAO for their support with these observations.
GCN Circular 46170
Subject
EP261105a: VLT/FORS2 optical detection
Date
2026-11-06T11:52:47Z (11 hours ago)
From
Roberto Ricci at INAF-IRA <ricci@ira.inaf.it>
Via
Web form
Hira Waseem, Muskan Yadav, Nicolas Monsalves, Narges Shahamat, Roberto Ricci, Niccolò Passaleva, Yuhan Yang, and Eleonora Troja (U Rome) report on behalf of the ERC BHianca team:
We observed the field of EP261105a detected by Einstein Probe (Guo et al., GCN 46155; Guo et al. 46168) with the FORS2 imager on the ESO VLT UT1 (Antu). FORS2 observations began on 2026-11-06 at 04:10 UT, 18.0 hours after the trigger and were carried out in the R-band at an average airmass ~1.5 and with an average seeing ~0.6 arcsec.
At the position of the candidate optical afterglow reported by SVOM/VT (Ma et al., GCN 46160) we detect a source with R ~ 24.3 AB mag, consistent with the non-detection reported by LCO at 2.6 hours (van Hoof et al., GCN 46162). Compared with the SVOM/VT detection (VT_R = 22.3 at 0.85 hours; Ma et al., GCN 46160), our measurement implies a power-law decay with temporal index alpha ~ -0.5. Magnitudes are calibrated using nearby stars in the Legacy Survey DR10 catalog (Dey et al. 2019), and are not corrected for Galactic extinction.
No catalogued source is visible at the position of the optical counterpart, implying that any underlying galaxy would be faint. We note that the counterpart is located ~4 arcsec from the centre of a bright (r~18 AB mag) galaxy with photometric redshift of z = 0.055 +/- 0.014 in the Legacy Survey DR10. The chance coincidence probability for this galaxy is P_cc ~ 0.01 (Bloom et al. 2002) . If the association is confirmed, the projected offset corresponds to ~4.5 kpc at z = 0.055.
Further observations are planned.
We thank the staff at the VLT for the rapid execution of these observations.
GCN Circular 46168
Subject
EP261105a: refined analysis of the EP-WXT and follow-up EP-FXT observations
Date
2026-11-06T08:33:37Z (15 hours ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
C. L. Guo, B. B. Zhang, Q.Y. Wu, W.D. Zhang (NAO, CAS), Y. Q. Zhao(PRIC, USTC)
on behalf of the Einstein Probe (EP) team:
The fast X-ray transient EP261105a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Guo et al., GCN 46155), and followed by several telescopes (Ma et al. GCN 46160, van Hoof et al. GCN 46162, Buckley et al. GCN 46165). The WXT observation started at T0=2026-11-05 10:03:24 (UTC), and lasted for around 270 s before being interrupted by autonomous follow-up. The WXT light curve shows an increase in flux from about T0+180 s, and starts to decreas from about T0+200 s. The average WXT 0.5–4 keV spectrum can be fitted with an absorbed power-law model with a fixed Galactic hydrogen column density of 4.84 × 10^20 cm^−2 and a photon index of 0.92 (+0.83/−0.77). The derived average unabsorbed 0.5–4 keV flux is 2.58 (+1.75/−1.14) × 10^−10 erg s^−1 cm^−2.
The autonomous follow-up observation with the Follow-up X-ray Telescope (FXT) on board EP started at 2026-11-05 10:10:39 (UTC), 435 s after T0. The exposure time was 4354 s. The on-ground analysis of the FXT data detected an uncatalogued X-ray source at R.A. = 91.0018 deg, DEC = -54.2637 deg (J2000), with an uncertainty of 10 arcsec in radius (90% C.L., including statistical and systematic uncertainties). The average FXT 0.5–10 keV spectrum can be fitted with an absorbed power-law model with a fixed Galactic hydrogen column density of 4.84 × 10^20 cm^−2 and a photon index of 2.11 (+0.11/−0.11). The derived average unabsorbed 0.5–10 keV flux is 4.12 (+0.30/−0.28) × 10^−12 erg s^−1 cm^−2. The uncertainties quoted above are at the 90% confidence level.
Launched on January 9, 2024, EP is a space X-ray observatory designed 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 46165
Subject
EP261105a: Global MASTER-Net observations report
Date
2026-11-05T23:09:25Z (a day ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
Via
email
D.Buckley (SAAO),
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 (Lomonosov MSU)
A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity)
A.Sosnovskij (Lomonosov MSU)
A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory)
L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez,
A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory)
R.Rebolo (The Instituto de Astrofisica de Canarias)
O.Gress, N.Budnev(ISU)
M. Segura, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA)
MASTER-SAAO robotic telescope [1] located in South Africa (South African Astronomical Observatory) was pointed to the EP261105a ( EP Team at NAOC/CAS <ep_ta@bao.ac.cn> et al., GCN 46155) errorbox 38697 sec after notice time and 46304 sec after trigger time at 2026-11-05 22:59:38 UT, with upper limit up to 19.5 mag. The observations began at zenith distance = 36 deg. The sun altitude is -40.8 deg.
The galactic latitude b = -28 deg., longitude l = 262 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=3532321
We obtain a following upper limits.
Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________
46335 | 2026-11-05 22:59:38 | MASTER-SAAO | (06h 02m 58.52s , -54d 29m 16.9s) | C | 60 | 18.6 |
46395 | 2026-11-05 22:59:38 | MASTER-SAAO | (06h 02m 58.52s , -54d 29m 16.9s) | C | 180 | 19.5 | Coadd
46335 | 2026-11-05 22:59:39 | MASTER-SAAO | (05h 59m 51.92s , -54d 13m 30.1s) | C | 60 | 18.3 |
46395 | 2026-11-05 22:59:39 | MASTER-SAAO | (05h 59m 51.93s , -54d 13m 30.0s) | C | 180 | 19.4 | Coadd
46427 | 2026-11-05 23:01:11 | MASTER-SAAO | (06h 03m 01.41s , -54d 27m 57.4s) | C | 60 | 18.8 |
46427 | 2026-11-05 23:01:11 | MASTER-SAAO | (05h 59m 54.89s , -54d 12m 11.8s) | C | 60 | 18.5 |
46524 | 2026-11-05 23:02:48 | MASTER-SAAO | (06h 02m 56.04s , -54d 28m 48.6s) | C | 60 | 18.8 |
46524 | 2026-11-05 23:02:48 | MASTER-SAAO | (05h 59m 49.31s , -54d 13m 03.7s) | C | 60 | 18.6 |
46617 | 2026-11-05 23:04:20 | MASTER-SAAO | (06h 02m 54.37s , -54d 27m 49.7s) | C | 60 | 18.9 |
46617 | 2026-11-05 23:04:20 | MASTER-SAAO | (05h 59m 47.59s , -54d 12m 05.2s) | C | 60 | 18.6 |
46709 | 2026-11-05 23:05:53 | MASTER-SAAO | (06h 03m 01.54s , -54d 28m 50.1s) | C | 60 | 19.0 |
46710 | 2026-11-05 23:05:53 | MASTER-SAAO | (05h 59m 54.54s , -54d 13m 05.7s) | C | 60 | 18.8 |
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 46162
Subject
EP261105a: LCO optical upper limits
Date
2026-11-05T17:07:33Z (a day ago)
From
J. Sánchez-Sierras at Radboud University <javisansie@gmail.com>
Via
Web form
A. P. C. van Hoof (Radboud), G. Corcoran (UCD), J. Sanchez-Sierras (Radboud), A. Martin-Carrillo (UCD), P. G. Jonker (Radboud) report on behalf of a larger collaboration:
We observed the field of the fast X-ray transient EP261105a detected by Einstein Probe (Guo et al., GCN 46155) with the LCO 1-m telescope located at Siding Spring (Australia) and equipped with the SINISTRO instrument. Observations consisted of a sequence of 9 x 300 s exposures in SDSS r-band and started at 2026-11-05 at 12:41:00 UT (~2.55 h after the trigger).
We performed image subtraction against archival Legacy Survey and Skymapper images. We do not detect any new source inside the Einstein Probe Follow-up X-ray Telescope uncertainty region, including the counterpart candidate detected by Ma et al. (GCN 46160), down to a 3-sigma upper limiting magnitude of:
r > 23.0
This upper limit is in AB magnitude, calibrated using nearby stars from the Legacy Survey catalogue, and is not corrected for Galactic extinction.
GCN Circular 46160
Subject
EP261105a: SVOM/VT optical candidate
Date
2026-11-05T15:11:02Z (a day ago)
From
Yinuo Ma <mayn@bao.ac.cn>
Via
Web form
Y. N. Ma, H. L. Li, L. P. Xin, Y. L. Qiu, C. Wu, Z. H. Yao, J. R. Xu, X. H. Han, Y. Xu, J. Wang, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, 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 EP261105a detected by EP/WXT (Guo et al., GCN 46155). SVOM/VT began observing the field at 2026-11-05T10:51:11 UTC, 0.72 hours after the trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
With X-band data available, an uncatalogued candidate (compared to the Legacy Survey), within the 20 arcsec EP/FXT error circle (Guo et al., GCN 46155), is detected in our stacked VT_R image at coordinates R.A., Dec. 91.00143, -54.26428 degrees, corresponding to:
R.A. (J2000)= 06:04:00.34
Dec. (J2000)= -54:15:51.38
with an uncertainty of ~0.5 arcsec.
The preliminary photometric measurements in AB magnitudes are as follows:
mid time (h) | exposure time (s) | band | mag (AB)
-------------|-------------------|------|-----------------
0.87 | 20*50 | VT_B | >23.1 (3-sigma)
0.85 | 18*50 | VT_R | 22.3+/-0.2
Our photometry was not corrected for Galactic extinction. More detailed investigation will be performed once more data are available.
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 46155
Subject
EP261105a: Einstein Probe detection of an X-ray transient
Date
2026-11-05T12:13:57Z (a day ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
C.L. Guo, B.B. Zhang(NAO, CAS), Y. Q. Zhao(PRIC, USTC), Q. Y. Wu, W. D. Zhang(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 EP261105a. The transient triggered EP-WXT (ID: 01709322270) at 2026-11-05T10:07:54(UTC). The WXT position of the source is R.A. = 91.013 deg, DEC = -54.231 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. = 91.0035 deg, DEC = -54.2664 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic).
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).