EP250111a
GCN Circular 38940
Subject
EP250111a: SAO RAS optical upper limit
Date
2025-01-14T15:52:04Z (a year ago)
From
Moskvitin Alexander at SAO RAS <mosk@sao.ru>
Via
Web form
A. S. Moskvitin and O. I. Spiridonova (SAO RAS),
report on behalf of the GRB follow-up team.
We observed the field of X-ray transient EP250111a detected by EP
(Zhao et al., GCN 38905) and Swift (Kennea et al., GCN 38910)
with the SAO RAS 1-m telescope Zeiss-1000 on January 11,
18:51:53--19:56:25 UT (t_mid - T0 = 18.057 hours = 0.7524 days).
We obtained 10 x 300 sec. images in Rc band.
We did not detect the OT (Fu et al., GCN 38906; Pankov et al.,
GCN 38913; Zheng et al., GCN 38916) in the stacked image
down to the limiting magnitude of R_lim > 21.15 (calibrated anainst
nearby USNO-B1 stars and not corrected for the MW extinction).
GCN Circular 38916
Subject
EP250111a: KAIT optical observations
Date
2025-01-12T05:08:43Z (a year ago)
From
Weikang Zheng at UC Berkeley <weikang@berkeley.edu>
Via
email
WeiKang Zheng (UCB), Xuhui Han (NAOC), Pinpin Zhang (NAOC) and
Alexei V. Filippenko (UCB) report on behalf of the KAIT GRB team:
The 0.76-m Katzman Automatic Imaging Telescope (KAIT), located at
Lick Observatory, observed the field of EP250111a (Zhao et al.,
GCN 38905) starting at 02:53:32 UT on 2025-01-11, ~1.55 hr after
the trigger. A set of clear (roughly R) band images were obtained.
We marginally detect the optical afterglow (Fu et al., GCN 38906;
Pankov et al., GCN 38913) in the 11x60s coadd image and measure
its brightness to be 20.5 +/- 0.3 (Vega) at a mid time of ~2.70 hr
after the trigger.
GCN Circular 38913
Subject
EP250111a: Mondy optical observation
Date
2025-01-11T23:14:49Z (a year ago)
From
Alexei Pozanenko at IKI, Moscow <grb.alex@gmail.com>
Via
email
N. Pankov (HSE, IKI), A. Pozanenko (IKI), E. Klunko (ISTP) report on
behalf of the IKI GRB FuN collaboration:
We performed optical observations of the field of EP250111a (Zhao et. al,
GCN 38905; Kennea et. al, GCN 38910) in the R filter with the 1.5-meter
AZT-33IK telescope of the Sayan Solar Observatory (Mondy). The observations
started on 2025-01-11 11:57 UT, i.e. ~0.46 days since trigger. We detect
the optical source proposed by Fu et. al, GCN 38906 as an optical transient
of EP250111a. Preliminary photometry of the source is the following:
Date UT start t-T0 Exp. Filter OT Err. UL(3sigma)
(mid, days) (s)
2025-01-11 11:57:42 0.46301 51*70 R 21.20 0.15 21.4
GCN Circular 38911
Subject
EP250111a: Global MASTER-Net observations report
Date
2025-01-11T16:27:37Z (a year ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
Via
email
V.Lipunov, E.Gorbovskoy, N.Tiurina, P.Balanutsa, , D.Vlasenko, I.Panchenko,
A.Kuznetsov, G.Antipov, A.Sankovich, A.Sosnovskij, Yu.Tselik, M.Gulyaev, 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. 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-Kislovodsk robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) was pointed to the EP250111a ( EP Team et al., GCN 38905) errorbox 22034 sec after notice time and 48770 sec after trigger time at 2025-01-11 14:53:34 UT, with upper limit up to 17.1 mag. Observations started at twilight. The observations began at zenith distance = 50 deg. The sun altitude is -10.3 deg.
The galactic latitude b = 20 deg., longitude l = 158 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=2740256
We obtain a following upper limits.
Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________
48800 | 2025-01-11 14:53:34 | MASTER-Kislovodsk | (06h 27m 26.49s , +56d 59m 55.8s) | C | 60 | 16.7 |
48845 | 2025-01-11 14:53:34 | MASTER-Kislovodsk | (06h 27m 26.49s , +56d 59m 55.8s) | C | 150 | 17.1 | Coadd
48880 | 2025-01-11 14:54:54 | MASTER-Kislovodsk | (06h 27m 31.58s , +57d 00m 09.6s) | C | 60 | 16.7 |
48945 | 2025-01-11 14:56:13 | MASTER-Kislovodsk | (06h 27m 29.58s , +57d 01m 53.7s) | C | 30 | 16.4 |
48994 | 2025-01-11 14:57:03 | MASTER-Kislovodsk | (06h 27m 30.55s , +57d 00m 00.6s) | C | 30 | 16.4 |
49059 | 2025-01-11 14:57:52 | MASTER-Kislovodsk | (06h 27m 34.60s , +57d 01m 58.6s) | C | 60 | 16.7 |
49139 | 2025-01-11 14:59:12 | MASTER-Kislovodsk | (06h 27m 27.57s , +57d 01m 01.9s) | C | 60 | 16.7 |
49218 | 2025-01-11 15:00:32 | MASTER-Kislovodsk | (06h 27m 27.53s , +57d 02m 04.4s) | C | 60 | 16.7 |
49299 | 2025-01-11 15:01:52 | MASTER-Kislovodsk | (06h 27m 32.46s , +57d 01m 06.5s) | C | 60 | 16.8 |
49378 | 2025-01-11 15:03:12 | MASTER-Kislovodsk | (06h 27m 26.35s , +57d 00m 09.3s) | C | 60 | 16.8 |
49458 | 2025-01-11 15:04:31 | MASTER-Kislovodsk | (06h 27m 32.25s , +57d 00m 29.7s) | C | 60 | 16.8 |
49537 | 2025-01-11 15:05:51 | MASTER-Kislovodsk | (06h 27m 30.17s , +57d 02m 06.8s) | C | 60 | 16.8 |
49617 | 2025-01-11 15:07:11 | MASTER-Kislovodsk | (06h 27m 29.07s , +57d 00m 33.5s) | C | 60 | 16.8 |
49697 | 2025-01-11 15:08:30 | MASTER-Kislovodsk | (06h 27m 32.95s , +57d 01m 50.4s) | C | 60 | 16.8 |
49777 | 2025-01-11 15:09:51 | MASTER-Kislovodsk | (06h 27m 25.83s , +57d 01m 23.6s) | C | 60 | 16.8 |
49887 | 2025-01-11 15:11:10 | MASTER-Kislovodsk | (06h 27m 25.75s , +57d 02m 27.6s) | C | 120 | 16.9 |
50027 | 2025-01-11 15:13:30 | MASTER-Kislovodsk | (06h 27m 33.48s , +57d 01m 32.6s) | C | 120 | 17.0 |
50166 | 2025-01-11 15:15:50 | MASTER-Kislovodsk | (06h 27m 25.14s , +57d 00m 38.8s) | C | 120 | 16.9 |
50306 | 2025-01-11 15:18:10 | MASTER-Kislovodsk | (06h 27m 29.80s , +57d 00m 54.7s) | C | 120 | 16.9 |
50446 | 2025-01-11 15:20:29 | MASTER-Kislovodsk | (06h 27m 28.56s , +57d 02m 34.7s) | C | 120 | 17.0 |
50586 | 2025-01-11 15:22:50 | MASTER-Kislovodsk | (06h 27m 28.31s , +57d 01m 22.1s) | C | 120 | 17.0 |
50726 | 2025-01-11 15:25:09 | MASTER-Kislovodsk | (06h 27m 30.15s , +57d 02m 55.1s) | C | 120 | 17.0 |
50866 | 2025-01-11 15:27:29 | MASTER-Kislovodsk | (06h 27m 23.97s , +57d 02m 04.2s) | C | 120 | 16.9 |
51006 | 2025-01-11 15:29:49 | MASTER-Kislovodsk | (06h 27m 23.64s , +57d 03m 10.2s) | C | 120 | 16.9 |
51145 | 2025-01-11 15:32:09 | MASTER-Kislovodsk | (06h 27m 30.20s , +57d 02m 15.1s) | C | 120 | 16.9 |
51285 | 2025-01-11 15:34:29 | MASTER-Kislovodsk | (06h 27m 22.93s , +57d 01m 20.6s) | C | 120 | 16.9 |
51425 | 2025-01-11 15:36:49 | MASTER-Kislovodsk | (06h 27m 29.84s , +57d 01m 53.1s) | C | 120 | 16.8 |
Filter C is a clear (unfiltred) band.
The observation and reduction will continue.
The message may be cited.
GCN Circular 38910
Subject
EP250111a: Swift/XRT detection and fading
Date
2025-01-11T14:46:54Z (a year ago)
From
Jamie Kennea at Penn State <jak51@psu.edu>
Via
Web form
J. A. Kennea (PSU), P. A. Evans and K. L. Page (Leicester) on behalf of the Swift/XRT report:
At 04:08UT on January 9th, 2025 Swift began a 1.7ks target-of-opportunity observation of the Einstein Probe discovered transient EP250111a (GCN #38905), approximately 2.8 hours after the EP trigger. XRT detects a previously uncatalogued point source at the following coordinates: RA/Dec(J2000) = 97.17996, +56.8970, which is equivalent to:
RA(J2000) = 06h 28m 43.19s
Dec(J2000) = +56° 53′ 49.1″
with an estimated uncertainty of 5.8 arc-seconds radius (90% confidence). This position lies 5 arc-seconds from the reported localization by the EP FXT reported in GCN #38905. This position lies 5.6 arc-seconds from the reported NOT optical candidate (GCN #38906).
The X-ray flux of this source is 3.9(+1.4/-1.1) x 10^-13 erg/s/cm^2 (0.3-10 keV), approximately an order of magnitude fainter than the FXT flux.
GCN Circular 38906
Subject
EP250111a: NOT likely optical counterpart
Date
2025-01-11T09:42:34Z (a year ago)
From
Dong Xu at NAOC/CAS <dxu@nao.cas.cn>
Via
Web form
S.Y. Fu, J. An, S.Q. Jiang, X. Liu, Z.P. Zhu, D. Xu (NAOC), J.P.U. Fynbo (DAWN/NBI), A. H. de la Fuente, S. G. Sorensen (NOT) report on behalf of a large collaboration:
We observed the field of EP250111a detected by Einstein Probe (EP, Zhao et al., GCN 38905), using the ALFOSC instrument mounted on the Nordic Optical Telescope (NOT). Observations started at 02:58:45.5 UT on 2025-01-11, i.e. 1.63 hr after the trigger, and 9 x100 s frames were obtained in the SDSS-r band.
An uncatalogued source is detected in the stacked frame within the EP/FXT error circle (EP, Zhao et al., GCN 38905) and localized at coordinates
R.A. (J2000) = 06:28:43.29
Dec. (J2000) = +56:53:54.76
with an uncertainty of ~ 0.5 arcsec. The source has r ~ 20.7 mag, calibrated with Pan-STARRS DR1 and not corrected for Galactic extinction. There was no known NEO object at the above position by checking MPC.
We thus conclude the source is very likely the optical counterpart of EP250111a.
Further observations are encouraged.
GCN Circular 38905
Subject
EP250111a: a new X-ray transient detected by Einstein Probe
Date
2025-01-11T08:44:14Z (a year ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
T. Zhao (NAO, CAS), X. L. Chen (YNU), Q. C. Shui (IHEP, CAS), Kaushik Chatterjee (YNU), T. Y. Lian and C. C. Jin (NAO, CAS) report on behalf of the Einstein Probe team
We report on the detection of an X-ray transient designated EP250111a by the Einstein Probe (EP) mission, which triggered the on-board processing unit at 2025-01-11T01:20:44 (UTC) (trigger ID: 01709130131). The transient event started at 2025-01-11T01:20:24 (UTC) and lasted for 83s before the observation was interrupted by 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 equivalent hydrogen column density of 1.11 x 10^21 cm^-2 and a photon index of 1.01 (-0.52/+0.54). The derived average observed 0.5-4 keV flux is 1.39 (-0.40/+0.53) x 10^(-9) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters.
An autonomous observation was performed by the Follow-up X-ray Telescope (FXT) about four minutes later. An uncatalogued source was detected at R.A. = 97.1809, DEC = 56.8983 (J2000) with an uncertainty of about 20 arcsec (radius, 90% C.L. statistical and systematic). The average FXT 0.5-10 keV spectrum can be fitted with an absorbed power law with a fixed Galactic equivalent hydrogen column density of 1.11 x 10^21 cm^-2 and a photon index of 2.42 (-0.14/+0.15). The derived average observed 0.5-10 keV flux is 3.43 (-0.33/+0.36) x 10^(-12) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters.
More information on this source will be updated when the full telemetry data is received. Further follow-up observations are encouraged to identify the nature of this X-ray transient.
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).