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EP251124a

GCN Circular 43063

Subject
EP251124a: Mondy optical upper limit
Date
2025-12-10T11:55:55Z (7 days ago)
From
Alina Volnova at IKI RAS <alinusss@gmail.com>
Via
Web form
A. A. Volnova (IKI), E. Klunko (ISTP), A. S. Pozanenko, N. S. Pankov (HSE, IKI) (IKI) report on behalf of IKI-GRB-FuN:

We observed the field of the EP251124a triggered by EP/WXT (Zhou et al., GCN 42816; GCN 42832) with the AZT-33IK 1.5m telescope of the Sayan Solar Observatory (Mondy) taking several 120-second expositions in R-band starting on Nov.24 UT 14:36:01 in the R filter. In the error boxes reported by Zhou et al. (GCN 42816) we do not detect any new optical transient in the stacked frame. The photometry and observational details are the following: 

Date        UT start  t-T0       Exp.    Filter   UL         Site/Telescope
                     (mid,days)  (n*s)           (3sigma)
2025-11-24  14:36:01  0.16386    30*120  R        22.3       Mondy/AZT-33IK

The photometry is based on several nearby stars from the USNO-B1 catalogue (R2 magnitudes) and is not corrected for the Galactic extinction.

Our upper limit is in agreement with previously reported limits (Mohan et al., GCN 42817; Wang et al., GCN 42824; Lipunov et al., GCN 42828; van Hoof et al., GCN 42829; Ma et al, GCN 42833; Gillanders et al., GCN 42862).

GCN Circular 42862

Subject
EP251124a: Pan-STARRS ri-band imaging and photometry
Date
2025-11-27T13:50:26Z (20 days ago)
From
James Gillanders at University of Oxford <jhgillanders.astro@gmail.com>
Via
Web form
J. H. Gillanders (Oxford), M. Huber, K. C. Chambers (IfA, Univ. Hawaii), S. J. Smartt, K. W. Smith (Oxford/QUB), S. Srivastav (Oxford), M. Nicholl, D. Young, M. Fulton (QUB), T.-W. Chen (NCU, Taiwan) A. S. B. Schultz, T. de Boer, J. Fairlamb, G. Paek, C. C. Lin, T. Lowe, E. Magnier, P. Minguez, I. A. Smith, R. J. Wainscoat (IfA, Univ. Hawaii).

We observed the optical counterpart of EP251124a (Zhou et al., GCN 42816), using the Pan-STARRS telescope system (Chambers et al., 2016, arXiv e-prints, 1612.05560) on MJD 61004.36 (2025-11-25 08:38:24 UTC), 0.90 days after the EP-WXT detection (Zhou et al., GCN 42816). The Pan-STARRS system consists of 2x1.8m telescope units located at the summit of Haleakala on the Hawaiian island of Maui, employing an SDSS-like filter system denoted as grizy, and a broad w filter, which is a composite of the gri filters.

Our observation consisted of 6x150s exposures in both the r and i filters with Pan-STARRS1. The images were processed with the Pan-STARRS pipeline. After astrometric and photometric calibration, reference images were subtracted from the target stacked images (Magnier et al., 2020a, ApJS, 251, 3; Magnier et al., 2020b, ApJS, 251, 6; Waters et al., 2020, ApJS, 251, 4).

From these difference images, we do not detect any optical counterpart down to 3.5-sigma limiting AB magnitudes of r~22.3 and i~22.3. Our upper limits are in agreement with previously reported limits from Mohan et al. (GCN 42817), Wang et al. (GCN 42824), Lipunov et al. (GCN 42828), van Hoof et al. (GCN 42829), and Ma et al. (GCN 42833).

GCN Circular 42833

Subject
EP251124a: Xinglong GWAC-F60A optical observation
Date
2025-11-25T09:48:40Z (22 days ago)
From
Yinuo Ma <mayn@bao.ac.cn>
Via
Web form
Y. N. Ma, L. P. Xin, Y. L. Qiu, C. Wu, J. Wang, X. H. Han, P. P. Zhang, H. L. Li, Z. H. Yao, J. Y. Wei (NAOC) report on behalf of SVOM follow-up team:

We observed the field of EP251124a triggered by EP/WXT (Zhou et al., GCN 42816; GCN 42832) using the GWAC-F60A telescope located at Xinglong observatory, China. We obtained a series of frames in R-band, starting at 2025-11-24T11:22:30 UTC, about 12.42 minutes after the trigger.

No uncataloged sources were detected in our single or stacked images within the error box provided by EP/FXT (Zhou et al., GCN 42816) and Swift/XRT (Evans et al., GCN 42827), the three sigma limit is: 

   mid-time  | exposure time   | band  | upper limit  
----------- -|-----------------|-------|------------- 
19.5 minutes |  10*50 sec      |   R   |   19.5 mag

None of the known sources showed significant brightness variations within EP/FXT and Swift/XRT errorbox compared with USNO-B1.0 catalog. Our results are consistent with GIT (Mohan et al., GCN 42817), Kinder (Wang et al., GCN 42824), MASTER (Lipunov et al., GCN 42828), and NOT (van Hoof et al., GCN 42829).

Our photometry was not corrected for Galactic extinction.

We thank the staff at Xinglong observatory for their excellent support.

GCN Circular 42832

Subject
EP251124a (EP-WXT trigger 01709248862) is triggered by the known source AWM 7
Date
2025-11-25T09:23:49Z (22 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
H.Zhou (PMO, CAS), J.-Y. Cao (IHEP), H.-N. Yang, and Z.-X. Ling (NAO, CAS) on behalf of the Einstein Probe (EP) team:

Refined analysis of the WXT data shows that EP251124a (GCN #42816) is associated with the Cluster of Galaxies AWM 7. The estimated flux is ~6.17e-11 erg/cm2/s.

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 42829

Subject
EP251124a: NOT r- and z-band optical upper limits
Date
2025-11-24T23:32:52Z (22 days ago)
From
Agnes van Hoof at Radboud University <agnes.vanhoof@ru.nl>
Via
Web form
A. P. C. van Hoof (Radboud), G. Corcoran (UCD), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), J. N. D. van Dalen (Radboud), P. G. Jonker (Radboud), Shilpa Bijavara Seshashayana (NOT and Malmo Univ.), report on behalf of a larger collaboration:

We observed the field of the fast X-ray transient EP251124a (Zhou et al., GCN 42816) using the Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. Observations were obtained in the r (3x300 s) and z (3x200 s) bands, starting on 2025-11-24 at 21:34:32 UTC (10.4 hr after the WXT trigger). 

No new source is detected within any of the X-ray error circles provided by EP/FXT (Zhou et al., GCN 42816) and Swift/XRT (Evans et al., GCN 42827). From the stacked images we obtain the following 3-sigma upper limits:

r > 24.4
z > 23.0

These upper limits are in AB magnitudes and were calibrated using nearby stars from the Pan-STARRS catalog and are not corrected for Galactic extinction. The upper limits are consistent with previously reported upper limits in r-band (Mohan et al., GCN 42817; Wang et al., GCN 42824).

GCN Circular 42828

Subject
EP251124a: Global MASTER-Net observations report
Date
2025-11-24T21:09:29Z (22 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-Kislovodsk robotic telescope  [1]  located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) was pointed to the EP251124a ( EP Team et al., GCN 42816) errorbox  21097 sec after notice time and 28845 sec after trigger time at 2025-11-24 19:10:50 UT, with upper limit up to  18.2 mag. The observations began at zenith distance =  7 deg. The sun  altitude  is -58.5 deg. 

The galactic latitude b = -15 deg., longitude l = 147 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=3050758

We obtain a following upper limits.  

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

   28935 | 2025-11-24 19:10:50 |   MASTER-Kislovodsk | (02h 53m 11.63s , +41d 55m 39.9s) |   C |   180 | 18.2 |        
   28935 | 2025-11-24 19:10:50 |   MASTER-Kislovodsk | (02h 53m 47.32s , +41d 32m 52.8s) |   C |   180 | 12.7 |        
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 42827

Subject
EP251124a: Swift-XRT observations
Date
2025-11-24T17:36:48Z (22 days ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
P.A. Evans (U. Leicester), J.A. Kennea (PSU), E. Ambrosi  (INAF-IASFPA) , A.P.
Beardmore (U. Leicester), M.G. Bernardini (INAF-OAB), R. Brivio (INAF-OAB), D.N.
Burrows (PSU), S. Campana (INAF-OAB), M. Capalbi (INAF-OAR), A. D'Ai (INAF-IASFPA),
P. D'Avanzo (INAF-OAB), V. D'Elia (SSDC & INAF-OAR), S. Dichiara (PSU), M. Ferro
(INAF-OAB), A. Melandri (INAF-OAR), J.P. Osborne (U. Leicester), K.L. Page (U.
Leicester), M. Perri (SSDC & INAF-OAR), C. Salvaggio (INAF-OAB), T. Sbarrato
(INAF-OAB), B. Sbarufatti (INAF-OAB), M.A. Williams (PSU) report on behalf of the
Swift-XRT team:

Swift-XRT has performed follow-up observations of the Einstein Probe/WXT-detected
source EP251124a, collecting 2.5 ks of Photon Counting (PC) mode data between T0+5.1
ks and T0+11 ks after the trigger. The field is full of extended emission due to a
cluster of galaxies. We have detected 3 sources.  These have been automatically
classified as follows:
  * 0 likely counterparts
  * 0 candidate counterparts
  * 3 uncatalogued X-ray sources
  * 0 known X-ray sources

Uncatalogued X-ray sources
--------------------------

  Source 2 (SWIFT J025449.9+413724):
  ==================================
    RA (J2000.0):   43.7081  =	02 54 49.94
    Dec (J2000.0):  +41.6234  =  +41 37 24.2
    Error:	    5.4 (arcsec, radius, 90% confidence).
    Detect flag:    GOOD
    Distance:	    3.0 arcmin from the Einstein Probe/WXT position.
    Mean rate:	    (-1.0 +/- -1.0)e0 ct s^-1
    Mean flux:	    (-2.1 +/- -2.1)e-11 erg cm^-2 s^-1
    Peak rate:	    (8.5 [+3.4, -3.0])e-3 ct s^-1
    Peak flux:	    (1.80 [+0.71, -0.63])e-13 erg cm^-2 s^-1
    ECF:	    2.12e-11 erg cm^-2 ct^-1
		      assuming NH=2.22e+22 cm^-2, gamma=5.93
		      determined from a spectral fit.
    LSXPS UL:	    1.0e-02 ct/sec, (0.3-10 keV)
		      so the source is not above this 3-sigma upper limit.
    There is no evidence for fading.
    A SIMBAD object `2MASX J02544959+4137278' is 5.1" away.
    There is 1 2MASS object within the source's 3-sigma error radius.

  Source 3 (SWIFT J025510.5+413444):
  ==================================
    RA (J2000.0):   43.7940  =	02 55 10.56
    Dec (J2000.0):  +41.5789  =  +41 34 44.0
    Error:	    5.7 (arcsec, radius, 90% confidence).
    Detect flag:    POOR
    Distance:	    2.8 arcmin from the Einstein Probe/WXT position.
    Mean rate:	    (-1.0 +/- -1.0)e0 ct s^-1
    Mean flux:	    (-1.6 +/- -1.6)e-10 erg cm^-2 s^-1
    Peak rate:	    (3.8 [+2.5, -2.2])e-3 ct s^-1
    Peak flux:	    (6.0 [+4.0, -3.4])e-13 erg cm^-2 s^-1
    ECF:	    1.57e-10 erg cm^-2 ct^-1
		      assuming NH=2.84e+21 cm^-2, gamma=0.31
		      determined from a spectral fit.
    LSXPS UL:	    1.6e-02 ct/sec, (0.3-10 keV)
		      so the source is not above this 3-sigma upper limit.
    There is no evidence for fading.

  Source 6 (SWIFT J025445.0+413429):
  ==================================
    RA (J2000.0):   43.6876  =	02 54 45.02
    Dec (J2000.0):  +41.5749  =  +41 34 29.6
    Error:	    5.4 (arcsec, radius, 90% confidence).
    Detect flag:    POOR
    Distance:	    2.0 arcmin from the Einstein Probe/WXT position.
    Mean rate:	    0.0245 [+0.0084, -0.0071] ct s^-1
    Mean flux:	    (8.9 [+3.1, -2.6])e-13 erg cm^-2 s^-1
    Peak rate:	    0.043 [+0.022, -0.018] ct s^-1
    Peak flux:	    (1.56 [+0.81, -0.66])e-12 erg cm^-2 s^-1
    ECF:	    3.63e-11 erg cm^-2 ct^-1
		      assuming NH=1.20e+21 cm^-2, gamma=1.87
		      determined from a spectral fit.
    LSXPS UL:	    3.2e-02 ct/sec, (0.3-10 keV)
		      so the source is not above this 3-sigma upper limit.
    There is no evidence for fading.

All fluxes are 0.3-10 keV, observed. For all flux conversions and comparisons with
catalogues and upper limits  from other missions, we assumed a power-law spectrum
with NH=3x10^20 cm^-2 and photon index (Gamma)=1.7 unless otherwise stated.

The results of the XRT-team automatic analysis of the XRT observations, including a
position-specific upper limit calculator, are available at
https://www.swift.ac.uk/EP/EP_FIELD00083.

This circular is an official product of the Swift-XRT team.

GCN Circular 42824

Subject
EP251124a: Optical upper limit with Kinder observations
Date
2025-11-24T17:15:34Z (22 days ago)
From
Janet Chen at National Central University <janetstars@gmail.com>
Via
Web form
Z. N. Wang (HNAS), A. Aryan, T.-W. Chen, W.-J. Hou, Y.-H. Lee (all NCU), A. K. H. Kong (NTHU), J. H. Gillanders, S. J. Smartt (both Oxford), Y. J. Yang (NYUAD), A. Sankar.K, Y.-C. Pan, C.-C. Ngeow, M.-H. Lee, C.-H. Lai, H.-C. Lin, C.-S. Lin, H.-Y. Hsiao, J.-K. Guo (all NCU), S. Yang, L. L. Fan, G. H. Sun (all HNAS), H.-W. Lin (UMich), H. F. Stevance, S. Srivastav, L. Rhodes (all Oxford), M. Nicholl, M. Fulton, T. Moore, K. W. Smith, C. Angus, A. Aamer (all QUB), A. Schultz and M. Huber (both IfA, Hawaii) report: 

We observed the field of the fast X-ray transient EP251124a (Zhou et al., GCN 42816) using the 40cm SLT at Lulin Observatory in Taiwan as part of the Kinder collaboration (Chen & Yang et al. 2025, ApJ, 983, 86, doi:10.3847/1538-4357/adb428). Our SLT observation started at 16:21 UTC on the 24th of November 2025 (MJD 61003.477), 0.27 hr after the EP-WXT trigger. 

We utilized the astroalign (Beroiz et al. 2020, A&C, 32, 100384) and astropy (Astropy Collaboration et al. 2022, ApJ, 935, 167) packages to align and stack the individual frames. We utilised the Python-based package AutoPhOT (Brennan & Fraser 2022, A&A, 667, A62) to perform template subtraction with the Pan-STARRS1 3Pi archive image (Chambers et al. 2016, arXiv:1612.05560) using the 'hotpants' (Becker 2015, ascl.soft. ascl:1504.004) algorithm. In the difference image, we do not detect any uncataloged sources within the 20" error circle, for each of the three EP-FXT positions reported. We note that the position of FXTB-2 is not covered by Pan-STARRS1. Although this field is included in SDSS DR14 (Abolfathi et al. 2018, arXiv:1707.09322), we do not find any new or uncataloged sources by eye within the 20″ error circle of FXTB-2.

Moreover, we further utilized AutoPhOT to perform the PSF photometry. The details of the observations and the 3-sigma upper limit (in the AB system) are as follows:

Telescope | Filter | MJD (start) | t-t0 (hr) | Exposure (s) | Magnitude | avg. Seeing | med. Airmass
SLT       | r      | 61003.477   | 0.27      | 300 * 24     | >21.7     | 1".40       | 1.19

The presented magnitude is calibrated using the field stars from the ATLAS-RefCat2 catalog from MAST (Tonry et al. 2018, ApJ, 867, 105) and is not corrected for the expected Galactic foreground extinction of A_r = 0.27 mag in the direction of the transient (Schlafly & Finkbeiner 2011). Our observation agrees with Mohan et al. (GCN 42817) and provides a deeper constraint. The methodology, details on the Lulin observatory telescopes, and a compilation of our optical follow-up campaign for FXTs discovered within the first year of operation of the Einstein-Probe mission can be found in Aryan et al. 2025, ApJS, 281, 20. doi:10.3847/1538-4365/adfc69.

GCN Circular 42817

Subject
EP251124a: GROWTH-India Telescope optical upper limits
Date
2025-11-24T15:02:41Z (23 days ago)
From
V. Swain at IIT Bombay <vishwajeet.s@iitb.ac.in>
Via
Web form

T. Mohan (IITB), S. Patil (IITB), D. Eappachen (IIA), V.Swain (IITB), A.P. Saikia (IITB), V. Bhalerao (IITB), G.C. Anupama (IIA), S. Barway (IIA) and K. Angail (IAO) report on behalf of the GIT team:

We observed the field of EP transient (Zhou et al., GCN 42816

Loading...
 
 
), with 0.7m GROWTH-India Telescope (GIT). We started the observation at 2025-11-24T13:25:59 UT, i.e., about 2.27 hours after the EP-WXT trigger. Two exposures were obtained each in r' and g' filters. We did not detect any transient in our images within the WXT localization region and at the position of FXT sources - FXTA, FXTB1, and FXTB2. The photometric upper limits are as follows:

MJD (mid)Filtertmid-t0 (min)Exposure Time (sec)Upper limit (AB)
61003.55971r'135.930020.5
61003.56539g'144.130020.8

The measurement is calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected for Galactic extinction.

The GROWTH India Telescope (GIT; Kumar et al. 2022) is a 70-cm telescope with a 0.7-degree field of view, set up by the Indian Institute of Astrophysics (IIA) and the Indian Institute of Technology Bombay (IITB) with funding from DST-SERB and IUSSTF. It is located at the Indian Astronomical Observatory (Hanle), operated by IIA. We acknowledge funding by the IITB alumni batch of 1994, which partially supports the operations of the telescope. Telescope technical details are available at https://sites.google.com/view/growthindia/.

GCN Circular 42816

Subject
EP251124a: Einstein Probe detection of an X-ray transient
Date
2025-11-24T13:17:56Z (23 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
H.Zhou (PMO, CAS), J. -Y. Cao (IHEP), H.-N. Yang, and Z.-X. Ling (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 EP251124a. The transient triggered EP-WXT (ID: 01709248862) at 2025-11-24T11:10:05 (UTC). The WXT position of the source is R.A. = 43.732 deg, DEC = 41.577 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. According to the FXT onboard alert, which provided coordinates calculated autonomously on board the satellite, FXTA detected an X-ray source and FXTB detected two X-ray sources (denoted as FXTB-1 and FXTB-2) within the WXT error circle. Their coordinates (J2000) are:

FXTA: R.A. = 43.7117 deg, DEC = 41.5715 deg

FXTB-1: R.A. = 43.7188 deg, DEC = 41.5692 deg
FXTB-2: R.A. = 43.7061 deg, DEC = 41.6121 deg

All FXT localizations are reported with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic). FXTB-1 is consistent with the source detected by FXTA. 

Further information will be updated when the telemetry data is received. 

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).
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