- GCN Circular #39429
T. Y. Lian, W. J. Zhang (NAOC, CAS), Y. Wang (PMO, CAS), X. Tian (GXU), R. Z. Li(YNAO, CAS), H. W. Pan (NAOC, CAS) report on behalf of the Einstein Probe 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 EP250223a. The transient triggered EP-WXT (ID: 01709131863) at 2025-02-23T15:04:35.749 (UTC). The WXT position of the source is R.A. = 98.258 deg, DEC = -22.432 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 cirlce, an uncatalogued X-ray source was detected at R.A. = 98.2722 deg, DEC = -22.4442 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic).
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).
- GCN Circular #39434
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-SAAO robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa (South African Astronomical Observatory) was pointed to the EP250223a ( EP Team et al., GCN 39429) errorbox 6703 sec after notice time and 11479 sec after trigger time at 2025-02-23 18:15:54 UT, with upper limit up to 18.4 mag. Observations started at twilight. The observations began at zenith distance = 13 deg. The sun altitude is -12.2 deg.
The galactic latitude b = -13 deg., longitude l = 232 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=2788235
We obtain a following upper limits.
Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________
11509 | 2025-02-23 18:15:54 | MASTER-SAAO | (06h 31m 54.68s , -22d 37m 59.1s) | C | 60 | 18.4 |
Filter C is a clear (unfiltred) band.
The observation and reduction will continue.
The message may be cited.
- GCN Circular #39436
Benjamin N. Hauptmann (NOT and DTU Space), Yfke Bethlehem (Kapteyn Astronomical Institute, Groningen, and ING), Andrew J. Levan (Radboud and Warwick), Daniele B. Malesani (DAWN/NBI and Radboud), Antonio Martin-Carrillo (UCD), Franz E. Bauer (PUC), Peter G. Jonker (Radboud) and Dong Xu (NAOC), report on behalf of a larger collaboration:
We observed the location of EP250223a (Lian et al. GCN 39429) with the Nordic Optical Telescope (NOT). Observations in the r-band began at 20:36 UT, approximately 5.53 hr after the trigger time. In the first 300 s exposure we clearly detect a new point source, not visible in archival DSS and Pan-STARRS imaging of this field, at a location of
RA(J2000) = 06:33:05.723
DEC(J2000) = -22:26:40.32
These coordinates are within the FXT X-ray uncertainty region, making this source the likely afterglow of EP250223a.
The source has an AB magnitude r = 19.7, calibrated against nearby Pan-STARRS objects. Further observations are in progress.
- GCN Circular #39437
J. A. Kennea, C. Gronwall (PSU) and P. A. Evans (Leicester) report on behalf of the Swift Team:
At 16:36:15UT Swift began a target-of-opportunity observation of the transient EP250223a (GCN #39429), approximately 1.6 hours after the Einstein Probe trigger. We detect an an uncatalogued point source above the RASS limit at the following location: RA/Dec(J2000) = 98.27464, -22.4449, which is equivalent to:
RA(J2000) = 06h 33m 05.91s,
Dec(J2000) = -22° 26′ 41.8″,
with an estimated uncertainty radius of 3.8 arc-seconds (90% confidence). This position lies 8.5 arc-seconds from the EP WXT position reported in GCN #39429. The peak flux during the XRT observation was 5.4 (±1.0) × 10^-12 erg cm^-2 s^-1 (0.3 - 10 keV).
- GCN Circular #39438
Andrew J. Levan (Radboud and Warwick), Luca Izzo (INAF, Naples and DARK/NBI), Daniele B. Malesani (DAWN/NBI and Radboud), Antonio Martin-Carrillo (UCD), Franz E. Bauer (PUC), Peter G. Jonker (Radboud), Benjamin N. Hauptmann (NOT and DTU Space), Yfke Bethlehem (Kapteyn Astronomical Institute, Groningen, and ING), and Dong Xu (NAOC), report on behalf of a larger collaboration:
Further to the identification of the likely optical counterpart (Hauptmann et al., GCN 39436) of EP 250223a (Lian et al., GCN 39429), we obtained spectroscopic observations with the Nordic Optical Telescope, beginning at 21:18 UT. A total of 4x900 s observations were obtained using grism #4.
The observations reveal a strong continuum with a pronounced suppression at ~4550 AA, which we interpret as arising from damped Lyman-alpha absorption. In addition we detect a number of narrow metal lines, among which Fe II, Al II, C II, O I, Si II, which allow us to fix the redshift to z = 2.756.
The spectral shape and redshift, as well as the detection of an X-ray counterpart at a consistent position with Swift (Kennea et al., GCN 39437), secure the source as the counterpart of EP250223a.
- GCN Circular #39439
S.-Y. Wu, I. Perez-Garcia, E. Fernandez-Garcia, M. D. Caballero-Garcia, G. Garcia-Segura, S. Guziy, R. Sanchez-Ramirez and A. J. Castro-Tirado (IAA-CSIC, Granada), C. Perez del Pulgar (Univ. de Malaga), M. Gritsevich (Univ. of Helsinki), Y.-D. Hu (GXU), and D. R. Xiong, J. M. Bai, Y. F. Fan, C. J. Wang, Y. X. Xin, X. H. Zhao, J. R. Mao, B. K. Lun, K. Ye (Yunnan Observatories/CAS, Kunming) on behalf of a larger collaboration, report:
Following the detection of EP250223a by EP/WXT (Lian et al. GCNC 39429), the 0.6m BOOTES-4/MET robotic telescope at Lijiang Astronomical Observatory (China) automatically responded to this burst starting on Feb. 23, 15:16:38 UT (~12 min after trigger). At the position of the EP/FXT X-ray source (also recorded by Swift/XRT, Kennea et al. GCNC 39437), an optical counterpart is detected, for which we measure a magnitude of 18.4 +/- 0.1 (60s, clear filter, comparable with Gmag of Gaia DR3), which also consistent with the object reported by NOT at a later stage (Hauptmann et al. GCNC 39426, Levan et al. GCNC 39438). Further analysis of the additional images is ongoing.
We thank the staff at Lijiang observatory for their excellent support.
- GCN Circular #39440
I. Pérez-Fournon, F. Poidevin, D. Aguado, J.A. Acosta-Pulido, A. López-Oramas, D. Nespral (IAC and ULL), F. Acero (CEA Saclay and IAC), N.C. Sun (UCAS), W. Li, Y. Wang, Z. Niu (NAOC), D. Cano-Morales, I. Correa-Plasencia, and A.E. Hernández-Díaz (ULL)
We observed the location of EP250223a (Lian et al., GCN circ. 39429), detected also by Swift XRT (Kennea et al., GCN circ. 39437), with two Las Cumbres Observatory Global Telescope network (LCOGT) 1-m telescopes, equipped with Sinistro cameras, located at the LCOGT node at Sutherland Observatory (South Africa). We obtained first a 600-sec exposure in the SDSS r' filter, that started at 2025-02-23 19:47:12 UT, e.g. 4.71 hr after the EP trigger, followed by 300-sec exposures in the SDSS i' and g' filters. The optical afterglow candidate reported by Hauptmann et al. (GCN circ. 39436) is clearly detected in the three images.
We measured the following magnitudes, calibrated against PanSTARRS DR2 stars and not corrected for Galactic extinction:
Date | UT start | T (mid) - T0 (hours) | mag | error | filter |
----------------------------------------------------------------------
2025-02-23 19:47:12 4.79 19.73 0.03 r'
2025-02-23 21:38:41 6.61 19.74 0.06 i'
2025-02-23 21:42:28 6.67 20.77 0.10 g'
A redshift of z = 2.756 has been reported by Levan et al. (GCN circ. 39438).
This work makes use of observations from the Las Cumbres Observatory global telescope network (LCOGT observing programme IAC2025A-009, SGLF).
- GCN Circular #39441
L. Izzo (INAF-OACn and DARK/NBI), and D. B. Malesani (DAWN/NBI and Radboud Univ.) report:
We observed the field of EP250223a (Lian et al., GCN #39429) using the 0.5-m T1 telescope of the Osservatorio Astronomico S. Di Giacomo, located in Agerola, Italy. Our observations started on 2025 February 23 at 18:15 UT, approximately 3.19 hours after the GRB trigger. We acquired a series of 6x300 s images in the Rc filter.
In the stacked image, we detect a faint source consistent with the X-ray afterglow reported by EP/FXT (Lian et al., GCN #39429), and by Swift-XRT (Kennea et al., GCN #39437), and with the optical counterpart reported by several other telescopes (Hauptmann et al., GCN #39436; Levan et al., GCN #39438; Wu et al., GCN #39439; Perez-Fournon et al., GCN #39440). We measure a preliminary magnitude of Rc = 19.6 +/- 0.2 mag (AB), calibrated against nearby stars from the Pan-STARRS catalog.
- GCN Circular #39445
L.P. Xin, Y.L. Qiu(NAOC), Y. Wang(PMO),H.L. Li, C. Wu, Z.H. Yao, Y. N. Ma, X.H. Han, H.B. Cai, J. Wang, Y. Xu, J.Y. Wei(NAOC), J. T. Palmerio(CEA/Irfu) report on behalf of the SVOM team:
The SVOM/VT conducted a ToO follow-up observations of the EP250223a (Lian et al., GCN 39429) in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channel simultaneously.
The afterglow(Benjamin et al., GCN 39436) was clearly detected within the errorbox of EP/FXT (Lian et al., GCN 39429) in VT_R and VT_B images.
The afterglow was fading during our observations and the brightness was estimated to be 19.21+/-0.05 mag in AB magnitude in VT_R, and 20.11+/-0.05 mag in AB magnitude in VT_B, at the mid time of 3.7 hours post the burst.
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 #39447
Helong Guo, Guowang Du, Yu Pan, Xinlei Chen, Brajesh Kumar, Xiaotong Chen, Yiheng Xie, Yuan Fang, Xingzhu Zou, Yuanpei Yang, Jinghua Zhang, Dezi Liu, Xiangkun Liu, Xiaowei Liu (all SWIFAR, YNU) report on behalf of the Mephisto Team:
The field of EP250223a detected by EP Team (Lian et al., GCN 39429) was observed with the 1.6m Multi-channel Photometric Survey Telescope (Mephisto) and 50cm array facilities of Yunnan University located at Lijiang Observatory. Simultaneous uvgr band images with different exposure times were acquired with Mephisto starting from 15:20:12 2025-02-23 UT (~15.6 minutes after the trigger) and with 50cm array in iz bands starting from 15:49:08 2025-02-23 UT (~44.5 minutes after the trigger). The afterglow candidate (Lipunov et al., GCN 39434; Hauptmann et al., GCN 39436; Kennea et al., GCN 39437; Levan et al., GCN 39438; Wu et al., GCN 39439; Pérez-Fournon et al., GCN 39440; Izzo et al., GCN 39441; Xin et al., GCN 39445) is clearly detected in each v, g, r band and in the stacked u band images taken with Mephisto. The candidate is also visible in the stacked i band image of 50 cm array but not in the stacked z band. The preliminary magnitudes and 3-sigma upper limit are below:
1.6m Mephisto
Start_Time(UT) | Band | Exp(s) | Mag/LimMag(AB)
--------------------|------|--------|----------------
2025-02-23T16:00:53 | u | 300*3 | 20.97 +/- 0.29
2025-02-23T15:25:14 | v | 180 | 19.93 +/- 0.22
2025-02-23T15:20:12 | g | 10 | 18.11 +/- 0.12
2025-02-23T15:25:14 | r | 50 | 18.17 +/- 0.07
50CM array
Start_Time(UT) | Band | Exp(s) | Mag/LimMag(AB)
--------------------|------|--------|---------------
2025-02-23T15:49:08 | i | 300*3 | 18.89 +/- 0.11
2025-02-23T15:49:08 | z | 300*3 | >18.81
-------------------------------------------------------------------------------------------------
Mephisto (Multi-channel Photometric Survey Telescope) is a 1.6-m wide-field multi-channel telescope, the first of its type in the world, capable of imaging the same field of view in three optical bands simultaneously. It provides real-time, high-quality colors of stellar objects. The on-site telescope assemblage and commissioning were carried out in September 2022. The first light in all three channels was achieved on 2023 December 21.
The 50cm array consists of two 50cm telescopes for wide-field surveys and also serves as the supporting facility for monitoring the Mephisto detected targets.
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- GCN Circular #39448
Y. Wang (PMO, CAS), T. Y. Lian, W. J. Zhang (NAOC, CAS), X. Tian (GXU), R. Z. Li(YNAO, CAS), H. W. Pan (NAOC, CAS) report on behalf of the Einstein Probe team:
The X-ray transient EP250223a triggered the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Lian et al., GCN 39429), and followed by the Swift XRT (Kennea et al., GCN 39437) and several optical telescopes (Levan et al., GCN 39436, Wu et al., GCN 39439, Pérez-Fournon et al., GCN 39440, Izzo et al., GCN 39441, Xin et al., GCN 39445) at the redshift of 2.756 (Levan et al., GCN 39438). The refined analysis of the WXT data shows that the event started at 2025-02-23T15:02:05.66 (UTC) and lasted for 140 s with the peak flux of 2 x 10^(-9) erg/s/cm^2, 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 1.36 x 10^21 cm^-2 and a photon index of 2.1 (-/+0.6). The derived average unabsorbed 0.5-4 keV flux is 4.4 (-1.1/+1.4) x 10^(-10) erg/s/cm^2.
The autonomous observation by the Follow-up X-ray Telescope (FXT) was performed about two minutes later. The on-ground analysis shows that an uncatalogued source was detected at R.A. = 98.2748, DEC = -22.4443 (J2000) with an uncertainty of about 10 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 Galactic equivalent hydrogen column density of 1.36 x 10^21 cm^-2 and a photon index of 1.97 (-/+0.05). The derived average unabsorbed 0.5-10 keV flux is 2.5 (-/+0.1) x 10^(-11) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters.
Further follow-up observations with EP-FXT have been scheduled.
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 #39449
J. An, S.Q. Jiang, N.C. Sun (NAOC), S. Tinyanont, R. Anutarawiramkul, P. Butpan (NARIT), Z. Fan, W.X. Li, Y.N. Wang, D. Xu (NAOC) report on behalf of a large collaboration:
We observed the field of EP250223a detected by EP (Lian et al., GCN 39429; Wang et al., GCN 39448), and observed by Swift/XRT (Kennea et al., GCN 39437), using the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at Cerro Tololo Inter-American Observatory, Chile. Observations started at 00:37:15.66 UTC on 2025-02-24, i.e., 9.544 hrs after the EP trigger, and a series of 200 s frames were obtained in B, V, R and I bands.
The optical afterglow (Wu et al., GCN 39439; Guo et al., GCN 39447; Izzo et al., GCN 39441; Xin et al., GCN 39445; Pérez-Fournon et al., GCN 39440; Hauptmann et al., GCN 39436; Levan et al., GCN 39438) is clearly detected in our stacked images with:
| T (mid) - T0 (hours)| band | mag | error |
| 9.816 | B | 21.32 | 0.14 |
| 9.996 | V | 20.17 | 0.07 |
| 10.176 | R | 19.86 | 0.07 |
| 10.356 | I | 19.41 | 0.12 |
calibrated with Panstarrs-DR2 stars in the field and not corrected for Galactic extinction.
- GCN Circular #39450
R. Brivio, M. Ferro, P. D'Avanzo, S. Covino, D. Fugazza (INAF-OAB) report on behalf of the REM team:
We observed the field of EP250223a (Lian et al., GCN 39429; Wang et al., GCN 39448), also detected by Swift/XRT (Kennea et al., GCN 39437) with the REM 60 cm robotic telescope located at the ESO observatory of La Silla (Chile). The observations were carried in the J, H, and K bands, started on 2025 February 24 at 01:29:31 UT (i.e. 10.4 hr after the burst), and lasted for about 1 hour.
From preliminary inspection, we do not find any counterpart at the position of the reported optical afterglow (Hauptmann et al., GCN 39436; Levan et al., GCN 39438; Wu et al., GCN 39439; Pérez-Fournon et al., GCN 39440; Izzo & Malesani, GCN 39441; Xin et al., GCN 39445; Guo et al., GCN 39447; An et al., GCN 39449) down to the following 3sigma limit:
H > 17.6 (Vega; calibrated against the 2MASS catalogue),
at a mid-time of 10.85 hours after the trigger.
- GCN Circular #39453
Jean-Grégoire Ducoin (CPPM), Francesco Magnani (CPPM), Benjamin Schneider (LAM), Alan M. Watson (UNAM), Kin Ocelotl López (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Camila Angulo (UNAM), Dalya Akl (AUS), Sarah Antier (OCA), Jean-Luc Atteia (IRAP), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Francis Fortin (IRAP), Noémie Globus (UNAM), Diego López-Cámara (UNAM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), and Antonio de Ugarte Postigo (LAM) report:
We imaged the field of EP250223a (Lian et al., GCN Circ. 39429), detected also by Swift/XRT (Kennea et al., GCN Circ. 39437), with the DDRAGO wide-field imager on the COLIBRÍ telescope at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir in Mexico.
We observed from 2025-02-24 04:59 to 07:19 UTC (13.9 to 16.3 hours after the trigger) and obtained 96 minutes of exposure in the r filter. The data were coadded with the COLIBRÍ pipeline and analyzed in STDWeb/STDPipe (Karpov 2021), with photometric calibration against Pan-STARRS DR1 and image subtraction against Pan-STARRS DR2. Our photometry is in the AB system and is not corrected for Galactic extinction.
In a stacked image of our first 50 minutes of exposure, we detect a source at the position of the optical afterglow candidate reported by Hauptmann et al. (GCN Circ. 39436) and many other groups (GCN Circs. 39439, 39440, 39441, 39445, 39447, and 39449) with magnitude:
r = 19.87 +/- 0.01
Comparing our r magnitude to the similar ones reported by Hauptmann et al. (GCN Circ. 39436) and Pérez-Fournon et al. (GCN Circ. 39440), we see no more than slow fading between about 6 and 15 hours. We encourage continued monitoring of this source.
We warmly thank the COLIBRÍ and DDRAGO engineering teams and the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir.
- GCN Circular #39455
D. O’Neill, B. P. Gompertz, A. J. Levan, K. Ulaczyk, G. Ramsay, A. Kumar, R. Starling, K. Ackley, M. J. Dyer, J. Lyman, F. Jimenez-Ibarra, D. Steeghs, D. K. Galloway, V. Dhillon, P. O'Brien, K. Noysena, R. Kotak, R. P. Breton, L. K. Nuttall, E. Pall'e and D. Pollacco report on behalf of the GOTO collaboration:
We report on optical observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) in response to the EP/WXT alert WXT01709131863 (Lian et al. GCN 39429). Three epochs of targeted observations were performed: at 2025-02-24 09:56:36 UT (+18.9h post trigger), 2025-02-24 11:04:37 UT (+20.0h post trigger), and 2025-02-24 12:12:37 UT (+21.1h post trigger). Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations of the same pointings.
We detect the optical afterglow (Hauptmann et al., GCN 39436; Levan et al., GCN 39438; Wu et al., GCN 39439; Pérez-Fournon et al., GCN 39440; Izzo et al., GCN 39441; Xin et al., GCN 39445; Guo et al., GCN 39447; An et al., GCN 39449; Brivio et al., GCN 39450; Ducoin et al., GCN 39453) with magnitudes of L (400-700 nm) = 20.04 ± 0.15 mag (+18.9h), L = 19.78 ± 0.11 mag (+20.0h) and L = 19.97 ± 0.14 mag (+21.1h). Our measurements indicate no fading of the afterglow between 18 and 21 hours after trigger, continuing the shallow evolution noted by Ducoin et al. during the first 6 - 15 hours (GCN 39453).
GOTO (https://goto-observatory.org) is a network of telescopes that is principally funded by the STFC and operated at the Roque de los Muchachos Observatory on La Palma, Spain, and Siding Spring Observatory in NSW, Australia, on behalf of a consortium including the University of Warwick, Monash University, Armagh Observatory & Planetarium, the University of Leicester, the University of Sheffield, the National Astronomical Research Institute of Thailand (NARIT), the University of Turku, the University of Portsmouth, the University of Manchester and the Instituto de Astrofisica
de Canarias (IAC).
- GCN Circular #39464
A. Aryan (NCU), A. K. H. Kong (NTHU), T.-W. Chen, W.-J. Hou, H.-Y. Hsiao (all NCU), J. Gillanders (Oxford), S. J. Smartt (Oxford/QUB), Y. J. Yang, A. Sankar. K, Y.-C. Pan, C.-C. Ngeow, M.-H. Lee, H.-C. Lin, C.-H. Lai, C.-S. Lin, J.-K. Guo (all NCU), S. Yang, L. L. Fan, Z. N. Wang, 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 EP250223a (Lian et al., GCN 39429) using the 40cm SLT telescope and Lulin One-meter Telescope (LOT) at Lulin Observatory in Taiwan as part of the Kinder collaboration (Chen & Yang et al. 2024, arXiv:2406.09270). The first SLT epoch of observations in the i-band started at 12:00:02 UT on the 24th of February 2024 (MJD = 60730.500), 20.92 hrs after the EP trigger. The first LOT epoch of observations in the r-band started at 14:42:53 UT on the 24th of February 2024 (MJD = 60730.613), 23.64 hrs after the EP 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. In the stacked images, we clearly detected the optical counterpart candidate proposed by Hauptmann et al. (GCN 39436) and confirmed by several other observations (e.g., Levan et al al., GCN 39438; Wu et al., GCN 39439; Pérez-Fournon et al., GCN 39440; Izzo et al., GCN 39441; Xin et al., GCN 39445; Guo et al., GCN 39447; An et al., GCN 39449; Ducoin et al., GCN 39453; and O’Neill et al., GCN39455).
We utilized the Python-based package AutoPhOT (Brennan & Fraser, 2022, A&A, 667, A62) to perform PSF photometry on our stacked frames. The details of the observations and measured photometry (in the AB system) are as follows:
---------------------------------------------------------------------------------------------------------------------------
Telescope | Filter | MJD (start) | t-t0 (hr) | Exposure (s) | Magnitude | avg. Seeing | med. Airmass
SLT | i | 60730.500 | 20.92 | 300 * 24 | 19.23 +/- 0.03 | 2".06 | 1.51
LOT | r | 60730.613 | 23.64 | 300 * 6 | 19.79 +/- 0.01 | 1".43 | 2.10
The presented magnitudes were calibrated using the field stars from the Pan-STARRS1 catalog and were not corrected for the expected Galactic foreground extinction corresponding to a reddening of A_i = 0.16 mag and A_r = 0.22 mag, respectively, in the direction of the transient (Schlafly & Finkbeiner 2011).
- GCN Circular #39472
A.P. Saikia, T. Mohan, V. Swain, V. Bhalerao (IITB), D. Eappachen, G.C. Anupama, S. Barway (IIA) and K. Angail (IAO) report on behalf of the GIT team:
We observed the field of EP250223a reported by EP-WXT (Lian et al., GCN 39429) with the 0.7m GROWTH-India Telescope (GIT). We started the observation at 2025-02-23T17:05:58 UT, i.e., 2.02 hours after the EP trigger. We obtained a single exposure of 420 seconds each in r' and g' filters. We clearly detected the afterglow in our image at the position given by NOT (Hauptmann et. al., GCN 39436). The photometry result follows as:
| MJD (mid) | tmid-t0 (hours) | Filter | Total Exposure (s) | Magnitude (AB) | Limiting Magnitude |
| ----------------- | ----------- |------- | ------------------ | -------------- | ------ |
| 60729.714907 | 2.08 | r' | 1x420 | 19.18 +/- 0.18 | 19.66 |
| 60729.720081 | 2.15 | g' | 1x420 | - | 19.62 |
Our result is consistent with Hauptmann et al., (GCN 39436), Wu et al., (GCN 39439), Péréz-Fournon et al., (GCN 39440), Izzo et al., (GCN 39441), Xin et al., (GCN 39445), Guo et al., (GCN 39447).
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 #39476
B.-T. Wang, R.-Z. Li, F.-F. Song, J. Mao, D.-Q. Wang, and J.-M. Bai (YNAO, CAS) report:
We observed the field of EP250223a (Lian et al., GCN 39429, T0 at 2025-02-23T15:04:35.749) using the GMG-2.4m telescope at the Lijiang Observatory. The observation began at 2025-02-25T12:45:36.92, about 45.68 hours after the trigger. The optical counterpart of EP250223a (Hauptmann et al., GCN 39436; Wu et al., GCN 39439; Pérez-Fournon et al., GCN 39440; Izzo et al., GCN 39441; Xin et al., GCN 39445; Guo et al., GCN 39447; An et al., GCN 39449; Ducoin et al., GCN 39453; O’Neill et al., GCN 39455; Aryan et al., GCN 39464; Saikia et al., GCN 39472), with a redshift of 2.756 (Levan et al., GCN 39438), was detected within the error box of EP/FXT (Lian et al., GCN 39429).
The preliminary analysis results are shown as follows:
| tmid-t0 (hours) | Filter | Exposure (s) | Magnitude (AB) | 5-sigma U.L. |
| ----------- |------- | ------------------ | -------------- | ------ |
| 45.85 | sdssr | 1200 | 20.82 +/- 0.08 | 21.9 |
The given magnitudes are derived based on calibration against Pan-STARRS1 field stars and are not corrected for the expected Galactic foreground extinction.
We warmly thank the staff at the Lijiang Observatory for their efforts in conducting the observation.
- GCN Circular #39496
E. Mazaeva (IKI), V. Rumyantsev (CrAO), A. Pozanenko (IKI), N. Pankov
(HSE, IKI), A. Volnova (IKI) report on behalf of IKI GRB-FuN collaboration:
We observed the field of EP250223a (Lian et al., GCN 39429) 2.6-meter ZTSh
telescope of CrAO starting on (UT) 2025-02-25 18:01:15.
The optical counterpart of EP250223a (Hauptmann et al., GCN 39436; Wu et
al., GCN 39439; Pérez-Fournon et al., GCN 39440; Izzo et al., GCN 39441;
Xin et al., GCN 39445; Guo et al., GCN 39447; An et al., GCN 39449; Ducoin
et al., GCN 39453; O’Neill et al., GCN 39455; Aryan et al., GCN 39464;
Saikia et al., GCN 39472; Wang et al., GCN 39476) at the redshift of 2.756
(Levan et al., GCN 39438) is clearly detected.
The preliminary photometry of the optical counterpart is the following:
Date UT start T-T0 Exp. Filter OT Err. UL(3sigma)
(mid, days) (s)
2025-02-25 18:01:15 2.15250 41x120 R 20.62 0.05 22.2
The magnitudes were calibrated using nearby PS1 stars using Lupton
transformations to R-magnitude. No correction has been made for a Galactic
extinction towards the counterpart.
- GCN Circular #39528
Wei-Sen Huang, Jin-Ji Li, Chun Chen, Zhong-Nan Dong, Jia-Qi Lin, Pu Lin, Hao-Nan Yang, Yan Yu, Hao-Ran Zhang, Si-Yuan Zhu, P H Thomas Tam, Rong-Feng Shen, Bin Ma (Sun Yat-sen University) report on behalf of the SYSU 80cm telescope team:
We observed the field of EP250223a (Lian et al., GCN 39429; Kennea et al., GCN 39437; Wang et al., GCN 39448) using the Sun Yat-sen University 80cm infrared telescope in J band. The calculated position is R.A. = 98.2712, DEC = -22.4449 (J2000), from EP/FXT observation. Our first observations began at 2025-02-24 12:10:00 UTC, 21.09 hours after the EP trigger, with 180 x 20 s exposures. The second observations began at 2025-02-25 12:54:00 UTC, 45.82 hours after the EP trigger, with 90 x 20 s exposures.
We do not detect any counterpart in the stacked images at the position of the optical afterglow(Lipunov et al., GCN 39434; Hauptmann et al., GCN 39436; Levan et al., GCN 39438; Wu et al., GCN 39439; Pérez-Fournon et al., GCN 39440; Izzo et al., GCN 39441; Xin et al., GCN 39445; Guo et al., GCN 39447; An et al., GCN 39449; Ducoin et al., GCN 39453; O’Neill et al., GCN 39455; Aryan et al., GCN 39464; Saikia et al., GCN 39472; Wang et al., GCN 39476; Mazaeva et al., GCN39496), down to a 5-sigma depth of J~17.2 Vega magnitudes on 2025-02-24 and J~17.0 Vega magnitudes on 2025-02-25.
- GCN Circular #39537
M. E. Ravasio (Radboud Univ.), E. Burns (LSU), and P.G. Jonker (Radboud Univ.) report on behalf of the Fermi-GBM Team:
Fermi-GBM had full spatial coverage of the transient EP250223A detected by EP-WXT (Lian et al., GCN 39429). There was no Fermi-GBM onboard trigger around the EP starting time T0=2025-02-23T15:02:05.66 UTC (Wang et al., GCN 39448).
The GBM targeted search [1], the most sensitive, coherent search for GRB-like signals, was run in the time interval [T0-50;T0+500] s, seeking signals between 64 ms and 32.768 s in duration. No signal consistent with the EP transient both temporally and spatially is identified, as confirmed by visual inspection of the data.
Assuming a “soft” spectral template (Band function with Epeak = 70 keV, alpha = -1.9, beta = -3.7), and a duration of 8.192 s, we derive a sky-averaged flux upper limit of 3.1e-08 erg/cm2/s in the energy band 10-1000 keV.
[1] Goldstein et al. 2019 arXiv:1903.12597
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