EP241126a
GCN Circular 38335
Subject
EP241126a: EP detection of a fast X-ray transient
Date
2024-11-27T03:48:24Z (6 months ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
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D.F. Hu, T. C. Zheng (PMO, CAS), B.-T. Wang (YNAO, CAS), M. J. Liu, H. Q. Cheng, C. C.Jin (NAO, CAS) on behalf of the Einstein Probe team
We report on the detection of a fast X-ray transient detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, EP241126a (Obs.ID: 06800000262). The transient was first detected with WXT at around 2024-11-26 19:39:41 (UTC) and lasted for over 60 seconds. The WXT position of EP241126a is R.A.= 33.744 deg, DEC = 11.705 deg (J2000) with an uncertainty of 2.429 arcmin (radius, 90% C.L. statistical and systematic). It has a peak flux of ~2 x 10^(-8) erg/s/cm^2 in the 0.5-4 keV band. The average 0.5-4 keV spectrum can be fitted with an absorbed power law with a photon index of 0.9 (+0.4/-0.4) (with a column density fixed at the Galactic value of 7.4 x 10^20 cm^-2). The derived average unabsorbed 0.5-4 keV flux is 3.3 (+0.9/-0.7) x 10^(-9) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters.
We have performed a target of opportunity (ToO) observation with the Follow-up X-ray Telescope (FXT) on board EP. The FXT onboard trigger shows an X-ray detection within the WXT error circle, at a position of R.A. = 33.7394 deg, DEC = 11.7001 deg (J2000) with an uncertainty of 20 arcsec (radius, 90% C.L. statistical and systematic). More details will be updated once the telemetry data is received.
No previously known bright X-ray sources are found within the error circle around the source position. More follow-up observations are encouraged to identify its nature.
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 38337
Subject
EP241126a: TRT optical counterpart detection
Date
2024-11-27T08:39:43Z (6 months ago)
From
Dong Xu at NAOC/CAS <dxu@nao.cas.cn>
Via
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S.Y. Fu, S.Q. Jiang (NAOC), S. Tinyanont, R. Anutarawiramkul, P. Butpan (NARIT), Z. Fan, W.X. Li, N.C. Sun, Y.N. Wang, D. Xu (NAOC) report on behalf of a large collaboration:
We observed the field of EP241126a detected by Einstein Probe (EP, Hu et al., GCN 38335), using the 0.7-m telescope of the Thai Robotic Telescope (TRT) network, located at Cerro Tololo Inter-American Observatory, Chile. Observations started at 02:29:48 UT on 2024-11-27, i.e., 6.84 hr after the EP trigger, and 10 x 300 s frames were obtained in the R-band.
An uncatalogued optical source is detected in the stacked frame within the EP/FXT error circle (Hu et al., GCN 38335) and localized at coordinates
R.A. (J2000) = 02:14:57.96
Dec. (J2000) = +11:42:04.76
with an uncertainty of ~ 0.8 arcsec. The source has R ~ 22.0 mag at a median time of 7.59 hr after the EP trigger, calibrated with PanSTARRS and not corrected for Galactic extinction. In the Legacy Survey there is no source at the above position, down to limiting magnitude r ~ 24.0.
We thus conclude that the source is the optical counterpart of EP241126a.
GCN Circular 38338
Subject
EP241126a: GSP detects optical counterpart
Date
2024-11-27T08:59:09Z (6 months ago)
From
Wenxiong Li <liwenxiong1992@gmail.com>
Via
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W. X. Li, S. J. Xue (NAOC), M. Andrews, J. Farah, D. A. Howell, M. Newsome, E. Padilla Gonzalez, C. McCully, and G. Terreran (Las Cumbres Observatory), on behalf of a larger collaboration, report:
Following the detection of the fast X-ray transient EP241126a by the Einstein Probe (Hu et al., GCN 38335) with the Sinistro instrument mounted on the 1-m telescope of the LCO, we initiated observations of the fast X-ray transient location starting on 2024 November 27 at 5:03 UT (~9.5 hours after the EP/WXT trigger) in the r band. These observations were conducted using the 1-meter telescope at the Las Cumbres Observatory node located at Cerro Tololo Interamerican Observatory in Chile.
The optical counterpart (Fu et al., GCN 38337) was detected in the co-added images with r = 22.2+-0.2.
These observations were taken as part of the Global Supernova Project.
GCN Circular 38339
Subject
EP241126a: EP-FXT follow-up observation update
Date
2024-11-27T09:51:05Z (6 months ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
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T. C. Zheng, D. F. Hu (PMO, CAS), B.-T. Wang (YNAO, CAS), M. J. Liu, H. Q. Cheng, C. C. Jin (NAO, CAS) on behalf of the Einstein Probe team
Following the detection of the fast X-ray transient EP241126a (Hu et al., GCN 38335), we performed an observation of EP241126a with the Follow-up X-ray Telescope (FXT) on board the Einstein Probe. The observation started at 2024-11-27T03:08:53 (UTC), about 7.5 hours after the EP-WXT detection, with an exposure time of 2980 seconds. An uncatalogued X-ray source is detected at R.A. = 33.7444 deg, DEC = 11.7013 deg (J2000) with an uncertainty of 10 arcsec in radius (90% C.L. statistical and systematic). The average FXT spectrum in 0.5-10 keV band can be fitted by an absorbed power law with a photon index of 2.2(+0.7/-0.7) (with a column density fixed at the Galactic one of 7.4 x 10^20 cm^-2), giving an average unabsorbed flux of 1.3(+1.1/-0.5) x 10^(-13) erg/s/cm^2 in the 0.5-10 keV band. The FXT position is ~10 arcsec away from the likely optical counterpart detected by TRT (Fu et al., GCN 38337) and LCO (Li et al. GCN 38338). We thus suggest the FXT detection being associated with EP241126a.
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 38344
Subject
EP241126a: Optical Upper limits with Kinder observations
Date
2024-11-27T13:42:19Z (6 months ago)
From
Amar Aryan at National Central University, Institute of Astronomy (NCUIA) <amararyan941@gmail.com>
Via
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C.-H. Lai, A. Aryan, T.-W. Chen, Y. J. Yang, C.-S. Lin (all NCU), A. K. H. Kong (NTHU), J. Gillanders (Oxford), S. J. Smartt (Oxford/QUB), A. Sankar. K, Y.-C. Pan, C.-C. Ngeow, M.-H. Lee, H.-C. Lin, W.-J. Hou, H.-Y. Hsiao, J.-K. Guo (all NCU), S. Yang, Z. N. Wang, 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 EP241126a (Hu et al., GCN 38335, Fu et al., GCN 38337; Li et al., GCN 38338; Zheng et al., GCN 38339) using the 1m LOT at the Lulin Observatory in Taiwan as part of the Kinder collaboration (Chen & Yang et al., 2024 arXiv:2406.09270). The first LOT epoch of observations started at 11:53 UTC on 27th November 2024 (MJD 60641.495), 16.23 hr after the EP-WXT trigger.
We utilize 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 our combined frame, we do not detect the optical counterpart proposed by Fu et al. (GCN 38337). The optical counterpart seems to have faded beyond our detection limit.
Moreover, we utilize 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 3-sigma limits (in the AB system) are as follows:
------------------------------------------------------------------------------------------------------ Telescope | Filter | MJD (start) | t-t0 (hr) | Exposure (s) | Magnitude | avg. Seeing | med. Airmass
LOT | r | 60641.495 | 16.23 | 300 * 6 | > 22.5 | 1".37 | 1.10
The presented magnitude was calibrated using the field stars from the Pan-STARRS1 catalog and was not corrected for the expected Galactic foreground extinction corresponding to a reddening of A_r = 0.38 mag in the direction of the transient (Schlafly & Finkbeiner 2011).
GCN Circular 38357
Subject
EP241126a: WFST Observations
Date
2024-11-28T02:53:42Z (6 months ago)
From
Tianrui Sun at Purple Mountain Obs,CAS <trsun@pmo.ac.cn>
Via
Web form
Jin-Jun Geng, Ji-An Jiang, Ning Jiang, Ming-Xin Wu, Min-Xuan Cai, Jia-Zheng Zhu, Kun Yan, Qing-Yi Hai, Xue-Feng Wu on behalf of the WFST Collaboration:
Following the detection of the fast X-ray transient EP241126a by WXT (Hu et al., GCN 38335) and FXT on board Einstein Probe (Zheng et al., GCN 38339), TRT (Fu et al., GCN 38337) and GSP (Li et al., GCN 38338), we carried out image observations using the newly deployed Wide Field Survey Telescope (WFST Collaboration; arXiv:2306.07590) at Lenghu Astronomical Observation Base (Qinghai province, China) to search and follow up its afterglow in the error box.
The optical counterpart candidate (Fu et al., GCN 38337 and Li et al., GCN 38338) was detected in the r band on the co-added images with an exposure time of 8 x 60s.
Our preliminary results are as follows:
|RA |DEC | DATE-OBS |Filter | Magnitude
|02:14:57.974 |+11:42:05.34 |2024-11-27T11:47 |r | 22.55+/-0.23
We used the PanStarrs DR1 (Flewelling,2020) catalog as the magnitude reference for calibration.
GCN Circular 38378
Subject
EP241126a: SVOM/VT observations
Date
2024-11-29T03:41:17Z (6 months ago)
From
Huali Li at at NAOC, SVOM <lhl@nao.cas.cn>
Via
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SVOM/VT commissioning team: Y. L. Qiu, L. P. Xin, C. Wu, H. L. Li, X. H. Han, J. Wang, W. J. Xie, H. B. Cai, Y. Xu, Y. J. Xiao, P. P. Zhang, J. S. Deng, L. Lan, X. M. Lu, R. S. Zhang, (NAOC), J. Zhang, L. J. Dan, G. Y. Zou, C. J. Wang, Y. F. Du, C. Huang (XIOPM), H. Zhou (PMO), L. Zhang (IHEP), Y.D. Hu(GXU), X.L. Chen (YNU), K. Chatterjee (YNU)
SVOM JSWG: Jian-Yan Wei (NAOC), Bertrand Cordier (CEA), Shuang-Nan Zhang (IHEP), Stéphane Basa (LAM), Arnaud Claret (CEA), Zi-Gao Dai (USTC), Frédéric Daigne (IAP), Jin-Song Deng (NAOC), Olivier Godet (IRAP), Andrea Goldwurm (APC), Diego Götz (CEA), Xu-Hui Han (NAOC), Cyril Lachaud (APC), En-Wei Liang (GXU), Yu-Lei Qiu (NAOC), Susanna Vergani (Obs.Paris), Jing Wang (NAOC), Chao Wu (NAOC), Li-Ping Xin (NAOC), Shao-Lin Xiong (IHEP), Bing Zhang (UNLV)
report on behalf of the SVOM team:
VT started to observe the fast X-ray transient EP241126a (EP-WXT，Hu et al., GCN 38335；EP-FXT，Zheng et al., GCN 38339; SVOM/GRM, Zheng et al., GCN 38342) in ToO mode from 2024-11-28T02:02:37.5 UT, about 30.38 hours after the burst. The VT conducted observations in VT_B band (400-650nm) and VT_R band (650-1000nm) simultaneously.
The optical counterpart (TRT, Fu et al., GCN 38337; GSP, Li et al., GCN 38338; WFST, Geng et al, GCN 38357) was detected in VT_R combined image with the brightness of 22.95 +/- 0.15 mag at the midtime of 33.27 hours after the burst. It was not detected in VT_B combined image, with the 3 sigma limit magnitudes of VT_B~24.1 mag. The exposure time of images in VT_R and VT_B are 5670 sec and 5760 sec respectively.
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 38385
Subject
EP241126a: NOT optical observations
Date
2024-11-29T22:23:22Z (6 months ago)
From
Daniele B. Malesani at IMAPP / Radboud University <d.malesani@astro.ru.nl>
Via
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Daniele B. Malesani (DAWN/NBI and Radboud Univ.), Peter G. Jonker (Radboud Univ.), Franz E. Bauer (PUC), Maria E. Ravasio (Radboud Univ.), Jonathan Quirola-Vasquez (Radboud Univ.), Javi Sanchez-Sierras (Radboud Univ.), Andrew J. Levan (Radboud Univ. and Warwick Univ.), on behalf of a larger collaboration, and Jacco H. Terwel (NOT and TCD), report:
We observed the optical counterpart (Fu et al., GCN 38337; Li et al., GCN 38338; Geng et al., GCN 38357; Qiu et al., GCN 38378) of the X-ray transient EP241126a (Hu et al., GCN 38335; Zheng et al., GCN 38339), using the Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. Observations were carried out in the SDSS r band and were unfortunately affected by "non-ideal" seeing (>2.5"). The mean time of our observation was 2024 Nov 27.836 UT, that is 24.4 hr after the EP trigger, and the total exposure time was 9x240 s.
The optical counterpart is marginally detected in our stacked image, with a magnitude r = 23.4 +- 0.3 (AB, calibrated against nearby sources from the Pan-STARRS catalog).
GCN Circular 38404
Subject
EP241126a: 1.6m Mephisto Optical Upper Limits
Date
2024-12-01T15:38:10Z (6 months ago)
From
Brajesh Kumar at SWIFAR, YNU <brajesh@ynu.edu.cn>
Via
Web form
Xingzhu Zou, Helong Guo, Xinlei Chen, Yu Pan, Yaosong Yu, Guowang Du, Xufeng Zhu, Tao Wang, Brajesh Kumar, Yuan Fang, Jinghua Zhang, Yuanpei Yang, Xiangkun Liu, Xiaowei Liu (SWIFAR, YNU) report on behalf of the Mephisto Team:
The field of fast X-ray transient EP241126a (Hu et al., GCN 38335; Zheng et al., GCN 38339) was observed with the 1.6m Multi-channel Photometric Survey Telescope (Mephisto) of Yunnan University located at Lijiang Observatory. The observations were carried out in the v and r bands, ~15.8 hours after the EP trigger. We do not detect the optical counterpart (Fu et al., GCN 38337; Li et al., GCN 38338; Geng et al., GCN 38357; Qiu et al., GCN 38378; Malesani et al., GCN 38385) in the stacked images (total exposure 420 sec in each band). The 3-sigma upper limits in v and r bands (mid-UT 2024-11-27T11:28:36) are 22.2 and 22.3 mag respectively, which is consistent with Lai et al. (GCN 38344).
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Mephisto (Multi-channel Photometric Survey Telescope) is a 1.6m 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.
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GCN Circular 38409
Subject
EP241126a: SOAR observations of the optical counterpart
Date
2024-12-01T21:45:36Z (6 months ago)
From
James Freeburn at Swinburne University of Technology <jamesfreeburn54@gmail.com>
Via
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J. Freeburn (Swinburne/OzGrav), I. Andreoni (UNC), J. Carney (UNC)
We observed the optical counterpart to the X-ray transient, EP241126a (Hu et al., GCN 38335; Zheng et al., GCN 38339), with the Goodman High Throughput Spectrograph mounted on the SOAR telescope in imaging mode. We took three 300s exposures in r-band between 2024-11-28T03:48:34 and 2024-11-28T04:07:23 UTC corresponding to ~32 hours after the initial trigger.
We detect the optical counterpart associated with EP241126a (Fu et al., GCN 38337; Li et al., GCN 38338; Geng et al., GCN 38357; Qiu et al., GCN 38378; Malesani et al., GCN 38385; Zou, GCN 38404). With photometric calibration using the Pan-STARRS1 catalogue, we measure r= 23.325 +/- 0.090 AB magnitude.