EP240518a
GCN Circular 36512
Subject
EP240518a: EP-WXT detection of a new X-ray transient
Date
2024-05-18T15:01:23Z (a year ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
Q.Y. Wu (NAOC, CAS), A. Li (BNU), Y. Liu, W. Yuan, Z. X. Ling, C. Zhang, H. Q. Cheng, W. Chen, C. Z. Cui, D. W. Fan, H. B. Hu, J. W. Hu, M. H. Huang, H. Y. Liu, M. J. Liu, Z. Z. Lv, T. Y. Lian, X. Mao, H. W. Pan, H. Sun, W. X. Wang, Y. L. Wang, Q. Y. Wu, X. P. Xu, Y. F. Xu, H. N. Yang, M. Zhang, W. D. Zhang, W. J. Zhang, Z. Zhang (NAOC,CAS), Y. Chen, S. M. Jia, S. N. Zhang (IHEP, CAS), E. Kuulkers, A. Santovincenzo (ESA), P. O'Brien (Univ. of Leicester), K. Nandra, A. Rau (MPE), B. Cordier (CEA) on behalf of the Einstein Probe team
We report on the detection of a new X-ray transient, designated EP240518a, by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission during a calibration observation. The transient triggered the WXT on-board processing unit at 2024-05-18T13:01:50 (UTC). The position of the source is R.A. = 216.955 deg, DEC = -49.565 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic). The transient event lasts for more than 1000 seconds and has an average flux of 8 x 10^-11 erg/s/cm^2 in the 0.5-4 keV band.
No previously known X-ray sources at a similar flux level are found within the 3 arcmin region around the source position. More information will be provided once the data has been transmitted through a ground station. Further multi-wavelength follow-up observations are encouraged to identify the nature of this X-ray flare.
The above observation was made with the WXT instrument during the commissioning phase of EP. 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). EP is a mission of the Chinese Academy of Sciences in collaboration with ESA, MPE and CNES.
GCN Circular 36514
Subject
EP240518a: possibly identified with a flare star by EP-FXT
Date
2024-05-19T16:22:25Z (a year ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
Q.Y. Wu (NAOC, CAS), A. Li (BNU), Y. Liu, W. Yuan, Z. X. Ling, C. Zhang, C. C. Jin, H. Q. Cheng, W. Chen, C. Z. Cui, D. W. Fan, H. B. Hu, J. W. Hu, M. H. Huang, H. Y. Liu, M. J. Liu, Z. Z. Lv, T. Y. Lian, X. Mao, H. W. Pan, H. Sun, W. X. Wang, Y. L. Wang, X. P. Xu, Y. F. Xu, H. N. Yang, M. Zhang, W. D. Zhang, W. J. Zhang, Z. Zhang (NAOC,CAS), Y. Chen, S. M. Jia, S. N. Zhang (IHEP, CAS), E. Kuulkers, A. Santovincenzo (ESA), P. O'Brien (Univ. of Leicester), K. Nandra, A. Rau (MPE), B. Cordier (CEA) on behalf of the Einstein Probe team
Following the detection of the X-ray transient EP240518a (Wu et al., GCN 36512) by the Wide-field X-ray Telescope (WXT) of Einstein Probe (EP), we performed an observation with the Follow-up X-ray Telescope (FXT) on board EP. The observation started at 2024-05-18T15:46:11, about 3 hours after the WXT detection, with a net exposure time of 6.0 ks.
Within the error circle of EP240518a, an X-ray source was clearly detected at R.A. = 216.954 deg, DEC = -49.584 deg, with an uncertainty of 30 arcsec (radius, 90% C.L. statistical and systematic). It is 7.9 arcsec away from a known X-ray source 1eRASS J142749.6-493505 with an archived flux of 6.0 x 10^-14 erg/s/cm^2 in 0.2-2.3 keV. The absorbed flux of the FXT source is 1.1(+0.3/-0.2) x 10^-13 erg/s/cm^2 (90% C.L.) in 0.5-10 keV, which is generally consistent with the eRASS flux but is about 3 orders of magnitude lower than the peak flux of EP240518a (~8 x 10^-11 erg/s/cm^2). This suggests that the time scale of EP240518a, if associated with the FXT source, is shorter than several hours. The FXT spectrum can be well fitted with the tbabs*apec model with the plasma temperature kT = 0.21(+0.10/-0.06) keV (90% C.L.). A possible M-type dwarf star named Gaia DR3 5899529595616014848, with a distance of about 35 pc, is located around 7 arcsec from the FXT position. If the FXT source is related to the eRASS source and the dwarf, then EP240518a may be a stellar flare with a luminosity of 1.3 x 10^31 erg/s in 0.5-4.0 keV.
Please note that EP-FXT is currently undergoing in-flight calibration. The derived source parameters may be subject to larger uncertainties, so please use them with caution. 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). EP is a mission of the Chinese Academy of Sciences in collaboration with ESA, MPE and CNES.
GCN Circular 36529
Subject
EP240518a: GSP optical upper limit
Date
2024-05-22T09:08:13Z (a year ago)
From
Wenxiong Li <liwenxiong1992@gmail.com>
Via
Web form
W. X. Li, S. J. Xue (NAOC), M. Andrews, J. Farrah, 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 EP240518a by the Einstein Probe (Wu et al., GCN 36512; Wu et al., GCN 36514), we initiated observations of the transient's location in the r band on May 18 at 16:46 UT, ~4 hours after the trigger. These observations were conducted using the 1-meter telescope at the Las Cumbres Observatory node located at Siding Spring Observatory in Australia.
We report that no new optical source was detected in the co-added images within the EP/FXT error box down to a limiting magnitude of ~21.5. The possible M-type dwarf star named Gaia DR3 5899529595616014848, mentioned in Wu et al. (GCN 36514), was detected without significant variation compared to archival DECam images.
These observations were taken as part of the Global Supernova Project.