EP240816b
GCN Circular 37185
Subject
EP240816b: EP-WXT detection and EP-FXT follow-up observation of a fast X-ray transient
Date
2024-08-16T11:43:36Z (10 months ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
H. N. Yang, W. J. Zhang, W. X. Wang, W. Yuan, Z. X. Ling, C. C. Jin, Y. Liu, C. Zhang, H. Q. Cheng, W. Chen, C. Z. Cui, D. W. Fan, H. B. Hu, J. W. Hu, M. H. Huang, D. Y. Li, H. Y. Liu, M. J. Liu, Z. Z. Lv, T. Y. Lian, X. Mao, H. W. Pan, X. Pan, H. Sun, Y. L. Wang, Q. Y. Wu, X. P. Xu, Y. F. Xu, M. Zhang, W. D. Zhang, Z. Zhang, D. H. Zhao (NAOC, CAS), Y. Chen, S. M. Jia, W. W. Cui, D. W. Han, C. K. Li, L. M. Song, X. F. Zhao, J. Zhang, 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 fast X-ray transient, designated EP240816b, by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission. The transient event started at 2024-08-16T01:44:27 (UTC) and triggered the WXT on-board processing unit (trigger ID: 01709034033).
The light curve lasts for more than 50 seconds. The WXT position of the source is R.A. = 16.013 deg, DEC = 15.398 deg (J2000) with an uncertainty of 3.33 arcmin in radius (90% C.L. statistical and systematic). The average 0.5-4 keV spectrum can be fitted with an absorbed power law with a photon index of 1.6(+0.7/-0.7) (with a frozen column density value of 5.2 x 10^20 cm^-2). The derived average unabsorbed 0.5-4 keV flux is 1.3(+0.7/-0.5) x 10^-9 erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters.
The follow-up observation by the Follow-up X-ray Telescope (FXT) on board EP was triggered automatically at 2024-08-16T01:47:34 (UTC). An uncatalogued X-ray source is detected at R.A. = 16.0161 deg, DEC = 15.4151 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 1.69(+0.23/-0.22) (with a freely fitted column density value of 9.5(+6.9/-6.7) x 10^20 cm^-2), giving an average unabsorbed flux in 0.5-10 keV of 4.3(+0.6/-0.5) x 10^-12 erg/s/cm^2.
No previously known bright X-ray sources are found within the error circle around the source position. 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).
GCN Circular 37186
Subject
EP240816b: TRT optical upper limit
Date
2024-08-16T12:34:32Z (10 months ago)
From
Dong Xu at NAOC/CAS <dxu@nao.cas.cn>
Via
Web form
J. An, S.Q. Jiang (NAOC), S. Tinyanont, R. Anutarawiramkul, P. Butpan (NARIT), X. Liu, S.Y. Fu, Z.P. Zhu, S.Y. Gao, D. Xu, Z. Fan, W.X. Li, N.C. Sun, Y.N. Wang (NAOC) report on behalf of a large collaboration:
We observed the field of EP240816b (Yang et al., GCN 37185) using the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at Fresno, California, U.S.A. Observations started at 07:10:37 UTC on 2024-08-16, i.e., 5.436 hr after the EP trigger, and 4 x 300 s frames were obtained in R-band.
No uncatalogued optical source is detected in the stacked image within the 10-arcsec EP/FXT error circle, down to a 5-sigma limiting magnitude of R ~ 20.0, calibrated with PanSTARRS sources in the field.
GCN Circular 37187
Subject
EP EP240816b: Global MASTER-Net observations report
Date
2024-08-16T14:18:21Z (10 months ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
Via
legacy email
V. Lipunov, V.Kornilov, E. Gorbovskoy, K. Zhirkov, N.Tyurina, P.Balanutsa, A.Kuznetsov, V.Senik, D. Vlasenko,
G.Antipov, D.Zimnukhov, E.Minkina, A.Chasovnikov, V.Topolev, D.Kuvshinov, D. Cheryasov, Ya.Kechin, Yu.Tselik, A. Sosnovskij
(Lomonosov Moscow State University, SAI, Physics Department),
R. Podesta, C.Lopez, F. Podesta, C.Francile
(Observatorio Astronomico Felix Aguilar OAFA),
R. Rebolo, M. Serra
(The Instituto de Astrofisica de Canarias),
D. Buckley
(South African Astronomical Observatory),
O.A. Gress, N.M. Budnev, O.Ershova
(Irkutsk State University, API),
L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez,
A.R.Corella, L.H.Rodriguez
(INAOE, Guillermo Haro Astrophysics Observatory),
A. Tlatov, D. Dormidontov
(Kislovodsk Solar Station of the Pulkovo Observatory),
V. Yurkov, A. Gabovich
(Blagoveschensk Educational State University)
MASTER-Amur robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Blagoveshchensk State Pedagogical University) was pointed to the EP EP240816b ( EP Team et al., GCN 37185) errorbox 7216 sec after notice time and 43322 sec after trigger time at 2024-08-16 13:46:29 UT, with upper limit up to 16.6 mag. The observations began at zenith distance = 70 deg. The sun altitude is -22.1 deg.
The galactic latitude b = -47 deg., longitude l = 128 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=2565229
We obtain a following upper limits.
Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________
43353 | 2024-08-16 13:46:29 | MASTER-Amur | (01h 05m 15.59s , +15d 55m 23.8s) | C | 60 | 16.5 |
43353 | 2024-08-16 13:46:29 | MASTER-Amur | (01h 05m 52.23s , +15d 28m 12.3s) | C | 60 | 15.3 |
43632 | 2024-08-16 13:51:09 | MASTER-Amur | (01h 05m 12.15s , +15d 54m 16.6s) | C | 60 | 16.6 |
43632 | 2024-08-16 13:51:09 | MASTER-Amur | (01h 05m 47.89s , +15d 27m 13.4s) | C | 60 | 15.2 |
Filter C is a clear (unfiltred) band.
The observation and reduction will continue.
The message may be cited.
GCN Circular 37191
Subject
EP240816b: KAIT optical upper limit
Date
2024-08-16T17:14:11Z (10 months ago)
From
Weikang Zheng at UC Berkeley <weikang@berkeley.edu>
Via
legacy 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, responded to the fast X-ray transient EP240816b
from the Einstein Probe (Yang et al. GCN 37185) starting at 07:42
UT, Aug 16th, ~6.0 hours after the trigger. A set of 30x60s images
were obtained in the clear (roughly R) filters. Preliminary analysis
do not reveal any new optical counterpart candidate within the 10
arcsec radius EP-FXT error box (Yang et al. GCN 37185), neither in
single image, nor in the co-add images, consistent with the reports
from An et al. (GCN 37186) and Lipunov et al. (GCN 37187). The
typical limiting magnitude of our single clear image is about 19.5
mag, and about 20.5 mag in the co-add image.
GCN Circular 37201
Subject
EP240816b: Liverpool Telescope optical follow-up observations
Date
2024-08-18T15:34:10Z (9 months ago)
From
A. Bochenek at Liverpool John Moores University <a.m.bochenek@2023.ljmu.ac.uk>
Via
Web form
A. Bochenek, D. A. Perley (LJMU) report:
We observed the field of the X-ray transient EP240816b (Yang et al. GCN 37185) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 5x150s exposures with the SDSS-R and SDSS-I filters between 2024-08-17 03:01:07 UT and 2024-08-17 03:29:10 UT, approximately 25.5 hours after the transient.
The images were stacked and the background was subtracted relative to Pan-STARRS reference imagining using PSF matching with the help of PSFEx. No uncatalogued optical source was detected within the 90% confidence 10 arcsec EP/FXT error-circle, nor within the 3.33 arcmin EP/WXT error circle. The 3-sigma limiting magnitudes on our stacked images are r > 22.2 mag and i > 21.8 mag.