GRB 240913C, EP240913a
GCN Circular 37584
Subject
EP240913A/GRB 240913C: AbAO optical upper limit
Date
2024-09-21T10:33:25Z (a year ago)
From
Alexei Pozanenko at IKI, Moscow <grb.alex@gmail.com>
Via
legacy email
S. Belkin (HSE, IKI), R. Ya. Inasaridze (AbAO), A. Pozanenko (IKI), N.
Pankov (HSE, IKI) report on behalf of GRB-IKI-FuN:
We observed the field of EP240913A/GRB 240913C (Li et al., GCN 37492; Yin
et al., GCN 37493; Dasgupta et al., GCN 37505; Bissaldi et al., GCN 37509;
Pawar et al., GCN 37510) using the 70-cm AS-32 telescope at the Abastumani
Observatory (AbAO) in the R-filter, starting on 2024-09-14 at 23:44:17
(UT). We did not detect the optical counterpart in the stacked image within
the Swift-XRT error circle (Jiang et al., GCN 37497), consistent with
reports from Asquini et al., GCN 37499; Zhu et al., GCNs 37500, 37501;
Zheng et al., GCN 37511; Schneider et al., GCN 37515; Lipunov et al., GCN
37521. Preliminary photometry is as follows:
Date UT Start t-T0 (days) Filter Exposure (s) OT Err UL (3σ)
2024-09-14 23:44:17 1.53211 R 113×60 n/d n/d 22.2
The magnitudes were calibrated using nearby USNO-B1.0 stars:
RA: 01:06:52.7994912, DEC: +16:43:24.121128, R2: 15.96
RA: 01:07:11.4427176, DEC: +16:49:54.951564, R2: 17.09
GCN Circular 37582
Subject
EP240913a/GRB 240913C: 1.6m Mephisto observations
Date
2024-09-21T03:16:25Z (a year ago)
From
Brajesh Kumar at SWIFAR, YNU <brajesh@ynu.edu.cn>
Via
Web form
Xingzhu Zou, Xiangkun Liu, Yangwei Zhang, Xin Chang, Yaosong Yu, Jinghua Zhang, Yuan Fang, Guowang Du, Yu Pan, Xinlei Chen, Brajesh Kumar, Yuanpei Yang, Xinzhong Er and Xiaowei Liu (SWIFAR, YNU) report on behalf of Mephisto Team:
We observed the fast X-ray transient EP240913a (Li et al., GCN 37492, which has been proposed to be a GRB event by Yin et al., GCN 37493) with 1.6m Multi-channel Photometric Survey Telescope (Mephisto) of Yunnan University located at Lijiang Observatory. Multiple frames in ugi and vrz bands were simultaneously acquired on 2024-09-14 starting from 14:35:17 (~26.9 hrs after EP T0). In the co-added frames, no evidence of any new uncataloged optical source was detected within the WXT error circle of 2.5 arcmin reported by Li et al. (GCN 37492). Existing sources within this error circle exhibited no significant optical enhancement. The table below provides details of the observations and the measured 3-sigma upper limits on co-added frames (in the AB magnitude system) taken with Mephisto. This non-detection result of the transient is in agreement with the previous circulars (Asquini et al., GCN 37499, Zhu et al., GCN 37500, 37501, Zheng et al., 37511, Schneider et al., GCN 37515, Lipunov et al., GCN 37521).
Time-start Time-end Filter Exposure U.L.(AB)
14:35:17 14:44:46 u 180s*3 21.29
14:46:15 14:52:29 v 180s*2 20.87
14:35:18 14:44:45 g 50s*9 21.90
14:46:16 14:52:26 r 50s*6 21.42
14:35:17 14:44:48 i 79s*6 21.25
14:49:30 14:52:28 z 79s*4 19.52
------------------------------------------------------------------------------------------------------
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.
------------------------------------------------------------------------------------------------------
GCN Circular 37538
Subject
IPN triangulation of GRB 240913C / EP 240913a
Date
2024-09-17T20:48:24Z (a year ago)
Edited On
2024-09-25T15:08:44Z (a year ago)
From
Dmitry Svinkin at Ioffe Institute <svinkin@mail.ioffe.ru>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of Dmitry Svinkin at Ioffe Institute <svinkin@mail.ioffe.ru>
Via
Web form
A.S. Kozyrev, D.V. Golovin, M.L. Litvak, I.G. Mitrofanov, and A.B. Sanin
on behalf of the HEND/Mars Odyssey team,
D. Svinkin, D. Frederiks, A. Ridnaia, A. Lysenko,
and T. Cline on behalf of the Konus-Wind team,
A. Goldstein, M. S. Briggs, C. Wilson-Hodge,
and E. Burns on behalf of the Fermi GBM team,
E. Bozzo and C. Ferrigno, on behalf of the INTEGRAL SPI-ACS GRB team,
S. Barthelmy, J. Cummings, H. Krimm, D. Palmer, and A. Tohuvavohu
on behalf of the Swift-BAT team,
G. Waratkar, V. Jethwani, J.Joshi, V. Bhalerao, D. Bhattacharya,
and S. Vadawale, on behalf of the Astrosat-CZTI team,
and
W. Boynton, C. Fellows, K. Harshman, H. Enos, R. Starr,
and A.S. Gardner on on behalf of the GRS-Odyssey GRB team,
report:
The long-duration GRB 240913C
(AstroSat-CZTI detection: Dasgupta et al., GCN 37505;
ETJASMIN Joint location: Zhang et al., GCN 37507;
Fermi-GBM detection: Bissaldi and Meegan, GCN 37509;
INTEGRAL-SPI-ACS detection: Pawar et al., GCN 37510)
was detected by AstroSat (CZTI), Fermi (GBM trigger 747920561),
Konus-Wind, INTEGRAL (SPI-ACS), Swift (BAT), and Mars-Odyssey (HEND)
at about 42156 s UT (11:42:36).
The burst was outside the coded field of view of the BAT.
We have triangulated it to the following annuli:
---------------------------------------------------
annulus R.A. Dec. R dR (3sigma)
(deg) (deg) (deg) (deg)
---------------------------------------------------
Konus-GBM 333.897 -8.566 50.692 1.965
Konus-SPI-ACS 334.296 -2.846 47.219 3.486
GBM-SPI-ACS 56.462 86.015 62.390 17.278
GBM-HEND 95.231 23.495 73.181 0.024
---------------------------------------------------
The Konus-GBM, GBM-SPI-ACS and GBM-HEND annuli
intersect to form a long box, whose area is 3075 sq. arcmin,
and its maximum dimension is 20.8 deg (the minimum one is 3.2 arcmin).
The Sun distance was 142 deg.
This localization may be improved.
The IPN localization is consistent with, but reduces the area of,
the Fermi-GBM and ETJASMIN joint localizations. The position of
the fast X-ray transient EP240913a (Li et al., GCN 37492;
Jiang et al., GCN 37497) is inside the IPN localization,
strengthening the association of GRB 240913C with the EP240913a
initially suggested by Dasgupta et al. (GCN 37505) and Zhang et al. (GCN 37507).
A triangulation map and HEALPix FITS file are posted at
http://www.ioffe.ru/LEA/GRBs/GRB240913_T42159/IPN/
The HEALPix triangulation map is the multi-order HEALPix in units of
probability density.
The Konus-Wind time history and spectrum will be given
in a forthcoming GCN Circular.
GCN Circular 37521
Subject
EP EP240913a: Global MASTER-Net observations report
Date
2024-09-16T09:18:29Z (a year 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-OAFA robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Argentina (OAFA observatory of San Juan National University) was pointed to the EP EP240913a ( EP Team et al., GCN 37492) errorbox 3325 sec after notice time and 2 days 75829 sec after trigger time at 2024-09-16 08:43:22 UT, with upper limit up to 18.4 mag. The observations began at zenith distance = 61 deg. The sun altitude is -23.9 deg.
The galactic latitude b = -46 deg., longitude l = 129 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=2603446
We obtain a following upper limits.
Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________
248688 | 2024-09-16 08:43:20 | MASTER- | (01h 00m 36.47s , +16d 08m 09.0s) | C | 120 | 19.3 |
248689 | 2024-09-16 08:43:22 | MASTER-OAFA | (01h 10m 06.79s , +16d 36m 57.6s) | C | 120 | 18.4 |
Filter C is a clear (unfiltred) band.
The observation and reduction will continue.
The message may be cited.
GCN Circular 37515
Subject
EP240913a: VLT/HAWK-I near-infrared upper limits
Date
2024-09-15T14:13:04Z (a year ago)
From
Benjamin Schneider at MIT <bschn@mit.edu>
Via
Web form
B. Schneider (MIT), Z.P. Zhu (NAOC), A. J. Levan (Radboud), P. D'Avanzo (INAF-OAB), D. Xu (NAOC), D. B. Malesani (Radboud and DAWN/NBI) report on behalf of the Stargate collaboration:
We observed the field of EP240913a detected by Einstein Probe (EP, Li et al., GCN 37492) with the ESO Very Large Telescope, equipped with the HAWK-I near-infrared camera. We obtained 10 min exposure in both the Y and Ks bands, as well as 8 min exposure in J and H. Observations started at 06:54:36 UT on 2024-09-14, i.e. 19.2 hr after the EP trigger.
No new source is detected within the error circle of the proposed X-ray counterpart (Jiang et al., GCN 37497) in any of the four bands. We obtained a 3-sigma limiting magnitude of J ~ 23.7 (Vega), calibrated against nearby sources from the 2MASS catalog.
We acknowledge the excellent support provided by the Paranal staff, in particular Marco Berton and Fuyan Bian.
GCN Circular 37511
Subject
EP240913a/GRB 240913C: KAIT optical upper limit
Date
2024-09-14T21:19:56Z (a year 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 EP240913a/GRB 240913C (Li et al.,
GCN 37492; Yin et al., GCN Circ. 37493; Dasgupta et al., GCN 37505;
Pawar et al., GCN 37510) starting at 06:12 UT, Sep 14th, ~18.6
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 Swift-XRT error
circle of the X-ray counterpart candidate (Jiang et al., GCN 37497)
neither in single image, nor in the co-add images, consistent with
the reports from Asquini et al. (GCN 37499) and Zhu et al. (GCN
37500, 37501). 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 37510
Subject
EP240913a / GRB 240913C INTEGRAL SPI ACS LIGHT CURVE
Date
2024-09-14T18:37:22Z (a year ago)
From
Devraj Pawar at R. J. College, Mumbai - 86, India <devrajdp@gmail.com>
Via
Web form
Devraj Pawar (R. J. College, Mumbai-86, India) on behalf of a collaboration studying transients.
Li et al. (GCN 37492) reported X-ray transient EP240913a at 2024-09-13T11:39:33 UTC and Yin et al. (GCN 37493) reported the occurrence of bright gamma-ray transient in the Fermi/GBM data approximately 180 seconds after time of EP240913a. We analyzed the INTEGRAL SPI ACS data around the time of EP240913a given in GCN 37492 and detected a peak in the light curve after a lag of ~177 s. The SPI ACS is sensitive above 80 keV; the peak of the burst is at ~3630 counts/s and the steady rate preceding the event is around 3300 counts/s, this may be affected by the instruments orientation with respect to the direction of the source given in GCN 37507. The light curve indicating the peak with respect to EP240913a time and the profile is given in the link below.
[https://docs.google.com/document/d/1VmCF7dktgNCYbGKSV8uegpFCkx11WIfES9D5Z9Ua7EE/edit?usp=sharing]()
This work is based on observations with INTEGRAL, an ESA project with instruments and a science data center funded by ESA member states (especially the PI countries: Denmark, France, Germany, Italy, Switzerland, Spain), and with the participation of Russia and the USA. The SPI-ACS detector system has been provided by MPE Garching/Germany.
GCN Circular 37509
Subject
GRB 240913C: Fermi GBM detection
Date
2024-09-14T18:00:44Z (a year ago)
From
Elisabetta Bissaldi at Politecnico and INFN Bari <elisabetta.bissaldi@ba.infn.it>
Via
Web form
E. Bissaldi (Politecnico and INFN Bari) and C. Meegan (UAH)
report on behalf of the Fermi GBM Team:
"At 11:42:36.12 UT on 13 September 2024, the Fermi Gamma-Ray Burst Monitor (GBM)
triggered and located GRB 240913C (trigger 747920561 / 240913488),
which was also detected by the Einstein Probe (GCN #37492, #37493).
The on-ground calculated location, using the GBM trigger
data, is RA = 14.6, DEC = 12.3 (J2000 degrees,
equivalent to 00h 58m, 12d 18'), with a statistical uncertainty
of 3.8 degrees (radius, 1-sigma containment,
statistical only; there is additionally a systematic
error which we have characterized as a core-plus-tail model, with 90% of
GRBs having a 3.7 deg error and a small tail suffering a larger than 10 deg
systematic error [Connaughton et al. 2015, ApJS, 216, 32] ).
The angle from the Fermi LAT boresight at the GBM trigger time is 104 degrees.
The GBM light curve consists of a bright peak
with a duration (T90) of about 6.3 s (50-300 keV).
The time-averaged spectrum from T0-1.3 s to T0+3.8 s is
best fit by a Band function with Epeak = 68 +/- 6 keV,
alpha = 0.08 +/- 0.23, and beta = -2.41 +/- 0.12.
The event fluence (10-1000 keV) in this time interval is
(2.35 +/- 0.01)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+0.26 s in the 10-1000 keV band
is 15.1 +/- 2.6 ph/s/cm^2.
The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog:
https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html
For Fermi GBM data and info, please visit the official Fermi GBM Support Page:
https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/"
GCN Circular 37507
Subject
GRB 240913C: Joint location by ETJASMIN
Date
2024-09-14T15:05:33Z (a year ago)
From
yqzhang_cl@163.com
Via
Web form
Yanting Zhang, Yanqiu Zhang, Shaolin Xiong, Yue Huang, Shuo Xiao, Xiaoyun Zhao, Ping Wang, report on behalf of a larger collaboration team:
Yin et al. (GCN Circ. 37493) reported that the burst, GRB 240913C, detected by Fermi/GBM at 2024-09-13T11:42:36.12 UTC coincide with EP240913a detected by EP/WXT (Li et al., GCN Circ. 37492) in terms of timing and location. We noticed that this burst was also detected by INTEGRAL/SPI-ACS (trignum=10902). With the public data of Fermi/GBM and INTEGRAL/SPI-ACS, we did a joint location for this burst with the ETJASMIN pipeline (Energetic Transients joint analysis system for Multi-INstrument, Xiao et al., MNRAS, 514, 2397, 2022). In this pipeline, we applied the Li-CCF method (Xiao et al., ApJ, 920, 43, 2021) to the high temporal resolution (~0.1 ms) light curve of Fermi/GBM and the low-latency 50 ms light curve of INTEGRAL/SPI-ACS, and derived a low-latency triangulation location as the following annuli:
--------------------------------------------------------------------------------------------------
Annulus R.A. (deg) Dec (deg) Radius (deg) Radius-Error (deg, 1sigma)
GBM + SPI-ACS 56.378 86.003 73.064 13.17
--------------------------------------------------------------------------------------------------
This location is well consistent with the EP location within the error, supporting that GRB 240913C is the high energy counterpart of EP240913a.
We note that this ETJASMIN location may be improved as more data from other instruments are used.
ETJASMIN is dedicated for joint observation of high energy transients with multiple instruments. ETJASMIN was initially developed for GECAM satellites and has been extended to accommodate other instruments. We acknowledge the public data of Fermi/GBM and INTEGRAL/SPI-ACS.
GCN Circular 37505
Subject
EP240913A / GRB 240913C: AstroSat CZTI detection
Date
2024-09-14T13:31:29Z (a year ago)
From
Gaurav Waratkar at IIT Bombay <gauravwaratkar@iitb.ac.in>
Via
Web form
A. Dasgupta (BITS Pilani, Hyderabad), S. Srijan (IITB), G. Waratkar (IITB), J. Joshi (IUCAA), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration:
Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of a long-duration GRB 240913C, a burst potentially related to EP240913A, which was also detected by Fermi/GBM (Yin et al., GCN Circ. 37493). Our detection time is consistent with that of Fermi/GBM, which is about 180 s after the EP/WXT detection time (Li et al., GCN Circ. 37492).
The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2024-09-13 11:42:36.46 UTC. The measured peak count rate associated with the burst is 352 (+59, -62) counts/s above the background in the combined data of all quadrants, with a total of 510 (+142, -155) counts. The local mean background count rate was 294 (+4, -5) counts/s. Using cumulative rates, we measure a T90 of 5.2 (+3.1, -2.3) s.
We also had a faint detection in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2024-09-13 11:42:36.8 UTC. The measured peak count rate is 132 (+64, -65) counts/s above the background in the combined Veto data of all quadrants, with a total of 639 (+522, -561) counts. The local mean background count rate was 1216 (+12, -13) counts/s. We measure a T90 of 6.9 (+1.8, -4.1) s from the cumulative Veto light curve.
CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project.
CZTI GRB detections are reported regularly on the payload site at:
http://astrosat.iucaa.in/czti/?q=grb
GCN Circular 37501
Subject
EP240913a: NOT optical upper limits
Date
2024-09-14T11:40:33Z (a year ago)
From
Dong Xu at NAOC/CAS <dxu@nao.cas.cn>
Via
Web form
Z.P. Zhu, S.Y. Fu, S.Q. Jiang, J. An, X. Liu, D. Xu (NAOC), J.P.U. Fynbo (DAWN/NBI), P. Hakala (NOT) report on behalf of a large collaboration:
We observed the field of EP240913a detected by Einstein Probe (EP, Li et al., GCN 37492), using the ALFOSC instrument mounted on the 2.56-m Nordic Optical Telescope (NOT), with 3 x 300 s photometry in the SDSS-r band and 5 x 200 s in the SDSS-z band. Observations started at 01:13:39 UT on 2024-09-13, i.e., 13.6 hr after the EP trigger.
No new optical source is detected within the error circle of the proposed X-ray counterpart (Jiang et al., GCN 37497), down to the following 3-sigma upper limits:
T_mid (UT) | T_mid (hr) | filter | Exposue(s)| U.L. (AB)
2024-09-14T01:21:35 | 13.701 | r | 3x300 | 24.0
2024-09-14T01:39:43 | 14.003 | z | 5x200 | 23.0
calibrated with nearby PanSTARRS stars and not corrected for Galactic extinction.
GCN Circular 37500
Subject
EP240913a: JinShan optical upper limits
Date
2024-09-14T11:31:29Z (a year ago)
From
Dong Xu at NAOC/CAS <dxu@nao.cas.cn>
Via
Web form
Z.P. Zhu, S.Y. Fu, S.Q. Jiang, J. An, X. Liu, D. Xu (NAOC), J.Z. Liu (XAO) report on behalf of a large collaboration:
We observed the field of EP240913a detected by Einstein Probe (EP, Li et al., GCN 37492), using the 100cm-C telescope (100C) of the JinShan project, located at Altay, Xinjiang, China. Observations started at 16:48:02 UT on 2024-09-13, i.e., 5.1 hr after the EP trigger, and a series of frames were obtained in the Sloan r- and z-bands.
No new optical source is detected within the error circle of the proposed X-ray counterpart (Jiang et al., GCN 37497), down to the following 5-sigma upper limits:
T_mid (UT) | T_mid (hr) | filter | Exposue|5-sigma U.L. (AB)
2024-09-13T17:59:25 | 6.331 | r | 13x200s +10x300s | 21.9
2024-09-13T17:29:08 | 5.827 | z | 9x200s | 19.3
calibrated with nearby PanSTARRS stars and not corrected for Galactic extinction.
We acknowledge the excellent support from X. Yao, S.W. Luo, and Z.K. Feng for enabling these observations.
GCN Circular 37499
Subject
EP240913a: ESO-NTT optical observations
Date
2024-09-14T11:26:08Z (a year ago)
From
Paolo D'Avanzo at INAF - OAB <paolo.davanzo@inaf.it>
Via
email
L. Asquini, M. Landoni, P. D'Avanzo, S. Campana (INAF-Brera), C. Farias (ESO/ La Silla) report:
We observed the field of EP 240913A (Li et al., GCN Circ. 37492), which has been proposed to be a GRB event (Yin et al., GCN Circ. 37493), with the ESO-NTT telescope equipped with EFOSC2 starting at 2024-09-14T05:58:49 UT (i.e. about 18.3 hours after the EP T0), during an on-site test run for the scheduler of the incoming SOXS instrument.
Observations have been carried out in imaging mode with the Gunn r and i filters.
No optical counterpart is detected within the Swift-XRT error circle of the proposed X-ray counterpart (Jian et al., GCN Circ. 37497).
From preliminary photometry, we estimate a 3sigma limit of r ~ 23.5 mag (AB; calibrated against the PanSTARRS catalogue),.
Further analysis is ongoing.
GCN Circular 37497
Subject
EP240913a: Swift/XRT detection of an X-ray source within the EP/WXT error circle
Date
2024-09-14T10:49:22Z (a year ago)
From
Dong Xu at NAOC/CAS <dxu@nao.cas.cn>
Via
Web form
S.Q. Jiang, Z.P. Zhu, D.Y. Li, C.C. Jin, J. An, X. Liu, S.Y. Fu, D. Xu (NAOC) report on behalf of a large collaboration:
A Swift ToO observation (ID: 16809) of the X-ray transient of EP240913a (Li et al., GCN 37492) was carried out. The observation started at 2024-09-13 19:47:21.024 (UTC) , i.e, 8.13 hr after the EP/WXT trigger, and lasted ~1.65 ks.
An X-ray source is detected in the Swift/XRT image within the EP/WXT error circle (Li et al., GCN 37492) at coordinates
R.A. (J2000) = 01:06:46.69
Dec (J2000) = +16:43:47.20
with an uncertainty of 6.2 arcsec (radius, 90% C.L. statistical and systematic).
The Swift/XRT spectrum, which can be fitted with an absorbed power-law with a photon index of 1.40 (-0.83, +0.80) modified by Galactic absorption of 5.1 x 10^20 cm^-2, gives an unabsorbed 0.3-10 keV flux of 7.8 (-3.6, +9.7) x 10^(-13) erg/s/cm^2.
We didn't find any other credible X-ray source within the EP/WXT error circle. And there is no previously known bright X-ray source at the above position. We thus think the source is likely the counterpart of EP240913a, which could be a GRB event (Yin et al., GCN 37493).
We thank the Swift team for performing the ToO observation.
GCN Circular 37493
Subject
EP240913a: A GRB Event
Date
2024-09-14T04:10:41Z (a year ago)
Edited On
2024-09-14T13:57:29Z (a year ago)
From
Iris Yin at Nanjing University <iris.yin@smail.nju.edu.cn>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of Iris Yin at Nanjing University <iris.yin@smail.nju.edu.cn>
Via
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Yi-Han Iris Yin (NJU), Jun Yang (NJU), Bin-Bin Zhang (NJU), Hui Sun (NAOC) and Xuefeng Wu (PMO) report on behalf of large collaboration:
Our team has conducted a follow-up high-energy data search of the X-ray transient detected by the Einstein Probe (EP) at 2024-09-13T11:39:33 UTC (EP240913a; GCN Circular 37492). We discovered a bright gamma-ray transient in the Fermi/GBM data approximately 180 seconds after T0 of EP240913a, coinciding with the peak time of the X-ray transient. Additionally, we note that this event is listed as a burst trigger (bn240913488) in the GBM database.
The GBM light curve shows a single emission episode with a duration (T90) of approximately 5 seconds (10-1000 keV). The time-averaged spectrum from T0+181 to T0+188 seconds is well fitted by a cutoff power-law function, N(E) = A*(E^-Gamma)*exp(-E*(2-Gamma)/Ep), with a peak energy of about 100 keV and a photon index, Gamma, of approximately 0.5. The fluence (10-1000 keV) during this interval is estimated to be ~ 1.88e-6 erg/cm^2, and the 0.26-s binned peak flux in the 10-1000 keV band is ~ 1.74e-6 erg/s/cm^2.
Given that the gamma-ray transient is consistent with EP240913a in both timing and location, we propose that this is a GRB event.
We strongly recommend further follow-up observations of EP240913a to confirm its physical nature and to search for potential afterglows.
GCN Circular 37492
Subject
EP240913a: EP-WXT detection of a fast X-ray transient
Date
2024-09-14T01:40:12Z (a year ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
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D. Y. Li, X. P. Xu (NAOC, CAS), B. T. Wang (YNAO, CAS), Y. J. Zhang (THU), D. F. Hu (PMO, CAS), C. C. Jin, Z. X. Ling, W. D. Zhang, Y. Liu, 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, X. Pan, H. Sun, W. X. Wang, Y. L. Wang, Q. Y. Wu, Y. F. Xu, H. N. Yang, W. Yuan, M. Zhang, W. J. 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 EP240913a, by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission. The transient started at T0=2024-09-13T11:39:33(UTC). The WXT position of EP240913a is R.A.= 16.681 deg, DEC = 16.750 deg (J2000) with an uncertainty of 2.5 arcmin (radius, 90% C.L. statistical and systematic). At ~T0+180s, the light curve shows a fast pulse lasting around 50s, followed by a week emission up to 1100s. It has a peak flux of ~2 x 10^-9 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 0.5(-0.6, +0.6) (with the absorption fixed at the Galactic value of 5.1 x 10^20 cm^-2). The derived average unabsorbed 0.5-4 keV flux is 1.1(-0.4, +0.5) x 10^(-10) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters.
No previously known bright X-ray sources are found within the error circle around the source position. Follow-up observations by EP-FXT and Swift will be requested, and further 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).