Gamma-ray Burst 240802A = EP 240802a

(All information courtesy of the instrument teams.)

Previous IAU Circulars

none

Results of Observations

GCN Circular #37018
G. Waratkar (IITB), A. Dasgupta (BITS Pilani, Hyderabad), 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 240802A which was also detected by INTEGRAL/SPI-ACS (Trigger 10829) and Konus/WIND (IPN notices).
The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2024-08-02 10:34:04.5 UTC. The measured peak count rate associated with the burst is 213 (+35, -29) counts/s above the background in the combined data of three quadrants (out of four), with a total of 2026 (+291, -328) counts. We caution that there is a 0.3 s readout dead time in CZT data during the burst which affects the calculated peak count rate and total counts. The local mean background count rate was 259 (+2, -2) counts/s. Using cumulative rates, we measure a T90 of 39 (+3, -8) s.
The source was clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2024-08-02 10:34:07.1 UTC. The measured peak count rate associated with the burst is 205 (+63, -71) counts/s above the background in the combined data of all quadrants, with a total of 4553 (+1494, -1658) counts. The local mean background count rate was 1332 (+9, -9) counts/s. We measure a T90 of 46 (+1, -2) 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 #37019
Y. L. Wang (NAOC, CAS), A. Li (BNU), W. X. Wang, H. W. Pan, Z. X. Ling, C. C. Jin, Y. Liu, C. Zhang, H. Q. Cheng, W. Chen, C. Z. Cui, D. W. Fan, H. B. Hu, M. H. Huang, D. Y. Li, H. Y. Liu, M. J. Liu, Z. Z. Lv, T. Y. Lian, X. Mao, X. Pan, H. Sun, Y. L. Wang, Q. Y. Wu, X. P. Xu, Y. F. Xu, H. N. Yang, W. Yuan, M. Zhang, W. D. 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 EP240802a, by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission. A follow-up observation by the Follow-up X-ray Telescope (FXT) on board EP was triggered about 14 hours after the WXT detection, and an uncatalogued X-ray source is detected at R.A. = 287.8070 deg, DEC = -2.3125 deg (J2000) with an uncertainty of 10 arcsec in radius (90% C.L. statistical and systematic).
The transient event was observed to start at 2024-08-02T10:27:22 (UTC). The WXT position of the source is R.A. = 287.802 deg, DEC = -2.354 deg (J2000) with an uncertainty of 1.9 arcmin in radius (90% C.L. statistical and systematic). The transient event lasts for more than 500 seconds. The lightcurve of the transient observed by the WXT exhibits three sequentially weakened peaks. The average 0.5-4 keV spectrum can be fitted with an absorbed power law with a photon index of 0.94(+0.59/-0.56) (with a freely fitted column density value of 2.5(+2.0/-1.8) x 10^21 cm^-2). The derived average unabsorbed 0.5-4 keV flux is 1.7(+0.4/-0.3) x 10^-9 erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters.
The average FXT spectrum in 0.5-10 keV band can be fitted by an absorbed power law with a photon index of 1.89(+0.33/-0.31) (with a freely fitted column density value of 4.8(+1.4/-1.2) x 10^21 cm^-2), giving an average unabsorbed flux of 1.3(+0.2/-0.1) 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 #37021
A. Aryan, T.-W. Chen (both NCU), S. Yang (HNAS), A. K. H. Kong (NTHU), W.-J. Hou, H.-Y. Hsiao, Y. J. Yang, Y.-C. Pan, C.-C. Ngeow, C.-S. Lin, C.-H. Lai, A. Sankar. K, M.-H. Lee, H.-C. Lin, J.-K. Guo (all NCU), S. J. Smartt (Oxford/QUB), H.-W. Lin (UMich), G. H. Sun, Z. N. Wang (both HNAS), J. Gillanders, 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 EP240802a (Wang et al., GCN 37019) using the One-meter Telescope (LOT) at Lulin Observatory in Taiwan as part of the Kinder collaboration (Chen & Yang et al., 2024arXiv240609270C). The first LOT epoch of observations started at 15:46 UTC on 3rd of August 2024 (MJD = 60525.657), 1.22 days after the EP trigger.
In particular, we highlight a time coincidence between EP240802a and GRB 240802A (Waratkar et al. GCN 37018). The EP transient was observed to start at 2024-08-02T10:27:22 (UTC) and lasted for more than 500 seconds. AstroSat CZTI detected a long burst GRB 240802A with a T90 of 39 (+3, -8) seconds, showing multiple emission peaks, with the strongest peak at 2024-08-02T10:34:04.5 (UTC). The durations of these two events overlap and could potentially be physically related. Waratkar et al. also mentioned that GRB 240802A was detected by INTEGRAL/SPI-ACS (Trigger 10829) and Konus/WIND (IPN notices). There is no positional information from INTEGRAL at the time of writing and we cannot confirm if they overlap spatially. However, given the time coincidence, we strongly encourage further follow-up investigations.
We use the Kinder pipeline (Yang et al. A&A 646, A22) to stack six reduced frames, and to subtract the stacked image with the Pan-STARRS1 template image. However, we do not detect any optical counterpart in the errorbox of 10 arcseconds around the FXT reported position of the EP240802a in the subtracted frames. The details of the observations and measured 3-sigma upper limit (in the AB system) are as follow:
```
Telescope | Filter | MJD (start) | t-t0 | Exposure | Magnitude | avg. Seeing | med. Airmass
LOT | r | 60525.657 | 1.22 days | 300 sec * 6 | > 21.32 | 1".6 | 1.26
```
The presented magnitudes are calibrated using the field stars from the Pan-STARRS1 catalog and are not corrected for the expected Galactic foreground extinction corresponding to a reddening of E_(B-V) = 0.56 mag in the direction of the transient (Schlafly & Finkbeiner 2011).
GCN Circular #37022
SVOM/GRM team: Chen-Wei Wang, Yan-Ting Zhang, Wen-Hui Yu, Yong-Wei Dong, Jiang-Tao Liu, Shi-Jie Zheng, Jian-Chao Sun, Wen-Jun Tan, Jiang He, Min Gao, Hao-Xuan Guo, Yue Huang, Lu Li, Yong-Ye Li, Hong-Wei Liu, Xin Liu, Hao-Li Shi, Li-Ming Song, You-Li Tuo, Hao-Xi Wang, Jin Wang, Jin-Zhou Wang, Ping Wang, Rui-Jie Wang, Yu-Xi Wang, Bo-Bing Wu, Shao-Lin Xiong, Jian-Ying Ye, Yi-Tao Yin, Wen-Hui Yu, Fan Zhang, Li Zhang, Peng Zhang, Shuang-Nan Zhang, Wen-Long Zhang, Shu-Min Zhao, Xiao-Yun Zhao, Chao Zheng (IHEP), Maria-Grazia Bernardini (LUPM/INAF-OAB), Laurent Bouchet (IRAP), David Corre (CEA), Patrick Maeght (LUPM), Fr=C3=A9d=C3=A9ric Piron (LUPM), St=C3=A9phane Schanne (CEA), Jingwei Wang (IAP)
SVOM JSWG: Jian-Yan Wei (NAOC), Bertrand Cordier (CEA), Shuang-Nan Zhang (IHEP), St=C3=A9phane Basa (LAM), JeanLuc Att=C3=A9ia (IRAP), Arnaud Claret (CEA), Zi-Gao Dai (USTC), Fr=C3=A9d=C3=A9ric Daigne (IAP), Jin-Song Deng (NAOC), Andrea Goldwurm (APC), Diego G=C3=B6tz (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), Bing Zhang (UNLV)
report on behalf of the SVOM team:
During the commissioning phase, the SVOM/GRM was triggered in-flight by a long GRB 240802A at 2024-08-02T10:34:03.300 UT (T0), which also triggered INTEGRAL/SPI-ACS (TrigID 10829) and AstroSat (GCN 37018).
With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of multiple pulses with a duration of about 60 s.
The GRM light curve can be found here: https://www.bursthub.cn/admin/static/svgrb240802A.png
The SVOM/GRM on-ground localization of this burst is (J2000):
```
RA: 282.6 deg
DEC: 2.6 deg
Error: 21.4 deg (1 sigma, statistical only)
```
We caution that the calibration of SVOM/GRM is undergoing and this localization is subject to systematic errors. The localization may be improved in the refined analysis.
At the time of this burst ECLAIRs was not in operational mode.
We note that the time coincidence (GCN 37021) and localization coincidence between EP240802a (GCN 37019) and GRB 240802A suggest the association of these two events. Further follow-up observations are strongly encouraged.
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. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS.
The SVOM point of contact for this burst is: Chen-Wei Wang (IHEP)(cwwang@ih= ep.ac.cn)
GCN Circular #37023
U.Quadri, L.Strabla and P.Madurini (Bassano Bresciano Astronomical Observatory)
Members of: AAVSO - American Association of Variable Star Observers. UAI/SSV - Unione Astrofili Italiani/SSV-GRB section. GAC - Gruppo Astrofili Cremonesi.
In a large collaboration with: M.G. Dainotti (National Astronomical Observatory of Japan), Y. Niino (Tokyo University, Institute of Astronomy), K. Kalinowski (Aarhus University, Department of Physics and Astronomy), B. De Simone (Universita' degli Studi Di Salerno) report:
We imaged the field of EP240802A detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission with the robotic telescope of the (IAU station 565) Bassano Bresciano Observatory, Italy. The observations started 34.31 hour after the trigger, At the end of twilight, with our Newton telescope D=450 mm F/D=4.5.
Weather conditions were good.
We co-added 2 series of 45 exposures of 60 sec each.
```
  Start T0+      End T0+      Vlim
  34.31 hour   34.88 hour     20.5
  34.88 hour   35.45 hour     20.5
```
We did not found any optical counterpart in the error box of the XRTcandidate. Wang et al. (GCN 37019), A. Aryan et al.(GCN 37021).
Magnitudes were estimated with the pan-STARRS cat. and are derived using Lupton (2005) equations. Not corrected for galactic dust extinction.
Reference: http://www.osservatoriobassano.org
The message may be cited.
GCN Circular #37026
D. Svinkin, D. Frederiks, A. Ridnaia, A. Lysenko, and T. Cline on behalf of the Konus-Wind team,
E. Bozzo and C. Ferrigno, on behalf of the INTEGRAL SPI-ACS GRB team,
G. Waratkar, V. Jethwani, J.Joshi, V. Bhalerao, D. Bhattacharya, and S. Vadawale, on behalf of the Astrosat-CZTI team, report:
The long-duration GRB 240802A (AstroSat-CZTI detection: Waratkar et al., GCN 37018; SVOM-GRM detection: Wang et al., GCN 37022) was detected by Astrosat (CZTI), Konus-Wind, and INTEGRAL (SPI-ACS), and SVOM (GRM) at about 38044 s UT (10:34:04).
We have triangulated it to a preliminary, 3 sigma error region whose area is 394 sq. deg, and its maximum dimension is 51 deg (the minimum one is 6.7 deg).
This localization may be improved.
The X-ray transient EP 240802a (Wang et al., GCN 37019) is inside the region (at the distance of 0.7 deg from the center line of the Konus-SPI-ACS annulus and 0.4 deg from the center line of Konus-CZTI annulus), supporting the association of the GRB and EP 240802a.
A triangulation map and HEALPix FITS file are posted at http://www.ioffe.ru/LEA/GRBs/GRB240802_T38048/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 #37078
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,
E. Burns, on behalf of the IPN,
E. Bozzo and C. Ferrigno, on behalf of the INTEGRAL SPI-ACS GRB 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:
Using the Mars-Odyssey (HEND) data we have improved the previous IPN error box (Svinkin et al., GCN 37026).
The coordinates of the updated 3 sigma error box are:
```
  ---------------------------------------------
   RA(2000), deg                 Dec(2000), deg
  ---------------------------------------------
  Center:
   287.477 (19h 09m 54s)  -1.718 ( -1d 43' 05")
  Corners:
   285.131 (19h 00m 31s)  +2.050 ( +2d 03' 01")
   285.257 (19h 01m 02s)  +2.088 ( +2d 05' 15")
   289.523 (19h 18m 05s)  -5.648 ( -5d 38' 51")
   289.393 (19h 17m 34s)  -5.668 ( -5d 40' 03")
  ---------------------------------------------
```
The error box area is 1.11 sq. deg, and its maximum dimension is 8.9 deg (the minimum one is 7.6 arcmin). The Sun distance was 146 deg.
The IPN localization may be further improved.
The EP240802a localization is inside the improved box.
Updated triangulation map and HEALPix FITS files are posted at http://www.ioffe.ru/LEA/GRBs/GRB240802_T38048/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 #37079
D. Frederiks, A.Lysenko, A. Ridnaia, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report:
The long GRB 240802A (AstroSat CZTI detection: Waratkar et al., GCN 37018; SVOM/GRM observation: Wang et al., GCN 37022; IPN triangulation: Svinkin et al., GCN 37026; Kozyrev et al., GCN 37078), associated with the fast X-ray transient EP240802a (Wang et al., GCN 37019; Aryan et al., GCN 37021; Svinkin et al., GCN 37026; Kozyrev et al., GCN 37078), triggered Konus-Wind (KW) at T0=38048.482 s UT (10:34:08.482).
The burst light curve shows a multi-peaked emission pulse, which starts at ~T0-13 s and has the total duration of ~47 s. Two main peaks in the light curve are located around ~T0 and ~T0+29 s, respectively.
The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB240802_T38048/
As observed by Konus-Wind, the burst had the total fluence of 1.63(-0.14,+0.15)x10^-5 erg/cm^2 and a 2.944-s peak energy flux, measured from T0+0.032 s, of 8.21(-2.63,+3.09)x10^-6 erg/cm^2/s (both in the 20 keV - 10 MeV energy range).
Due to telemetry errors in the KW triggered-mode spectra, the spectral analysis was performed using the 3-channel waiting-mode count rates. Modeling the time-integrated spectrum (measured from T0-13.161 s to T0+33.943 s) by a power law with exponential cutoff (CPL) function dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) yields alpha = -1.38(-0.11, + 0.12) and Ep = 226(-36,+51) keV. A CPL fit to the spectrum near the peak count rate (measured from T0-1.385 s to T0+1.559 s) results in alpha = -1.02(-0.15,+0.17) and Ep = 273(-42,+55) keV.
All the quoted errors are estimated at the 68% confidence level. All the presented results are preliminary.
GCN Circular #37094
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 EP240802a from the Einstein Probe (Wang et al. GCNC 37019) starting at 04:17 UT, Aug 3rd, ~0.74 days after the trigger. EP240802a was also found to be coincidence with GRB 240802A (Waratkar et al., GCN 37018; Aryan et al., GCN 37021; Kozyrev et al., GCN 37078). We obtained a set of clear (roughly R) filter images, we do not detect any new optical counterpart in the FXT errorbox (Wang et al. GCNC 37019), neither in single image, nor in the co-add images. We measure the limiting mag to be ~21.0 in 28x60s co-add image at a mid time of ~0.80 days after the trigger. Our result is consistent with the upper limit reported from Aryan et al. (GCN 37021), Quadri et al. (GCN 37023) and Leonini et al. (GCN 37029).

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