GRB 240919A, EP240919a
GCN Circular 37952
Subject
EP240919a / GRB 240919A: ATCA Detection of Radio Counterpart
Date
2024-10-30T00:44:32Z (a year ago)
From
agul8829@uni.sydney.edu.au
Via
Web form
A. Gulati (USyd), A. J. Castro-Tirado (IAA-CSIC Granada), T. Murphy (USyd)
We observed fast X-ray transient EP240919a (Liang et al. GCN 37561; Liang et al. GCN 37563) with the Australia Telescope Compact Array (ATCA) at multiple frequencies post-burst. In our preliminary analysis, we detect a radio counterpart at 9 GHz with a flux density of ~73.5 uJy at a position consistent with the X-ray afterglow position (GCNC 37585). Further observations are planned.
We thank the CSIRO Space and Astronomy staff for supporting these observations.
We acknowledge the Gomeroi people as the traditional owners of the Observatory site. The Australia Telescope Compact Array is part of the Australia Telescope National Facility (https://ror.org/05qajvd42) which is funded by the Australian Government for operation as a National Facility managed by CSIRO.
GCN Circular 37610
Subject
EP240919a / GRB 240919A: SVOM/VT upper limit
Date
2024-09-26T04:01:58Z (a year ago)
From
Liping Xin at NAOC, SVOM <xlp@nao.cas.cn>
Via
Web form
SVOM/VT commissioning team: Y. L. Qiu, L. P. Xin, H. L. Li, C. Wu, X. H. Han, 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) and Shaolin Xiong (IHEP).
SVOM JSWG: Jian-Yan Wei (NAOC), Bertrand Cordier (CEA), Shuang-Nan Zhang (IHEP), Stéphane Basa (LAM), Jean-Luc Atteia (IRAP), Arnaud Claret (CEA), Zi-Gao Dai (USTC), Frédéric Daigne (IAP), Jin-Song Deng (NAOC), 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), Bing Zhang (UNLV)
report on behalf of the SVOM team:
During the commissioning phase of SVOM mission, we observed the field of the EP240919a (Liang et al., GCN 37561) which is also confirmed as GRB 240919A (Liang et al., GCN 37563; Rodi et al., GCN 37572; Wang et al., GCN 37574) with SVOM/VT telescope in ToO mode. The observation started at 2024-09-21T14:12:58 UT, about 47.5 hours after the burst, and the total exposure time was 6160 seconds. VT made the observations with two channels simultaneously, VT_B (400nm-650nm) and VT_R (650nm-1000nm).
No any uncatalogued sources were detected in the 5.5 ks stacked images within the error circles of EP/FXT(Liang et al., GCN 37561) compared to DESI Legacy DR10 catalog, down to the following 3 sigma upper limit of VT_B=24.0 mag and VT_R=24.0 mag in AB magnitude.
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 37585
Subject
EP240919a: EP-FXT follow-up observation update
Date
2024-09-21T12:26:54Z (a year ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
Y. F. Liang (PMO, CAS), M. J. Liu, H. Q. Cheng, X. Pan, X. P. Xu, H. N. Yang(NAOC, CAS), Z. J. Zhang (HKU), C. Y. Dai (NJU), C. X. Zhang (HUST), C. C. Jin, H. W. Pan, Z. X. Ling, W. M. Yuan, Y. Liu, C. Zhang, W. Chen, C. Z. Cui, D. W. Fan, H. B. Hu, J. W. Hu, M. H. Huang, D. Y. Li, H. Y. Liu, Z. Z. Lv, T. Y. Lian, X. Mao, H. Sun, W. X. Wang, Y. L. Wang, Y. F. Xu, 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 have reported the detection of the fast X-ray transient EP240919a by the Einstein Probe (EP) mission (Liang et al. GCN 37561). An automonous follow-up observation with the EP-FXT was triggered by the onboard processing and triggering system of EP, starting at 2024-09-19T14:57:50 (UTC), 4 minutes after the onboard triggering. An uncatalogued X-ray source is clearly detected, at R.A. = 334.2790 deg, DEC = -9.7361 deg (J2000) with an uncertainty of 10 arcsec in radius (90% C.L. statistical and systematic). The source position is consistent with that of the WXT transient within the uncertainties. The EP-FXT light curve shows a fast decline and the flux decreased to around 1.0 x 10^(-12) erg/s/cm^2 within about 400 s. The average 0.5-10 keV spectrum can be fitted with an absorbed power-law with a photon index of 2.0(+0.4/-0.4) (with the column density fixed at the Galactic value of 5.4 x 10^20 cm^-2). The absorbed average flux in 0.5-10 keV is 5.8(+2.2/-1.4) x 10^(-12) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters.
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 onboard X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics).
GCN Circular 37583
Subject
EP240919a / GRB 240919A: Mondy optical upper limit
Date
2024-09-21T10:30:10Z (a year ago)
From
Alexei Pozanenko at IKI, Moscow <grb.alex@gmail.com>
Via
legacy email
S. Belkin (HSE, IKI), E. Klunko (ISTP), A. Pozanenko (IKI), N. Pankov (HSE,
IKI) report on behalf of GRB-IKI-FuN:
We observed the field of EP240919a (Liang et al., GCN 37561) which is also
confirmed as GRB 240919A (Liang et al., GCN 37563; Rodi et al., GCN 37572;
Wang et al., GCN 37574) using the AZT-33IK telescope of Mondy Observatory
in R-filter, starting on 2024-09-20 (UT) 14:33:23. We did not detect the
optical counterpart. Preliminary photometry is the following:
Date UT Start t-T0 (days) Filter Exposure (s) OT Err UL (3σ)
2024-09-20 14:33:23 1.01091 R 30*120 n/d n/d 22.5
The magnitudes were calibrated using nearby USNO-B1.0 stars:
RA DEC R2
22:16:57.1780584 -09:42:25.963092 15.91
22:17:14.9879832 -09:45:26.931528 17.1
GCN Circular 37580
Subject
Fermi GBM Sub-Threshold Detection of GRB240919A / EP240919a
Date
2024-09-20T21:33:48Z (a year ago)
From
Oliver J Roberts at USRA/NASA <oliver.roberts@nasa.gov>
Via
Web form
O.J. Roberts (USRA/NASA-MSFC), J. Wood (NASA-MSFC), A. Goldstein (USRA/NASA-MSFC), C.M. Hui (NASA-MSFC) and R. Hamburg (CNRS/IN2P3/IJCLab), report on behalf of the Fermi-GBM Team:
The Einstein Probe Wide-field X-ray Telescope (EP-WXT) detected the fast X-ray transient EP240919a on 2024-09-19 at 14:47:40 UTC (GCN #37561). There was no Fermi-GBM onboard trigger around this event time. An automated, blind search for gamma-ray bursts below the onboard triggering threshold in Fermi-GBM identified no candidates. The GBM Targeted Search [1], the most sensitive, coherent search for GRB-like signals, identified a transient starting 80 seconds after the EP-WXT trigger time most significantly on the 8.192 s timescale, with a false alarm rate of 1.6e-5 Hz. The Fermi-MET of the start time of this transient is 748450145s. Using the standard search protocol, the Targeted Search localization was found to be spatially consistent with the EP-WXT event, with RA=331.9 deg., Dec.=-11.1 deg., and an error of 15.7 deg. (includes the systematic error), at a SNR of 12. Therefore, the Targeted Search localization confirms the emission initially reported to be only temporally coincident with the EP-WXT trigger by Jiang et al. (GCN #37563), as very probably belonging to the same event as the initial EP-WXT transient reported in GCN #37561.
Additionally, the GBM Targeted Search event was found with the highest significance using a "normal" spectrum (Band function with Epeak = 230 keV, alpha = -1.0, beta = -2.3) for a GRB. The emission shows hard-soft spectral evolution over a duration of about 30 seconds. This provides further evidence that EP240919a / GRB240919A is a long GRB.
The Targeted Search data release product for this event can be found here: https://zenodo.org/records/13821343
[1] Goldstein et al. 2019 arXiv:1903.12597
GCN Circular 37579
Subject
EP240919a / GRB 240919A: REM optical and NIR upper limits
Date
2024-09-20T18:12:34Z (a year ago)
From
Riccardo Brivio at INAF-OAB <riccardo.brivio@inaf.it>
Via
Web form
R. Brivio, M. Ferro, P. D'Avanzo, Y.-D. Hu, S. Covino, D. Fugazza (INAF-OAB), D.B. Malesani (DAWN/NBI and Radboud Univ.) report on behalf of the REM team:
We observed the field of EP240919a (Liang et al., GCN 37561), also identified as GRB 240919A (Liang et al., GCN 37564; Rodi et al., GCN 37573; Wang et al., GCN 37574) with the REM 60 cm robotic telescope located at the ESO observatory of La Silla (Chile). The observations were carried in the g, r, i, z, J, H, and K bands, started on 2024 September 19 at 23:27:28 UT (i.e. 8.6 hr after the burst), and lasted for about 1 hour.
From preliminary inspection of the images, we do not find any optical/NIR counterpart within the EP error circle down to the following 3sigma limit:
r > 20.8 (AB; calibrated against the Pan-STARRS catalogue);
H > 17.3 (Vega; calibrated against the 2MASS catalogue);
at a mid-time of 9.1 hours after the trigger.
GCN Circular 37578
Subject
EP240919a / GRB 240919A: KAIT optical upper limit
Date
2024-09-20T16:40:23Z (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 EP240919a/GRB 240919A (Liang et al.,
GCN 37561; Liang et al., GCN Circ. 37563; Rodi et al., GCN 37572;
Wang et al., GCN 37574) starting at 03:03 UT, Sep 20th, ~12.7
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 EP-FXT error
circle of the X-ray counterpart (Liang et al., GCN 37561) neither
in single image, nor in the co-add images. 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 37575
Subject
EP240919a: Optical upper limit with Kinder observations
Date
2024-09-20T14:32:59Z (a year ago)
From
Amar Aryan at National Central University, Institute of Astronomy (NCUIA) <amararyan941@gmail.com>
Via
Web form
A. Aryan (NCU), A. K. H. Kong (NTHU), Y. J. Yang, T.-W. Chen, C.-H. Lai, H.-Y. Hsiao, C.-S. Lin (all NCU), S. Yang (HNAS), S. J. Smartt (Oxford/QUB), A. Sankar. K, W.-J. Hou, C.-C. Ngeow, M.-H. Lee, Y.-C. Pan, H.-C. Lin, J.-K. Guo (all NCUIA), H.-W. Lin (UMich), H. F. Stevance, S. Srivastav, J. Gillanders, 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 EP240919a (Liang et al., GCN 37561, GCN 37564; Jiang et al., GCN 37565; Kumar et al., GCN 37566; Malesani et al., GCN 37567, Lipunov et al., GCN 37570; Rodi et al., GCN 37573; Wang et al., GCN 37574) using the 40cm SLT at Lulin Observatory in Taiwan as part of the Kinder collaboration (Chen & Yang et al., 2024arXiv240609270C). The first SLT epoch of observations started at 16:04 UTC on the 19th of September 2024 (MJD = 60572.669), 1.27 hr after the EP-WXT detection.
We utilized 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 the stacked frames, we did not detect any evidence of a new uncataloged source within the EP-FXT error circle of 20" reported by Liang et al. (GCN 37555).
Moreover, we utilized the Python-based package AutoPhOT (Brennan & Fraser, 2022, A&A, 667, A62) to perform the photometry on our stacked frame. The details of the observations and measured 3-sigma upper limit (in the AB system) are as follows:
Telescope | Filter | MJD (start) | t-t0 | Exposure | Magnitude | avg. Seeing | med. Airmass
SLT | r | 60572.669 | 1.27 hr | 11 * 300 s | >19.8 | 2".19 | 1.46
We did not find any significant source at the specified location by Malesani et al. (GCN 37567).
The presented magnitude was calibrated using the field stars from the Pan-STARRS1 catalog, and was not corrected for the expected Galactic foreground extinction of E(B-V) = 0.06 mag (Schlafly & Finkbeiner 2011) in the direction of the transient.
GCN Circular 37574
Subject
GRB 240919A / EP240919a: SVOM/GRM observation
Date
2024-09-20T13:43:44Z (a year ago)
From
Chenwei Wang at IHEP <cwwang@ihep.ac.cn>
Via
Web form
SVOM/GRM team: Chen-Wei Wang, 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, Yan-Ting Zhang, Shu-Min Zhao, Xiao-Yun Zhao, Chao Zheng (IHEP), Maria-Grazia Bernardini (LUPM/INAF-OAB), Laurent Bouchet (IRAP), David Corre (CEA), Tais Maiolino (LUPM), Frédéric Piron (LUPM), Stéphane Schanne (CEA), Jingwei Wang (IAP)
SVOM JSWG: Jian-Yan Wei (NAOC), Bertrand Cordier (CEA), Shuang-Nan Zhang (IHEP), Stéphane Basa (LAM), JeanLuc Attéia (IRAP), Arnaud Claret (CEA), Zi-Gao Dai (USTC), Frédéric Daigne (IAP), Jin-Song Deng (NAOC), 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), Bing Zhang (UNLV)
report on behalf of the SVOM team:
During the commissioning phase, the SVOM/GRM detected a weak long burst, GRB 240919A, at about 80 s after the trigger time (2024-09-19T14:47:40 UT, T0) of EP240919a (Liang et al., GCN 37561).
With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of a single pulse with a duration of about 20 s (i.e. T0+82 s to T0+102 s) in the energy range of 30-300 keV.
The GRM light curve can be found here:
https://www.bursthub.cn/admin/static/svgrb240919A.png
Although this burst is quite weak in GRM, it was also detected by Fermi/GBM (Liang et al., GCN 37563) and INTEGRAL/SPI-ACS (James Rodi et al., GCN 37573), supporting that it is of astrophysical origin.
Due to the weakness of GRB 240919A, GRM is unable to localize it reliably on its own. However, using the EP240919a localization of R.A. = 334.2797, DEC = -9.7362 (J2000) from EP (Liang et al., GCN 37561), the incident angles of the three GRDs of GRM are about 96, 69 and 46 degrees respectively. The facts that the smallest-angle detector (i.e. GRD03) has the highest signal of this burst and that there is a time coincidence between GRB 240919A and EP240919a support that GRB 240919A is very likely associated with EP240919a (also by Liang et al., GCN 37563).
At the time of this burst ECLAIRs was not in operational mode.
Further follow-up observations are 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@ihep.ac.cn)
GCN Circular 37573
Subject
EP240919a: INTEGRAL SPI-ACS confirmation of reported high-energy counterpart
Date
2024-09-20T13:35:36Z (a year ago)
From
Aishwarya L Thakur at INAF-IAPS, Rome <aishth@outlook.com>
Via
Web form
James Rodi, Aishwarya Linesh Thakur, Luigi Piro, Lorenzo Natalucci and Giulia Gianfagna (INAF-IAPS) report:
Following the detection of the fast X-ray transient EP 240919a by the WXT (GCN 37561) and the associated gamma-ray counterpart (Fermi-GBM, GCN 37563), we searched for corresponding emission in the INTEGRAL SPI-ACS data. In a 1s binning light curve above 80 keV, we tentatively find an untriggered pulse temporally coincident with the WXT and GBM detections, with an approximate duration of 20 sec.
The approximate peak count rate is 33000 cts/s over a median background rate of 32600 cts/s.
This work is based on observations with INTEGRAL, an ESA project with instruments and a science data centre funded by ESA member states (especially the PI countries: Denmark, France, Germany, Italy, Switzerland, and Spain), and with the participation of Russia and the USA. The SPI-ACS detector system has been provided by MPE Garching/Germany.
GCN Circular 37572
Subject
EP240919a: INTEGRAL SPI-ACS confirmation of reported high-energy counterpart
Date
2024-09-20T13:35:34Z (a year ago)
From
Aishwarya L Thakur at INAF-IAPS, Rome <aishth@outlook.com>
Via
Web form
James Rodi, Aishwarya Linesh Thakur, Luigi Piro, Lorenzo Natalucci and Giulia Gianfagna (INAF-IAPS) report:
Following the detection of the fast X-ray transient EP 240919a by the WXT (GCN 37561) and the associated gamma-ray counterpart (Fermi-GBM, GCN 37563), we searched for corresponding emission in the INTEGRAL SPI-ACS data. In a 1s binning light curve above 80 keV, we tentatively find an untriggered pulse temporally coincident with the WXT and GBM detections, with an approximate duration of 20 sec.
The approximate peak count rate is 33000 cts/s over a median background rate of 32600 cts/s.
This work is based on observations with INTEGRAL, an ESA project with instruments and a science data centre funded by ESA member states (especially the PI countries: Denmark, France, Germany, Italy, Switzerland, and Spain), and with the participation of Russia and the USA. The SPI-ACS detector system has been provided by MPE Garching/Germany.
GCN Circular 37570
Subject
EP EP240919a: Global MASTER-Net observations report
Date
2024-09-20T12:36:38Z (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-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 EP240919a ( EP Team et al., GCN 37561) errorbox 12623 sec after notice time and 73512 sec after trigger time at 2024-09-20 11:12:52 UT, with upper limit up to 17.0 mag. Observations started at twilight. The observations began at zenith distance = 69 deg. The sun altitude is -16.3 deg.
The galactic latitude b = -50 deg., longitude l = 52 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=2609045
We obtain a following upper limits.
Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________
73602 | 2024-09-20 11:12:52 | MASTER-Amur | (22h 21m 01.02s , -09d 49m 04.0s) | C | 180 | 15.3 |
73602 | 2024-09-20 11:12:52 | MASTER-Amur | (22h 20m 20.62s , -09d 22m 23.0s) | C | 180 | 16.8 |
73802 | 2024-09-20 11:16:11 | MASTER-Amur | (22h 21m 00.87s , -09d 48m 23.3s) | C | 180 | 15.6 |
73802 | 2024-09-20 11:16:11 | MASTER-Amur | (22h 20m 20.81s , -09d 21m 42.3s) | C | 180 | 17.0 |
Filter C is a clear (unfiltred) band.
The observation and reduction will continue.
The message may be cited.
GCN Circular 37567
Subject
EP240919a: NOT and Gemini optical observations
Date
2024-09-20T10:07:08Z (a year ago)
From
Daniele B. Malesani at IMAPP / Radboud University <d.malesani@astro.ru.nl>
Via
Web form
D. B. Malesani (DAWN/NBI and Radboud Univ.), A. Martin-Carrillo (UCD), J. An (NAOC/CAS), P. G. Jonker (Radboud Univ.), A. J. Levan (Radboud Univ. and Warwick Univ.), J. Quirola-Vasquez (Radboud Univ.), F. E. Bauer (PUC), D. Xu (NAOC/CAS), H. Sun (NAOC, CAS), report on behalf of the EP collaboration:
We observed the field of EP240919a (Liang et al., GCN 37561; see also Liang et al., GCN 37563), using the Nordic Optical Telescope (NOT) and the ALFOSC camera. The night conditions were not ideal, with clouds and high humidity, but a total of 3x300 and 5x200 s could be secured in the r and z bands, respectively, at mean epochs of 11.2 and 11.5 hr after the EP trigger.
No significant new sources are visible in either band, compared to archival images from Pan-STARRS and the Legacy surveys, down to limiting mangitudes r = 22.5 and z = 22 (AB). A few objects are located within the FXT localization region, but have magnitudes consistent with their archival values.
We note however the presence of a marginally significant source, visible only in the z band, detected at the 1.5-sigma level. It has approximate coordinates (1" error, J2000):
RA = 22:17:06.49
Dec = -09:44:03.1
Follow-up observations were conducted with the Gemini-North telescope equipped with the GMOS-N instrument. Observations began on 2024-09-20 at 08:47 UT (18.0 hr after the EP trigger). In a preliminary analysis, the object is not detected to a limit z > 23.7 (AB). This limit would imply a rather steep decay (power-law index >~ 2.5). Given the low significance and lack of independent confirmation, we do not consider the NOT source as a convincing candidate.
GCN Circular 37566
Subject
EP240919a: GOTO optical upper limits
Date
2024-09-20T09:09:33Z (a year ago)
From
Amit Kumar at University of Warwick, UK <amitkundu515@gmail.com>
Via
Web form
A. Kumar, B. P. Gompertz, M. Kennedy, D. O'Neill, G. Ramsay, S. Belkin, D. Steeghs, J. Lyman, R. Starling, K. Ackley, M. J. Dyer, K. Ulaczyk, F. Jimenez-Ibarra, D. K. Galloway, V. Dhillon, P. O'Brien, K. Noysena, R. Kotak, R. P. Breton, L. K. Nuttall, E. Palle and D. Pollacco report on behalf of the GOTO collaboration:
We report on observations with the Gravitational-wave Optical Transient Observer (GOTO, Steeghs et al. 2022; Dyer et al. 2024) in response to fast X-ray transient EP240919a (Liang et al. GCN 37561; Liang et al. GCN 37563). Targeted observations of the FXT localisation were performed by GOTO South (Siding Spring Observatory) at 2024-09-19 15:11:11 UT (23.5 minutes after the X-ray detection). The observation consisted of 4x90s exposures in the GOTO L-band (400-700 nm).
Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations. Source candidates were initially filtered using a classifier (Killestein et al. 2021) and cross-matched against a variety of contextual and minor planet catalogues. Human vetting was carried out in real time on any candidates that passed the above checks.
No candidate optical counterparts are identified within FXT localisation (Liang et al. GCN 37561) up to a 3-sigma limiting L-band magnitudes of >19.3. This field was also covered by GOTO South as part of its routine all-sky survey 44.7 minutes pre-detection (at 2024-09-19 14:03:01 UT), and no new transient sources were seen in a 4x45s stacked image up to a 3-sigma limiting magnitude of >19.4 (L-band) compared to previous template images.
Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and were not corrected for Galactic extinction.
GOTO (https://goto-observatory.org) is a network of telescopes that is principally funded by the STFC and operated at the Roque de los Muchachos Observatory on La Palma, Spain, and Siding Spring Observatory in NSW, Australia, on behalf of a consortium including the University of Warwick, Monash University, Armagh Observatory & Planetarium, the University of Leicester, the University of Sheffield, the National Astronomical Research Institute of Thailand (NARIT), the University of Turku, the University of Portsmouth, the University of Manchester and the Instituto de Astrofisica de Canarias (IAC).
GCN Circular 37565
Subject
EP240919a: JinShan optical upper limits
Date
2024-09-20T09:08:37Z (a year ago)
From
Dong Xu at NAOC/CAS <dxu@nao.cas.cn>
Via
Web form
S.Q. Jiang, J. An, X. Liu, S.Y. Fu, Z.P. Zhu, D. Xu (NAOC), J.Z. Liu (XAO) report on behalf of a large collaboration:
We observed the field of EP240919a detected by EP/WXT (Liang et al., GCN 37561) and likely Fermi/GBM (Liang et al., GCN 37563), using the 100cm-B telescope (100B) of the JinShan project, located at Altay, Xinjiang, China. Observations started at 15:08:25 UT on 2024-09-19, i.e., 14.71 min after the EP/FXT trigger, and a series of frames were obtained in the Sloan r- and i- bands.
No new optical source is detected within the EP/FXT error circle (Liang et al., GCN 37561), down to the following 5-sigma upper limits:
|T_mid(min)|filter|U.L.(AB)|
|47.46 |r| 20.0|
|35.79 |i| 19.5|
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 37564
Subject
EP240919a is likely a GRB event (duplicate submission of 37563)
Date
2024-09-20T08:19:25Z (a year ago)
Edited On
2024-09-30T20:28:48Z (a year ago)
From
yfliang@pmo.ac.cn
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov>
Via
Web form
This was a duplicate submission of GCN 37563.
GCN Circular 37563
Subject
EP240919a is likely a GRB event
Date
2024-09-20T08:19:17Z (a year ago)
From
yfliang@pmo.ac.cn
Via
Web form
Yi-Fang Liang (PMO, CAS), Jun Yang (NJU), Yi-Han Iris Yin (NJU), An Li (BNU), Ye Li (PMO, CAS), Bin-Bin Zhang (NJU), Hui Sun (NAOC, CAS) and Xuefeng Wu (PMO, CAS) report on behalf of large collaboration:
We have conducted a follow-up high-energy data search of the X-ray transient detected by the Einstein Probe (EP) at 2024-09-19T14:47:40 UTC (T0 of EP240919a; GCN Circular 37561). We discovered an untriggered gamma-ray transient in the Fermi/GBM data approximately 80 seconds after T0 of EP240919a, coinciding with the timing of the X-ray transient.
The GBM light curve shows a single emission episode with a duration (T90) of approximately 50 seconds (10-1000 keV) and a peak at about T0+90 seconds. The time-averaged spectrum from T0+83 to T0+108 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 95 (+19/-12) keV and a photon index, Gamma, of 0.6 (+0.3/-0.4). The average flux (10-1000 keV) during this interval is estimated to be 4.5 (+0.5/-0.5) x 10^(-8) erg/s/cm^2.
Given that the gamma-ray transient is consistent with EP240919a in both timing and location, we propose that this is likely a GRB event.
We strongly recommend further follow-up observations of EP240919a to confirm its physical nature and to search for potential afterglows.
GCN Circular 37561
Subject
EP240919a: EP-WXT detection of a fast X-ray transient
Date
2024-09-20T07:39:06Z (a year ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
Y. F. Liang (PMO, CAS), H. Q. Cheng, M. J. Liu, X. Pan, X. P. Xu, H. N. Yang(NAOC, CAS), Z. J. Zhang (HKU), C. Y. Dai (NJU), C. X. Zhang (HUST), C. C. Jin, H. W. Pan, Z. X. Ling, W. M. Yuan, Y. Liu, C. Zhang, W. Chen, , C. Z. Cui, D. W. Fan, H. B. Hu, J. W. Hu, M. H. Huang, D. Y. Li, H. Y. Liu, Z. Z. Lv, T. Y. Lian, X. Mao, H. Sun, W. X. Wang, Y. L. Wang, Y. F. Xu, 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 EP240919a, which was detected by EP-WXT at 2024-09-19T14:47:40 (UTC), and triggered the on-board processing unit at 2024-09-19T14:53:43 (trigger ID: 01709054141). An autonomous observation was performed by the Follow-up X-ray Telescope (FXT) about five minutes later. Afterwards, the FXT on-board processing unit was also triggered, showing that an uncatalogued source was detected at R.A. = 334.2797, DEC = -9.7362 (J2000) with an uncertainty of about 20 arcsec (radius, 90% C.L. statistical and systematic). The light curve of the transient observed by the WXT lasts more than 400 seconds. The average 0.5-4 keV spectrum can be fitted with an absorbed power-law with a photon index of 1.3(+0.3/-0.3) (with the column density fixed at the Galactic value of 5.4x10^20 cm^-2). The absorbed average flux in 0.5-4 keV is 7.0(+1.8/-1.5) x 10^(-10) erg/s/cm^2. The quoted 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. 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 onboard X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics).