EP240703a, GRB 240703A
GCN Circular 36832
Subject
EP240703a: TRT further optical observation
Date
2024-07-05T15:25:25Z (2 years ago)
From
S. Tinyanont at National Astronomical Research Institute of Thailand <samaporn@narit.or.th>
Via
Web form
S. Tinyanont, R. Anutarawiramkul, P. Butpan (NARIT), X. Liu, S.Q. Jiang, J. An, S.Y. Fu, Z.P. Zhu, 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 the fast X-ray transient EP240703a (Wang et al., GCN 36807) using the 0.7-m telescope of the Thai Robotic Telescope (TRT) network, located at Spring Brook Observatory, Australia. Observations started at 10:16:15 UTC on 2024-07-04, i.e., 1.40 day after the EP trigger, and 5 x 360 s I-band frames were obtained.
No uncatalogued optical transient is detected in the stacked image within the 3-arcmin EP/WXT error circle, down to a 5-sigma limiting magnitude of I ~ 20.0, calibrated with Pan-STARRS sources in the field.
GCN Circular 36827
Subject
EP240703a and EP240703b: Swift/XRT upper limits
Date
2024-07-05T08:51:47Z (2 years ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
Q. C. Shui, J. Q. Peng (IHEP, CAS), C. Y. Dai (NJU), Y. L. Wang, C. C. Jin, Z. X. Ling, W. Yuan, 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, W. X. Wang, S. X. Wen, Q. Y. Wu, X. P. Xu, Y. F. Xu, H. N. Yang, M. Zhang, W. D. Zhang, W. J. Zhang, Z. Zhang, D. H. Zhao (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 fast X-ray transients EP240703a (Wang et al., GCN 36807) and EP240703b (Peng et al., GCN 36810) by the Einstein Probe, we triggered two Swift target of opportunity observations, one for each source.
The Swift observation of EP240703a (observation ID: 00016698001) began at 2024-07-03T18:16:06, about 17.5 hours after the WXT detection, with an exposure time of 1845 s in the Photon Counting mode. No significant X-ray source was detected within the 3 arcmin region around the WXT position of EP240703a. Assuming an absorbed power-law model with a Galactic column density of 5.68 × 10^21 cm^-2 and a photon index of 1.0, the estimated flux upper limit in 0.3-10 keV at the 90% confidence level is 1.62 × 10^-13 erg/cm^2/s.
The Swift observation of EP240703b (observation ID: 00016699001) began at 2024-07-03T19:58:00, about 14.5 hours after the WXT detection, with an exposure time of 1738 s in the Photon Counting mode. No significant X-ray source was detected within the 3 arcmin region around the WXT position of EP240703b. Assuming an absorbed power-law model with a Galactic column density of 9.52 × 10^20 cm^-2 and a photon index of 1.0, the estimated flux upper limit in 0.3-10 keV at the 90% confidence level is 1.06 × 10^-13 erg/cm^2/s.
We thank the Neil Gehrels Swift Observatory team for making the X-ray observations possible.
GCN Circular 36825
Subject
EP240703a: KAIT optical upper limit
Date
2024-07-05T01:45:56Z (2 years 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 EP240703a
from the Einstein Probe (Wang et al. GCNC 36807) starting at 1.28 days
after the trigger. A set of 30x60s images were obtained in the clear
(roughly R) filters. Preliminary analysis do not reveal any optical
counterpart candidate within the 3 arcmin radius EP-WXT error box
(Wang et al. GCN 36807) neither in single image, nor in the co-add
images, consistent with the reports from Aryan et al. (GCN 36819),
An et al. (GCN 36820), Bochenek & Perley (GCN 36821), Fernandez-Garcia
et al. (GCN 36822) and Volnova et al. (GCN 36824). The typical limiting
magnitude of our single clear image is about 19.0 mag.
GCN Circular 36824
Subject
EP240703a: BTA observations
Date
2024-07-04T22:54:06Z (2 years ago)
From
Alexei Pozanenko at IKI, Moscow <grb.alex@gmail.com>
Via
legacy email
A. Volnova (IKI), A. Moskvitin (SAO RAS), A. Pozanenko (IKI), D. Oparin
(SAO RAS), N. Pankov (IKI, HSE), S. Belkin (IKI, HSE) on behalf of GRB IKI
FuN report:
We observed the TRT candidate afterglow position (An et al., GCN 36815) of
the X-ray transient EP240703a (Wang et al., GCN 36807) and probable
gamma-ray burst GRB 240703A (Frederiks et al., GCN 36809) with BTA SAO RAS
telescope equipped with SCORPIO-1 camera in Ic filter starting on
2024-07-03 (UT) 20:50:07, i.e. 0.856 days after burst.
We did not detect the TRT candidate afterglow (An et al., GCN 36815) which
might be a spurious event (An et al., GCN 36820). At the stacked images of
9x180 s we obtained an upper limit of Ic= 24.6m (3 sigma). We cannot
confirm that the TRT afterglow candidate (An et al., GCN 36815) is real.
Our result is consistent with reported results (Aryan et al., GCN 36819,
Bochenek and Perley GCN 36821; Fernandez-Garcia et al., GCN 36822).
We are grateful to the Directorate of the Special Astrophysical Observatory
for allocation of the TOO observation.
GCN Circular 36822
Subject
EP240703a: BOOTES-3 optical upper limit
Date
2024-07-04T19:24:51Z (2 years ago)
From
Alberto Castro-Tirado at Inst.de Astro. de Andalucia <ajct@iaa.es>
Via
legacy email
E. Fernandez-Garcia, I. Perez-Garcia, S.-Y. Wu, A. J. Castro-Tirado, M. D. Caballero-Garcia, I, Olivares, R. Sanchez-Ramirez and S. Guziy (IAA-CSIC), Y.-D. Hu (INAF-OAB), A. Castellon, S. Castillo, A. Reina and C. Perez del Pulgar (Univ. de Malaga), Ph. Yock (Univ. of Auckland), and R. Querel (NIWA), on behalf of a larger collaboration, report:
Following the detection of EP240703a by EP-WXT (Wang et al., GCNC 36807) and Konus-Wind (Frederiks et al., GCNC 36809), we triggered the 60cm BOOTES-3/YA robotic telescope at NIWA Lauder in Otago (New Zealand) to observe the fast X-ray transient location on Jul. 3 at 14:28 UT (13.9 hrs after the detection). No new optical source is detected on the co-added images (60 x 30 s, clear-filter) within the 3 arcmin radius EP error box (Wang et al. GCNC 36807) down to 20.5 mag, which is consistent with the reports from Kinder (Aryan et al. GCNC 36819), TRT (An et al. GCNC 36820) and LT (Bochenek and Perley GCNC 36821) later on.
We thank the staff at NIWA at Lauder for its excellent support and especially to Bill Allen (1940-2023) for his invaluable contribution in the early times at the Blenheim site where our former BOOTES-3 station was initially deployed on his vineyard (until it was moved to Lauder in 2014). Bill Allen, a vintner (besides an engineer & astronomer!) remains in our hearts and we remember him every night we are looking to the heavens thru our Yock-Allen (YA) robotic telescope at the new BOOTES-3 station.
GCN Circular 36821
Subject
EP240703a: Liverpool Telescope optical follow-up observations
Date
2024-07-04T17:53:09Z (2 years ago)
From
A. Bochenek at Liverpool John Moores University <a.m.bochenek@2023.ljmu.ac.uk>
Via
Web form
A. Bochenek and D. A. Perley (LJMU) report:
We observed the field of the X-ray transient and probable gamma-ray burst EP240703a (Wang et al., GCN 36807; Frederiks et al., GCN 36809) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 5x180s exposures with the SDSS-I filter between 2024-07-04 02:27:40 UT and 2024-07-04 02:45:02 UT, approximately 1.1 days after the transient.
The limiting magnitude of the stacked image is i > 21.9 mag (AB) for a three-sigma detection limit, with mid-observation time being 2024-07-04 02:34:51 UT. No new sources were identified within the 90% confidence 3 arcmin error circle compared to the Pan-STARRS catalogue. Additionally, no source was detected at the TRT candidate afterglow position (An et al., GCN 36815), now thought to be a probable cosmic ray (An et al., GCN 36820).
GCN Circular 36820
Subject
EP240703a/GRB 240703A: TRT optical candidate likely not real
Date
2024-07-04T10:42:33Z (2 years ago)
From
Dong Xu at NAOC/CAS <dxu@nao.cas.cn>
Via
Web form
J. An (NAOC), S. Tinyanont, R. Anutarawiramkul, P. Butpan (NARIT), S.Q. Jiang, X. Liu, S.Y. Fu, Z.P. Zhu, D. Xu, Z. Fan, W.X. Li, N.C. Sun, Y.N. Wang (NAOC) report on behalf of a large collaboration:
Regarding our previously reported afterglow candidate of EP240703a/GRB 240703A (An et al., GCN 36815), we have checked the five 360 s R-band TRT images one by one.
First, the candidate is only present in one of the five images, and not in the other four images. Second, it looks sharper than its neighboring sources, although it does cover multiple pixels in the image. We thus re-did cosmic ray removal with a revised script, and this time the candidate basically disappeared while its neighboring sources were almost unaffected by the same cosmic ray removal process.
We thus conclude that the candidate is very likely not real.
GCN Circular 36819
Subject
EP240703a: Kinder optical follow-up observations
Date
2024-07-04T10:31:37Z (2 years ago)
From
Amar Aryan at National Central University, Institute of Astronomy (NCUIA) <amararyan941@gmail.com>
Via
Web form
A. Aryan (NCUIA), S. Yang (HNAS), T.-W. Chen, Y.-J. Yang, C.-S. Lin, M.-H. Lee, Y.-C. Pan, H.-Y. Hsiao, W.-J. Hou, C.-C. Ngeow, C.-H. Lai, A. Sankar.K, H.-C. Lin, J.-K. Guo (all NCUIA), S. J. Smartt (Oxford/QUB), H. F. Stevance, S. Srivastav, J. Gillanders, L. Rhodes (all Oxford), M. Fulton, T. Moore, K. W. Smith, C. Angus, A. Aamer (all QUB), A. Schultz and M. Huber (IfA, University of Hawaii) report:
We observed the field of the fast X-ray transient EP240703a (Wang et al., GCN 36807) 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 12:48 UT on 03rd of July 2024 (MJD = 60494.540), 12.32 hrs after the EP trigger.
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. We subtracted the stacked images with the Pan-STARRS1 template image using hotpants (Becker A., 2015, ascl.soft. ascl:1504.004).
We do not detect the presence of the proposed optical transient source at R.A. = 18:15:03.89 and Dec. = -09:42:02.96, as reported by An et al., GCN 36815, in the difference and stacked images. Our observations were 1.58 hours before those of the TRT observations and reach 2 magnitudes deeper.
However, we detect a slight enhancement in the brightness of the eclipsing binary, ZTF J181510.36-094110.1 (Chen et al. 2020, ApJS, 249, 18) in the difference image at R.A. = 18:15:10.36 and Dec. = -09:41:10.1, which is close to the reported coordinate of EP240703a being only 0.66 arcmin away.
Morever, we utilized the python based package, AutoPhOT (Brennan & Fraser, 2022, A&A, 667, A62) to perform the PSF photometry on our stacked frame. The current magnitudes of the eclipsing binary in our stacked frame are r = 19.02 +/- 0.04 mag and i = 18.18 +/- 0.05 mag.
Besides ZTF J181510.36-094110.1, we do not detect any new optical source in the reference and stacked frames. The details of the observations and measured 3-sigma upper limit are as follow:
Telescope | Filter | MJD (start) | t-t0 | Exposure | Magnitude | avg. Seeing | med. Airmass LOT | r | 60494.540 | 12.32 hrs | 300 sec * 6 | > 22.3 | 1".48 | 1.47 LOT | i | 60494.598 | 13.72 hrs | 300 sec * 6 | > 21.8 | 1".34| 1.22
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) = 1.225 mag in the direction of the burst (Schlafly & Finkbeiner 2011).
GCN Circular 36815
Subject
EP240703a/GRB 240703A: TRT and JinShan decaying optical afterglow candidate
Date
2024-07-03T18:28:56Z (2 years 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, 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 the X-ray transient, EP240703a, detected by EP/WXT (Wang et al., GCN 36807), and also by Konus-Wind (Frederiks et al., GCN 36809), thus confirming that it is likely GRB 240703A, using the Thai Response Telescope (TRT) SBO node and the JinShan 100C & 50A telescopes.
Image subtraction of the stacked 5 x 360 s R-band TRT image against the PanSTARRS archival r-band image reveals multiple optical afterglow candidates, among which an uncatalogued optical transient (OT) is localized at coordinates
R.A. (J2000) = 18:15:03.89
Dec. (J2000) = -09:42:02.96
with an uncertainty of ~ 0.5 arcsec. The OT has r ~ 20.4 +/- 0.1 mag at a median time of ~ 13.9 hr post-trigger, calibrated with nearby PanSTARRS stars and not corrected for Galactic extinction of A_r ~ 3 mag.
We then obtained 10 x 300 s frames in the Sloan r-band and 10 x 300 s in the Sloan z-band at the JinShan 100C telescope. The OT is not detected in the stacked r-band image down to r ~ 22.2 mag at a median time of 16.07 hr post-trigger, also not detected in z-band down to z ~ 20.6 mag at a median time of 16.91 hr post-trigger, both calibrated with the nearby PanSTARRS field.
The presence and the decay of the OT make it an optical afterglow candidate of EP240703a/GRB 240703A.
GCN Circular 36809
Subject
Konus-Wind detection of GRB 240703A (a counterpart of EP240703a)
Date
2024-07-03T13:48:00Z (2 years ago)
Edited On
2024-07-04T16:48:30Z (2 years ago)
From
Dmitry Frederiks at Ioffe Institute <fred@mail.ioffe.ru>
Edited By
Leo P. Singer at NASA/GSFC <leo.p.singer@nasa.gov> on behalf of Dmitry Frederiks at Ioffe Institute <ddfrederiks@gmail.com>
Via
legacy email
D. Frederiks, A.Lysenko, A. Ridnaia, D. Svinkin,
A. Tsvetkova, M. Ulanov, and T. Cline,
on behalf of the Konus-Wind team, report:
A long-duration GRB 240703A was detected by Konus-Wind (KW)
in the waiting mode at ~00:38:32 UT.
The burst source is located in the northern ecliptic hemisphere.
Corrected for the propagation time, the burst was detected
~2 s before the start time of the fast X-ray transient EP240703a
(T0=T0(EP)=00:38:40 UT; Wang et al., GCN 36807).
The positional and temporal coincidence of this burst with
the EP transient supports the conclusion that EP240703A
is the GRB counterpart.
A Bayesian block analysis of the KW waiting mode data
in the 20-1250 keV band reveals a >12 sigma count rate
increase in the interval from T0-2 s to T0+136 s.
The burst light curve shows a multi-peaked structure
with the brightest peak around ~T0+13 s.
The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB240703A/
The time-integrated spectrum of the burst, measured from T0-2 s to T0+136 s,
is best described by a power law with exponential cutoff (CPL) model
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with alpha = -1.09(-0.30,+0.47) and Ep = 180(-44,+62) keV.
The spectrum near the peak count rate, measured from T0-2 s to T0+33 s,
can be described by a CPL model with
alpha = -0.75(-0.33,+0.41) and Ep = 276(-58,+81) keV.
The total burst fluence is 1.36(-0.18,+0.18)x10^-5 erg/cm^2,
and the 2.944 s peak energy flux, measured from T0+12.5 s,
is 2.8(-0.4,+0.4)x10^-7 erg/cm^2.
(both in the 20 keV - 10 MeV energy range).
All the quoted errors are estimated at the 68% confidence level.
All the presented results are preliminary.
GCN Circular 36807
Subject
EP240703a: EP-WXT detection of a fast X-ray transient
Date
2024-07-03T10:00:25Z (2 years ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
Y.L. Wang (NAOC, CAS), C. Y. Dai (NJU), J. Q. Peng, Q. C. Shui (IHEP, CAS), C. C. Jin, Z. X. Ling, W. Yuan, Y. Liu, C. Zhang, H. Q. Cheng, 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, W. X. Wang, Y. L. Wang, S. X. Wen, Q. Y. Wu, X. P. Xu, Y. F. Xu, H. N. Yang, M. Zhang, W. D. Zhang, W. J. Zhang, Z. Zhang, D. H. Zhao (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 fast X-ray transient, designated EP240703a, by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission. The transient started at 2024-07-03T00:38:40 (UTC). The position of the source is R.A. = 273.803 deg, DEC = -9.681 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic). The corresponding Galactic coordinates are l = 20.174, b = 3.521.
The transient lasted for approximately 300 seconds and had a peak absorbed flux of ~5 x 10^-9 erg/s/cm^2 in the 0.5-4 keV band. The average 0.5-4 keV spectrum can be fitted by an absorbed power law with a column density of 1.5(+0.7/-0.6) x 10^22 cm^-2 and a photon index of 2.0(+1.0/-0.9). The derived average unabsorbed 0.5-4 keV flux is 5.9(+8.6/-2.6) x 10^-9 erg/s/cm^2. If the column density is fixed at the Galactic value of 4.5 x 10^21 cm^-2, the derived photon index is 0.4(+/-0.3) and the average unabsorbed 0.5-4 keV flux is 2.5(+0.4/-0.3) x 10^-9 erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. No previously known X-ray sources at a similar flux level are found within the 3 arcmin region around the source position.
We have triggered a Swift target of opportunity observation. Further follow-up observations are encouraged to identify the nature of this X-ray transient.
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.