TITLE: GCN CIRCULAR
NUMBER: 35937
SUBJECT: X-ray transient EP240315a: GROND J-band detection
DATE: 24/03/17 07:54:44 GMT
FROM: Arne Rau at MPE <arau(a)mpe.mpg.de>
Arne Rau (MPE):
The location of the optical transient AT2024eju (Srivastav et al., GCN35932), discovered within the error circle of the fast X-ray transient EP240315a reported by Einstein Probe n (Zhang et al., GCN 35931), was observed with the optical/NIR imager GROND (Greiner et al. 2008) at the MPG 2.2m telescope at the ESO La Silla Observatory on 2024 March 17th 02:50:23 UT (MJD 60386.118).
With an exposure of 1200s, the source is detected in the J-band at m_vega=19.6+/-0.2 (m_AB=20.5+/-0.2).
We thank the 2.2m staff member, Paul Eigenthaler, for the rapid execution of the observation.
View this GCN Circular online at https://gcn.nasa.gov/circulars/35937.
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TITLE: GCN CIRCULAR
NUMBER: 35936
SUBJECT: X-ray transient EP240315a: VLT/X-shooter spectroscopic redshift of z = 4.859
DATE: 24/03/17 06:54:26 GMT
FROM: Andrea Saccardi at Observatoire de Paris <andrea.saccardi(a)obspm.fr>
A. Saccardi (GEPI/Obs. de Paris), A. J. Levan (Radboud Univ. & Warwick Univ.), Z. Zhu (NAOC), B. P. Gompertz (U. Birmingham), S. D. Vergani (GEPI/Obs. de Paris & IAP & INAF/OABr), G. Pugliese (API), D. Xu (NAOC), D. B. Malesani (DAWN/NBI and Radboud Univ.), report on behalf of the Stargate collaboration:
We observed the field of the ATLAS optical counterpart AT2024eju (Srivastav et al., GCN 35932) of the fast X-ray transient EP240315a reported by the WXT instrument during the commissioning phase of the Einstein Probe mission (Zhang et al, GCN 35931) using the ESO/VLT UT3 (Melipal) equipped with the X-shooter spectrograph. Our spectra cover the wavelength range 3000-21000 AA, and consist of 4 exposures of 1200 s each. Observations started at 01:02:52 UT on Mar 17 2024 (~29 hr after the trigger). We detect a clear continuum across both VIS and NIR arms. From the detection of a Lya absorption at ~7120 AA and multiple absorption features, which we interpret as being due to OI, SiII, NV, CIV and SiIV, we infer a redshift of z = 4.859. We also note the presence of additional absorption features likely due to multiple intervening systems. The high redshift of the transient suggests a highly energetic event and potentially links this Fast X-ray Transient to a GRB-like phenomena.
We acknowledge the excellent support from the ESO staff in Paranal, in particular Joe Anderson and Matias Jones.
View this GCN Circular online at https://gcn.nasa.gov/circulars/35936.
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TITLE: GCN CIRCULAR
NUMBER: 35935
SUBJECT: X-ray transient EP240315a: Nanshan/HMT optical upper limit
DATE: 24/03/17 06:52:41 GMT
FROM: Dong Xu at NAOC/CAS <dxu(a)nao.cas.cn>
S.Q. Jiang, Z.P. Zhu, X. Liu, J. An, S.Y. Fu, T.H. Lu, D. Xu (NAOC), X. Gao (Urumqi No.1 Senior High School), J.Z. Liu (XAO) report on behalf of a large collaboration:
We observed the field of EP240315a detected by Einstein Probe (EP, Zhang et al., GCN 35931) using the HMT-0.5m telescope located at Nanshan, Xinjiang, China. We obtained 30 x 90 s frames without any filter.
No uncatalogued optical transient is detected within or near the EP/WXT error circle, down to a limiting magnitude of r ~ 20.9 at a median time of 20.44 hr post-trigger, calibrated with the nearby PanSTAR field.
The previously reported ATLAS optical counterpart candidate, AT2024eju, (Srivastav et al., GCN 35932) is not present in the HMT co-added image, indicating that it has decayed significantly. Our non-detection is consistent with that from LT (Srivastav et al., GCN 35933).
View this GCN Circular online at https://gcn.nasa.gov/circulars/35935.
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TITLE: GCN CIRCULAR
NUMBER: 35933
SUBJECT: AT2024eju: followup observations with Liverpool Telescope suggest a fading transient
DATE: 24/03/17 00:38:27 GMT
FROM: S. Srivastav at Oxford <shubhamsrivastav(a)gmail.com>
S. Srivastav, S. J. Smartt (Oxford), M. D. Fulton and K. W. Smith (QUB) report on behalf of a larger collaboration:
We report follow-up photometry of AT2024eju, the possible optical counterpart (Srivastav et al., GCN 35932) of the fast X-ray transient EP240315a (Zhang et al., GCN 35931). The images were obtained with the 2m Liverpool Telescope in g, r and i bands starting on MJD 60385.848, 1.01 days following the discovery of the X-ray transient.
The transient was not detected in any of the 3 bands with the following upper limits:
MJD Filter Limit (AB mag)
60385.848 g >19.55
60385.851 r >19.72
60385.853 i >20.02
This suggests that AT2024eju has likely faded since the ATLAS detection ~1 day ago, further follow-up observations are encouraged.
View this GCN Circular online at https://gcn.nasa.gov/circulars/35933.
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TITLE: GCN CIRCULAR
NUMBER: 35932
SUBJECT: X-ray transient EP240315a: ATLAS detection of a possible optical counterpart AT2024eju
DATE: 24/03/16 22:08:06 GMT
FROM: S. Srivastav at Oxford <shubhamsrivastav(a)gmail.com>
S. Srivastav, S. J. Smartt (Oxford), M. D. Fulton, K. W. Smith, A. Aamer, C. R. Angus, M. McCollum, T. Moore, M. Nicholl, X. Sheng, J. Weston, D. R. Young (QUB), P. Ramsden (QUB/Birmingham), L. Shingles (GSI/QUB), A. Andersson, J. H. Gillanders, L. Rhodes, H. Stevance (Oxford), J. Sommer (LMU/QUB), L. Denneau, J. Tonry, H. Weiland, A. Lawrence, R. Siverd (IfA, University of Hawaii), N. Erasmus, W. Koorts (South African Astronomical Observatory), A. Jordan, V. Suc (UAI, Obstech), A. Rest (STScI), T.-W. Chen (NCU), C. Stubbs (Harvard):
Here we report the ATLAS detection of an optical transient AT2024eju, discovered within the error circle of the fast X-ray transient EP240315a reported by the Einstein Probe mission (Zhang et al, GCN 35931).
ATLAS is a quadruple 0.5-m telescope system with two units in Hawaii, one in Chile and one in South Africa (see Tonry et al. 2018, PASP, 130:064505), routinely surveying the visible sky on a daily basis. We promptly process all data with our transient science server (Smith et al. 2020, PASP, 132:085002).
ATLAS detected AT2024eju (TNS Astronomical Transient Report No. 205383) during normal survey mode observations at an AB magnitude of 19.37 +/- 0.14 in the ATLAS-cyan band on MJD 60384.887, around 1.1 hrs following the detection of the X-ray transient. The position of AT2024eju is 0.8 arcmin offset from the coordinates reported by Zhang et al. We found no historical detections of any excess optical flux in ATLAS at this position through forced photometry.
Spectroscopic classification of this transient is encouraged.
View this GCN Circular online at https://gcn.nasa.gov/circulars/35932.
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TITLE: GCN CIRCULAR
NUMBER: 35931
SUBJECT: Einstein Probe detected of a fast X-ray transient EP240315a
DATE: 24/03/16 15:49:37 GMT
FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn>
W. J. Zhang (NAOC, CAS), X. Mao (NAOC, CAS), W. D. Zhang (NAOC, CAS), H. Y. Liu (NAOC, CAS), Y. Liu (NAOC, CAS), C. Zhang (NAOC, CAS),
Z. X. Ling (NAOC, CAS), C. C. Jin (NAOC, CAS), H. Q. Cheng (NAOC, CAS), W. Chen (NAOC, CAS), C. Z. Cui (NAOC, CAS), D. W. Fan (NAOC, CAS),
H. B. Hu (NAOC, CAS), J. W. Hu (NAOC, CAS), M. H. Huang (NAOC, CAS), D. Y. Li (NAOC, CAS), T. Y. Lian (NAOC, CAS), M. J. Liu (NAOC, CAS),
Z. Z. Lv (NAOC, CAS), H. W. Pan (NAOC, CAS), X. Pan (NAOC, CAS), H. Sun (NAOC, CAS), W. X. Wang (NAOC, CAS),Y. L. Wang (NAOC, CAS),
Q. Y. Wu (NAOC, CAS), X. P. Xu (NAOC, CAS), Y. F. Xu (NAOC, CAS), H. N. Yang (NAOC, CAS), M. Zhang (NAOC, CAS), S. N. Zhang (IHEP, CAS),
Z. Zhang (NAOC, CAS), D. H. Zhao (NAOC, CAS), E. Kuulkers (ESA), P. O'Brien (Univ. of Leicester) and W. Yuan (NAOC, CAS), on behalf of the Einstein Probe team
We report on the detection of a fast X-ray transient EP240315a at 2024-03-15T20:10:44 (UTC) by the Wide-field X-ray Telescope (WXT) on board
the Einstein Probe (EP) mission during a calibration observation. The position of the source is R.A. = 141.644 deg, DEC = -9.547 deg (J2000)
with an uncertainty of 3 arcmin (radius, 90% C.L. statistical and systematic). The light curve of the source shows a multi-peak profile.
The transient event lasts for ~1600 seconds and has a peak flux of ~3e-9 erg/s/cm^2 in the 0.5-4 keV band. The averaged spectrum can be fitted
by an absorbed power-law with NH = 1.5(-0.9/+1.0) x 10^21 cm^-2 and a photon index of 1.7(-0.4/+0.4). The derived average unabsorbed 0.5 - 4.0 keV
flux is 5.3(-0.7/+1.0) x 10^-10 erg/s/cm^2. However, we note that the derived source parameters may be subject to larger uncertainties than those
quoted here since in-orbit calibration of the instrument is still in progress.
No previously known bright X-ray sources have been found within the 3 arcmin region around the source position, with only one optical counterpart
of white dwarf candidate located at the distance of ~380 pc. Based on the shape and timescale of the observed flare light curve, we tend to consider
that the source is not a stellar flare, although this cannot be ruled out. A Swift target of opportunity observation has been proposed, and further
follow-up observations are strongly encouraged to identify the nature of this X-ray flare.
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.
View this GCN Circular online at https://gcn.nasa.gov/circulars/35931.
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TITLE: GCN CIRCULAR
NUMBER: 35930
SUBJECT: GRID detection of GRB 240306A
DATE: 24/03/16 12:53:36 GMT
FROM: GRID Student Team at Tsinghua University <grid(a)tsinghua.edu.cn>
Chenyu Wang, Zirui Yang and Longhao Li report on behalf of the GRID Collaboration:
GRID-03B reports the detection of the long-duration GRB 240306A, which was also detected by Fermi/GBM, Swift/BAT-GUANO and AstroSat CZTI (GCN Circular 35885, 35889 and 35892).
The event was triggered with GRID on 2024-03-06 at 06:45:48 UTC. The measured burst duration (T90) in the 30-2000 keV range is approximately 10.0 ± 1.0 seconds. Due to its proximity to Earth's atmosphere in the view of GRID-03B, the spectral data from GRID for this event may not be accurate.
The GRID light curve of this event can be found at https://mirrors.tuna.tsinghua.edu.cn/GRID/data/GRID-GCN/GRB240306A/GRID_GRB….
GRID is a student-led project to monitor the transient gamma-ray sky with multiple detectors onboard different nanosatellites in the era of multi-messenger astronomy. For more information about GRID, please refer to the following references: https://doi.org/10.1007/s10686-019-09636-w and https://doi.org/10.1007/s10686-021-09819-4.
View this GCN Circular online at https://gcn.nasa.gov/circulars/35930.
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TITLE: GCN CIRCULAR
NUMBER: 35929
SUBJECT: Changes to the Fermi-GBM Triggering Thresholds
DATE: 24/03/15 18:28:40 GMT
FROM: Oliver J Roberts at USRA/NASA <oliver.roberts(a)nasa.gov>
O.J. Roberts reports on behalf of the GBM Team
At 15:00 UTC on March 14th, 2024, the triggering thresholds on Fermi-GBM triggering algorithms 8-11, were reduced from 4.5 sigma to 4.0 sigma. These algorithms are designed to trigger on short (256 and 512 ms) timescales over 50-300 keV. More information on these and other triggering algorithms that Fermi-GBM uses can be found in Table 1 of the first GBM Catalog [1]. This was undertaken to obtain additional short GRBs that will be rapidly down-linked for multi messenger science. The external coincidence search RAVEN [2,3] will automatically ingest the GBM localizations from these GRBs and issue joint GW-GRB detection skymaps through the LVK alert stream.
Further testing is ongoing, during which time, these and possibly other triggering algorithm thresholds may be reduced further. Consequently, Fermi-GBM may trigger and localize spurious events. We note that the trigger algorithm and significance are listed in the Fermi-GBM Alert GCN notice type. We will report on any spurious events, and provide a final update on the threshold values of the triggering algorithms that were amended, in a further GCN notice once testing has concluded.
[1] Paciesas, W.S., et al., 2012 ApJS 199 18, https://iopscience.iop.org/article/10.1088/0067-0049/199/1/18/pdf
[2] Urban, A.L., 2016, Ph.D. Thesis. https://dc.uwm.edu/etd/1218/
[3] Piotrzkowski, B.J., 2022, Ph.D. Thesis https://dc.uwm.edu/etd/3060
View this GCN Circular online at https://gcn.nasa.gov/circulars/35929.
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TITLE: GCN CIRCULAR
NUMBER: 35928
SUBJECT: Swift Triggers 1220155, 1220156, 1220157, 1220158, 1220160 and 1220161 were not astrophysical
DATE: 24/03/15 12:27:50 GMT
FROM: Boris Sbarufatti at INAF-OAB <boris.sbarufatti(a)inaf.it>
B. Sbarufatti (INAF-OAB) report on behalf of the Neil Gehrels Swift
Observatory Team:
Swift Triggers 1220155, 1220156, 1220157, 1220158, 1220160 and 1220161 were due to an outage of the star trackers, and therefore are not astrophysical.
View this GCN Circular online at https://gcn.nasa.gov/circulars/35928.
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