TITLE: GCN CIRCULAR
NUMBER: 36826
SUBJECT: LIGO/Virgo/KAGRA S240705at: Identification of a GW compact binary merger candidate
DATE: 24/07/05 06:21:20 GMT
FROM: Sayantan Ghosh at Indian Institute of Technology Bombay <stanghosh(a)iitb.ac.in>
The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report:
We identified the compact binary merger candidate S240705at during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2024-07-05 05:32:15.917 UTC (GPS time: 1404192753.917). The candidate was found by the CWB [1], GstLAL [2], MBTA [3], and PyCBC Live [4] analysis pipelines.
S240705at is an event of interest because its false alarm rate, as estimated by the online analysis, is 7.1e-16 Hz, or about one in 1e8 years. The event's properties can be found at this URL:
https://gracedb.ligo.org/superevents/S240705at
The classification of the GW signal, in order of descending probability, is BBH (>99%), Terrestrial (<1%), BNS (<1%), or NSBH (<1%).
Assuming the candidate is astrophysical in origin, the probability that the lighter compact object is consistent with a neutron star mass (HasNS) is <1%. [5] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is <1%. [5] Both HasNS and HasRemnant consider the support of several neutron star equations of state. The probability that either of the binary components lies between 3 and 5 solar masses (HasMassGap) is <1%.
Two sky maps are available at this time and can be retrieved from the GraceDB event page:
* bayestar.multiorder.fits,0, an initial localization generated by BAYESTAR [6], distributed via GCN notice about 27 seconds after the candidate event time.
* bayestar.multiorder.fits,1, an initial localization generated by BAYESTAR [6], distributed via GCN notice about 5 minutes after the candidate event time.
The preferred sky map at this time is bayestar.multiorder.fits,1. For the bayestar.multiorder.fits,1 sky map, the 90% credible region is 724 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 3564 +/- 851 Mpc (a posteriori mean +/- standard deviation).
For further information about analysis methodology and the contents of this alert, refer to the LIGO/Virgo/KAGRA Public Alerts User Guide https://emfollow.docs.ligo.org/.
[1] Klimenko et al. PRD 93, 042004 (2016) doi:10.1103/PhysRevD.93.042004
[2] Tsukada et al. PRD 108, 043004 (2023) doi:10.1103/PhysRevD.108.043004 and Ewing et al. (2023) arXiv:2305.05625
[3] Aubin et al. CQG 38, 095004 (2021) doi:10.1088/1361-6382/abe913
[4] Dal Canton et al. ApJ 923, 254 (2021) doi:10.3847/1538-4357/ac2f9a
[5] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe
[6] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013
View this GCN Circular online at https://gcn.nasa.gov/circulars/36826.
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TITLE: GCN CIRCULAR
NUMBER: 36825
SUBJECT: EP240703a: KAIT optical upper limit
DATE: 24/07/05 01:45:56 GMT
FROM: Weikang Zheng at UC Berkeley <weikang(a)berkeley.edu>
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.
View this GCN Circular online at https://gcn.nasa.gov/circulars/36825.
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TITLE: GCN CIRCULAR
NUMBER: 36825
SUBJECT: EP240703a: KAIT optical upper limit
DATE: 24/07/05 01:45:56 GMT
FROM: Weikang Zheng at UC Berkeley <weikang(a)berkeley.edu>
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.
View this GCN Circular online at https://gcn.nasa.gov/circulars/36825.
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TITLE: GCN CIRCULAR
NUMBER: 36824
SUBJECT: EP240703a: BTA observations
DATE: 24/07/04 22:54:06 GMT
FROM: Alexei Pozanenko at IKI, Moscow <grb.alex(a)gmail.com>
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.
View this GCN Circular online at https://gcn.nasa.gov/circulars/36824.
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TITLE: GCN CIRCULAR
NUMBER: 36823
SUBJECT: EP240703c: Kinder optical follow-up and Swift XRT observations
DATE: 24/07/04 21:01:36 GMT
FROM: Janet Chen at National Central University <janetstars(a)gmail.com>
Y. J. Yang, A. Aryan (both NCU), S. Yang (HNAS), T.-W. Chen (NCU), H. F. Stevance (Oxford), S. J. Smartt (Oxford/QUB), W.-J. Hou, C.-S. Lin, M.-H. Lee, Y.-C. Pan, H.-Y. Hsiao, C.-C. Ngeow, C.-H. Lai, A. Sankar.K, H.-C. Lin, J.-K. Guo (all NCUIA), 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 (both IfA, University of Hawaii) report:
We observed the field of the fast X-ray transient EP240703c (Zhang et al., GCN 36818) 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 14:51 UT on 4th of July 2024 (MJD = 60495.619), 20.6 hrs after the EP trigger and we observed for a total of 4500 seconds on source. We used the Kinder pipeline (Yang et al. A&A 646, A22) to stack the images and subtract the stacked images with the SkyMapper template images.
We do not detect any optical counterpart in the errorbox of 3 arcminute around the position of the EP source specified by Zhang et al., (GCN 36818). The details of the observations and the corresponding 2.5 sigma upper limit (in the AB system) in our combined image are as follows:
Telescope | Filter | MJD (start) | t-t0 | Exposure | Magnitude | avg. Seeing | med. Airmass
SLT | r | 60495.619 | 20.6 hrs | 300 sec * 15 | > 21.41 | 2".3 | 1.74
The presented magnitudes are calibrated using the field stars from the SkyMapper catalog and are not corrected for the expected Galactic foreground extinction corresponding to a reddening of E_(B-V) = 0.09 mag in the direction of the burst (Schlafly & Finkbeiner 2011).
The EP team triggered the Swift ToO observations (PI: EP) for EP240703c (Zhang et al., GCN 36818). They noticed that there is a previous Swift X-ray observation of a high proper motion star LP 924-17 (Evans+, 2020). The new Swift observation was carried out from 2024-07-04T11:41:37 to 2024-07-04T12:00:53. We obtained some initial results from the quick-look data using the Swift-XRT products provided by the UK Swift Science Data Centre. Applying a simple power-law model with absorption, we derived a column density NH ≈ 5.0 × 10^21 cm^-2, a photon index of approximately 4.2, which indicates a relatively soft spectrum, and an unabsorbed flux in the 0.3-10 keV band of ~ 2 × 10^-11 erg cm^-2 s^-1.
For the UVOT data, the source is visible in the images across all bands. It is clearly detected in the V band with a magnitude of 17.76 ± 0.20 (stat) ± 0.01 (sys) in the AB system. However, the source cannot be well constrained in the B, U, UVM2, UVW1, and UVW2 bands. Further, we report the PSF photometry measurement on this high proper motion star LP 924-17, which has no significant brightness change during our SLT observations, with an average magnitude of r = 16.88 +/- 0.05 mag.
View this GCN Circular online at https://gcn.nasa.gov/circulars/36823.
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TITLE: GCN CIRCULAR
NUMBER: 36822
SUBJECT: EP240703a: BOOTES-3 optical upper limit
DATE: 24/07/04 19:24:51 GMT
FROM: Alberto Castro-Tirado at Inst.de Astro. de Andalucia <ajct(a)iaa.es>
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.
View this GCN Circular online at https://gcn.nasa.gov/circulars/36822.
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TITLE: GCN CIRCULAR
NUMBER: 36821
SUBJECT: EP240703a: Liverpool Telescope optical follow-up observations
DATE: 24/07/04 17:53:09 GMT
FROM: A. Bochenek at Liverpool John Moores University <a.m.bochenek(a)2023.ljmu.ac.uk>
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).
View this GCN Circular online at https://gcn.nasa.gov/circulars/36821.
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TITLE: GCN CIRCULAR
NUMBER: 36820
SUBJECT: EP240703a/GRB 240703A: TRT optical candidate likely not real
DATE: 24/07/04 10:42:33 GMT
FROM: Dong Xu at NAOC/CAS <dxu(a)nao.cas.cn>
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.
View this GCN Circular online at https://gcn.nasa.gov/circulars/36820.
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TITLE: GCN CIRCULAR
NUMBER: 36819
SUBJECT: EP240703a: Kinder optical follow-up observations
DATE: 24/07/04 10:31:37 GMT
FROM: Amar Aryan at National Central University, Institute of Astronomy (NCUIA) <amararyan941(a)gmail.com>
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).
View this GCN Circular online at https://gcn.nasa.gov/circulars/36819.
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TITLE: GCN CIRCULAR
NUMBER: 36819
SUBJECT: EP240703a: Kinder optical follow-up observations
DATE: 24/07/04 10:31:37 GMT
FROM: Amar Aryan at National Central University, Institute of Astronomy (NCUIA) <amararyan941(a)gmail.com>
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).
View this GCN Circular online at https://gcn.nasa.gov/circulars/36819.
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