TITLE: GCN CIRCULAR
NUMBER: 36728
SUBJECT: LIGO/Virgo/KAGRA S240621eb: Identification of a GW compact binary merger candidate
DATE: 24/06/21 20:37:18 GMT
FROM: Keita Kawabe at LIGO Hanford <kkawabe(a)caltech.edu>
The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report:
We identified the compact binary merger candidate S240621eb during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2024-06-21 20:09:35.532 UTC (GPS time: 1403035793.532). The candidate was found by the CWB [1], GstLAL [2], MBTA [3], and PyCBC Live [4] analysis pipelines.
S240621eb is an event of interest because its false alarm rate, as estimated by the online analysis, is 4.3e-08 Hz, or about one in 8 months. The event's properties can be found at this URL:
https://gracedb.ligo.org/superevents/S240621eb
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 26 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 1777 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 4433 +/- 1299 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/36728.
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TITLE: GCN CIRCULAR
NUMBER: 36727
SUBJECT: LIGO/Virgo/KAGRA S240621dy: Identification of a GW compact binary merger candidate
DATE: 24/06/21 20:30:11 GMT
FROM: hsiang-yu.huang(a)ligo.org
The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report:
We identified the compact binary merger candidate S240621dy during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2024-06-21 19:50:59.425 UTC (GPS time: 1403034677.425). The candidate was found by the CWB [1], GstLAL [2], MBTA [3], and PyCBC Live [4] analysis pipelines.
S240621dy is an event of interest because its false alarm rate, as estimated by the online analysis, is 4e-20 Hz, or about one in 1e12 years. The event's properties can be found at this URL:
https://gracedb.ligo.org/superevents/S240621dy
The classification of the GW signal, in order of descending probability, is BBH (>99%), BNS (<1%), NSBH (<1%), or Terrestrial (<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 well fit by an ellipse with an area of 37 deg2 described by the following DS9 region (right ascension, declination, semi-major axis, semi-minor axis, position angle of the semi-minor axis):
icrs; ellipse(03h12m, +44d49m, 4.90d, 2.40d, 97.02d)
Marginalized over the whole sky, the a posteriori luminosity distance estimate is 1181 +/- 249 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/36727.
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TITLE: GCN CIRCULAR
NUMBER: 36726
SUBJECT: IPN triangulation of GRB 240615A (short)
DATE: 24/06/21 17:27:05 GMT
FROM: Dmitry Svinkin at Ioffe Institute <svinkin(a)mail.ioffe.ru>
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,
A. Goldstein, M. S. Briggs, C. Wilson-Hodge,
and E. Burns on behalf of the Fermi GBM team,
E. Bozzo and C. Ferrigno, on behalf of the INTEGRAL SPI-ACS GRB team,
S. Barthelmy, J. Cummings, H. Krimm, D. Palmer, and A. Tohuvavohu
on behalf of the Swift-BAT 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:
The short-duration GRB 240615A
(Fermi-GBM detection: The Fermi GBM team, GCN 36671;
Swift-BAT/GUANO detection and localization: DeLaunay et al., GCN 36672;
Konus-Wind detection: Frederiks et al., GCN 36677;
GECAM-C detection: Tan et al., GCN 36682)
was detected by Fermi (GBM trigger 740166710), Swift (BAT),
Konus-Wind, INTEGRAL (SPI-ACS), GECAM-C, and Mars-Odyssey (HEND)
at about 64305 s UT (17:51:45).
We have triangulated it to a preliminary, 3 sigma error box
whose coordinates are:
---------------------------------------------
RA(2000), deg Dec(2000), deg
---------------------------------------------
Center:
326.163 (21h 44m 39s) +38.634 (+38d 38' 02")
Corners:
326.204 (21h 44m 49s) +38.689 (+38d 41' 21")
326.141 (21h 44m 34s) +38.735 (+38d 44' 07")
326.122 (21h 44m 29s) +38.578 (+38d 34' 42")
326.186 (21h 44m 45s) +38.532 (+38d 31' 56")
---------------------------------------------
The error box area is 31 sq. arcmin, and its maximum
dimension is 12 arcmin (the minimum one is 3.3 arcmin).
The Sun distance was 95 deg.
The IPN localization is consistent with, but reduces the area of,
the Swift-BAT/GUANO localization. All the sources reported by Swift-XRT (GCN 36683) are outside the IPN box.
This localization may be improved.
A triangulation map and HEALPix FITS file are posted at
http://www.ioffe.ru/LEA/GRBs/GRB240615_T64306/IPN
The HEALPix triangulation map is the multi-order HEALPix in units of probability density.
View this GCN Circular online at https://gcn.nasa.gov/circulars/36726.
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TITLE: GCN CIRCULAR
NUMBER: 36725
SUBJECT: X-ray transient EP240618a: Fermi/GBM non-detection
DATE: 24/06/21 15:56:04 GMT
FROM: mariaedvige.ravasio(a)ru.nl
M. E. Ravasio (Radboud University) and P.G. Jonker (Radboud University) report on behalf of a larger collaboration:
Following the detection of the fast X-ray transient EP240618a by the Einstein Probe WXT and FXT (Sun et al., GCN 36690), we inspected the Fermi/GBM daily data for the presence of a possible gamma-ray counterpart. Fermi was operational (it was not in the SAA) and the location of the source was visible (i.e. it was not Earth-occulted).
Inspecting CSPEC data of the 4 best source-angle detectors (n7, n6, nb, b1) in the energy range 8-900 keV (for n7, n6, nb) and 300-40000 keV (for b1), with a time resolution of 4 s, we found no significant gamma-ray source within the time interval [T0; T0+100] s (same duration reported by Sun et al., GCN 36690, where T0 = 2024-06-18T05:43:43).
Assuming a power-law model with a photon index of 2, the estimated upper limit to the flux in the energy range 10-1000 keV at the 90% confidence level over the time interval mentioned above is 8.5 x 10^-9 erg/cm^2/s.
View this GCN Circular online at https://gcn.nasa.gov/circulars/36725.
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TITLE: GCN CIRCULAR
NUMBER: 36725
SUBJECT: X-ray transient EP240618a: Fermi/GBM non-detection
DATE: 24/06/21 15:56:04 GMT
FROM: mariaedvige.ravasio(a)ru.nl
M. E. Ravasio (Radboud University) and P.G. Jonker (Radboud University) report on behalf of a larger collaboration:
Following the detection of the fast X-ray transient EP240618a by the Einstein Probe WXT and FXT (Sun et al., GCN 36690), we inspected the Fermi/GBM daily data for the presence of a possible gamma-ray counterpart. Fermi was operational (it was not in the SAA) and the location of the source was visible (i.e. it was not Earth-occulted).
Inspecting CSPEC data of the 4 best source-angle detectors (n7, n6, nb, b1) in the energy range 8-900 keV (for n7, n6, nb) and 300-40000 keV (for b1), with a time resolution of 4 s, we found no significant gamma-ray source within the time interval [T0; T0+100] s (same duration reported by Sun et al., GCN 36690, where T0 = 2024-06-18T05:43:43).
Assuming a power-law model with a photon index of 2, the estimated upper limit to the flux in the energy range 10-1000 keV at the 90% confidence level over the time interval mentioned above is 8.5 x 10^-9 erg/cm^2/s.
View this GCN Circular online at https://gcn.nasa.gov/circulars/36725.
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TITLE: GCN CIRCULAR
NUMBER: 36724
SUBJECT: GRB 240619A: GRBAlpha detection
DATE: 24/06/21 14:40:54 GMT
FROM: Marianna Dafčíková at Masaryk University <500025(a)mail.muni.cz>
M. Dafcikova, J. Ripa, M. Kolar (Masaryk U.), A. Pal (Konkoly Observatory), N. Werner (Masaryk U.), M. Ohno, H. Takahashi (Hiroshima U.), L. Meszaros, B. Csak (Konkoly Observatory), N. Husarikova, F. Munz , M. Topinka, M. Duriskova, L. Szakszonova, J.-P. Breuer, F. Hroch (Masaryk U.), T. Urbanec, M. Kasal, A. Povalac (Brno U. of Technology), J. Hudec, J. Kapus, M. Frajt (Spacemanic s.r.o), R. Laszlo, M. Koleda (Needronix s.r.o), M. Smelko, P. Hanak, P. Lipovsky (Technical U. of Kosice), G. Galgoczi (Wigner Research Center/Eotvos U.), Y. Uchida, H. Poon, H. Matake (Hiroshima U.), N. Uchida (ISAS/JAXA), T. Bozoki (Eotvos U.), G. Dalya (Eotvos U.), T. Enoto (Kyoto U.), Zs. Frei (Eotvos U.), G. Friss (Eotvos U.), Y. Fukazawa, K. Hirose (Hiroshima U.), S. Hisadomi (Nagoya U.), Y. Ichinohe (Rikkyo U.), K. Kapas (Eotvos U.), L. L. Kiss (Konkoly Observatory), T. Mizuno (Hiroshima U.), K. Nakazawa (Nagoya U.), H. Odaka (Univ of Tokyo), J. Takatsy (Eotvos U.), K. Torigoe (Hiroshima U.), N. Kogiso, M. Yoneyama (Osaka Metropolitan U.), M. Moritaki (U. Tokyo), T. Kano (U. Michigan) -- the GRBAlpha collaboration.
The long-duration GRB 240619A (Fermi/GBM detection: GCN 36694; CALET/CGBM detection: GCN 36719; INTEGRAL/SPI-ACS peak detection at 2024-06-19 ~03:43:31 UT) was observed by the GRBAlpha 1U CubeSat (Pal et al. 2023, A&A, 677, 40; https://ui.adsabs.harvard.edu/abs/2023A%26A...677A..40P/abstract).
The detection was confirmed at the peak time 2024-06-19 03:43:30.7 UTC. The T90 duration measured by GRBAlpha is 4.5 s and the overall significance during T90 reaches 10 sigma.
The light curve obtained by GRBAlpha is available here: https://grbalpha.konkoly.hu/static/share/GRB240619A_GCN.pdf
All GRBAlpha detections are listed at: https://monoceros.physics.muni.cz/hea/GRBAlpha/
GRBAlpha, launched on 2021 March 22, is a demonstration mission for a future CubeSat constellation (Werner et al. Proc. SPIE 2018). The detector of GRBAlpha consists of a 75 x 75 x 5 mm3 CsI scintillator read out by a SiPM array, covering the energy range from ~50 keV to ~1000 keV. To increase the duty cycle and the downlink rate, the upgrade of the on-board data acquisition software stack is in progress. The ground segment is also supported by the radio amateur community and it takes advantage of the SatNOGS network for increased data downlink volume.
View this GCN Circular online at https://gcn.nasa.gov/circulars/36724.
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TITLE: GCN CIRCULAR
NUMBER: 36723
SUBJECT: EP240618a: Swift/XRT upper limit
DATE: 24/06/21 10:21:36 GMT
FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn>
W. Chen, H. Sun (NAOC, CAS), H. Zhou (PMO, CAS), W. D. Zhang, D. Y. Li, Z. X. Ling, Y. Liu, C. Zhang, C. C. Jin, H. Q. Cheng, C. Z. Cui, D. W. Fan, H. B. Hu, J. W. Hu, M. H. Huang, H. Y. Liu, M. J. Liu, Z. Z. Lv, T. Y. Lian, X. Mao, H. W. Pan, X. Pan, W. X. Wang, 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, 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 transient EP240618a by the Einstein Probe (Sun et al., GCN 36690), we triggered a Swift target of opportunity observation (ObsID: 00016670001). The XRT onboard Swift began the observation at 2024-06-20T15:56:06 UTC, about 58 hours after the WXT detection, with an exposure time of 2.0 ks in the Photon Counting mode.
No significant X-ray source was detected within the 30 arcsec region around the reported FXT position. Assuming an absorbed power-law model with a Galactic column density of 1.98 x 10^21 cm^-2 and a photon index of 2, the estimated flux upper limit in 0.3-10 keV at the 90% confidence level is 1.2 x 10^-13 ergs/cm^2/s.
We thank the Neil Gehrels Swift Observatory team for making the X-ray observation possible.
View this GCN Circular online at https://gcn.nasa.gov/circulars/36723.
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TITLE: GCN CIRCULAR
NUMBER: 36722
SUBJECT: EP240617a: tentative Swift/XRT detection of the afterglow
DATE: 24/06/21 09:36:34 GMT
FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn>
H. Sun, W. Chen (NAOC, CAS), H. Zhou (PMO, CAS), W. D. Zhang, D. Y. Li, Z. X. Ling, Y. Liu, C. Zhang, C. C. Jin, H. Q. Cheng, C. Z. Cui, D. W. Fan, H. B. Hu, J. W. Hu, M. H. Huang, H. Y. Liu, M. J. Liu, Z. Z. Lv, T. Y. Lian, X. Mao, H. W. Pan, X. Pan, W. X. Wang, 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, 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 transient EP240617a by the Einstein Probe (Zhou et al., GCN 36691), which is likely a gamma-ray burst based on Fermi/GBM data (Yang et al., GCN 36692), we triggered a Swift target of opportunity observation (ObsID: 00016669001). The XRT onboard Swift began the observation at 2024-06-20T17:57:41 UTC, about 77 hours after the WXT detection, with an exposure time of 1.69 ks in the Photon Counting mode.
Within the 3 arcmin error radius of the WXT position, we have tentatively detected a weak signal with a significance of 5.3 sigma (as evaluated by the Li-Ma formula, Li & Ma 1983, ApJ, 272, 317) at R.A.=19:00:06.0, DEC=-22:33:29.9 (J2000) with an uncertainty of 7.5 arcsec (radius, 90% C.L. statistical and systematic). The position of the source is 0.3 arcmin away from the WXT detection and is thus spatially consistent with EP240617a, suggesting that we detected the X-ray afterglow. The source has an average count rate of 5.1 x 10^-3 cps. Assuming an absorbed power-law model with a Galactic column density of 1.7 x 10^21 cm^-2 and a photon index of 2, the estimated flux in 0.3-10 keV is 1.9 x 10^-13 ergs/cm^2/s.
Further follow-up observations are encouraged to search for the multi-band afterglows.
We thank the Neil Gehrels Swift Observatory team for making the X-ray observation possible.
View this GCN Circular online at https://gcn.nasa.gov/circulars/36722.
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TITLE: GCN CIRCULAR
NUMBER: 36721
SUBJECT: GRB 240619A: Swift-XRT probable afterglow detection
DATE: 24/06/21 08:07:28 GMT
FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk>
M. Capalbi (INAF-IASFPA), M. Perri (SSDC & INAF-OAR), V. D'Elia (SSDC &
INAF-OAR), S. Dichiara (PSU), J.A. Kennea (PSU), A. Tohuvavohu (U.
Toronto), A.P. Beardmore (U. Leicester), J.P. Osborne (U. Leicester)
and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team:
Swift-XRT has performed follow-up observations of the
Fermi/GBM-detected burst GRB 240619A (GCN Circ. 36694), collecting 1.7
ks of Photon Counting (PC) mode data between T0+174.0 ks and T0+175.7
ks at the location of the GOTO afterglow candidate AT 2024lw (Gompertz
et al., GCN Circ. 36715).
An uncatalogued X-ray source is detected at RA, Dec=162.3944, +17.2829
which is equivalent to:
RA (J2000): 10:49:34.66
Dec(J2000): +17:16:58.5
with an uncertainty of 4.3 arcsec (radius, 90% confidence). This
position is 0.7 arcsec from the GOTO position and thus we suggest it is
related to that object and likely the GRB afterglow. The source has a
mean count rate of 2.5e-02 ct/sec; we cannot determine at the present
time whether it is fading.
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00021697.
The results of the full analysis of the XRT observations are available
at https://www.swift.ac.uk/ToO_GRBs/00021697.
This circular is an official product of the Swift-XRT team.
View this GCN Circular online at https://gcn.nasa.gov/circulars/36721.
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TITLE: GCN CIRCULAR
NUMBER: 36720
SUBJECT: GRB 240619A: Swift ToO observations
DATE: 24/06/21 07:31:35 GMT
FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk>
P. A. Evans (U. Leicester) reports on behalf of the Swift team:
Swift has initiated a ToO observation of the Fermi/GBM GRB 240619A.
Automated analysis of the XRT data will be presented online at
https://www.swift.ac.uk/ToO_GRBs/00021697
Any uncatalogued X-ray sources detected in this analysis will be
reported on this website and via GCN COUNTERPART notices. These are
not necessarily related to the Fermi/GBM event. Any X-ray source
considered to be a probable afterglow candidate will be reported via a
GCN Circular after manual consideration.
Details of the XRT automated analysis methods are detailed in Evans et
al. (2007, A&A, 469, 379; 2009, MNRAS, 397, 1177 and 2014, ApJS, 210, 8).
This circular is an official product of the Swift-XRT team.
View this GCN Circular online at https://gcn.nasa.gov/circulars/36720.
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