TITLE: GCN CIRCULAR
NUMBER: 34128
SUBJECT: LIGO/Virgo/KAGRA S230627c: Upper limits from Swift/BAT-GUANO
DATE: 23/07/01 03:37:08 GMT
FROM: Samuele Ronchini at PSU <sjs8171(a)psu.edu>
Gayathri Raman (PSU), Samuele Ronchini (PSU), Aaron Tohuvavohu (U Toronto), James DeLaunay (U Alabama), Jamie A. Kennea (PSU), Tyler Parsotan (NASA GSFC) report:
Swift/BAT was observing 99.2% of the GW localization probability (Bilby.multiorder.fits,0) at merger time.
The entirety of the GW 90% credible region is contained inside the coded FoV.
The LVK notice, distributed in near real-time, triggered the Swift Mission Operations Center operated Gamma-ray Urgent Archiver for Novel Opportunities (GUANO; Tohuvavohu et al. 2020, ApJ, 900, 1).
Upon trigger by this notice, GUANO sent a command to the Swift Burst Alert Telescope (BAT) to save 200 seconds of BAT event-mode data from [-50,+150] seconds around the time of the burst. All the requested event mode data was delivered to the ground.
Using the NITRATES analysis (DeLaunay + Tohuvavohu 2022, ApJ, 941, 169), we searched for emission on 8 timescales from 0.128s to 16.384s in the interval [-20,+20] seconds around the merger time. We find no evidence for a signal, and derive the following upper limits.
We quote the 5-sigma flux upper limits in the 15-350 keV band, weighted over the GW localization, for four spectral templates (soft, normal, and hard GRB-like templates described in [arXiv:1612.02395], and spectral shape from GRB170817A [arXiv:1710.05446]) and for four time bins.
In units of 10^-8 erg/s/cm^2:
Bin duration (s) | hard normal soft GRB 170817A
----------------------------------------------------
0.256 | 7.0 7.7 4.9 8.3
1.024 | 3.6 4.0 2.5 4.2
4.096 | 1.9 2.2 1.4 2.3
16.384 | 1.2 1.3 0.8 1.4
For a median distance of 291 Mpc, we derive luminosity upper limits (in units of 10^47 erg/s) as follows:
Bin duration (s) | hard normal soft GRB 170817A
-----------------------------------------------------
0.256 | 7.1 7.8 5.0 8.4
1.024 | 3.6 4.0 2.5 4.3
4.096 | 2.0 2.2 1.4 2.3
16.384 | 1.2 1.3 0.8 1.4
The upper limits as function of sky position are plotted here, alongside the GW localization:
https://doi.org/10.5281/zenodo.8102958
The corresponding fits file can be found here:
https://doi.org/10.5281/zenodo.8102951
GUANO is a fully autonomous, extremely low latency, spacecraft
commanding pipeline designed for targeted recovery of BAT event mode
data around the times of compelling astrophysical events to enable
more sensitive GRB searches.
A live reporting of Swift/BAT event data recovered by GUANO can be
found at: https://www.swift.psu.edu/guano/
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TITLE: GCN CIRCULAR
NUMBER: 34127
SUBJECT: LIGO/Virgo/KAGRA S230630bq: Identification of a GW compact binary merger candidate
DATE: 23/07/01 00:55:44 GMT
FROM: David Hui at Chungnam National University <huichungyue(a)gmail.com>
The LIGO Scientific Collaboration, the Virgo Collaboration, and the
KAGRA Collaboration report:
We identified the compact binary merger candidate S230630bq during
real-time processing of data from LIGO Hanford Observatory (H1) and
LIGO Livingston Observatory (L1) at 2023-06-30 23:45:32.407 UTC (GPS
time: 1372203950.407). The candidate was found by the MBTA [1], GstLAL
[2], PyCBC Live [3], and SPIIR [4] analysis pipelines.
S230630bq is an event of interest because its false alarm rate, as
estimated by the online analysis, is 7.7e-09 Hz, or about one in 4
years. The event's properties can be found at this URL:
https://gracedb.ligo.org/superevents/S230630bq
The classification of the GW signal, in order of descending
probability, is BBH (97%), Terrestrial (3%), NSBH (<1%), or BNS (<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 8%.
Two sky maps are available at this time and can be retrieved from the
GraceDB event page:
* bayestar.multiorder.fits,1, an initial localization generated by
BAYESTAR [6], distributed via GCN notice about 33 seconds after the
candidate event time.
* bayestar.multiorder.fits,2, 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,2. For
the bayestar.multiorder.fits,2 sky map, the 90% credible region is
1976 deg2. Marginalized over the whole sky, the a posteriori
luminosity distance estimate is 1150 +/- 360 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/userguide/.
[1] Aubin et al. CQG 38, 095004 (2021)
[2] Tsukada et al. arXiv:2305.06286 (2023) and Ewing et al.
arXiv:2305.05625 (2023)
[3] Dal Canton et al. ApJ 923, 254 (2021)
[4] Chu et al. PRD 105, 024023 (2022)
[5] Chatterjee et al. ApJ 896, 54 (2020)
[6] Singer & Price PRD 93, 024013 (2016)
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