LIGO/Virgo/KAGRA S240807h
GCN Circular 37119
Subject
LIGO/Virgo/KAGRA S240807h: Updated Sky localization and EM Bright Classification
Date
2024-08-09T21:03:39Z (10 months ago)
From
jgolomb@caltech.edu
Via
Web form
The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report:
We have conducted further analysis of the LIGO Livingston Observatory (L1) and Virgo Observatory (V1) data around the time of the compact binary merger (CBC) candidate S240807h (GCN Circular 37096). Parameter estimation has been performed using Bilby [1] and a new sky map, Bilby.multiorder.fits,0, distributed via GCN Notice, is available for retrieval from the GraceDB event page:
https://gracedb.ligo.org/superevents/S240807h
Based on posterior support from parameter estimation [1], under the assumption that the candidate S240807h is astrophysical in origin, the probability that the lighter compact object is consistent with a neutron star mass (HasNS) is <1%. [2] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is <1%. [2] 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 28%.
For the Bilby.multiorder.fits,0 sky map, the 90% credible region is 12857 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 1018 +/- 295 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] Ashton et al. ApJS 241, 27 (2019) doi:10.3847/1538-4365/ab06fc and Morisaki et al. (2023) arXiv:2307.13380
[2] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe
GCN Circular 37380
Subject
LIGO/Virgo/KAGRA S240807h: Upper limits from Swift/BAT-GUANO
Date
2024-09-04T02:16:08Z (9 months ago)
From
Samuele Ronchini at PSU <sjs8171@psu.edu>
Via
Web form
Samuele Ronchini (PSU), Aaron Tohuvavohu (U Toronto), Tyler Parsotan (NASA GSFC), Jamie A. Kennea (PSU), James DeLaunay (PSU), Gayathri Raman (PSU) report:
Swift/BAT was observing 63% of the GW localization probability ([bayestar.multiorder.fits](https://gracedb.ligo.org/api/superevents/S240807h/files/bayestar.multiorder.fits)) at merger time. A fraction 35% of the GW localization posterior is contained inside the BAT 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](https://iopscience.iop.org/article/10.3847/1538-4357/aba94f)).
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](https://iopscience.iop.org/article/10.3847/1538-4357/ac9d38)), 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^-7 erg/s/cm^2:
|time_bin (s) |soft |normal| hard | GRB170817
|-|-|-|-|-|
|0.256 |6.68 | 5.08 | 4.61 | 5.55
|1.024 |3.40 | 2.59 | 2.35 | 2.83
|4.096 |1.83 | 1.39 | 1.26 | 1.52
|16.384 |1.12 | 0.86 | 0.78 | 0.93
The upper limits as function of sky position are plotted here, alongside the GW localization:
[https://doi.org/10.5281/zenodo.13652732]()
The solid and dashed lines indicate the 90% and 50% GW contour levels, respectively. The corresponding fits file is also included.
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/]()