On 2017 August 17 at 12:41:06 UTC the Fermi Gamma-ray Burst Monitor (GBM) detected and triggered on the short gamma-ray burst (GRB) 170817A. Approximately 1.7 s prior to this GRB, the Laser ...Interferometer Gravitational-wave Observatory triggered on a binary compact merger candidate associated with the GRB. This is the first unambiguous coincident observation of gravitational waves and electromagnetic radiation from a single astrophysical source and marks the start of gravitational-wave multi-messenger astronomy. We report the GBM observations and analysis of this ordinary short GRB, which extraordinarily confirms that at least some short GRBs are produced by binary compact mergers.
We derive a Bayesian criterion for assessing whether signals observed in two separate data sets originate from a common source. The Bayes factor for a common versus unrelated origin of signals ...includes an overlap integral of the posterior distributions over the common-source parameters. Focusing on multimessenger gravitational-wave astronomy, we apply the method to the spatial and temporal association of independent gravitational-wave and electromagnetic (or neutrino) observations. As an example, we consider the coincidence between the recently discovered gravitational-wave signal GW170817 from a binary neutron star merger and the gamma-ray burst GRB 170817A: we find that the common-source model is enormously favored over a model describing them as unrelated signals.
Fermi-Gamma-ray Burst Monitor observed a 1 s long gamma-ray signal (GW150914-GBM) starting 0.4 s after the first gravitational-wave detection from the binary black hole (BH) merger GW150914. ...GW150914-GBM is consistent with a short gamma-ray burst origin; however, no unambiguous claims can be made as to the physical association of the two signals due to a combination of low gamma-ray flux and the unfavorable location of Fermi-GBM. Here we answer the following question: if GW150914 and GW150914-GBM were associated, how many LIGO-Virgo binary BH mergers would Fermi-GBM have to follow up to detect a second source? To answer this question, we perform simulated observations of binary BH mergers with LIGO-Virgo and adopt different scenarios for gamma-ray emission from the literature. We calculate the ratio of simulated binary BH mergers detected by LIGO-Virgo to the number of gamma-ray counterpart detections by Fermi-GBM, the BBH-to-GRB ratio. A large majority of the models considered here predict a BBH-to-GRB ratio in the range of 5-20, but for optimistic cases it can be as low as 2, while for pessimistic assumptions it can be as high as 700. Hence, we expect that the third observing run, with its high rate of binary BH detections and assuming the absence of a joint detection, will provide strong constraints on the presented models.
The Fermi Gamma-ray Burst Monitor (GBM) is currently the most prolific detector of gamma-ray bursts (GRBs). Recently the detection rate of short GRBs (SGRBs) has been dramatically increased through ...the use of ground-based searches that analyze GBM continuous time-tagged event (CTTE) data. Here, we examine the efficiency of a method developed to search CTTE data for sub-threshold transient events in temporal coincidence with LIGO/Virgo compact binary coalescence triggers. This targeted search operates by coherently combining data from all 14 GBM detectors by taking into account the complex spatial and energy dependent response of each detector. We use the method to examine a sample of SGRBs that were independently detected by the Burst Alert Telescope on board the Neil Gehrels Swift Observatory, but which were too intrinsically weak or viewed with unfavorable instrument geometry to initiate an onboard trigger of GBM. We find that the search can successfully recover a majority of the BAT detected sample in the CTTE data. We show that the targeted search of CTTE data will be crucial in increasing the GBM sensitivity, and hence the gamma-ray horizon, to weak events such as GRB 170817A. We also examine the properties of the GBM signal possibly associated with the LIGO detection of GW150914 and show that it is consistent with the observed properties of other sub-threshold SGRBs in our sample. We find that the targeted search is capable of recovering true astrophysical signals as weak as the signal associated with GW150914 in the untriggered data.
Abstract
The recent discovery of a kilonova from the long-duration gamma-ray burst (GRB) GRB 211211A challenges classification schemes based on temporal information alone. Gamma-ray properties of GRB ...211211A reveal an extreme event, which stands out among both short and long GRBs. We find very short variations (few milliseconds) in the lightcurve of GRB 211211A and estimate ∼1000 for the Lorentz factor of the outflow. We discuss the relevance of the short variations in identifying similar long GRBs resulting from compact mergers. Our findings indicate that in future gravitational-wave follow-up campaigns, some long-duration GRBs should be treated as possible strong gravitational-wave counterparts.
In light of the joint multimessenger detection of a binary neutron star merger as the gamma-ray burst GRB 170817A and in gravitational waves as GW170817, we reanalyze the Fermi Gamma-ray Burst ...Monitor data of one of the closest short gamma-ray bursts (SGRBs): GRB 150101B. We find that this burst is composed of a short hard spike followed by a comparatively long soft tail. This apparent two-component nature is phenomenologically similar to that of GRB 170817A. While GRB 170817A was distinct from the previously known population of SGRBs in terms of its prompt intrinsic energetics, GRB 150101B is not. Despite these differences, GRB 150101B can be modeled as a more on-axis version of GRB 170817A. Identifying a similar signature in two of the closest SGRBs suggests that the soft tail is common, but generally undetectable in more distant events. If so, it will be possible to identify nearby SGRBs from the prompt gamma-ray emission alone, aiding the search for kilonovae.
We describe a multivariate classifier for candidate events in a templated search for gravitational-wave (GW) inspiral signals from neutron-star–black-hole (NS-BH) binaries, in data from ground-based ...detectors where sensitivity is limited by non-Gaussian noise transients. The standard signal-to-noise ratio (SNR) and chi-squared test for inspiral searches use only properties of a single matched filter at the time of an event; instead, we propose a classifier using features derived from a bank of inspiral templates around the time of each event, and also from a search using approximate sine-Gaussian templates. The classifier thus extracts additional information from strain data to discriminate inspiral signals from noise transients. We evaluate a random forest classifier on a set of single-detector events obtained from realistic simulated advanced LIGO data, using simulated NS-BH signals added to the data. The new classifier detects a factor of 1.5–2 more signals at low false positive rates as compared to the standard “reweighted SNR” statistic, and does not require the chi-squared test to be computed. Conversely, if only the SNR and chi-squared values of single-detector events are available, random forest classification performs nearly identically to the reweighted SNR.
ABSTRACT
The European Space Agency is studying two large-class missions bound to operate in the decade of the 30s, and aiming at investigating the most energetic and violent phenomena in the ...Universe. Athena is poised to study the physical conditions of baryons locked in large-scale structures from the epoch of their formation, as well as to yield an accurate census of accreting supermassive black holes down to the epoch of reionization; LISA will extend the hunt for Gravitational Wave (GW) events to the hitherto unexplored mHz regime. We discuss in this paper the science that their concurrent operation could yield, and present possible Athena observational strategies. We focus on Supermassive (M$\lesssim 10^7\, \rm {M_\odot }$) Black Hole Mergers (SMBHMs), potentially accessible to Athena up to z ∼ 2. The simultaneous measurement of their electromagnetic (EM) and GW signals may enable unique experiments in the domains of astrophysics, fundamental physics, and cosmography, such as the magnetohydrodynamics of fluid flows in a rapidly variable space–time, the formation of coronae and jets in Active Galactic Nuclei, and the measurement of the speed of GW, among others. Key to achieve these breakthrough results will be the LISA capability of locating a SMBHM event with an error box comparable to, or better than the field-of-view of the Athena Wide Field Imager ($\simeq 0.4\,$ deg2) and Athena capability to slew fast to detect the source during the inspiral phase and the post-merger phase. Together, the two observatories will open in principle the exciting possibility of truly concurrent EM and GW studies of the SMBHMs
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