An official website of the United States government
Abstract We present a study aimed at quantifying the detectability of radio counterparts of binary neutron star (BNS) mergers with total masses ≲3M⊙, which may form neutron star remnants. We focus on mergers localized by gravitational-wave (GW) observations to sky areas ≲10 deg2, a precision that greatly facilitates optical counterpart identification and enables radio discovery even without detections at other wavelengths. Widely separated GW detectors are essential for building samples of well-localized BNS mergers accessible to radio telescopes, with minimum yearly detection rates (assuming the smallest values of the BNS local merger rate) ranging from a few with current GW detectors to hundreds with next-generation GW instruments. Current GW networks limit well-localized detections toz ≲ 0.2, while next-generation GW detectors extend the reach toz ≲ 0.8, encompassing the median redshift of short gamma-ray bursts (GRBs). With next-generation radio arrays operating at several tens of GHz and providing an order of magnitude improvement in sensitivity compared to the most sensitive ones available today, short GRB-like jet afterglows can be detected for a large fraction of the considered BNS mergers. At lower radio frequencies, detections with current radio interferometric arrays are feasible, though subject to synchrotron self-absorption effects. The enhanced sensitivity and survey speed of future radio interferometers operating at a few GHz, combined with the higher detection rate of well-localized BNSs enabled by next-generation GW observatories, are key to probing disk-wind and dynamical ejecta afterglows, as well as remnant diversity.
more »
« less
This content will become publicly available on June 3, 2027
Chasing Gamma-Ray Signals from Binary Neutron Star Coalescences with the Cherenkov Telescope Array: Prospects and Observing Strategies
Abstract The detection of gravitational waves (GWs) from a binary neutron star (BNS) merger by Advanced LIGO and Advanced Virgo (GW170817), together with its electromagnetic counterpart, the short gamma-ray burst GRB 170817A, heralded the birth of multimessenger astronomy. The detection of TeV emission from GRBs motivates follow-up observations with the Cherenkov Telescope Array Observatory (CTAO), which is ideal for detecting such signals due to its unprecedented sensitivity, rapid response, and wide-field survey capabilities. The aim of this work is to evaluate GeV–TeV GW follow-up strategies for CTAO using a multistep simulation pipeline and to estimate the expected rate of joint GW–GRB detections during observing run O5. Using a simulated sample of BNS systems with corresponding GW detections, gamma-ray emission is simulated through phenomenological prescriptions based on the observed population of short GRBs, including off-axis jet scenarios. CTAO observations are simulated to account for instrument response, sky tiling strategies, integration times, and varying observing conditions. Strategies with variable and constant integration times are investigated. We find that, via an optimized follow-up strategy, about 5% of simulated GW-associated short GRBs produce GeV–TeV radiation detectable by CTAO. Detectability is strongly influenced by the jet opening angle and viewing angle, suggesting that even rough estimates of the viewing angle in GW alerts could enhance targeting. This framework motivates future follow-ups of GW-detectable events, including neutron star–black hole mergers, and further supports the development of advanced strategies incorporating galaxy distributions and synergies with future detectors such as the Einstein Telescope.
more »
« less
- PAR ID:
- 10700085
- Author(s) / Creator(s):
- ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; more »
- Publisher / Repository:
- IOP Science
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 1004
- Issue:
- 1
- ISSN:
- 0004-637X
- Page Range / eLocation ID:
- 46
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract The multimessenger detection of GW170817 showed that binary neutron star (BNS) mergers are progenitors of (at least some) short gamma-ray bursts (GRBs), and that short GRB jets (and their afterglows) can have structures (and observational properties) more complex than predicted by the standard top-hat jet scenario. Indeed, the emission from the structured jet launched in GW170817 peaked in the radio band (centimeter wavelengths) at ≈100 days since merger—a timescale much longer than the typical time span of radio follow-up observations of short GRBs. Moreover, radio searches for a potential late-time radio flare from the fast tail of the neutron-rich debris that powered the kilonova associated with GW170817 (AT 2017gfo) have extended to even longer timescales (years after the merger). In light of this, here we present the results of an observational campaign targeting a sample of seven, years-old GRBs in the Swift/BAT sample with no redshift measurements and no promptly identified X-ray counterpart. Our goal is to assess whether this sample of short GRBs could harbor nearby BNS mergers, searching for the late-time radio emission expected from their ejecta. We found one radio candidate counterpart for one of the GRBs in our sample, GRB 111126A, though an origin related to emission from star formation or from an active galactic nucleus in its host galaxy cannot be excluded without further observations.more » « less
-
Abstract With GW170817 being the only multimessenger gravitational-wave (GW) event with an associated kilonova detected so far, there exists a pressing need for realistic estimation of the GW localization uncertainties and rates, as well as optimization of available telescope time to enable the detection of new kilonovae. We simulate GW events assuming a data-driven distribution of binary parameters for the LIGO/Virgo/KAGRA fourth and fifth observing runs (O4 and O5). We map the binary neutron star (BNS) and neutron star–black hole (NSBH) properties to the kilonova optical light curves. We use the simulated population of kilonovae to generate follow-up observing plans, with the primary goal of optimizing detection with the Gravitational Wave Multi-Messenger Astronomy DECam Survey. We explore the dependence of kilonova detectability on the mass, distance, inclination, and spin of the binaries. Assuming that no BNS was detected during O4 until the end of 2024, we present updated GW BNS (NSBH) merger detection rates. We expect to detect BNS (NSBH) kilonovae with DECam at a per-year rate of 0–2.0 (0) in O4 and 2.0–19 (0–1.0) in O5. We expect the majority of BNS detections and also those accompanied by a detectable kilonova to produce a hypermassive NS remnant, with a significant fraction of the remaining BNSs promptly collapsing to a BH. We release GW simulations and depths required to detect kilonovae based on our predictions to support the astronomical community in their multimessenger follow-up campaigns and analyses.more » « less
-
One of the most surprising gamma-ray burst (GRB) features discovered with theSwiftX-ray telescope (XRT) is a plateau phase in the early X-ray afterglow light curves. These plateaus are observed in the majority of long GRBs, while their incidence in short GRBs (SGRBs) is still uncertain due to their fainter X-ray afterglow luminosity with respect to long GRBs. An accurate estimate of the fraction of SGRBs with plateaus is of utmost relevance given the implications that the plateau may have for our understanding of the jet structure and possibly of the nature of the binary neutron star (BNS) merger remnant. This work presents the results of an extensive data analysis of the largest and most up-to-date sample of SGRBs observed with the XRT, and for which the redshift has been measured. We find a plateau incidence of 18–37% in SGRBs, which is a significantly lower fraction than that measured in long GRBs (> 50%). Although still debated, the plateau phase could be explained as energy injection from the spin-down power of a newly born magnetized neutron star (NS; magnetar). We show that this scenario can nicely reproduce the observed short GRB (SGRBs) plateaus, while at the same time providing a natural explanation for the different plateau fractions between short and long GRBs. In particular, our findings may imply that only a minority of BNS mergers generating SGRBs leave behind a sufficiently stable or long-lived NS to form a plateau. From the probability distribution of the BNS remnant mass, a fraction 18–37% of short GRB plateaus implies a maximum NS mass in the range ∼2.3 − 2.35 M⊙.more » « less
-
Abstract The Wide-Field Infrared Transient Explorer (WINTER) is a new 1 deg 2 seeing-limited time-domain survey instrument designed for dedicated near-infrared follow-up of kilonovae from binary neutron star (BNS) and neutron star–black hole mergers. WINTER will observe in the near-infrared Y , J , and short- H bands (0.9–1.7 μ m, to J AB = 21 mag) on a dedicated 1 m telescope at Palomar Observatory. To date, most prompt kilonova follow-up has been in optical wavelengths; however, near-infrared emission fades more slowly and depends less on geometry and viewing angle than optical emission. We present an end-to-end simulation of a follow-up campaign during the fourth observing run (O4) of the LIGO, Virgo, and KAGRA interferometers, including simulating 625 BNS mergers, their detection in gravitational waves, low-latency and full parameter estimation skymaps, and a suite of kilonova lightcurves from two different model grids. We predict up to five new kilonovae independently discovered by WINTER during O4, given a realistic BNS merger rate. Using a larger grid of kilonova parameters, we find that kilonova emission is ≈2 times longer lived and red kilonovae are detected ≈1.5 times further in the infrared than in the optical. For 90% localization areas smaller than 150 (450) deg 2 , WINTER will be sensitive to more than 10% of the kilonova model grid out to 350 (200) Mpc. We develop a generalized toolkit to create an optimal BNS follow-up strategy with any electromagnetic telescope and present WINTER’s observing strategy with this framework. This toolkit, all simulated gravitational-wave events, and skymaps are made available for use by the community.more » « less
