arXiv subjects

Tom Y. Wu

Publications and source records attributed to Tom Y. Wu.

2 recordsLinked to original sources

arXiv2026

Implications of low neutron star merger rates for gamma-ray bursts, r-process production and Galactic double neutron stars

The first multimessenger discovery of a binary neutron star (BNS) merger, GW170817, proved that such mergers can source short gamma-ray bursts (SGRBs) and produce r-process elements. The initial merger rate from this single event was found to be broadly consistent with the SGRB rate, the Milky Way (MW) r-process mass, and the Galactic population of double neutron star (DNS) systems that will merge in a Hubble time. However, only one additional BNS merger has been detected since, and the BNS merger rate has been consistently revised downwards with recent gravitational wave (GW) catalog updates. Analyzing GWTC-4, we find a total BNS merger rate of $28$--$300\,\mathrm{Gpc}^{-3}\,\mathrm{yr}^{-1}$ consisting of $53^{+176}_{-49}\,\mathrm{Gpc}^{-3}\mathrm{yr}^{-1}$ in GW170817-like $\sim(1.3,1.3)\,M_\odot$ BNSs (90\% credibility). We revisit the consistency of the BNS merger rate with SGRBs, r-process and Galactic DNSs. In all cases, there is an emerging tension with the BNS (and EM-bright neutron star--black hole, NSBH) merger rate. Comparing to a BNS merger rate of $100\,\mathrm{Gpc}^{-3}\mathrm{yr}^{-1}$, the cosmological SGRB rate is a factor of 3.6--18 higher (despite kilonova followup of SGRBs implying a significant fraction of SGRBs are of BNS origin), the r-process rate is a factor of 0.9--4.1 higher (even though we consider only r-process elements above the second peak), and the rate inferred from Galactic DNSs is a factor of 2.3--5.1 higher than the BNS rate. We discuss how various uncertainties in the inferred rates either alleviate or exacerbate this tension, which point to the various physical processes that can be constrained by such rate comparisons.

astro-ph.HE↗

arXiv2024

Are long gamma-ray bursts progenitors to merging binary black holes?

The distribution of delay times between the formation of binary black hole (BBH) progenitors and their gravitational-wave (GW) merger provides important clues about their unknown formation histories. When inferring the delay time distribution, it is typically assumed that BBH progenitor formation traces the star formation rate (SFR). In this work, we consider the rate of long gamma-ray bursts (LGRBs) instead of the SFR. LGRBs are thought to correspond to the formation of (possibly spinning) black holes, and may therefore be related to the BBH progenitor population. By comparing the redshift evolution of the LGRB rate as inferred by Ghirlanda & Salvaterra (2022) and the BBH merger rate inferred by LIGO-Virgo-KAGRA (LVK) observations, we find that the delay time distribution between LGRBs and BBH mergers is well-described by a power law with minimum delay time $10$ Myr and slope $α={-0.96}^{+0.64}_{-0.76}$ (90% credibility). This matches theoretical expectations for the BBH delay time distribution, which in turn lends support to the hypothesis that LGRBs trace BBH progenitor formation. However, comparing the absolute rates of these two populations, we find that at most $f = {4}^{+10}_{-2}\%$ of LGRBs may evolve into merging BBH. We also consider the possibility that LGRBs only produce BBH systems with large aligned spins (with effective inspiral spin $χ_\mathrm{eff} > 0.2$). In this case, we find $f = 0.3^{+1.0}_{-0.2}\%$ and the delay time distribution favors the steepest power-law slopes we consider ($α= -2$). We argue that asynchronous observations of LGRBs and GWs provide a powerful multimessenger probe of black hole lifecycles across cosmic history.

astro-ph.HE↗