Binary neutron star mergers with evolving merger rates or yields are strongly preferred over constant scenarios to explain Milky Way r-process enrichment, with Bayes factors exceeding 10^20, yet remain in tension with short gamma-ray burst observations.
Implications of low neutron star merger rates for gamma-ray bursts, r-process production and Galactic double neutron stars
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abstract
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 \rprocess elements. The initial merger rate from this single event in the first two observing runs of the LIGO-Virgo observatory network, $110$--$3840\,\mathrm{Gpc}^{-3}\,\mathrm{yr}^{-1}$, 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 the past few gravitational wave (GW) catalog updates. Analyzing GW data from the latest catalog GWTC-4, we find a total BNS merger rate of $28$--$300\,\mathrm{Gpc}^{-3}\,\mathrm{yr}^{-1}$ (consistent with the most recently published values from LIGO-Virgo-KAGRA) consisting of $53^{+176}_{-49}\,\mathrm{Gpc}^{-3}\mathrm{yr}^{-1}$ in GW170817-like $\sim(1.3,1.3)\,M_\odot$ BNSs (90\% credibility). In light of this updated GW rate, 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, the r-process rate is a factor of 0.9--4.1 higher, 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.
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UNVERDICTED 4representative citing papers
Simulations show double neutron star mergers peak 80-250 million years after star formation across metallicities, with 15% quick mergers and over 20% delayed over a billion years.
TeV-selected PWNe and unidentified sources yield beaming fractions of 0.1-0.3 across radio, gamma-ray, and X-ray bands, with survey-to-survey differences explained by selection biases or older pulsars and reproducible via time-dependent opening angles.
Latest GW neutron star merger rates are consistent with short GRBs being produced by BNS mergers if jets are wide or rates low, with NSBH mergers subdominant.
citing papers explorer
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Binary Neutron Star Merger Evolution and r-Process Enrichment in the Milky Way Disk
Binary neutron star mergers with evolving merger rates or yields are strongly preferred over constant scenarios to explain Milky Way r-process enrichment, with Bayes factors exceeding 10^20, yet remain in tension with short gamma-ray burst observations.
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Double Neutron Star Delay Times Across Cosmic Metallicities: The Role of Helium Star Progenitors
Simulations show double neutron star mergers peak 80-250 million years after star formation across metallicities, with 15% quick mergers and over 20% delayed over a billion years.
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Constraining the Pulsar Beaming Fraction with TeV-Selected Galactic Pulsar Wind Nebulae and unidentified TeV Sources
TeV-selected PWNe and unidentified sources yield beaming fractions of 0.1-0.3 across radio, gamma-ray, and X-ray bands, with survey-to-survey differences explained by selection biases or older pulsars and reproducible via time-dependent opening angles.
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Wide Jets or Low Rates: Reconciling Short GRB and Gravitational-Wave Neutron Star Merger Rates
Latest GW neutron star merger rates are consistent with short GRBs being produced by BNS mergers if jets are wide or rates low, with NSBH mergers subdominant.