Kilonova Emission from Black Hole–Neutron Star Mergers. II. Luminosity Function and Implications for Target-of-opportunity Observations of Gravitational-wave Triggers and Blind Searches

Zhu, Jinwei; Wu, Shichao; Yang, Yuan-Pei; Zhang, Bing; Yu, Yun-Wei; Li, Zhuo; Cao, Zhoujian; Liu, Liang-Duan; Huang, Yan; Zhang, Xing-Han

doi:10.3847/1538-4357/abfe5e

Cited by 41 publications

(42 citation statements)

References 269 publications

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“…We note that NSBH mergers may have a lower event rate density, that NSBH kilonovae may be dimmer than BNS kilonovae (e.g., Zhu et al 2020) and that most NSBH mergers in the universe are likely plunging events (e.g., Abbott et al 2021a;Zappa et al 2019;Drozda et al 2020;Zhu et al 2021c;Broekgaarden et al 2021). As a result, the detection rates of kilonova and afterglow emissions from NSBH mergers should be much lower than those from BNS mergers (Zhu et al 2021f). In the following calculations, we only consider kilonova and afterglow emissions from BNS mergers.…”

Section: Introductionmentioning

confidence: 98%

Kilonova and Optical Afterglow from Binary Neutron Star Mergers. II. Optimal Search Strategy for Serendipitous Observations and Target-of-opportunity Observations of Gravitational-wave Triggers

Zhu¹,

Wu²,

Yang³

et al. 2021

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In the second work of this series, we explore the optimal search strategy for serendipitous and gravitational-wave-triggered target-of-opportunity observations of kilonovae and optical short-duration gamma-ray burst (sGRB) afterglows from binary neutron star (BNS) mergers, assuming that cosmological kilonovae are AT2017gfo-like (but with viewing-angle dependence) and that the properties of afterglows are consistent with those of cosmological sGRB afterglows. A one-day cadence serendipitous search strategy with an exposure time of ∼ 30 s can always achieve an optimal search strategy of kilonovae and afterglows for various survey projects. We show that the optimal detection rates of the kilonova-dominated (afterglow-dominated) events are ∼ 0.2/0.5/0.8/20 yr −1 (∼ 500/300/600/3000 yr −1 ) for ZTF/Mephisto/WFST/LSST, respectively. A better search strategy for SiTian is to increase the exposure time. SiTian can find ∼ 5(6000) yr −1 kilonova-dominated (afterglow-dominated) events. We predict abundant off-axis orphan afterglows may be recorded in the survey database although not been identified. For target-of-opportunity observations, we simulate the maximum BNS gravitational-wave (GW) detection rates, which are ∼ 27/210/1800/2.0 × 10 5 yr −1 , in the networks of 2nd/2.5th/3rd(Voyager)/3rd(ET&CE)-generation GW detectors. In the upcoming 2nd-generation networks, follow-up observations with a limiting magnitude of m limit 22 − 23 mag can discover all EM signals from BNS GW events. Among these detected GW events, ∼ 60% events (∼ 16 yr −1 ) can detect clear kilonova signals, while afterglow-dominated events would account for the other ∼ 40% events (∼ 11 yr −1 ). In the 2.5th-and 3rd(Voyager)-generation era, the critical magnitudes for the detection of EM emissions from all BNS GW events would be ∼ 23.5 mag and ∼ 25 mag, respectively. Foreseeable optical survey projects cannot detect all EM signals of GW events detected during the ET&CE era.

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Section: Introductionmentioning

confidence: 98%

Kilonova and Optical Afterglow from Binary Neutron Star Mergers. II. Optimal Search Strategy for Serendipitous Observations and Target-of-opportunity Observations of Gravitational-wave Triggers

Zhu¹,

Wu²,

Yang³

et al. 2021

Preprint

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“…Besides, the possible additional energy injection from the remnant BH via fall-back accretion (Rosswog 2007) or the Blandford-Payne mechanism (Ma et al 2018), or from a long-lived NS through magnetic spindown (Yu et al 2013;Metzger & Piro 2014) may enhance the brightness of the kilonova. Because the BNS kilonova emission may display significant diversity and NSBH kilonovae will also contribute to the kilonova magnitude distribution (Zhu et al 2021f), it is expected that cosmological kilonova luminosity function should be more complicated than our simulation result. We also showed that the afterglows have a wider magnitude distribution compared with kilonovae.…”

Section: Discussionmentioning

confidence: 75%

“…Sun et al (2015) suggested the lognormal delay model is one of the favoured delay time model to explain the observations of sGRBs. Hereafter, we adopt the log-normal delay model as our merger delay model whose analytical fitting expression of f (z) is adopted as Equation (A8) of Zhu et al (2021f).…”

Section: Redshift Distributionmentioning

confidence: 99%

Kilonova and Optical Afterglow from Binary Neutron Star Mergers. I. Luminosity Function and Color Evolution

Zhu¹,

Yang²,

Zhang³

et al. 2021

Preprint

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In the first work of this series, we adopt an AT2017gfo-like viewing-angle-dependent kilonova model and the standard afterglow model with lightcurve distribution based on the cosmological short gammaray bursts afterglows to simulate the luminosity functions and color evolution of both kilonovae and optical afterglow emissions from binary neutron star mergers. Only a small fraction of (∼ 20%) on-axis afterglows are dimmer than the associated kilonovae at the kilonovae peak time. At a very large viewing angle, e.g., sin θ v 0.40, most kilonovae at the peak time would be much brighter than associated afterglows. Therefore, a large fractional of detectable kilonovae would be significantly polluted by associated afterglow emissions. We find that the maximum possible apparent magnitude for cosmological kilonovae is ∼ 27 − 28 mag. Afterglow emission has a wider luminosity function compared with kilonova emission. At brightness dimmer than ∼ 25 − 26 mag, according to their luminosity functions, the number of afterglows is much larger than that of kilonovae. Since the search depth of almost all the present and foreseeable survey projects is < 25 mag, the number of afterglow events detected via serendipitous observations would be much higher than that of kilonova events, consistent with the current observations. We find that it may be difficult to use the fading rate in a single band to directly identify kilonovae and afterglows among various fast-evolving transients by serendipitous surveys, especially if the observations have missed the peak time. However, the color evolution between optical and infrared bands can identify them, since their color evolution patterns are unique compared with those of other fast-evolving transients.

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“…This scenario would lead to a group of NSBH mergers with a unique spin distribution, which has not been discovered by present GW detections. Zhu et al (2021e) further found that the brightness of kilonova is strongly dependent on the spin magnitude of the BH in the NSBH mergers. The possible energy injection from BH-torus would also be affected by the primary BH spin (e.g., Ma et al 2018;Qi et al 2021).…”

Section: Implications For the Formation Channelmentioning

confidence: 88%

“…where P det is the probability that a NSBH event can be detected. χ eff and χ p have less influence on the detection probability of a NSBH event (e.g., Zhu et al 2021e) so that we ignore the effect of them on the detection probability. We then simulate P det (m 1 , m 2 ) based on the method introduced in Abbott et al (2021c).…”

Section: Hierarchical Population Modelmentioning

confidence: 99%

Population Properties of Gravitational-Wave Neutron Star--Black Hole Mergers

Zhu,

Wu,

Qin

et al. 2021

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Over the course of the third observing run of LIGO-Virgo-KAGRA Collaboration, several gravitational-wave (GW) neutron star-black hole (NSBH) candidates have been announced. By assuming these candidates are of astrophysical origins, we analyze the population properties of the mass and spin distributions for GW NSBH mergers. We find that the primary BH mass distribution of NSBH systems, whose shape is consistent with that inferred from the GW binary BH (BBH) primaries, can be well described as a power-law with an index of α = 4.8 +4.5 −2.8 plus a high-mass Gaussian component peaking at ∼ 33 +14 −9 M . The NS mass spectrum could be shaped as a near flat distribution between ∼ 1.0 − 2.1 M . The constrained NS maximum mass agrees with that inferred from NSs in our Galaxy. If GW190814 and GW200210 are NSBH mergers, the posterior results of the NS maximum mass would be always larger than ∼ 2.5 M and significantly deviate from that inferred in the Galactic NSs. The effective inspiral spin and effective precession spin of GW NSBH mergers are measured to potentially have near-zero distributions. The negligible spins for GW NSBH mergers imply that most events in the universe should be plunging events, which supports the standard isolated formation channel of NSBH binaries. More NSBH mergers to be discovered in the fourth observing run would help to more precisely model the population properties of cosmological NSBH mergers.

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Kilonova Emission from Black Hole–Neutron Star Mergers. II. Luminosity Function and Implications for Target-of-opportunity Observations of Gravitational-wave Triggers and Blind Searches

Cited by 41 publications

References 269 publications

Kilonova and Optical Afterglow from Binary Neutron Star Mergers. II. Optimal Search Strategy for Serendipitous Observations and Target-of-opportunity Observations of Gravitational-wave Triggers

Kilonova and Optical Afterglow from Binary Neutron Star Mergers. II. Optimal Search Strategy for Serendipitous Observations and Target-of-opportunity Observations of Gravitational-wave Triggers

Kilonova and Optical Afterglow from Binary Neutron Star Mergers. I. Luminosity Function and Color Evolution

Population Properties of Gravitational-Wave Neutron Star--Black Hole Mergers

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