Multimessenger astronomy aims to utilize all accessible information from the universe: electromagnetic waves, particles (e.g., neutrinos), and gravitational waves. The discovery of ...GW170817/GRB170817A and the international follow-up observations showed the power of multimessenger astronomy in understanding cosmic phenomena. The best candidates for multimessenger astronomy are compact binary coalescences, gamma-ray bursts, or supernovae. In particular, binaries consisting of neutron stars or black holes are the most attractive candidates for standard sirens in the context of gravitational-wave astrophysics. The possibility of measuring a Hubble constant with compact binaries has drawn strong attention as an independent method from electromagnetic-wave observations. In addition to the 20–2000 Hz band available on Earth, multimessenger astronomy with gravitational-wave observations in lower frequencies below ~10 mHz would be fruitful for understanding the underlying properties and cosmological implications for Galactic binaries and massive black holes. The lowest gravitational-wave frequencies (µHz–nHz) would allow us to explore supermassive black hole mergers and the stochastic GW background from the early universe. In this review paper, we summarize recent progress of and prospects for multimessenger astronomy, focusing on compact binaries.
Performing N-body simulations, we examine the dynamics of black hole-black hole (BH-BH) (10 M... each) and neutron star-neutron star (NS-NS) (1.4 M... each) binaries formed in a cluster and its ...implications for gravitational wave detection. A significant fraction of compact binaries are ejected from a globular cluster after core collapse. Among the total number of ejected compact objects, 30 per cent of them are in binaries. Merging time-scales of ejected binaries, which depend on the cluster's velocity dispersion, are in some cases shorter than the age of the Universe. During the merging event, these dynamically formed compact mergers are expected to produce gravitational waves that can be detectable by the advanced ground-based interferometers. Based on our reference assumptions, merger rates of ejected BH-BH and NS-NS binaries per globular cluster are estimated to be 2.5 and 0.27 per Gyr, respectively. Assuming the spatial density of globular clusters to be 8.4 h3 clusters Mpc-3 and extrapolating the merger rate estimates to the horizon distance of the advanced Laser Interferometer Gravitational Wave Observatory-Virgo network, we expect the detection rates for BH-BH and NS-NS binaries with cluster origin to be 15 and 0.024 yr^sup -1^, respectively. We find out that some of the dynamically formed binaries are ejected with a large escape velocity. They can be responsible for short gamma-ray bursts whose locations are far from host galaxies. (ProQuest: ... denotes formulae/symbols omitted.)
Neutron stars in the galactic center Kim, Chunglee; Davies, Melvyn B.
Journal of the Korean Astronomical Society,
10/2018, Letnik:
51, Številka:
5
Journal Article
Odprti dostop
The Galactic Center is one of the most dense stellar environments in the Galaxy and is considered to be a plausible place to harbor many neutron stars. In this brief review, we summarize ...observational efforts in search of neutron stars within a few degrees about the Galactic Center. Up to 10% of Galactic neutron stars may reside in this central region and it is possible that more than a thousand neutron stars are located within only ~ 25′′ (≤ 1 pc) about the Galactic Center. Based on observations, we discuss prospects of detecting neutron stars in the Galactic Center via gravitational waves as well as electromagnetic waves.
Abstract
We investigate properties of black hole (BH) binaries formed in globular clusters via dynamical processes, using direct
N-body simulations. We pay attention to effects of BH mass function on ...the total mass and mass ratio distributions of BH binaries ejected from clusters. First, we consider BH populations with two different masses in order to learn basic differences from models with single-mass BHs only. Secondly, we consider continuous BH mass functions adapted from recent studies on massive star evolution in a low metallicity environment, where globular clusters are formed. In this work, we consider only binaries that are formed by three-body processes and ignore stellar evolution and primordial binaries for simplicity. Our results imply that most BH binary mergers take place after they get ejected from the cluster. Also, mass ratios of dynamically formed binaries should be close to 1 or likely to be less than 2:1. Since the binary formation efficiency is larger for higher-mass BHs, it is likely that a BH mass function sampled by gravitational-wave observations would be weighed towards higher masses than the mass function of single BHs for a dynamically formed population. Applying conservative assumptions regarding globular cluster populations such as small BH mass fraction and no primordial binaries, the merger rate of BH binaries originated from globular clusters is estimated to be at least 6.5 yr−1 Gpc−3. Actual rate can be up to more than several times of our conservative estimate.
We present the current estimates of the Galactic merger rate of double-neutron-star (DNS) systems. Using a statistical analysis method, we calculate the probability distribution function (PDF) of the ...rate estimates, which allows us to assign confidence intervals to the rate estimates. We calculate the Galactic DNS merger rate based on the three known systems B1913+16, B1534+12, and J0737-3039. The discovery of J0737-3039 increases the estimated DNS merger rate by a factor ∼6 than what is previously known. The most likely values of DNS merger rate lie in the range 3–190
Myr
−1 depending on different pulsar models. Motivated by a strong correlation between the peak rate estimates and a pulsar luminosity function, we calculate a
global probability distribution as a single representation of the parameter space covered by different pulsar population models. We compare the global PDF with the observed supernova Ib/c rate, which sets an upper limit on the DNS merger rate. Finally, we remark on implications of new discoveries such as of J1756-2251, the 4th DNS in the Galactic disk, and J1906+0746, a possible DNS system.
The KaVA and KVN pulsar project Dodson, Richard; Kim, Chunglee; Sohn, Bongwon ...
Publications of the Astronomical Society of Japan,
12/2014, Letnik:
66, Številka:
6
Journal Article
Recenzirano
Odprti dostop
Abstract
We present our work towards using the Korean VLBI (Very Long Baseline Interferometer) Network (KVN) and VLBI Exploration of Radio Astronomy (VERA) arrays combined into the KVN and VERA Array ...(KaVA) for observations of radio pulsars at high frequencies (≃ 22 GHz). Pulsar astronomy is generally focused at frequencies approximately 0.3 to several GHz and pulsars are usually discovered and monitored with large, single-dish, radio telescopes. For most pulsars, reduced radio flux is expected at high frequencies due to their steep spectrum, but there are exceptions where high frequency observations can be useful. Moreover, some pulsars are observable at high frequencies only, such as those close to the Galactic Center. The discoveries of a radio-bright magnetar and a few dozen extended Chandra sources within 15′ of the Galactic Center provide strong motivations to make use of the KaVA frequency band to search for pulsars in this region. Here, we describe the science targets and report progress made from the KVN test observations for known pulsars. We then discuss why KaVA pulsar observations are compelling.
The Double Pulsar (PSR J0737−3039) is the only neutron star–neutron star (NS–NS) binary in which both NSs have been detectable as radio pulsars. The Double Pulsar has been assumed to dominate the ...Galactic NS–NS binary merger rate
${\cal R}_{\rm g}$
among all known systems, solely based on the properties of the first-born, recycled pulsar (PSR J0737−3039A, or A) with an assumption for the beaming correction factor of 6. In this work, we carefully correct observational biases for the second-born, non-recycled pulsar (PSR J0737−0737B, or B) and estimate the contribution from the Double Pulsar on
${\cal R}_{\rm g}$
using constraints available from both A and B. Observational constraints from the B pulsar favour a small beaming correction factor for A (∼2), which is consistent with a bipolar model. Considering known NS–NS binaries with the best observational constraints, including both A and B, we obtain
${\cal R}_{\rm g}=21_{-14}^{+28}$
Myr−1 at 95 per cent confidence from our reference model. We expect the detection rate of gravitational waves from NS–NS inspirals for the advanced ground-based gravitational-wave detectors is to be
$8^{+10}_{-5}$
yr−1 at 95 per cent confidence. Within several years, gravitational-wave detections relevant to NS–NS inspirals will provide us useful information to improve pulsar population models.
PDF
