Gpc-3 Yr-1 Research Articles

Binary black hole mergers from Population III star clusters

Binary black holes (BBHs) that are born from the evolution of Population III (Pop. III) stars are one of the main high-redshift targets for next-generation ground-based gravitational-wave (GW) detectors. Their predicted initial mass function and lack of metals make them the ideal progenitors of black holes above the upper edge of the pair-instability mass gap, that is, with a mass higher than ~134 (241) M⊙ for stars that become (or do not become) chemically homogeneous during their evolution. We investigate the effects of cluster dynamics on the mass function of BBHs that are born from Pop. III stars by considering the main uncertainties on the mass function of Pop. III stars, the orbital properties of the binary systems, the star cluster mass, and the disruption time. In our dynamical models, at least ~5% and up to 100% BBH mergers in Pop. III star clusters have a primary mass m1 above the upper edge of the pair-instability mass gap. In contrast, only ≲3% isolated BBH mergers have a primary mass above the gap, unless their progenitors evolved as chemically homogeneous stars. The lack of systems with a primary and/or secondary mass inside the gap defines a zone of avoidance with sharp boundaries in the plane of the primary mass-mass ratio. Finally, we estimate the merger rate density of BBHs. In the most optimistic case, we find a maximum of ℛ ~ 200 Gpc-3 yr-1 at ɀ ~ 15 for BBHs that formed via dynamical capture. For comparison, the merger rate density of isolated Pop. III BBHs is ℛ ≤ 10 Gpc−3 yr−1 for the same model of Pop. III star formation history.

GW230529_181500: a potential primordial binary black hole merger in the mass gap

During the fourth observing run of the LIGO-Virgo-KAGRA detector network, the LIGO Livingston observatory detected a coalescing compact binary, GW230529_181500, with component masses of 2.5–4.5 M ⊙ and 1.2–2.0 M ⊙ at the 90% credible level. The gravitational-wave data alone is insufficient to determine whether the components are neutron stars or black holes. In this paper, we propose that GW230529_181500 originated from the merger of two primordial black holes (PBHs). We estimate a merger rate of 5.0+47.0 -4.9 Gpc-3 yr-1 for compact binary coalescences with properties similar to GW230529_181500. Assuming the source is a PBH-PBH merger, GW230529_181500-like events lead to approximately 1.7+36.2 -1.5 × 10-3 of the dark matter in the form of PBHs. The required abundance of PBHs to explain this event is consistent with existing upper limits derived from microlensing, cosmic microwave background observations and the null detection of gravitational-wave background by LIGO-Virgo-KAGRA.

First all-flavor search for transient neutrino emission using 3-years of IceCube DeepCore data

Since the discovery of a flux of high-energy astrophysical neutrinos, searches for their origins have focused primarily at TeV-PeV energies. Compared to sub-TeV searches, high-energy searches benefit from an increase in the neutrino cross section, improved angular resolution on the neutrino direction, and a reduced background from atmospheric neutrinos and muons. However, the focus on high energy does not preclude the existence of sub-TeV neutrino emission where IceCube retains sensitivity. Here we present the first all-flavor search from IceCube for transient emission of low-energy neutrinos, focusing on the energy region of 5.6-100 GeV using three years of data obtained with the IceCube-DeepCore detector. We find no evidence of transient neutrino emission in the data, thus leading to a constraint on the volumetric rate of astrophysical transient sources in the range of ∼ 705-2301 Gpc-3 yr-1 for sources following a subphotospheric energy spectrum with a mean energy of 100 GeV and a bolometric energy of 1052 erg.

First Release of High-Redshift Superluminous Supernovae from the Subaru HIgh- Z SUpernova CAmpaign (SHIZUCA). I. Photometric Properties

We report our first discoveries of high-redshift supernovae from the Subaru HIgh-Z sUpernova CAmpaign (SHIZUCA), the transient survey using Subaru/Hyper Suprime-Cam. We report the discovery of three supernovae at the spectroscopically-confirmed redshifts of 2.399 (HSC16adga), 1.965 (HSC17auzg), and 1.851 (HSC17dbpf), and two supernova candidates with the host-galaxy photometric redshifts of 3.2 (HSC16apuo) and 4.2 (HSC17dsid), respectively. In this paper, we present their photometric properties and the spectroscopic properties of the confirmed high-redshift supernovae are presented in the accompanying paper (Curtin et al. 2019). The supernovae with the confirmed redshifts of z ~ 2 have the rest ultraviolet peak magnitudes close to -21 mag and they are likely superluminous supernovae. The discovery of three supernovae at z ~ 2 roughly corresponds to the approximate event rate of ~ 900 +/- 520 Gpc-3 yr-1 with Poisson error, which is consistent with the total superluminous supernova rate estimated by extrapolating the local rate based on the cosmic star-formation history. Adding unconfirmed superluminous supernova candidates would increase the event rate. Our superluminous supernova candidates at the redshifts of around 3 and 4 indicate the approximate superluminous supernova rates of ~ 400 +/- 400 Gpc-3 yr-1 (z ~ 3) and ~ 500 +/- 500 Gpc-3 yr-1 (z ~ 4) with Poisson errors. Our initial results demonstrate the outstanding capability of Hyper Suprime-Cam to discover high-redshift supernovae.

Intrinsic properties of a complete sample ofHETE-2 gamma-ray bursts

Aims: Taking advantage of the forthcoming Catalog of the HETE-2 mission, the aim of this paper is to evaluate the main properties of HETE-2 GRBs - the E_peak, the T_90 and the E_iso - in their source frames and to derive their unbiased distribution. Methods: We first construct a complete sample containing all the bursts localized by the WXM on-board HETE-2, which are selected with a uniform criterion and whose observed parameters can be constrained. We then derive the intrinsic E_peak, T_90 and E_iso distributions using their redshift when it is available, or their pseudo-redshift otherwise. We finally compute the number of GRB (N_Vmax) within the visibility volume (V_max) of each GRB, in order to derive a weight for each detected burst accounting both for the detection significance and the star formation history of the universe. Results: The unbiased distributions obtained clearly show the predominence of X-ray flashes (XRFs) in the global GRB population. We also derive the rate of local GRBs: R0^H2 > 11 Gpc-3 yr-1, which is intermediate between the local rate obtained by considering only the high-luminosity bursts (~1 Gpc-3 yr-1) and that obtained by including the low-luminosity bursts (>200 Gpc-3 yr-1).

On the Rates of Gamma-Ray Bursts and Type Ib/c Supernovae

We measure the local rates of low-luminosity gamma-ray bursts (LL GRBs; i.e., L 1049 ergs s-1) and high-luminosity gamma-ray bursts (HL GRBs). The values are in the range 0 = 100-1800 Gpc-3 yr-1 and 0 = 100-550 Gpc-3 yr-1, respectively, and their ratios to Type Ibc supernovae (SNe Ibc) are ~1%-9% and 0.4%-3%, respectively. These data may suggest the existence of two physically distinct classes of GRBs in which LL GRBs are (intrinsically) more frequent events than HL GRBs. However, with the present data, we cannot exclude the possibility of a single population of GRBs that gives rise to both an isotropic low-luminous emission (LL GRBs: detectable only in nearby GRBs) and to a highly collimated high luminous emission (HL GRBs: detectable preferentially at high z). We also compute the rate of SNe Ibc characterized by broad-lined spectra (hypernovae [HNe]) and find it to be about 1.5 × 10-4 yr-1 per 1010 LB, ☉ (i.e., less than 10% of SNe Ibc occurring in spiral galaxies). This result implies that the ratio of HL GRBs to HNe is smaller than 1, possibly in the range of 0.04-0.3. We have used the ratio between HNe and LL GRBs to constrain their beaming factor to f ~ 10 or less.

The Local Rate and the Progenitor Lifetimes of Short‐Hard Gamma‐Ray Bursts: Synthesis and Predictions for the Laser Interferometer Gravitational‐Wave Observatory

The recent discovery of the first four afterglows of short-hard gamma-ray bursts (SHBs) suggests that they typically result from long-lived progenitor systems. The most popular progenitor model invokes the merger of either double neutron star (DNS) binaries or neutron star-black hole (NS-BH) systems. Such events are strong sources of gravitational waves (GWs) and might be detected by ground-based GW observatories. In this work we combine the census of SHB observations with refined theoretical analysis to perform a critical evaluation of the compact binary model. We then explore the implications for GW detection of these events. Beginning from the measured star formation rate through cosmic time, we consider what intrinsic luminosity and lifetime distributions can reproduce the known SHB redshifts and luminosities as well as the peak flux distribution of the large BATSE SHB sample. We find the following: (1) The typical progenitor lifetime is long. Assuming lognormal lifetime distribution, the typical lifetime is >4 (1) Gyr (2 σ [3 σ] c.l.). If the lifetime distribution is a power law with index η, then η > -0.5 (-1) (2 σ [3 σ] c.l.). This result is difficult to reconcile with the properties of the observed Galactic DNS population, suggesting that if SHBs do result from DNS mergers, then the observed Galactic binaries do not represent the cosmic one. (2) We find that the local rate of SHBs is larger than 10 Gpc-3 yr-1 and may be higher by several orders of magnitude, significantly above previous estimates. (3) Assuming that SHBs do result from compact binaries, our predictions for the LIGO and VIRGO event rates are encouraging: the chance for detection by current facilities is not negligible, while a coincident detection of GW and electromagnetic radiation from an SHB is guaranteed for next-generation observatories.

Constraining the Structure of Gamma‐Ray Burst Jets through the logN–logSDistribution

A general formalism is developed for calculating the luminosity function and the expected number N of observed gamma-ray bursts (GRBs) above a peak photon flux S for an arbitrary GRB jet structure. This formalism directly provides the true GRB rate for any jet model, instead of first calculating the GRB rate assuming isotropic emission and then introducing a "correction factor" to account for effects of the GRB jet structure, as was done in previous works. We apply it to the uniform jet (UJ) and universal structured jet (USJ) models for the structure of GRB jets and perform fits to the observed log N- log S distribution from the GUSBAD catalog, which contains 2204 BATSE bursts. We allow for a scatter in the peak luminosity L for a given jet half-opening angle θj (viewing angle θobs) in the UJ (USJ) model, which is implied by observations. A core angle θc and an outer edge at θmax are introduced for the structured jet, and a finite range of opening angles θmin ≤ θj ≤ θmax is assumed for the uniform jets. The efficiency for producing γ-rays, γ, and the energy per solid angle in the jet, , are allowed to vary with θj (θobs) in the UJ (USJ) model, γ ∝ θ-b and ∝ θ-a. We find that a single power-law luminosity function provides a good fit to the data. Such a luminosity function arises naturally in the USJ model, while in the UJ model it implies a power-law probability distribution for θj, P(θj) ∝ θ. The value of q cannot be directly determined from the fit to the observed log N- log S distribution, and an additional assumption on the value of a or b is required. Alternatively, an independent estimate of the true GRB rate would enable one to determine a, b, and q. The implied values of θc (or θmin) and θmax are close to the current observational limits. The true GRB rate for the USJ model is found to be RGRB(z = 0) = 0.86 Gpc-3 yr-1 (1 σ), while for the UJ model it is higher by a factor f(q), which strongly depends on the unknown value of q.

Jets in Gamma‐Ray Bursts: Tests and Predictions for the Structured Jet Model

The two leading interpretations of achromatic breaks that are observed in the light curves of GRBs afterglow are (1) the manifestation of the edge of a jet, which has a roughly uniform energy profile and a sharp edge, and (2) a line-of-sight effect in jets with a variable energy profile. The first scenario requires the inner engine to produce a jet with a different opening angle each explosion, while the latter requires a standard engine. The physical structure of the jet is a crucial factor in understanding GRB progenitors, and therefore discriminating the two jet scenarios is particularly relevant. In the structured jet case, specific predictions can be made for the distribution of observed break angles θbr, while that distribution is arbitrary in the first scenario. We derive the theoretical distribution for the structured jet model. Specifically, we predict the most common angle to be about 0.12 rad, in rough agreement with the sample. If this agreement holds as the sample size increases, it would strengthen the case for the standard jet hypothesis. We show that a prediction of this model is that the average viewing angle is an increasing function of the survey sensitivity and in particular that a mission such as Swift will find the typical viewing angle to be about 0.3 rad. The local event rate predicted by this model is RGRB(z = 0) ~ 0.5 Gpc-3 yr-1.

Luminosity Function of Gamma‐Ray Bursts Derived without Benefit of Redshifts

We show that the Euclidean value of for gamma-ray bursts (GRBs) selected on a timescale of 1024 ms is correlated with spectral hardness. The value of ranges from ~0.42 for soft bursts to ~0.26 for the hardest bursts. Given that the Euclidean value of for cosmological objects in a well-defined sample is a distance indicator, the hard bursts must reside at larger redshifts and therefore be more luminous than the soft bursts. The resulting luminosity-hardness correlation cannot be shown explicitly as a result of the small number of observed GRB redshifts at the present time. Based on the -hardness correlation, we derive the luminosity function of GRBs without using any redshifts, but we have to make an assumption how the comoving GRB rate varies with redshift. We present luminosity functions for three models of the GRB rate as a function of redshift, based on star formation rates. The peak luminosity functions are approximately broken power laws with an isotropic-equivalent break luminosity of ~1051.5 ergs s-1 in the 50-300 keV range and total local rate densities of ~0.5 Gpc-3 yr-1. Predicted GRB counts as a function of flux and redshift are presented. Based on the GRB luminosity function, we carry out a simulation to produce the luminosity-hardness correlation, which shows that the hardest GRBs are ~20 times more luminous than the softest ones.

Luminosities and Space Densities of Gamma-Ray Bursts

We use a homogeneous sample of gamma-ray bursts (GRBs) extracted from 5.9 yr of BATSE DISCLA data and a variety of assumed broken power-law luminosity functions to derive GRB luminosities and space densities. Luminosity functions that are narrow or exhibit no density evolution produce expected redshift distributions that are incompatible with the observation of a GRB redshift of 3.4. For q0 = 0.1 and density evolution rising to 10 at z = 1, we find for a variety of slopes of the luminosity function values of the local space density around 0.18 Gpc-3 yr-1 with a range of only 40%. Characteristic 50-300 keV peak luminosities exhibit a range of a factor of 6 around 6 ? 1051 ergs s-1, corresponding to a characteristic total luminosity of 1.2 ? 1053 ergs in the 10-1000 keV band. For q0 = 0.5, densities are higher and luminosities lower, both by a factor of 2.5. The local emissivity of GRBs is 1.0 ? 1052 ergs Gpc-3 yr-1 in the 10-1000 keV band.