Search

GRB 070707 was the first short gamma-ray burst (GRB) detected by INTEGRAL and the optical afterglow was attributed to the prolonged activity of the central engine in the literature. Here, we reanalyse the afterglow data and examine the physical origin of the emission. The redshift of this burst is uncertain and in this work we assume an association with a galaxy at the redshift of 0.2394 for a chance coincidence probability P cc = 0.046. It is found that the sole forward shock radiation cannot well reproduce the data, while including a kilonova component similar to AT2017gfo is very helpful in reproducing the multiwavelength afterglow emission. The properties of the candidate host galaxy have been studied in detail; its high metallicity, low star formation rate, and old stellar population age are similar to the host galaxies of other GRBs associated with kilonovae. In view of the facts that a kilonova signal was identified in the first short GRB with detected optical emission (i.e. GRB 050709) and the first short GRB with gravitational wave detection (i.e. GRB 170817A), and now the identification of a kilonova signature in the first INTEGRAL short GRB strongly indicates that kilonovae are rather common among the neutron star merger events. [ABSTRACT FROM AUTHOR]

Long gamma-ray bursts (GRBs) are typically associated with massive star core collapse, while the short GRBs are associated with compact binary mergers. However, recent evidence indicates that some peculiar long-duration bursts may correspond to compact binary mergers origins. In this paper, we use the data of the Fermi Gamma-ray Burst Monitor to search for peculiar long-duration bursts which may be from compact binary mergers based on outlier events in the |$E_{p,z}\!-\!E_{\gamma ,\rm iso}$| relation. We obtained 10 outlier events by systematically analysing bursts with |$T_{90}\gt 4.2 \rm \ s$| from 2008 August to 2021 July. In order to determine whether these outlier events were from compact binary mergers, we analysed their properties, including spectral lag, hardness ratio, and energy-hardness parameter. Based on the distributions of T 90 − HR and T 90 − Ep , we calculated the probability of outlier events belonging to the short GRBs. Our analysis indicates that GRB 120304B is likely to arise from the merger of a neutron star and a massive white dwarf. GRB 150210A is likely to arise from massive star core collapse. The other eight GRBs are fuzzy bursts that have both long and short GRBs properties. Additionally, we find that outlier samples have relatively high Ep and low fluences. [ABSTRACT FROM AUTHOR]

Observations of the long-lived X-ray plateau in short gamma-ray burst (SGRB) afterglow suggest that a portion of binary neutron star mergers would leave behind a rapidly spinning, strongly magnetized neutron star (millisecond magnetar). The new-born magnetar may undergo large deformation due to magnetic distortion or unstable oscillation, which would emit the extended gravitational wave (GW) associated with the SGRB X-ray plateau. In this work, we focus on the spin-down luminosity evolution of magnetar by considering the spin energy loss due to the GW and magnetic dipole radiation, and systematically analyse the SGRB light curves of our magnetar sample. The results show that GW emission signatures have existed in the spin-down stage of GRB 090426 and GRB 150424A. We also present constraints on the ellipticity of the new-born magnetar as ε < 1.58 × 10−3(B /1015 G)(P /1 ms). The magnetar can lose significant spin energy via GW radiation if the ellipticity ε ≥ 10−3 and magnetic field strength B ∼ 1015 G. In addition, we derive the evolution of GW strain for magnetars through their spin-down processes. This result shows that the GW signals from these magnetars may be detectable for the Einstein Telescope (ET). For a rapidly spinning magnetar (P ∼ 1 ms), the detection horizons for aLIGO O3, aLIGO O5, and ET detectors are ∼60, ∼210, and ∼900 Mpc, respectively. The detection of the GW emission from new-born millisecond magnetar may reveal the interior composition of magnetar in the near future. [ABSTRACT FROM AUTHOR]

The measurements of the bulk properties of most isolated neutron stars (INSs) are challenging tasks. Tang et al. have developed a new method, based on the equation of state (EoS) of neutron star (NS) material constrained by the observational data, to infer the gravitational masses of a few INSs whose gravitational redshifts are available. However, in that work, the authors only considered the constraints on the EoS from nuclear experiments/theories and the gravitational wave data of GW170817; the possible phase transition has not been taken into account. In this work, we adopt three EoS models (including the one incorporates a first-order strong phase transition) that are constrained by the latest multimessenger NS data, including in particular the recent massâ€"radius measurements of two NSs by Neutron Star Interior Composition Explorer, to update the estimation of the gravitational masses of RBS 1223, RX J0720.4-3125, and RX J1856.5-3754. In comparison to our previous approach, the new constraints are tighter, and the gravitational masses are larger by about 0.1 M ⊙. All the inferred gravitational masses are within the range of the NS masses measured in other ways. We have also calculated the radius, tidal-deformability, and moment of inertia of these sources. The inclusion of the first-order strong phase transition has little influence on modifying the results. [ABSTRACT FROM AUTHOR]

The post-merger gravitational-wave (GW) radiation of the remnant formed in the binary neutron star (BNS) coalescence has not been directly measured yet. We show in this work that the properties of the BNS involved in GW170817, additionally constrained by PSR J0030+0451, the lower limit on the maximum gravitational mass of nonrotating neutron star (NS), and some nuclear data, are in favor of strong post-merger GW radiation. This conclusion applies to the mergers of Galactic BNS systems as well. Significant post-merger GW radiation is also preferred to improve the consistency between the maximum gravitational mass of the nonrotating NS inferred from GW170817/GRB170817A/AT2017gfo and the latest mass measurements of pulsars. The prominent post-merger gravitational radiation of GW170817-like events are expected to be detectable by advanced LIGO/Virgo detectors in the next decade and then shed valuable light on the properties of the matter in the extremely high density. [ABSTRACT FROM AUTHOR]

As revealed recently by the modeling of the multiwavelength data of the emission following GW170817/GRB 170817A, there was an off-axis energetic relativistic outflow component launched by this historic double neutron star merger event. In this work we use the results of this model to examine the energy extraction process of the central engine. We show that the magnetic process (i.e., the Blandford–Znajek mechanism) is favored, while the neutrino process usually requires an accretion disk that is too massive if the duration of the central engine activity Tact is comparable to the observed T90 of GRB 170817A. If Tact is less than ∼0.2 s, the two models are indistinguishable. We propose that the GRB observations are helpful to constrain the combined tidal parameter , and by adopting the accretion disk mass distribution estimated in the BZ mechanism, the 90% credible interval of for the progenitor of GW170817 is inferred as 309 − 954. [ABSTRACT FROM AUTHOR]