Search

The milestone discovery of GW170817-GRB 170817A-AT 2017gfo has shown that gravitational waves (GWs) could be produced during the merger of a neutron star–neutron star/black hole and that in electromagnetic (EM) waves, a gamma-ray burst (GRB) and a kilonova (KN) are generated in sequence after the merger. Observationally, however, EM properties before the merger phase are still unclear. Here we report a peculiar precursor in a KN-associated long-duration GRB 211211A, providing evidence of the EM before the merger. This precursor lasts ∼0.2 s, and the waiting time between the precursor and the main burst is ∼1 s, comparable to that between GW170817 and GRB 170817A. The spectrum of the precursor could be well fit with a nonthermal cutoff power-law model instead of a blackbody. In particular, a ∼22 Hz quasiperiodic oscillation candidate (∼3 σ) is detected in the precursor. These temporal and spectral properties indicate that this precursor is probably produced by a catastrophic flare accompanied with magnetoelastic or crustal oscillations of a magnetar in a binary compact merger. The strong magnetic field of the magnetar can also account for the prolonged duration of GRB 211211A. However, it poses a challenge to reconcile the rather short lifetime of a magnetar with the rather long spiraling time of a binary neutron star system only by the GW radiation before the merger. [ABSTRACT FROM AUTHOR]

The formation of black hole–neutron star (BH–NS) or BH–BH systems may be accompanied by special supernova (SN) signals, due to the accretion feedback from the companion BH. The additional heating, which is mainly attributed to the Blandford–Payne mechanism, would disrupt the isotropic nature of the luminosity distribution on the surface of the SN ejecta, leading to the appearance of polarization. Here we develop a three-dimensional Monte Carlo polarization simulation code to conduct simulations for these special SNe. We find that the maximum polarization level of ∼2% occurs at the peak time of SN emission in the "close-binary" scenario, while in the "faraway-binary" case maximum polarization (i.e., ∼0.7%) is observed at a considerably later time than the peak of the SN. The magnitude of polarization is dependent on the degree of unevenness in the luminosity distribution and the angle between the line of sight and the equatorial direction. When considering the geometric distortion of SN ejecta at the same time, the magnitude of polarization may either increase (for a oblate ellipsoidal shape) or decrease (for a prolate ellipsoidal shape). The polarization signatures represent a promising auxiliary instrument to facilitate the identification of the companion-fed SNe. Moreover, comparing the event rate of these special SNe with the event rate density of LIGO-Virgo-detected BH–NS/BH systems could further help to distinguish the BH–NS/BH formation channel. [ABSTRACT FROM AUTHOR]

Primordial black holes (PBHs) has been considered to form a part of dark matter for a long time but the possibility has been poorly constrained over a wide mass range, including the stellar mass range (⁠|$1{-}100\ {\rm M}_{\odot }$|⁠). However, due to the discovery of merger events of black hole binaries by LIGO-Virgo gravitational wave observatories, the interest for PBHs in the stellar mass window has been aroused again. Fast radio bursts (FRBs) are bright radio transients with millisecond duration and very high all-sky occurrence rate. Lensing effect of these bursts has been proposed as one of the optimal probes for constraining the abundance of PBHs in the stellar mass range. In this paper, we first investigate constraints on the abundance of PBHs from the latest 593 FRB observations for both the monochromatic mass distribution and three other popular extended mass distributions related to different formation mechanisms of PBHs. It is found that constraints from currently public FRB observations are relatively weaker than those from existing gravitational wave detections. Furthermore, we forecast constraining power of future FRB observations on the abundance of PBHs with different mass distributions of PBHs and different redshift distributions of FRBs taken into account. Finally, We find that constraints of parameter space on extended mass distributions from ∼105 FRBs with |$\overline{\Delta t}\le 1 ~\rm ms$| would be comparable with what can be constrained from gravitational wave events. It is foreseen that upcoming complementary multimessenger observations will yield considerable constraints on the possibilities of PBHs in this intriguing mass window. [ABSTRACT FROM AUTHOR]

Over the course of the third observing run of the LIGOâ€"Virgoâ€"KAGRA Collaboration, several gravitational-wave (GW) neutron starâ€"black hole (NSBH) candidates have been announced. By assuming that these candidates are real signals with 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 âˆ' 2.8 + 4.5 plus a high-mass Gaussian component peaking at ∼ 33 âˆ' 9 + 14 M ⊙ . The NS mass spectrum could be shaped as a nearly flat distribution between ∼1.0 and 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 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 support 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. [ABSTRACT FROM AUTHOR]

The possibility that primordial black holes (PBHs) form some part of dark matter has been considered for a long time but poorly constrained over a wide mass range. Fast radio bursts (FRBs) are bright radio transients with millisecond duration. Their lensing effect has been proposed to be one of the cleanest probes for constraining the presence of PBHs in the stellar-mass window. In this paper, we first apply the normalized cross-correlation algorithm to search and identify candidates for lensed FRBs in the latest public FRB observations, i.e., 593 FRBs, which mainly consist of the first Canadian Hydrogen Intensity Mapping Experiment FRB catalog, and then derive constraints on the abundance of PBHs from the null search result of the lensing signature. For a monochromatic mass distribution, the fraction of dark matter made up of PBHs could be constrained to ≤87% for ≥500 M ⊙ at the 95% confidence level by assuming signal-to-noise ratios dependent on the flux ratio threshold for each FRB and that apparently one-off events are intrinsic single bursts. This result would be improved by a factor of 3 when a conventional constant flux ratio threshold is considered. Moreover, we derive constraints on PBHs with a log-normal mass function naturally predicted by some popular inflation models and often investigated with gravitational-wave detections. We find that, in this mass distribution scenario, the constraint from the current public FRB observations is relatively weaker than the one from gravitational-wave detections. It is foreseen that upcoming complementary multimessenger observations will yield considerable constraints on the possibilities of PBHs in this intriguing mass window. [ABSTRACT FROM AUTHOR]

Evidence for the central engine of gamma-ray bursts (GRBs) has been collected in the Neil Gehrels Swift data. For instance, some GRBs show an internal X-ray plateau followed by very steep decay, which is difficult interpret within the framework of a black hole (BH) central engine, but is consistent within a rapidly spinning magnetar engine picture. The very steep decay at the end of the plateau suggests a sudden cessation of the central engine, which is explained as the collapse of a supramassive magnetar into a BH when it spins down. Here we propose that some additional evidence, such as a second X-ray plateau feature, would show up if the fallback accretion could activate the newborn BH and sufficient energy could be transferred from the newborn BH to the GRB blast wave. With a systematic data analysis for all long GRBs, we find three candidates in the Swift sample, i.e., GRBs 070802, 090111, and 120213A, whose X-ray afterglow lightcurves contain two plateaus, with the first one being an internal plateau. We find that in a fairly loose and reasonable parameter space, the second X-ray plateau data for all 3 GRBs could be interpreted with our proposed model. Future observations are likely to discover similar events, which could offer more information on the properties of the magnetar, as well as the newborn BH. [ABSTRACT FROM AUTHOR]

The post-merger product of the first binary neutron star merger event detected in gravitational waves, GW170817, depends on neutron star equation of state (EoS) and is not well determined. We generally discuss the constraints one may pose on the maximum mass of a non-spinning neutron star, MTOV, based on the observations and some EoS-independent universal relations of rapidly spinning neutron stars. If the merger product is a black hole after a brief hypermassive neutron star (HMNS) phase, we derive at the 2σ (1σ) level. The cases for a massive neutron star (MNS), neither a supramassive neutron star (SMNS) nor even a stable neutron star (SNS) are also allowed by the data. We derive for the SMNS case and for the SNS case, at the 2σ (1σ) confidence level. In the MNS cases, we also discuss the constraints on the neutron star parameters (the dipolar magnetic field strength at the surface Bp and the ellipticity ϵ) that affect the spin down history, by considering different MNS survival times, e.g., 300 s, 1 day, and 155 days after the merger, as suggested by various observational arguments. We find that once an SMNS is formed, without violating the electromagnetic observational constraints, there always exist a set of () parameters that allow the SMNS to survive for 300 s, 1 day, 155 days, or even longer. [ABSTRACT FROM AUTHOR]

For non-spinning, charged (Reissner–Nordström) black holes, the particles with an opposite sign of charge with respect to that of the black hole will be pulled into the black hole by the extra electromagnetic force. Such a hole will be quickly neutralized so that there should not exist significantly charged, non-spinning black holes in the universe. The case of spinning, charged (Kerr–Newmann, KN) black holes is more complicated. For a given initial position and initial velocity of the particle, an oppositely charged particle does not always more easily fall into the black hole than a neutral particle. The possible existence of a magnetosphere further complicate the picture. One therefore cannot straightforwardly conclude that a charged spinning black hole will be neutralized. In this paper, we make the first step to investigate the neutralization of KN black holes without introducing a magnetosphere. We track the particle trajectories under the influence of the curved space–time and the electromagnetic field carried by the spinning, charged black hole. A statistical method is used to investigate the neutralization problem. We find a universal dependence of the falling probability into the black hole on the charge of the test particle, with the oppositely charged particles having a higher probability of falling. We therefore conclude that charged, spinning black holes without a magnetosphere should be quickly neutralized, consistent with people's intuition. The neutralization problem of KN black holes with a corotating force-free magnetosphere is subject to further studies. [ABSTRACT FROM AUTHOR]

The giant X-ray bump of GRB 121027A observed by Swift is different from the typical X-ray flares in gamma-ray bursts. The observed structural variability in the rise and decay phases of the bump has four components. Of these four components, only the data in the bump from about 5300 to about 6100 s is of good enough quality to be analysed using the stepwise filter correlation method. A $86^{+5.9}_{-9.4} \rm s$ periodic oscillation is postulated, which is confirmed by the Lomb–Scargle method. A jet precession model is proposed to account for this variability. [ABSTRACT FROM AUTHOR]

The continued observations of Sw J1644+57 in X-ray and radio bands accumulated a rich data set to study the relativistic jet launched in this tidal disruption event. The X-ray light curve of Sw J1644+57 from 5-30 days presents two kinds of quasi-periodic variations: a 200 s quasi-periodic oscillation (QPO) and a 2.7 day quasi-periodic variation. The latter has been interpreted by a precessing jet launched near the Bardeen-Petterson radius of a warped disk. Here we suggest that the ∼200 s QPO could be associated with a second, narrower jet sweeping the observer line-of-sight periodically, which is launched from a spinning black hole in the misaligned direction with respect to the black hole's angular momentum. In addition, we show that this two-component jet model can interpret the radio light curve of the event, especially the re-brightening feature starting ∼100 days after the trigger. From the data we infer that inner jet may have a Lorentz factor of Γj ∼ 5.5 and a kinetic energy of Ek, iso ∼ 3.0 × 1052 erg, while the outer jet may have a Lorentz factor of Γj ∼ 2.5 and a kinetic energy of Ek, iso ∼ 3.0 × 1053 erg. [ABSTRACT FROM AUTHOR]