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Extreme stripped-envelope supernovae (SESNe), including Type Ic superluminous supernovae (SLSNe), broad-line Type Ic SNe (SNe Ic-BL), and fast blue optical transients (FBOTs), are widely believed to harbor a newborn fast-spinning highly-magnetized neutron star (``magnetar''), which can lose its rotational energy via spin-down processes to accelerate and heat the ejecta. The progenitor(s) of these magnetar-driven SESNe, and the origin of considerable angular momentum (AM) in the cores of massive stars to finally produce such fast-spinning magnetars upon core-collapse are still under debate. Popular proposed scenarios in the literature cannot simultaneously explain their event rate density, SN and magnetar parameters, and the observed metallicity. Here, we perform a detailed binary evolution simulation that demonstrates that tidal spin-up helium stars with efficient AM transport mechanism in close binaries can form fast-spinning magnetars at the end of stars' life to naturally reproduce the universal energy-mass correlation of these magnetar-driven SESNe. Our models are consistent with the event rate densities, host environments, ejecta masses, and energetics of these different kinds of magnetar-driven SESNe, supporting that the isolated common-envelope formation channel could be a major common origin of magnetar-driven SESNe. The remnant compact binary systems of magnetar-driven SESNe are progenitors of some galactic systems and gravitational-wave transients., Comment: Main text (17 pages, 5 Figures) and Supplementary Information (18 pages, 6 Figures, 2 tables)

The LIGO, Virgo, and KAGRA (LVK) collaboration has announced 90 coalescing binary black holes (BBHs) with $p_{\rm astro} > 50\%$ to date, however, the origin of their formation channels is still an open scientific question. Given various properties of BBHs (BH component masses and individual spins) inferred using the default priors by the LVK, independent groups have been trying to explain the formation of the BBHs with different formation channels. Of all formation scenarios, the chemically homogeneous evolution (CHE) channel has stood out with distinguishing features, namely, nearly-equal component masses and preferentially high individual spins aligned with the orbital angular momentum. We perform Bayesian inference on the BBH events officially reported in GWTC-3 with astrophysically-predicted priors representing different formation channels of the isolated binary evolution (CEE: common-envelope evolution channel; CHE; SMT: stable mass transfer). Given assumed models, we report strong evidence for GW190517\_055101 being most likely to have formed through the CHE channel. Assuming the BBH events in the subsample are all formed through one of the isolated binary evolution channels, we obtain the lower limits on the local merger rate density of these channels at $11.45 ~\mathrm{Gpc^{-3}~yr^{-1}}$ (CEE), $0.18 ~\mathrm{Gpc^{-3}~yr^{-1}}$ (CHE), and $0.63 ~\mathrm{Gpc^{-3}~yr^{-1}}$ (SMT) at $90\%$ credible level., 13 pages, 4 figures, 1 table

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 real signals and 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 $\alpha = 4.8^{+4.5}_{-2.8}$ plus a high-mass Gaussian component peaking at $\sim33^{+14}_{-9}\,M_\odot$. The NS mass spectrum could be shaped as a near flat distribution between $\sim1.0-2.1\,M_\odot$. 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 $\sim2.5\,M_\odot$ 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., Comment: 14 pages, 5 figures, 3 tables, accepted for publication in ApJ

After the successful detection of a gravitational-wave (GW) signal and its associated electromagnetic (EM) counterparts from GW170817, neutron star--black hole (NSBH) mergers have been highly expected to be the next type of multi-messenger source. However, despite the detection of several of NSBH merger candidates during the GW third observation run, no confirmed EM counterparts from these sources have been identified. The most plausible explanation is that these NSBH merger candidates were plunging events mainly because the primary BHs had near-zero projected aligned-spins based on GW observations. In view that NSs can be easily tidally disrupted by BHs with high projected aligned-spins, we study an evolution channel to form NSBH binaries with fast-spinning BHs, the properties of BH mass and spin, and their associated tidal disruption probability. We find that if the NSs are born firstly, the companion helium stars would be tidally spun up efficiently, and would thus finally form fast-spinning BHs. If BHs do not receive significant natal kicks at birth, these NSBH binaries that can merge within the Hubble time would have BHs with the projected aligned-spins $\chi_{z}\gtrsim0.8$ and, hence, can certainly allow tidal disruption to happen. Even if significant BH kicks are considered for a small fraction of NSBH binaries, the projected aligned-spins of BHs are $\chi_z\gtrsim0.2$. These systems can still be disrupted events unless the NSs are very massive. Thus, NS-first-born NSBH mergers would be promising multi-messenger sources. We discuss various potential EM counterparts associated with these systems and their detectability in the upcoming fourth observation run., Comment: Minor changes to match the final version in ApJ

Here we collect three unique bursts, GRBs\,060614, 211211A and 211227A, all characterized by a long-duration main emission (ME) phase and a rebrightening extended emission (EE) phase, to study their observed properties and the potential origin as neutron star-black hole (NSBH) mergers. NS-first-born (BH-first-born) NSBH mergers tend to contain fast-spinning (non-spinning) BHs that more easily (hardly) allow tidal disruption to happen with (without) forming electromagnetic signals. We find that NS-first-born NSBH mergers can well interpret the origins of these three GRBs, supported by that: (1) Their X-ray MEs and EEs show unambiguous fall-back accretion signatures, decreasing as $\propto{t}^{-5/3}$, which might account for their long duration. The EEs can result from the fall-back accretion of $r$-process heating materials, predicted to occur after NSBH mergers. (2) The beaming-corrected local event rate density for this type of merger-origin long-duration GRBs is $\mathcal{R}_0\sim2.4^{+2.3}_{-1.3}\,{\rm{Gpc}}^{-3}\,{\rm{yr}}^{-1}$, consistent with that of NS-first-born NSBH mergers. (3) Our detailed analysis on the EE, afterglow and kilonova of the recently high-impact event GRB\,211211A reveals it could be a merger between a $\sim1.23^{+0.06}_{-0.07}\,M_\odot$ NS and a $\sim8.21^{+0.77}_{-0.75}\,M_\odot$ BH with an aligned-spin of $\chi_{\rm{BH}}\sim0.62^{+0.06}_{-0.07}$, supporting an NS-first-born NSBH formation channel. Long-duration burst with rebrightening fall-back accretion signature after ME, and bright kilonova might be commonly observed features for on-axis NSBHs. We estimate the multimessenger detection rate between gravitational waves, GRBs and kilonovae from NSBH mergers in O4 (O5) is $\sim0.1\,{\rm{yr}}^{-1}$ ($\sim1\,{\rm{yr}}^{-1}$)., Comment: 15 pages, 5 figures, 2 tables, accepted by ApJL

We fit the multi-band lightcurves of 40 fast blue optical transients (FBOTs) with the magnetar engine model. The mass of the FBOT ejecta, the initial spin period and polar magnetic field of the FBOT magnetars are respectively constrained to $M_{\rm{ej}}=0.18^{+0.52}_{-0.13}\,M_\odot$, $P_{\rm{i}}=9.4^{+8.1}_{-3.9}\,{\rm{ms}}$, and $B_{\rm p}=7^{+16}_{-5}\times10^{14}\,{\rm{G}}$. The wide distribution of the value of $B_{\rm p}$ spreads the parameter ranges of the magnetars from superluminous supernovae (SLSNe) to broad-line Type Ic supernovae (SNe Ic-BL; some are observed to be associated with long-duration gamma-ray bursts), which are also suggested to be driven by magnetars. Combining FBOTs with the other transients, we find a strong universal anti-correlation as $P_{\rm{i}}\propto{M_{\rm{ej}}^{-0.45}}$, indicating them could share a common origin. To be specific, it is suspected that all of these transients originate from collapse of extreme-stripped stars in close binary systems, but with different progenitor masses. As a result, FBOTs distinct themselves by their small ejecta masses with an upper limit of ${\sim}1\,M_\odot$, which leads to an observational separation in the rise time of the lightcurves $\sim12\,{\rm d}$. In addition, the FBOTs together with SLSNe can be separated from SNe Ic-BL by an empirical line in the $M_{\rm peak}-t_{\rm rise}$ plane corresponding to an energy requirement of a mass of $^{56}$Ni of $\sim0.3M_{\rm ej}$, where $M_{\rm peak}$ is the peak absolute magnitude of the transients and $t_{\rm rise}$ is the rise time., 15 pages, 5 figures, 2 tables, accepted by ApJL

White dwarfs (WDs) embedded in gaseous disks of active galactic nucleus (AGNs) can rapidly accrete materials from the disks and grow in mass to reach or even exceed the Chandrasekhar limit. Binary WD (BWD) mergers are also believed to occur in AGN accretion disks. We study observational signatures from these events. We suggest that mass-accreting WDs and BWD mergers in AGN disks can lead to thermonuclear explosions that drive an ejecta shock breakout from the disk surface and power a slow-rising, relatively dim Type Ia supernova (SN). Such SNe Ia may be always outshone by the emission of the AGN disk around the supermassive black hole (BH) with a mass of $M_{\rm SMBH}\gtrsim 10^8\,M_\odot$. Besides, accretion-induced collapses (AICs) of WDs in AGN disks may occur sometimes, which may form highly-magnetized millisecond neutron stars (NSs). The subsequent spin-down process of this nascent magnetar can deposit its rotational energy into the disk materials, resulting in a magnetar-driven shock breakout and a luminous magnetar-powered transient. We show that such an AIC event could power a rapidly evolving and luminous transient for a magnetic field of $B\sim10^{15}\,{\rm G}$. The rising time and peak luminosity of the transient, powered by a magnetar with $B\sim10^{14}\,{\rm G}$, are predicted to have similar properties with those of superluminous supernovae. AIC events taking place in the inner parts of the disk around a relatively less massive supermassive BHs ($M_{\rm SMBH}\lesssim10^8\,M_\odot$) are more likely to power the transients that are much brighter than the AGN disk emission and hence easily to be identified., Comment: 13 pages, 3 figures, ApJL, 2021, 914, L19. We have changed the title. The original title is "Electromagnetic Signatures from Thermonuclear Explosions and Accretion-Induced Collapses of White Dwarfs Embedded in AGN disks"

In the first work of this series, we adopt a GW170817-like, viewing-angle-dependent kilonova model and the standard afterglow model with the lightcurve distribution based on the properties of cosmological short gamma-ray bursts afterglows to simulate the luminosity functions and color evolution of both kilonovae and optical afterglow emissions from binary neutron star (BNS) mergers. {We find that $\sim10\%$ afterglows are brighter than the associated kilonovae at the peak time, most of which are on-axis or nearly-on-axis. These kilonovae would be significantly polluted by the associated afterglow emission. Only at large viewing angles with $\sin\theta_{\rm v}\gtrsim 0.20$, the EM signals of most BNS mergers would be kilonova-dominated and some off-axis afterglows may emerge at $\sim5-10$\,day after the mergers.} At brightness dimmer than $\sim23-24$\,mag, according to their luminosity functions, the number of afterglows is much larger than that of kilonovae. Since the search depth of the present survey projects is $, Comment: 18 pages, 8 figures, 1 table, accepted by ApJ

We analyse the tidal disruption probability of potential neutron star--black hole (NSBH) merger gravitational wave (GW) events, including GW190426_152155, GW190814, GW200105_162426 and GW200115_042309, detected during the third observing run of the LIGO/Virgo Collaboration, and the detectability of kilonova emission in connection with these events. The posterior distributions of GW190814 and GW200105_162426 show that they must be plunging events and hence no kilonova signal is expected from these events. With the stiffest NS equation of state allowed by the constraint of GW170817 taken into account, the probability that GW190426_152155 and GW200115_042309 can make tidal disruption is $\sim24\%$ and $\sim3\%$, respectively. However, the predicted kilonova brightness is too faint to be detected for present follow-up search campaigns, which explains the lack of electromagnetic (EM) counterpart detection after triggers of these GW events. Based on the best constrained population synthesis simulation results, we find that disrupted events account for only $\lesssim20\%$ of cosmological NSBH mergers since most of the primary BHs could have low spins. The associated kilonovae for those disrupted events are still difficult to be discovered by LSST after GW triggers in the future, because of their low brightness and larger distances. For future GW-triggered multi-messenger observations, potential short-duration gamma-ray bursts and afterglows are more probable EM counterparts of NSBH GW events., Comment: 13 pages, 6 figures, 3 tables, accepted for publication in ApJ

Mergers of double neutron stars (DNSs) could lead to the formation of a long-lived massive remnant NS, which has been previously suggested to explain the AT 2017gfo kilonova emission in the famous GW170817 event. For an NS-affected kilonova, it is expected that a non-thermal emission component can be contributed by a pulsar wind nebula (PWN), which results from the interaction of the wind from the remnant NS with the preceding merger ejecta. Then, the discovery of such a non-thermal PWN emission can provide an evidence for the existence of the remnant NS. Similar to GRB 170817A, GRB 160821B is also one of the nearest short gamma-ray bursts (SGRBs). A candidate kilonova is widely believed to appear in the ultraviolet-optical-infrared afterglows of GRB 160821B. Here, by modeling the afterglow light curves and spectra of GRB 160821B, we find that the invoking of a non-thermal PWN emission can indeed be well consistent with the observational data. This may indicate that the formation of a stable massive NS could be not rare in the DNS merger events and, thus, the equation of state of the post-merger NSs should be stiff enough., Comment: 7 pages, 2 figures

In this paper, we present a numerical method to study the predicted lightcurves as a function of viewing angle. We extrapolate the fitting formulae for the mass and velocity of tidal dynamical ejecta across a wide range of mass ratio validated with 66 simulations and use them in the calculations of the kilonova lightcurves. The calculated peak luminosity of a BH-NS merger kilonova is typically about a few times $10^{41}\ {\rm erg\ s^{-1}}$, which is always $\lesssim4.5\times10^{41}\ {\rm erg\ s^{-1}}$. This corresponds to the AB absolute magnitudes fainter than $\sim -15\ {\rm mag}$ in optical and $\sim -16\ {\rm mag}$ in infrared. Since the projected photosphere area of the dynamical ejecta is much larger than that of the disk wind outflows, the dynamical ejecta usually contribute to the majority of the kilonova emission from BH-NS mergers. The fitted blackbody temperature and the shape of the observed multi-band lightcurves are insensitive to the line of sight. The peak time of the observed multi-band lightcurves, affected by the light propagation effect, is related to the relative motion direction between the dynamical ejecta and the observer. The observed luminosity varies with the projected photosphere area determined by the viewing angles. However, the predicted peak luminosity only varies by a factor of $\sim (2 - 3)$ (or by $\sim1\ {\rm mag}$) for different viewing angles. When the short-duration gamma-ray burst afterglow is taken into account, for an on-axis geometry, the kilonova emission is usually outshone by the afterglow emission and can be only observed in the redder bands, especially in the $K$-band at late times. Compared with GW170817/AT2017gfo, the BH-NS merger kilonovae are optically dim but possibly infrared bright. At the same epoch after the merger, the blackbody fitting temperature of the BH-NS merger kilonovae is lower than that of GW170817/AT2017gfo., Comment: 44 pages, 19 figures, 3 tables, accepted for publication in ApJ

The Breakthrough Starshot project aims to send centimeter-sized, gram-scale "StarChip" probes to Alpha Centauri at a speed of $\sim0.2c$. On the other hand, Zhang \& Li recently proposed that trans-relativistic cameras may be sent to any direction to study astronomical objects and test special relativity. To conduct such "relativistic astronomy", one needs to solve the motion of the probe in flight. We solve the motion of the probe (including the moving direction and the velocity) by comparing the positions of three or more point sources observed in the Earth rest frame and in the probe's comoving frame. When the positions of enough point sources are taken into account, the motion of the probe can be solved with an error which is even smaller than the diffraction limit of the transrelativistic camera. After solving the motion, when the measurement of the position of an additional point source is introduced, one can use the data to test the light aberration effect in special relativity. The upper limit of the photon mass can be placed from the deviation of aberration to slightly lower than the energy of the photon, e.g. $\sim 1 \rm {eV}$., 12 pages, 2 figures, 3 tables, accepted for publication in ApJ

We present detailed simulations of black hole-neutron star (BH-NS) mergers kilonova and gamma-ray burst (GRB) afterglow and kilonova luminosity function, and discuss the detectability of electromagnetic (EM) counterpart in connection with gravitational wave (GW) detections, GW-triggered target-of-opportunity observations, and time-domain blind searches. The predicted absolute magnitude of the BH-NS kilonovae at $0.5\,{\rm days}$ after the merger falls in $[-10,-15.5]$. The simulated luminosity function contains the potential viewing-angle distribution information of the anisotropic kilonova emission. We simulate the GW detection rates, detectable distances and signal duration, for the future networks of 2nd/2.5th/3rd-generation GW detectors. BH-NSs tend to produce brighter kilonovae and afterglows if the BH has a higher aligned-spin, and a less massive NS with a stiffer EoS. The detectability of kilonova is especially sensitive to the BH spin. If BHs typically have low spins, the BH-NS EM counterparts are hard to discover. For the 2nd generation GW detector networks, a limiting magnitude of $m_{\rm limit}\sim23-24\,{\rm mag}$ is required to detect the kilonovae even if BH high spin is assumed. Thus, a plausible explanation for the lack of BH-NS associated kilonova detection during LIGO/Virgo O3 is that either there is no EM counterpart (plunging events), or the current follow-ups are too shallow. These observations still have the chance to detect the on-axis jet afterglow associated with an sGRB or an orphan afterglow. Follow-up observations can detect possible associated sGRB afterglows, from which kilonova signatures may be studied. For time-domain observations, a high-cadence search in redder filters is recommended to detect more BH-NS associated kilonovae and afterglows., Accepted for Publication in ApJ, 36 pages, 17 figures, 6 tables

Both long-duration gamma-ray bursts (LGRBs) from the core collapse of massive stars and short-duration GRBs (SGRBs) from mergers of a binary neutron star or a neutron star–black hole are expected to occur in the accretion disk of active galactic nuclei (AGNs). We show that GRB jets embedded in the migration traps of AGN disks are promised to be choked by the dense disk material. Efficient shock acceleration of cosmic rays at the reverse shock is expected, and high-energy neutrinos would be produced. We find that these sources can effectively produce detectable TeV–PeV neutrinos through pγ interactions. From a choked LGRB jet with isotropic equivalent energy of 1053 erg at 100 Mpc, one expects ∼2(7) neutrino events detectable by IceCube (IceCube-Gen2). The contribution from choked LGRBs to the observed diffuse neutrino background depends on the unknown local event rate density of these GRBs in AGN disks. For example, if the local event rate density of choked LGRBs in an AGN disk is ∼5% that of low-luminosity GRBs (∼10 Gpc−3 yr−1), the neutrinos from these events would contribute to ∼10% of the observed diffuse neutrino background. Choked SGRBs in AGN disks are potential sources for future joint electromagnetic, neutrino, and gravitational wave multimessenger observations.

When the magnetosphere of a magnetar is perturbed by crustal deformation, an electric field $E_\parallel$ parallel to the magnetic field line would appear via Alvf��n waves in the charge starvation region. The electron-positron pair bunches will be generated via two-stream instability in the magnetosphere, and these pairs will undergo charge separation in the $E_\parallel$ and in the meantime emit coherent curvature radiation. Following the approach of Yang & Zhang (2018), we find that the superposed curvature radiation becomes narrower due to charge separation, with the width of spectrum depending on the separation between the electron and positron clumps. This mechanism can interpret the narrow spectra of FRBs, in particular, the spectrum of Galactic FRB 200428 recently detected in association with a hard X-ray burst from the Galactic magnetar SGR J1935+2154., 7 pages, 3 figures, accepted for publication in ApJL

By fitting the bolometric light curves of 31 super-luminous supernovae (SLSNe) with the magnetar engine model, we derive the ejecta masses and magnetar parameters for these SLSNe. The lower boundary of magnetic field strengths of SLSN magnetars can be set just around the critical field strength $B_{\rm c}$ of electron Landau quantization. In more details, SLSN magnetars can further be divided into two subclasses of magnetic fields of $\sim(1-5)B_{\rm c}$ and $\sim(5-10)B_{\rm c}$, respectively. It is revealed that these two subclasses of magnetars are just associated with the slow-evolving and fast-evolving bolometric light curves of SLSNe. In comparison, the magnetars harbored in gamma-ray bursts (GRBs) and associated hypernovae are usually inferred to have much higher magnetic fields with a lower boundary about $\sim10B_{\rm c}$. This robustly suggests that it is the magnetic fields that play the crucial role in distinguishing SLSNe from GRBs/hypernovae. The rotational energy of SLSN magnetars are found to be correlated with the masses of supernova ejecta, which provides a clue to explore the nature of their progenitors. Moreover, the distribution of ejecta masses of SLSNe is basically intermediate between those of normal core-collapse supernovae and hypernovae. This could indicate an intrinsic connection among these different stellar explosions., 18 pages, 10 figures, 3 tables, accepted for publication in ApJ

The "Breakthrough Starshot" program is planning to send transrelativistic probes to travel to nearby stellar systems within decades. Since the probe velocity is designed to be a good fraction of the light speed, \citet{zha18} recently proposed that these transrelativistic probes can be used to study astronomical objects and to test special relativity. In this work, we further propose some methods to test special relativity and constrain photon mass using the Doppler effect with the images and spectral features of astronomical objects as observed in the transrelativistic probes. We introduce more general theories to set up the framework of testing special relativity, including a parametric general Doppler effect and Doppler effect with massive photon. We find that by comparing the spectra of a certain astronomical object, one can test Lorentz invariance and constrain photon mass. Besides, using imaging and spectrograph capabilities of transrelativistic probes, one can test time dilation and constrain photon mass. For a transrelativistic probe with velocity $v\sim0.2c$, aperture $D\sim3.5~{\rm cm}$ and spectral resolution $R\sim100$ (or $1000$), we find that the probe velocity uncertainty can be constrained to $\sigma_v\sim0.01c$ (or $0.001c$), and the time dilation factor uncertainty can be constrained to $\Delta\gamma=|\hat\gamma-\gamma|\lesssim0.01$ (or $0.001$), where $\hat\gamma$ is the time dilation factor and $\gamma$ is the Lorentz factor. Meanwhile, the photon mass limit is set to $m_\gamma\lesssim10^{-33}~{\rm g}$, which is slightly lower than the energy of the optical photon., Comment: 8 pages, 3 figures, accepted for publication in ApJ