摘要：
Neutron star mergers are believed to occur in accretion disks around supermassive black holes. Here we show that a putative jet launched from the merger of a binary neutron star (BNS) or a neutron star-black hole (NSBH) merger occurring at the migration trap in an active galactic nucleus (AGN) disk would be choked. The jet energy is deposited within the disk materials to power a hot cocoon. The cocoon is energetic enough to break out from the AGN disk and produce a bright X-ray shock breakout transient peaking at similar to 0.15 days after the merger. The peak luminosity is estimated as similar to 10(46) erg s(-1), which can be discovered by the Einstein Probe from z less than or similar to 0.5. Later on, the nonrelativistic ejecta launched from the merger would break out the disk, powering an X-ray/UV flare peaking at similar to 0.5 days after the merger. This second shock breakout signal may be detected by UV transient searches. The cocoon cooling emission and kilonova emission are outshone by the disk emission and are difficult to detect. Future joint observations of gravitational waves from BNS/NSBH mergers and associated two shock breakout signatures can provide strong support for the compact binary coalescence formation channel in AGN disks.
摘要：
A rapidly rotating and highly magnetized neutron star (NS) could be formed from explosive phenomena such as superluminous supernovae and gamma-ray bursts. This newborn NS can substantially influence the emission of these explosive transients through its spin-down. The spin-down evolution of the NS can sometimes be affected by fallback accretion, although it is usually regulated by the magnetic dipole radiation and gravitational wave radiation of the NS. Under appropriate conditions, the accreting material can be first ejected and subsequently recycled back, so that the accretion disk can remain in a quasi-steady state for a long time. Here we describe the interaction of the NS with such a propeller-recycling disk and their coevolution. Our result shows that the spin-down of the NS can be initially dominated by the propeller, which prevents the disk material from falling onto the NS until hundreds or thousands of seconds later. It is suggested that the abrupt fall of the disk material onto the NS could significantly suppress the magnetic dipole radiation and then convert the NS from a normal magnetar to a low-field magnetar. This evolution behavior of the newborn NS can help us understand the very different influence of the NS on the early GRB afterglows and the late supernova/kilonova emission.
关键词：
Radio bursts;Radio transient sources;Neutron stars;Magnetars;X-ray transient sources;Non-thermal radiation sources
摘要：
The nature of fast radio bursts (FRBs) is currently unknown. Repeating FRBs offer better observation opportunities than nonrepeating FRBs because their simultaneous multiwavelength counterparts might be identified. The magnetar flare model of FRBs is one of the most promising models that predict high-energy emission in addition to radio burst emission. To investigate such a possibility, we have searched for simultaneous and quasi-simultaneous short-term hard X-ray bursts in all Swift/BAT event mode data, which covered the periods when FRB detections were reported in the repeating FRB 121102, by making use of BAT's arcminute-level spatial resolution and wide field of view. We did not find any significant hard X-ray bursts that occurred simultaneously with those radio bursts. We also investigated potential short X-ray bursts that occurred quasi-simultaneously with those radio bursts (occurrence time differs in the range from hundreds of seconds to thousands of seconds) and concluded that even the best candidates are consistent with background fluctuations. Therefore, our investigation concluded that there were no hard X-ray bursts detectable with Swift/BAT that occurred simultaneously or quasi-simultaneously with those FRBs in the repeating FRB 121102.
作者机构：
[Yu, Yun-Wei] Cent China Normal Univ, Inst Astrophys, Wuhan 430079, Peoples R China.;[Yu, Yun-Wei] Cent China Normal Univ, Minist Educ, Key Lab Quark & Lepton Phys, Wuhan 430079, Peoples R China.;[Zou, Yuan-Chuan] Huazhong Univ Sci & Technol, Sch Phys, Wuhan 430074, Peoples R China.;[Dai, Zi-Gao] Nanjing Univ, Sch Astron & Space Sci, Nanjing 210093, Peoples R China.;[Yu, Wen-Fei] Chinese Acad Sci, Shanghai Astron Observ, Key Lab Res Galaxies & Cosmol, 80 Nandan Rd, Shanghai 200030, Peoples R China.
通讯机构：
[Yu, Yun-Wei] C;Cent China Normal Univ, Inst Astrophys, Wuhan 430079, Peoples R China.;Cent China Normal Univ, Minist Educ, Key Lab Quark & Lepton Phys, Wuhan 430079, Peoples R China.
关键词：
stars: magnetar;stars: neutron;radio continuum: general
摘要：
The association of FRB 200428 with an X-ray burst (XRB) from the Galactic magnetar SGR 1935+2154 offers important implications for the physical processes responsible for the fast radio burst (FRB) phenomena. By assuming that the XRB emission is produced in the magnetosphere, we investigate the possibility that the FRB emission is produced by shock-powered synchrotronmaser (SM), which is phenomenologically described with a number of free parameters. The observational constraints on the model parameters indicate that the model can in principle be consistent with the FRB 200428 observations, if the ejecta lunched by magnetar activities can have appropriate ingredients and structures and the shock processes occur on the line of sight. To be specific, a complete burst ejecta should consist of an ultra-relativistic and extremely highly collimated e(+/-) component and a sub-relativistic and wide-spreading baryonic component. The internal shocks producing the FRB emission arise from a collision between the e(+/-) ejecta and the remnant of a previous baryonic ejecta at the same direction. The parameter constraints depend on the uncertain spectrum and efficiency of the SM emission. While the spectrum is tentatively described by a spectral index of -2, we estimate the emission efficiency to be around 10(-4) by requiring that the synchrotron emission of the shocked material cannot be much brighter than the magnetosphere XRB emission.
作者机构：
[Dai, Z. G.; Wang, F. Y.; Wang, Y. Y.] Nanjing Univ, Sch Astron & Space Sci, Nanjing 210093, Peoples R China.;[Dai, Z. G.; Wang, F. Y.] Nanjing Univ, Minist Educ, Key Lab Modern Astron & Astrophys, Nanjing 210093, Peoples R China.;[Yang, Yuan-Pei] Yunnan Univ, South Western Inst Astron Res, Kunming, Yunnan, Peoples R China.;[Yu, Y. W.] Cent China Normal Univ, Inst Astrophys, Wuhan 430079, Peoples R China.;[Zuo, Z. Y.] Xi An Jiao Tong Univ, Sch Sci, Xian 710049, Peoples R China.
通讯机构：
[Wang, F. Y.] N;Nanjing Univ, Sch Astron & Space Sci, Nanjing 210093, Peoples R China.;Nanjing Univ, Minist Educ, Key Lab Modern Astron & Astrophys, Nanjing 210093, Peoples R China.
关键词：
Radio bursts;Gamma-ray bursts;Magnetars;Binary stars;Gravitational waves
作者机构：
[Yu, Yun-Wei] Cent China Normal Univ, Inst Astrophys, Wuhan 430079, Peoples R China.;[Yu, Yun-Wei] Cent China Normal Univ, Key Lab Quark & Lepton Phys, Minist Educ, Wuhan 430079, Peoples R China.
通讯机构：
[Yu, Yun-Wei] C;Cent China Normal Univ, Inst Astrophys, Wuhan 430079, Peoples R China.;Cent China Normal Univ, Key Lab Quark & Lepton Phys, Minist Educ, Wuhan 430079, Peoples R China.
作者机构：
[Tan, Wei-Wei] Hubei Univ Educ, Sch Phys & Mech Elect Engn, Wuhan 430205, Peoples R China.;[Tan, Wei-Wei] Hubei Univ Educ, Res Ctr Astron, Wuhan 430205, Peoples R China.;[Yu, Yun-Wei] Cent China Normal Univ, Inst Astrophys, Wuhan 430079, Peoples R China.
通讯机构：
[Yu, Yun-Wei] C;Cent China Normal Univ, Inst Astrophys, Wuhan 430079, Peoples R China.
关键词：
Gamma-ray bursts (629)
摘要：
The joint observation of GW170817 and GRB 170817A indicated that short gamma-ray bursts (SGRBs) can originate from binary neutron star mergers. Moreover, some SGRBs could be detected off axis, while the SGRB jets are highly structured. Then, by assuming a universal angular distribution of the jet emission for all SGRBs, we reproduce the flux and redshift distributions of the cosmological SGRBs detected by Swift and Fermi. For self-consistency, this angular distribution is simultaneously constrained by the luminosity and event rate of GRB 170817A. As a result, it is found that the universal jet structure of SGRBs could approximately have a two-Gaussian profile. Meanwhile, the intrinsic luminosity function (LF) of the on-axis emission of the jets can be simply described by a single power law with a low-luminosity exponential cutoff. The usually discovered broken-power-law apparent LF for relatively high luminosities can naturally result from the coupling of the intrinsic LF with the angular distribution of the jet emission, as the viewing angles to the SGRBs are arbitrarily distributed.
期刊：
Chinese Astronomy and Astrophysics,2019年43(2):178-198 ISSN：0275-1062
作者机构：
[Yu Yun-wei] College of Physical Science and Technology, Central China Normal University, Wuhan 430079
摘要：
The neutron star-neutron star and neutron star-black hole mergers may cause the intense radiation of high-frequency gravitational waves (GWs), they can also produce various electromagnetic emissions by ejecting materials outwards. Therefore, these merger events are the most important targets of current multi-messenger astronomical studies. The thermal transient radiation emitted from merger ejecta is called the kilonova or, more generally, the mergernova, which is powered by the radioactive decays of r-process elements, and the energy injection from the central merger product. This phenomenon was first predicted theoretically by Li and Paczynski in 1998, and confirmed by the optical-infrared observations of the GW170817 event in 2017. As a result, the kilonova/mergernova observation had played a crucial role in locating GW170817, identifying its astrophysical origin, and even constraining the nature of the merger product of this event. This paper briefly reviews the primary progress of kilonova/mergernova researches, including the initiative, improvement, and development of the model, the observational discoveries of candidates, and the optical electromagnetic counterpart of GW170817.
作者机构：
[Yu, Yun-Wei] Cent China Normal Univ, Inst Astrophys, Wuhan 430079, Hubei, Peoples R China.;Cent China Normal Univ, Key Lab Quark & Lepton Phys, Wuhan 430079, Hubei, Peoples R China.
通讯机构：
[Yu, Yun-Wei] C;Cent China Normal Univ, Inst Astrophys, Wuhan 430079, Hubei, Peoples R China.
关键词：
gamma ray bursts: general;gravitational waves
摘要：
During the in-spiral stage of a compact binary, a wind bubble could be blown into the interstellar meditun, if electromagnetic radiation due to the binary orbital motion is strong enough. Therefore, short-duration gamma-ray bursts (SGRBs) due to double neutron star mergers would in principle happen in a wind bubble environment, which can influence the propagation of the SGRB jet and consequent afterglow emission. By calculating the dynamics and synchrotron radiation of the jet-driven external shock, we reveal that an abrupt jump could appear in the afterglow light curves of SGRBs and the observational time of the jump is dependent on the viewing angle. This light curve jump provides an observational signature to constrain the radius of the wind bubble and thus the power of the electromagnetic radiation of the binary, by combining with gravitational wave detection.
作者：
Chen, A. M.*;Takata, J.;Yi, S. X.;Yu, Y. W.（俞云伟）;Cheng, K. S.
期刊：
ASTRONOMY AND ASTROPHYSICS,2019年627:A87- ISSN：0004-6361
通讯作者：
Chen, A. M.
作者机构：
[Yu, Y. W.; Chen, A. M.] Cent China Normal Univ, Inst Astrophys, Wuhan 430079, Hubei, Peoples R China.;[Chen, A. M.; Yi, S. X.; Cheng, K. S.] Univ Hong Kong, Dept Phys, Pokfulam Rd, Hong Kong, Peoples R China.;[Takata, J.] Huazhong Univ Sci & Technol, Sch Phys, Wuhan 430074, Hubei, Peoples R China.;[Yi, S. X.] Radboud Univ Nijmegen, Dept Astrophys, POB 9010, NL-6500 GL Nijmegen, Netherlands.
通讯机构：
[Chen, A. M.] C;[Chen, A. M.] U;Cent China Normal Univ, Inst Astrophys, Wuhan 430079, Hubei, Peoples R China.;Univ Hong Kong, Dept Phys, Pokfulam Rd, Hong Kong, Peoples R China.
关键词：
Binaries: close;Gamma rays: stars;Pulsars: individual: PSR B1259-63;X-rays: binaries
摘要：
The redshift and luminosity distributions of 36 Swift short gamma-ray bursts (GRBs) are fitted by connecting their event rates with cosmic star formation rates using power-law distributed delay times f (tau) proportional to tau(-1), where a broken-power-law luminosity function is assumed and some empirical observational selection effects are taken into account. As a result, the most-likely model parameters are constrained to be nu(1) = 0.91, nu(2) = 1.66 as power-law indices, with a break at L-b = 2.51 x 10(51) erg s(-1) for the luminosity function and tau(c) = 6.0 Gyr for a typical gravitational wave decay timescale of the binary orbit. The corresponding local rate of short GRBs is found to be similar to (3 - 4) Gpc(-3) yr(-1). With these parameters, the detectable nwnbers of short GRBs are estimated within the horizon of Advanced LIGO.
