Gravitational Waves of Jet Precession in Gamma-ray Bursts

The physical nature of gamma-ray bursts (GRBs) are believed to involve an ultra-relativistic jet. The observed complex structure of light curves motivate the idea of jet precession. In this work, we study the gravitational waves of jet precession based on neutrino-dominated accretion disks around black holes, which may account for the central engine of GRBs. In our model, the jet and the inner part of the disk may precess along with the black hole, which is driven by the outer part of the disk. Gravitational waves are therefore expected to be significant from this black hole-inner disk precession system. By comparing our numerical results with the sensitivity of some detectors, we find that it is possible for DECIGO and BBO to detect such gravitational waves, particularly for GRBs in the Local Group.Comment: 19 pages, 6 figures, accepted for publication in Ap

ORIGIN OF MULTI-BAND EMISSION FROM THE MICROQUASAR CYGNUS X-1

National Natural Science Foundation of China [11233006, 11363003]; Science and Technology Foundation of Guizhou Province [LKT[2012] 27]; Tongren University [S1224]We study the origin of non-thermal emissions from the Galactic black hole X-ray binary Cygnus X-1, which is a confirmed high-mass microquasar. By analogy with the methods used in studies of active galactic nuclei, we propose a two-dimensional, time-dependent radiation model from the microquasar Cygnus X-1. In this model, the evolution equation for relativistic electrons in a conical jet are numerically solved by including escape, adiabatic, and various radiative losses. The radiative processes involved are synchrotron emission, its self-Compton scattering, and inverse Compton scatterings of an accretion disk and its surrounding stellar companion. This model also includes an electromagnetic cascade process of an anisotropic gamma-gamma interaction. We study the spectral properties of electron evolution and its emission spectral characteristic at different heights of the emission region located in the jet. We find that radio data from Cygnus X-1 are reproduced by the synchrotron emission, the Fermi Large Area Telescope measurements by the synchrotron emission and Comptonization of photons of the stellar companion, and the TeV band emission fluxes by the Comptonization of the stellar photons. Our results show the following. (1) The radio emission region extends from the binary system scales to the termination of the jet. (2) The GeV band emissions should originate from the distance close to the binary system scales. (3) The TeV band emissions could be inside the binary system, and these emissions could be probed by the upcoming Cherenkov Telescope Array. (4) The MeV tail emissions, which produce a strongly linearly polarized signal, are emitted inside the binary system. The location of the emissions is very close to the inner region of the jet

The Dynamical Effects of a Large-Scale Ordered Magnetic Field on Slim Disks

National Basic Research Program of China [2009CB824800]; National Natural Science Foundation of China [11143003, 11233006, 11073015]; Natural Science Foundation of Fujian Province [2011J01023]The dynamics of slim disk under the influence of a large-scale ordered magnetic field is investigated. The global solutions show that the radial velocity increases and the disk temperature decreases with enhancing magnetic field. The fraction of mass loss becomes smaller when the accretion rate is higher. The ratio of the jet kinetic power to disk luminosity is less than 0.1, which indirectly supports the argument that radio-loud narrow-line Seyfert 1 galaxies share similarities with blazars

NEUTRINO-COOLED ACCRETION MODEL WITH MAGNETIC COUPLING FOR X-RAY FLARES IN GAMMA-RAY BURSTS

National Natural Science Foundation of China [11073015, 11103015, 11222328, 11233006]The neutrino-cooled accretion disk, which was proposed to work as the central engine of gamma-ray bursts, encounters difficulty in interpreting the X-ray flares after the prompt gamma-ray emission. In this paper, the magnetic coupling (MC) between the inner disk and the central black hole (BH) is taken into consideration. For mass accretion rates around 0.001 similar to 0.1 M-circle dot s(-1), our results show that the luminosity of neutrino annihilation can be significantly enhanced due to the coupling effects. As a consequence, after the gamma-ray emission, a remnant disk with mass M-disk less than or similar to 0.5 M-circle dot may power most of the observed X-ray flares with the rest frame duration less than 100 s. In addition, a comparison between the MC process and the Blandford-Znajek mechanism is shown on the extraction of BH rotational energy

Variability of the giant X-ray bump in GRB 121027A and possible origin

The particular giant X-ray bump of GRB 121027A triggered by \emph{Swift} is quite different from the typical X-ray flares in gamma-ray bursts. There exhibit four parts of the observed structural variabilities in the rise and decay phase of the bump. Considering the quality of four parts of the data, we can only analyze the data from about 5300 s to about 6100 s in the bump using the stepwise filter correlation method (Gao et al. 2012), and find that the $86^{+5.9}_{-9.4}~\rm s$ periodic oscillation may exist, which is confirmed by the Lomb-Scargle method (Scargle 1982). Furthermore, a jet precession model (Liu et al. 2010) is proposed to account for such a variability.Comment: 5 pages, 3 figures, accepted for publication in MNRA

RELATIVISTIC GLOBAL SOLUTIONS OF NEUTRINO-DOMINATED ACCRETION FLOWS

National Basic Research Program (973 Program) of China [2009CB824800]; National Natural Science Foundation of China [11003016, 11073015, 11103015, 11222328, 11233006]; Natural Science Foundation of Fujian Province of China [2010J01017]Neutrino-dominated accretion flows (NDAFs) around rotating stellar-mass black holes are plausible candidates for the central engines of gamma-ray bursts (GRBs). We investigate one-dimensional global solutions of NDAFs, taking into account general relativity in the Kerr metric, neutrino physics, and nucleosynthesis more precisely than previous works. We calculate 16 solutions with different characterized accretion rates and black hole spins to exhibit the radial distributions of various physical properties in NDAFs. We confirm that the electron degeneracy has important effects in NDAFs and we find that the electron fraction is about 0.46 in the outer region for all 16 solutions. From the perspective of the mass fraction, free nucleons, He-4, and Fe-56 dominate in the inner, middle, and outer regions, respectively. The influence of neutrino trapping on the annihilation is of importance for the superhigh accretion ((M) over dot = 10 M-circle dot s(-1)) and most of the 16 solutions have an adequate annihilation luminosity for GRBs

THE ORIGIN OF THE PLATEAU AND LATE REBRIGHTENING IN THE AFTERGLOW OF GRB 120326A

National Basic Research Program of China (973 Program) [2013CB834900, 2014CB845800]; National Natural Science Foundation of China [11322328, 11233006, 11103015, 11033002, U1331101]; One-Hundred-Talents Program; Youth Innovation Promotion Association; Strategic Priority Research Program "The Emergence of Cosmological Structures" of the Chinese Academy of Sciences [XDB09000000]GRB 120326A is an unusual gamma-ray burst (GRB) that has a long plateau and a very late rebrightening in both X-ray and optical bands. The similar behavior of the optical and X-ray light curves suggests that they may share a common origin. The long plateau starts at several hundred seconds and ends at tens of thousands of seconds, and the peak time of the late rebrightening is about 30,000 s. We analyze the energy injection model by means of numerical and analytical solutions, considering both the wind environment and the interstellarmedium environment for GRB afterglows. We particularly study the influence of the injection starting time, ending time, stellar wind density (or density of the circumburst environment), and injection luminosity on the shape of the afterglow light curves, respectively. In the wind model, we find that the light curve is largely affected by the parameters and that there is a "bump" in the late stage. In the wind environment, we found that the longer the energy is injected, the more obvious the rebrightening will be. We also find that the peak time of the bump is determined by the stellar wind density. We use the late continuous injection model to interpret the unusual afterglow of GRB 120326A. The model fits the observational data well; however, we find that the timescale of the injection must be higher than 10,000 s, which implies that the timescale of the central engine activity must also be more than 10,000 s. This information can give useful constraints on the central engines of GRBs-we consider a newborn millisecond pulsar with a strong magnetic field to be the central engine. On the other hand, our results suggest that the circumburst environment of GRB 120326A is very likely a stellar wind

DO INTERMEDIATE-MASS BLACK HOLES EXIST IN GLOBULAR CLUSTERS?

National Basic Research Program (973 Program) of China [2014CB845800]; National Natural Science Foundation of China [11073015, 11103015, 11222328, 11233006, 11333004, U1331101]The existence of intermediate-mass black holes (IMBHs) in globular clusters (GCs) remains a crucial problem. Searching for IMBHs in GCs reveals a discrepancy between radio observations and dynamical modelings: the upper mass limits constrained by radio observations are systematically lower than that of dynamical modelings. One possibility for such a discrepancy is that, as we suggest in this work, there exist outflows in accretion flows. Our results indicate that, for most sources, current radio observations cannot rule out the possibility that IMBHs may exist in GCs. In addition, we adopt an (M)over dot - L-R relation to revisit this issue, which confirms the results obtained by the fundamental plane relation

REVISITING THE LIGHT CURVES OF GAMMA-RAY BURSTS IN THE RELATIVISTIC TURBULENCE MODEL

National Basic Research Program (973 Program) of China [2014CB845800]; National Natural Science Foundation of China [11073015, 11103015, 11222328, 11233006, 11025313]; Guangxi Science Foundation [2013GXNSFFA019001]Rapid temporal variability has been widely observed in the light curves of gamma-ray bursts (GRBs). One possible mechanism for such variability is related to the relativistic eddies in the jet. In this paper, we include the contribution of the inter-eddy medium together with the eddies to the gamma-ray emission. We show that the gamma-ray emission can either lead or lag behind the observed synchrotron emission, where the latter originates in the inter-eddy medium and provides most of the seed photons for producing gamma-ray emission through inverse Compton scattering. As a consequence, we argue that the lead/lag found in non-stationary short-lived light curves may not reveal the intrinsic lead/lag of different emission components. In addition, our results may explain the lead of gamma-ray emission with respect to optical emission observed in GRB 080319B

TIME EVOLUTION OF FLARES IN GRB 130925A: JET PRECESSION IN A BLACK HOLE ACCRETION SYSTEM

National Basic Research Program of China (973 Program) [2013CB834900, 2014CB845800]; National Natural Science Foundation of China [11103015, 11222328, 11233006, 11322328, 11333004, U1331101]; One-Hundred-Talents Program; Youth Innovation Promotion Association of Chinese Academy of Sciences; China Scholarship Council [[2013] 3009]GRB 130925A, composed of three gamma-ray emission episodes and a series of orderly flares, has been detected by Swift, Fermi, Konus-Wind, and INTEGRAL. If the third weakest gamma-ray episode can be considered a giant flare, we find that after the second gamma-ray episode observed by INTEGRAL located at about 2000 s, a positive relation exists between the time intervals of the adjacent flares and the time since the episode. We suggest that the second gamma-ray episode and its flares originate from the resumption of the accretion process due to the fragments from the collapsar falling back; such a relation may be related to a hyperaccretion disk around a precessed black hole (BH). We propose that the origin and time evolution of the flares, and the approximately symmetrical temporal structure and spectral evolution of the single flare can be explained well by a jet precession model. In addition, the mass and spin of the BH can be constrained, which indicates a stellar-mass, fast-rotating BH located in the center of GRB 130925A