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Recent observations on both microquasars and AGNs with radio and X‐ray telescopes have revealed remarkable radio/X‐ray correlation of these objects. Because the radio and X‐ray emissions are mainly emitted from jet and accretion flow, the radio/X‐ray correlation can be used to probe the accretion‐jet physics in these accreting black hole systems. Using a uniform broad line SDSS AGN sample, we derived the black hole fundamental plane relationship among the 1.4 GHz radio luminosity (Lr), 0.1–2.4 keV X‐ray luminosity (LX), and black hole mass (M). We found from our sample that the fundamental plane relation has a very weak dependence on the black hole mass, and a tight correlation also exists between the Eddington luminosity scaled X‐ray and radio luminosities for the radio quiet subsample. In addition, we noticed that radio‐loud AGNs have steeper power‐law slope in the radio/X‐ray correlation than radio‐quiet AGNs. This is mainly due to the different origin of X‐ray emissions in radio‐loud and radio‐quiet A...

Observations of surface emission from isolated neutron stars (NSs) provide unique challenges to theoretical modeling of radiative transfer in magnetized NS atmospheres. Recent work has demonstrated the critical role of vacuum polarization effects in determining NS spectra and polarization signals, in particular the conversion of photon modes (due to the “vacuum resonance” between plasma and vacuum polarization) propagating in the density gradient of the NS atmosphere. Previous NS atmosphere models incorporated the mode conversion effect approximately, relying on transfer equations for the photon modes. Such treatments are inadequate near the vacuum resonance, particularly for magnetic field strengths around B∼Bl≃7×1013 G, where the resonance occurs near the photosphere. In this proceeding, we describe our accurate treatment of the mode conversion effect in magnetized NS atmosphere models, employing both the modal radiative transfer equations coupled with the mode conversion probability at the vaccum reson...

Correlation of a puzzling 3:2 ratio of High frequency quasi‐periodic oscillations with the jets in black hole X‐ray binaries are discussed based on the model of the coexistence of the Blandford‐Znajek mechanism and the Magnetic Coupling mechanism. Similar astrophysical phenomena in black hole systems of different scales are also discussed.

The compactness of short‐period white‐dwarf binaries allows strong electro‐magnetic interaction between their component stars. For systems with a magnetic white dwarf a large e.m.f can be generated via unipolar induction, and it drives the flows of electric currents between the two white dwarfs. The electro‐magnetic interaction between the white dwarfs and the tidal interaction between the orbit leads to spin‐orbit coupling. This alters the orbital dynamics and evolution of the system. It also modifies the gravitational waves emitted from the system. The converging of current flows at the field foot points of the magnetic white dwarf may lead to the development of particle instabilities and the generation of electron‐cyclotron masers. The unipolar induction model of ultra‐compact white‐dwarf binaries is also applicable to white‐dwarf planetary systems. The model predicts electron‐cyclotron masers from white‐dwarf planetary systems, and the masers provide a useful mean for the study of ‘dead’ solar systems.

It is possible that the first detection of gravitational waves (GWs) will be made by pulsar timing experiments. Precise observations of millisecond pulsars over a period of ∼5 yr will provide the sensitivity required to detect ultra‐low frequency GWs if they are at the level predicted by current models. Such GWs may be detected as a single burst event or from slowly evolving individual supermassive black‐hole binary systems. Additionally, models of galaxy mergers, the inflationary era and cosmic strings all predict the existence of a potentially detectable stochastic GW background. This paper reviews the current status of the Parkes Pulsar Timing Array project and describes the detectable gravitational wave sources.

In this paper, we study the perturbative treatment of Diffusive Synchrotron Radiation. The random and small‐scale magnetic field may be generated by the turbulence. We find that the multi‐band spectrum of the knot in Cen A produced by DSR is well constrained by the feature of stochastic magnetic field.

We present detailed, ab initio numerical simulations of the distorted magnetic structure of an accreting neutron star as a function of accreted mass Ma:(i) we evolve an initial dipole through a quasi‐static sequence of Grad‐Shafranov equilibria while maintaining strict flux‐freezing for the first time and (ii) we import these equilibria into the time‐dependent, ideal‐magnetohydrodynamic (MHD) code ZEUS‐3D and load additional mass on to the star dynamically We investigate the stability of these hydromagnetic equilibria by perturbing them in ZEUS‐3D in two and three dimeinsions. Surprisingly, in both cases, the equilibria are marginally stable for all Ma⩽6×10−4 M⊙. On extending the ZEUS‐3D simulations to non‐ideal MHD, preliminary results indicate that the equilibria are still not disrupted. The ohmic diffusion time‐scale is 105(102) times longer than the accretion time‐scale in 2D (3D). The equilibria (“magnetic mountains”) are in general, offset from the spin axis and thus generate gravitational waves. We...

We model the population characteristics of the sample of millisecond pulsars (MSPs) within a distance of 1.5 kpc. Our study, which takes into consideration acceleration effects on the observed spin‐down rate, shows that most MSPs are born with periods that are close to the currently observed values and with average characteristic ages that are typically larger by a factor ∼1.5 compared to the true age. The galactic birth rate of the MSPs is deduced to be ≳3.2×10−6 yr−1. We also discuss the possibility that accretion induced collapse (AIC) may constitute the main route to the formation of the MSPs.

In this paper, we show that the range in magnetic fluxes that is observed in the chemically peculiar Ap, Bp and Op stars is similar to that measured in the High Field Magnetic White Dwarfs and the Neutron Stars, which suggests that the magnetic flux is approximately conserved during stellar evolution at least for intermediate to high mass stars. We also discuss the recent evidence of a bi‐modal distribution of magnetic fields in white dwarfs and its implications for the accretion induced collapse hypothesis for the origin of the binary millisecond pulsars.

Forty years after the discovery of rotation‐powered pulsars, we still do not understand many aspects of their pulsed emission. In the last few years there have been some fundamental developments in acceleration and emission models. I will review both the basic physics of the models as well as the latest developments in understanding the high‐energy emission of rotation‐powered pulsars. The prospects for a revolution of the field is about to take place with the launch of AGILE and GLAST. Prospects for using this large increase in γ‐ray data for the study of pulsar physics will be discussed.

Dwarf novae (DNe) are a subclass of Cataclysmic Variables (CVs) with outbursts powered by a disk instability leading to a sudden increase in the accretion rate. The Digital Access to a Sky Century at Harvard (DASCH) Collaboration is preparing to digitize over 500,000 Harvard plates from the 1880s to the 1980s with limiting magnitudes ranging from B∼14–19. As a demonstration project, we have scanned more than 500 plates in the fields centered on the galactic open cluster M44. There are 21 CVs in the fields within 10 degrees of M44 covered by the scans. Here we present the preliminary results of DN outbursts of the known CVs to derive long‐term DN outburst duty cycles. In addition, a 100y lightcurve for a XMM–Newton source is also presented to demonstrate DASCH capabilities.

We have calculated the evolution of close binaries consisting of a white dwarf and a main‐sequence or subgiant companion. We assume that, once Roche lobe overflow occurs a small fraction of the lost mass from the system forms a circumbinary disk, which extracts the orbital angular momentum from the system through tidal torques. Our calculations indicate that the existence of circumbinary disk can enhance the mass transfer rate so that the white dwarf can grow in mass efficiently to trigger type Ia supernovae even with relatively low‐mass (⩽2 M⊙) donor stars. This scenario suggest a new evolutionary channel to type Ia supernovae with delay times ∼1–3 Gyr.

There are several kinds of probes for the Galactic magnetic fields. Among them, pulsars are the best. In the Galactic disk, from the rotation measures (RMs) of a large number of newly discovered pulsars, the large‐scale magnetic fields along the spiral arms have been delineated in a much larger region than ever before, with alternating directions in the arm and interarm regions. The RM data of extragalactic radio sources are consistent with such magnetic field directions in the tangential regions. The strength of large‐scale fields obtained from pulsar RM data has been found to increase exponentially towards the Galactic center. Since pulsar RMs are an integration of electron density and magnetic fields along the lines of sight from pulsars to us, which contain the information of magnetic field fluctuation on different scales for pulsars with different distances. We derived the spatial magnetic field energy spectrum from pulsar RM data, which shows a shallow broken spectrum compared to the steep Kolmogorov spectrum of magnetic energy at small scales.

Tidal disruptions of stars by super‐massive black holes are one of the most spectacular phenomena that can occur in the Galactic center. Studying this process can give us much information on the black hole itself, the environment around it, and the growth and evolution of super‐massive black holes. Here we consider different types of stars in calculating physical quantities during tidal disruptions and apply our results to three astrophysical problems: X‐ray flares in normal galaxies, TeV gamma‐ray emissions from our Galactic center and the growth of the black holes harbored in the centers of galaxies, which grow solely through capturing stars even if they never experienced other modes of mass growth.

We present results of our population synthesis of normal and millisecond pulsars from the Galactic disk. Over the past several years, a program has been developed to simulate pulsar birth, evolution, and emission using Monte Carlo techniques. We have added to the program the capability to simulate millisecond pulsars, which are old, recycled pulsars with extremely short periods. We model the spatial distribution of millisecond pulsars by assuming they start with a random kick velocity and then evolve through the Galactic potential. We use a polar cap/slot gap model for gamma‐ray emission from both millisecond and normal pulsars. We also include gamma‐ray emission from an outer‐gap model to compare the statistics of radio‐loud and radio‐faint gamma‐ray pulsars on the same footing as pulsars from our polar cap/slot gap model. From our studies of radio pulsars that have clearly identifiable core and cone components, in which we fit the polarization sweep as well as the pulse profiles to constrain the viewing...

The nonthermal radio source Sgr A* at the Galactic center has been known to be extremely compact since its discovery. Following a brief introduction to its size measurements (including its discovery, interstellar scattering effect and its elongated structure), we describe the detection of an intrinsic size of only 1 AU for Sgr A*. When combined with the mass estimate of Sgr A*, these size measurements provide strong evidence that Sgr A* is a super‐massive black hole. Results from the simulation of the black hole shadow image and the corresponding visibility analysis indicate that future sub‐millimeter VLBI experiments are critical and promising to probe the Galactic center black hole. High quality multi‐epoch radio interferometric images of Sgr A* with a wavelength coverage from long centimeter to short millimeter are needed in order to pursue the two‐dimensional structure for the scattering angle and the intrinsic source structure, and the corresponding size variation.

It is a pity that the real state of matter in pulsar-like stars is still not determined confidently because of the uncertainty about cold matter at supranuclear density, even 40 years after the discovery of pulsar. Nuclear matter (related to neutron stars) is one of the speculations for the inner constitution of pulsars even from the Landau's time more than 70 years ago, but quark matter (related to quark stars) is an alternative due to the fact of asymptotic freedom of interaction between quarks as the standard model of particle physics develops since 1960s. Therefore, one has to focus on astrophysical observations in order to answer what the nature of pulsars is. In this presentation, I would like to summarize possible observational evidence/hints that pulsar-like stars could be quark stars, and to address achievable clear evidence for quark stars in the future experiments., 6 pages, 2 figures; a talk at the international conference "Astrophysics of Compact Objects" (July 1-7, 2007; Huangshan, China); http://vega.bac.pku.edu.cn/rxxu/publications/index_C.htm. A mistake in Fig.1 is corrected; Correction of typos

We show three‐dimensional numerical simulations on the core collapse of a rotating massive star threaded by strong magnetic fields. The initial magnetic field is nearly uniform in the core and inclined with respect to the rotation axis. We have made 17 models having different angular velocity and magnetic field of the progenitor. All the models show nearly spherical prompt shock just after the core bounce. The magnetic field is amplified by rotation in a torus region around the protoneutron star. The azimuthal component of magnetic field changes its sign with a semiregular interval in the torus. This is due to the inclination of initial magnetic field. After the twisted magnetic field is accumulated, the bipolar jets are launched along the initial rotation axis. When the initial magnetic field is weak, the magnetic energy is dissipated substantially by numerical diffusion before the launch of jets.

26Al is an unstable isotope with the mean lifetime of 1 Myr. It is mainly synthesized in massive stars, before and during their evolution to core‐collapse supernovae. Since the gamma‐ray line is transparent to the interstellar medium, studies of 26Al could probe the nucleosynthesis activity and supernova explosions in the whole Galaxy in last few million years. INTEGRAL/SPI has a high spectral resolution to study the 1809 keV gamma‐ray line from 26Al. We have detected 26Al from the Galactic plane and nearby star‐formation regions. From 26Al measurements, we obtain the current Galactic core‐collapse supernova rate of 1.9 events per century. Correlation between the distribution of 26Al candidate sources and the distributions of detected SNRs and pulsars in the Galaxy is discussed.

We present our work to study the origin of the massive stars observed close to Sgr A*, the Galactic super‐massive black hole, and the dynamics of the massive stars' winds. We argue that the stars were formed in a ∼104 M⊙ accretion disc that existed around Sgr A* in the past. We find that the stellar dynamics constrain the total mass of the stellar population, requiring the mass function to be dominated by massive stars. We present a numerical study of star formation in a massive disc and show the influence of radiative cooling on the resulting mass function. We also present simulations of the accretion of stellar winds onto Sgr A*. We first discuss the strong influence of the stellar dynamics on the accretion onto the central black hole. From realistic simulations of Sgr A* accretion we find that slow winds shock and rapidly cool, forming cold gas clumps and filaments that coexist with the hot X‐ray emitting gas. The accretion rate is highly variable on time‐scales of tens to hundreds of years. Such varia...

I briefly review the physical properties of neutron star surface layers, important for the stellar thermal radiation, taking into consideration the effects of strong magnetic fields.

To investigate physical states of “Z” sources, which are a subclass of low‐mass X‐ray binaries consisting of a weakly‐magnetized neutron star and a companion star, two Z sources (LMC X‐2 and GX 349+2) were observed by the Suzaku satellite. Since the interstellar absorption toward LMC X‐2 is relatively low, its X‐ray signal was detected down to a ∼0.4 keV energy band. From horizontal branch through normal branch to flaring branch, the soft count rate below 1 keV was observed to increase continuously, while the hard one above 6 keV decreased at the normal branch. This result confirms the existence of the additional soft component with temperature of sub keV, proposed by [4, 5], where luminous LMXB spectra have been shown to consist of three optically‐thick components; the softest one from a retreated disk, the hardest one from the NS surface, and an additional intermediate component presumably from outflows caused by the increased radiation pressure. A broad‐band energy spectrum of GX 349+2 in flaring branc...

Based on the Konigl's inhomogeneous jet model, we estimate the jet parameters, such as bulk Lorentz factor Γ, viewing angle θ and electron number density ne from radio VLBI and X‐ray data for a sample of active galactic nuclei (AGNs). The kinetic luminosity of jets is then calculated using the derived jet parameters. We find a strong correlation between the total luminosity of broad emission lines and the kinetic luminosity of the jets, which supports the scenario that the accretion process are tightly linked with the radio jets. Moreover, we find a significant correlation between the kinetic luminosity and radio extended luminosity. This implies that the emission from the radio lobes are closely related with the energy flux transported through jets from the central part of AGNs.

We have discovered a group of linearly aligned four molecular clouds over about 400 pc nearly perpendicular to the galactic plane at a distance of 6 kpc toward ∼348.5° in galactic longitude and that of molecular clouds on a straight line nearly coincident with the X‐ray jet axis on the both side up to 150 pc, three times larget than previously known by X‐ray, from SS433 from the NANTEN 12CO dataset. We argue that they represent molecular clouds which might be created by the interaction between the jet and the interstellar medium. We present a scenario that the interaction between the jet and interstellar medium induced the formation of molecular clouds and/or enhanced the molecular emission ⩾105 yrs ago. This scenario explains the molecular jet quantitatively if we assume the same physical parameters with those derived for the SS433 jet, the most‐developed jet from compact object in the Milky Way known to date. The finding might offer a new tool, “galactic vapor trail”, to search for relativistic jet driv...

The properties of the X‐ray reflection spectra from accretion discs and their variability (or lack of it) are briefly reviewed. Particular emphasis is given to X‐ray observations of two remarkable active galaxies, MCG–6‐30‐15 and the Narrow–Line Seyfert 1 1H 0707–495, and to the short–timescale variability of the Fe emission in NGC 3783

The black hole candidate XTE J1817-330 was discovered in outburst on 26 January 2006 with RXTE/ASM. One year later, on 28 February 2007, another X-ray transient discovered in 1996, XTE J1856+053, was detected by RXTE during a new outburst. We report on the spectra obtained by XMM-Newton of these two black hole candidates., Comment: Replaced with corrected version

Ultra‐relativistic shockwaves occur in the study of several classes of astrophysical objects, including pulsar wind nebulae and active galactic nuclei, and are widespread in research on gamma‐ray bursts. This work investigates generalizations of the familiar Blandford‐McKee solutions to the fluid equations for the case of an ultra‐relativistic shockwave propagating in a continuous, varying external medium. We obtain a semi‐analytic result in which the post‐shock material behaves locally as an “almost self‐similar” solution, evolving adiabatically with the external medium. We discuss the implications of our results for GRB observations.

This study reports pulse variation analysis results for the forth discovered accretion‐powered millisecond pulsar XTE J1807‐294 during its 2003 outburst observed by Rossi Timing Explorer (RXTE). The fine orbital parameters with Porb = 40.073601(8) min and ax sin i = 4.823(5) lt‐ms were first obtained after applying trend removal for the daily phase drift. The binary barycenter corrected pulse phases show smooth variation plus clear negative phase shifts coincident with the flares seen on the light curve as well as enhancements of fractional pulse amplitude. The non‐flare pulse phases are well described as a fourth order polynomial implying that the neutron star was spun‐up during the ourburst. Significant soft phase lags up to ∼500 μs between 2 to 20 keV were detected for the non‐flare pulse phases. The variations of pulse phases during the flares and their energy‐dependent shifts indicate that the anomalous phase shifts are a result from the “hot spot” shifting on the surface of neutron star.

Radiation processes in the closed field line regions of pulsar magnetospheres are discussed. It is argued that trapped particles form radiation belts in the closed field line regions in the majority of pulsars. It is proposed that transient radio emission, seen as rotating radio transients (RRATs), results from events that trigger precipitation of these trapped particles.

This review summarizes our current understanding of low‐luminosity AGNs in the context of the advection‐dominated accretion flow (ADAF). Special attention is paid to the best investigated source, the supermassive black hole in our galactic center, Sgr A*. ADAF can naturally explain the most important features of these sources such as the low luminosity and the lack of the big blue bump in their spectral energy distribution. The emission from the jet usually dominates over the ADAF in the radio waveband and sometimes in other wavebands as well especially the X‐ray

The ability to correct dispersion measure (DM) variations due to the interstellar and interplanetary medium is essential for high precision pulsar timing. Here we present an analysis of the variations in DM for 20 millisecond pulsars. We show how they affect pulsar timing residuals and how they can be corrected. We also show that our new model of the solar wind electron density implemented into the TEMPO2 pulsar timing package is more accurate than previous models. This paper summarises the work presented in [1, 2].

The paradigm for Anomalous X-ray Pulsars (AXPs) has evolved recently with the discovery by INTEGRAL and RXTE of flat, hard X-ray components in three AXPs. These non-thermal spectral components differ dramatically from the steeper quasi-power-law tails seen in the classic X-ray band in these sources, and can naturally be attributed to activity in the magnetosphere. Resonant, magnetic Compton upscattering is a candidate mechanism for generating this new component, since it is very efficient in the strong fields present near AXP surfaces. In this paper, results from an inner magnetospheric model for upscattering of surface thermal X-rays in AXPs are presented, using a kinetic equation formalism and employing a QED magnetic scattering cross section. Characteristically flat and strongly-polarized emission spectra are produced by non-thermal electrons injected in the emission region. Spectral results depend strongly on the observer's orientation and the magnetospheric locale of the scattering, which couple directly to the angular distributions of photons sampled. Constraints imposed by the Comptel upper bounds for these AXPs are mentioned., 8 pages, 2 embedded figures, in Proc. of the Huangshan conference "Astrophysics of Compact Objects," (2008) eds. Y.-F. Yuan, X.-D. Li and D. Lai, (AIP Conf. Proc. 968, New York) p. 93

Due to the relativistic motion of gamma‐ray burst remnant and its deceleration in the circumburst medium, the equal arrival time surface (EATS) is not spherical, but ellipsoidal. Here the EATS effects are studied numerically. A direct comparison for the cases when the effects are or are not included is presented. Generally speaking, the EATS effect slightly hardens the spectra and postpones the peak time of the afterglows, but does not change the shapes of the spectra and light curves significantly In the cases of a density jump or an energy‐injection, the effect smears out the variations in the afterglows markedly For the rapid rebrightening observed in the optical afterglow of GRB 030329 at t∼1.6 d, the energy‐injection model can give a best explanation as compared with the density jump model and two‐component jet model. However, the predicted rebrightening is still not as rapid as observations due to EATS effect.

Soft Gamma‐ray Repeaters (SGRs) were the first objects interpreted as magnetars: isolated neutron stars powered by the decay of extremely high magnetic fields. I review the results obtained in the last few years with X‐ray and γ‐ray observations of the four confirmed SGRs.

Millisecond quasi‐periodic oscillations (QPOs) in neutron star low mass X‐ray binaries (LMXBs) are signals that can be used to probe general relativistic effects, constrain neutron star mass and radius, and study the physical processes in the vicinity of compact objects. Here I review current understanding of these key issues and present some preliminary results based on our studies of the effect of the radiation force from the neutron star on the maximum kHz QPO frequency.

The condensation of matter from a corona to a cool, optically thick inner disk is investigated for black hole X-ray transient systems in the low/hard state. A description of a simple model for the exchange of energy and mass between corona and disk originating from thermal conduction is presented, taking into account the effect of Compton cooling of the corona by photons from the underlying disk. It is found that a weak, condensation-fed inner disk can be present in the low/hard state of black hole transient systems for a range of luminosities that depends on the magnitude of the viscosity parameter. For alpha similar to 0.1-0.4, an inner disk can exist for luminosities in the range similar to(0.001-0.02) L-Edd. The model is applied to the X-ray observations of the black hole candidate sources GX 339 -4 and SWIFT J1753.5 -0127 in their low/hard state. It is found that Compton cooling is important in the condensation process, leading to the maintenance of cool inner disks in both systems. As the results of the evaporation/condensation model are independent of the black hole mass, it is suggested that such inner cool disks may contribute to the optical and ultraviolet emission of low-luminosity active galactic nuclei.

We present a power spectral analysis survey of 24 active galactic nuclei (AGN). We combine X‐ray observations to produce a power spectrum covering a broad range of Fourier frequencies and fit the power spectrum of each AGN using a single‐bend power‐law model. Using the resultant bend time‐scales of 18 AGN, and of the Galactic black hole X‐ray binaries Cyg X‐1 and GRS1915+105, we present a plot of observed bend time‐scales versus the predicted bend time‐scales determined from published masses and bolometric luminosities. The results confirm our previously proposed scaling relation of bend time‐scale with mass divided by accretion rate. All work presented herein can be found in Summons et al. [1].

Before 2004, nearly all GRB afterglow data could be understood in the context of the external shocks model. This situation has changed in the past two years, when it became clear that some afterglow components should be attributed to the activity of the central engine; i.e., the {\it central engine afterglow}. We review here the afterglow emission that is directly related to the GRB central engine. Such an interpretation proposed by Katz, Piran & Sari, peculiar in pre-{\it Swift} era, has become generally accepted now., 4 pages including 1 figure. Presented at the conference "Astrophysics of Compact Objects" (July 1-7, 2007; Huangshan, China)

We obtained steady solutions of magnetized black hole accretion disks taking into account the gas pressure, magnetic pressure, and radiation pressure. We assumed the bremsstrahlung cooling in the optically thin limit and the black body cooling in the optically thick limit. W assumed that magnetic fields inside the disk are turbulent and dominated by azimuthal component and that the azimuthally averaged Maxwell stress is proportional to the total pressure. We found that when accretion rate exceeds the threshold for the onset of the thermal instability for optically thin disks, a magnetic pressure dominated, cool branch appears in the thermal equilibrium curve. This disk corresponds to the “Bright/Hard” state in black hole candidates observed during the transition from a Low/Hard state to a High/Soft state.

We present the profiles of reprocessing emission lines originating in a relativistic, warped accretion disk around a non‐rotating black hole. Our calculations are aimed at providing a possibility that the variability of double‐peaked emission line which can not be explained by a circular Keplerian disk may be induced by disk warping. The warped disk can also provide a solutoin for the energy budget problem due to the disk warping can enhance the solid angle of the outer disk portion subtended to the inner part of the disk. In the calculation a parameterize disk geometry and a central point‐like source of ionizing radiation are adopted. We find that the ratio between the red and blue peaks of the line profiles cross unity can be naturally predicted by a twisted warp disk, and a third peak can be produced in some cases.

We review recent results from the X-ray timing of accreting millisecond pulsars in LMXBs. This is the first time a timing analysis is performed on accreting millisecond pulsars, and for the first time we can obtain information on the behavior of a very fast pulsar subject to accretion torques. We find both spin-up and spin-down behaviors, from which, using available models for the accretion torques, we derive information on the mass accretion rate and magnetic field of the neutron star in these systems. We also report here the first measure of the orbital period derivative for an accreting millisecond pulsar, derived for SAX J1808.4-3658 over a timespan of more 7 years.

Khz QPO infers the millisecond oscillation close to the neutron star in the binary system. By means of the twin kHz QPOs, we can constrain the neutron star mass and radius. As the examples, we studied the sources Cir X‐1, Cgy X‐2, Sax J 1808.4‐3658, XTE 1807‐294 and the fastest nuclear‐powered millisecond pulsar XTE J1739‐285 with the spin frequency 1122 Hz.

By adopting the correct vertical gravitational force in studies of thermal equilibrium solutions, we find that there exists a maximal possible accretion rate for each radius in the outer region of optically thick accretion flows, such that only the inner regions of these flows can possibly take the form of slim disks.

Since 1994 there have been five major outbursts with corresponding superluminal motion observed in microquasar GRS 1915+105. This paper shows that interval between two outbursts is approximately 3.5 years. The origin of the periodicity can be interpreted in term of the precession resulting in the torque induced by the gravitation field of the companion star. The assumption can be consistent with the measurement of binary parameter as well as the magnitude of proper motion of GRS 1915+105. It is predicted that the next outburst should be Dec 2007 to Oct 2008.

It was widely shown that the cosmological parameters and dark energy can be constrained by using data from type‐Ia supernovae (SNe Ia), cosmic microwave background (CMB) anisotropy, cosmic large scale structure, and so on. Recently gamma‐ray bursts (GRBs) were also argued to be promising standard candles for cosmography. In this paper, we summarize the results of Wang et al. (2007). We present constraints on the cosmological parameters and dark energy by combining a recent GRB sample with other cosmological probes. We find that for the ΛCDM cosmology this combination makes the constraints stringent and the best fit is close to the flat universe. We also find that several dark energy models used usually are consistent with the ΛCDM cosmology. Furthermore, we reconstruct the dark energy equation‐of‐state parameter w(z) and the deceleration parameter q(z), and obtain the transition redshift of cosmic past deceleration to present acceleration.

Neutrino‐cooled hyperaccretion disks around stellar mass black holes are plausible candidates for the central engine of gamma‐ray bursts. We calculate the one‐dimensional structure and the annihilation luminosity of such disks. The resulting neutrino annihilation luminosity is still likely to be adequate for gamma‐ray bursts, and it is ejected mainly from the inner region of the disk and has an anisotropic distribution.

We present two formulations for general relativistic radiative transfer for astrophysical systems. The first considers absorption and emission only, and the second includes also scattering. We use these formulations to calculate emission from relativistic accretion disks and tori around rotating black holes.

I will provide a brief introduction to the emerging field of ground‐based gamma‐ray astrophysics. Selected recent results will be presented to show the progress of the field, with a special focus on the TeV gamma‐ray radiation from active galactic nuclei, microquasars, and gamma ray bursts.