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1.
Estimates of AGN Black Hole Mass and Minimum Variability Timescale   总被引：4，自引：0，他引：4  
Black hole mass is one of the fundamental physical parameters of active galactic nuclei (AGNs), for which many methods of estimation have been proposed. One set of methods assumes that the broad-line region (BLR) is gravitationally bound by the central black hole potential, so the black hole mass can be estimated from the orbital radius and the Doppler velocity. Another set of methods assumes the observed variability timescale is determined by the orbital timescale near the innermost stable orbit around the Schwarzschild black hole or the Kerr black hole, or by the characteristic timescale of the accretion disk. We collect a sample of 21 AGNs, for which the minimum variability timescales have been obtained and their black hole masses (Mσ) have been well estimated from the stellar velocity dispersion or the BLR size-luminosity relation. Using the minimum variability timescales we estimated the black hole masses for 21 objects by the three different methods, the results are denoted by Ms, Mk and Md, respectively. We compared each of them with Mσindividually and found that: (1) using the minimum variability timescale with the Kerr black hole theory leads to small differences between Mσand Mk, none exceeding one order of magnitude, and the mean difference between them is about 0.53 dex; (2) using the minimum variability timescale with the Schwarzschild black hole theory leads to somewhat larger difference between Mσand Ms: larger than one order of magnitude for 6 of the 21 sources, and the mean difference is 0.74 dex; (3) using the minimum variability timescale with the accretion disk theory leads to much larger differences between Mσand Md, for 13 of the 21 sources the differences are larger than two orders of magnitude; and the mean difference is as high as about 2.01 dex.  相似文献   

2.
A Periodicity Analysis of the Light Curve of 3C 454.3   总被引：2，自引：0，他引：2  
We analyzed the radio light curves of 3C 454.3 at frequencies 22 and 37 GHz taken from the database of Metsahovi Radio Observatory, and found evidence of quasi-periodic activity. The light curves show great activity with very complicated non-sinusoidal variations. Two possible periods, a very weak one of 1.57±0.12 yr and a very strong one of 6.15±0.50 yr were consistently identified by two methods, the Jurkevich method and power spectrum estimation. The period of 6.15±0.50 yr is consistent with results previously reported by Ciaramella et al. and Webb et al. Applying the binary black hole model to the central structure we found black hole masses of 1.53×109M⊙and 1.86×108M⊙, and predicted that the next radio outburst is to take place in 2006 March and April.  相似文献   

3.
Low mass black hole binaries are generally transient sources and spend most of their time in the quiescent state. It is believed that the inner accretion flow in the quiescent state is in the form of advection dominated accretion flow and the cold outer accretion disk is truncated far away from the central black hole. During the onset of an outburst, the disk gradually extends towards the central black hole.However, the observational evidence for this general picture is indirect at best. Here we present the results of a study performed to understand the variation of the inner disk radius during the early phase of an outburst. We investigated the variation of the inner disk radius during the 2010 outburst of the black hole candidate MAXI J1659-152 using the method of simultaneous spectral fitting. We found that the inner edge of the disk is truncated at a large radius in the beginning of the outburst when the source was in the hard state. We found a systematic decrease in the inner disk radius as the outburst progressed. We also estimated an upper limit on the mass of the black hole to be 8.1 ± 2.9 M within the uncertainty of the distance and inclination angle.  相似文献   

4.
Binary neutron star(NS)mergers may result in remnants of supra-massive or even stable NS,which have been supported indirectly by observed X-ray plateau of some gamma-ray burst(GRB)afterglows.Recently,Xue et al.(2019)discovered an X-ray transient CDF-S XT2 that is powered by a magnetar from merger of double NS via X-ray plateau and following stepper phase.However,the decay slope after the plateau emission is slightly larger than the theoretical value of spin-down in electromagnetic(EM)dominated by losing its rotation energy.In this paper,we assume that the feature of X-ray emission is caused by a supra-massive magnetar central engine for surviving thousands of seconds to collapse into a black hole.Within this scenario,we present the comparisons of the X-ray plateau luminosity,break time,and the parameters of magnetar between CDF-S XT2 and other short GRBs with internal plateau samples.By adopting the collapse time to constrain the equation of state(EOS),we find that three EOSs(GM1,DD2,and DDME2)are consistent with the observational data.On the other hand,if the most released rotation energy of magnetar is dominated by GW radiation,we also constrain the upper limit of ellipticity of NS for given EOS,and its range is[0.32-1.3]×10-3.Its GW signal cannot be detected by Advanced LIGO or even for more sensitive Einstein Telescope in the future.  相似文献   

5.
The detection of very high energy γ-ray emission from the Galactic center has been reported by four independent groups. One of these γ-ray sources, the 10 TeV -γ-ray radiation reported by HESS, has been suggested as having a hadronic origin when relativistic protons are injected into and interact with the dense ambient gas. Assuming that such relativistic protons required by the hadronic model come from the tidal disruption of a star by the massive black hole of Sgr A＊, we explore the spectrum of the relativis- tic protons. In the calculations, we investigate cases where different types of stars are tidally disrupted by the black hole of Sgr A＊, and we consider that different diffusion mechanisms are used for the propagation of protons. The initial energy distribution of the injected spectrum of protons is assumed to follow a power-law with an exponential cut-off, and we derive the different indices of the injected spectra for the tidal disruption of different types of stars. For the best fit to the spectrum of photons detected by HESS, the spectral index of the injected relativistic protons is about 2.05 when a red giant is tidally disrupted by the black hole of Sgr A＊ and the diffusion mechanism is the Effective Confinement of Protons.  相似文献   

6.
We investigate a unique accreting millisecond pulsar with X-ray eclipses,SWIFT J1749.4-2807(hereafter J1749),and try to set limits on the binary system by various methods including use of the Roche lobe,the mass-radius relations of both main sequence(MS)and white dwarf(WD)companion stars,as well as the measured mass function of the pulsar.The calculations are based on the assumption that the radius of the companion star has reached its Roche radius(or is at 90%),but the pulsar's mass has not been assumed to be a certain value.Our results are as follows.The companion star should be an MS one.For the case that the radius equals its Roche one,we have a companion star with mass M(～-)0.51 M⊙ and radius Rc(～-)0.52 R⊙,and the inclination angle is i(～-)76.5°; for the case that the radius reaches 90% of its Roche one,we have M(～-)0.43 M⊙,Re()0.44 R⊙ and i(～-)75.7°.We also obtain the mass of J1749,Mp(～-)1 M⊙,and conclude that the pulsar could be a quark star if the ratio of the critical frequency of rotation-mode instability to the Keplerian one is higher than～0.3.The relatively low pulsar mass(about～M⊙)may also challenge the conventional recycling scenario for the origin and evolution of millisecond pulsars.The results presented in this paper are expected to be tested by future observations.  相似文献   

7.
Recent analysis of the long term radio light curve of the extremely variable BL Lacertae object AO 0235+16 by Raiteri et al. have revealed the presence of recurrent outbursts with a period of ～ 5.7±0.5 yr. Periodicity analysis of the optical light curve also shows evidence for a shorter period. Here we discuss whether such a behavior can be explained by a binary black hole model where the accretion disk of one of the supermassive black holes is precessing due to the tidal effects of the companion. We estimate the mass of the accreting hole and analyze constraints on the secondary mass and the orbital parameters of the system. It is possible to provide a viable interpretation of the available multiwavelength data.  相似文献   

8.
It has been firmly established that there exists a tight correlation between the mass of the central black hole and velocity dispersion (or luminosity) in elliptical galaxies, “pseudobulges” and bulges of galaxies, although the nature of this correlation still remains unclear. We explore the possibility of extrapolating such a correlation to less massive, spherical systems like globular clusters. In particular, motivated by the apparent success in the globular cluster M15, we present an estimate of the central black hole mass for a number of globular clusters with available velocity dispersion data.  相似文献   

9.
In many astrophysical black hole systems, episodic jets of plasma blobs have been observed, which are much faster and more powerful than continuous jets. A magnetohydrodynamical model was proposed by Yuan et al. to study the formation of episodic jets in Sgr A*. By taking Sgr A* and a stellar mass black hole as examples, we modify the model of Yuan et al. by including the effects of relativity, and further study the relativistic motion and expansion of episodic jets of plasma blobs. Then we study the collision between two consecutive ejections in the modified model, and calculate the magnetic energy released in the collision. Our results show two consecutive blobs can collide with each other, and the released magnetic energy is more than 1050 erg,which supports the idea that a gamma-ray burst is powered by the collision of episodic jets, as suggested by Yuan & Zhang.  相似文献   

10.
We study the interaction between supermassive binary black holes in an elliptical orbit and their surrounding disk with a gap. The gap in the disk is a low density region formed due to the tidal effects of the less massive black hole. The binary we have investigated has a sub-parsec separation and is coplanar with the disk. We find that the maximum variation of the surface density in the gap reaches 50% during an orbital period. However, in other regions of the disk, the density variation is much less than 1%. Furthermore, we calculate the corresponding variation of spectral energy distribution within a period, but little variation is found. The reason for these results is that the viscosity timescale of the disk at the binary radius is much longer than the orbital period of the binary.  相似文献   

11.
In a previous paper, it was suggested that contamination of the nuclear luminosity by the host galaxy plays an important role in determining the parameters of the standard a disk of AGNs. Using the nuclear absolute B band magnitude instead of the total absolute B band magnitude, we have recalculated the central black hole masses, accretion rates and disk inclinations for 20 Seyfert 1 galaxies and 17 Palomar-Green (PG) quasars. It is found that a small value of a is needed for the Seyfert 1 galaxies than for the PG quasars. This difference in a possibly leads to the different properties of Seyfert 1 galaxies and quasars. Furthermore, we find most of the objects in this sample are not accreting at super-Eddington rates if we adopt the nuclear optical luminosity in our calculation.  相似文献   

12.
Inspired by the General Relativity for many decades, experimental physicists and astronomers have a solid dream to detect gravitational waves(GWs) from mergers of black holes, which came true until the excellent performance of the Laser Interferometer Gravitational-Wave Observatory(LIGO) at hundreds Hz. Nano-Hz GWs are expected to be radiated by close-binaries of supermassive black holes(CB-SMBHs;defined as those with separations less than ～0.1 pc) formed during galaxy mergers and detected through the Pulsar Timing Array(PTA) technique. As of the writing, there remains no nano-Hz GWs detection.Searching for CB-SMBHs is also observationally elusive though there exist a number of possible candidates.In this review, we focus on observational signatures of CB-SMBHs from theoretic expectations, simulations and observations. These signatures appear in energy distributions of multiwavelength continuum, long term variations of continuum, jet morphology, reverberation delay maps and spectroastrometry of broad emission lines, AGN type transitions between type-1 and type-2(changing-look), and gaseous dynamics of circumbinary disks, etc. Unlike hundred-Hz GWs from stellar mass black hole binaries, the waveform chirping of nano-Hz GWs is too slow to detect in a reasonable human timescale. We have to resort to electromagnetic observations to measure orbital parameters of CB-SMBHs to test nano-Hz GW properties.Reverberation mapping is a powerful tool for probing kinematics and geometry of ionized gas in the gravitational well of SMBHs(single or binary) and therefore provides a potential way to determine orbital parameters of CB-SMBHs. In particular, a combination of reverberation mapping with spectroastrometry(realized at the Very Large Telescope Interferometer) will further reinforce this capability. The Atacama Large Millimeter/submillimeter Array(ALMA) and the forthcoming Square Kilometre Array(SKA) are suggested to reveal dynamics of circumbinary disks through molecular emission lines.  相似文献   

13.
We formulate the general relativistic force-free electrodynamics in a new 3 1 language. In this formulation,when we have properly defined electric and magnetic fields,the covariant Maxwell equations could be cast in the traditional form with new vacuum con-stitutive constraint equations. The fundamental equation governing a stationary,axisymmet-ric force-free black hole magnetosphere is derived using this formulation which recasts the Grad-Shafranov equation in a simpler way. Compared to the classic 3 1 system of Thorne and MacDonald,the new system of 3 1 equations is more suitable for numerical use for it keeps the hyperbolic structure of the electrodynamics and avoids the singularity at the event horizon. This formulation could be readily extended to non-relativistic limit and find applica-tions in flat spacetime. We investigate its application to disk wind,black hole magnetosphere and solar physics in both flat and curved spacetime.  相似文献   

14.
The mechanism of formation for double-peaked optical outbursts observed in blazar OJ 287 is studied. It is shown that they could be explained in terms of a lighthouse effect for superluminal optical knots ejected from the center of the galaxy that move along helical magnetic fields. It is assumed that the orbital motion of the secondary black hole in the supermassive binary black hole system induces the 12-year quasi-periodicity in major optical outbursts by the interaction with the disk around the primary black hole. This interaction between the secondary black hole and the disk of the primary black hole(e.g. tidal effects or magnetic coupling) excites or injects plasmons(or relativistic plasmas plus magnetic field) into the jet which form superluminal knots. These knots are assumed to move along helical magnetic field lines to produce the optical double-peaked outbursts by the lighthouse effect. The four double-peaked outbursts observed in 1972, 1983, 1995 and 2005 are simulated using this model. It is shown that such lighthouse models are quite plausible and feasible for fitting the double-flaring behavior of the outbursts. The main requirement may be that in OJ 287 there exists a rather long(～40–60 pc) highly collimated zone, where the lighthouse effect occurs.  相似文献   

15.
We investigate a hybrid numerical algorithm aimed at large-scale cosmological N-body simulation for on-going and future high precision sky surveys.It makes use of a truncated Fast Multiple Method(FMM)for short-range gravity,incorporating a Particle Mesh(PM)method for long-range potential,which is applied to deal with extremely large particle number.In this work,we present a specific strategy to modify a conventional FMM by a Gaussian shaped factor and provide quantitative expressions for the interaction kernels between multipole expansions.Moreover,a proper Multipole Acceptance Criterion for the hybrid method is introduced to solve potential precision loss induced by the truncation.Such procedures reduce the amount of computation compared to an original FMM and decouple the global communication.A simplified version of code is introduced to verify the hybrid algorithm,accuracy and parallel implementation.  相似文献   

16.
During the period 1966.5–2006.2 the 15GHz and 8GHz light curves of 3C 454.3 (z = 0.859) show a quasi-periodicity of ～12.8 yr (～6.9 yr in the rest frame of the source) with a double-bump structure. This periodic behaviour is interpreted in terms of a rotating double-jet model in which the two jets are created from the black holes of a binary system and rotating with the period of the orbital motion. The periodic variations in the radio fluxes of 3C 454.3 are suggested to be mainly due to the lighthouse effects (or the variation in Doppler boosting) of the precessing jets caused by the orbital motion. In addition, variations in the rate of mass accreting onto the black holes may be also involved.  相似文献   

17.
It has been suggested that Type Ia supernovae(SNe Ia) could be produced in the conditions of the violent merger scenario of the double-degenerate model, in which a thermonuclear explosion could be produced when a double carbon-oxygen white dwarf(CO WD) merges. It has been recently found that the nucleus of the bipolar planetary nebula Henize 2–428 consists of a double CO WD system that has a total mass of~1.76 M⊙, a mass ratio of~1 and an orbital period of~4.2 h, which is the first and only discovered progenitor candidate for an SN Ia predicted by the violent merger scenario. In this work, we aim to reproduce the evolutionary history of the central double CO WD of Henize 2–428. We find that the planetary nebula Henize 2–428 may originate from a primordial binary that has a~5.4 M⊙primary and a~2.7 M⊙secondary with an initial orbital period of~15.9 d. The double CO WD was formed after the primordial binary experienced two Roche-lobe overflows and two common-envelope ejection processes.According to our calculations, it takes about~840 Myr for the double CO WD to merge and form an SN Ia driven by gravitational wave radiation after their birth. To produce the current status of Henize 2–428,a large common-envelope parameter is needed. We also estimate that the rate of SNe Ia from the violent merger scenario is at most 2.9 × 10~(-4) yr~(-1), and that the delay time is in the range of~90 Myr to the Hubble time.  相似文献   

18.
The second phase of the Chang’E Program (also named Chang’E-3) has the goal to land and perform in-situ detection on the lunar surface. A VIS/NIR imaging spectrometer (VNIS) will be carried on the Chang’E-3 lunar rover to detect the distribution of lunar minerals and resources. VNIS is the first mission in history to perform in-situ spectral measurement on the surface of the Moon, the reflectance data of which are fundamental for interpretation of lunar composition, whose quality would greatly affect the accuracy of lunar element and mineral determination. Until now, in-situ detection by imaging spectrometers was only performed by rovers on Mars. We firstly review reflectance conversion methods for rovers on Mars (Viking landers, Pathfinder and Mars Exploration rovers, etc). Secondly, we discuss whether these conversion methods used on Mars can be applied to lunar in-situ detection. We also applied data from a laboratory bidirectional reflectance distribution function (BRDF) using simulated lunar soil to test the availability of this method. Finally, we modify reflectance conversion methods used on Mars by considering differences between environments on the Moon and Mars and apply the methods to experimental data obtained from the ground validation of VNIS. These results were obtained by comparing reflectance data from the VNIS measured in the laboratory with those from a standard spectrometer obtained at the same time and under the same observing conditions. The shape and amplitude of the spectrum fits well, and the spectral uncertainty parameters for most samples are within 8%, except for the ilmenite sample which has a low albedo. In conclusion, our reflectance conversion method is suitable for lunar in-situ detection.  相似文献   

19.
Blazars are characterized by large intensity and spectral variations across the electromagnetic spectrum It is believed that jets emerging from them are almost aligned with the line-of-sight. The majority of identified extragalactic sources in γ-ray catalogs of EGRET and Fermi are blazars. Observationally,blazars can be divided into two classes: flat spectrum radio quasars(FSRQs) and BL Lacs. BL Lacs usually exhibit lower γ-ray luminosity and harder power law spectra at γ-ray energies than FSRQs. We attempt to explain the high energy properties of FSRQs and BL Lacs from Fermi γ-ray space telescope observations. It was argued previously that the difference in accretion rates is mainly responsible for the large mismatch in observed luminosity in γ-ray. However, when intrinsic luminosities are derived by correcting for beaming effects, this difference in γ-ray luminosity between the two classes is significantly reduced. In order to explain this difference in intrinsic luminosities, we propose that spin plays an important role in the luminosity distribution dichotomy of BL Lacs and FSRQs. As the outflow power of a blazar increases with increasing spin of a central black hole, we suggest that the spin plays a crucial role in making BL Lac sources low luminous and slow rotators compared to FSRQ sources.  相似文献   

20.
We present details of a work aiming at the overestimation of Lyapunov exponents defined by the geodesic deviation equations in the previous work. The geodesic deviation vector with post-stabilization is used to compute the fast Lyapunov indicator, considered to be a very sensitive tool for discrimination between ordered or weakly chaotic motions. We make a detailed study of the dynamics in the superposed Weyl field between a black hole and shell of octopoles by using the fast Lyapunov indicator with the Poincare surface of section. In particular, we examine the effects on the dynamics around the fixed points, of varying one of the three parameters (specific energy E, specific angular momentum L and octopolar moment O), while keeping the other two fixed, and identify the intervals of the varying parameter where the motion is regular or chaotic.  相似文献   

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