Neutron star high mass binaries as the origin of SGR/AXP

A close high-mass binary system consisting of a neutron star (NS) and a massive OB supergiant companion is expected to lead to a TZO structure, which consists of a NS core and a stellar envelope. We use the scenario machine program to calculate the formation tracks of TZOs in close high mass NS binaries and their subsequent evolution. We propose and demonstrate that the explosion and instant contraction of a TZO structure leave its stellar remnant as a soft gamma ray repeater and an anomalous X-ray pulsar respectively.Comment: This paper has been withdrawn by the author due to new calculations to be performe

RXTE Observation of PSR B0656+14

PSR B0656+14 was observed by the {\it Rossi X-ray Timing Explorer (RXTE)} with the proportional counter array (PCA) and the high-energy x-ray timing experiment (HEXTE) for 160 ksec during August 22 -- September 3, 1997. No pulsation was firmly found in the timing analysis, in which the contemporaneous radio ephemeris and various statistical tests were applied for searching evidence of pulsation. A marginal detection of pulsation at a confidence level of 95.5% based on the $H$-test was found with data in the whole HEXTE energy band. In the energy band of 2-10 keV the {\it RXTE} PCA upper limits are about one order of magnitude lower than that from {\it ASCA} GIS data. If the {\it CGRO} EGRET detection of this pulsar is real, considering the common trait that most EGRET-detected pulsars have a cooling spectrum in hard x-ray and gamma ray energy bands, the estimated {\it RXTE} upper limits indicate a deviation (low-energy turn-over) from a cooling spectrum starting from 20 keV or higher. It in turn suggests an outer-magnetospheric synchrotron-radiation origin for high-energy emissions from PSR B0656+14. The {\it RXTE} PCA upper limits also suggest that a reported power-law component based on {\it ASCA} SIS data in 1-10 keV fitted jointly with {\it ROSAT} data, if real, should be mainly unpulsed.Comment: 10 pages, LaTeX (aaspp4.sty), figures (eps) included. To appear in ApJ 501 on Jan. 1, 199

Effects of Turbulent Viscosity on A Rotating Gas Ring Around A Black Hole: Results in Numerical Simulation

In this paper, we present the time evolution of a rotationally axisymmetric gas ring around a non rotating black hole using two dimensional grid-based hydrodynamic simulation. We show the way in which angular momentum transport is included in simulations of non-self-gravitating accretion of matter towards a black hole. We use the Shakura-Sunyaev {\alpha} viscosity prescription to estimate the turbulent viscosity for all major viscous stress tensors. We investigate how a gas ring which is initially assumed to rotate with Keplerian angular velocity is accreted on to a black hole and hence forms accretion disc in the presence of turbulent viscosity. We show that the centrifugal pressure supported sub-Keplerian flow with shocks forms when the ring starts to disperse with inclusion of relatively small amount of viscosity. But, if the viscosity is above the critical value, the shock disappears altogether and the whole disc becomes Kepleiran which is subsonic everywhere except in a region close to the horizon, where it supersonically enters to the black hole. We discovered a multiple valued Mach number solution and the corresponding density distributions that connects matter (a) from the initial Keplerian gas ring to a sub-Keplerian disc with shocks in presence of small amount of viscosity and (b) from the sub-Keplerian flow to a Keplerian disc in presence of huge amount of viscosity. We calculate the temporal variations of the magnitude of various time scales which ensure us about the stability of the flow.Comment: 8 pages, 7 figs, Accepted for Publication in AN. arXiv admin note: text overlap with arXiv:1307.3635, arXiv:1210.3515 by other author

Neptune migration model with one extra planet

We explore conventional Neptune migration model with one additional planet of mass at 0.1-2.0 Me. This planet inhabited in the 3:2 mean motion resonance with Neptune during planet migration epoch, and then escaped from the Kuiper belt when Jovian planets parked near the present orbits. Adding this extra planet and assuming the primordial disk truncated at about 45 AU in the conventional Neptune migration model, it is able to explain the complex structure of the observed Kuiper belt better than the usual Neptune migration model did in several respects. However, numerical experiments imply that this model is a low-probability event. In addition to the low probability, two features produced by this model may be inconsistent with the observations. They are small number of low-inclination particles in the classical belt, and the production of a remnant population with near-circular and low-inclination orbit within a = 50-52 AU. According to our present study, including one extra planet in the conventional Neptune migration model as the scenario we explored here may be unsuitable because of the low probability, and the two drawbacks mentioned above, although this model can explain better several features which is hard to produce by the conventional Neptune migration model. The issues of low-probability event and the lack of low-inclination KBOs in the classical belt are interesting and may be studied further under a more realistic consideration.Comment: 42 pages, 12 figure

Quasi-quantized Disk Structure around Rotating Neutron Stars

In accreting neutron star (NS) low-mass X-ray binary (LMXB) systems, NS accretes material from its low-mass companion via a Keplerian disk. In a viscous accretion disk, inflows orbit the NS and spiral in due to dissipative processes, such as the viscous process and collisions of elements. The dynamics of accretion flows in the inner region of an accretion disk is significantly affected by the rotation of NS. The rotation makes NS, thus the space-time metric, deviate from the originally spherical symmetry, and leads to gravitational quadrupole, on one hand. On the other hand, a rotating NS drags the local inertial frame in its vicinity, which is known as the rotational frame-dragging effect. In this paper, {\bf we investigate the orbital motion of accretion flows of accreting NS/LMXBs and demonstrate that the rotational effects of NS result in a band of quasi-quantized structure in the inner region of the accretion disk, which is different, in nature, from the scenario in the strong gravity of black hole arising from the resonance for frequencies related to epicyclic and orbital motions. We also demonstrate that such a disk structure may account for frequencies seen in X-ray variability, such as quasi-periodic oscillations, and can be a potential promising tool of investigation for photon polarization.Comment: 6 pages, no figure, Accepted by IJMP

Hunting for Gravitational Waves with Massive Gravitons from Inspiralling Double Neutron Star Systems with Pulsar Clocks

Pulsars, especially millisecond pulsars, are intrinsically very stable celestial clocks, and their great pulse period stability open up a wide range of potential applications to astronomical phenomena, such as a natural detector for very low frequency ($10^{-7}-10^{-9}$ Hz) gravitational waves (GWs) background from supermassive black hole binaries. Double neutron star (DNS) binary systems, containing one or two radio pulsars, lose orbital energy by gravitational radiation, which leads to the orbital shrink. As a result, two neutron stars get closer and closer, during which it contributes to the emission of high frequency GWs of $1-10^4$ Hz. In this paper, we investigate the frequency shift of pulse signal for radio pulsars in DNS system that is induced by the emission of GWs from the system. We point out that the pulse frequency shift of radio signal in these systems can be a potential tool to hunt for the high-frequency GWs, with massive gravitons, from DNS systems, which resorts to a temporal shift of gravitational constant $\delta G(t)/G$. The sensitivity to high-frequency GWs from DNS by radio pulse frequency shift is discussed. The correlation between timing residuals of pulsar pair in double radio pulsars, such as the system PSR 0737-3039 A(B), is also considered.Comment: This paper has been withdrawn by the author due to an error in eq, (7

Periodicity Search of Possible X-ray Counterparts to Radio-quiet Gamma-ray Pulsar Candidates

Periodicity search in gamma-ray data is usually difficult because of the small number of detected photons. A periodicity in the timing signal at other energy bands from the counterpart to the gamma-ray source may help to establish the periodicity in the gamma-ray emission and strengthen the identification of the source in different energy bands. It may, however, still be difficult to find the period directly from X-ray data because of limited exposure. We developed a procedure, by cross-checking two X-ray data sets, to find candidate periods for X-ray sources which are possible counterparts to gamma-ray pulsar candidates. Here we report the results of this method obtained with all the currently available X-ray data of 8 X-ray sources. Some tempting periodicity features were found. Those candidate periods can serve as the target periods for future search when new data become available so that a blind search with a huge number of trials can be avoided.Comment: 7 pages, 6 figures and 2 table

The power-law component of the X-ray emissions from pulsar wind nebulae and their pulsars

To look for possible phenomenological connections between pulsar's timing properties and emissions from pulsar wind nebulae and their pulsars, we studied the power-law component of the X-ray emissions from 35 pulsar wind nebulae which have a detected pulsar in X-rays. Our major results are in the following: (1) The power-law component of the X-ray luminosities, in the energy range from 0.5 keV to 8 keV, of the nebulae and of the pulsar both show a strong correlation with the pulsar spin-down power ($\dot{E}$), consistent with earlier studies. However, equally significant correlations with the magnetic field strength at the light cylinder ($B_{\rm lc}$) are also found. The similar significance level of the correlations with $\dot{E}$ and with $B_{\rm lc}$ suggests that not only $\dot{E}$ but also $B_{\rm lc}$ plays an important role in understanding these power-law emissions. (2) Thermal X-ray emissions are detected in 12 pulsars among the 35 samples. With derived temperature as one additional variable, we found that the photon indices of pulsar's non-thermal X-ray power-law spectra can be well described by a linear function of $\log P$, $\log\dot{P}$ and temperature logarithm $\log T$. It indicates that the surface temperature of neutron stars plays an important role in determining the energy distribution of the radiating pair plasma in pulsar's magnetospheres.Comment: 10 pages, 5 figures, accepted for publication in MNRA

Launching and Quenching of Black Hole Relativistic Jets at Low Accretion Rate

Relativistic jets are launched from black hole (BH) X-ray binaries and active galactic nuclei when the disk accretion rate is below a certain limit (i.e., when the ratio of the accretion rate to the Eddingtion accretion rate, $\dot{m}$, is below about 0.01) but quenched when above. We propose a new paradigm to explain this observed coupling between the jet and the accretion disk by investigating the extraction of the rotational energy of a BH when it is surrounded by different types of accretion disk. At low accretion rates (e.g., when $\dot{m}\lesssim0.1$), the accretion near the event horizon is quasi-spherical. The accreting plasmas fall onto the event horizon in a wide range of latitudes, breaking down the force-free approximation near the horizon. To incorporate the plasma inertia effect, we consider the magnetohydrodynamical (MHD) extraction of the rotational energy from BHs by the accreting MHD fluid, as described by the MHD Penrose process. It is found that the energy extraction operates, and hence a relativistic jet is launched, preferentially when the accretion disk consists of an outer Shakura-Sunyaev disk (SSD) and an inner advection-dominated accretion flow. When the entire accretion disk type changes into an SSD, the jet is quenched because the plasmas brings more rest-mass energy than what is extracted from the hole electromagnetically to stop the extraction. Several other observed BH disk-jet couplings, such as why the radio luminosity increases with increasing X-ray luminosity until the radio emission drops, are also explained.Comment: Accepted for publication in the Astrophysical Journal. 17pages, 9 figure

Upper limits to the number of Oort Cloud Objects based on serendipitous occultation events search in X-rays

Using all the RXTE archival data of Sco X-1 and GX 5-1, which amount to about 1.6 mega seconds in total, we searched for possible occultation events caused by Oort Cloud Objects. The detection efficiency of our searching approach was studied with simulation. Our search is sensitive to object size of about 300 m in the inner Oort Cloud, taking 4000 AU as a representative distance, and of 900 m in the outer Oort Cloud, taking 36000 AU as the representative distance. No occultation events were found in the 1.6 Ms data. We derived upper limits to the number of Oort Cloud Objects, which are about three orders of magnitude higher than the highest theoretical estimates in the literature for the inner Oort Cloud, and about six orders higher for the outer Oort Cloud. Although these upper limits are not constraining enough, they are the first obtained observationally, without making any model assumptions about comet injection. They also provide guidance to such serendipitous occultation event search in the future.Comment: 10 pages, 6 figures, 3 tables, accepted on 2016 July 19 to publish in MNRA