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arXiv2003

Spectral properties of anomalous X-ray pulsars

In this paper, the spectra of the persistent emission from anomalous X-ray pulsars (AXPs) and their variation with spin-down rate $\dotΩ$ is considered. Firstly, based on an accretion-powered model, the influences of both magnetic field and mass accretion rate on the spectra properties of AXPs are addressed. Subsequently, the relation between the spectral property of AXPs and mass accretion rate $\dot{M}$ is investigated. The result shows that there exists a linear correlation between the photon index and mass accretion rate, and the spectral hardness increases with increasing $\dot{M}$. A possible emission mechanism for the explanation of spectral properties of AXPs is also discussed.

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arXiv2004

Intrinsic spectra and energetics of cosmological Gamma-Ray Bursts

We extend a previous work on the intrinsic spectral properties and energetics of GRBs with known redshift based on 12 BeppoSAX events by including in the sample a total of 10 more events detected either by BATSE, BeppoSAX or HETE-2. An indication of a trend of the total isotropic equivalent radiated energy, E_rad, with redshift is found and, remarkably, the previously found relationship between the peak energy of the rest-frame nuFnu spectrum, E_p,rest , and E_rad is confirmed and its significance increased. The implications of these results are briefly discussed in the framework of standard models for the prompt emission of GRBs.

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arXiv2005

GRBs-SN and SGR-X-Pulsar as blazing Jets

Old and recent puzzles of GRBs and SGRs find a solution with a model based on the fast blazing of very collimated thin gamma Jets. Damped oscillating afterglows in GRB030329 find a natural explanation assuming a very thin Jet whose persistent activity and different angle of view maybe combined at once with the Supernovae power and the apparent huge GRBs output. The same thin beaming offer an understanding of the apparent SGR-Pulsar power connection. A thin collimated precessing Gamma Jet model for both GRBs and SGRs, at their different scaled luminosity (10^{44} - 10^{38}erg s^-1), explains the existence of few identical energy spectra and time evolution of these sources leading to a unified model. Their similarity with the huge precessing Jets in AGN, QSRs and Radio-Galaxies inspires this smaller scale SGR-GRB model. The spinning-precessing Jet explains the rare mysterious X-Ray precursors in GRBs and SGRs events. Any large Gamma Jet off-axis beaming to the observer might lead to the X-Flash events without any GRB signals, as the most recent XRF030723. Its possible re-brightening would confirm the evidence of the variable pointing of the jet in or off line towards the observer. Indeed a multi-precessing Jet at peak activity in all bands may explain the puzzling X or optical re-brightening bumps found in the GRB 021004, GRB030329 and the SGR 1900+ 14 on 27 August 1998 and once again on the 18 April 2001. Rarest micro-quasars neutron star in our galaxy as SS433, and Herbig Haro objects and Cir-X-1 describe these thin precessing Jet imprints in the spectacular shapes of their relic nebulae.

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arXiv2004

Muon and Tau Neutrinos Spectra from Solar Flares

Solar neutrino flares and mixing are considered. Most power-full solar flare as the ones occurred on 23th February 1956, September 29th 1989, 28th October and on 2nd-4th November 2003 are sources of cosmic rays, X, gamma and neutrino bursts. These flares took place both on front or in the edge and in the hidden solar disk. The observed and estimated total flare energy should be a source of a prompt secondary neutrino burst originated, by proton-proton-pion production on the sun itself; a more delayed and spread neutrino flux signal arise by the solar charged flare particles reaching the terrestrial atmosphere. Our first estimates of neutrino signals in largest underground detectors hint for few events in correlation with, gamma,radio onser. Our approximated spectra for muons and taus from these rare solar eruption are shown over the most common background. The muon and tau signature is very peculiar and characteristic over electron and anti-electron neutrino fluxes. The rise of muon neutrinos will be detectable above the minimal muon threshold of 113 MeV. The rarest tau appearence will be possible only for hardest solar neutrino energies above 3.471 GeV

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arXiv2003

Color-redshift Relations and Photometric Redshift Estimations of Quasars in Large Sky Surveys

With a recently constructed composite quasar spectrum and the χ^2 minimization technique, we demonstrated a general method to estimate the photometric redshifts of a large sample of quasars by deriving the theoretical color-redshift relations and comparing the theoretical colors with the observed ones. We estimated the photometric redshifts from the 5-band SDSS photometric data of 18678 quasars in the first major data release of SDSS and compare them with the spectroscopic redshifts. The redshift difference is smaller than 0.1 for 47% of quasars and 0.2 for 68 % of them. Based on the calculation of the theoretical color-color diagrams of stars, galaxies and quasars in both the SDSS and BATC photometric systems, we expected that with the BATC system of 15 intermediate filters we would be able to select candidates of high redshift quasars more efficiently than in the SDSS, provided the BATC survey could detect objects with magnitude fainter than 21.

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arXiv2003

Difference of $α$-disks between Seyfert 1 galaxies and Quasars

In a previous paper (Bian & Zhao 2002), it was suggested that contamination to the luminosity of galactic nucleus from the host galaxies play an important role in determining parameters of the standard $α$ disk for AGNs. Using the nuclear absolute B band magnitude instead of the total absolute B band magnitude, the central black hole masses, the accretion rates and the disk inclinations to the line of sight for 20 Seyfert 1 galaxies and 17 Palomar-Green (PG) quasars were recalculated. It was found that small value of $α$ is needed in the accretion disk for Seyfert 1 galaxies compared with PG quasars. The difference of $α$ maybe lead to the different properties between Seyfert 1 galaxies and Quasars. Furthermore, we found most of the objects in this sample are not accreting at super-Eddington rates when we adopted the nuclear optical luminosity in our calculation.

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arXiv2003

New analysis in the field of open cluster Collinder 223

The present study of the open cluster Collinder 223 (Cr 223) has been mainly depended on the photoelectric data of Claria & Lapasset (1991; hereafter CL91). This data of CL91 has been used with the cluster's image of AAO-DSS in order to re-investigate and improve the main parameters of Cr 223. Stellar count has been achieved to determine the stellar density, the cluster's center and the cluster's diameter. In addition, the luminosity function, mass function, and the total mass of the cluster have been estimated.

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arXiv2004

The amplitude of mass fluctuations and mass density of the Universe constrained by strong gravitational lensing

We investigate the linear amplitude of mass fluctuations in the universe, $σ_8$, and the present mass density parameter of the Universe, $Ω_\mathrm{m}$, from the statistical strong gravitational lensing. We use the two populations of lens halos model with fixed cooling mass scale $M_\mathrm{c}=3\times 10^{13}h^{-1}M_{\sun}$ to match the observed lensing probabilities, and leave $σ_8$ or $Ω_\mathrm{m}$ as a free parameter to be constrained by data. Another varying parameter is the equation of state of dark energy $ω$, and its typical values of -1, -2/3, -1/2 and -1/3 are investigated. We find that $σ_8$ is degenerate with $Ω_\mathrm{m}$ in a way similar to that suggested by present day cluster abundance as well as cosmic shear lensing measurements: $σ_8Ω_\mathrm{m}^{0.6}\approx 0.33$ (Bahcall & Bode\cite{bahcall03a} and references therein). However, both $σ_8\leq 0.7$ and $Ω_\mathrm{m}\leq 0.2$ can be safely ruled out, the best value is when $σ_8=1.0$, $Ω_\mathrm{m}=0.3$ and $ω=-1$. This result is different from that obtained by Bahcall & Bode (\cite{bahcall03a}), who gives $σ_8 =0.98\pm 0.1$ and $Ω_m =0.17\pm 0.05$. For $σ_8=1.0$, higher value of $Ω_\mathrm{m}=0.35$ requires $ω=-2/3$ and $Ω_\mathrm{m}=0.40$ requires $ω=-1/2$.

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arXiv2004

Thermal Bremsstrahlung Radiation in a Two-Temperature Plasma

In the normal one-temperature plasma the motion of ions is usually neglected when calculating the Bremsstrahlung radiation of the plasma. Here we calculate the Bremsstrahlung radiation of a two-temperature plasma by taking into account of the motion of ions. Our results show that the total radiation power is always lower if the motion of ions is considered. We also apply the two-temperature Bremsstrahlung radiation mechanism for an analytical Advection-Dominated Accretion Flow (ADAF) model; we find the two-temperature correction to the total Bremsstrahlung radiation for ADAF is negligible.

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arXiv2004

UBVI Surface Photometry of the Spiral Galaxy NGC 300 in the Sculptor Group

We present UBVI surface photometry for 20.'5 X 20.'5 area of a late-type spiral galaxy NGC 300. In order to understand the morphological properties and luminosity distribution characteristics of NGC 300, we have derived isophotal maps, surface brightness profiles, ellipticity profiles, position angle profiles, and color profiles. By merging the I-band data of our surface brightness measurements with those of Boeker et al. (2002) based on Hubble Space Telescope observations, we have made combined I-band surface brightness profiles for the region of 0."02 < r < 500" and decomposed the profiles into three components: a nucleus, a bulge, and an exponential disk.

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arXiv2004

Afterglow Light Curves of Jetted Gamma-ray Burst Ejecta in Stellar Winds

Optical and radio afterglows arising from the shocks by relativistic conical ejecta running into pre-burst massive stellar winds are revisited. Under the homogeneous thin-shell approximation and a realistic treatment for the lateral expansion of jets, our results show that a notable break exists in the optical light curve in most cases we calculated in which the physical parameters are varied within reasonable ranges. For a relatively tenuous wind which cannot decelerate the relativistic jet to cause a light curve break within days, the wind termination shock due to the ram pressure of the surrounding medium occurs at a small radius, namely, a few times 10^{17} cm. In such a structured wind environment, the jet will pass through the wind within several hours and run into the outer uniform dense medium. The resulting optical light curve flattens with a shallower drop after the jet encounters the uniform medium, and then declines deeply, triggered by runaway lateral expansion.

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arXiv2004

Global axisymmetric stability analysis for a composite system of two gravitationally coupled scale-free discs

In a composite system of gravitationally coupled stellar and gaseous discs, we perform linear stability analysis for axisymmetric coplanar perturbations using the two-fluid formalism. The background stellar and gaseous discs are taken to be scale-free with all physical variables varying as powers of cylindrical radius $r$ with compatible exponents. The unstable modes set in as neutral modes or stationary perturbation configurations with angular frequency $ω=0$.

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arXiv2004

Timescale Analysis of Spectral Lags

A technique for timescale analysis of spectral lags performed directly in the time domain is developed. Simulation studies are made to compare the time domain technique with the Fourier frequency analysis for spectral time lags. The time domain technique is applied to studying rapid variabilities of X-ray binaries and $γ$-ray bursts. The results indicate that in comparison with the Fourier analysis the timescale analysis technique is more powerful for the study of spectral lags in rapid variabilities on short time scales and short duration flaring phenomena.

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arXiv2005

Polarization in Gamma-Ray Bursts Produced by Pinch Discharge

Large-voltage and high-temperature plasma columns produced by pinch discharge can generate gamma-ray flashes with energy spectra and spectral evolution consistent with that observed in gamma-ray bursts (GRBs). The inverse Compton scattering (ICS) during the discharge process can produce high linear polarization. The calculation indicates that the observed polarization depends on the angle between the observer's line-of-sight to the GRB and the direction of the pinch discharge, but only weakly depends on observed gamma-ray energy.

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arXiv2005

Particle acceleration in astrophysical shear flows

We consider the acceleration of particles due to a velocity shear in relativistic astrophysical flows. The basic physical picture and the formation of power law momentum spectra is discussed for a non-relativistic velocity field using a microscopic approach. We identify possible sites for shear acceleration in relativistic astrophysical jets and analyze their associated acceleration timescales. It is shown in particular that for a mean scattering time $τ$ scaling with the gyro-radius, the acceleration timescale for gradual shear scales in the same manner as the synchrotron cooling timescale, so that losses may no longer be able to stop the acceleration once it has started to work efficiently. Finally, the possible role of shear acceleration is discussed with reference to the relativistic jet in the quasar 3C~273.

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arXiv2004

Outflows and inflows in astrophysical systems

We seek for self-similar solutions describing the time-dependent evolution of self-gravity systems with either spherical symmetry or axisymmetric disk geometry. By assuming self-similar variable $x\equiv r/at$ where $a$ is isothermal sound speed we find self-similar solutions extending from the initial instant $t=0$ to the final stage $t\to \infty$ using standard semi-analytical methods. Different types of solutions are constructed, which describe overall expansion or collapse, envelope expansion with core collapse (EECC), the formation of central rotationally supported quasi-equilibrium disk as well as shocks. Though infinitely many, these self-similarity solutions have similar asymptotic behaviors which may impose diagnosis on the velocity and density structures in astrophysical systems.

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arXiv2004

Microquasar models for 3EG J1828+0142 and 3EG J1735-1500

Microquasars are promising candidates to emit high-energy gamma-rays. Moreover, statistical studies show that variable EGRET sources at low galactic latitudes could be associated with the inner spiral arms. The variable nature and the location in the Galaxy of the high-mass microquasars, concentrated in the galactic plane and within 55 degrees from the galactic center, give to these objects the status of likely counterparts of the variable low-latitude EGRET sources. We consider in this work the two most variable EGRET sources at low-latitudes: 3EG J1828+0142 and 3EG J1735-1500, proposing a microquasar model to explain the EGRET data in consistency with the observations at lower energies (from radio frequencies to soft gamma-rays) within the EGRET error box.

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arXiv2004

Helical motion and the origin of QPO in blazar-type sources

Recent observations and analysis of blazar sources provide strong evidence for (i) the presence of significant periodicities in their lightcurves and (ii) the occurrence of helical trajectories in their radio jets. In scenarios, where the periodicity is caused by differential Doppler boosting effects along a helical jet path, both of these facts may be naturally tied together. Here we discuss four possible driving mechanisms for the occurrence of helical trajectories: orbital motion in a binary system, Newtonian-driven jet precession, internal jet rotation and motion along a global helical magnetic field. We point out that for non-ballistic helical motion the observed period may appear strongly shortened due to classical travel time effects. Finally, the possible relevance of the above mentioned driving mechanisms is discussed for Mkn~501, OJ 287 and AO 0235+16.

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