共查询到20条相似文献，搜索用时 93 毫秒
1.
Diego F. Torres Shu Zhang Olaf Reimer Xavier Barcons Amalia Corral Valentí Bosch-Ramon Josep M. Paredes Gustavo E. Romero Jin Qu Werner Collmar Volker Schönfelder Yousaf Butt 《Astrophysics and Space Science》2007,309(1-4):17-21
The COMPTEL unidentified source GRO J 1411-64 was observed by INTEGRAL and XMM-Newton in 2005. The Circinus Galaxy is the
only source detected within the 4σ location error of GRO J1411-64, but in here excluded as the possible counterpart. At soft X-rays, 22 reliable and statistically
significant sources (likelihood >10) were extracted and analyzed from XMM-Newton data. Only one of these sources, XMMU J141255.6-635932,
is spectrally compatible with GRO J1411-64 although the fact the soft X-ray observations do not cover the full extent of the
COMPTEL source position uncertainty make an association hard to quantify and thus risky. At the best location of the source,
detections at hard X-rays show only upper limits, which, together with MeV results obtained by COMPTEL suggest the existence
of a peak in power output located somewhere between 300–700 keV for the so-called low state. Such a spectrum resembles those
in blazars or microquasars, and might suggest at work by the models accordingly. However, an analysis using a microquasar
model consisting on a magnetized conical jet filled with relativistic electrons, shows that it is hard to comply with all
observational constrains. This fact and the non-detection at hard X-rays introduce an a-posteriori question mark upon the
physical reality of this source, what is discussed here. 相似文献
2.
We report first evidence for a new unidentified and variable MeV source, located near the galactic plane at (l,b)∼(284.5°,
2.5°). The source, GRO J1036-55, is found at a significance level of ∼5.6σ by COMPTEL in its 3–10 MeV band. The energy spectrum indicates a spectral maximum at 3–4.3 MeV with a steep slope at higher
energies. Since the COMPTEL 3–4.3 MeV data contain contamination by an instrumental background line, we performed several
consistency checks, which all are consistent with an astrophysical nature of this emission feature. 相似文献
3.
Peter L. Gonthier Sarah A. Story Brian D. Clow Alice K. Harding 《Astrophysics and Space Science》2007,309(1-4):245-251
We present results of our pulsar population synthesis of normal and millisecond pulsars in the Galactic plane. 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 the simulated pulsars by assuming that they start with a random kick velocity
and then evolve through the Galactic potential. We use a polar cap/slot gap model for γ-ray emission from both millisecond and normal pulsars. 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 in order to constrain the viewing
geometry, we develop a model describing the ratio of radio core-to-cone peak fluxes. In this model, short period pulsars are
more cone-dominated than in our previous studies. We present the preliminary results of our recent study and the implications
for observing these pulsars with GLAST and AGILE.
相似文献
4.
Alice K. Harding Isabelle A. Grenier Peter L. Gonthier 《Astrophysics and Space Science》2007,309(1-4):221-230
Radio-quiet γ-ray pulsars like Geminga may account for a number of the unidentified EGRET sources in the Galaxy. The number of Geminga-like
pulsars is very sensitive to the geometry of both the γ-ray and radio beams. Recent studies of the shape and polarization of pulse profiles of young radio pulsars have provided
evidence that their radio emission originates in wide cone beams at altitudes that are a significant fraction (1–10%) of their
light cylinder radius. Such wide radio emission beams will be visible at a much larger range of observer angles than the narrow
core components thought to originate at lower altitude. Using 3D geometrical modeling that includes relativistic effects from
pulsar rotation, we study the visibility of such radio cone beams as well as that of the γ-ray beams predicted by slot gap and outer gap models. From the results of this study, one can obtain revised predictions
for the fraction of Geminga-like, radio quiet pulsars present in the γ-ray pulsar population.
相似文献
5.
Luigi Costamante 《Astrophysics and Space Science》2007,309(1-4):487-495
The study of the TeV emission from extragalactic sources is hindered by the uncertainties on the diffuse Extragalactic Background
Light (EBL). The recent H.E.S.S. results on the blazars 1ES 1101-232 and H 2356-309 represent a breakthrough on this issue.
Their unexpectedly hard spectra allow an upper limit to be derived on the EBL in the optical/near-infrared range, which is
very close to the lower limit given by the resolved galaxy counts. This result seems to exclude a large contribution to the
EBL from other sources (e.g. Population III stars) and indicates that the intergalactic space is more transparent to γ-rays than previously thought. A discussion of EBL absorption effects and further observational tests with Cherenkov telescopes
are presented.
For the H.E.S.S. collaboration. 相似文献
6.
In this paper, we investigate the dynamics of Born–Infeld (B–I) phantom model in the ω–ω′ plane, which is defined by the equation of state parameter for the dark energy and its derivative with respect to N (the logarithm of the scale factor a). We find the scalar field equation of motion in ω–ω′ plane, and show mathematically the property of attractor solutions which correspond to ω
φ
∼−1, Ω
φ
=1, which avoid the “Big rip” problem and meets the current observations well.
相似文献
7.
In this paper we have considered the Universe to be filled with Modified Gas and the Cosmological Constant Λ to be time-dependent
with or without the Gravitational Constant G to be time-dependent. We have considered various phenomenological models for Λ, viz.,
and
. Using these models it is possible to show the accelerated expansion of the Universe at the present epoch. Also we have shown
the natures of G and Λ over the total age of the Universe. Using the statefinder parameters we have shown the diagrammatical representation
of the evolution of the Universe starting from radiation era to ΛCDM model. 相似文献
8.
Multiwavelength observations of the two unidentified EGRET sources 3EG J0616-3310 and 3EG J1249-8330
N. La Palombara R. P. Mignani E. Hatziminaoglou M. Schirmer G. F. Bignami P. Caraveo 《Astrophysics and Space Science》2007,309(1-4):209-213
We report on the X-ray and optical observation of the two unidentified EGRET sources 3EG J0616-3310 and 3EG J1249-8330. The X-ray coverage performed by the ESA space telescope XMM–Newton provided ∼150 X-ray sources within each of the two γ-ray error-circles. The optical follow-up carried on with the Wide Field Imager at the ESO/MPG 2.2 m telescope have found no candidate counterpart for 125 of these X-ray sources. Among these, we have selected
9 sources with f
X/f
opt≥100, which we consider promising INS candidates. 相似文献
9.
There are indications now that globular clusters contain a large number of low magnetic field millisecond pulsars. Since millisecond
pulsars are expected to emit γ-rays due to curvature radiation, it is likely that globular clusters will themselves be sources
of γ-rays bright enough to be detectable by present day instruments. Using the expression derived by Scharlemann, Arons &
Fawley (1978) of the energy acquired by the electrons moving along the open magnetic field lines of the pulsars we have calculated
the likely luminosity of γ-rays from globular clusters. We discuss our results in the light of the calculations reported in
the literature based on some of the other models. 相似文献
10.
We discuss the implications of the recent X-ray and TeV γ-ray observations of the PSR B1259–63 system (a young rotation powered pulsar orbiting a Be star) for the theoretical models
of interaction of pulsar and stellar winds. We show that previously considered models have problems to account for the observed
behaviour of the system. We develop a model in which the broad band emission from the binary system is produced in result
of collisions of GeV–TeV energy protons accelerated by the pulsar wind and interacting with the stellar disk. In this model
the high energy γ-rays are produced in the decays of secondary neutral pions, while radio and X-ray emission are synchrotron and inverse Compton
emission produced by low-energy (≤100 MeV) electrons from the decays of secondary charged π
± mesons. This model can explain not only the observed energy spectra, but also the correlations between TeV, X-ray and radio
emission components.
相似文献
11.
We study variations of the lifetimes of high-ℓ solar p modes in the quiet and active Sun with the solar activity cycle. The lifetimes in the degree range ℓ=300 – 600 and ν=2.5 – 4.5 mHz were computed from SOHO/MDI data in an area including active regions and quiet Sun using the time – distance
technique. We applied our analysis to the data in four different phases of solar activity: 1996 (at minimum), 1998 (rising
phase), 2000 (at maximum), and 2003 (declining phase). The results from the area with active regions show that the lifetime
decreases as activity increases. The maximal lifetime variations are between solar minimum in 1996 and maximum in 2000; the
relative variation averaged over all ℓ values and frequencies is a decrease of about 13%. The lifetime reductions relative to 1996 are about 7% in 1998 and about
10% in 2003. The lifetime computed in the quiet region still decreases with solar activity, although the decrease is smaller.
On average, relative to 1996, the lifetime decrease is about 4% in 1998, 10% in 2000, and 8% in 2003. Thus, measured lifetime
increases when regions of high magnetic activity are avoided. Moreover, the lifetime computed in quiet regions also shows
variations with the activity cycle. 相似文献
12.
Sanjay Oli 《Astrophysics and Space Science》2008,314(1-3):89-94
This paper presents anisotropic, homogeneous two-fluid cosmological models in a Bianchi type I space–time with a variable
gravitational constant G and cosmological constant Λ. In the two-fluid model, one fluid represents the matter content of the universe and another fluid is chosen to model the
CMB radiation. We find a variety of solutions in which the cosmological parameter varies inversely with time t. We also discuss in detail the behavior of associated fluid parameters and kinematical parameters. This paper pictures cosmic
history when the radiation and matter content of the universe are in an interactive phase. Here, Ω is closing to 1 throughout
the cosmic evolution.
相似文献
13.
The concept of central configuration is important in the study of total collisions or the relative equilibrium state of a rotating system in the N-body problem. However, relatively few such configurations are known. Aided by a new global optimizer, we have been able to construct new families of coplanar central configurations having particles of equal mass, and extend these constructions to some configurations with differing masses and the non-coplanar case. Meyer and Schmidt had shown that a theorem of Palmore concerning coplanar central configurations was incorrect for N equal masses where 6 N 20 but presented a simple analytic argument only for N = 6. Using straightforward analytic arguments and inequalities we also disprove this theorem for 2N equal masses with N 3. 相似文献
14.
Alan Almeida santos 《Celestial Mechanics and Dynamical Astronomy》2004,90(3-4):213-238
We consider some questions on central configurations of five bodies in space. In the first one, we get a general result of
symmetry for the restricted problem of n+1 bodies in dimension n-1. After that, we made the calculation of all c.c. for n=4.
In our second result, we extend a theorem of symmetry due to [Albouy, A. and Libre, I.: 2002, Contemporary Math.
292, 1-16] on non-convex central configurations with 4 unit masses and an infinite central mass. We obtain similar results in
the case of a big, but finite central mass. Finally, we continue the study by [Schmidt, D.S.: 1988, Contemporary Math.
81 ] of the bifurcations of the configuration with four unit masses located at the vertices of a equilateral tetrahedron and
a variable mass at the barycenter. Using Liapunov-Schmidt reduction and a result on bifurcation equations, which appear in
[Golubitsley, M., Stewart, L. and Schaeffer, D.: 1988, Singularties and Groups in Bifurcation Theory, Vol. II, Springer-Verlag, New York], we show that there exist indeed seven families of central configurations close to a
regular tetrahedron parameterized by the value of central mass. 相似文献
15.
Amongst the sources seen in very high gamma-rays several are associated with Pulsar Wind Nebulae (“TeV plerions”). The study
of hard X-ray/soft gamma-ray emission is providing an important insight into the energetic particle population present in
these objects. The unpulsed emission from pulsar/pulsar wind nebula systems in the energy range accessible to the INTEGRAL satellite is mainly synchrotron emission from energetic and fast cooling electrons close to their acceleration site. Our
analyses of public INTEGRAL data of known TeV plerions detected by ground based Cherenkov telescopes indicate a deeper link between these TeV plerions
and INTEGRAL detected pulsar wind nebulae. The newly discovered TeV plerion in the northern wing of the Kookaburra region (G313.3+0.6
powered by the middle aged PSR J1420-6048) is found to have a previously unknown INTEGRAL counterpart which is besides the Vela pulsar the only middle aged pulsar detected with INTEGRAL. We do not find an INTEGRAL counterpart of the TeV plerion associated with the X-ray PWN “Rabbit” G313.3+0.1 which is possibly powered by a young pulsar. 相似文献
16.
A major legacy of the EGRET experiment aboard the Compton Gamma-Ray Observatory (CGRO) is the detection of a large number
of unidentified Gamma-ray sources. Out of the 271 EGRET sources are 170 not identified yet [Hartman et al. ApJS (123) (1999) 79]. To provide additional information on these unidentified EGRET sources, we derived simultaneous MeV fluxes
or flux limits for each source by analyzing the contemporaneous COMPTEL data. Then we compare these MeV fluxes to the extrapolations
of the published EGRET spectra. Our results can be grouped into 4 categories [Zhang et al. A&A (421) (2004) 983]: (1) non-constraining upper limits (∼120 sources), (2) hints (> 2 sigma) or detections with consistent
MeV fluxes (∼16 sources), (3) enhanced MeV emission (2 sources), and (4) constraining MeV flux limits, requiring a spectral
break (∼22 sources). In summary, for about 40 of the unidentified EGRET sources we can provide supplementary spectral information
in the neighboring gamma-ray band, which – together with other source parameters – might provide clues to the underlying source
nature. 相似文献
17.
Du Jiulin 《Astrophysics and Space Science》2007,312(1-2):47-55
By a natural nonextensive generalization of the conservation of energy in the q-kinetic theory, we study the nonextensivity and the power-law distributions for the many-body systems with the self-gravitating
long-range interactions. It is shown that the power-law distributions describe the long-range nature of the interactions and
the non-local correlations within the self-gravitating system with the inhomogeneous velocity dispersion. A relation is established
between the nonextensive parameter q≠1 and the measurable quantities of the self-gravitating system: the velocity dispersion and the mass density. Correspondingly,
the nonextensive parameter q can be uniquely determined from the microscopic dynamical equation and thus the physical interpretation of q different from unity can be clearly presented. We derive a nonlinear differential equation for the radial density dependence
of the self-gravitating system with the inhomogeneous velocity dispersion, which can correctly describe the density distribution
for the dark matter in the above physical situation. We also apply this q-kinetic approach to analyze the nonextensivity of self-gravitating collisionless systems and self-gravitating gaseous dynamical
systems, giving the power-law distributions the clear physical meaning.
相似文献
18.
We derive general results on the existence of stationary configurations for N co-orbital satellites with small but otherwise arbitrary masses m
i
, revolving on circular and planar orbits around a massive primary. The existence of stationary configurations depends on
the parity of N. If N is odd, then for any arbitrary angular separation between the satellites, there always exists a set of masses (positive or
negative) which achieves stationarity. However, physically acceptable solutions (m
i
> 0 for all i) restrict this existence to sub-domains of angular separations. If N is even, then for given angular separations of the satellites, there is in general no set of masses which achieves stationarity. The case N=3 is treated completely for small arbitrary satellite masses, giving all the possible solutions and their stability, to within
our approximations. 相似文献
19.
P. N. Bhat P. V. Ramana Murthy P. R. Vishwanath 《Journal of Astrophysics and Astronomy》1988,9(3):155-160
Cygnus X-3, an X-ray binary with an orbital period 4.8 hr was seen to be emitting γ-rays with the same period at TeV energies
by several groups. In addition the Durham group (Chadwicket al. 1985) published their observations on the existence of a pulsar in the Cyg X-3 system, emitting TeV γ-rays with a periodicity
of approximately 12.6 ms. We observed this object during 1986 October-November and did not detect any pulsed emission of TeV
γ-rays in the range of periods from 12.5850 to 12.5967 ms. 相似文献
20.
A. G. Aksenov 《Astronomy Letters》2002,28(8):553-559
We consider the problem of strange-star (SS) radiation. The bare quark SS surface and electrons on the stellar surface generate an electric field that is strong enough for electron-positron pairs to be produced from a vacuum at a nonzero temperature. The luminosity in pairs is assumed to be within ?1049 erg s?1 from a surface with a characteristic radius of 10 km. We consider the energy transfer from pairs to photons by taking into account the well-studied reactions between e, e +, γ and obtain a change in the photon spectrum with luminosity. Our analysis is restricted to the spherically symmetric case. The magnetic field is disregarded. To solve the problem, we developed a new numerical method of integrating the Boltzmann kinetic equations for pairs and photons. This method is used to calculate the problem up to a luminosity of 1042 erg s?1 This region is difficult to investigate when the optical path for pairs or photons is considerably larger than unity but the two optical depths are not simultaneously much larger than unity (when hydrodynamics with heat conduction is applicable). It turns out that the mean photon energy is approximately equal to $\bar \in _\gamma \approx m_e c^2$ (the annihilation line for pairs) at a modest luminosity, L?1×1037 erg s?1, and decreases to ≈210 keV at L?1038 erg s?1. Hydrodynamic estimates point to an increase in the mean energy $\bar \in _\gamma$ to 1 MeV as the luminosity further increases to L?1049 erg s?1. Our calculations may prove to be useful in interpreting soft gamma repeaters (SGRs) and are of methodological interest. 相似文献