共查询到20条相似文献，搜索用时 31 毫秒
1.
The result of the search for, and the observations of radio emission from two groups of isolated neutron stars: AXP 1E 2259+586
and XDINS 1RXS J1308.6+212708 and 1RXS J214303.7+065419 are reported. The observations were carried out on two sensitive transit
radio telescopes at a few frequencies in the range 42–112 MHz. The flux densities, mean pulse profiles, as well as, the estimation
of the dispersion measures, distances and integrated radio luminosities of all objects are presented. Comparison with X-ray
data shows large differences in the mean pulse widths and luminosities.
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2.
R. N. Manchester 《Journal of Astrophysics and Astronomy》1995,16(2):107-117
Observations of mean or average pulse profiles and their polarization give us much information on the shape of pulsar beams.
The observed polarization variations, profile symmetry and frequency dependence of profile shape strongly suggest that the
emission beam is conical and emitted from the vicinity of a magnetic pole. Central and outer parts of the beam have somewhat
different properties, but the evidence is that they are emitted by the same basic mechanism. Recent observations suggest that
the highly polarized pulse components seen in young pulsars may be emitted at a large angle to the magnetic axis. 相似文献
3.
Polarization observations of 66 southern pulsars 总被引：1，自引：0，他引：1
R. N.Manchester J. L.Han G. J.Qiao 《Monthly notices of the Royal Astronomical Society》1998,295(2):280-298
Mean pulse profiles and polarization parameters at 435, 660 or 1500 MHz obtained using the ATNF Parkes radio telescope are presented for 66 southern pulsars. About half of these pulsars were discovered in the Parkes southern pulsar survey and most have no previously published polarization parameters. Where possible, beam impact parameters and inclination angles are computed assuming a circular beam geometry and the rotating-vector model. Implications of the results for models of the pulse emission mechanism are briefly discussed. 相似文献
4.
We examine the problem related to the scattering of a solar radio pulse in a turbulent coronal plasma, taking into account
strong regular refraction. Based on an integral representation of the wave field as an interference integral, we analyze the
distortions of the mean profile of the radio pulse in spike events, for the case of the sources located in high coronal arches.
It is shown that strong regular refraction of radio emission in the coronal arch plays an important role for pulse structuring
during spike events. 相似文献
5.
6.
The dynamics of an electron beam is considered when the initial electron distribution is localized in a space region. Analysis is conducted for the parameters of the beam and plasma that give radio emission. We demonstrate both numerically and analytically that beam electrons propagate as a beam-plasma structure at large distances. The speed of the beam-plasma structure is equal to half of the maximum velocity of the electrons involved in this structure. The structure conserves the shape of the initial spatial distribution of electrons. A plateau with a constant maximum velocity is formed at the electron distribution function in each spatial point. 相似文献
7.
Extensive air showers, induced by high energy cosmic rays impinging on the Earth’s atmosphere, produce radio emission that is measured with the LOFAR radio telescope. As the emission comes from a finite distance of a few kilometers, the incident wavefront is non-planar. A spherical, conical or hyperbolic shape of the wavefront has been proposed, but measurements of individual air showers have been inconclusive so far. For a selected high-quality sample of 161 measured extensive air showers, we have reconstructed the wavefront by measuring pulse arrival times to sub-nanosecond precision in 200 to 350 individual antennas. For each measured air shower, we have fitted a conical, spherical, and hyperboloid shape to the arrival times. The fit quality and a likelihood analysis show that a hyperboloid is the best parameterization. Using a non-planar wavefront shape gives an improved angular resolution, when reconstructing the shower arrival direction. Furthermore, a dependence of the wavefront shape on the shower geometry can be seen. This suggests that it will be possible to use a wavefront shape analysis to get an additional handle on the atmospheric depth of the shower maximum, which is sensitive to the mass of the primary particle. 相似文献
8.
Fast electrons in the solar atmosphere are detected by their hard X-ray bremsstrahlung and by type III radio bursts caused
by ‘bump-on-tail’ plasma wave generation. This paper investigates empirically the effect of wave generation on the HXR spectrum.
Purely collisional propagation of an electron beam generates a bump in the distribution function, due to stopping of low-velocity
electrons. The consequent positive gradient means there is a possibility of wave generation, production of type III radio
bursts, and energy redistribution of the electron beam. We have represented this relaxation parametrically and calculated
the global bremsstrahlung HXR emission spectrum. We show that for a range of relaxed forms, with different local electron
spectral shapes, the bremsstrahlung spectrum integrated over the whole target is identical in shape to the purely collisionally
evolved beam. Our results show that spatially integrated HXR spectral measurements would be unable to distinguish between
the presence or absence of relaxation effects. Only spatially resolved hard X-ray spectra, such as anticipated from the HESSI
mission, will be able to remove this ambiguity in HXR diagnostics of beam relaxation. 相似文献
9.
Li-Ming Dou Wei-Min Yuan 《中国天文和天体物理学报》2008,8(6)
We report on our results of X-ray spectral analysis for a sample of radio-loud quasars covering a wide range of the radio core-dominance parameter, R, from core-dominated to lobe-dominated objects, using data obtained mostly with the XMM-Newton Observatory. We find that the spectral shape of the underlying power-law continuum is flat even for the lobe-dominated objects (average photon index ～ 1.5), indistinguishable from that of core-dominated quasars. For lobe-dominated objects, contribution of X-rays from the jets is expected to be very small based on previous unification schemes, more than one order of magnitude lower than the observed X-ray luminosities. Assuming that radio-loud quasars follow the same X-ray-UV/optical luminosity relation for the disk-corona emission as found for radio-quiet quasars, we estimate the X-ray flux contributed by the disk-corona component from the optical/UV continuum. We find that neither the luminosity, nor the spectral shape, of the disk-corona X-ray emission can account for the bulk of the observed X-ray properties. Thus in lobe-dominated quasars, either the disk-corona X-ray emission is much enhanced in strength and flatter in spectral shape (photon index～1.5) compared to normal radio-quiet quasars, or their jet X-ray emission is much enhanced compared to their weak radio core-jet emission. If the latter is the case, our result may imply that the jet emission in X-rays is less Doppler beamed than that in the radio. As a demonstrating example, we test this hypothesis by using a specific model in which the X-ray jet has a larger opening angle than the radio jet. 相似文献
10.
This review describes the observational properties of radio pulsars, fast rotating neutron stars, emitting radio waves. After the introduction we give a list of milestones in pulsar research. The following chapters concentrate on pulsar morphology: the characteristic pulsar parameters such as pulse shape, pulsar spectrum, polarization and time dependence. We give information on the evolution of pulsars with frequency since this has a direct connection with the emission heights, as postulated in the radius to frequency mapping (RFM) concept. We deal successively with the properties of normal (slow) pulsars and of millisecond (fast-recycled) pulsars. The final chapters give the distribution characteristics of the presently catalogued 1300 objects.Received: 5 December 2003, Published online: 15 April 2004
Correspondence to: Richard Wielebinski 相似文献
11.
Dynamic spectra of a Jovian non-Io-A storm recorded simultaneously by the Voyager 1 spacecraft and by the Kiiminki radio spectrograph are compared. It seems that the emission beam of the storm co-rotates with the planet and has a sloped leading edge, in accordance with the result of Maeda and Carr (1984). 相似文献
12.
We have made a statistical analysis on the subpulse width, the mean pulse width and the rate of change of polarization angle in pulsars. We obtained a number of empirical relations showing how these radio emission characteristics are related to the magnetic inclination and discussed the physical implications of the relations. 相似文献
13.
Patrick Weltevrede Geoff Wright 《Monthly notices of the Royal Astronomical Society》2009,395(4):2117-2126
We present a geometric study of the radio and γ-ray pulsar B1055−52 based on recent observations at the Parkes radio telescope. We conclude that the pulsar's magnetic axis is inclined at an angle of 75° to its rotation axis and that both its radio main pulse and interpulse are emitted at the same height above their respective poles. This height is unlikely to be higher or much lower than 700 km, a typical value for radio pulsars.
It is argued that the radio interpulse arises from emission formed on open fieldlines close to the magnetic axis which do not pass through the magnetosphere's null (zero-charge) surface. However, the main pulse emission must originate from fieldlines lying well outside the polar cap boundary beyond the null surface, and farther away from the magnetic axis than those of the outer gap region where the single γ-ray peak is generated. This casts doubt on the common assumption that all pulsars have closed, quiescent, corotating regions stretching to the light cylinder. 相似文献
It is argued that the radio interpulse arises from emission formed on open fieldlines close to the magnetic axis which do not pass through the magnetosphere's null (zero-charge) surface. However, the main pulse emission must originate from fieldlines lying well outside the polar cap boundary beyond the null surface, and farther away from the magnetic axis than those of the outer gap region where the single γ-ray peak is generated. This casts doubt on the common assumption that all pulsars have closed, quiescent, corotating regions stretching to the light cylinder. 相似文献
14.
H. S. Knight 《Monthly notices of the Royal Astronomical Society》2007,378(2):723-729
We report on 685-MHz observations of PSR J1823–3021A using the Parkes radio telescope. A total of 120 giant pulses (GPs) were found by searching for spiky emission at 16-μs time resolution. The energies of these pulses follow a power law that has a very steep exponent of −3.1. This means that the emission mechanism that gives rise to the GPs almost always produces pulses that only have moderate energies. The profile formed by adding all the GPs has components that are narrower and more widely separated than the profile formed from all pulses. Aberration and retardation of emission from a corotating volume mean that components emitted at high altitude will have asymmetric phases compared to those emitted at low altitude. By assuming that the components of the pulse profile form conal pairs, we use this effect to limit the GPs to be emitted no higher than 4 km above ordinary emission. The arrival times of the GPs are well modelled by Poisson statistics at time-scales around 100 s. We report a GP with spikes of emission at the phases of both components. The probability of two independent GPs occurring within a single pulse period is , so an interpretation can be conjectured that the two pulses are not independent. This may mean that the magnetosphere can remain in a state that is susceptible to discrete 'giant' emission events for as long as 2 ms. 相似文献
15.
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.
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16.
17.
Guo-Jun Qiao Xu-Dong Wang Hong-Guang Wang Ren-Xin XuDepartment of Astronomy CAS-PKU Joint Beijing Astrophysics Center Peking University Beijing 《中国天文和天体物理学报》2002,2(4)
Pulsar radio emission beams have been studied observationally for a long time, and the suggestion is that they consist of the so-called core and conal components. To reproduce these components is a challenge for any emission model, and that the pulse profile of pulsars changes with frequency presents even a greater challenge. Assuming a local surface magnetic structure (to produce the core or central beam) and a global dipole magnetic field (to produce the conal beams), Gil & Krawczyk (1997) applied curvature radiation to the pulse profile simulation of PSR J0437-4715 (hereafter the GK model). Here we present an alternative multi-frequency simulation of the same profiles within the framework of the Inverse Compton Scattering (ICS) model. It is obtained from our simulation (1) that besides the core, the inner cone and the outer cone, there is an outer-outer cone; (2) that the emission components of the core and cones evolve strongly with frequency. Some important differences between the ICS model and the 相似文献
18.
On October 24, 1991, a white-light flare was observed both from space and from the ground. A multi-waveband spectral analysis shows that the peak time of the continuum emission coincides well with that of a radio burst at 2840 MHz and with the hard X-ray emission. Three semi-empirical models, corresponding to the pre-flare condition and to the peak time of continuum emission both with and without non-thermal excitation and ionization of hydrogen by an electron beam, have been obtained. The results indicate that there is fast heating both in the chromosphere and the photosphere. Some evidence is given that this WLF is very likely a result of bombardment by an electron beam. By taking into account non-thermal effects, the chromospheric temperature of the semi-empirical model is significantly reduced. 相似文献
19.
A specific combination of spectral fine structures in meter – decimeter dynamic spectra of solar radio burst emission is
reported in observations carried out at the Astrophysical Institute Potsdam. We describe and interpret the occurrence of zebra
patterns in fast drifting (type III burst-like) envelopes of absorbed continuum emission. A possible mechanism of the origin
of such an involved spectral pattern is put forward, leading to a necessarily multinonequlibrium component coronal plasma.
The suggested mechanism is based on the fact that during the passage of a fast electron beam through the corona the loss cone
instability (which is caused by electrons captured in a magnetic trap generating the continuum) is quenched. As result, a
fast drift burst appears in absorption, and the zebra pattern becomes visible on the low background emission. This zebra pattern
is generated by a group of electrons with a nonequilibrium distribution over transverse velocities. In the absence of the
beam the pattern is invisible against the background of the stronger continuum. It is shown that the mechanism is sensitive
to the distribution parameters of the different electron ensembles. Therefore the effect in dynamic radio spectra is comparatively
rare but its proper existence underlines that the simultaneous presence of different ensembles of electrons in the flaring
corona can be quite a frequent situation. This can explain some problems in deconvolving X-ray photon spectra to electron
energy spectra. 相似文献
20.
S. A. Petrova 《Monthly notices of the Royal Astronomical Society》2009,395(3):1723-1732
The induced Compton scattering of radio emission off the particles of the ultrarelativistic electron–positron plasma in the open field line tube of a pulsar is considered. We examine the scattering of a bright narrow radio beam into the background over a wide solid angle and specifically study the scattering in the transverse regime, which holds in a moderately strong magnetic field and gives rise to the scattered component nearly antiparallel to the streaming velocity of the scattering particles. Making use of the angular distribution of the scattered intensity and taking into account the effect of rotational aberration in the scattering region, we simulate the profiles of the backscattered components as applied to the Crab pulsar. It is suggested that the interpulse (IP), the high-frequency interpulse (IP') and the pair of so-called high-frequency components (HFC1 and HFC2) result from the backward scattering of the main pulse (MP), precursor (PR) and low-frequency component (LFC), respectively. The components of the high-frequency profiles, the IP' and HFCs, are interpreted for the first time. The HFC1 and HFC2 are argued to be a single component split by the rotational aberration close to the light cylinder. It is demonstrated that the observed spectral and polarization properties of the profile components of the Crab pulsar as well as the giant pulse phenomenon outside the MP can be explained in terms of our model. 相似文献