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1.
Using a well-known method for calculating the propagation of waves in an inhomogeneous medium, we have managed to reduce the problem of wave propagation in pulsar magnetospheres to a system of two ordinary differential equations that allow the polarization characteristics of the radio emission to be quantitatively described for any magnetic field structure and an arbitrary density profile of the outflowing plasma. We confirm that for ordinary pulsars (period P ∼ 1 s, magnetic field B 0 ∼ 1012 G, particle production multiplicity parameter λ ∼ 104), the polarization is formed inside the light cylinder at a distance of the order of a thousand neutron star radii. For reasonable magnetic field strengths and plasma densities on the emission propagation path, the degree of circular polarization is found to be ∼5–20%, in good agreement with observations.  相似文献   

2.
A case is made that in encounters with the earth's atmosphere, astrophysical little black holes (LBH) can manifest themselves as the core energy source of ball lightning (BL). Relating the LBH incidence rate on earth to BL occurrence has the potential of shedding light on the distribution of LBH in the universe, and their velocities relative to the earth. Most BL features can be explained by a testable LBH model. Analyses are presented to support this model. LBH produce complex and many-faceted interactions in air directly and via their exhaust, resulting in excitation, ionization, and light due to processes such as gravitational tidal force, bremsstrahlung, pair production and annihilation, orbital electron near-capture by interaction with a charged LBH. Gravitational tidal force interaction of LBH with polarization and atmospheric atoms can result in an enhanced cross-section for polarization and ionization. An estimate for the power radiated by BL ∼ Watts is in agreement with observation. An upper limit is found for the largest masses that can produce ionization and polarization excitation. It is shown that the effects of LBH high power exhaust radiation are consistent with observations. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

3.
The raytracing technique was used to derive a suitable design for the HEGRA system of Cherenkov telescopes, which is at present commissioned at La Palma. The reflectors with a diameter of 3.9 m consist of 30 spherical mirrors with focal lengths in the range of 4.88 – 4.94 m. It is shown that 93% of the photons from the Cherenkov light emitted by an extended air shower are contained in the camera pixels, 0.25° in diameter, for the full field of view of = ± 2.5°. The optical performance of the HEGRA design is compared to other layouts.  相似文献   

4.
We analyze the spectropolarimetric observations of 12 candidates for quasars from the spectroscopic database of the SDSS Catalog. The magnetic fields of these objects are estimated in the context of a theory that includes the Faraday rotation of the polarization plane on the mean free path of a photon in the outflow from an accretion disk. As a result, we have determined the column density in the outflow, N H ∼ 6 × 1023 cm−2, and the radial, B ∼ 1 G, and toroidal, B ∼ 600 G, magnetic fields.  相似文献   

5.
A re-analysis of data near Cygnus X-3 in 1989–1990 using the Whipple Observatory atmospheric Cherenkov imaging telescope confirms the existence of the TeV J2032 + 4130 source first reported at a conference by the Crimean Astrophysical Observatory and confirmed independently by the HEGRA Collaboration in a referred publication. The significance of the Whipple observations at the a priori HEGRA position is 3.3σ. The peak signal was found at RA = 20 h 32 m, Dec = +41^∘ 33′. This is 0.6^∘ north of Cygnus X-3. The flux level (12% of the level of the Crab Nebula) is intermediate between that reported by the Crimean (100%) and HEGRA (3%) groups.  相似文献   

6.
The Atacama Large Millimeter/Submillimeter Array (ALMA) is an international millimeter-wavelength radio telescope under construction in the Atacama Desert of northern Chile. ALMA will be situated on a high-altitude site at 5000 m elevation which provides excellent atmospheric transmission over the instrument wavelength range of 0.3 to 3 mm. ALMA will be comprised of two key observing components—a main array of up to sixty-four 12-m diameter antennas arranged in a multiple configurations ranging in size from 0.15 to ∼18 km, and a set of four 12-m and twelve 7-m antennas operating in a compact array ∼50 m in diameter (known as the Atacama Compact Array, or ACA), providing both interferometric and total-power astronomical information. High-sensitivity dual-polarization 8 GHz-bandwidth spectral-line and continuum measurements between all antennas will be available from two flexible digital correlators. At the shortest planned wavelength and largest configuration, the angular resolution of ALMA will be 0.005″. The instrument will use superconducting (SIS) mixers to provide the lowest possible receiver noise contribution, and special-purpose water vapor radiometers to assist in calibration of atmospheric phase distortions. A complex optical fiber network will transmit the digitized astronomical signals from the antennas to the correlators in the Array Operations Site Technical Building, and post-correlation to the lower-altitude Operations Support Facility where the array will be controlled, and initial construction and maintenance of the instrument will occur. ALMA Regional Centers in the US, Europe, Japan and Chile will provide the scientific portals for the use of ALMA; early science observations are expected in 2010, with full operations in 2012.  相似文献   

7.
McCARTHY  D.  STOLOVY  S.  KERN  S.  SCHNEIDER  G.  FERRO  A.  SPINRAD  H.  BLACK  J.  SMITH  B. 《Earth, Moon, and Planets》1997,78(1-3):243-249
Near-infrared images of comet Hale-Bopp (C/1995 O1) were obtained from NICMOS/HST on UT August 27–28, 1997, when the comet emerged from the 50 degree solar elongation limit at 2.99 AU from Earth. Diffraction-limited images were obtained with camera 2 filters centered at 1.87, 1.90, 2.04 and 2.22 μm with ∼0.2″ resolution (0.076″/pixel; 165 km/pixel). Over the 1.7-hour baseline of observation, a recent (<7 hours) outburst is seen in the form of an expanding spiral arm with a projected expansion velocity of ∼80 m/s. Other asymmetric features include a jet emanating from the nucleus and several static linear features. Comparisons of the flux distribution in the 2.04 and 2.22 μm filters indicate that the region near the nucleus exhibits a slight, ∼3%, water ice absorption. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

8.
The structure of the AGN object 1803+784 has been investigated at a wavelength of 7 mm with a limiting angular resolution reaching 20 μas. The ejector nozzle surrounded by a ring structure, an accretion disk, has been identified. The nozzle size is ∼0.1 pc, the diameter of the ring structure is ∼1.4 pc, and its width is ∼0.25 pc. The reaction of the plasma flow produces a multimode precession responsible for the conical helical structure of the jet with a variable step and a curved axis. The viewing angle of the flow ejection is ∼40°. The central part of the ejected flow moving along the axis accelerates to a relativistic velocity. The apparent velocity reaches 12 s at a distance of ∼1 mas or ∼6 pc from the ejector. The outer part of the flow moves along a helix around a high-velocity component whose step is a factor of 4 smaller, because the longitudinal velocity is relatively low. The plasma is ejected almost toward the observer, as confirmed by its high brightness temperature T b ≈ 8 × 1013 K and highly beamed emission. The polarized emission from the nozzle is axisymmetric. The orientation of the polarization of the flow along the whole length is aligned with the direction of its motion, suggesting the excitation of a ring magnetic field around it and self-focusing.  相似文献   

9.
From an analysis of the interstellar extinction we conclude that interstellar grains are of three main kinds: graphite spheres of radii ∼ 0.02 μmmaking up ∼ ;10% of the total grain mass, small dielectric spheres of radius about 0.04 μm making up ∼ 25% of the mass, and hollow dielectric cylinders containing metallic iron with diameters of ∼ 2/3 μmmaking up ∼ 45% of the mass. The remaining ∼ 20%consists of other metals and metal oxides. The main dielectric component of the grains appears to be comprised of organic material. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

10.
In a novel approach in observational high-energy gamma-ray astronomy, observations carried out by imaging atmospheric Cherenkov telescopes provide necessary templates to pinpoint the nature of intriguing, yet unidentified EGRET gamma-ray sources. Using GeV-photons detected by EGRET and taking advantage of high spatial resolution images from H.E.S.S. observations, we were able to shed new light on the EGRET observed gamma-ray emission in the Kookaburra complex, whose previous coverage in the literature is somewhat contradictory. 3EG J1420–6038 very likely accounts for two GeV gamma-ray sources (E>1 GeV), both in positional coincidence with the recently reported pulsar wind nebulae (PWN) by HESS in the Kookaburra/Rabbit complex. PWN associations at VHE energies, supported by accumulating evidence from observations in the radio and X-ray band, are indicative for the PSR/plerionic origin of spatially coincident, but still unidentified Galactic gamma-ray sources from EGRET. This not only supports the already suggested connection between variable, but unidentified low-latitude gamma-ray sources with pulsar wind nebulae (3EG J1420–6038 has been suggested as PWN candidate previously), it also documents the ability of resolving apparently confused EGRET sources by connecting the GeV emission as measured from a large-aperture space-based gamma-ray instrument with narrow field-of-view but superior spatial resolution observations by ground-based atmospheric Cherenkov telescopes, a very promising identification technique for achieving convincing individual source identifications in the era of GLAST-LAT.   相似文献   

11.
Very-high spectral resolution observations of the neutral Na emission have enabled measurements of the velocity dispersions of the Na atoms within ∼40,000 km of the opto center of Hale-Bopp. Asymmetric Na D line profiles imply both an in situ or core Na source and a secondary Na source at locations within the inner coma. The core velocity distribution had a FWHM of 2 km s-1. The extended source FWHM increased with distance from the nucleus (up to ∼6 km s-1, but appeared smaller in the more dusty regions (∼2.5–3.0 km s-1) of the inner coma. The D2/D1 line strength ratio was consistent with an optically thin inner coma. Within 5,000 km of the opto center the continuum spatial intensity profiles decreased as ∼r-1 while the Na D emission decreased at less than r-1. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

12.
The imminent return of the Genesis Sample Return Capsule (SRC) from the Earth’s L1 point on September 8, 2004, represents the first opportunity since the Apollo era to study the atmospheric entry of a meter-sized body at or above the Earth’s escape speed. Until now, reentry heating models are based on only one successful reentry with an instrumented vehicle at higher than escape speed, the 22 May 1965 NASA “FIRE 2” experiment. In preparation of an instrumented airborne and ground-based observing campaign, we examined the expected bolide radiation for the reentry of the Genesis SRC. We find that the expected emission spectrum consists mostly of blackbody emission from the SRC surface (T∼ ∼2630 K@peak heating), slightly skewed in shape because of a range of surface temperatures. At high enough spectral resolution, shock emission from nitrogen and oxygen atoms, as well as the first positive and first negative bands of N2+, will stand out above this continuum. Carbon atom lines and the 389-nm CN band emission may also be detected, as well as the mid-IR 4.6-μm CO band. The ablation rate can be studied from the signature of trace sodium in the heat shield material, calibrated by the total amount of matter lost from the recovered shield. A pristine collection of the heat shield would also permit the sampling of products of ablation.  相似文献   

13.
We present here rigorous analytical solutions for the Boltzmann-Poisson equation concerning the distribution of stars above the galactic plane. The number density of stars is considered to follow a behaviour n(m,0) ∼H(m - m0)m−x, wherem is the mass of a star andx an arbitrary exponent greater than 2 and also the velocity dispersion of the stars is assumed to behave as < v2(m)> ∼ m−θ the exponent θ being arbitrary and positive. It is shown that an analytic expression can be found for the gravitational field Kz, in terms of confluent hypergeometric functions, the limiting trends being Kz∼z for z →0, while Kz → constant for z → infinity. We also study the behaviour of < |z(m)|2>,i.e. the dispersion of the distance from the galactic disc for the stars of massm. It is seen that the quantity < |z(m)|2>∼ mt-θ, for m→ t, while it departs significantly from this harmonic oscillator behaviour for stars of lighter masses. It is suggested that observation of < |z(m)|2> can be used as a probe to findx and hence obtain information about the mass spectrum.  相似文献   

14.
We present X-ray data of the middle-aged radio pulsar PSR B0355+54. The XMM-Newton and Chandra observations show not only emission from the pulsar itself, but also compact diffuse emission extending ∼50″ in the opposite direction to the pulsar’s proper motion. Our analysis also indicates the presence of fainter diffuse emission extending ∼5′ from the point source. The morphology of the diffuse component is similar to the ram-pressure confined pulsar wind nebulae detected for other sources. We find that the compact diffuse component is well-fitted with a power-law, with an index that is consistent with the values found for other pulsar wind nebulae. The core emission from the pulsar can be characterized with a thermal plus power-law fit, with the thermal emission most likely originating in a hot polar cap.  相似文献   

15.
It is shown that if neutron stars contain dynamically de-coupled components, most plausibly discrete superfluid zones, then it is possible for the spin axes of these components o become slightly misaligned with respect to the crustal spin following a series of glitches. The crust will then undergo Lense-Thirring precession about the total angular moment with a period of ∼ 6–7.5P (assuming a crustal superfluid) and ∼ 3–6P (if the core superfluid is not tightly coupled to the crust). The precise precessional period is diagnostic of the mass distribution within each component. The implications of recent observational inferences concerning glitching pulsars are discussed. The conditions necessary for precession to be observable are analysed phenomenologically and a search of pulse-timing data for evidence of a Lense-Thirring modulation within the period range ∼ 3–8P is proposed.  相似文献   

16.
In this exploratory simulation study, we compare the event-progenitor classification potential of a variety of measurable parameters of atmospheric Cherenkov pulses which are produced by ultrahigh energy γ-ray and hadron progenitors and are likely to be recorded by the TACTIC (TeV atmospheric Cherenkov telescope with imaging camera) array of atmospheric Cherenkov telescopes. The parameters derived from Cherenkov images include Hillas, fractal and wavelet moments, while those obtained from non-image Cherenkov data consist of pulse profile rise time and base width and the relative ultraviolet to visible light content of the Cherenkov event. It is shown by a neural-net approach that these parameters, when used in suitable combinations, can bring about a proper segregation of the two event types, even with modest sized data samples of progenitor particles.  相似文献   

17.
The BL Lac-type object 3C 66A was observed at the Crimean Astrophysical Observatory during the international project OJ-94. Observations were made over 10 nights from February through December 2003 at the Cassegrain focus of the 125-cm AZT-11 telescope with a photopolarimeter capable of simultaneous measurements in the UBVRI bands. In the course of our measurements the brightness of the object increased by more than 1 magnitude in all these bands. Its color indices varied and the degree of polarization decreased from ∼16% in February to ∼3% at the end of our observations. In December 2003 a rapid change in the position angle from 15° to 40° was noticed. The spectral energy distribution Fn is well described by a power law with a spectral index a (Fν ∝ ν −α . The increase in brightness was accompanied by a reduction in the spectral index. The most probable mechanism for the observed changes in the brightness, degree of polarization, and spectral index may be a decrease in the magnetic field strength or a change in its configuration owing to a increase in the chaotic component of the field. __________ Translated from Astrofizika, Vol. 49, No. 1, pp. 41–59 (February 2006).  相似文献   

18.
The problems of measuring the variations in the gravitational and inertial fields on Phobos related to librational oscillations, tidal effects, and seismic impacts have been considered in the paper. It has been indicated that thermal equilibrium noise in a mechanical oscillator, which forms the basis for a sensor, is responsible for the oscillator’s maximal sensitivity at a level of 8 × 10−9 m/s2. The actual sensitivity of the designed three-dimensional seismogravimeter, which was estimated based on the calibration results, is ∼2 × 10−8 m/s2. This makes it possible to measure the anticipated variations in the gravitational field and to obtain information about the seismic noise level with a surface oscillation amplitude resolution at a level of 2.5 × 10−7 m at frequencies of 0.1 Hz to ∼10−10 m at frequencies higher than 5 Hz.  相似文献   

19.
Remote sensing of atmosphere is conventionally done via a study of extinction/scattering of light from natural (Sun, Moon) or artificial (laser) sources. Cherenkov emission from extensive air showers generated by cosmic rays provides one more natural light source distributed throughout the atmosphere. We show that Cherenkov light carries information on three-dimensional distribution of clouds and aerosols in the atmosphere and on the size distribution and scattering phase function of cloud/aerosol particles. Therefore, it could be used for the atmospheric sounding. The new atmospheric sounding method could be implemented via an adjustment of technique of imaging Cherenkov telescopes. The atmospheric sounding data collected in this way could be used both for atmospheric science and for the improvement of the quality of astronomical gamma-ray observations.  相似文献   

20.
Weaver  H. A.  Brooke  T. Y.  Chin  G.  Kim  S. J.  Bockelée-Morvan  D.  Davies  J. K. 《Earth, Moon, and Planets》1997,78(1-3):71-80
High resolution (λ/δλ ∼ 20,000) spectra of comet C/1995 O1 (Hale-Bopp) in the 2–5 μm region were obtained during UT 2–5 March 1997 using CSHELL at the NASA Infrared Telescope Facility (IRTF) on Mauna Kea. The heliocentric and geocentric distances of the comet were ∼1.1 AU and ∼1.5 AU,respectively. We detected emission lines of the gas-phase molecules H2O, 4, C2H6, C2H2, HCN, and CO and derived absolute production rates and relative abundances for all species. We also used the 2-dimensional nature of the CSHELL data to investigate the spatial distribution of the molecules and find evidence that CO was derived at least partly from an extended source in the coma. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

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