共查询到20条相似文献,搜索用时 46 毫秒
1.
V. A. Stolyarov Yu. N. Parijskij N. N. Bursov M. G. Mingaliev T. A. Semenova P. G. Tsybulev 《Astrophysical Bulletin》2012,67(1):29-43
We present the estimates of Galactic synchrotron and free-free emission power at intermediate and small scales (500 < l < 1000, 20′ < θ < 40′), based on the RATAN-600 radio telescope observations (SAO RAS). The observations were conducted in the frequency range
of 2.3–11.2 GHz using the transit scan mode, in the declination range of 40.7° s δ < 42.3°. The power spectrum estimates of synchrotron and free-free components were obtained. They can be further used in
the data processing stage of the high-resolution cosmological experiments like Planck. 相似文献
2.
H. S. Sawant R. Ramesh J. R. Cecatto C. Faria F. C. R. Fernandes R. R. Rosa M. C. Andrade S. Stephany L. B. T. Cividanes C. A. I. Miranda L. C. L. Botti J. W. S. V. Boas J. H. Saito C. E. Moron N. D. Mascarenhas K. R. Subramanian M. S. Sundararajan E. Ebenezer M. R. Sankararaman 《Solar physics》2007,242(1-2):213-220
An East – West, one-dimensional radio interferometer array consisting of five parabolic dish antennas has been set up at Cachoeira
Paulista (longitude 45°0′20″ W, latitude 22°41′19″ S) for observations of the Sun and some of the strong sidereal sources
by the Instituto Nacional de Pesquisas Espaciais (INPE), Brazil. This is Phase-I of the proposed Brazilian Decimetric Array
and can be operated at any frequency in the range 1.2 – 1.7 GHz. The instrument has been in operation since November 2004
onwards at 1.6 GHz. The angular and temporal resolutions at this frequency are ∼3′ and 100 ms, respectively. Details of the
array, analog/digital receiver system, and a preliminary East – West one-dimensional solar image at the 1.6 GHz are presented
in this paper. 相似文献
3.
K. S. Dwarakanath Siddharth Malu Ruta Kale 《Journal of Astrophysics and Astronomy》2011,32(4):529-532
We have discovered a giant radio halo in the massive merging cluster MACSJ0417.5-1154. This cluster, at a redshift of 0.443,
is one of the most X-ray luminous galaxy cluster in the MAssive Cluster Survey (MACS) with an X-ray luminosity in the 0.1–2.4
keV band of 2.9×1045 erg s − 1. Recent observations from GMRT at 230 and 610 MHz have revealed a radio halo of ∼ 1.2 × 0.3 Mpc2 in extent. This halo is elongated along the North-West, similar to the morphology of the X-ray emission from Chandra. The
1400 MHz radio luminosity (L
r) of the halo is ∼2 × 1025 W Hz − 1, in good agreement with the value expected from the L
x − L
r correlation for cluster halos. 相似文献
4.
J. A. Docobo N. D. Melikian V. S. Tamazian M. H. Eritsian A. A. Karapetian 《Astrophysics》1998,41(3):254-260
The results of photometric and polarimetric observations of 16 double and multiple stars carried out in 1997 at Byurakan Observatory
are presented. The variability of SAO 64769 and SAO 87297 is confirmed and their slow brightness variations are shown. Irregular
brightness variations as well as six UV Ceti type flares have been detected for SAO 107425 = COU 14. For the first time the
polarization was found for SAO 88631.
Published in Astrofizika, Vol. 41, No. 3, pp. 389–398, July–September, 1998. 相似文献
5.
A. V. Meshcheryakov M. G. Revnivtsev M. N. Pavlinsky I. Khamitov I. F. Bikmaev 《Astronomy Letters》2010,36(10):738-751
The variability of the optical and X-ray fluxes from the binary GS 1826-238 is investigated. An epoch-folding analysis of
the optical data obtained with the RTT-150 telescope in 2003–2004 has revealed periodic brightness variations in the source
with a period P
orb = 2.24940 ± 0.00015 h with a high statistical significance. When estimating the detection significance of the periodic signal,
we have specially taken into account the presence of a powerful aperiodic component (“red noise”) in the source’s brightness
variability. The source’s power density spectra in the frequency range ∼10−5–0.01 Hz have been obtained. We have detected a statistically significant break in the power density spectrum of GS 1826-238
at a frequency ν
br ≈ (8.48 ± 0.14) × 10−5 Hz in both optical and X-ray energy bands. We have estimated the orbital period of the binary GS 1826-238 using the correlation
between the break frequency in the power density spectrum and the orbital period of binaries, P
orb ∝ 1/ν
br, found by Gilfanov and Arefiev (2005): P
orb = 3.7 ± 0.8 h and P
orb = 11.3 ± 5.9 h when using Sco X-1 and 1H 16267-273, respectively, as reference sources. It seems to us that the method for
estimating the orbital periods of low-mass X-ray binaries using the correlation P
orb ∝ 1/ν
br may turn out to be very promising, especially for persistent low-luminosity X-ray binaries. 相似文献
6.
GianLuca Israel 《Astrophysics and Space Science》2007,308(1-4):25-31
On 27th December 2004 SGR 1806–20, one of the most active Soft γ-ray Repeaters (SGRs), displayed an extremely rare event, also known as giant flare, during which up to 1047 ergs were released in the ∼1–1000 keV range in less than 1 s. Before and after the giant flare we carried out IR observations
by using adaptive optics (NAOS-CONICA) mounted on VLT which provided images of unprecedented quality (FWHM better than 0.1″).
We discovered the likely IR counterpart to SGR 1806–20 based on positional coincidence with the VLA uncertainty region and
flux variability of a factor of about 2 correlated with that at higher energies.
Moreover, by analysing the Rossi-XTE/PCA data we have discovered rapid Quasi-Periodic Oscillations (QPOs) in the pulsating
tail of the 27th December 2004 giant flare of SGR 1806–20. QPOs at ∼92.5 Hz are detected in a 50 s interval starting 170 s
after the onset of the giant flare. These QPOs appear to be associated with increased emission by a relatively hard unpulsed
component and are seen only over phases of the 7.56 s spin period pulsations away from the main peak. QPOs at ∼18 and ∼30 Hz
are also detected ∼200–300 s after the onset of the giant flare. This is the first time that QPOs are unambiguously detected
in the flux of a Soft Gamma-ray Repeater, or any other isolated neutron star. We interpret the highest QPOs in terms of the
coupling of toroidal seismic modes with Alfvén waves propagating along magnetospheric field lines. The lowest frequency QPO
might instead provide indirect evidence on the strength of the internal magnetic field of the neutron star.
相似文献
7.
P. Goldoni M. Ribó T. Di Salvo J. M. Paredes V. Bosch-Ramon M. Rupen 《Astrophysics and Space Science》2007,309(1-4):293-297
LS 5039 is the only X-ray binary persistently detected at TeV energies by the Cherenkov HESS telescope. It is moreover a γ-ray emitter in the GeV and possibly MeV energy ranges. To understand important aspects of jet physics, like the magnetic
field content or particle acceleration, and emission processes, such as synchrotron and inverse Compton (IC), a complete modeling
of the multiwavelength data is necessary. LS 5039 has been detected along almost all the electromagnetic spectrum thanks to
several radio, infrared, optical and soft X-ray detections. However, hard X-ray detections above 20 keV have been so far elusive
and/or doubtful, partly due to source confusion for the poor spatial resolution of hard X-ray instruments. We report here
on deep (∼300 ks) serendipitous INTEGRAL hard X-ray observations of LS 5039, coupled with simultaneous VLA radio observations. We obtain a 20–40 keV flux of 1.1±0.3 mCrab
(5.9 (±1.6) ×10−12 erg cm−2 s−1), a 40–100 keV upper limit of 1.5 mCrab (9.5×10−12 erg cm−2 s−1), and typical radio flux densities of ∼25 mJy at 5 GHz. These hard X-ray fluxes are significantly lower than previous estimates
obtained with BATSE in the same energy range but, in the lower interval, agree with extrapolation of previous RXTE measurements. The INTEGRAL observations also hint to a break in the spectral behavior at hard X-rays. A more sensitive characterization of the hard
X-ray spectrum of LS 5039 from 20 to 100 keV could therefore constrain key aspects of the jet physics, like the relativistic
particle spectrum and the magnetic field strength. Future multiwavelength observations would allow to establish whether such
hard X-ray synchrotron emission is produced by the same population of relativistic electrons as those presumably producing
TeV emission through IC. 相似文献
8.
A. Baudry J. Brillet J. M. Desbats J. Lacroix G. Montignac P. Encrenaz R. Lucas G. Beaudin P. Dierich A. Germont P. Landry G. Rerat 《Journal of Astrophysics and Astronomy》1980,1(2):193-196
A new millimeter-wave facility is in operation at the Bordeaux Observatory for spectroscopic observations of interstellar
and stratospheric molecules. A cooled receiver has been installed on a 2·5m radio telescope. The overall system temperature
is in the range 400 to 600 K (single side band) in the operating frequency range 75 to 115 GHz. The relatively broad beam
of the telescope (∼ 5 arcmin) combined with a sensitive receiver will permit studies of extended molecular cloud complexes. 相似文献
9.
V. T. Doroshenko S. G. Sergeev E. Yu. Vovk Yu. S. Efimov S. A. Klimanov S. V. Nazarov 《Astronomy Letters》2010,36(9):611-633
Based on our UBV RI observations and X-ray data from the RXTE satellite, we have investigated the variability of the galaxy NGC 7469 over the
period 1995–2009. In 1995–2000, the optical brightness of the galactic nucleus changed almost by 1
m
in the U band. In 2000–2009, the amplitude of the optical variations was considerably lower. Regular X-ray observations began only
in 2003. The X-ray fractional variability amplitude is higher than the optical one. The optical variability amplitude decreases
with increasing wavelength. The full width at half maximum of the X-ray and B-band autocorrelation functions is about 8 and 62 days, respectively. The structure functions (SF) in the X-ray range on time scales up to 7 days and in the optical range on time scales up to 100 days have the form of a
power law SF(τ) ∼ τ
b
, where τ is the time shift. On time scales of more than a day, where both structure functions have been determined rather reliably,
their slopes differ markedly: b = 1.34 ± 0.06 and b = 0.25 ± 0.05 for the optical and X-ray ranges, respectively. The X-ray and B-band structure functions begin to flatten, respectively, near 6–8 days and on time scales of about 90 days. The observed
structure functions can be described by the model of a superposition of independent Gaussian flares whose number changes with
duration ω as n(ω) ∼ ω
α and whose amplitudes depend on duration as A(ω) ∼ ω
β. The flux distribution and the flux-amplitude relation are consistent with the model of a light curve in the form of a superposition
of random flares. Once the fast intensity variations have been filtered out on long time scales, the X-ray light curve correlates
well with the optical one. No lag of the X-ray variations relative to those in the B band is detected. The light variations in the R and I bands lag behind those in the B band calculated from the centroid of the cross-correlation function by 2.6 and 3.5 days, respectively, at a 3σ confidence level. 相似文献
10.
The Reuven Ramaty High-Energy Solar Spectroscopic Imager RHESSI telescope produces hard X-ray images by Fourier imaging techniques
that are capable of determining the sizes and shapes of sources with spatial scales in the range ∼ 2′′–180′′. Applying the
method of Unpixelized Forward Fitting to RHESSI modulation profiles from simple flares, we have identified the presence of
`halo' sources whose size scale (∼ 40′′) greatly exceeds the `core' sizes (≤ 6′′–14′′). Although such `core-halo' structures
have been observed at radio wavelengths using a similar technique, the radio and hard X-ray phenomena may be different. These
observations raise questions about the nature of these `halos'. Among the possibilities are that they are albedo sources,
thin-target loops, or unidentified diffuse structures.
Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1022484822851 相似文献
11.
N. N. Chugai 《Astronomy Letters》2010,36(8):540-548
We investigate the possibility of constructing a unified model for the radio and X-ray outbursts of nova CI Cam 1998 in terms
of the shock interaction of the nova envelope with circumstellar gas. In a spherical model, we manage to describe the kinematics
and evolution of the radio source flux and very roughly the evolution of the X-ray flux. The X-ray spectrum in this model
is appreciably harder. Better agreement with observations in all respects is shown by the model for the interaction of a spherical
nova envelope with a nonspherical circumstellar medium. The latter is simulated in our model by a combination of rarefied
bipolar conical outflows of stationary wind with an opening angle of 120° and a dense equatorial disk. In the optimal model,
the initial kinetic energy of the nova envelope is ∼5 × 1043 erg and its mass lies within the range (1–5) × 10−7
M
⊙. The energy and mass of the nova envelope as well as the mass loss rate in the nonspherical model are close to those obtained
in the spherical model by Filippova et al. (2008). 相似文献
12.
We present the results of a detailed analysis of RXTE observations of classω (Klein-Woltet al. 2002) which show an unusual state transition between high-soft and low-soft states in the Galactic microquasar GRS 1915 +
105. Out of about 600 pointed RXTE observations, the source was found to exhibit such state transition only on 16 occasions.
An examination of the RXTE/ASM data in conjunction with the pointed observations reveals that these events appeared as a series
of quasi-regular dips in two stretches of long duration (about 20 days during each occasion) when hard X-ray and radio flux
were very low. The X-ray light curve and colour-colour diagram of the source during these observations are found to be different
from any reported so far. The duration of these dips is found to be of the order of a few tens of seconds with a repetition
time of a few hundred seconds. The transition between these dips and non-dips which differ in intensity by a factor of ∼ 3.5,
is observed to be very fast (∼ a few seconds). It is observed that the low-frequency narrow QPOs are absent in the power density
spectrum (PDS) of the dip and non-dip regions of classω and the PDS is a power law in the 0.1–10 Hz frequency range. There is a remarkable similarity in the spectral and timing
properties of the source during the dip and non-dip regions in this set of observations. These properties of the source are
distinctly different from those seen in the observations of other classes. This indicates that the basic accretion disk structure
during both dip and non-dip regions of classω is similar, but differ only in intensity. To explain these observations, we invoke a model in which the viscosity is very
close to critical viscosity and the shock wave is weak or absent. 相似文献
13.
E.A. Richards 《Astrophysics and Space Science》2001,276(2-4):1169-1178
We describe an observational programme aimed at understanding the radio emission from distant, rapidly evolving galaxy populations.
These observations were carried out at 1.4 and 8.5 GHz with the VLA, centred on the Hubble Deep Field, obtaining limiting
flux densities of 40 and 8 μJy respectively. The differential count of the radio sources is marginally sub-Euclidean to the
completeness limits(γ = − 2.4 ± 0.1) and fluctuation analysis suggests nearly 60 sources per arcmin2 at the 1 μJy level. Using high-resolution 1.4 GHz observations obtained with MERLIN, we resolve all radio sources detected
in the VLA complete sample and measure a median angular size for the microjansky radio population of 1-2". This clue, coupled
with the steep spectral index of the 1.4 GHz selected sample, suggests diffuse synchrotron radiation in z ∼ 1 galactic discs. The wide-field HST and ground-based optical exposures show that the radio sources are identified primarily
with disc systems composed of irregulars, peculiars, interacting/merging galaxies and a few isolated field spirals. Only 20%
of the radio sources can be attributed to AGN – the majority are probably associated with starburst activity. The available
redshifts range from 0.1 to 3, with a mean of about 0.8. We are plrobably witnessing a major episode of starburst activity
in these luminous (L > L
*) systems, occasionallyaccompanied by an embedded AGN.About 20% of the radio sources remain unidentified to I = 26-28 inthe HDF and flanking fields. Several of these objectshave extremely red counterparts. We suggestthat these are
high-redshift dusty protogalaxies.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
14.
Chuan Peng Zhang Jarken Esimbek Jian Jun Zhou Gang Wu Zhi Mao Du 《Astrophysics and Space Science》2012,337(1):283-302
There are relatively few H2CO mappings of large-area giant molecular cloud (GMCs). H2CO absorption lines are good tracers for low-temperature molecular clouds towards star formation regions. Thus, the aim of
the study was to identify H2CO distributions in ambient molecular clouds. We investigated morphologic relations among 6-cm continuum brightness temperature
(CBT) data and H2CO (111−110; Nanshan 25-m radio telescope), 12CO (1–0; 1.2-m CfA telescope) and midcourse space experiment (MSX) data, and considered the impact of background components
on foreground clouds. We report simultaneous 6-cm H2CO absorption lines and H110α radio recombination line observations and give several large-area mappings at 4.8 GHz toward W49 (50′×50′), W3 (70′×90′),
DR21/W75 (60′×90′) and NGC2024/NGC2023 (50′×100′) GMCs. By superimposing H2CO and 12CO contours onto the MSX color map, we can compare correlations. The resolution for H2CO, 12CO and MSX data was ∼10′, ∼8′ and ∼18.3″, respectively. Comparison of H2CO and 12CO contours, 8.28-μm MSX colorscale and CBT data revealed great morphological correlation in the large area, although there
are some discrepancies between 12CO and H2CO peaks in small areas. The NGC2024/NGC2023 GMC is a large area of HII regions with a high CBT, but a H2CO cloud to the north is possible against the cosmic microwave background. A statistical diagram shows that 85.21% of H2CO absorption lines are distributed in the intensity range from −1.0 to 0 Jy and the ΔV range from 1.206 to 5 km s−1. 相似文献
15.
Paolo Ciliegi Carlotta Gruppioni Richard McMahon Michhael Rowan-Robinson 《Astrophysics and Space Science》2001,276(2-4):957-964
The optical identification programme is presented for a complete sample of 867 radio sources that were observed with the Very
Large Array (VLA) within 4.22 deg2 to S
1.4 GHz ≥ 0.135 mJy (5 σ). The area covered by the VLA survey is part of the regions of the sky that have been surveyed in the mid
and far Infrared over the wavelength range 6.7–175 μmwith ISO as part of the European Large Area ISO Survey (ELAIS). Optical
identifications are made using the Automatic Plate-measuring Machine (APM) optical catalogue in E (∼ R) and O (∼ B) bands with approximate limiting magnitudes of ∼ 20.0 and 21.5 mag, respectively. For 220 out of the 867 radio sources, likely
identifications are proposed with an a posteriori identification percentage of 25%. The sample of identification has a reliability
of 96% and a completeness of 80%.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
16.
The radio recombination line intensities of heavy elements of helium, carbon and oxygen are calculated with accounting for
dielectronic recombination. Dielectronic recombination rates are determined accurate to the second order of a perturbation
theory and the rates are described as function of principal quantum number for helium-like atom or ion. Balance equations
are solved for the departure coefficients from LTE bn. The collision and spontaneous transition rates are accounted for the balance equations, in which non-equilibrium distribution
source is dielectronic recombination. Non-equilibrium amplification coefficients are found as functions of a medium temperature,
density and ion charge z = 1–3 for radio recombination lines.
Optical depths are calculated for the heavy element low-frequency lines with the numbers 300 > n > 1200. For the chosen electronic temperatures and densities Te = 0.8× 104–10× 104 K, Ne = 0.05–0.1 cm−3 the line optical depth is determined by the values τL∼ 0.1× 10−4–100× 10−4. Calculated for free-free transition rates, the optical depth is given by using the value τff∼ 10−2τL. 相似文献
17.
E. Sánchez-Ayaso J. A. Combi J. F. Albacete Colombo J. López-Santiago J. Martí A. J. Mu?oz-Arjonilla 《Astrophysics and Space Science》2012,337(2):573-579
We report XMM-Newton observations of the Galactic supernova remnant G296.8-0.3, together with complementary radio and infrared data. The spatial
and spectral properties of the X-ray emission, detected towards G296.8-0.3, was investigated in order to explore the possible
evolutionary scenarios and the physical connexion with its unusual morphology detected at radio frequencies. G296.8-0.3 displays
diffuse X-ray emission correlated with the peculiar radio morphology detected in the interior of the remnant and with the
shell-like radio structure observed to the northwest side of the object. The X-ray emission peaks in the soft/medium energy
range (0.5–3.0 keV). The X-ray spectral analysis confirms that the column density is high (N
H∼0.64×1022 cm−2) which supports a distant location (d>9 kpc) for the SNR. Its X-ray spectrum can be well represented by a thermal (PSHOCK) model, with kT∼0.86 keV, an ionization timescale of 6.1×1010 cm−3 s, and low abundance (∼0.12 Z
⊙). The 24 μm observations show shell-like emission correlated with part of the northwest and southeast boundaries of the SNR.
In addition a point-like X-ray source is also detected close to the geometrical center of the radio SNR. The object presents
some characteristics of the so-called compact central objects (CCO). Its X-ray spectrum is consistent with those found at
other CCOs and the value of N
H is consistent with that of G296.8-0.3, which suggests a physical connexion with the SNR. 相似文献
18.
The Eridanus galaxies follow the well-known radio—FIR correlation. The majority (70%) of these galaxies have their star formation
rates below that of the Milky Way. The galaxies that have a significant excess of radio emission are identified as low luminosity
AGNs based on their radio morphologies obtained from the GMRT observations. There are no powerful AGNs (L
20cm > 1023 W Hz−1) in the group. The two most far-infrared and radio luminous galaxies in the group have optical and HI morphologies suggestive
of recent tidal interactions. The Eridanus group also has two far-infrared luminous but radio-deficient galaxies. It is believed
that these galaxies are observed within a few Myr of the onset of an intense star formation episode after being quiescent
for at least a 100 Myr. The upper end of the radio luminosity distribution of the Eridanus galaxies (L
20cm ∼ 1022 W Hz−1) is consistent with that of the field galaxies, other groups, and late-type galaxies in nearby clusters. 相似文献
19.
T. A. Polyakova 《Astrophysics》2006,49(2):164-172
The hypothesis that W Cep has an eclipsing variability is discussed on the basis of our photometric and polarimetric observations
of it from 1983–2003. Here we attempt to use our observations of W Cep to construct an average light curve, after separating
out the slow variation, with the elements JDmin=2448105d+2090d. A strong variability is found from period to period at phases of 0.1–0.3 that may be caused by a variable flow of matter
between the components.
__________
Translated from Astrofizika, Vol. 49, No. 2, pp. 187–196 (May 2006). 相似文献
20.
Plots of 12-month moving averages of the radio emission values for 1947–2002 indicated that the ratios (maximum/minimum) of
the solar cycles 19–23 were low (∼ 1.2) in the upper chromosphere and lower corona (frequencies near 15 000 MHz), rose to
maximum levels of ∼ 3.5 in the middle corona (frequencies ∼ 2000±500 MHz), and dropped thereafter to ∼ 2.5. In some cycles,
there were two maxima separated by about 2 years. In cycles 20 and 23, mostly the second maximum was larger than the first
maximum, but in cycles 21 and 22, some parameters showed the first maximum larger while others showed the second maximum larger.
There was no systematic shift from first maximum to second maximum, with frequency or temperature (or altitude). 相似文献