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1.
A 3 mm low noise beam-lead Schottky diode mixer has been developed. At cryogenic temperatures the conversion loss is 6.3 dB, and the DSB mixer noise temperature is 75 K, respectively. The mixer was installed into the cooled receiver for radioastronomical observations at the Metsähovi 13.7-m radio telescope. Total DSB noise temperature of the cooled receiver with an ultra low noise HEMT IF amplifier was 110 K at 103 GHz. The tuning range of the mixer mount was from 70 GHz to 115 GHz.  相似文献   

2.
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3.
Seventy-one occurrences of coronal mass ejections(CMEs) associated with radio bursts,seemingly associated with type Ⅲ bursts/fine structures(FSs),in the centimeter-metric frequency range during 2003-2005,were obtained with the spectrometers at the National Astronomical Observatories,Chinese Academy of Sciences(NAOC) and the Culgoora radio spectrometer and are presented.The statistical results of 68 out of 71 events associated with the radio type III bursts or FSs during the initiation or early stages of the...  相似文献   

4.
《New Astronomy Reviews》2002,46(2-7):357-360
We highlight a group of peculiar double radio sources we christen HYMORS: HYbrid MOrphology Radio Sources. These HYMORS appear to have an FR I type radio lobe on one side of the active nucleus but an FR II type lobe on the opposite side. Such objects range in size from ∼0.01 Mpc to ∼1 Mpc. The mere existence of these hybrid sources causes severe difficulties for models which attribute the differences between FR I and FR II radio sources to some intrinsic property of the compact central engine, or the composition of the jet plasma. HYMORS support models for the FR dichotomy based upon the interaction of the jet plasma with the ambient medium, in that asymmetries in the external environment could more naturally produce the observed hybrid morphologies.  相似文献   

5.
The implications of the intrinsic luminosity evolution with cosmological epoch on the value of the density parameter () and evolution of radio sizes of extragalactic radio sources have been considered. It is shown that a power law evolution model of the sortP (1 +z) can be used to contrain the value of . In the presence of a strong luminosity evolution, the model yields an upper limit of 0.5.It is also shown that the angular diameter redshift ( – z) relation for quasars can be interpreted in terms of the assumed luminosity evolution combined with a luminosity-linear size correlation with little or no linear size evolution required. On the other hand, strong linear size evolution is needed to explain the – z data for radio galaxies independent of luminosity.  相似文献   

6.
We investigate the X-ray emission from the central regions of the prototypical starburst galaxy M82. Previous observations have shown a bright central X-ray point source, with suggestions as to its nature including a low-luminosity active galactic nucleus or an X-ray binary. A new analysis of ROSAT HRI observations finds four X-ray point sources in the central kiloparsec of M82, and we identify radio counterparts for the two brightest X-ray sources. The counterparts are probably young radio supernovae (SNe) and are amongst the most luminous and youthful SNe in M82. We therefore suggest that we are seeing X-ray emission from young SNe in M82, and in particular that the brightest X-ray source is associated with the radio source 41.95+57.5. We discuss the implications of these observations for the evolution of X-ray-luminous SNe.  相似文献   

7.
In the paper we present the results of search for transient sources using the data from the surveys conducted onRATAN-600 at 7.6 cmin the time period of 1980–1994.We detected three events at a level of 3–5σ. A search for coincidenceswith detected transient events was carried out. Using the data from radio and optical surveys and the VizieR, SIMBAD, and NED databases, we made assumptions on the possible nature of these events. The first transient is probably associated with AGN activity, the second—with a cataclysmic GRB event or with a supernova, the origin of the third is not determined. The inference on the possibility of search for variable sources and transients using the data from the RATAN-600 blind surveys was drawn. Searching for transients, we have found twenty-two radio sources which are associated with the NVSS objects but are not included in the RCR catalog. Three of them turned out to be presumably variable.  相似文献   

8.
Active galactic nuclei(AGNs) can be divided into two major classes, namely radio-loud and radio-quiet AGNs. A small subset of the radio-loud AGNs is called blazars, which are believed to be unified with Fanaroff-Riley type Ⅰ/Ⅱ(FRI/Ⅱ) radio galaxies. Following our previous work(Fan et al.), we present a sample of 2400 sources with measured radio flux densities of the core and extended components. The sample contains 250 BL Lacs, 520 quasars, 175 Seyferts, 1178 galaxies, 153 FRI or FRⅡ galaxies and 104 unidentified sources. We then calculate the radio core-dominance parameters and spectral indices, and study their relationship. Our analysis shows that the core-dominance parameters and spectral indices are quite different for different types of sources. We also confirm that the correlation between core-dominance parameter and spectral index exists for a large sample presented in this work.  相似文献   

9.
Active galactic nuclei(AGNs) can be divided into two major classes,namely radio-loud and radio-quiet AGNs.A small subset of the radio-loud AGNs is called blazars,which are believed to be unified with Fanaroff-Riley type Ⅰ and type Ⅱ(FRIⅡ) radio galaxies.Following our previous work,we present a latest sample of 966 sources with measured radio flux densities of the core and extended components.The sample includes 83 BL Lacs,473 flat spectrum radio quasars,101 Seyferts,245 galaxies,52 FRIsⅡs and12 unidentified sources.We then calculate the radio core-dominance parameters and spectral indices and study their relationship.Our analysis shows that the core-dominance parameters and spectral indices are quite different for different types of sources.We also confirm that the correlation between core-dominance parameter and radio spectral index extends over all the sources in a large sample presented.  相似文献   

10.
We present the results of modelling of the radio spectrum evolution and dispersion measure variations of PSR B1259–63, a pulsar in a binary system with Be star LS 2883.We base our model on a hypothesis that the observed variations of the spectrum are caused by thermal free-free absorption occurring in the pulsar surroundings. We reproduce the observed pulsar spectral shapes in order to examine the influence of the stellar wind of LS 2883 and the equatorial disc on the pulsar’s radiation.The simulations of the pulsar’s radio emission and its consequent free-free absorption give us an insight into the impact of stellar wind and equatorial disc of LS 2883 has on the shapes of PSR B1259–63 radio spectra, providing an evidence for the connection between gigahertz-peaked spectra phenomenon and the close environment of the pulsar. Additionally, we supplement our model with an external absorbing medium, which results in a good agreement between simulated and observational data.  相似文献   

11.
The results of analysis of approximately 3 years of gamma-ray observations (August 2008-July 2011) of the radio galaxy Centaurus A with the Fermi Large Area Telescope (Fermi LAT) are presented. By modeling the surrounding (background) sources including the giant lobes of Centaurus A, and using the standard binned likelihood analysis method, the energy spectrum of the core is derived. In the energy range below several GeV it is described by a single power-law with photon index Γ = 2.73 ± 0.06 in agreement with the report of the Fermi LAT collaboration based on the first 10 months observations of the source. However, at higher energies the new data show significant excess above the extrapolation of the energy spectrum from low energies. The total flux between 200 MeV to 50 GeV is estimated to be (1.63 ± 0.14) × 10−7 ph cm−2 s−1. The comparison of the corresponding Spectral Energy Distribution (SED) at GeV energies with the SED in the TeV energy band reported by the H.E.S.S. collaboration shows that we deal with two or perhaps even three components of gamma-radiation originating from different regions located within the central 10 kpc of Centaurus A.  相似文献   

12.
A number of inconsistencies between simple theory and observations of solar radio bursts indicate that mode-mode coupling in the solar corona is much stronger than predicted. The inconsistencies include the absence of predicted reversal of the sense of polarization in a type 1 storm at CMP, and the anomalously weak polarization of type II and type III emission. The strong mode coupling could be explained in terms of small scale inhomogeneities (L N? 100 km) throughout the relevant regions of the corona. The relevant regions are those with open magnetic field lines overlying active regions. It is suggested that the coronal plasma is confined to magnetically self-pinched sheets, and it is pointed out that another inconsistency, namely the anomalously small amount of Faraday variation in type III bursts, could be explained if the value of n e B in the inter-sheet region were two orders of magnitude less than in the sheets.  相似文献   

13.
《New Astronomy Reviews》2002,46(2-7):197-201
The FR II radio galaxy PKS 0349−27 contains a luminous emission-line nebula, extending over several tens of kpc around its host galaxy. We investigate the spatial distribution of the kinematics, line ratios and total emission-line flux of the gas by means of a detailed series of long-slit spectra that cover its entire extent. We show that the physical properties of the line-emitting gas, in particular its ionization properties, excitation state, dynamics and energetics, suggest a scenario involving auto-ionizing shocks as the dominant ionization mechanism.  相似文献   

14.
Bumba  V.  KlvaŇa  M. 《Solar physics》1997,173(1):111-120
An attempt is presented to explain the large difference in the intensity, frequency range and number of radio-activity events following the large flares in the two complex active regions of June 1982 (NOAA 3763 and NOAA 3776). The topology of their local magnetic fields in relation to the global solar field is discussed as one of the main factors causing this effect. The development of a specific, magnetically bipolar super-region is described.  相似文献   

15.
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   

16.
Analyzing 205 radio bursts observed by the Ondejov radiospectrograph in the 1–4 GHz frequency range during 1992 and 1993, we found 6 examples of type II-like radio bursts coinciding with impulsive phases of solar flares. These bursts were interpreted as radio manifestations of MHD (shock) waves generated during impulsive phases of flares in the vicinity of the transition region. Assuming a magnetic-field perturbation origin of these waves, we studied pinch processes in the current sheet near the transition region. In the 2-D MHD numerical model of this current sheet we demonstrated that 2-D pinch processes induced by radiative losses can trigger the impulsive phase of some flares and so generate the observed high-frequency type II-like radio bursts.  相似文献   

17.
During March 20, 1993, from 12:00 to 16:00 UT, repeated radio burst activity was observed in the 0.8–1.2 GHz frequency range. Periods in intervals 0.1–0.5, 0.7–1.0, 2.8–3.9, 75–170 s, and 15–25 min were recognized. This long-lasting narrowband activity consisted mainly of pulsations and continua. In some intervals it was accompanied not only by spikes, broadband pulsations, and fibers in the 1–2 GHz frequency range, but also by type III and U burst activity at lower frequencies as well as by hard X-ray bursts. From several radio bursts, two characterized by different fine structures were selected and compared. The observed differences are explained by different distribution functions of superthermal electrons. The position of the 0.8–1.2 GHz radio source above the photosphere and the magnetic field in the fiber burst source were estimated to be 66 000–75 000 km and 120–135 G, respectively.Presented at te CESRA-Workshop on Coronal Magnetic Energy Release at Caputh near Potsdam in May 1994.  相似文献   

18.
We investigated 64 pairs of interacting-CME events identified from simultaneous observations by the SOHO and STEREO spacecraft from January 2010 to August 2014, to examine the relationship between large SEP events in the energy range of ～25 to～60 MeV and properties of the interacting CMEs.We found that during CME interactions, the large SEP events in this study were all generated by CMEs with the presence of enhanced type Ⅱ radio bursts, which also have wider longitudinal distributions compared to events without a type Ⅱ radio burst or its enhancement(almost always associated with small SEP events).It seems that the signature of type Ⅱ radio burst enhancement is a good discriminator between large SEP and small or no SEP event producers during CME interactions. The type Ⅱ radio burst enhancement is more likely to be generated by CME interactions, with the main CME having a larger speed(v), angular width(WD), mass(m) and kinetic energy(Ek), and taking over the preceding CMEs. The preceding CMEs in these instances have higher v, WD, m and Ekthan those in CME pairs missing type Ⅱ radio bursts or enhancements. Generally, the values of these properties in the type-Ⅱ-enhanced events are typically higher than the corresponding non-type-Ⅱ or non-type-Ⅱ-enhanced cases for both the main and preceding CMEs. Our analysis also revealed that the intensities of associated SEP events correlate negatively with the intersection height of the two CMEs. Moreover, the overlap width of two CMEs is typically larger in type-Ⅱ-enhanced events than in non-type-Ⅱ or non-type-Ⅱ-enhanced events. Most type-Ⅱ-enhanced events and SEP events are coincident and are almost always made by the fast and wide main CMEs that sweep fully over relatively slower and narrower preceding CMEs. We suggest that a fast CME with enough energy completely overtaking a relatively narrower preceding CME, especially at low height, can drive a more energetic shock signified by the enhanced type Ⅱ radio bursts. The shock may accelerate ambient particles(likely provided by the preceding CME) and lead to large SEP events more easily.  相似文献   

19.
Solar type Ⅲ radio bursts are an important diagnostic tool in the understanding of solar accelerated electron beams. They are a signature of propagating beams of nonthermal electrons in the solar atmosphere and the solar system. Consequently, they provide information on electron acceleration and transport, and the conditions of the background ambient plasma they travel through. We review the observational properties of type Ⅲ bursts with an emphasis on recent results and how each property can help identify attributes of electron beams and the ambient background plasma. We also review some of the theoretical aspects of type Ⅲ radio bursts and cover a number of numerical efforts that simulate electron beam transport through the solar corona and the heliosphere.  相似文献   

20.
During 1967–1970, the greatness of 90 large flares (H importance 2) was influenced by the orientation of the large-scale ( 100 000 km) magnetic field structure over the flare site. Although the average X-ray and optical emissions are only slightly larger for flares with their overlying fields directed southward, as opposed to northward, the meter-wave-length prompt flux maxima are, on average, an order of magnitude greater for the flares with southward oriented magnetic fields. There is a comparable, but possibly smaller difference in the 10 cm- fluxes. We therefore conclude that, during this period, the orientation of the overlying magnetic field affects the amount of electromagnetic flare energy radiated promptly in the corona (10 cm- and m-), relative to that radiated in the chromosphere (X-ray and optical). We demonstrate that this statistical effect shows some variability in degree during the period, although the trend is consistent throughout.  相似文献   

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