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1.
Results of a search for and study of variability in a complete sample of flat-spectrum radio sources (83 objects) on time scales longer than a day are reported. The data were obtained in six series of daily observations on the RATAN-600 radio telescope made over 77–103 days at six frequencies from 0.97 to 21.7 GHz and at declinations of 10°–12°30′ (J2000). Variability on time scales of 3–30 days with significance levels below 1% was detected for 19 sources. The time scales, modulation indices, and spectra of the variability derived from an analysis of the light curves, structure functions, and autocorrelation functions are presented for these sources. For a number of them, intrinsic variability and extrinsic variability due to scintillations in the turbulent interstellar medium have been separated. The obtained source characteristics are compared with those for sources at declinations 4°–6° (B1950).  相似文献   

2.
Results of a study of the variability of the BL Lac object S5 0716+714 are reported. The data were obtained in 150 daily observations on the RATAN-600 radio telescope at six frequencies from 0.97 to 21.7 GHz and 13 day-long sessions at a wavelength of 6.2 cm on the 32 m radio telescopes of the Zelenchukskaya, Svetloe, and Badary observatories (Quasar-KVO complex, Institute of Applied Astronomy, Russian Academy of Sciences). The RATAN-600 observations detected three “anti-flares,” or eclipses, when the flux density decreased from an initially constant level and then returned to this level. The eclipse time scales obtained from an analysis of light curves, structure functions, and autocorrelation functions are 12–20 days; the eclipse spectra were determined. Intraday variability (IDV) with time scales of 10–12 hours was detected in three sessions on the 32-m radio telescopes.  相似文献   

3.
We present the results of our observations of compact extragalactic radio sources near the north celestial pole (+75° ≤ δ ≤ +88°) obtained on the RATAN-600 radio telescope. Our sample consists of 51 radio sources with spectra that are either flat or inverted (growing toward shorter wavelengths) and with flux densities at 1.4 GHz S ν ≥ 200 mJy. We observed the sources at 1–21.7 GHz. Multi-frequency instantaneous spectra are presented for 1999–2007. We observed 33 of our sample source daily for 30 days in August 2007. As a result, we revealed 15 objects exhibiting rapid variations on time scales of a day. The multi-frequency instantaneous spectra of these sources indicate that radio flux variations on one-day timescales are characteristic of objects of various spectral types. More than half the sources exhibiting rapid variations demonstrate a growth in the variability amplitude with increasing frequency. For some of the objects, the variability amplitude is virtually independent of frequency.  相似文献   

4.
The tropopause height and tropopause temperature are sensitive to temperature changes in troposphere and stratosphere. These are the measures of global climatic variability. Atmospheric profiles of temperature, refractivity and water vapour are always needed for communication, navigation and atmospheric modeling studies. The tropopause characteristics over the Indian region have been studied using radio occultation measurements (CHAMP) on the basis of cold point criterion. Tropopause height shows large variation in the latitude range ∼30°–40°N during winter. Tropopause temperature less than −82°C, assumed to facilitate troposphere to stratosphere air transport, is observed at a number of tropical Indian locations and no seasonal pattern is observed in its occurrence. The bias in temperature and refractivity deduced from radiosonde and radio occultation measurements is also presented.  相似文献   

5.
Results of observations of the five candidate GPS sources J0626+8202, J0726+7911, J1044+8054, J1823+7938, and J1935+8130 are presented. GPS sources are extragalactic sources whose spectral peaks are near several GHz. These objects were observed on the RATAN-600 radio telescope from 1999 through 2010 at 1.1, 2.3, 4.8, 7.7, 11.2, and 21.7 GHz. These radio sources were selected from a complete sample (S v ≥ 200 mJy at 1.4 GHz) in the vicinity of the North Celestial Pole (+75° ≤ δ ≤ +88°); four are considered as GPS candidates for the first time here. Their spectral properties, variability and morphology are analyzed, and confirms that these can be classified as GPS sources. These four to five GPS sources probably comprise a complete sample of this class of object in this region of the celestial sphere.  相似文献   

6.
We present optical identifications, classifications, and radio spectra for 19 radio sources from a complete sample in flux density with declinations 10°–12°30′ (J2000) obtained with the 6-m optical telescope (4000–9000 Å) and RATAN-600 radio telescope (0.97–21.7 GHz) of the Special Astrophysical Observatory. Twelve objects with redshifts from 0.573 to 2.694 have been classiffied as quasars, and two objects with featureless spectra as BL Lac objects. Four objects are emission-line radio galaxies with redshifts from 0.204 to 0.311 (one also displaying absorption lines), and one object is an absorption-line galaxy with a redshift of 0.214. Radio flux densities have been obtained at six frequencies for all the sources except for two extended objects. The radio spectra of five of the sources can be separated into extended and compact components. Three objects display substantial rapid (on time scales from several days to several weeks) and long-term variability of their flux densities.  相似文献   

7.
Results of radio observations of the cosmic gamma-ray burst GRB 080319B at 8.45 GHz during the afterglow are reported. The observations were carried out on telescopes of the Zelenchukskaya and Svetloe Observatories of the Institute of Applied Astronomy, Russian Academy of Sciences. Two outbursts in the radio brightness were detected in the afterglow of GRB 080319B. A total of 148 radio observations were performed at 3.5, 6.2, and 13 cm. The observations were conducted in a mode with smooth scanning in elevation, which was also used to update the flux densities of the primary reference sources. The first powerful radio outburst was recorded on March 28, 2008, 6.86d after the gamma-ray burst, when the maximum flux density was F 8.45 GHz = 44 ± 12 mJy. Almost two months later, a second increase in the radio brightness was observed. The flux density monotonically increased from 19 mJy (59.55d) to 34mJy (59.79d) over 6.5 h; 1.17 d later, the flux density fell to 12mJy.At this last epoch, the radio flux demonstrated variability within 3σ on timescales of 9d−10d. The detected radio brightness increases are interpreted in terms of MHD interactions of a fast plasma outflow with a cloud of inhomogeneous surrounding medium. This interaction is accompanied by restructuring of the relativistic plasma outflow; the analysis of this process has been carried out.  相似文献   

8.
Spatial variation of seismicity parameters across India and adjoining areas   总被引：2，自引：2，他引：0  
An attempt has been made to quantify the variability in the seismic activity rate across the whole of India and adjoining areas (0–45°N and 60–105°E) using earthquake database compiled from various sources. Both historical and instrumental data were compiled and the complete catalog of Indian earthquakes till 2010 has been prepared. Region-specific earthquake magnitude scaling relations correlating different magnitude scales were achieved to develop a homogenous earthquake catalog for the region in unified moment magnitude scale. The dependent events (75.3%) in the raw catalog have been removed and the effect of aftershocks on the variation of b value has been quantified. The study area was divided into 2,025 grid points (1°×1°) and the spatial variation of the seismicity across the region have been analyzed considering all the events within 300 km radius from each grid point. A significant decrease in seismic b value was seen when declustered catalog was used which illustrates that a larger proportion of dependent events in the earthquake catalog are related to lower magnitude events. A list of 203,448 earthquakes (including aftershocks and foreshocks) occurred in the region covering the period from 250 B.C. to 2010 A.D. with all available details is uploaded in the website .  相似文献   

9.
The presented observation results of the blazar J0238+1636 were obtained in: 2014–2019 with the RATAN-600 radio telescope from the Special Astrophysical Observatory of the Russian Academy of Sciences at 2.3, 4.8, 8.2, 11.2, and 21.7 GHz; and 2015–2017 with the 32-m Zelenchuk and Badary radio telescopes of the Institute of Applied Astronomy of the Russian Academy of Sciences at 4.84 and 8.57 GHz. Two flares were detected on the long-term light curve. The time scale for variability on the rising branch of the first flare is τvar = 0.5 year, and the upper limit for the linear and angular sizes of the emitting region at 21.7 GHz are 0.3 pc and 0.05 mas, respectively. The brightness temperature is Tb ≥ 2.6 × 1013 K, and the Doppler factor is δ ≥ 3. In three sets of the source’s daily observations, which lasted up to three months each, no significant variability on the day-to-day scale was found after subtracting the long-term variability. In the RT-32 data, the intraday variability (IDV) was found at a frequency of 4.84 GHz in three out of 15 sessions and at 8.57 GHz in two out of 13 sessions. The characteristic times for variability are 4−5 hours.  相似文献   

10.
The paper reports the results of ten-year centimeter-wavelength observations with the RATAN-600 radio telescope of a complete sample of 83 flat-spectrum sources from the GB6 catalog of the MGB Survey, with S 4.85 > 200 mJy at declinations 10°?C12°30??. Starting in 2000, the observations were conducted simultaneously at six frequencies in the range 0.97?C21.7 GHz. Seventy-six sources (including 54 quasars) have been identified with optical objects, which have redshifts in the range z = 0.331?C3.601. Analysis of light curves and spectra at different activity phases has shown that, in most cases, the dynamics of the development of flares is consistent with a model in which the variability results from the evolution of a shock in a radio jet. A relationship between the time scales for the rise and fall of the flares has been found. There is no redshift dependence of the true linear dimensions of the radiating regions and the variability indices obtained over ten years. These facts can be interpreted as an absence of cosmological evolution of quasars at least up to z ?? 3.  相似文献   

11.
The Lianhuashan tungsten deposit occurs in the volcanic terrain in the coastal area of Southeast China,where rhyolite,quartz porphyry and granite consitute a complee magmatic series.The orebodies are located in the endo-and exo-contacts between the quartz porphyry and the metasandstone of the Xiaoping coal measues.Hongenization temperatures of melt inclusions in zircon and quartz are 1100℃and 1050℃ for rhyolite,1000℃ and 860℃for quartz porphyry,and 950-1000℃and 820℃ for granite,respectively,demonstrating that the rockforming temperatures dropped successively from the eruptive to the intrusive rocks and that the homogenization temperatures of melt inclusions in zircon are 50-180℃higher than those in quartz.Homogenization temperatures of gas-liquid inclusions in quartz are 230-520℃（mostly 230-270℃）for quartz porphyry,200-450℃（mostly 200-360℃）for ore-bearing quartz veins,150-210℃for granite 170-200℃ for the vein quartz in it.Quartz from the quartz porphyry and from the ore-earing quartz veins show similar characteristics in inclusion type and homogenization temperature,indicating that intergranular solutions must have been formed upon cooling of magma and that ore-forming solutions for the tungstem mineralization were evolved mainly from ore-bearing intergranular solutions in the quartz porphyry.  相似文献   

12.
In hard-rock terrain, due to the lack of primary porosity in the bedrock, joints, fault zones, and weathered zones are the sources for groundwater occurrence and movement. To study the groundwater potential in the hard-rock terrain and drought-prone area in the Niva River basin, southern Andhra Pradesh state, India, Landsat 5 photographic data were used to prepare an integrated hydrogeomorphology map. Larsson's integrated deformation model was applied to identify the various fracture systems, to pinpoint those younger tensile fracture sets that are the main groundwater reservoirs, and to understand the importance of fracture density in groundwater prospecting. N35°–55°E fractures were identified as tensile and N35°–55°W fractures as both tensile and shear in the study area. Apparently, these fractures are the youngest open fractures. Wherever N35°–55°E and N35°–55°W fracture densities are high, weathered-zone thickness is greater, water-table fluctuations are small, and well yields are high. Groundwater-potential zones were delineated and classified as very good, good to very good, moderate to good, and poor. Electronic Publication  相似文献   

13.
We present optical identifications and radio spectra for ten radio sources from two flux-density-complete samples. Radio variability characteristics are presented for four objects. The observations were obtained on the RATAN-600 radio telescope at 0.97–21.7 GHz and the 2.1 m telescope of the Haro Observatory in Cananea, Mexico at 4200–9000 Å. Among the ten objects studied, three are quasars, four are BL Lac objects, two are radio galaxies, and one is a Sy 1 galaxy. Two of the sources identified with BL Lac objects, 0509+0541 and 0527+0331, show rapid variability on time scales of 7–50 days.  相似文献   

14.
Antarctic ice core records have provided unprecedented information on past climatic changes and forcing factors on decadal to millennial timescales. The glaciochemical and stable isotope records of a shallow ice core from the coastal Dronning Maud Land (East Antarctica) were used here to reconstruct the coastal Antarctic environmental variability during the past ∼470 years. Sea salt ion data indicate a significant additional contribution of chloride ions compared to sea water values, possibly through atmospheric scavenging. The nitrate (NO3 −) profile exhibit significant temporal shifts than that of the sulphate (SO4 2−), with a major shift around 1750 AD. The changes in NO3 − record are synchronous with the proxy record of solar activity (10Be profile from a South Pole ice core), suggesting enhanced NO3 − values during periods of reduced solar activity like the Dalton Minimum (∼1790–1830 AD) and Maunder Minimum (∼1640–1710 AD). The δ18O records reveal that the more negative δ18O values were coeval with several events of increased NO3 − concentrations, suggesting enhanced preservation of NO3 − during periods of reduced air temperatures. The δ18O and δD records of the core also suggest significant short-term and long-tem variability with more negative values indicating relatively lower air temperatures prior to 1715 AD. The δ18O records also revealed a significant warming of 2.7°C for the past 470 years, with a warming of ∼0.6°C per century.  相似文献   

15.
We present classifications, optical identifications, and radio spectra for 19 radio sources from three complete samples, with declinations 4°–6° (B1950, S 3.9 GHz > 200 mJy), 10°–12°30′ (J2000, S 4.85 GHz > 200 mJy), and 74°–75° (J2000, S 4.85 GHz > 100 mJy). We also present corresponding information for the radio source J0527+0331. The right ascensions are 0–24h and the Galactic latitudes |b| > 15° for all the samples. Our observations were obtained with the 6 m telescope from the Special Astrophysical Observatory in the range 4000–9000 Å or 4000–7500 Å and the RATAN-600 radio telescope at frequencies in the range 0.97–21.7 GHz. We obtained flux densities for the radio sources and optical spectra for their optical counterparts. Nine objects were classified as quasars with redshifts from z = 1.029 to 3.212; nine objects are emission-line galaxies with redshifts from 0.172 to 0.546, and one is a galaxy with burstlike star formation at z = 0.156, and one is a BL Lac object with z = 0.509. The spectra of five radio sources were decomposed into extended and compact components. The radio source J0527+0331, identified with a BL Lac object, displays significant variations of time scales from several days to several years. Data on flux variations are presented for 11 radio sources, as well as their spectra at several epochs.  相似文献   

16.
To estimate the behavior of Au, Pd, REE, and Y in magmatic and postmagmatic processes, a series of experimental studies on the solubility of noble metals and REE in magma, magmatic fluid, and hydrothermal solutions has been performed in wide temperature and pressure ranges (300–400°C, 860–1350°C; 1–14 kbar). The coefficients of Au and Pd partitioning (D F/L) between fluid and tholeiitic melt have been determined. Depending on P, T, and the composition of the system, they vary from 1 to 11 for Au and 0.02 to 1 for Pd. The phase solubility technique was used to determine Au and Pd solubility in hydrothermal fluid. The effects of temperature, composition, and fluid acidity on Au and Pd solubility have been estimated. The high solubility of these metals in aqueous chloride solutions has been established for both Au (28–803 mg/kg at T = 300°C, 305–1123 mg/kg at T = 350°C, and 330–1400 mg/kg at T = 400°C) and Pd (40–126 mg/kg at T = 300°C, 62–152 mg/kg at T = 350°C, and 20–210 mg/kg at T = 400°C). The coefficients of REE and Y partitioning (D F/L) between fluid and tholeiitic or alkaline melts have been determined. They vary from 0.00n to 2 depending on P, T, and fluid composition. The experimental data on Au and Pd solubility in solutions and magmatic fluids and the wide variation of REE D F/L between fluid and melt show that magmatic and hydrothermal fluids are efficient agents of Au, Pd, and REE transfer and fractionation. The obtained experimental data were used for elucidating sources of fluids and their role in the genesis of Au-Pd-REE occurrences in the Subpolar Urals.  相似文献   

17.
A temperature–time path was constructed for high-temperature low-pressure (HT–LP) migmatites of the Bayerische Wald, internal zone of the Variscan belt, Germany. The migmatites are characterised by prograde biotite dehydration melting, peak metamorphic conditions of approximately 850 °C and 0.5–0.7 GPa and retrograde melt crystallisation at 800 °C. The time-calibration of the pressure–temperature path is based on U–Pb dating of single zircon and monazite grains and titanite separates, on 40Ar/39Ar ages obtained by incremental heating experiments on hornblende separates, single grains of biotite and K-feldspar, and on 40Ar/39Ar spot fusion ages of biotite determined in situ from sample sections. Additionally, crude estimates of the duration of peak metamorphism were derived from garnet zoning patterns, suggesting that peak temperatures of 850 °C cannot have prevailed much longer than 2.5 Ma. The temperature–time paths obtained for two areas approximately 30 km apart do not differ from each other considerably. U–Pb zircon ages reflect crystallisation from melt at 850–800 °C at 323 Ma (southeastern area) and 326 Ma (northwestern area). The U–Pb ages of monazite mainly coincide with those from zircon but are complicated by variable degrees of inheritance. The preservation of inherited monazite and the presence of excess 206Pb resulting from the incorporation of excess 230Th in monazite formed during HT–LP metamorphism suggest that monazite ages in the migmatites of the Bayerische Wald reflect crystallisation from melt at 850–800 °C and persistence of older grains at these temperatures during a comparatively short thermal peak. The U–Pb ages of titanite (321 Ma) and 40Ar/39Ar ages of hornblende (322–316 Ma) and biotite (313–309 Ma) reflect cooling through the respective closure temperatures of approximately 700, 570–500 and 345–310 °C published in the literature. Most of the feldspars' ages (305–296 Ma) probably record cooling below 150–300 °C, while two grains most likely have higher closure temperatures. The temperature–time paths are characterised by a short thermal peak, by moderate average cooling rates and by a decrease in cooling rates from 100 °C/my at temperatures between 850–800 and 700 °C to 11–16 °C/my at temperatures down to 345–310 °C. Further cooling to feldspar closure for Ar was probably even slower. The lack of decompressional features, the moderate average cooling rates and the decline of cooling rates with time are not easily reconciled with a model of asthenospheric heating, rapid uplift and extension due to lithospheric delamination as proposed elsewhere. Instead, the high peak temperatures at comparatively shallow crustal levels along with the short thermal peak require external advective heating by hot mafic or ultramafic material. Received: 7 July 1999 / Accepted: 28 October 1999  相似文献   

18.
We use daily satellite estimates of sea surface temperature (SST) and rainfall during 1998–2005 to show that onset of convection over the central Bay of Bengal (88–92°E, 14–18°N) during the core summer monsoon (mid-May to September) is linked to the meridional gradient of SST in the bay. The SST gradient was computed between two boxes in the northern (88–92°E, 18–22°N) and southern (82–88°E, 4–8°N) bay; the latter is the area of the cold tongue in the bay linked to the Summer Monsoon Current. Convection over central bay followed the SST difference between the northern and southern bay (ΔT) exceeding 0.75°C in 28 cases. There was no instance of ΔT exceeding this threshold without a burst in convection. There were, however, five instances of convection occurring without this SST gradient. Long rainfall events (events lasting more than a week) were associated with an SST event (ΔT ≥ 0.75°C); rainfall events tended to be short when not associated with an SST event. The SST gradient was important for the onset of convection, but not for its persistence: convection often persisted for several days even after the SST gradient weakened. The lag between ΔT exceeding 0.75°C and the onset of convection was 0–18 days, but the lag histogram peaked at one week. In 75% of the 28 cases, convection occurred within a week of ΔT exceeding the threshold of 0.75°C. The northern bay SST, T N , contributed more to ΔT, but it was a weaker criterion for convection than the SST gradient. A sensitivity analysis showed that the corresponding threshold for T N was 29°C. We hypothesise that the excess heating (∼1°C above the threshold for deep convection) required in the northern bay to trigger convection is because this excess in SST is what is required to establish the critical SST gradient.  相似文献   

19.
Garnet-spinel peridotites form small, isolated, variably retrogressed bodies within the low-pressure high-temperature gneisses and migmatites of the Variscan basement of the Schwarzwald, southwest Germany. Detailed mineralogical and textural studies as well as geothermobarometric calculations on samples from three occurrences are presented. Two of the garnet-spinel peridotites have equilibrated at 680–770°C, 1.4–1.8 GPa within the garnet-spinel peridotite stability field, one of the samples having experienced an earlier stage within the spinel peridotite stability field (790°C, <1.8 GPa). The third sample, with only garnet and spinel preserved, probably equilibrated within the garnet peridotite stability field at higher pressures. These findings are in line with the distinction of two groups of ultramafic garnet-bearing high-pressure rocks with different equilibration conditions within the Schwarzwald (670–740°C, 1.4–1.8 GPa and 740–850°C, 3.2–4.3 GPa) which has previously been established (Kalt et al. 1995). The equilibration conditions of 670–770°C and 1.4–1.8 GPa for garnet-spinel peridotites from the Central Schwarzwald Gneiss Complex (CSGC) are similar to those for eclogites of the Schwarzwald and also correspond quite well to those for garnet-spinel peridotites from the Moldanubian zone of the Vosges mountains and of ecologites from the Moldanubian s.str. of the Bohemian Massif.  相似文献   

20.
《Quaternary Science Reviews》2007,26(5-6):579-584
High-resolution analyses of allochthonous pollen input into crater lake sediments of Laguna Potrok Aike in the semi-arid Patagonian steppe reflect the variability of zonal wind intensities during the Holocene at 52° southern latitude. These indicators for Southern Hemisphere westerlies (SHW) strength vary on centennial timescales in concert with carbon/nitrogen (C/N) ratios and titanium (Ti) contents, interpreted as differential organic matter sources and minerogenic input to the sediment, respectively. The correlations underline a linkage between hydrological variability and west wind variability in Extra-Andean Patagonia. A shift to generally more intense SHW suggests intensification towards modern wind conditions at that latitude since 9.2 ka cal BP.  相似文献   

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