Identification of a Likely Radio Counterpart of the Rapid Burster

We have identified a likely radio counterpart to the low-mass X-ray binary MXB 1730-335 (the Rapid Burster). The counterpart has shown 8.4 GHz radio on/off behavior correlated with the X-ray on/off behavior as observed by the RXTE/ASM during six VLA observations. The probability of an unrelated, randomly varying background source duplicating this behavior is 1-3% depending on the correlation time scale. The location of the radio source is RA 17h 33m 24.61s; Dec -33d 23' 19.8" (J2000), +/- 0.1". We do not detect 8.4 GHz radio emission coincident with type II (accretion-driven) X-ray bursts. The ratio of radio to X-ray emission during such bursts is constrained to be below the ratio observed during X-ray persistent emission at the 2.9-sigma level. Synchrotron bubble models of the radio emission can provide a reasonable fit to the full data set, collected over several outbursts, assuming that the radio evolution is the same from outburst to outburst, but given the physical constraints the emission is more likely to be due to ~hour-long radio flares such as have been observed from the X-ray binary GRS 1915+105.Comment: 28 pages, 4 figures; accepted for publication in ApJ (no changes

Multifrequency spectra of solar brightness temperature derived from eclipse observations

Changes in solar radio-brightness temperature were derived at 2.8,19.3 and 22.2 GHz from the observations of radio flux during the total eclipse of 1980 February 16. High-resolution MEM spectra of the brightness temperature fluctuations at the three frequencies showed periodicities ranging from 3.5 min to 128 min. Between 3.5 min and 14.6 min there are several periodicities of comparable significance common to the three operating frequencies. If the corresponding variations in brightness temperature are assumed to result from spatial variations in the solar radio emission, the observed periodicities imply scale sizes in the range 76000 km to 320000 km

Multi-Frequency observations of radio sun during total solar eclipse of February 16, 1980

Measurements of radio flux of the Sun duirng the total solar eclipse on February 16, 1980 were made from the Japal-Rangapur Observatory near Hyderabad, at radio frequencies of 2.8, 10, 19 and 22.2 GHz. Observations for both ingress and egress are available. Residual fluxesat totality for 2.8, 10 and 19 GHz were 23, 3.5 and 3 per cent respectively. The minimum fluxes were observed from 2 to 7 minutes prior to the mid-eclipse

Applications of microwave in remote sensing

343-358The unique potentials of microwaves in remote sensing and the various types of microwave sensors used for this purpose have been described. Each type of sensor has been described along with the Indian experience in respect of design, development and utilization of some of these. Various parameters of microwave sensors for different application needs have been discussed and optimum system parameters for each sensor have been suggested. A methodology for arriving at an integrated microwave remote sensing mission has been described. According, possible sensor packages based on application needs of natural resources survey, meteorology and atmospheric sciences, have been suggested with optimum parameters for flying onboard the satellites for space-based microwave remote sensing

Emission behaviour of foam covered water surface at microwave frequencies

98-103An estimation of emissivity of foam covered water surface has been proposed, based on the layered media approach applicable for horizontal and vertical polarization. The results show that the emissivity increases with vertical polarization and has higher value than the horizontal polarization

Measurement of forward scattering coefficient of different water bodies at different frequencies

178-185The thrust of this study is to analyse the effect of scattering of electromagnetic waves on microwave links and tracking of low flying objects in the presence of strong ground bounce return from water bound areas. For this purpose, a ground based bi-static forward scatterometer has been used to generate co-polarized specular data at CJ, X, and Ku bands. The measurements are carried out on three types of water surfaces, i.e. tap water, natural lake water and saline water. All the three water surfaces are assumed to be slightly rough surfaces at the frequency of interest. Therefore, small perturbation model of slightly rough surface for forward scattering is a good selection to analyse data. The scattered microwave power from the terrain measured for 25° - 70° scattering angle (s) with an interval of 5° in specular direction with transmitting antenna placed at an incidence angle (i) of 45° from nadir illuminates the terrain keeping i = s = 0° at 5.825, 9.472 and 13.4 GHz in CJ, X and KU bands, respectively for vv and hh polarization with different antenna heights. The forward scattering coefficient computed with the help of experimental geometry parameters, which then compared with estimated value of scattering coefficient <span style="font-family:Times-Bold;mso-bidi-font-family: Times-Bold;mso-bidi-font-weight:bold" lang="EN-GB">obtained from small perturbation model of slightly rough surface.<span style="font-family:Times-Bold;mso-bidi-font-family:Times-Bold;mso-bidi-font-weight: bold" lang="EN-GB"> A good agreement between observed and estimated scattering coefficient for horizontal (hh) and vertical (vv) polarization has been found in X and KU bands with a polarization reversal in CJ band. It is also observed that dissolved salt or impurities increase the value of scattering coefficient. The basic purpose of this study is to map and monitor the natural resources and to provide timely inputs for the planners to develop appropriate strategies for optimum utilisation of the resources. </span

Study of emissivity of dry and wet loamy sand soil at microwave frequencies

140-145Results of estimation of emissivity from dielectric constant of dry and wet soil using emissivity model for microwave frequencies ranging from 2 GHz to 20 GHz are presented. The measurements of the dielectric constant of d1y and wet soil had been carried out using HP network analyzer and HP dielectric probe employing co-axial probe method. The estimations are made with incidence angles 0°, 30°, 45° and 60° for both horizontal and vertical polarization. The emissivity, which is less than one, increases with frequency and decreases with moisture content.In both the cases emissivity for vertical polarization is higher than that for horizontal polarization