Instantaneous radio spectra of giant pulses from the crab pulsar from decimeter to decameter wavelengths

The results of simultaneous multifrequency observations of giant radio pulses from the Crab pulsar, PSR B0531+21, at 23, 111, and 600 MHz are presented and analyzed. Giant pulses were detected at a frequency as low as 23 MHz for the first time. Of the 45 giant pulses detected at 23 MHz, 12 were identified with counterparts observed simultaneously at 600 MHz. Of the 128 giant pulses detected at 111 MHz, 21 were identified with counterparts observed simultaneously at 600 MHz. The spectral indices for the power-law frequency dependence of the giant-pulse energies are from ?3.1 to ?1.6. The mean spectral index is ?2.7 ± 0.1 and is the same for both frequency combinations (600–111 MHz and 600–23 MHz). The large scatter in the spectral indices of the individual pulses and the large number of unidentified giant pulses suggest that the spectra of the individual giant pulses do not actually follow a simple power law. The observed shapes of the giant pulses at all three frequencies are determined by scattering on interstellar plasma inhomogeneities. The scatter-broadening of the pulses and its frequency dependence were determined as τ _sc = 20(ν/100)^?3.5±0.1 ms, where frequency ν is in MHz.     

Radio astronomy ultra-low-noise amplifier for operation at 91 cm wavelength in high RFI environment

An ultra-low-noise input amplifier intended for a use in a radio telescope operating at 91 cm wavelength is presented. The amplifier noise temperatures are 12.8?±?1.5 and 10.0?±?1.5?K at ambient temperatures of 293 and 263?K respectively. The amplifier does not require cryogenic cooling. It can be quickly put in operation thus shortening losses in the telescope observation time. High linearity of the amplifier (output power at 1 dB gain compression P_1dB?≥?22 dBm, output third order intercept point OIP3?≥?37 dBm) enables the telescope operation in highly urbanized and industrialized regions. To obtain low noise characteristics along with high linearity, high-electron-mobility field-effect transistors were used in parallel in the circuit developed. The transistors used in the amplifier are cost-effective and commercially available. The circuit solution is recommended for similar devices working in ultra-high frequency band.     

Study of the Rapid Variability of the BL Lac Object MRK 421 in the Optical Range

Astrophysics - MRK 421 is a giant elliptical galaxy in the Ursa Major constellation whose core has all the properties of a BL Lac object. It manifests a high activity and variability from the radio...     

OH 1720-MHz lines as tracers of bipolar outflows in the vicinity of Class I methanol masers

A sample of Class I methanol masers (MMI) has been surveyed at 1720 MHz to search for possible associations between MMI and 1720-MHz OH masers, which should be formed by the same collisional pumping mechanism. If the model for methanol masers is correct, the sample should contain a statistically significant number of 1720-MHz OH masers at the positions of MMI. The observations were conducted on the 70-meter radio telescope of the National Academy of Sciences of Ukraine (NASU). The results show that ??50% of 72 MMI are associated with OH emission at 1720 MHz. In many sources, strong absorption lines are also observed. In most cases, the OH (1720) lines are narrow (linewidths of <2 km/s) suggesting they may be maser lines. The OH column densities obtained from Gaussian fitting of these narrow OH lines are, on average, 1.5 × 10¹⁷ cm^?2. TheH² density in the emitting medium reaches 10⁷ cm^?3 if the region of the OH (1720) emission has been subject to interaction with a bipolar-outflow front. This is sufficient to excite MMI, and the presence of narrow, possibly masing OH (1720) lines at the MMI velocities indicates the likely presence of shocks from bipolar outflows in the vicinity of the maser condensations, supporting models in which these molecules are collisionally pumped.     

Re-Os同位素定年方法进展及ICP-MS精确定年测试关键技术

本文介绍了Re-Os同位素定年的基本原理、技术发展及应用现状;综述了样品分解和Re-Os分离富集的主要方法,重点对ICP-MS法进行Re-Os同位素定年做了较详尽的介绍,包括质量分馏校正、干扰校正、含量初测、取样量的确定、稀释剂的稀释比及稀释剂加入量等,以确保高精度测试;评述了ICP-MS最常见的测定对象-辉钼矿中Re-Os的失耦现象及降低其对Re-Os同位素定年影响的对策,文中描述了由测定同位素比值计算含量时的误差传递公式并重申了最佳稀释比。最后,指出了Re-Os同位素定年方法研究中应该关注的工作方向。     

Decametric survey of discrete sources in the northern sky

This paper presents results and describes the improved data processing algorithm of the low frequency sky survey of discrete sources carried out with the UTR-2 radio telescope. The measurements were conducted within the frequency range 10 to25 MHz. Coordinates and flux densities of the sources detected were obtained. Identification with sources from the 4C survey has been done. The resulting catalogue contains parameter estimates for 483 sources on a set of frequencies within the UTR-2 range. This revised version was published online in July 2006 with corrections to the Cover Date. This revised version was published online in July 2006 with corrections to the Cover Date.     

The New Preamplification System for the UTR-2 Radio Telescope

The paper describes the preamplification antenna system (PAS) ofthe decameter radio telescope UTR-2. The new PAS have the continuous frequency range 8 to 40 MHz. The dynamic range is: 54 dbm at low frequencies and 30 dbm at high frequencies. To extendthe dynamic range the signal spectrum is divided and summed up with the aid of frequency selective devices, each consisting oftwo identical antimetric bandpass filters of even order and twohybrid adders. Within each of the three bands, the signal is amplified in multistage amplifiers with a deep linear frequencyindependent negative feedback in each stage. Part One presents thegoals, underlying ideas and structure of the PAS. Part Twodescribes details of the design, specific parameters and some observational results.     

Energy of anomalously intense pulsar pulses at decameter wavelengths

Cumulative and differential energy distributions are derived for the subpulse radio emission from the pulsars B0809+74, B0943+10, B0950+08, and B1133+16 at decameter wavelengths. The obtained cumulative distributions are compared with the analogous characteristic distributions for giant pulsar pulses. The analysis suggests that the amplification mechanisms in pulsar magnetospheres producing giant pulses and anomalously intense pulses may be similar.