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Register a new userSimultaneous Observations of Giant Pulses from Pulsar PSR B0031-07 at 38 MHz and 74 MHz
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The first station of the Long Wavelength Array (LWA1) was used to study PSR~B0031-07 with simultaneous observations at 38 and 74~MHz. We found that 158 (0.35%) of the observed pulses at 38~MHz and 221 (0.49%) of the observed pulses at 74~MHz qualified as giant pulses in a total of 12 hours of observations. Giant pulses are defined as having flux densities of a factor of $geq$ 90 times that of an average pulse at 38~MHz and $geq$ 80 times that of an average pulse at 74~MHz. The cumulative distribution of pulse strength follows a power law, with an index of $-$4.2 at 38~MHz and $-$4.9 at 74~MHz. This distribution has a much more gradual slope than would be expected if observing the tail of a Gaussian distribution of normal pulses. The dispersion measure value which resulted in the largest signal-to-noise for dedispersed pulses was DM $=10.9$~pc~cm$^{-3}$. No other transient pulses were detected in the data in the wide dispersion measure range from 1 to 5000~pc~cm$^{-3}$. There were 12 giant pulses detected within the same period from both 38 and 74~MHz, meaning that the majority of them are not generated in a wide band.
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We report the detection of giant pulse emission from PSR~B0950+08 in 12 hours of observations made simultaneously at 42~MHz and 74~MHz, using the first station of the Long Wavelength Array, LWA1. We detected 275 giant pulses (in 0.16% of the pulse periods) and 465 giant pulses (0.27%) at 42 and 74~MHz, respectively. The pulsar is weaker and produces less frequent giant pulses than at 100~MHz. Here, giant pulses are taken as having $geq$ 10 times the flux density of an average pulse; their cumulative distribution of pulse strength follows a power law, with a index of $-$4.1 at 42~MHz and $-$5.1 at 74~MHz, which is much less steep than would be expected if we were observing the tail of a Gaussian distribution of normal pulses. We detected no other transient pulses in a wide dispersion measure range from 1 to 5000~pc~cm$^{-3}$. There were 128 giant pulses detected within in the same periods from both 42 and 74~MHz, which means more than half of them are not generated in a wide band. We use CLEAN-based algorithm to analyze the temporal broadening and conclude that the scattering effect from the interstellar medium can not be observed. We calculated the altitude $r$ of the emission region using the dipolar magnetic field model. We found $r$(42~MHz) = 29.27~km ($0.242%$ of $R_{LC}$) and $r$(74~MHz) = 29.01~km ($0.240%$ of $R_{LC}$) for the average pulse, while for giant pulses, $r$(42~MHz) = 29.10~km ($0.241%$ of $R_{LC}$) and $r$(74~MHz) = 28.95~km ($0.240%$ of $R_{LC}$). Giant pulses, which have a double-peak structure, have a smaller mean peak-to-peak separation compared to the average pulse.
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We report 1405 MHz measurements of the flux density of the approximately 320 year old supernova remnant Cassiopeia A, relative to the flux density of Cygnus A, made between 1995 and 1999. When compared to measurements made between 1957 and 1976, we find that the rate at which Cassiopeia A has been fading at this and nearby frequencies has changed from approximately 0.9 % yr^-1 in the 1960s to approximately 0.6 - 0.7 % yr^-1 now. Furthermore, we have collected from the literature measurements of this fading rate at lower (38 - 300 MHz) and higher (7.8 - 16.5 GHz) frequencies. We show that the fading rate has dropped by a factor of approximately 3 over the past 50 years at the lower frequencies, while remaining relatively constant at the higher frequencies, which is in agreement with the findings of others. Our findings at 1405 MHz, in conjunction with a measurement of the fading rate at the nearby frequency of 927 MHz by Vinyajkin (1997), show an intermediate behavior at intermediate frequencies. We also find that Cassiopeia A, as of approximately 1990, was fading at about the same rate, approximately 0.6 - 0.7 % yr^-1, at all of these frequencies. Future measurements are required to determine whether the fading rate will continue to decrease at the lower frequencies, or whether Cassiopeia A will now fade at a relatively constant rate at all of these frequencies.
Reaching the thermal noise at low frequencies with the next generation of instruments (e.g. SKA, LOFAR etc.) is going to be a challenge. It requires the development of more advanced techniques of calibration compared to those used from the traditional radio astronomy until now. This revolution has slowly started, from self-cal, going through field based correction and SPAM up to the formulation and application of a general Measurement Equation. We will describe and compare the several approaches of calibration used so far to reduce low frequency data. We will present some results of a 74 MHz VLA observation in exceptional ionospheric conditions of the giant radio galaxy 3C326 for which some of these methods have been successfully applied.
Although originally discovered as a radio-quiet gamma-ray pulsar, J1732-3131 has exhibited intriguing detections at decameter wavelengths. We report an extensive follow-up of the pulsar at 327 MHz with the Ooty radio telescope. Using the previously observed radio characteristics, and with an effective integration time of 60 hrs, we present a detection of the pulsar at a confidence level of 99.82%. The 327 MHz mean flux density is estimated to be 0.5-0.8 mJy, which establishes the pulsar to be a steep spectrum source and one of the least-luminous pulsars known to date. We also phase-aligned the radio and gamma-ray profiles of the pulsar, and measured the phase-offset between the main peaks in the two profiles to be 0.24$pm$0.06. We discuss the observed phase-offset in the context of various trends exhibited by the radio-loud gamma-ray pulsar population, and suggest that the gamma-ray emission from J1732-3131 is best explained by outer magnetosphere models. Details of our analysis leading to the pulsar detection, and measurements of various parameters and their implications relevant to the pulsars emission mechanism are presented.
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