MSPES - Meterwavelength Single-pulse Polarimetric Emission Survey
Observations
The pulsar observations were carried out at the GMRT (Giant Metrewave Radio Telescope) between January and August 2014 covering 25 observing days and roughly 180 hours Telescope time. In order to reach sufficient sensitivity for single pulse studies we used around 20 antennas in the phased-array which included all the available antennas in the central square and the two nearest arm antennas. The extreme arm antennas were not included since they would dephase very fast (within 15 minutes), as a result of ionospheric variations, and would reduce the effective S/N. We observed at two separate frequency bands roughly between 317−333 MHz and 602−618 MHz. We used a total bandwidth of 16.67 MHz spread over 256 channels with time resolution of 0.245 milliseconds. The final time-series data were equivalent to a large single dish and similar polarization calibration can be applied to get the calibrated Stokes parameters. The polarization data were gain corrected and converted to the four Stokes parameters (I, Q, U, V) for each individual spectral channels. Finally, we searched for and rejected spectral channels affected by radio frequency interference (RFI) before averaging the channels, adjusted to the upper edge of the band at 333 MHz and 618 MHz, respectively, for each of the four Stokes parameters. During each observing run the data quality was frequently monitored by interspersing the test pulsars B0950+08, B1133+16 and B1929+10 at regular intervals and different parallactic angles.
Sample selection
In recent years a large number of pulsars have been discovered by the Parkes radio telescope in the declination range south of +25° which are largely inaccessible to the majority of radio telescopes located at higher northern latitudes. This has resulted in a dearth of single pulse polarization data for most of these pulsars particularly at meter wavelengths. The GMRT operating at meter wavelengths and located at relatively low latitudes is suited for these studies in pulsars located north of -50° declination. The GMRT is one of the most sensitive radio telescope at meter wavelengths, second only to the Arecibo radio telescope in terms of sensitivity (the collecting area of full GMRT is 0.67 times that of the Arecibo telescope), but with a greater sky coverage (Arecibo telescope can observe in the declination range between 0° and +35°). We have selected our sample from the ATNF pulsar database to be observed with the GMRT at 333 and 618 MHz in the declination range -50° to +25°. The selection criterion were as follows; we restricted the sources to dispersion measures (DM) lower than 200 pc cm−3 primarily to avoid scattering. However, some of the pulsars with DM > 150 pc cm−3 were affected by scattering at 333 MHz, but even in these cases the 618 MHz data remained unaffected and suitable for our studies. In addition we only selected pulsars with estimated flux larger than 5 mJy at 618 MHz. This was motivated by our desire to study single pulses with a signal to noise ratio (S/N) in excess of 10 using the GMRT. The selection criterion yielded 123 pulsars in the period range of 0.1 seconds to 8.5 second. The majority of the pulsars have no previous single pulse polarization data, but we have also included a few well studied pulsars in our sample for calibration and verifying our analysis schemes.
Papers
Meterwavelength Single-pulse Polarimetric Emission Survey
We have conducted the Meterwavelength Single-pulse Polarimetric Emission Survey to study the radio emission properties of normal pulsars. A total of 123 pulsars with periods between 0.1 seconds and 8.5 seconds were observed in the survey at two different frequencies, 105 profiles at 333 MHz, 118 profiles at 618 MHz and 100 pulsars at both. In this work we concentrate primarily on the time-averaged properties of the pulsar emission. The measured widths of the pulsar profiles in our sample usually exhibit the radius to frequency mapping. We validate the existence of lower bounds for the distribution of profile widths with pulsar period (P), which is seen for multiple definitions of the width, viz. a lower boundary line (LBL) at 2.7° P -0.5 with width measured at 50% level of profile peak, a LBL at 5.7° P -0.5 for 10% level of peak and LBL at 6.3° P -0.5 for width defined as 5σ above the baseline level. In addition we have measured the degree of linear polarization in the average profile of pulsars and confirmed their dependence on pulsar spindown energy loss (Edot). The single pulse polarization data show interesting trends with the polarization position angle (PPA) distribution exhibiting the simple rotating vector model for high Edot pulsars while the PPA becomes more complex for medium and low Edot pulsars. The single pulse total intensity data is useful for studying a number of emission properties from pulsars like subpulse drifting, nulling and mode changing which is being explored in separate works.
Meterwavelength Single-pulse Polarimetric Emission Survey II: The phenomenon of Drifting Subpulses
A large sample of pulsars was observed as part of the Meterwavelength Single-pulse Polarimetric Emission Survey. We carried out a detailed fluctuation spectral analysis which revealed periodic features in 46% pulsars including 22 pulsars where drifting characteristics were reported for the first time. The pulsar population can be categorized into three distinct groups, pulsars which show systematic drift motion within the pulse window, the pulsars showing no systematic drift but periodic amplitude fluctuation and pulsars with no periodic variations. We discovered the dependence of the drifting phenomenon on the spin down energy loss (Edot), with the three categories occupying distinctly different regions along the Edot axis. The estimation of the drift periodicity (P3) from the peak frequency in the fluctuation spectra is ambiguous due to the aliasing effect. However, using basic physical arguments we were able to determine P3 in pulsars showing systematic drift motion. The estimated P3 values in these pulsars were anti-correlated with Edot which favoured the Partially Screened Gap model of Inner Acceleration Region in pulsars.
Disclaimer
Dear website user, if any data is used for your publication the following papers need to be refered:
Dipanjan Mitra, Rahul Basu, Krzysztof Maciesiak, Anna Skrzypczak, George I. Melikidze, Andrzej Szary, Krzysztof Krzeszowski, 2016, ApJ
Rahul Basu, Dipanjan Mitra, George I. Melikidze, Krzysztof Maciesiak, Anna Skrzypczak, Andrzej Szary, 2016, ApJ
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