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The UTR-2 decametre pulsar and transient survey I. Transient detection

V. V. Zakharenko, I. P. Kravtsov, I. Y. Vasylieva, P. Zarka, O. M. Ulyanov, O. O. Konovalenko, A. I. Shevtsova, A. O. Skoryk, K. Y. Mylostna

Abstract

Context. This paper presents a detailed description of the Decametre Pulsar and Transient Survey of the Northern Sky that was carried out in 2012-2017 using the world's largest radio telescope at decametre wavelengths - UTR-2 in Ukraine. This extensive survey covers the northern sky from declination -10 to +80 deg , with a temporal resolution of 8 ms, and explores dispersion measures up to 30 pc/cc. Aims. The major advantage of the decametre wavelength range is a comparatively wide band, in which the dispersive delay due to the interstellar plasma reaches hundreds of seconds, giving us the opportunity to determine the dispersion measure with a very high accuracy. This enables us to discover new transients, while avoiding data contamination from numerous weak signals of a different nature. Methods. The drift-scan survey in 5-beam mode of UTR-2 was carried out at night time. To cover the entire sky along the right ascension, the duration of the sessions was more than 12 hours at a time close to the autumn and spring equinoxes (to obtain the same conditions for the interference situation). 90 degrees along the declination were covered by five beams in 40 days (each equinox). Results. We discovered 380 individual transient signals with dispersion measures significantly differ from those of known sources. We determined the parameters of each single transient signal. We show that they cannot be explained by ionospheric scintillations. Repeated observations have shown that some detected transient signals are repetitive and are thus likely to originate from pulsars or rotating radio transients. Key words. Stars: neutron - pulsars: general - Methods: data analysis - Methods: observational - Astronomical databases: Surveys

The UTR-2 decametre pulsar and transient survey I. Transient detection

Abstract

Context. This paper presents a detailed description of the Decametre Pulsar and Transient Survey of the Northern Sky that was carried out in 2012-2017 using the world's largest radio telescope at decametre wavelengths - UTR-2 in Ukraine. This extensive survey covers the northern sky from declination -10 to +80 deg , with a temporal resolution of 8 ms, and explores dispersion measures up to 30 pc/cc. Aims. The major advantage of the decametre wavelength range is a comparatively wide band, in which the dispersive delay due to the interstellar plasma reaches hundreds of seconds, giving us the opportunity to determine the dispersion measure with a very high accuracy. This enables us to discover new transients, while avoiding data contamination from numerous weak signals of a different nature. Methods. The drift-scan survey in 5-beam mode of UTR-2 was carried out at night time. To cover the entire sky along the right ascension, the duration of the sessions was more than 12 hours at a time close to the autumn and spring equinoxes (to obtain the same conditions for the interference situation). 90 degrees along the declination were covered by five beams in 40 days (each equinox). Results. We discovered 380 individual transient signals with dispersion measures significantly differ from those of known sources. We determined the parameters of each single transient signal. We show that they cannot be explained by ionospheric scintillations. Repeated observations have shown that some detected transient signals are repetitive and are thus likely to originate from pulsars or rotating radio transients. Key words. Stars: neutron - pulsars: general - Methods: data analysis - Methods: observational - Astronomical databases: Surveys
Paper Structure (22 sections, 5 equations, 27 figures)

This paper contains 22 sections, 5 equations, 27 figures.

Table of Contents

  1. Introduction
  2. Instruments, parameters of the Survey, and data processing
  3. Selected parameters of the UTR-2 radiation pattern
  4. Receiving equipment and recording parameters
  5. Observations and data processing
  6. Search for candidate signals
  7. Multi-parameter analysis of candidate signals
  8. Test with 'inverse' dispersion measure
  9. Criteria of natural origin of transient signals
  10. Results
  11. Test results with the 'inverse' dispersion measure and choice of detection threshold
  12. Distribution of the selected transient signals over the observational time
  13. Distribution of detections by the S/N
  14. DM distribution of the detections
  15. Distribution of detected signals over galactic latitude
  16. ...and 7 more sections

Figures (27)

  • Figure 1: Top panel: Pulses of PSR B0809+74 before (left) and after dedispersion with the frequency dependence $\propto f^{-2}$ (right). On the bottom panel, a terrestrial signal with a linear frequency dependence ($\propto f^{-1}$) after dedispersion at $f^{-2}$ is shown. It radically differs from the pulses of a cosmic source after the dedispersion procedure: even in the uppermost frequency band (0.1 of the total operating range, 31.5--33 MHz), the difference in dispersion delay is tenths of a second, which is much larger than the signal width (ten milliseconds). Such interference signals are easily identified and eliminated.
  • Figure 2: 'Time vs $DM$' pulse plane, shown for the signal from the bottom panel in Fig. \ref{['fig4']}. For the linear frequency dependence ($\propto f^{-1}$), the 'dispersion measure' (when the frequency-integrated signal exceeds the set threshold 5.5 standard deviation) is close to 13.5±0.6 pc/cm$^3$.
  • Figure 3: Result of PSR B0834+06 individual pulse detection: the sequence of red spots (each one consists of red circles) with radii proportional to S/N in their centres at $DM$ = 12.88 pc/cm$^3$.
  • Figure 4: Example of RFI on a 'Time vs $DM$' plane. The presentation of the results over the entire range of $DM$ allows us to highlight the very weak influence of noise on the $DM$ values more than 10 pc/cm$^3$.
  • Figure 5: Example of a transient signal from an unknown source, $DM$ = 3.676 pc/cm$^3$, (left panel) and a single pulse of PSR B0809+74 (right panel), $DM$ = 5.754 pc/cm$^3$. The top panels are dynamic spectra, the middle panels are pulse frequency averaging, and the bottom panel is the 'Time vs $DM$' plane.
  • ...and 22 more figures