A Search for Astrophysical Radio Transients at Meter Wavelengths
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We describe a method to carry out an agnostic single-dispersed-pulse search, and apply it to data collected with the Eight-meter-wavelength Transient Array (ETA). ETA is a radio telescope dedicated to searching for transient pulses. It consists of 12 crossed-dipole antenna stands with Galactic-noise-limited performance from 29-47 MHz. There is a vast amount of data collected from an ETA observation. It is therefore greatly beneficial to use a computer cluster, which works in parallel on different parts of a data set, in order to carry out a single-pulse search quickly and efficiently. Each spectrogram in a data set needs to be analyzed individually, without reference to the rest, in order to utilize a computer cluster's capabilities. The data reduction software has been developed for single-dispersed-pulse searches, and is described in this thesis. The data reduction involves sweeping through the collected data with a dedispersion routine assuming a range of dispersion measures. The resulting time series are searched with multiple matched filters for signals above a signal-to-noise threshold.
Applying the single pulse search to ~ 30 hours of ETA data did not yield a compelling detection of an astrophysical signal. However, from ~ 5 hours of interference-free data we find an observational upper limit to the rate of exploding PBHs of r â 4.8 Ã 10-7 pc-3 y-1 for a PBH with a fireball Lorentz-factor f = 104.3. This limit is applicable to PBHs in the halo of the Galaxy to distances ~ 2 kpc, and dispersion measures ~ 80 pc cm-3 . We also find a source-agnostic rate limit ~ 0.25 events y-1 deg-2 for pulses of duration < 3 s, and having apparent energy densities â ¥ 2.6 Ã 10-23 J m-2 Hz-1 at 38 MHz.
- Doctoral Dissertations