A Search for Astrophysical Radio Transients at Meter Wavelengths
|dc.description.abstract||Astrophysical phenomena such as exploding primordial black holes (PBHs), gamma-ray
bursts (GRBs), compact object mergers, and supernovae, are expected to produce a single
pulse of electromagnetic radiation detectable at the low-frequency end of the radio spectrum.
Detection of any of these pulses would be significant for the study of the objects themselves,
their host environments, and the interstellar/intergalactic medium. Furthermore, a detection of a radio transient from an exploding PBH could be a signature of an extra spatial dimension, which would drastically alter our perception of spacetime. However, even upper limits on the existence of PBHs, from transient searches, would be important to discussions of cosmology.|
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.
|dc.rights||I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to Virginia Tech or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report.||en_US|
|dc.subject||Primordial Black Holes||en_US|
|dc.title||A Search for Astrophysical Radio Transients at Meter Wavelengths||en_US|
|thesis.degree.grantor||Virginia Polytechnic Institute and State University||en_US|
|dc.contributor.committeechair||Simonetti, John H.||en_US|
|dc.contributor.committeemember||Ellingson, Steven W.||en_US|
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