Astronomy and Astrophysics – Astronomy
Scientific paper
Oct 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999phdt.........3b&link_type=abstract
Thesis (PhD). PRINCETON UNIVERSITY, Source DAI-B 60/04, p. 1648, Oct 1999, 136 pages.
Astronomy and Astrophysics
Astronomy
4
Remote Sensing
Scientific paper
For a few seconds, a gamma-ray burst (GRB) can be the brightest object in the hard X-ray and soft γ-ray sky. Despite over twenty years of observations, the origin of GRBs remains a mystery. Even two years ago, the basic question of whether GRBs are objects in our own galaxy at a distance of ~100 kpc, or are in very distant galaxies, ~1 Gpc away, was still unanswered. These energetic explosions remain mysterious largely because, prior to early last year, no convincing counterpart at energies below 20 keV had ever been found. Since then, dramatic progress has been made in counterpart searches all across the electromagnetic spectrum. This thesis describes one such experiment, a dedicated search for counterparts to GRBs in the radio band. We repaired and remotely operated a 74 MHz, 1000 m2 phased array located in Fallbrook, California, to search for radio emission associated with GRBs. We used a low-cost, custom-built receiving system with coarse spectral resolution. If GRBs emit radio waves, this low frequency signal will be delayed by dispersion in the interstellar and intergalactic medium. With our spectrometer, we can easily distinguish dispersed signals of astronomical origin from the non- dispersed terrestrial interference that is the major background for all radio transient studies. Measuring the dispersion of radio transients associated with GRBs would constrain their distances and the density of the intervening galactic or intergalactic plasma. Our experiment ran autonomously and could respond within ~10 s to the detection of a GRB by an Earth-orbiting satellite. This is the fastest triggered response that has been achieved with observations at any wavelength. We have taken high-quality data on 32 GRBs. In this sample, two radio transients were detected in close temporal association with GRBs, but a physical association between these signals and the GRBs is unlikely. Taken as upper limits, our observations constrain prompt radio emission from GRBs to a few kJy or less.
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