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Gamma-ray bursts (GRBs) are amongst the most
energetic phenomena
in the universe. Those with longer durations (t > several seconds)
represent the explosive deaths of massive stars collapsing to a
black hole. The evidence for this assertion includes the detection
of star-forming galaxies spatially consistent with the events
(e.g. Figure on left) at high z and spatially and temporally consistent
core-collapse supernovae at low z.
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Spectroscopy of the
bright (R < 21 mag) afterglows emitted by many of these GRBs
provide measurements of the ISM surrounding the events
as well as the IGM along the sightline to Earth. The figure
on the right shows a 'zoom-in' of the Lya profile from HI gas
in the host galaxy of GRB 050730. At wavelengths redward of
6000Ang, one observes the quantum-mechanic damping wing of Lya
with a few metal transitions superimposed. An analysis of this
profile indicates a very large HI column density (10^22 atoms per
cm^2). To the blue of the line center, one notes absorption by
the so-called Lya forest, HI gas from the intergalactic medium
that lies between Earth and the GRB host galaxy.
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The ISM features associated with the GRB host galaxy
may include absorption-line signatures of the circumstellar
medium (CSM) from the progenitor, the molecular cloud and/or
HII region associated with the presumed star-forming region,
and the `ambient' ISM surrounding this SF region.
High-resolution spectra of H2 and metal-line transitions
constrains the metallicity, ionization state, differential
depletion, molecular fraction, kinematic characteristics,
and distance of the gas from the GRB.
The figure
on the left shows two sets of metal-line transitions observed
from GRB 051111 (left) and GRB 050730 (right).
The SiII 1808 and SII 1250 profiles are resonance-line
transitions of dominant ions in neutral gas (so called low-ion
transitions). These data primarily constrain the abundance
of the gas. The MgI 2026 and fine-structure transitions
(designated with the *) constrain the distance of the gas
from the GRB (100pc to a few kpc). Finally, the CIV and NV
doublets may trace gas associated with the HII region surrounding
the GRB and/or gas in the galactic halo of the host galaxy.
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Professor Prochaska leads the research on GRB afterglow
spectroscopy at UCSC through his involvement with the
GRAASP collaboration and the
Dark Cosmology Center.
PhD students Prochter and Pollack are involved in projects
to study the galaxies showing strong MgII absorption along
GRB sightlines as well as the galaxies hosting the GRB itself.
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Selected Publications
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| Title |
Author |
Publication |
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On the Incidence of Strong Mg II Absorbers along Gamma-Ray Burst Sight Lines
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Prochter, Gabriel E.; Prochaska, Jason X.; Chen, Hsiao-Wen; Bloom, Joshua S.; Dessauges-Zavadsky, Miroslava; Foley, Ryan J.; Lopez, Sebastian; Pettini, Max; Dupree, Andrea K.; Guhathakurta, P.
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ApJ, 2006, 648, 93L |
Dissecting the Circumstellar Environment of Gamma-Ray Burst Progenitors
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Prochaska, Jason X.; Chen, Hsiao-Wen; Bloom, Joshua S.
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ApJ, 2006, 648, 95 |
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Probing the Interstellar Medium near Star-forming Regions with Gamma-Ray Burst Afterglow Spectroscopy: Gas, Metals, and Dust |
Prochaska, Jason X.; Chen, Hsiao-Wen; Dessauges-Zavadsky, Miroslava; Bloom, Joshua S. |
ApJ, 2007, 666, 267 |
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Missing Molecular Hydrogen and the Physical Conditions of GRB Host Galaxies
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Tumlinson, Jason; Prochaska, Jason X.; Chen, Hsiao-Wen; Dessauges-Zavadsky, Miroslava; Bloom, Joshua S. |
ApJ, 2008, in press |
