Gamma-Ray Bursts and Cosmology

The unrivalled, extreme luminosities of gamma-ray bursts (GRBs) make them the favored beacons for sampling the high redshift Universe. To employ GRBs to study the cosmic terrain -- e.g., star and galaxy formation history -- GRB luminosities must be calibrated, and the luminosity function versus redshift must be measured or inferred. Several nascent relationships between gamma-ray temporal or spectral indicators and luminosity or total energy have been reported. These measures promise to further our understanding of GRBs once the connections between the luminosity indicators and GRB jets and emission mechanisms are better elucidated. The current distribution of 33 redshifts determined from host galaxies and afterglows peaks near z ~ 1, whereas for the full BATSE sample of long bursts, the lag-luminosity relation predicts a broad peak z ~ 1-4 with a tail to z ~ 20, in rough agreement with theoretical models based on star formation considerations. For some GRB subclasses and apparently related phenomena -- short bursts, long-lag bursts, and X-ray flashes -- the present information on their redshift distributions is sparse or entirely lacking, and progress is expected in Swift era when prompt alerts become numerous.Comment: Invited talk given at the JENAM 2003 Minisymposium on Physics of Gamma-Ray Bursts, August 29-30, 2003, Budapest, Hungary; 6 pages, 1 figur

Experimental performance of a conical pressure probe at Mach numbers of 3.0, 4.5, and 6.0

Wind tunnel investigation of performance of conical pressure probe at hypersonic speed

Test for Time Dilation of Intervals Between Pulse Structures in GRBs

If $\gamma$-ray bursts are at cosmological distances, then not only their constituent pulses but also the intervals between pulses should be time-dilated. Unlike time-dilation measures of pulse emission, intervals would appear to require negligible correction for redshift of narrower temporal structure from higher energy into the band of observation. However, stretching of pulse intervals is inherently difficult to measure without incurring a timescale-dependent bias since, as time profiles are stretched, more structure can appear near the limit of resolution. This problem is compounded in dimmer bursts because identification of significant structures becomes more problematic. We attempt to minimize brightness bias by equalizing signal-to-noise (s/n) level of all bursts. We analyze wavelet-denoised burst profiles binned to several resolutions, identifying significant fluctuations between pulse structures and interjacent valleys. When bursts are ranked by peak flux, an interval time-dilation signature is evident, but its magnitude and significance are dependent upon temporal resolution and s/n level.Comment: 5 pages in LATeX, REVTEX style, 2 embedded figures. To appear in Third Huntsville GRB Workshop Proceeding

A GTC Study of the Afterglow and Host Galaxy of the Short-Duration GRB 100816A

We present the results from an optical monitoring campaign aimed at studying the afterglow properties of the short GRB 100816A. We implemented a new way of processing the Swift-BAT data, and based on it we reclassified this burst as short, discarding the initial classification as long. Observations were carried out mainly with the GTC Telescope within the four following days after the burst to investigate the optical photometry of its afterglow, and a year later to localize the host. We completed the optical imaging with the 1.23 m and 3.5 m CAHA Telescopes. We built and fitted the nIR-optical SED for the characterization of the host. The best fit of the SED (χ2/d.o.f. = 1.656) obtained for assumed values of a solar metallicity, and an extinction of AV = 0.2 mag is obtained for a starburst galaxy with a dominant stellar population aging about 360 Myr