619 research outputs found
Calibration of Tests for Time Dilation in GRB Pulse Structures
Two tests for cosmological time dilation in -ray bursts -- the peak
alignment and auto-correlation statistics -- involve averaging information near
the times of peak intensity. Both tests require width corrections, assuming
cosmological origin for bursts, since narrower temporal structure from higher
energy would be redshifted into the band of observation, and since intervals
between pulse structures are included in the averaging procedures. We analyze
long ( 2 s) BATSE bursts and estimate total width corrections for trial
time-dilation factors (TDF = [1+]/[1+]) by
time-dilating and redshifting bright bursts. Both tests reveal significant
trends of increasing TDF with decreasing peak flux, but neither provides
sufficient discriminatory power to distinguish between actual TDFs in the range
2--3.Comment: 5 pages in LATeX, REVTEX style, 2 embedded figures. To appear in
Third Huntsville GRB Workshop Proceeding
Test for Time Dilation of Intervals Between Pulse Structures in GRBs
If -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
An astrometric facility for planetary detection on the space station
An Astrometric Telescope Facility (ATF) for planetary detection is being studied as a potential space station initial operating capability payload. The primary science objective of this mission is the detection and study of planetary systems around other stars. In addition, the facility will be capable of other astrometric measurements such as stellar motions of other galaxies and highly precise direct measurement of stellar distance within the Milky Way Galaxy. The results of a recently completed ATF preliminary systems definition study are summarized. Results of this study indicate that the preliminary concept for the facility is fully capable of meeting the science objective without the development of any new technologies. A simple straightforward operations approach was developed for the ATF. A real-time facility control is not normally required, but does maintain a near real-time ground monitoring capability for the facility and science data stream on a full-time basis. Facility observational sequences are normally loaded once a week. In addition, the preliminary system is designed to be fail-safe and single-fault tolerant. Routine interactions by the space station crew with the ATF will not be necessary, but onboard controls are provided for crew override as required for emergencies and maintenance
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