Search

Contains reports on two research projects., National Aeronautics and Space Administration under Contract NASw-143, Lincoln Laboratory, Purchase Order DDL B-00283, U. S. Army, U. S. Navy, U. S. Air Force under Air Force Contract AF 19(604)-5200

Contains a report on a research project., National Aeronautics and Space Administration (Contract NASw-143), Lincoln Laboratory (Purchase Order B-00306), United States Army, United States Navy, United States Air Force (Contract AF19(604)-5200)

Contains a report on a research project., National Aeronautics and Space Administration (Contract NASw-143), Lincoln Laboratory (Purchase Order B-00306), United States Army, United States Navy, United States Air Force (Contract AF19(604)-5200)

Contains reports on two research projects., National Aeronautics and Space Administration under Contract NASw-143, Lincoln Laboratory, Purchase Order DDL B-00283, U. S. Army, U. S. Navy, U. S. Air Force under Air Force Contract AF 19(604)-5200

Contains reports on four research projects., National Aeronautics and Space Administration (Contract NASw-33), Lincoln Laboratory (Purchase Order DDL B-00283), United States Army, United States Navy, United States Air Force (Contract AF19(604)-5200)

We perform several nonparametric correlation tests on the BATSE 3B data to search for evidence of cosmological time dilation. These tests account for the effects of data truncation due to threshold effects in both limiting brightness and limiting duration, enabling us to utilize a larger number of bursts than in previous analyses. We find little significant evidence for correlation between various measures of peak intensity and duration, but the tests cannot conclusively rule out time dilation factors of 2 or less without more data. There is stronger evidence for a positive correlation between fluence and duration, which if confirmed would rule out simple no-evolution cosmological models unless there is a strong intrinsic correlation between the total radiant energy and the duration of bursts., Comment: 21 pages, 5 Postscript figures, uses aaspp4.sty and psfig.sty, to appear in ApJ volume 474. Paper also available at http://www-bigbang.stanford.edu/~ted/paper5.html

We investigate whether a simple cosmology can fit GRB results in both time dilation and Log N - Log P simultaneously. Simplifying assumptions include: all GRBs are spectrally identical to BATSE trigger 143, $\Omega=1$ universe, and no luminosity and number density evolution. Observational data used includes: the BATSE 3B peak brightness distribution (64-ms time scale), the Pioneer Venus Orbiter (PVO) brightness distribution, and the Norris et al. time dilation results for peak aligned profiles presented at this meeting. We find acceptable cosmological fits to the brightness distributions when placing BATSE trigger 143 at a redshift of 0.15 $\pm$ 0.10. This translates into a $(1 + z_{dim}) / (1 + z_{bright})$ factor of about 1.50 $\pm$ 0.50 between selected brightness extremes of the Norris et al. sample. Norris et al. estimate, however, that $(1 + z_{dim}) / (1 + z_{bright})$ $\approx$ 2.0 $\pm$ 0.5 when considering duration tests. The difference is marginal and could be accounted for by evolution. We therefore find that evolution of GRBs is preferred but not demanded., Comment: 5 pages in LATeX, REVTEX style, 2 embedded figures. To appear in Third Huntsville Symposium on Gamma Ray Bursts Proceedings

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 Proceedings

Two tests for cosmological time dilation in $\gamma$-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+$z_{\rm dim}$]/[1+$z_{\rm brt}$]) 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 Proceedings

We perform several nonparametric correlation tests on the BATSE 3B data to search for evidence of cosmological time dilation. These tests account for the effects of data truncation due to threshold effects in both limiting brightness and limiting duration, enabling us to utilize a larger number of bursts than in previous analyses. We find little significant evidence for correlation between various measures of peak intensity and duration, but the tests cannot conclusively rule out time dilation factors of 2 or less without more data. There is stronger evidence for a positive correlation between fluence and duration, which if confirmed would rule out simple no-evolution cosmological models unless there is a strong intrinsic correlation between the total radiant energy and the duration of bursts., Comment: 21 pages, 5 Postscript figures, uses aaspp4.sty and psfig.sty, to appear in ApJ volume 474. Paper also available at http://www-bigbang.stanford.edu/~ted/paper5.html

We investigate whether a simple cosmology can fit GRB results in both time dilation and Log N - Log P simultaneously. Simplifying assumptions include: all GRBs are spectrally identical to BATSE trigger 143, $\Omega=1$ universe, and no luminosity and number density evolution. Observational data used includes: the BATSE 3B peak brightness distribution (64-ms time scale), the Pioneer Venus Orbiter (PVO) brightness distribution, and the Norris et al. time dilation results for peak aligned profiles presented at this meeting. We find acceptable cosmological fits to the brightness distributions when placing BATSE trigger 143 at a redshift of 0.15 $\pm$ 0.10. This translates into a $(1 + z_{dim}) / (1 + z_{bright})$ factor of about 1.50 $\pm$ 0.50 between selected brightness extremes of the Norris et al. sample. Norris et al. estimate, however, that $(1 + z_{dim}) / (1 + z_{bright})$ $\approx$ 2.0 $\pm$ 0.5 when considering duration tests. The difference is marginal and could be accounted for by evolution. We therefore find that evolution of GRBs is preferred but not demanded., Comment: 5 pages in LATeX, REVTEX style, 2 embedded figures. To appear in Third Huntsville Symposium on Gamma Ray Bursts Proceedings

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 Proceedings

Two tests for cosmological time dilation in $\gamma$-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+$z_{\rm dim}$]/[1+$z_{\rm brt}$]) 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 Proceedings

We present analytic formulae for the integral number count distribution of cosmological bursting or steady sources valid over the entire range of fluxes, including density evolution and either standard candle or a power law luminosity function. These are used to derive analytic formulae for the mean redshift, the time dilations and the dispersion of these quantities for sources within a given flux range for Friedmann models with $\Omega=1,~ \Lambda=0$ without K-corrections, and we discuss the extension to cases with $\Omega <1$ and inclusion of K-corrections. Applications to the spatial distribution of cosmological gamma ray burst sources are discussed, both with and without an intrinsic energy stretching of the burst time profiles, and the implied ranges of redshift $z$ are considered for a specific time dilation signal value. The simultaneous consideration of time dilation information and of fits of the number distribution versus peak flux breaks the degeneracy inherent in the latter alone, allowing a unique determination of the density evolution index and the characteristic luminosity of the sources. For a reported time dilation signal of 2.25 and neglecting [including] energy stretching we find that the proper density should evolve more steeply with redshift than comoving constant, and the redshifts of the dimmest sources with stretching would be very large. However, the expected statistical dispersion in the redshifts is large, especially for power law luminosity functions, and remains compatible with that of distant quasars. For smaller time dilation values of 1.75 and 1.35 the redshifts are more compatible with conventional ideas about galaxy formation, and the evolution is closer to a comoving constant or a slower evolution. More generally, we have considered a wide range of possible measured time dilation, Comment: Ap.J., in press, uuencoded .ps file, 33 pages plus 5 figures

The isotropic distribution of gamma-ray bursts as observed with the Burst and Transient Experiment (BATSE) strongly suggests that the bursts are at cosmological distances. At such distances, the expansion of the universe should redshift the spectra and stretch the temporal structure. We relate the observed peak intensities, spectral shapes, and time dilation to distance. We include the uncertainties in our knowledge of the intrinsic spectrum and correct for the coupling between the spectral shape and the temporal structure. The reported time dilation between the dimmest BATSE bursts and the bright BATSE bursts (a factor of 2) requires a redshift of about 6 for the BATSE dimmest bursts rather than a redshift of 1 or 2 as previously reported. The large luminosity and distance determined from the time dilation is inconsistent with the observed Log N-Log P distribution. unless there is very strong evolution. The implied distance for the dimmest bursts is beyond where galaxies are thought to form. If true, the gamma-ray bursts would be orphans: no known objects would have the same distance scale. We conclude that either a large fraction (65%) of the observed time dilation between the BATSE bright and dimmest bursts is intrinsic to the bursts or that there are strong evolutionary effects in the Log N-Log P distribution and that it is only a coincidence that Log N-Log P shows a -3/2 power law at high intensities., Comment: 41 pages including figures, uuencoded compressed Postscript. Accepted for publication in the Astrophysical Journal. The preprint can also be found in Postscript form at http://sstcx1.lanl.gov/~jsbloom/ or at ftp://sstcx1.lanl.gov/pub/grb/time_dilation.ps

We present analytic formulae for the integral number count distribution of cosmological bursting or steady sources valid over the entire range of fluxes, including density evolution and either standard candle or a power law luminosity function. These are used to derive analytic formulae for the mean redshift, the time dilations and the dispersion of these quantities for sources within a given flux range for Friedmann models with $\Omega=1,~ \Lambda=0$ without K-corrections, and we discuss the extension to cases with $\Omega <1$ and inclusion of K-corrections. Applications to the spatial distribution of cosmological gamma ray burst sources are discussed, both with and without an intrinsic energy stretching of the burst time profiles, and the implied ranges of redshift $z$ are considered for a specific time dilation signal value. The simultaneous consideration of time dilation information and of fits of the number distribution versus peak flux breaks the degeneracy inherent in the latter alone, allowing a unique determination of the density evolution index and the characteristic luminosity of the sources. For a reported time dilation signal of 2.25 and neglecting [including] energy stretching we find that the proper density should evolve more steeply with redshift than comoving constant, and the redshifts of the dimmest sources with stretching would be very large. However, the expected statistical dispersion in the redshifts is large, especially for power law luminosity functions, and remains compatible with that of distant quasars. For smaller time dilation values of 1.75 and 1.35 the redshifts are more compatible with conventional ideas about galaxy formation, and the evolution is closer to a comoving constant or a slower evolution. More generally, we have considered a wide range of possible measured time dilation, Comment: Ap.J., in press, uuencoded .ps file, 33 pages plus 5 figures

The isotropic distribution of gamma-ray bursts as observed with the Burst and Transient Experiment (BATSE) strongly suggests that the bursts are at cosmological distances. At such distances, the expansion of the universe should redshift the spectra and stretch the temporal structure. We relate the observed peak intensities, spectral shapes, and time dilation to distance. We include the uncertainties in our knowledge of the intrinsic spectrum and correct for the coupling between the spectral shape and the temporal structure. The reported time dilation between the dimmest BATSE bursts and the bright BATSE bursts (a factor of 2) requires a redshift of about 6 for the BATSE dimmest bursts rather than a redshift of 1 or 2 as previously reported. The large luminosity and distance determined from the time dilation is inconsistent with the observed Log N-Log P distribution. unless there is very strong evolution. The implied distance for the dimmest bursts is beyond where galaxies are thought to form. If true, the gamma-ray bursts would be orphans: no known objects would have the same distance scale. We conclude that either a large fraction (65%) of the observed time dilation between the BATSE bright and dimmest bursts is intrinsic to the bursts or that there are strong evolutionary effects in the Log N-Log P distribution and that it is only a coincidence that Log N-Log P shows a -3/2 power law at high intensities., Comment: 41 pages including figures, uuencoded compressed Postscript. Accepted for publication in the Astrophysical Journal. The preprint can also be found in Postscript form at http://sstcx1.lanl.gov/~jsbloom/ or at ftp://sstcx1.lanl.gov/pub/grb/time_dilation.ps

cosmology: miscellaneous-supernovae Udgivelsesdato: August 1

cosmology: miscellaneous-supernovae Udgivelsesdato: August 1