204 research outputs found
Gamma-Ray Bursts: Temporal Scales and the Bulk Lorentz Factor
For a sample of Swift and Fermi GRBs, we show that the minimum variability
timescale and the spectral lag of the prompt emission is related to the bulk
Lorentz factor in a complex manner: For small 's, the variability
timescale exhibits a shallow (plateau) region. For large 's, the
variability timescale declines steeply as a function of (). Evidence is also presented for an intriguing
correlation between the peak times, t, of the afterglow emission and the
prompt emission variability timescale.Comment: Accepted for publication in Ap
Screening High-z GRBs with BAT Prompt Emission Properties
Detecting high-z GRBs is important for constraining the GRB formation rate,
and tracing the history of re-ionization and metallicity of the universe. Based
on the current sample of GRBs detected by Swift with known redshifts, we
investigated the relationship between red-shift, and spectral and temporal
characteristics, using the BAT event-by-event data. We found red-shift trends
for the peak-flux-normalized temporal width T90, the light curve variance, the
peak flux, and the photon index in simple power-law fit to the BAT event data.
We have constructed criteria for screening GRBs with high red-shifts. This will
enable us to provide a much faster alert to the GRB community of possible
high-z bursts.Comment: 4 pages, 4 figures, to be published in the proceedings of ''Gamma Ray
Bursts 2007'', Santa Fe, New Mexico, November 5-
A Correlation of Spectral Lag Evolution with Prompt Optical Emission in GRBs?
We report on observations of correlated behavior between the prompt gamma-ray
and optical emission from GRB 080319B, which (i) strongly suggest that they
occurred within the same astrophysical source region and (ii) indicate that
their respective radiation mechanisms were most likely dynamically coupled. Our
preliminary results, based upon a new cross-correlation function (CCF)
methodology for determining the time-resolved spectral lag, are summarized as
follows. First, the evolution in the arrival offset of prompt gamma-ray photon
counts between Swift-BAT 15-25 keV and 50-100 keV energy bands (intrinsic
gamma-ray spectral lag) appears to be anti-correlated with the arrival offset
between prompt 15-350 keV gamma-rays and the optical emission observed by
TORTORA (extrinsic optical/gamma-ray spectral lag), thus effectively
partitioning the burst into two main episodes at ~T+28+/-2 sec. Second, prompt
optical emission is nested within intervals of (a) trivial intrinsic gamma-ray
spectral lag (~T+12+-2 and ~T+50+/-2 sec) with (b) discontinuities in the hard
to soft evolution of the photon index for a power law fit to 15-150 keV
Swift-BAT data (~T+8+/-2 and ~T+48+/-1 sec), both of which coincide with the
rise (~T+10+/-1 sec) and decline (~T+50+/-1 sec) of prompt optical emission.
This potential discovery, robust across heuristic permutations of BAT energy
channels and varying temporal bin resolution, provides the first observational
evidence for an implicit connection between spectral lag and the dynamics of
shocks in the context of canonical fireball phenomenology.Comment: 5 pages. Adapted from a contribution to the Proceedings of the 2008
Nanjing GRB Conference. Edited by Y. F. Huang, Z. G. Dai and B. Zhan
Incorporation of biosolids in fired clay bricks
In Australia, thousands of tonnes of biosolids are produced and millions of dollars expended for their management annually. Biosolids are derived from wastewater sludge which is the major solid component collected from the wastewater treatment process. This study investigated the incorporation of biosolids into fired clay bricks. Geotechnical characteristics of three biosolids samples produced from Eastern Wastewater Treatment Plant (ETP) in Melbourne were investigated to assess their suitability as a partial replacement material for the clay in fired-clay bricks. Results of classification tests including liquid limit, plastic limit and sieve analysis indicated that the three biosolids samples are silty clayey sand with low to high plasticity. Linear shrinkage of biosolids samples varied from 10% to 15% and organic content from 6% to 14%. Control clay bricks with 0% biosolids and clay-biosolids bricks with 25% by weight biosolids were made and properties including compressive strength, shrinkage, density, initial rate of absorption (IRA), water absorption, thermal conductivity and other properties were determined. The overall results of this preliminary study are promising. Some of the results of this stage of this investigation are presented and discussed in this paper
A New Frequency-Luminosity Relation for Long GRBs?
We have studied power density spectra (PDS) of 206 long Gamma-Ray Bursts
(GRBs). We fitted the PDS with a simple power-law and extracted the exponent of
the power-law (alpha) and the noise-crossing threshold frequency (f_th). We
find that the distribution of the extracted alpha peaks around -1.4 and that of
f_th around 1 Hz. In addition, based on a sub-set of 58 bursts with known
redshifts, we show that the redshift-corrected threshold frequency is
positively correlated with the isotropic peak luminosity. The correlation
coefficient is 0.57 +/- 0.03.Comment: 9 pages, 17 figures, 1 table; Accepted for publication in MNRA
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