3,286 research outputs found
Spectral analysis of 50 GRBs detected by HETE-2
FREGATE, the gamma-ray detector of HETE-2 is entirely dedicated to the study
of GRBs. Its main characteristic is its broad energy range, from 7 keV to 400
keV. This energy range can be further extended down to 2 keV using the data
from the WXM, the X-ray detector of HETE-2. Such a large energy range allows to
study in details the prompt emission of GRBs, determining with a high precision
their spectral parameters. Moreover, because this energy range extends at low
energies, the sample of GRBs detected by both FREGATE and WXM contains a
significant fraction of X-Ray Rich GRBs and X-Ray Flashes.
We present here the distributions of the spectral parameters mesured for the
time integrated spectra of 50 GRBs. We put emphasis on the distribution of the
low energy spectral index alpha. Because FREGATE and WXM detected all classes
of GRBs, we also discuss the connection between GRBs, X-Ray Rich GRBs and X-Ray
Flashes.Comment: 4 pages aipTEX, contribution to the 2003 GRB Conference, held at
Santa Fe,N
Observation and implications of the Epeak - Eiso correlation in Gamma-Ray Bursts
The availability of a few dozen GRB redshifts now allows studies of the
intrinsic properties of these high energy transients. Amati et al. recently
discovered a correlation between Epeak, the intrinsic peak energy of the spectrum, and Eiso, the isotropic equivalent energy radiated by the
source. Lamb et al. have shown that HETE-2 data confirm and extend this
correlation. We discuss here one of the consequences of this correlation: the
existence of a 'spectral standard candle', which can be used to construct a
simple redshift indicator for GRBs.Comment: Proceedings of the GRB 2003 Conference in SantaFe, 5 pages, 4 figure
Evidence From HETE-2 For GRB Evolution With Redshift
After taking into account threshold effects, we find that the
isotropic-equivalent energies E_iso and luminosities L_iso of gamma-ray bursts
(GRBs) are correlated with redshift at the 5% and 0.9% signficance levels,
respectively. Our results are based on 10 BeppoSAX GRBs and 11 HETE-2 GRBs with
known redshifts. Our results suggest that the isotropic-equivalent energies and
luminosities of GRBs increase with redshift. They strengthen earlier clues to
this effect from analyses of the BATSE catalog of GRBs, using the variability
of burst time histories as an estimator of burst luminosities (and therefore
redshifts), and from an analysis of BeppoSAX bursts only. If the
isotropic-equivalent energies and luminosities of GRBs really do increase with
redshift, it suggests that GRB jets at high redshifts may be narrower and thus
the cores of GRB progenitor stars at high redshifts may be rotating more
rapidly. It also suggests that GRBs at very high redshifts may be more luminous
-- and therefore easier to detect -- than has been thought, which would make
GRBs a more powerful probe of cosmology and the early universe than has been
thought.Comment: 5 pages, 3 figures, to appear in proc. 2003 GRB Conference, Santa Fe,
N
Democratic leadership practices in Edo State Nigeria: A justification for a Biomimetic-based democratic alternative
This article - the last of a two-part assessment of leadership practices in community development processes, noted that since Nigeriaâs independence 6 decades ago, only the past 2 decades has experienced uninterrupted democracy. Considering the importance of ideal democratic processes in actualizing progressive community development, the paper examined participation in politics, relative to leadership among geese to justify the need for nature-based alternative leadership practices in egalitarian developing communities. Analysis of empirical evidences from literature was used to evaluate key leadership issues, discuss political situations, and models of citizensâ participation across Edo State communities in Nigeria. Observed democratic leadership in the study area turned out as âpractices that are alien to democracyâ because it lacked the basic tenets of democracy. Several indices of participation in politics were articulated and matched against practices among the geese towards articulating a Biomimetic-based Democratic Leadership Practices for community progression. Recommendations were made and implication drawn
Galileo photometry of Apollo landing sites
As of December 1992, the Galileo spacecraft performed its second and final flyby (EM2), of the Earth-Moon system, during which it acquired Solid State Imaging (SSI) camera images of the lunar surface suitable for photometric analysis using Hapke's, photometric model. These images, together with those from the first flyby (EM1) in December 1989, provide observations of all of the Apollo landing sites over a wide range of photometric geometries and at eight broadband filter wavelengths ranging from 0.41 micron to 0.99 micron. We have completed a preliminary photometric analysis of Apollo landing sites visible in EM1 images and developed a new strategy for a more complete analysis of the combined EM1 and EM2 data sets in conjunction with telescopic observations and spectrogoniometric measurements of returned lunar samples. No existing single data set, whether from spacecraft flyby, telescopic observation, or laboratory analysis of returned samples, describes completely the light scattering behavior of a particular location on the Moon at all angles of incidence (i), emission (e), and phase angles (a). Earthbased telescopic observations of particular lunar sites provide good coverage of incidence nad phase angles, but their range in emission angle is limited to only a few degrees because of the Moon's synchronous rotation. Spacecraft flyby observations from Galileo are now available for specific lunar features at many photometric geometries unobtainable from Earth; however, this data set lacks coverage at very small phase angles (a less than 13 deg) important for distinguishing the well-known 'opposition effect'. Spectrogoniometric measurements from returned lunar samples can provide photometric coverage at almost any geometry; however, mechanical properties of prepared particulate laboratory samples, such as particle compaction and macroscopic roughness, likely differ from those on the lunar surface. In this study, we have developed methods for the simultaneous analysis of all three types of data: we combine Galileo and telescopic observations to obtain the most complete coverage with photometric geometry, and use spectrogoniometric observations of lunar soils to help distinguish the photometric effects of macroscopic roughness from those caused by particle phase function behavior (i.e., the directional scattering properties of regolith particles)
Recent atmospheric neutrino results from Soudan 2
An updated measurement of the atmospheric nu_mu/nu_e ratio-of-ratios,
0.68+-0.11+-0.06, has been obtained using a 4.6-kty exposure of the Soudan-2
iron tracking calorimeter. The L/E distributions have been analyzed for effects
of nu_mu -> nu_x oscillations, and an allowed region in the Delta m^2 vs. sin^2
2 theta plane has been determined.Comment: 3 pages, 4 figures; presented at TAUP99, the 6th Int. Workshop on
Topics in Astroparticle and Underground Physics, Sept. 6-10, 1999, College de
France, Paris, Franc
Virtual Experimental Pharmacology an Alternative or Not? Ă¹ùâÂŹĂąâŹĆ A Global Assessment by Pharmacology Faculties and MBBS Students
Aim: To assess the preference and acceptance of the virtual and real animal experiment in experimental Pharmacology in undergraduate students. Materials and Methods:ĂâĂ Study was conducted in practical hall in the department of pharmacology, Saveetha Medical College. Students who came for the practical class were exposed to both virtual and real animal experiments. 131 students were exposed to both virtual and experimental experiments. Four typesĂâĂ of experiments has been exposed to the students. Virtual experiment exposed by Audio- visual aids. Real experiments were conducted by students themselves in groups of ten. Questionnaire was served to the students to find out their preference and acceptance. Questions were framed pertaining to 1. Knowledge 2. Recollection of subjectĂâĂ ĂâĂ 3. Research. The last question was about their acceptance. Faculties were also assessed on their preference. Results: The results were analysed to find out the knowledge gained, recollection of subject, and research orientation in both virtual and experimental pharmacology. Conclusion: Virtual experiments can be an alternative to animal experiments in experimental Pharmacology in undergraduate teaching
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