6,606 research outputs found
The origin of the optical flashes: The case study of GRB 080319B and GRB 130427A
Correlations between optical flashes and gamma-ray emissions in gamma-ray
bursts have been searched in order to clarify the question whether these
emissions occur at internal and/or external shocks. Among the most powerful
gamma-ray bursts ever recorded are GRB 080319B and GRB 130427A which at early
phase presented bright optical flashes possible correlated with -ray
components. Additionally, both bursts were fortuitously located within the
field of view of the TeV -ray Milagro and HAWC observatories, and
although no statistically significant excess of counts were collected, upper
limits were placed on the GeV - TeV emission. Considering the synchrotron
self-Compton emission from internal shocks and requiring the GeV-TeV upper
limits we found that the optical flashes and the -ray components are
produced by different electron populations. Analyzing the optical flashes
together the multiwavelength afterglow observation, we found that these flashes
can be interpreted in the framework of the synchrotron reverse-shock model when
outflows have arbitrary magnetizations.Comment: 9 pages, 5 figures and 4 tables. Accepted for publication in Ap
A survey of instabilities within centrifugal pumps and concepts for improving the flow range of pumps in rocket engines
Design features and concepts that have primary influence on the stable operating flow range of propellant-feed centrifugal turbopumps in a rocket engine are discussed. One of the throttling limitations of a pump-fed rocket engine is the stable operating range of the pump. Several varieties of pump hydraulic instabilities are mentioned. Some pump design criteria are summarized and a qualitative correlation of key parameters to pump stall and surge are referenced. Some of the design criteria were taken from the literature on high pressure ratio centrifugal compressors. Therefore, these have yet to be validated for extending the stable operating flow range of high-head pumps. Casing treatment devices, dynamic fluid-damping plenums, backflow-stabilizing vanes and flow-reinjection techniques are summarized. A planned program was undertaken at LeRC to validate these concepts. Technologies developed by this program will be available for the design of turbopumps for advanced space rocket engines for use by NASA in future space missions where throttling is essential
On the properties of the RHESSI intermediate-duration gamma-ray bursts
The intermediate-duration gamma-ray bursts (GRBs) identified in the data of
the RHESSI satellite are investigated with respect to their spectral lags, peak
count rates, redshifts, supernova observations, and star formation rates of
their host galaxies. Standard statistical tests like Kolmogorov-Smirnov and
Student t-test are used. It is discussed whether these bursts belong to the
group of so-called short or long GRBs, or if they significantly differ from
both groups.Comment: 4 pages, 4 figures, 2 table
Analysis of the BATSE Continuous MER data
The CGRO/BATSE database includes many types of data such as the 16-channel
continuous background or medium energy resolution burst data (CONT and MER data
types). We have calculated some four hundred burst's medium energy resolution
spectra and Principal Component Analysis has been applied. We found five
components can describe GRBs' spectra.Comment: 4 pages, 2 figures, accepted in Nuovo Ciment
Properties of the Intergalactic Magnetic Field Constrained by Gamma-ray Observations of Gamma-Ray Bursts
The magnetic field in intergalactic space gives important information about
magnetogenesis in the early universe. The properties of this field can be
probed by searching for radiation of secondary ee pairs created by TeV
photons, that produce GeV range radiation by Compton-scattering cosmic
microwave background (CMB) photons. The arrival times of the GeV "echo" photons
depend strongly on the magnetic field strength and coherence length. A Monte
Carlo code that accurately treats pair creation is developed to simulate the
spectrum and time-dependence of the echo radiation. The extrapolation of the
spectrum of powerful gamma-ray bursts (GRBs) like GRB 130427A to TeV energies
is used to demonstrate how the IGMF can be constrained if it falls in the
- G range for 1 Mpc coherence length.Comment: 8 pages, 6 figure
Optical observational biases in the GRB redshift
The measured redshifts of gamma-ray bursts (GRBs), which were first detected
by the Swift satellite, seem to be bigger on average than the redshifts of GRBs
detected by other satellites. We analyzed the redshift distribution of GRBs
triggered and observed by different satellites (Swift, HETE2, BeppoSax,
Ulyssses). After considering the possible biases {significant difference was
found at the p=95.70% level in the redshift distributions of GRBs measured by
HETE and the Swift.Comment: 3 pages, 1 table, 2 figures, to appear in the proceedings of the
Sixth Huntsville Gamma-Ray Burst Symposium, edited by C.A. Meegan, N.
Gehrels, and C. Kouvelioto
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