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 $\gamma$-ray components. Additionally, both bursts were fortuitously located within the field of view of the TeV $\gamma$-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 $\gamma$-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 e$^+$e$^-$ 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 $10^{-21}$ - $10^{-17}$ 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