ON THE MEASUREMENT OF A COSMOLOGICAL DIPOLE IN THE PHOTON NUMBER COUNTS OF GAMMA-RAY BURSTS

If gamma-ray bursts are cosmological or in a halo distribution their properties are expected to be isotropic (at least to 1st order). However, our motion with respect to the burst parent population (whose proper frame is expected to be that of the Cosmic Microwave Background (CMB), or that of a static halo) will cause a dipole effect in the distribution of bursts and in their photon number counts (together termed a Compton-Getting effect). We argue that the photon number count information is necessary to distinguish a genuine Compton-Getting effect from some other anisotropy and to fully test the proper frame isotropy of the bursts. Using the 2B burst catalogue and the dipole determined from the CMB, we find the surprising result that although the number weighted distribution is consistent with isotropy, the fluence weighted dipole has a correlation with the CMB dipole that has a probability of occuring only 10% of the time for an isotropic photon distribution. Furthermore, the photon and number dipoles are inconsistent under the hypothesis of isotropy, at the 2-sigma level. This could be an indication that a non-negligible fraction of gamma-ray bursts originate in the local, anisotropic universe. (shortened Abstract)Comment: Accepted by ApJ. Self-unpacking (use csh), uuencoded, compressed Postscript, 16 pages + 4 Figures (5 files

Electron-positron pair production in the external electromagnetic field of colliding relativistic heavy ions

The results concerning the $e^+e^-$ production in peripheral highly relativistic heavy-ion collisions presented in a recent paper by Baltz {\em{et al.}} are rederived in a very straightforward manner. It is shown that the solution of the Dirac equation directly leads to the multiplicity, i.e. to the total number of electron-positron pairs produced by the electromagnetic field of the ions, whereas the calculation of the single pair production probability is much more involved. A critical observation concerns the unsolved problem of seemingly absent Coulomb corrections (Bethe-Maximon corrections) in pair production cross sections. It is shown that neither the inclusion of the vacuum-vacuum amplitude nor the correct interpretation of the solution of the Dirac equation concerning the pair multiplicity is able the explain (from a fundamental point of view) the absence of Coulomb corrections. Therefore the contradiction has to be accounted to the treatment of the high energy limit.Comment: 6 pages, 4 Postscript figures, uses svjour.cls/svepj.cl

A turbojet-boosted two-stage-to-orbit space transportation system design study

The concept to use twin turbo-powered boosters for acceleration to supersonic staging speed followed by an all rocket powered orbiter stage was proposed. A follow-on design study was then made of the concept with the performance objective of placing a 29,483 Kg payload into a .2.6 X 195.3 km orbit. The study was performed in terms of analysis and trade studies, conceptual design, utility and economic analysis, and technology assessment. Design features of the final configuration included: strakes and area rule for improved take off and low transonic drag, variable area inlets, exits and turbine, and low profile fixed landing gear for turbojet booster stage. The payload required an estimated GLOW of 1,270,000 kg for injection in orbit. Each twin booster required afterburning turbojet engines each with a static sea level thrust rating of 444,800 N. Life cycle costs for this concept were comparable to a SSTO/SLED concept except for increased development cost due to the turbojet engine propulsion system

A possible dearth of hot gas in galaxy groups at intermediate redshift

We examine the X-ray luminosity of galaxy groups in the CNOC2 survey, at redshifts 0.1 < z < 0.6. Previous work examining the gravitational lensing signal of the CNOC2 groups has shown that they are likely to be genuine, gravitationally bound objects. Of the 21 groups in the field of view of the EPIC-PN camera on XMM-Newton, not one was visible in over 100 ksec of observation, even though three of the them have velocity dispersions high enough that they would easily be visible if their luminosities scaled with their velocity dispersions in the same way as nearby groups' luminosities scale. We consider the possibility that this is due to the reported velocity dispersions being erroneously high, and conclude that this is unlikely. We therefore find tentative evidence that groups at intermediate redshift are underluminous relative to their local cousins.Comment: 16 pages, 5 figures, reference added in section 1, typos corrected, published in Ap

Analytical Results for Random Band Matrices with Preferential Basis

Using the supersymmetry method we analytically calculate the local density of states, the localiztion length, the generalized inverse participation ratios, and the distribution function of eigenvector components for the superposition of a random band matrix with a strongly fluctuating diagonal matrix. In this way we extend previously known results for ordinary band matrices to the class of random band matrices with preferential basis. Our analytical results are in good agreement with (but more general than) recent numerical findings by Jacquod and Shepelyansky.Comment: 8 pages RevTex and 1 Figure, both uuencode

The statistical properties of the city transport in Cuernavaca (Mexico) and Random matrix ensembles

We analyze statistical properties of the city bus transport in Cuernavaca (Mexico) and show that the bus arrivals display probability distributions conforming those given by the Unitary Ensemble of random matrices.Comment: 4 pages, 3 figure

The 2-10 keV XRB dipole and its cosmological implications

The hard X-ray (>2 keV) emission of the local and distant Universe as observed with the HEAO1-A2 experiment is reconsidered in the context of large scale cosmic structure. Using all-sky X-ray samples of AGN and galaxy clusters we remove the dominant local X-ray flux from within a redshift of ~ 0.02. We evaluate the dipolar and higher order harmonic structure in 4 X-ray colours. The estimated dipole anisotropy of the unresolved flux appears to be consistent with a combination of the Compton-Getting effect due to the Local Group motion (dipole amplitude Delta = 0.0042) and remaining large scale structure (0.0023 <~ Delta <~ 0.0085), in good agreement with the expectations of Cold Dark Matter models. The observed anisotropy does however also suggest a non-negligible Galactic contribution which is more complex than current, simple models of >2 keV Galactic X-ray emission. Comparison of the soft and hard colour maps with a harmonic analysis of the 1.5 keV ROSAT all-sky data qualitatively suggests that at least a third of the faint, unresolved ~ 18 deg scale structure in the HEAO1-A2 data may be Galactic in origin. However, the effect on measured flux dipoles is small (<~3%). We derive an expression for dipole anisotropy and acceleration and demonstrate how the dipole anisotropy of the distant X-ray frame can constrain the amplitude of bulk motions of the universe. From observed bulk motions over a local ~ 50 Mpc/h radius volume we determine 0.14 <~ Omega^0.6/b_x(0) <~ 0.59.Comment: 39 pages, Revised version accepted ApJ Main Journal, 3 new Figures + additional tex

Physical instrumental vetoes for gravitational-wave burst triggers

We present a robust strategy to \emph{veto} certain classes of instrumental glitches that appear at the output of interferometric gravitational-wave (GW) detectors.This veto method is `physical' in the sense that, in order to veto a burst trigger, we make use of our knowledge of the coupling of different detector subsystems to the main detector output. The main idea behind this method is that the noise in an instrumental channel X can be \emph{transferred} to the detector output (channel H) using the \emph{transfer function} from X to H, provided the noise coupling is \emph{linear} and the transfer function is \emph{unique}. If a non-stationarity in channel H is causally related to one in channel X, the two have to be consistent with the transfer function. We formulate two methods for testing the consistency between the burst triggers in channel X and channel H. One method makes use of the \emph{null-stream} constructed from channel H and the \emph{transferred} channel X, and the second involves cross-correlating the two. We demonstrate the efficiency of the veto by `injecting' instrumental glitches in the hardware of the GEO 600 detector. The \emph{veto safety} is demonstrated by performing GW-like hardware injections. We also show an example application of this method using 5 days of data from the fifth science run of GEO 600. The method is found to have very high veto efficiency with a very low accidental veto rate.Comment: Minor changes, To appear in Phys. Rev.

Large Scale Fluctuations in the X-Ray Background

We present an attempt to measure the large angular scale fluctuations in the X-Ray Background (XRB) from the HEAO1-A2 data, expressed in terms of spherical harmonics. We model the harmonic coefficients assuming a power spectrum and an epoch-dependent bias parameter, and using a phenomenological scenario describing the evolution of the X-ray sources. From the few low-order multipoles detected above shot noise, we estimate the power-spectrum normalization on scales intermediate between those explored by local galaxy redshift surveys (~ 100 Mpc) and by the COBE Microwave Background measurements (~ 1000 Mpc). We find that the HEAO1 harmonics are consistent with present epoch rms fluctuations of the X-ray sources bx(0)sigma8 ~ 1-2 in 8 Mpc spheres. Therefore the observed fluctuations in the XRB are roughly as expected from interpolating between the local galaxy surveys and the COBE CMB experiment. We predict that an X-ray all-sky surface brightness survey resolving sources a factor of 10 fainter than HEAO1, may reveal fluctuations to significantly larger angular scales and therefore more strongly constrain the large scale structure of the Universe on scales of hundreds of Mpcs.Comment: 14 pages, 3 Postscript figures, uses aaspp4.sty and psfig. Revised following referee's report. Accepted for publication in Ap