A Bayesian method for pulsar template generation

Extracting Times of Arrival from pulsar radio signals depends on the knowledge of the pulsars pulse profile and how this template is generated. We examine pulsar template generation with Bayesian methods. We will contrast the classical generation mechanism of averaging intensity profiles with a new approach based on Bayesian inference. We introduce the Bayesian measurement model imposed and derive the algorithm to reconstruct a "statistical template" out of noisy data. The properties of these "statistical templates" are analysed with simulated and real measurement data from PSR B1133+16. We explain how to put this new form of template to use in analysing secondary parameters of interest and give various examples: We implement a nonlinear filter for determining ToAs of pulsars. Applying this method to data from PSR J1713+0747 we derive ToAs self consistently, meaning all epochs were timed and we used the same epochs for template generation. While the average template contains fluctuations and noise as unavoidable artifacts, we find that the "statistical template" derived by Bayesian inference quantifies fluctuations and remaining uncertainty. This is why the algorithm suggested turns out to reconstruct templates of statistical significance from ten to fifty single pulses. A moving data window of fifty pulses, taking out one single pulse at the beginning and adding one at the end of the window unravels the characteristics of the methods to be compared. It shows that the change induced in the classical reconstruction is dominated by random fluctuations for the average template, while statistically significant changes drive the dynamics of the proposed method's reconstruction. The analysis of phase shifts with simulated data reveals that the proposed nonlinear algorithm is able to reconstruct correct phase information along with an acceptable estimation of the remaining uncertainty.Comment: 21 pages, 16 figures, submitted to MNRA

Self-Generated Magnetic Fields in Galactic Cooling Flows

Interstellar magnetic fields in elliptical galaxies are assumed to have their origin in stellar fields that accompany normal mass loss from an evolving population of old stars. The seed fields are amplified by interstellar turbulence driven by stellar mass loss and supernova events. These disordered fields are further amplified by time-dependent compression in the inward moving galactic cooling flow and are expected to dominate near the galactic core. Under favorable circumstances, fields similar in strength to those observed $B \sim 1-10~(r/10~kpc)^{-1.2}\mu$G can be generated solely from these natural galactic processes. In general the interstellar field throughout elliptical galaxies is determined by the outermost regions in the interstellar gas where the turbulent dynamo process can occur. Because of the long hydrodynamic flow times in galactic cooling flows, currently observed magnetic fields may result from periods of intense turbulent field amplification that occurred in the outer galaxy in the distant past. Particularly strong fields in ellipticals may result from ancient galactic mergers or shear turbulence introduced at the boundary between the interstellar gas and ambient cluster gas.Comment: 21 pages in AASTEX LaTeX with 2 figures; accepted by Astrophysical Journa

Influence of the Lower Hybrid Drift Instability on the onset of Magnetic Reconnection

Two-dimensional and three-dimensional kinetic simulation results reveal the importance of the Lower-Hybrid Drift Instability LHDI to the onset of magnetic reconnection. Both explicit and implicit kinetic simulations show that the LHDI heats electrons anisotropically and increases the peak current density. Linear theory predicts these modifications can increase the growth rate of the tearing instability by almost two orders of magnitude and shift the fastest growing modes to significantly shorter wavelengths. These predictions are confirmed by nonlinear kinetic simulations in which the growth and coalescence of small scale magnetic islands leads to a rapid onset of large scale reconnection

Shuffle relations for regularised integrals of symbols

We prove shuffle relations which relate a product of regularised integrals of classical symbols to regularised nested (Chen) iterated integrals, which hold if all the symbols involved have non-vanishing residue. This is true in particular for non-integer order symbols. In general the shuffle relations hold up to finite parts of corrective terms arising from renormalisation on tensor products of classical symbols, a procedure adapted from renormalisation procedures on Feynman diagrams familiar to physicists. We relate the shuffle relations for regularised integrals of symbols with shuffle relations for multizeta functions adapting the above constructions to the case of symbols on the unit circle.Comment: 40 pages,latex. Changes concern sections 4 and 5 : an error in section 4 has been corrected, and the link between section 5 and the previous ones has been precise

ROSAT Evidence for Intrinsic Oxygen Absorption in Cooling Flow Galaxies and Groups

Using spatially resolved, deprojected ROSAT PSPC spectra of 10 of the brightest cooling flow galaxies and groups with low Galactic column densities we have detected intrinsic absorption over energies ~0.4-0.8 keV in half of the sample. Since no intrinsic absorption is indicated for energies below ~0.4 keV, the most reasonable model for the absorber is collisionally ionized gas at temperatures T=10^{5-6} K with most of the absorption arising from ionized states of oxygen but with a significant contribution from carbon and nitrogen. The soft X-ray emission of this warm gas can explain the sub-Galactic column densities of cold gas inferred within the central regions of most of the systems. Attributing the absorption to ionized gas reconciles the large columns of cold H and He inferred from EINSTEIN and ASCA with the lack of such columns inferred from ROSAT. Within the central ~10-20 kpc, where the constraints are most secure, the estimated mass of the ionized absorber is consistent with most (perhaps all) of the matter deposited by a cooling flow over the lifetime of the flow. Since the warm absorber produces no significant H or He absorption the large absorber masses are consistent with the negligible atomic and molecular H inferred from HI and CO observations of cooling flows. It is also found that if T > ~2x10^5 K then the optical and UV emission implied by the warm gas does not violate published constraints. Finally, we discuss how the prediction of warm ionized gas as the product of mass drop-out in these and other cooling flows can be verified with new CHANDRA and XMM observations. (Abridged)Comment: 17 pages (5 figures), Accepted for publication in ApJ, expanded discussion of multiphase spectral models, theoretical implications of warm gas in cooling flows, and the statistical significance of the oxygen absorptio

Non-thermal Processes in Black-Hole-Jet Magnetospheres

The environs of supermassive black holes are among the universe's most extreme phenomena. Understanding the physical processes occurring in the vicinity of black holes may provide the key to answer a number of fundamental astrophysical questions including the detectability of strong gravity effects, the formation and propagation of relativistic jets, the origin of the highest energy gamma-rays and cosmic-rays, and the nature and evolution of the central engine in Active Galactic Nuclei (AGN). As a step towards this direction, this paper reviews some of the progress achieved in the field based on observations in the very high energy domain. It particularly focuses on non-thermal particle acceleration and emission processes that may occur in the rotating magnetospheres originating from accreting, supermassive black hole systems. Topics covered include direct electric field acceleration in the black hole's magnetosphere, ultra-high energy cosmic ray production, Blandford-Znajek mechanism, centrifugal acceleration and magnetic reconnection, along with the relevant efficiency constraints imposed by interactions with matter, radiation and fields. By way of application, a detailed discussion of well-known sources (Sgr A*; Cen A; M87; NGC1399) is presented.Comment: invited review for International Journal of Modern Physics D, 49 pages, 15 figures; minor typos corrected to match published versio

The Giant Danio (D. aequipinnatus) as a Model of Cardiac Remodeling and Regeneration

The paucity of mammalian adult cardiac myocytes (CM) proliferation following myocardial infarction (MI) and the remodeling of the necrotic tissue that ensues, result in non-regenerative repair. In contrast, zebrafish (ZF) can regenerate after an apical resection or cryoinjury of the heart. There is considerable interest in models where regeneration proceeds in the presence of necrotic tissue. We have developed and characterized a cautery injury model in the giant danio (GD), a species closely related to ZF, where necrotic tissue remains part of the ventricle, yet regeneration occurs. By light and transmission electron microscopy (TEM), we have documented four temporally overlapping processes: 1) a robust inflammatory response analogous to that observed in MI, 2) concomitant proliferation of epicardial cells leading to wound closure, 3) resorption of necrotic tissue and its replacement by granulation tissue, 4) regeneration of the myocardial tissue driven by 5-EDU and [3H]thymidine incorporating CMs. In conclusion, our data suggest that the GD possesses robust repair mechanisms in the ventricle, and can serve as an important model of cardiac inflammation, remodeling and regeneration

The magnetar emission in the IR band: the role of magnetospheric currents

There is a general consensus about the fact that the magnetar scenario provides a convincing explanation for several of the observed properties of the Anomalous X-ray Pulsars and the Soft Gamma Repeaters. However, the origin of the emission observed at low energies is still an open issue. We present a quantitative model for the emission in the optical/infrared band produced by curvature radiation from magnetospheric charges, and compare results with current magnetars observations.Comment: 6 Pages, 2 Figures. Astrophysics and Space Science, in press. Proceedings of the ICREA Workshop on The High-Energy Emission from Pulsars and their Systems, Sant Cugat, April 12-16 201