Nucleosynthesis in Type I X-ray Bursts

Type I X-ray bursts are thermonuclear explosions that occur in the envelopes of accreting neutron stars. Detailed observations of these phenomena have prompted numerous studies in theoretical astrophysics and experimental nuclear physics since their discovery over 35 years ago. In this review, we begin by discussing key observational features of these phenomena that may be sensitive to the particular patterns of nucleosynthesis from the associated thermonuclear burning. We then summarize efforts to model type I X-ray bursts, with emphasis on determining the nuclear physics processes involved throughout these bursts. We discuss and evaluate limitations in the models, particularly with regard to key uncertainties in the nuclear physics input. Finally, we examine recent, relevant experimental measurements and outline future prospects to improve our understanding of these unique environments from observational, theoretical and experimental perspectives.Comment: Accepted by Prog. Part. Nucl. Phys., 45 pages, 14 figure

Discriminating between the von Neumann and L\"uders reduction rule

Given an ensemble of systems in an unknown state, as well as an observable $\hat A$ and a physical apparatus which performs a measurement of $\hat A$ on the ensemble, whose detailed working is unknown ('black box'), how can one test whether the L\"uders or von Neumann reduction rule applies?Comment: 5 page

Atmospheric neutrinos in a Large Liquid Argon detector

In view of the evaluation of the physics goals of a large Liquid Argon TPC, evolving from the ICARUS technology, we have studied the possibility of performing precision measurements on atmospheric neutrinos. For this purpose we have improved existing Monte Carlo neutrino event generators based on FLUKA and NUX by including the 3-flavor oscillation formalism and the numerical treatment of Earth matter effects. By means of these tools we have studied the sensitivity in the measurement of Theta(23) through the accurate measurement of electron neutrinos. The updated values for Delta m^2(23) from Super-Kamiokande and the mixing parameters as obtained by solar and KamLand experiments have been used as reference input, while different values of Theta(13) have been considered. An exposure larger than 500 kton yr seems necessary in order to achieve a significant result, provided that the present knowledge of systematic uncertainties is largely improved.Comment: Talk given at the worksgop "Cryogenic Liquid Detectors for Future Particle Physics", LNGS (Italy) March 13th-14th, 200

Decidability of the interval temporal logic ABBar over the natural numbers

In this paper, we focus our attention on the interval temporal logic of the Allen's relations "meets", "begins", and "begun by" (ABBar for short), interpreted over natural numbers. We first introduce the logic and we show that it is expressive enough to model distinctive interval properties,such as accomplishment conditions, to capture basic modalities of point-based temporal logic, such as the until operator, and to encode relevant metric constraints. Then, we prove that the satisfiability problem for ABBar over natural numbers is decidable by providing a small model theorem based on an original contraction method. Finally, we prove the EXPSPACE-completeness of the proble

Classical novae and type I X-ray bursts: challenges for the 21st century

Classical nova explosions and type I X-ray bursts are the most frequent types of thermonuclear stellar explosions in the Galaxy. Both phenomena arise from thermonuclear ignition in the envelopes of accreting compact objects in close binary star systems. Detailed observations of these events have stimulated numerous studies in theoretical astrophysics and experimental nuclear physics. We discuss observational features of these phenomena and theoretical efforts to better understand the energy production and nucleosynthesis in these explosions. We also examine and summarize studies directed at identifying nuclear physics quantities with uncertainties that significantly affect model predictions.Comment: 40 pages, accepted for AIP Advances: Stardust - Progress and Problems in Nuclear Astrophysic

The highly ionized disk wind of GRO J1655-40

Aims: The galactic superluminal microquasar GRO J1655-40 started a new outburst in February 2005, after seven years in quiescence, rising to a high/soft state in March 2005. In this paper we study the X-ray spectra during this rise. Methods: We observed GRO J1655-40 with XMM-Newton, on 27 February 2005, in the low/hard state, and on three consecutive days in March 2005, during the rise of the source to its high/soft state. The EPIC-pn camera was used in the fast-read Burst mode to avoid photon pile-up. Results: First, we contributed to the improvement of the calibration of the EPIC-pn, since the high flux received from the source required some refinements in the correction of the Charge Transfer Efficiency of the camera.Second, we find that the X-ray spectrum of GRO J1655-40 is dominated in the high/soft state by the thermal emission from the accretion disk, with an inner radius of 13-14(D/3.2kpc)km and a maximum temperature of 1.3 keV. Two absorption lines are detected in the EPIC-pn spectra, at 6.7-6.8 and 7.8-8.0 keV, which can be identified either as blended Fe XXV and Fe XXVI K-alpha and K-beta lines, or as blueshifted Fe XXV. We find no orbital dependence on the X-ray properties, which provides an upper limit for the inclination of the system of 73 degr. The RGS spectrometers reveal interstellar absorption features at 17.2AA, 17.5AA (Fe L edges) and 23.54AA (OI K-alpha). Finally, while checking the interstellar origin of the OI line, we find a general correlation of the OI K-alpha line equivalent width with the hydrogen column density using several sources available in the literature.Comment: 10 pages, 7 figures, 4 tables. Revised version with important change

Spacetime geometries and light trapping in travelling refractive index perturbations

In the framework of transformation optics, we show that the propagation of a locally superluminal refractive index perturbation (RIP) in a Kerr medium can be described, in the eikonal approximation, by means of a stationary metric, which we prove to be of Gordon type. Under suitable hypotheses on the RIP, we obtain a stationary but not static metric, which is characterized by an ergosphere and by a peculiar behaviour of the geodesics, which are studied numerically, also accounting for material dispersion. Finally, the equation to be satisfied by an event horizon is also displayed and briefly discussed.Comment: 14 pages, 7 figure

The supersoft X-ray source in V5116 Sgr I. The high resolution spectra

Classical novae occur on the surface of an accreting white dwarf in a binary system. After ejection of a fraction of the envelope and when the expanding shell becomes optically thin to X-rays, a bright source of supersoft X-rays arises, powered by residual H burning on the surface of the white dwarf. While the general picture of the nova event is well established, the details and balance of accretion and ejection processes in classical novae are still full of unknowns. The long-term balance of accreted matter is of special interest for massive accreting white dwarfs, which may be promising supernova Ia progenitor candidates. V5116 Sgr was observed as a bright and variable supersoft X-ray source by XMM-Newton 610~days after outburst. The light curve showed a periodicity consistent with the orbital period. During one third of the orbit the luminosity was a factor of seven brighter than during the other two thirds of the orbital period. In the present work we aim to disentangle the X-ray spectral components of V5116 Sgr and their variability. We present the high resolution spectra obtained with XMM-Newton RGS and Chandra LETGS/HRC-S in March and August 2007. The grating spectrum during the periods of high-flux shows a typical hot white dwarf atmosphere dominated by absorption lines of N VI and N VII. During the low-flux periods, the spectrum is dominated by an atmosphere with the same temperature as during the high-flux period, but with several emission features superimposed. Some of the emission lines are well modeled with an optically thin plasma in collisional equilibrium, rich in C and N, which also explains some excess in the spectra of the high-flux period. No velocity shifts are observed in the absorption lines, with an upper limit set by the spectral resolution of 500 km/s, consistent with the expectation of a non-expanding atmosphere so late in the evolution of the post-nova.Comment: 12 pages, 15 figures, 4 tables; accepted for publication in Astronomy and Astrophysic