The X-ray emission of the Crab-like pulsar PSR J0537-6910

In this paper we present some preliminary result on the spectral and timing analysis of the X-ray pulsed emission from the 16 ms pulsar PSR J0537-6910 in the energy range 0.1--30 keV, based on archival BeppoSAX and RossiXTE observations. This pulsar, discovered by Marshall et al.(1998) in the LMC field with RXTE, is the fastest spinning pulsar associated with a supernova remnant. It is characterized by strong glitch activity with the highest rate of all known Crab-like system.Comment: 4 pages, 2 figures. Contribution to the proceedings of "The Restless High-Energy Universe", Amsterdam, May 5-8, 2003. Editors: E.P.J. van den Heuvel, J.J.M. in't Zand, R.A.M.J. Wijer

A charging model for three-axis stabilized spacecraft

A charging model was developed for geosynchronous, three-axis stabilized spacecraft when under the influence of a geomagnetic substorm. The differential charging potentials between the thermally coated or blanketed outer surfaces and metallic structure of a spacecraft were determined when the spacecraft was immersed in a dense plasma cloud of energetic particles. The spacecraft-to-environment interaction was determined by representing the charged particle environment by equivalent current source forcing functions and by representing the spacecraft by its electrically equivalent circuit with respect to the plasma charging phenomenon. The charging model included a sun/earth/spacecraft orbit model that simulated the sum illumination conditions of the spacecraft outer surfaces throughout the orbital flight on a diurnal as well as a seasonal basis. Transient and steady-state numerical results for a three-axis stabilized spacecraft are presented

The optical to gamma-ray emission of the Crab pulsar: a multicomponent model

We present a multicomponent model to explain the features of the pulsed emission and spectrum of the Crab Pulsar, on the basis of X and gamma-ray observations obtained with BeppoSAX, INTEGRAL and CGRO. This model explains the evolution of the pulse shape and of the phase-resolved spectra, ranging from the optical/UV to the GeV energy band, on the assumption that the observed emission is due to more components. The first component, C_O, is assumed to have the pulsed double-peaked profile observed at the optical frequencies, while the second component, C_X, is dominant in the interpeak and second peak phase regions. The spectra of these components are modelled with log-parabolic laws and their spectral energy distributions have peak energies at 12.2 and 178 keV, respectively. To explain the properties of the pulsed emission in the MeV-GeV band, we introduce two more components, C_Ogamma and C_Xgamma, with phase distributions similar to those of C_O and C_X and log-parabolic spectra with the same curvature but peak energies at about 300 MeV and 2 GeV. This multicomponent model is able to reproduce both the broadband phase-resolved spectral behaviour and the changes of the pulse shape with energy. We also propose some possible physical interpretations in which C_O and C_X are emitted by secondary pairs via a synchrotron mechanism while C_Ogamma and C_Xgamma can originate either from Compton scattered or primary curvature photons.Comment: 14 pages, 16 figures; accepted by Astronomy and Astrophysic

Time properties of the the rho-class burst of the microquasar GRS 1915+105 observed with BeppoSAX in April 1999

We present a temporal analysis of a BeppoSAX observation of GRS 1915+105 performed on April 13, 1999 when the source was in the rho class, which is characterised by quasi-regular bursting activity. The aim of the present work is to confirm and extend the validity of the results obtained with a BeppoSAX observation performed on October 2000 on the recurrence time of the burst and on the hard X-ray delay. We divided the entire data set into several series, each corresponding to a satellite orbit, and performed the Fourier and wavelet analysis and the limit cycle mapping technique using the count rate and the average energy as independent variables. We found that the count rates correlate with the recurrence time of bursts and with hard X-ray delay, confirming the results previously obtained. In this observation, however, the recurrence times are distributed along two parallel branches with a constant difference of 5.2+/-0.5 s.Comment: Accepted for publication in Section 7. Stellar structure and evolution of Astronomy and Astrophysic

Interest Rate Rules with Heterogeneous Expectations

Recent macroeconomic literature stressed the importance of expectations heterogeneity in the formulation of monetary policy. We use a stylized macro model of Howitt (1992) to investigate the dynamical consequences of alternative interest rate rules when agents have heterogeneous expectations and update their beliefs over time along the lines of Brock and Hommes (1997). We find that the outcome of different monetary policies in terms of stability crucially depends on the ecology of forecasting rules and on the intensity of choice among different predictors. We also show that, when agents have heterogeneous expectations, an interest rate rule that obeys the Taylor principle does not always lead the system to converge to the rational expectations equilibrium but multiple equilibria may persist.

Individual Expectations and Aggregate Macro Behavior

The way in which individual expectations shape aggregate macroeconomic variables is crucial for the transmission and effectiveness of monetary policy. We study the individual expectations formation process and the interaction with monetary policy, within a standard New Keynesian model, by means of laboratory experiments with human subjects. We find that a more aggressive monetary policy that sets the interest rate more than point for point in response to inflation stabilizes inflation in our experimental economies. We use a simple model of individual learning, with a performance-based evolutionary selection among heterogeneous forecasting heuristics, to explain coordination of individual expectations and aggregate macro behavior observed in the laboratory experiments. Three aggregate outcomes are observed: convergence to some equilibrium level, persistent oscillatory behavior and oscillatory convergence. A simple heterogeneous expectations switching model fits individual learning as well as aggregate outcomes and outperforms homogeneous expectations benchmarks.

Lyapunov functions for a non-linear model of the X-ray bursting of the microquasar GRS 1915+105

This paper introduces a biparametric family of Lyapunov functions for a non-linear mathematical model based on the FitzHugh-Nagumo equations able to reproduce some main features of the X-ray bursting behaviour exhibited by the microquasar GRS 1915+105. These functions are useful to investigate the properties of equilibrium points and allow us to demonstrate a theorem on the global stability. The transition between bursting and stable behaviour is also analyzed.Comment: Published on International Journal of Non-Linear Mechanics, vol. 88, pp. 142-14

The complex time behaviour of the microquasar GRS 1915+105 in the \rho-class observed with BeppoSAX. III: The hard X-ray delay and limit cycle mapping

The microquasar GRS1915+105 was observed by BeppoSAX in October 2000 for about ten days while the source was in \rho-mode, which is characterized by a quasi-regular type I bursting activity. This paper presents a systematic analysis of the delay of the hard and soft X-ray emission at the burst peaks. The lag, also apparent from the comparison of the [1.7-3.4] keV light curves with those in the [6.8-10.2] keV range, is evaluated and studied as a function of time, spectral parameters, and flux. We apply the limit cycle mapping technique, using as independent variables the count rate and the mean photon rate. The results using this technique were also cross-checked using a more standard approach with the cross-correlation methods. Data are organized in runs, each relative to a continuous observation interval. The detected hard-soft delay changes in the course of the pointing from about 3 s to about 10 s and presents a clear correlation with the baseline count rate.Comment: accepted for publication in A&