Optimum low-thrust limited power transfers between neighbouring elliptic non-equatorial orbits in a non-central gravity field

A complete first-order analytical solution is developed for the problem of optimum low-thrust limited power transfers between neighbouring elliptic non-equatorial orbits in a non-central gravity field. The optimization problem is formulated as a Mayer problem of optimal control with Cartesian elements as state variables. After applying the Pontryagin maximum principle and determining the optimal thrust acceleration, an intrinsic canonical transformation is performed: the Cartesian elements are changed by suitable orbital elements. Hori's method is applied in determining a first-order analytical solution. Simple analytical solutions are obtained explicitly for long-time transfers.     

Real time localization of gamma ray bursts with INTEGRAL

The INTEGRAL satellite has been successfully launched in October 2002 and has recently started its operational phase. The INTEGRAL burst alert system (IBAS) will distribute in real time the coordinates of the gamma ray bursts (GRBs) detected with INTEGRAL. After a brief introduction on the INTEGRAL instruments, we describe the main IBAS characteristics and report on the initial results. During the initial performance and verification phase of the INTEGRAL mission, which lasted about two months, two GRBs have been localized with accuracy of 2–4 arcmin. These observations have allowed us to validate the IBAS software, which is now expected to provide quick (few seconds delay) and precise (few arcmin) localization for 10–15 GRBs per year.     

Some crucial X-ray observations — One or two SNR(s) in Crux?

A new EXOSAT (LE/CMA) observation of the region in Crux (R.A. 11h 45m, Dec. -62°) where Markert et al. (1981) reported the existence of two x-ray SNR's is presented. After cleaning the CMA field from the point source component, due to the UV emission of the numerous stars in the field, the smoothed x-ray contours are compared to the 408 MHz radio map of Caswell et al. (1983). The existence of two, well-separate x-ray emission regions is confirmed by EXOSAT, and the current x-ray/radio picture is not sufficent to distinguish clearly between the assumption of one or two (possibly interacting) SNR's in the region.     

Two magnetars: SGR 1627–41 and 1E 1547–5408

We describe the results obtained with Target of Opportunity observations of the galactic sources SGR 1627–41 and 1E 1547–5408. These two transients show several similarities supporting the interpretation of Anomalous X-ray Pulsars and Soft Gamma-ray Repeaters as a single class of strongly magnetized neutron stars.     

The multi-wavelength properties of Anomalous X-ray Pulsars and Soft Gamma-ray Repeaters

This paper reviews the multi-wavelength properties of two groups of pulsars, the Anomalous X-ray Pulsars (AXPs) and the Soft Gamma-ray Repeaters (SGRs), that are generally interpreted as isolated neutron stars with strong magnetic fields of 10¹⁴–10¹⁵ G. Most of these sources have now been observed at different wavelengths, from the radio band to hard X-rays. Several new members of these classes have been discovered in the last few years, due to their transient nature. The distinction between AXPs and SGRs is becoming less evident, as more observations are collected which show similar properties in all these sources.     

Einstein and EXOSAT observations of Geminga revisited

We have re-analyzed the archive Einstein IPC and EXOSAT CMA x-ray data of Geminga, in the light of the recent discoveries on this source. The results of a search for the 237 msec periodicity are consistent with a pulsed fraction decreasing with x-ray energy. We have combined the EXOSAT CMA and the Einstein data in order to limit the spectral parameters allowed by the IPC fit. This joint analysis confirms that the spectrum cannot be described by a single temperature blackbody component.     

Hori method for generalized canonical systems

In this paper, some special features on the canonical version of Hori method, when it is applied to generalized canonical systems (systems of differential equations described by a Hamiltonian function linear in the momenta), are presented. Two different procedures, based on a new approach for the integration theory recently presented for the canonical version, are proposed for determining the new Hamiltonian and the generating function for systems whose differential equations for the coordinates describe a periodic system with one fast phase. These procedures are equivalent and they are directly related to the canonical transformations defined by the general solution of the integrable kernel of the Hamiltonian. They provide the same near-identity transformation for the coordinates obtained through the non-canonical version of Hori method. It is also shown that these procedures are connected to the classic averaging principle through a canonical transformation. As examples, asymptotic solutions of a non-linear oscillations problem and of the elliptic perturbed problem are discussed.     

全球电离层对2000年4月6-7日磁暴事件的响应

利用分布于全球的电离层台站的测高仪观测数据,对扰动期间,foF2值与其宁静期间参考值进行比较,研究了2000年4月6—7日磁暴期间全球不同区域电离层的响应形态,并通过对比磁扰期间NmF2的变化与由MSISR90经验模式估算的中性大气浓度比(no／nN2)的变化,探讨了本次事件期间的电离层暴扰动机制．结果表明,在磁暴主相和恢复相早期,出现了全球性的电离层F2层负相暴效应．最大负相暴效应出现在磁暴恢复相早期,即电离层暴恢复相开始时间滞后于磁暴恢复相开始时间．在磁暴恢复相后期,一些台站出现正相扰动．研究结果表明,本次事件期间的电离层暴主要是由磁暴活动而诱发的热层暴环流引起的．     

Optimal low-thrust transfer between neighbouring quasi-circular orbits around an oblate planet

The problem of optimal low-thrust, limited power transfer between quasi-circular orbits (e 0) around an oblate planet is analysed. It is assumed that the orbital changes due to thrust acceleration and Earth oblateness are of the same order. A first order solution to the problem is obtained by application of Pontryagin's Maximum Principle. Subsequently, by application of Hori's method for generalized canonical systems, a first order solution in a small parameter ε is derived. Finally, three particular cases of long-time transfer and the orbit maintenance manoeuvre are considered. The results obtained are in agreement and represent an extension of the work done by Marec.