Supernova remnants' interactions with the inter-stellar medium

All-sky data at a number of different wavelengths are used to examine the Giant Radio Loops. The x-ray emission of Loop I is modelled as being due to a Supernova Remnant (SNR) that has evolved in a hot, homogeneous, quasi-isotropic medium. The shock is found to weaken towards higher latitudes, and this is attributed to an increase in the ambient gas temperature away from the galactic plane. Other evolutionary possibilities are examined. Radio spectral index maps from 38 to 1420MHz of the northern celestial hemisphere are produced, and the spectra of loops I and III are modelled on the assumption that the energy distribution of electrons accelerated in the shocks will have an upper energy cut-off due to the finite age of the remnants. It is found that the steepening spectra can be fitted by such a model. The electron distribution below the cut-off of order l0GeV is found to fit best if a flatter spectrum than predicted by simple shock theory is assumed. The idea that shocks. Interacting with clouds can explain this flatter spectrum and enhance the soft x-ray emission is put forward as an alternative evolutionary possibility, bringing together the two separate x-ray and radio emission mechanisms. Other galactic SNR are examined to support this idea, including a newly discovered SNR that exists inside the error circle of the COS-B source 2CG342-02. Although this remnant’s association with the γ-ray source cannot be excluded, no firm evidence is found to identify it as the source

System using leo satellites for centimeter-level navigation

Disclosed herein is a system for rapidly resolving position with centimeter-level accuracy for a mobile or stationary receiver [4]. This is achieved by estimating a set of parameters that are related to the integer cycle ambiguities which arise in tracking the carrier phase of satellite downlinks [5,6]. In the preferred embodiment, the technique involves a navigation receiver [4] simultaneously tracking transmissions [6] from Low Earth Orbit Satellites (LEOS) [2] together with transmissions [5] from GPS navigation satellites [1]. The rapid change in the line-of-sight vectors from the receiver [4] to the LEO signal sources [2], due to the orbital motion of the LEOS, enables the resolution with integrity of the integer cycle ambiguities of the GPS signals [5] as well as parameters related to the integer cycle ambiguity on the LEOS signals [6]. These parameters, once identified, enable real-time centimeter-level positioning of the receiver [4]. In order to achieve high-precision position estimates without the use of specialized electronics such as atomic clocks, the technique accounts for instabilities in the crystal oscillators driving the satellite transmitters, as well as those in the reference [3] and user [4] receivers. In addition, the algorithm accommodates as well as to LEOS that receive signals from ground-based transmitters, then re-transmit frequency-converted signals to the ground