arXiv subjects

J F Bell

Publications and source records attributed to J F Bell.

5 recordsLinked to original sources

arXiv2000

Radio Pulsars in Terzan 5

We report on searches of the globular cluster Terzan 5 for low luminosity and accelerated radio pulsars using the 64-m Parkes radio telescope. One new millisecond pulsar, designated PSR J1748-2446C, was discovered, having a period of 8.44ms. Timing measurements using the 76-m Lovell radio telescope at Jodrell Bank show that it is a solitary pulsar and lies close to the core of the cluster. We also present the results of timing measurements which show that the longer-period pulsar PSR J1748-2444 (formerly known as PSR B1744-24B) lies 10 arcmin from the core of the cluster and is unlikely to be associated with the cluster. We conclude that there are further pulsars to be detected in the cluster.

astro-ph↗

arXiv2000

The Future of Radio Astronomy: Options for Dealing with Human Generated Interference

Radio astronomy provides a unique window on the universe, allowing us to study: non-thermal processes (galactic nuclei, quasars, pulsars) at the highest angular resolution using VLBI, with low opacity. It is the most interesting wave band for SETI searches. To date it has yielded 3 Nobel prizes (microwave background, pulsars, gravitational radiation). There are both exciting possibilities and substantial challenges for radio astronomy to remain at the cutting edge over the next 3 decades. New instruments like ALMA and the SKA will open up new science if the challenge of dealing human generated interference can be met. We summarise some of the issues and technological developments that will be essential to the future success of radio astronomy.

astro-ph↗

arXiv2000

Radio Frequency Interference

We describe the nature of the interference challenges facing radio astronomy in the next decade. These challenges will not be solved by regulation only, negotiation and mitigation will become vital. There is no silver bullet for mitigating against interference. A successful mitigation approach is most likely to be a hierarchical or progressive approach throughout the telescope and signal conditioning and processing systems. We summarise some of the approaches, including adaptive systems.

astro-ph↗

arXiv2000

Cancellation of GLONASS signals from Radio Astronomy Data

Astronomers use the 1612 MHz OH spectral line emission as a unique window on properties of evolved stars, galactic dynamics, and putative proto-planetary disk systems around young stars. In recent years, experiments using this OH line have become more difficult because radio telescopes are very sensitive to transmissions from the GLONASS satellite system. The weak astronomical signals are often undetectable in the presence of these unwanted human generated signals. In this paper we demonstrate that GLONASS narrow band signals may be removed using digital signal processing in a manner that is robust and non-toxic to the weak astronomy signals, without using a reference antenna. We present results using real astronomy data and outline the steps required to implement useful systems on radio telescopes.

astro-ph↗

arXiv1996

A new test of conservation laws and Lorentz invariance in relativistic gravity

General relativity predicts that energy and momentum conservation laws hold and that preferred frames do not exist. The parametrised post-Newtonian formalism (PPN) phenomenologically quantifies possible deviations from general relativity. The PPN parameter alpha_3 (which identically vanishes in general relativity) plays a dual role in that it is associated both with a violation of the momentum conservation law, and with the existence of a preferred frame. By considering the effects of alpha_3 neq 0 in certain binary pulsar systems, it is shown that alpha_3 < 2.2 x 10^-20 (90% CL). This limit improves on previous results by several orders of magnitude, and shows that pulsar tests of alpha_3 rank (together with Hughes-Drever-type tests of local Lorentz invariance) among the most precise null experiments of physics.

gr-qc↗