A two day Workshop entitled PULSAR STUDIES IN AFRICA was held at the Hartebeesthoek Radio Astronomy Observatory on the 3rd and 4th December 2001
Photographs of the meeting may be viewed.
Abstracts of the presentations are given below.
The full text of the articles is available at the African Skies web edition. Note that you must click on the article names on the second (contents) page of this pdf file to reach the articles.
Programme 3rd Dec 2001
Binary evolution: Spin-up, spin-down and non-thermal (thermal) emission from accreting compact objects.
Author: Hannes Calitz e-mail: firstname.lastname@example.org Affiliation: Department of Physics, University of the Free State, Bloemfontein, South Africa Co-Author: Pieter.J. Meintjies e-mail: MeintjPJ@sci.uovs.ac.za Affiliation: Department of Physics, University of the Free State, Bloemfontein, South Africa Abstract: The spin-up or spin-down of accreting objects can be used as a diagnostic tool to investigate the mass transfer mechanism between the primary and secondary star in binary systems, as well as the evolution of the system. This can put tight contstraints on the non-thermal and thermal emission in the system. By getting a global view of system, potential non-thermal emitters can be identified for future studies by HESS and other new-generation gamma-ray telescopes.
AE Aquarii, the “binary milli-second radio pulsar” of Cataclysmic Variables
Author: Pieter.J. Meintjies e-mail: MeintjPJ@sci.uovs.ac.za Affiliation: Department of Physics, University of the Free State, Bloemfontein, South Africa Abstract: This is an investigation of the evolution of the binary system AE Aquarii and the relation it has on the spin-up and spin-down of the compact companion of the system, as well as the thermal and non-thermal emission in the system. The mechanisms causing the rapid non-thermal outbursts are investigated and constraints are put on the binary system parameters.
Observations, Past and Future, of X-ray pulsars from South Africa
Author: David A.H. Buckley e-mail: email@example.com Affiliation: South African Astronomical Observatory, Cape Town, South Africa Abstract: This talk covers two separate, but related, topics concerning X-ray emitting pulsars. Most of the talk concentrates on a description of an on-going optical/IR/Xray observational program on Be/X-ray binaries: early type Be stars whose mass loss powers the accretion energy of X-ray pulsars. This class of object is the most common of early spectral type X-ray binaries. Optical spectroscopy and IR photometry can help probe the circumstellar disks of Be stars, which are the mass "reservoirs" powering the accreting neutron stars. Understanding the states of these disks can help predict the X-ray activity of these, often transient, sources. Unlike the more massive systems, where Roche lobe overflow powers the accretion, neutron stars in Be/X-ray binaries are principally accreting from either a strong stellar wind or a circumstellar disk. In eccentric systems, the accretion rate can vary significantly over the orbit. Similarly the extent of the disk itself determines the X-ray properties. Recent work on these sources in the Magellanic Clouds will be discussed, particularly in relevance to the apparent discrepancies in populations between the two Clouds. The second part of the talk covers the interesting group of isolated accreting neutron stars, as typified by the 8.39 s spin period system, RX J0720.4-3125. This nearby system, although sharing some properties of the "anomolous 6 s pulsars", is clearly much less luminous and accreting from the ISM, rather than a remnant Thorne-Zytkow object, as proposed for the latter. Optical counterparts to this object, and a similar, but non-pulsing object (RX J1856.5-3754), have recently been identified. The paucity of similar objects has been at odds with the predictions of ~2000 isolated neutron stars supposed to be detectable from their hot thermal (soft X-ray) emission. I end with a discussion of the future role of SALT in this research, and the possible capabilities of instruments, including new generation photon detectors, with energy discrimination, like Superconduction Tunnel Junction (STJ) devices.
Neutron Star Magnetic Field Evolution
Author: Legesse W. Kebede e-mail: Observatory.firstname.lastname@example.org (Subject of mail must be Legesse Kebede as the address is shared with others.) Affiliation: Department of Physics, Addis Ababa University, Ethiopia Abstract: Based on the relativistic plasma diffusion theory for neutron star magnetic fields developed by the author, the evolution of surface magnetic fields of neutron stars is discussed. It is particularly shown that neutron star magnetic fields are temperature dependent and hence dissipate as a result of neutrino and photon cooling mechanisms. The decay law for the process seems to give results which are in good agreement with observations. Consequences of the decay law in relation to certain important astrophysical measurements are also discussed.
Implications of time dependant parameters for braking indices
Author: Adrian Tiplady e-mail: email@example.com Affiliation: Physics Department, Rhodes University, Grahamstown, South Africa Co-Author: Fabio Frescura e-mail: firstname.lastname@example.org Affiliations: Research Fellow in the Department of Physics, Rhodes University, Grahamstown, South Africa; Centre of Theoretical Physics, University of the Witwatersrand, South Africa; Research Associate at the Hartebeesthoek Radio Astronomy Observatory. Abstract: The determination of braking indices via experimental results has been allowed by a certain degree of assumption. An analytical approach is taken in exploring the nature of the braking index and its possible different forms by introducing a time varying parameter. This is a first step into understanding the reason for our measurement of differing braking indices.
Radio Observations and the Challenges of the Neutron Star Interior
Author: Johnson O. Urama presented by Augustine E. Chukwude e-mail: email@example.com Affiliation: Department of Physics and Astronomy, University of Nigeria, Nsukka, Nigeria Abstract: Radio pulsars are, by far, the most common observable manifestation of the fascinating neutron star. The timing observations of the emitted radio pulses remain one of the best probes of the neutron star interior. Such observations have led to a number of models describing the various components of the neutron star interior and the manner in which they couple with each other. This paper discusses the progress made in this regard.
The HartRAO Glitch-Monitoring Project: Part I – Catching Glitches
Author: Claire Flanagan e-mail: firstname.lastname@example.org Affiliation: Johannesburg Planetarium, University of the Witwatersrand, South Africa and the Hartebeesthoek Radio Astronomy Observatory, South Africa Abstract: The HartRAO glitch-monitoring project was set up in 1984, in response to the need for good observational coverage of the response of the Vela pulsar to spin-ups. We describe the (at the time unique) technique used to obtain post-glitch observations (commencing in one case within seven minutes of a glitch). New insight into the interior of the pulsar obtained from these observations is presented, and value of extending the project into the future is discussed.
Ground Based Observations with Third Generation Ground-Based Gamma-Ray Telescopes
Author: Okkie C. de Jager e-mail: email@example.com Affiliation: School of Physics, Potchefstroom University, South Africa Co-Authors: The MAGIC Pulsar Working Group (Magicfirstname.lastname@example.org) and the H.E.S.S. Pulsar Working Group (HESSemail@example.com) Abstract: Pulsar polar cap models predict gamma-ray/pair cascades resulting in a high multiplicity of pairs in the pulsar magnetosphere. This large multiplicity is also required to explain the plerionic emission from such systems. The consequence is that emergent gamma-ray energies are constrained to be well below a TeV. Emergent maximum energies up to 30 GeV (pulsed photons) were seen by EGRET from PSR B1706-44 and PSR B1951+32, whereas observations above these energies by past ground-based pulsars only resulted in upper limits, which confirm the existence of such spectral cutoffs. The next generation telescopes such as MAGIC (La Palma) and H.E.S.S. (Namibia) should have low enough thresholds to detect the high energy tails of pulsed emission from some of these pulsars. This opens a new window on Pulsar Astronomy, since the main contribution to the photon luminosity will be measured by such telescopes. This talk reviews the sensitivities of H.E.S.S., MAGIC and 5@5 for such detections within a single night of observation.
HartRAO Long-term Pulsar Timing Observations – Relevance and Prospect
Author: Augustine E. Chukwude e-mail:firstname.lastname@example.org; email@example.com (until 21 Dec 2001) Affiliation: Department of Physics and Astronomy, University of Nigeria, Nsukka, Nigeria; Hartebeesthoek Radio Astronomy Observatory, South Africa Abstract: Regular timing observations of some radio pulsars have now been conducted at the Hartebeesthoek Radio Astronomy Observatory (HartRAO) for more than a decade. Here we present some of the results of our current work on timing activity in radio pulsars. Our results highlight the relevance of such long-term timing program in our quest for better understanding of the dynamical behaviour of neutron stars. Arguments are also presented for the continuation and improvement of the current HartRAO pulsar monitoring program.
Programme 4th Dec 2001
Effects of Pulsar Timing Noise and Glitches on Gamma-Ray Pulsar Observations
Author: E. de Ona-Wilhelmi e-mail: firstname.lastname@example.org Affiliation: School of Physics, Potchefstroom University, South Africa Co-Authors: The MAGIC Pulsar Working Group (Magicemail@example.com) Abstract: Pulsed emission from a few Gamma-Ray pulsars may be detectable with Ground-Based Gamma-Ray Telescopes. The pulsar ephemerides from the archival data of HARTRAO and Princeton (between 1989 and 1998) provide an excellent opportunity to study the accuracy of extrapolations of such ephemerides to the present moment, if an appropriate time shift is introduced. The aim of this study is to investigate the smear in the gamma-ray pulse profile during a single night of observations, given the absence of contemporary radio pulsar observations during ON-line analyses when "quick look" procedures must be employed to determine the status of a candidate. Pulsars with typical gamma-ray parameters on the (P, Pdot) diagram will be employed in this study.
Constraining Pulsar Pair Production Multiplicity and Wind Magnetization Parameters with Multiwavelength Observations.
Authors: Rocky R. Sefako (firstname.lastname@example.org) Okkie C. de Jager (email@example.com) Affiliation: School of Physics, Potchefstroom University, South Africa Co-Authors: A. Konopelko, R.A. Burger Affiliation: School of Physics, Potchefstroom University, South Africa Abstract: The pair cascade above the pulsar polar cap, combined with the energy from the pulsar wind, results in a pair plasma which is injected into the environment around a pulsar. This wind, which consists of particles and fields, is shocked by the environment, resulting in synchrotron emission from "thermalized" pairs. We see this as a typical compact X-ray nebula which may extend into the optical part of the spectrum, depending on the pair multiplicity, spindown power and wind magnetization parameter. We review these parameters for the Crab Nebula, but show how such parameters are derived for the Vela and PSR B1706-44 pulsars. The multiplicity derived for these two pulsars agree with the theoretical predictions. We also show how the total number of pairs contribute to the diffuse gamma-ray signal through inverse Compton scattering of the Cosmic Microwave Background, galactic dust emission and optical starlight emission. With these target photon fields known, we can verify the injection rate of pairs into the "plerion" by measuring the high energy to very high energy gamma-ray spectrum. We will apply this to three pulsars and show that such TeV signals should be detectable from a few pulsar/plerion systems with the H.E.S.S. Telescope system.
Pulsars and Precession
Author: Fabio Frescura e-mail: firstname.lastname@example.org Affiliation: Research Fellow in the Department of Physics, Rhodes University, Grahamstown, South Africa; Centre of Theoretical Physics, University of the Witwatersrand, South Africa; Research Associate at the Hartebeesthoek Radio Astronomy Observatory. Abstract: We consider the implications of precession for pulsar timing measurements.
Cyclic behaviour in rotation and DM of PSR B1557-50
Author: Augustine Chukwude e-mail:email@example.com; firstname.lastname@example.org (until 21 Dec 2001) Affiliation: Department of Physics and Astronomy, University of Nigeria, Nsukka, Nigeria; Hartebeesthoek Radio Astronomy Observatory, South Africa Abstract: Analysis of pulsar timing data collected at regular intervals over a long timescale remains one the best probes of the long-term rotational behaviour of neutron stars. Here we summarize results of the analysis of 13 years of pulse arrival time data of the pulsar PSR 1557-50 collected at the Hartebeesthoek Radio Astronomy Observatory (HartRAO) between 1986 August and 1999 May. Our results show that over this period, both the timing residuals and dispersion measure of this pulsar exhibit sustained cyclic variations. No few than two cycles with peak-to-peak separation of about 1500 days are evident in our data. The DM variation is more than 60% anticorrelated with rotation parameters. The results are discussed in the context of our current understanding of the dynamics of neutron stars.
The HartRAO Glitch-Monitoring Project: Part II – Glitch-Monitoring By-Products
Author: Claire Flanagan e-mail: email@example.com Affiliation: Johannesburg Planetarium, University of the Witwatersrand, South Africa and the Hartebeesthoek Radio Astronomy Observatory, South Africa Abstract: The glitch-monitoring project described in an earlier paper results in the collection of a massive amount of data, whereas the targetted glitch transients endure for a few days or weeks once every three years or so. The insight this additional data gives us into the timing noise and underlying spin-down forces in the Vela pulsar is discussed.
Future Radio Pulsar Observing – Threats and Opportunities
Author: Michael J Gaylard e-mail: firstname.lastname@example.org Affiliation: Hartebeesthoek Radio Astronomy Observatory, South Africa Abstract: The increasing use being made of the existing 26-m radio telescope at Hartebeesthoek has steadily reduced the time available for pulsar observing. Even greater pressure on pulsar observing time is forseen from 2002. It is therefore appropriate to investigate the possibilities for a new radio telescope optimised for pulsar research, as part of strategic planning for the future of astronomy in South Africa. This is particularly relevant in view of the increasing number of people in Africa involved in pulsar research. Technically, a telescope optimised for pulsar studies would likely operate at frequencies below the 1.6 GHz lower end of the 26-m telescope. We investigate the sensitivity required for observing different types of pulsars and look at trade-offs in telescope design that could produce an instrument that is desirable and useful but affordable in the face of the massive expenditure on SALT.
Enabling Technologies for Radio Astronomy
Author: Justin Jonas e-mail: email@example.com Affiliation: Physics Department, Rhodes University, Grahamstown, South Africa Abstract: Recent advances in digital electronics, photonics and material science have provided the radio astronomy community with new tools for the implementation of new generation telescopes. Artificial magneto-electric materials allow the fabrication of novel low-cost antennas. Fibre optic technology and versatile, high-speed digital electronic devices facilitate the implementation of "large-N" interferometric arrays. The applicability of various new technologies to a pulsar telescope will be discussed. A dominant topic will be the use of digital electronics in radio astronomy receivers.
Development of a Digital Pulsar Timer
Author: Adrian Tiplady e-mail: firstname.lastname@example.org Affiliation: Physics Department, Rhodes University, Grahamstown, South Africa Abstract: A new, digital pulsar timer which will replace the existing one at HartRAO is presently being developed at Rhodes University. The timer makes use of cell phone technology and FGPAs, allowing for relatively cheap and simple implementation as well as the possibility of replacing existing, expensive equipment with affordable circuitry. The modularised system is generalised in order to allow for easy, limitless expansion at any time without further design adjustments while the use of new signal processing techniques allows for maximum bandwidth usage and efficiency.