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We present WALLABY pilot data release 1, the first public release of HI pilot survey data from the Wide-field ASKAP L-band Legacy All-sky Blind Survey (WALLABY) on the Australian Square Kilometre Array Pathfinder. Phase 1 of the WALLABY pilot survey targeted three $60~{\rm deg}^2$ regions on the sky in the direction of the Hydra and Norma galaxy clusters and the NGC 4636 galaxy group, covering the redshift range of z < 0.08. The source catalogue, images and spectra of nearly 600 extragalactic HI detections and kinematic models for 109 spatially resolved galaxies are available. As the pilot survey targeted regions containing nearby group and cluster environments, the median redshift of the sample of z ~ 0.014 is relatively low compared to the full WALLABY survey. The median galaxy HI mass is $2.3 \times 10^{9}~M_{\odot}$. The target noise level of 1.6 mJy per $30''$ beam and 18.5 kHz channel translates into a $5\sigma$ HI mass sensitivity for point sources of about $5.2 \times 10^{8} \, (D_{\rm L} / \mathrm{100~Mpc})^{2} \, M_{\odot}$ across 50 spectral channels (~200 km/s) and a $5\sigma$ HI column density sensitivity of about $8.6 \times 10^{19} \, (1 + z)^{4}~\mathrm{cm}^{-2}$ across 5 channels (~20 km/s) for emission filling the $30''$ beam. As expected for a pilot survey, several technical issues and artefacts are still affecting the data quality. Most notably, there are systematic flux errors of up to several 10% caused by uncertainties about the exact size and shape of each of the primary beams as well as the presence of sidelobes due to the finite deconvolution threshold. In addition, artefacts such as residual continuum emission and bandpass ripples have affected some of the data. The pilot survey has been highly successful in uncovering such technical problems, most of which are expected to be addressed and rectified before the start of the full WALLABY survey., Comment: 24 pages, 13 figures, 5 tables, accepted for publication in PASA

This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution, and reproduction in any medium, provided the original work is properly cited.--Full list of authors: Pingel, N. M.; Dempsey, J.; McClure-Griffiths, N. M.; Dickey, J. M.; Jameson, K. E.; Arce, H.; Anglada, G.; Bland-Hawthorn, J.; Breen, S. L.; Buckland-Willis, F.; Clark, S. E.; Dawson, J. R.; Denes, H.; Di Teodoro, E. M.; For, B-Q; Foster, Tyler J.; Gomez, J. F.; Imai, H.; Joncas, G.; Kim, C-G; Lee, M-Y; Lynn, C.; Leahy, D.; Ma, Y. K.; Marchal, A.; McConnell, D.; Miville-Deschenes, M-A; Moss, V. A.; Murray, C. E.; Nidever, D.; Peek, J.; Staveley-Smith, L.; Tepper-Garcia, T.; Tremblay, C. D.; Uscanga, L.; van Loon, J. Th; Vazquez-Semadeni, E.; Allison, J. R.; Anderson, C. S.; Ball, Lewis; Bell, M.; Bock, D. C-J; Bunton, J.; Cooray, F. R.; Cornwell, T.; Koribalski, B. S.; Gupta, N.; Hayman, D. B.; Harvey-Smith, L.; Lee-Waddell, K.; Ng, A.; Phillips, C. J.; Voronkov, M.; Westmeier, T.; Whiting, M. T.; Stanimirovic, S., We present the most sensitive and detailed view of the neutral hydrogen ( HI ) emission associated with the Small Magellanic Cloud (SMC), through the combination of data from the Australian Square Kilometre Array Pathfinder (ASKAP) and Parkes (Murriyang), as part of the Galactic Australian Square Kilometre Array Pathfinder (GASKAP) pilot survey. These GASKAP-HI pilot observations, for the first time, reveal HI in the SMC on similar physical scales as other important tracers of the interstellar medium, such as molecular gas and dust. The resultant image cube possesses an rms noise level of 1.1 K ( 1.6mJy beam−1 ) per 0.98km s−1 spectral channel with an angular resolution of 30′′ ( ∼10pc ). We discuss the calibration scheme and the custom imaging pipeline that utilises a joint deconvolution approach, efficiently distributed across a computing cluster, to accurately recover the emission extending across the entire ∼25deg2 field-of-view. We provide an overview of the data products and characterise several aspects including the noise properties as a function of angular resolution and the represented spatial scales by deriving the global transfer function over the full spectral range. A preliminary spatial power spectrum analysis on individual spectral channels reveals that the power law nature of the density distribution extends down to scales of 10 pc. We highlight the scientific potential of these data by comparing the properties of an outflowing high-velocity cloud with previous ASKAP+Parkes HI test observations. c The Author(s), 2022. Published by Cambridge University Press on behalf of the Astronomical Society of Australia., The Australian SKA Pathfinder is part of the Australia Telescope National Facility which is managed by CSIRO. Operation of ASKAP is funded by the Australian Government with support from the National Collaborative Research Infrastructure Strategy. ASKAP uses the resources of the Pawsey Supercomputing Centre. Establishment of ASKAP, the Murchison Radio-astronomy Observatory and the Pawsey Supercomputing Centre are initiatives of the Australian Government, with support from the Government of Western Australia and the Science and Industry Endowment Fund. We acknowledge the Wajarri Yamatji people as the traditional owners of the Observatory site. Pipeline development was tested on the OzSTAR supercomputer under the project code, oz145, which is available through Swinburne University’s Centre of Astrophysics and Supercomputing. This research was supported by the Australian Research Council (ARC) through grant DP190101571. N.M.-G. acknowledges the support of the ARC through Future Fellowship FT150100024. G. A. and J. F. G. acknowledge support from the State Agency for Research (10.13039/501100011033) of the Spanish MCIU, through grants AYA2017-84390-C2-1-R and PID2020-114461GB-I00 (co-funded by FEDER) and the ‘Center of Excellence Severo Ochoa’ award for the Instituto de Astrofsica de Andaluca (SEV-2017-0709). C. E. M. is supported by an NSF Astronomy and Astrophysics Postdoctoral Fellowship under award AST-1801471.

The Variables and Slow Transients Survey (VAST) on the Australian Square Kilometre Array Pathfinder (ASKAP) is designed to detect highly variable and transient radio sources on timescales from 5 s to$\sim\!5$yr. In this paper, we present the survey description, observation strategy and initial results from the VAST Phase I Pilot Survey. This pilot survey consists of$\sim\!162$h of observations conducted at a central frequency of 888 MHz between 2019 August and 2020 August, with a typical rms sensitivity of$0.24\ \mathrm{mJy\ beam}^{-1}$and angular resolution of$12-20$arcseconds. There are 113 fields, each of which was observed for 12 min integration time, with between 5 and 13 repeats, with cadences between 1 day and 8 months. The total area of the pilot survey footprint is 5 131 square degrees, covering six distinct regions of the sky. An initial search of two of these regions, totalling 1 646 square degrees, revealed 28 highly variable and/or transient sources. Seven of these are known pulsars, including the millisecond pulsar J2039–5617. Another seven are stars, four of which have no previously reported radio detection (SCR J0533–4257, LEHPM 2-783, UCAC3 89–412162 and 2MASS J22414436–6119311). Of the remaining 14 sources, two are active galactic nuclei, six are associated with galaxies and the other six have no multi-wavelength counterparts and are yet to be identified.

We present the data and initial results from the first Pilot Survey of the Evolutionary Map of the Universe (EMU), observed at 944 MHz with the Australian Square Kilometre Array Pathfinder (ASKAP) telescope. The survey covers 270 \sqdeg of an area covered by the Dark Energy Survey, reaching a depth of 25--30 \ujybm\ rms at a spatial resolution of $\sim$ 11--18 arcsec, resulting in a catalogue of $\sim$ 220,000 sources, of which $\sim$ 180,000 are single-component sources. Here we present the catalogue of single-component sources, together with (where available) optical and infrared cross-identifications, classifications, and redshifts. This survey explores a new region of parameter space compared to previous surveys. Specifically, the EMU Pilot Survey has a high density of sources, and also a high sensitivity to low surface-brightness emission. These properties result in the detection of types of sources that were rarely seen in or absent from previous surveys. We present some of these new results here., Accepted by PASA

The Square Kilometre Array (SKA) is an ambitious project to build the world's largest radio observatory. The Observatory will construct two telescopes: a low-frequency array (50-350 MHz) in Australia and a mid-frequency array (0:35 - 15 GHz) in South Africa. The Global Headquarters for the SKA is located at the Jodrell Bank Observatory in the UK. Once in steady-state operations, the SKA will have one of the largest data rates of any research infrastructure in the world. This paper describes the operational model for the SKA and the challenges faced by its globally distributed operations. The paper presents the modelling undertaken to better understand the workforce required to support the engineering operations and maintenance of the telescopes, and how the Observatory will interact and interface with a global network of SKA Regional Centres to support its scientific users.

We present extensive observations of the radio emission from the remnant of SN 1987A made with the Australia Telescope Compact Array (ATCA), since the first detection of the remnant in 1990. The radio emission has evolved in time providing unique information on the interaction of the supernova shock with the circumstellar medium. We particularly focus on the monitoring observations at 1.4, 2.4, 4.8 and 8.6 GHz, which have been made at intervals of 4-6 weeks. The flux density data show that the remnant brightness is now increasing exponentially, while the radio spectrum is flattening. The current spectral index value of -0.68 represents an 18+/-3% increase over the last 8 years. The exponential trend in the flux is also found in the ATCA imaging observations at 9 GHz, which have been made since 1992, approximately twice a year, as well as in the 843 MHz data set from the Molonglo Observatory Synthesis Telescope from 1987 to March 2007. Comparisons with data at different wavelengths (X-ray, H\alpha) are made. The rich data set that has been assembled in the last 22 years forms a basis for a better understanding of the evolution of the supernova remnant.

We review the theory of shock drift acceleration, developing the theory in detail for gyrophaseaveraged particles. It is shown howboth the upstream and downstream velocity spaces separate into different regions according to the interaction of the particles with the shock (reflection, transmission, head-on, overtaking). The effects of the cross-shock electric field and of the magnetic overshoot are discussed. The effectiveness of acceleration is estimated for Maxwellian and power law distributions. The condition for a beam instability to be generated by reflected particles is determined and found to be independent of the distribution function for isotropic inflowing electrons.

We summarise the proceedings of a workshop on ‘Supernova Remnants, Pulsars and the Interstellar Medium’ which was held at the Special Research Centre for Theoretical Astrophysics at the University of Sydney on 18 and 19 March 1999.

We derive light curves for the hard gamma-ray emission, at energies up to several TeV, expected from the unique pulsar/Be-star binary system PSR B1259-63. This is the only known system in our galaxy in which a radio pulsar is orbiting a main sequence star. We show that inverse Compton emission from the electrons and positrons in the shocked pulsar wind, scattering target photons from the Be star, produces a flux of hard gamma-rays that should be above the sensitivity threshold of present day atmospheric Cerenkov detectors. Furthermore, we predict that the flux of hard gamma-rays produced via this mechanism has a characteristic variation with orbital phase that should be observable, and which is not expected from any other mechanism., To be published in Astroparticle Physics. 24 pages, 8 figures

Electrons can experience superadiabatic heating at a collisionless shock due to the presence of a cross-shock electric potential. This heating can greatly exceed the temperature rise associated with the conservation of the magnetic moment of the electrons as they move into the stronger magnetic field downstream of the shock. The criterion for the onset of superadiabatic heating and the effects of the detailed structure of the shock are investigated for the special case where the magnetic field is perpendicular to the shock normal. A comparison of the natural length scale of the electron orbits and the shock thickness is used to derive a new criterion for the onset of superadiabatic heating. This new heating criterion facilitates an improved understanding of the role of various physical parameters in determining the degree of electron heating. It has the same functional form as the condition for the electron equations of motion to permit exponential divergence of electron orbits (an important feature of dynamical chaos) which it has previously been argued determines the onset of superadiabatic heating. However, we show that the orbits of individual electrons undergoing superadiabatic heating do not diverge significantly because of the very short time they spend within the shock, the only region in which the equations of motion are nonlinear. The techniques used to analyze dynamically chaotic systems are therefore of little assistance in understanding this potentially important process.

A simple model is presented for electron acceleration in extragalactic radio sources with two hot spots. The effect of diffusive shock acceleration by multiple shocks is calculated numerically, with adiabatic and synchrotron losses included. It is found for the sources 3C 20 and 3C 268·4 that a consistent set of model parameters exists which reproduce the observations. The model fails to reproduce the observations for the source 3C 196.

The Atacama Large Millimeter/submillimeter Array (ALMA) is a major new interferometer operated on Llano de Chajnantor at 5050 m altitude in the Chilean high Andes. This location is considered one of the world's outstanding sites for submillimeter astronomy. ALMA is still under construction, but science observations has started already in what is commonly known as ALMA Early Science Cycle 0. The purpose of ALMA Early Science Cycle 0 is to deliver scientically useful results to the astronomy community and to facilitate the ongoing characterization of ALMA systems and instrumentation as the capability of the array continues to grow. Early Science will continue through Cycle 1 and until construction and commissioning of ALMA is complete. This publication aims to give an insight into the challenges we face operating telescope of this scale at Chajnantor, a plateau 4800{5100 meter above sea level in one of the driest places of earth. It also will also present statistics from the proposal submission, describe the path from an accepted proposal to a calibrated data product, and nally an outlook for the future.

Shock drift acceleration of the electrons which produce herringbone structure in type II bursts is considered. A non-coplanar component of the magnetic field within the shock front and an electric field across the shock are taken into account. A quantitative difficulty with shock drift acceleration is identified, and possible ways of overcoming the difficulty are outlined.

Diffusive acceleration of electrons by the blast wave of SNR 1987A is shown to provide a reasonable fit to observations of the radio emission since it reappeared in 1990 July. As well as determining the diffusion coefficient in this model, the observations indicate that the compression ratio of the gas subshock embedded in the blast wave is ~2.7, much lower than the value of 4 expected of a strong shock front. We propose that protons accelerated by the shock front itself cause the weakening of the subshock by both heating and accelerating the upstream plasma, producing a structure with a precursor to the gas subshock. Preliminary calculations using a fluid model for the energetic particle population indicate that these effects can significantly weaken the subshock just a few years after the explosion, if the same rate of particle injection is assumed as in other models of the acceleration of cosmic rays.Subject headings: acceleration of particles — ISM: individual (SNR 1987 A) — radio continuum: ISM — shock waves

We discuss a generalisation of the synchrotron bubble model which has been applied to short-lived radio transients which can peak and decay over just a few days. The assumptions of the simple model imply that when the flux is increasing with time, it must also be an increasing function of frequency. Observations of two recent radio transients, Nova Muscae 1991 and the Galactic Centre Transient, include the first data showing such a rising phase, and in both cases the radio flux was a decreasing function of frequency during the observed rising phases. Thus the simple synchrotron bubble model is inadequate, at least for these events. A fundamental feature of the simple model is the assumption that the process accelerating the radiating electrons ceases before the radio emission can escape. We relax this assumption by including an injection of electrons, with a constant energy spectrum, into the synchrotron bubble.

We investigate ion energization and ion conic production by broadband electric field fluctuations. The roles played by resonant fluctuations (which can satisfy the cyclotron resonance condition), and nonresonant fluctuations well removed from the ion gyrofrequency, are compared. We show that in the resonant case the mean ion energy increases essentially linearly with time, while in the nonresonant case this energy rapidly reaches a maximum. Using observed electric spectra we find that nonresonant energization due to high spectral densities at frequencies well below the ion gyrofrequency may be important for the generation of some heavy ion conics, but confirm that heating by resonant electric fluctuations is sufficient to explain most ion conics.

The process of double-cyclotron absorption, where an ion simultaneously absorbs two waves whose frequencies sum to the ion gyrofrequency, can heat ions perpendicular to the ambient magnetic field. It has been suggested that this process may play a role in the production of ion conics. The low-energy oxygen (O{sup +}) distributions and the electric spectral densities observed by DE 1 in the cusp/cleft during an O{sup +} conic event are used as inputs to a Monte Carlo simulation of the heating of the O{sup +} ions due to double-cyclotron absorption of waves near half the ion gyrofrequency. The results are compared with the observed O{sup +} conics and with the results of simulations of ion heating via the process of cyclotron resonance involving left-hand polarized waves near the ion gyrofrequency. The simulations show that for any particular event cyclotron resonance can probably heat ions over a much greater altitude range than double-cyclotron absorption is capable of doing. They also demonstrate the much stronger dependence of the heating due to double-cyclotron absorption on local intensifications of the spectral density, and they indicate that a relatively narrow region of intense wave activity may be sufficient for this heating process to produce O{supmore » +} conics with energies comparable to those observed. Heating via double-cyclotron absorption may therefore be important for relatively local heating of O{sup +} ions. However, cyclotron resonance heating by waves around the gyrofrequency is probably more important in the majority of O{sup +} conic events in the cusp/cleft.« less

We report here on extensive radio observations of the binary system containing PSR B1259-63 and the Be star SS 2883, made around the time of the 2004 periastron. This is the fourth periastron to have been observed in detail. As in previous observations, changes in the pulsar's dispersion and rotation measures are detected over a period spanning 200 days. We show that the eclipse of the pulsed emission lasts from 16 days prior to periastron to 15 days after periastron and is consistent from one periastron to the next. We demonstrate that the timing solution proposed by Wang et al. (2004) provides a good fit through the 2004 periastron. The light curve of the transient unpulsed radio emission is broadly similar from one periastron to the next. For this periastron, however, the light curve is strongly peaked post-periastron with rather little enhancement prior to periastron, in contrast to the 2000 periastron where the peak flux densities were more equal. These observations remain consistent with the interpretation that the pulsar passes through the dense circumstellar disk of the Be star just before and just after periastron. The observed differences from one periastron to the next can be ascribed to variations in the local disk density and magnetic field structure at the time the pulsar enters the disk., Accepted by MNRAS. 7 pages, 5 figures

The high-energy gamma-ray light curve of the binary system PSR B1259 -63, is computed using the approach that successfully predicted the spectrum at periastron. The simultaneous INTEGRAL and H.E.S.S. spectra taken 16 days after periastron currently permit both a model with dominant radiative losses, high pulsar wind Lorentz factor and modest efficiency as well as one with dominant adiabatic losses, a slower wind and higher efficiency. In this paper we shown how the long-term light curve may help to lift this degeneracy., Comment: 4 pages, to appear in proceedings of: Astrophysical Sources of High Energy Particles and Radiation, Torun (2005)

We present calculations of the radio emission from supernovae based on high-resolution simulations of the hydrodynamics and radiation transfer, using simple energy density relations which link the properties of the radiating electrons and the magnetic field to the hydrodynamics. As a specific example we model the emission from SN1993J, which cannot be adequately fitted with the often-used analytic mini-shell model, and present a good fit to the radio evolution at a single frequency. Both free-free absorption and syncrotron self- absorption are needed to fit the light curve at early times and a circumstellar density profile of rho~r^-1.7 provides the best fit to the later data. We show that the interaction of density structures in the ejecta with the reverse supernova shock may produce features in the radio light curves such as have been observed. We discuss the use of high-resolution radio images of supernovae to distinguish between different absorption mechanisms and determine the origin of specific light curve features. Comparisons of VLBI images of SN1993J with synthetic model images suggest that internal free-free absorption completely obscures emission at 8.4 GHz passing through the center of the supernova for the first few tens of years after explosion. We predict that at 8.4 GHz the internal free-free absorption is currently declining, and that over the next 40 years the surface brightness of the center of the source should increase relative to the bright ring of emission seen in VLBI images. Similar absorption in a nearby supernova would make the detection of a radio pulsar at 1 GHz impossible for ~150 years after explosion., Comment: 17 pages, 9 figures, accepted for publication in ApJ

Rotation powered pulsars with main sequence star companions may provide a new class of sources of hard γ-rays. Relativistic electrons and positrons in the pulsar wind can inverse Compton scatter target photons from the companion star to energies as high as a few TeV. The best candidate binary pulsar system is PSR B1259−63/SS2883 in which the energy density of target photons at the pulsar reaches a maximum which is ∼1012 times that of background targets encountered at isolated pulsars.

The reappearance of radio emission from SN 1987A is discussed. We propose a model involving synchrotron radiation from electrons which are accelerated when the expanding supernova shock wave runs into a density jump in the circumstellar material, and which then expand adiabatically.

PSR B1259-63 is a 47ms radio pulsar with a high spin-down luminosity which is in a close, highly eccentric 3.5-year orbit about a bright stellar companion. The binary system may be a detectable source of hard gamma-rays produced by inverse Compton scattering of photons from the B2e star SS2883 by electrons and positrons in the pulsar wind. The star provides an enormous density of optical photons in the vicinity of the pulsar, particularly at epochs near periastron. We calculate the emission from the unshocked region of the pulsar wind, assuming that it terminates at a shock where it attains pressure balance with the companion's wind. The spectra and light curves for the inverse Compton emission from the shock-terminated wind are compared with those for an unterminated wind. If the pulsar's wind is weaker than that from the companion star, the termination of the wind decreases the inverse Compton flux, particularly near periastron. The termination shock geometry has the effect of decreasing the asymmetry of the gamma-ray light curve around periastron, which arises because of the asymmetrical variation of the scattering angle., To be published in the Publications of the Astrophysical Society of Australia, Volume 18 number 1, (10 pages, 6 postscript figures)

We report the flux densities of the evolving radio source SN1987A at 843 MHz measured from observations made with the Molonglo Observatory Synthesis Telescope between 1994 September and 2000 May. The radio light curve shows that the rate of increase of the flux density jumped markedly around days 2800-3000 (i.e. in the first half of 1995), and that since then the radio evolution has been remarkably well fitted by a simple linear increase of (62.7 +- 0.5) microJansky/day. We discuss in detail the relationship between the radio light curve and the recent brightening of the system at optical wavelengths., Comment: To be published in the Astrophysical Journal, 11 pages, 4 postscript figures

We investigate the effects of inverse Compton scattering by electrons and positrons in the unshocked winds of rotationally-powered binary pulsars. This process can scatter low energy target photons to produce gamma rays with energies from MeV to TeV. The binary radio pulsars PSR B1259-63 and PSR J0045-73 are both in close eccentric orbits around bright main sequence stars which provide a huge density of low energy target photons. The inverse Compton scattering process transfers momentum from the pulsar wind to the scattered photons, and therefore provides a drag which tends to decelerate the pulsar wind. We present detailed calculations of the dynamics of a pulsar wind which is undergoing inverse Compton scattering, showing that the deceleration of the wind of PSR B1259-63 due to `inverse Compton drag' is small, but that this process may confine the wind of PSR J0045-73 before it attains pressure balance with the outflow of its companion star. We calculate the spectra and light curves of the resulting inverse Compton emission from PSR B1259-63 and show that if the size of the pulsar wind nebula is comparable to the binary separation, then the gamma-ray emission from the unshocked wind may be detectable by atmospheric Cerenkov detectors or by the new generation of satellite-borne gamma-ray detectors such as INTEGRAL and GLAST. This mechanism may therefore provide a direct probe of the freely-expanding regions of pulsar winds, previously thought to be invisible., To be published in Astroparticle Physics. 27 pages, 5 figures

We discuss the interpretation of transient, unpulsed radio emission detected from the unique pulsar/Be-star binary system PSR B1259-63. Extensive monitoring of the 1994 and 1997 periastron passages has shown that the source flares over a 100-day interval around periastron, varying on time-scales as short as a day and peaking at 60 mJy (~100 times the apastron flux density) at 1.4 GHz. Interpreting the emission as synchrotron radiation, we show that (i) the observed variations in flux density are too large to be caused by the shock interaction between the pulsar wind and an isotropic, radiatively driven, Be-star wind, and (ii) the radio emitting electrons do not originate from the pulsar wind. We argue instead that the radio electrons originate from the circumstellar disk of the Be star and are accelerated at two epochs, one before and one after periastron, when the pulsar passes through the disk. A simple model incorporating two epochs of impulsive acceleration followed by synchrotron cooling reproduces the essential features of the radio light curve and spectrum and is consistent with the system geometry inferred from pulsed radio data., To be published in Astrophysical Journal Letters 7 pages, 1 postscript figure

The reappearance of radio emission from SN 1987A in July 1990 is discussed. We propose a model involving synchrotron radiation from electrons which are accelerated by the expanding supernova shock wave. From the observed delay in which the switch‐on between 843 MHz and 4.8 GHz we derive the mean free path of the electrons and the time at which the acceleration process must have started, presumably as a result of the shock encountering a density jump in the circumstellar material.

Unpulsed high energy (TeV) emission has been detected from several isolated pulsars (Aharonian 1999) and presumably results from relativistic electrons accelerated at the termination shock of an MHD wind driven by the pulsar itself. These electrons inverse Compton scatter target photons from either the cosmic microwave background, or from their own synchrotron radiation.The rotation-powered binary pulsar PSR B1259–63 (Johnston et al. 1996) is also thought to drive an MHD wind, and the synchrotron radiation of electrons accelerated at its termination shock is probably the source of the unpulsed X-rays seen from this object by ROSAT, OSSE and ASCA (Tavani & Arons 1997). Compared to the isolated pulsars, however, the the pulsar’s Be-star companion provides an energy density of target photons available for inverse Compton scattering which is some 11 orders of magnitude larger. Using delta-function approximations to the emissivities and a monochromatic approximation to the spectrum of the target photons, we modelled the observed X-ray synchrotron emission and predicted the TeV emission in a recent paper (Kirk et al. 1999). In this contribution we improve these calculations in two respects – by treating the target spectrum more precisely, as described in the companion paper (Ball & Kirk 1999), and by relaxing the approximations made in the emissivities.

The unique binary pulsar system PSR B1259–63, comprising a radio pulsar in an eccentric orbit about a hot, massive companion star, has been extensively monitored at radio frequencies between 843 MHz and 8.4 GHz during its 1994 and 1997 periastron passages. Unpulsed radio emission was detected for about 100 days around each periastron, varying on time scales as short as a day. We argue that the emission is synchrotron radiation generated as the pulsar passes through the Be-star’s excretion disk just before and just after periastron.

A short-lived (weeks-months) burst of radio emission, assumed to be synchrotron radiation, is sometimes associated with objects detected as soft X-ray transients. The “synchrotron bubble model” which has been applied to these radio transients assumes that the source is initially optically thick, and the model therefore takes no account of the details of the electron acceleration required. The initial increase in the radio flux is attributed to decreasing absorption in the expanding source. Observations of the soft X-ray transient GRS 1124 – 68 (X-ray Nova Muscae 1991) showed, for the first time, the rising phase of such a radio transient. Another radio source, the Galactic Center Transient, was discovered serendipitously in the radio and observed throughout its rise and decay. In both cases the radio flux was a decreasing function of frequency throughout the periods of increasing and decreasing flux, which is not consistent with the optically thick assumption of the synchrotron bubble model. When this assumption is discarded the mechanism responsible for producing the ultrarelativistic electrons, or at the very least the rate at which those electrons become available, must be considered. A generalization of the simple model to include a source which supplies relativistic electrons with a constant energy spectrum is discussed. While such a model can go some way toward matching the observations, it is suggested that the time is ripe for an explicit model of the electron acceleration mechanism. Some of the features such a model may have are presented.Subject headings: acceleration of particles — radio continuum: general — radiation mechanisms: nonthermal — X-rays: bursts

We present new radio images, including the highest resolution image obtained to date, of the known oxygen-rich supernova remnant 1E 0102.2-7219 in the Small Magellanic Cloud. These images, made with the Molonglo Observatory Synthesis Telescope (44″ resolution) and the Australia Telescope Compact Array (3″ resolution), reveal an almost complete shell of radio emission and a spectral index of ∼−0.7. The images also clearly show a previously unidentified compact component. The radio images are compared with previously published optical emission line and X-ray images, and the identification of the diameter of the supernova blast wave is briefly discussed

The suggestion by Bryant et al. (1992) that high flyers, which result from a statistical excess of head-on versus overtaking collisions in Fermi acceleration, can account for acceleration of cosmic rays to about 10 exp 20 eV is discussed critically. It is shown that the statistical approach of Bryant et al., with some corrections, is equivalent to diffusive Fermi acceleration. The high flyers result from diffusion in energy, which complements systematic acceleration by redistributing the particles in energy space, and does not lead to more effective acceleration to higher energies as claimed. 10 refs.

We suggest that synchrotron radiation emitted by electrons undergoing diffusive acceleration at the supernova blast wave is the cause of the reappearance of radio emission from SN 1987A in 1990 July. Making reasonable assumptions concerning adiabatic losses and the magnetic field in the preexplosion stellar wind, we find the light curve and spectrum which would be produced by a constant rate of particle injection occurring in a localized region of the shock front; i.e., in a clump or knot. Observations indicate that two such clumps have been encountered to date

We present calculations of the radio images and light curves from supernovae, based on high-resolution numerical simulations of the hydrodynamics and radiation transfer in a spherically symmetric medium. As a specific example we model the emission from SN1993J. This supernova does not appear to be expanding in a self-similar fashion, and cannot be adequately fitted with the often-used analytic mini-shell model. We present a good fit to the radio evolution at a single frequency. Both free-free absorption and synchrotron self-absorption are needed to fit the light curve at early times, and a circumstellar density profile of $\rho \sim r ^{-1.7}$ provides the best fit to the later data. Comparisons of VLBI images of SN1993J with synthetic model images suggest that internal free-free absorption completely obscures emission at 8.4 GHz passing through the center of the supernova for the first few tens of years after explosion.

The process where an ion in a magnetized plasma simultaneously absorbs two waves whose frequencies sum to the ion gyrofrequency may be referred to as double-cyclotron absorption as a source mechanism for oxygen (O{sup +}) conic distributions in the Earth's magnetosphere is investigated. The appropriate values of the relevant wave and plasma parameters are discussed and the applicability of approximate expressions for the average rate of perpendicular acceleration of O{sup +} ions due to double-cyclotron absorption, derived by Ball (1989), is reviewed. The acceleration rate which results from the approximations of Ball (1989) is shown to be exactly a factor of 5 larger than the corresponding result of Temerin and Roth (1986). A possible explanation for this discrepancy is presented. Rough numerical estimates of the average rate of perpendicular acceleration of O{sup +} ions along auroral field lines are considered, and it is shown that double-cyclotron absorption is indeed capable of producing O{sup +} ions at energies comparable to those observed by spacecraft. {copyright} American Geophysical Union 1989