The high-energy gamma-ray light curve of PSR B1259 -63

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

Shock geometry and inverse Compton emission from the wind of a binary pulsar

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.Comment: To be published in the Publications of the Astrophysical Society of Australia, Volume 18 number 1, (10 pages, 6 postscript figures

A MODEL FOR THE RADIO EMISSION FROM SNR 1987A

The observations of radio emission from SNR~1987A can be accounted for on the basis of diffusive shock acceleration of electrons by the supernova blast wave. However, with this interpretation the observed spectral index implies that the compression ratio of the gas subshock is roughly $2.7$ rather than the value of $4$ expected of a strong shock front. We propose that in SNR~1987A, ions also undergo diffusive acceleration at the shock, a process that is likely to be rapid. Unlike the electron population, the accelerated ions can have an important effect on the gas dynamics. We calculate this coupled gas and energetic particle dynamics on the basis of the two-fluid model, in which the accelerated ions provide an additional component to the total pressure acting on the fluid. By accelerating and possibly heating the upstream plasma, the initially strong shock is modified and a weaker subshock with an upstream precursor results. The electrons behave as test particles. They are accelerated at the evolving subshock, escape downstream, and emit synchrotron radiation in the swept up magnetic field. Two models are considered for the surroundings of the progenitor: that of a freely expanding wind of number density $n\propto r^{-2}$, and that of a wind confined by a shell of denser material, creating a stagnation zone of roughly constant density beyond the standing shock which terminates the free wind. We model the observed radio light curves and the relatively steep spectrum of SNR~1987A using similar values for the ion acceleration parameters to those used in models of cosmic ray acceleration in older SNRs which can also contain high Mach number shocks, and find a good fit for the case in which the termination shock is located at about $2\times 10^{15}\,$m from the progenitor.Comment: 18 pages of uuencoded, compressed postcript. Accepted for ApJ

Gamma-rays from PSR B1259 -63

The high-energy gamma-ray emission discovered using the H.E.S.S. telescopes from the binary system PSR B1259 -63, is modelled using an extension of the approach that successfully predicted it. We find that the simultaneous INTEGRAL and H.E.S.S. data 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. Additional, simultaneous, X-ray and TeV data sets are needed to lift this degeneracy.Comment: 4 pages, to appear in: Proceedings of the 29th International Cosmic Ray Conference, Pune (2005

Is operationalising natural capital risk assessment practicable?

Financial institutions are indirectly exposed to risks associated with the impacts and dependencies on natural capital and ecosystem services of the companies that they invest in, lend to, and insure. This is particularly true for banks lending to agriculture: a sector with both significant impacts and critical dependencies on natural capital. Bank lending is a vital source of new finance for the sector, which is essential to achieve sustainable intensification targets. Yet current credit decision-making practice is still based on conventional financial and management indicators, lacking any systematic assessment of natural capital risks, especially those associated with dependencies. Operationalising natural capital risk assessment requires practicable indicators and data to evaluate the most material natural capital risks for a given sub-sector and geography, but it is unclear to what extent these are available. We assess the practicability of natural capital dependency risk indicators and data sources for a critical case study of Australian sheep production. We find that at least moderately practicable indicators and data sources are available to assess the 11 major dependency risks that are material for this industry. Challenges remain in determining risk thresholds for most indicators, and quantifying risk impacts on profitability. © 2021 Elsevier B.V

Probing Pulsar Winds Using Inverse Compton Scattering

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.Comment: To be published in Astroparticle Physics. 27 pages, 5 figure

Radio Observations of PSR B1259-63 through the 2004 periastron passage

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.Comment: Accepted by MNRAS. 7 pages, 5 figure

Supernova Remnants, Pulsars and the Interstellar Medium - Summary of a Workshop Held at U Sydney, March 1999

We summarise the proceedings of the SRCfTA workshop on ``Supernova Remnants, Pulsars and the Interstellar Medium'' that was held at the University of Sydney on Mar 18 and 19, 1999.Comment: 13 pages, Latex. To be published in the Publications of the Astronomical Society of Australia, 2000, Vol 17, No

Modular bismacycles for the selective C–H arylation of phenols and naphthols

Given the important role played by 2-hydroxybiaryls in organic, medicinal and materials chemistry, concise methods for the synthesis of this common motif are extremely valuable. In seeking to extend the synthetic chemists’ lexicon in this regard, we have developed an expedient and general strategy for the ortho-arylation of phenols and naphthols using readily-available boronic acids. Our methodology relies on in situ generation of a uniquely reactive Bi(V) arylating agent from a bench stable Bi(III) precursor via telescoped B-to-Bi transmetallation and oxidation. By exploiting reactivity 2 that is orthogonal to conventional metal-catalyzed manifolds, diverse aryl and heteroaryl partners can be rapidly coupled to phenols and naphthols under mild conditions. Following arylation, highyielding recovery of the Bi(III) precursor allows for its efficient re-use in subsequent reactions. Mechanistic interrogation of each key step of the methodology informs its practical application and provides fundamental insight into the under-exploited reactivity of organobismuth compounds