Alida Odendaal

Optical and X-ray properties of CAL 83 – I. Quasi-periodic optical and supersoft variability

We have studied the long-term (∼ years) temporal variability of the prototype supersoft X-ray source (SSS) CAL 83 in the LMC, using data from the MACHOand OGLE projects. The CAL 83 light curve exhibits dramatic brightness changes of ∼ 1 mag on timescales of ∼ 450 days, and spends typically ∼ 200 days in the optical low state. Combined with archival XMM-NewtonX-ray observations these represent the most extensive X-ra y/optical study to date of this system, and reveal in much greater detail that th e X-ray light curve is anticorrelated with the optical behaviour. This is remarkably s imilar to the behaviour of the “transient” SSS, RX J0513.9-6951, where the SSS outbursts recur on a timescale of ∼ 168 days, and also anti-correlate with the optical flux. We performed s imple blackbody fits to both high and low state X-ray spectra, and find that the blackbody tempe rature and luminosity decrease when the optical counterpart brightens. We interpret these long-term variations in terms of the limit-cycle model of Hachisu & Kato (2003a), which provides further support for these systems containing massive (∼ 1.3 M⊙) white dwarfs. In addition, we have refined their orbital periods in the MACHO and OGLE-III light curves to values of 1.047529(1) days and 0.762956(5) days for CAL 83 and RX J0513.9-6951, respectively.

Anisotropic inverse Compton scattering of photons from the circumstellar disc in PSR B1259–63

The gamma-ray binary system PSR B1259-63 consists of a 48 ms pulsar orbiting a Be star. The system is particularly interesting because it is the only gamma-ray binary system where the nature of the compact object is known. The non-thermal radiation from the system is powered by the spin-down luminosity of the pulsar and the unpulsed radiation originates from the stand-off shock front which forms between the pulsar and stellar wind. The Be star/optical companion in the system produces an excess infrared flux from the associated circumstellar disc. This infrared excess provides an additional photon source for inverse Compton scattering. We discuss the effects of the IR excess near periastron, for anisotropic inverse Compton scattering and associated gamma-ray production. We determine the infrared excess from the circumstellar disc using a modified version of a curve of growth method, which takes into account the changing optical depth through the circumstellar disc during the orbit. The model is constrained using archive data and additional mid-IR observations obtained with the VLT during January 2011. The inverse Compton scattering rate was calculated for three orientations of the circumstellar disc. The predicted gamma-ray light curves show that the disc contribution is a maximum around periastron and not around the disc crossing epoch. This is a result of the disc being brightest near the stellar surface. Additional spectroscopic and near-infrared observations were obtained of the system and these are discussed in relation to the possibility of shock heating during the disc crossing epoch.

Supersoft X-Ray Source CAL 83: A Possible AE Aqr-like System

CAL83 is a close binary supersoft X-ray source in the Large Magellanic Cloud. A ~67 s periodicity detected in supersoft X-rays is most probably associated with the spin period of a highly spun-up white dwarf (WD). The variability in the period is ascribed to the obscuration of the WD by the hydrogen burning envelope surrounding it, rotating with a period that is close to, but not quite synchronized with, the WD rotation period. Optical spectra obtained with SALT exhibit accretion disc emission lines with broad wing structures and P Cyg profiles, indicating mass outflows. Timing analysis of photometrical observations performed at the South African Astronomical Observatory (SAAO) revealed variable signals at ≤1 mHz which are thought to be associated with quasi-periodic oscillations from an accretion disc. The short spin period inferred for CAL83 can be the result of spin-up by accretion disc torques during a long mass transfer history, placing this source on a similar evolutionary track as the cataclysmic variable AE Aqr.

Transient emission of selected CRTS Cataclysmic Variables

We present optical photometric and spectroscopic observations of three SU UMa-type dwarf novae, i.e. AR Pic, QW Ser and V521 Peg, conducted in 2016 and 2017. These sources were selected from the Catalina Real-Time Transient Survey and observed during quiescence, outburst (AR Pic and QW Ser) and superoutburst (V521 Peg). For AR Pic, strong flickering in the light curves and an asymmetric double-peaked H

Cataclysmic variables: New frontiers in multi-wavelength research

\beta

An adapted LIMA model for the 67-s periodicity in supersoft X-ray source CAL 83

emission line in the spectra, confirmed the presence of a very active hot spot. During outburst, detected on 18 February 2017, it exhibited a

CAL83 | The Prototypical Close Binary Supersoft X-ray Source in the LMC:A Short Review

\sim 3.3

Modelling the Multifrequency SED of AGN Candidates among the Unidentied EGRET and Fermi Gamma-Ray Sources

magnitude brightening. The projected velocity of the inner edge of the accretion disc is

Optical and X-ray properties of CAL 83 – II. An X-ray pulsation at ∼67 s

\sim 2000 \rm~km~s^{-1}

Optical spectroscopy of PSR B1259-63/LS 2883 during the 2014 periastron passage with the Southern African Large Telescope

. An outburst of QW Ser was detected on 8 August 2016. Absorption lines, characteristic of an optically thick disc during outburst, were detected and an outflow velocity of