B. van Soelen

Multi-wavelength observations of the binary system PSR B1259−63/LS 2883 around the 2014 periastron passage

We report on the results of the extensive multi-wavelength campaign from optical to GeV γ-rays of the 2014 periastron passage of PSR B1259−63, which is a unique high-mass γ-ray emitting binary system with a young pulsar companion. Observations demonstrate the stable nature of the post-periastron GeV flare and prove the coincidence of the flare with the start of rapid decay of the Hα equivalent width, usually interpreted as a disruption of the Be stellar disc. Intensive X-ray observations reveal changes in the X-ray spectral behaviour happening at the moment of the GeV flare. We demonstrate that these changes can be naturally explained as a result of synchrotron cooling of monoenergetic relativistic electrons injected into the system during the GeV flare.

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.

The effect of the infrared excess from the Be star on inverse Compton gamma-ray production in PSR B1259−63/SS 2883

The binary system PSR B 1259-63 consists of a 48-ms pulsar in a 3.4-yr orbit around a Be star, and unpulsed TeV gamma-ray emission has been detected near previous periastron passages. A likely source of the gamma-rays is the inverse Compton upscattering of target photons from the Be star by the ultrarelativistic electron/positron pulsar wind in the region of the plerion shock front. In this study, the effect of the infrared emission from the Be stars circumstellar disc on inverse Compton gamma-ray production in PSR B1259―63 is investigated by considering an isotropic photon/electron approximation. The modified photon density distribution is determined by using a curve of growth method fitted to previous optical and infrared observations. The inverse Compton scattering rate is calculated using the modified photon distribution and the exact scattering equation. It is shown that including the infrared emission increases the GeV gamma-ray flux by a factor of ≳2.

The orbital solution and spectral classification of the high-mass X-ray binary IGR J01054−7253 in the Small Magellanic Cloud

We present X-ray and optical data on the Be/X-ray binary (BeXRB) pulsar IGR J 01054−7253 = SXP11.5 in the Small Magellanic Cloud (SMC). Rossi X-ray Timing Explorer (RXTE) observations of this source in a large X-ray outburst reveal an 11.483 ± 0.002 s pulse period and show both the accretion-driven spin-up of the neutron star and the motion of the neutron star around the companion through Doppler shifting of the spin period. Model fits to these data suggest an orbital period of 36.3 ± 0.4 d and u P of (4.7±0.3)×10 −10 seconds s −1 . We present an orbital solution for this system, making it one of the best-described BeXRB systems in the SMC. The observed pulse period, spin-up and X-ray luminosity of SXP11.5 in this outburst are found to agree with the predictions of neutron star accretion theory. Timing analysis of the long-term optical light curve reveals a periodicity of 36.70 ± 0.03 d, in agreement with the orbital period found from the model fit to the X-ray data. Using blue-end spectroscopic observations we determine the spectral type of the counterpart to be O9.5-B0 IV–V. This luminosity class is supported by the observed V-band magnitude. Using optical and near-infrared photometry and spectroscopy, we study the circumstellar environment of the counterpart in the months after the X-ray outburst.

Optical spectroscopic classification of a selection of Southern Hemisphere Fermi -LAT unclassified blazars

The Fermi-LAT has detected more than 3000 sources in the GeV

ANISOTROPIC SCATTERING FROM THE CIRCUMSTELLAR DISC IN PSR B1259-63

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Simulating the synchrotron emission of AGN with grid based relativistic hydrodynamics

-ray regime. The majority are extra-galactic and these sources are dominated by blazars. However,

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

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Hunting misaligned radio-loud AGN (MAGN) candidates among the uncertain

per cent of the sources in Fermi 3LAC are listed as blazar candidates of uncertain type (BCU). Increasing the number of classified Fermi-LAT sources is important for improving our understanding of extra-galactic

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