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PSR B1259-63 is a 48 ms pulsar in a highly eccentric 3.4-year orbit around the young massive star LS 2883. During the periastron passage the system displays transient non-thermal unpulsed emission from radio to very high energy gamma rays. We observed PSR B1259-63 with the Australian Long Baseline Array (LBA) at 2.3 GHz to trace the milliarcsecond (mas) structure of the source at three different epochs during the 2007 periastron passage. We have discovered extended and variable radio structure. The peak of the radio emission is detected at distances between 23 and 46 AU from the system assuming a distance to the system of 2.3 kpc, and the total extent of the emission is 120 AU. This is the first observational evidence that non-accreting pulsars orbiting massive stars can produce variable extended radio emission at AU scales. We also present the new LBA campaign covering five different orbital phases during the 2010–2011 periastron passage. These observations will allow us to separate the pulsed radio component from the transient extended emission.

The supernova remnant SNR G016.8-01.1 is close to the gamma-ray binary system LS 5039, one of the five gamma-ray binaries currently known. LS 5039 appears to have been born in the SNR G016.8-01.1 just ~ 105 yr ago, as indicated by its proper motion. This association would provide direct implications on the nature and properties of the unknown compact object in the binary system. However, there is another source close to SNR G016.8-01.1 that could have been born during the SN explosion: the pulsar PSR J1825-1446, for which the proper motion is unknown. We are measuring the proper motion of both sources by means of VLBI radio observations in order to constrain their origin. Here we present the first results of a VLBA campaign on PSR J1825-1446 to measure its proper motion. We discuss the possible kinematical age of this pulsar, and the possible association of LS 5039 and PSR J1825-1446 with the supernova remnant.

Gamma-ray binaries allow us to study physical processes such as particle acceleration up to TeV energies as well as very high energy gamma-ray emission and absorption with changing geometrical configurations on a periodic basis. These sources produce outflows of radio-emitting particles whose structure can be imaged with very long baseline interferometry (VLBI). We observed the gamma-ray binary LS 5039 with the VLBA at 5 GHz during five consecutive days. We present the observed radio morphological changes, which display a periodic orbital modulation. Multifrequency and multiepoch VLBI observations conducted during the last decade confirm that the morphological periodicity is stable on timescales of years. Using a simple model we show that the observed behavior is compatible with the presence of a young non-accreting pulsar with an outflow behind it.

PSR B1259–63 is a 48 ms pulsar in a highly eccentric 3.4-year orbit around the young massive star LS 2883. During the periastron passage the system displays transient non-thermal unpulsed emission from radio to very high energy gamma rays. At radio wavelengths we can independently study the pulsations and the unpulsed transient emission, which was shown to be extended on AU scales and variable. The pulsed and unpulsed components provide valuable information on the binary system geometry, the physical properties of the pulsar, which is the main source of energy of the broadband emission, and the characteristics of the outflow of accelerated particles. We present a summary of the observational instruments and techniques at radio wavelengths used to observe PSR B1259–63 and we describe the observable and derived properties we can obtain. Finally, we summarize the main radio results of the last years and describe different observational radio campaigns currently ongoing for PSR B1259–63. We aim to provide a general insight on the observational approach to study this gamma-ray binary at radio wavelengths.