Among the many X-ray binaries that are known in the sky, only a handful emit up to gamma-ray energies. 2012 marks the year in which one such system was discovered first in GeV gamma rays, using a mathematical algorithm applied to all sources detected by the Large Area Telescope onboard the satellite Fermi. This discovery was featured in Science, as the first of a possible population to follow .
What is the physical nature of these gamma-ray binaries? Growing consensus mount as to that the compact object in these gamma-ray binaries is pulsar. One of the key pieces of the puzzle in this sense was the discovery of two very short X-ray flares lasting less than 1 second, coming from the system LS I +61 303, and with luminosities orders of magnitude larger than its usual emission at all wavelengths. Only magnetars behave this way. If some gamma-ray binaries are magnetar-composed, they would likely flip-flop between states along the orbital motion, traversing a variety of conditions that may explain the varied phenomenology at all frequencies .
Another 2012 discovery in this topic has been that the X-ray emission of the aforementioned system is modulated at long scales (>4 years), similar to -but dephased from- its radio emission. Hints for a TeV modulation in similar timescales were also already apparent. These two facts can provide clues as to finally disentangling the nature of these objects .