Three first-timers in Galactic high-energy astrophysics
As time goes by, continuing revolutions of the largest gamma-ray astronomy satellite ever flown, Fermi, allows for deeper and deeper studies of the sky. Joined by mature ground-based observational facilities at even higher gamma-ray frequencies, like MAGIC at TeV energies (TeV = 1e12 eV), as well as by a plethora of concurrent observations at lower energies (from radio to optical to X-rays), significant discoveries are driving theoretical research.
This year has seen the announcement of the most energetic light ever observed from a pulsar, for the first time with energies of more than trillion electron volts, about a thousand times larger than previously observed, arriving at the detector concurrently with the pulsar period. These photons are thus coming from the close proximity of the rotating neutron star, but exactly how and where they are generated is unknown. No theory to date can cope with such measurements.
Another first-timer this year has been the detection, at similarly such high energies, of a years-long recurrent variability. Every 4.2 years, the TeV emission from a gamma-ray binary has been seen to oscillate, in an effect theoretically predicted a few years before (Torres, D. F., et al. 2012, ApJ, 744, 106). Much is yet to learn from the recurrence of such oscillation and how can, perhaps, be driven by oscillations in the surrounding circumstellar disk of the companion.
Finally, the spatial connection of the archetypical, accreting millisecond pulsar with a gamma-ray source has been also noted for the first time. If this connections proves real, for instance via a detection of gamma-ray pulsations, it would imply rotationally-powered activity in quiescence mode, showing evidence of a transition to a rotation-powered radio pulsar state in X-ray quiescence, whilst it is observed as an accreting pulsar when it has a disk.