The optimization of the MAGIC telescope for pulsar observations

Abstract

MAGIC, a new 17-meter class optical reflector at La Palma, Canary Islands, is the first Imaging Atmospheric Cerenkov Telescope (IACT) able to detect pulsed γ-rays from neutron stars. Simulations to predict detection times and expected γ-ray fluxes from millisecond and canonical pulsars are performed, using the standard operational mode of MAGIC. Spectral cutoffs due to the pair production of energetic γ-rays in strong magnetic fields are expected: The low surface magnetic field strengths of millisecond pulsars (relative to that of canonical pulsars), result in much larger spectral cutoffs for millisecond pulsars (i.e. above 100 GeV), whereas for canonical pulsars, this cutoff is expected to be ≤ 30 GeV, with the upper limit corresponding to the the standard energy threshold of about 30 GeV for MAGIC. The relatively low spindown power associated with millisecond pulsars result in a low photon flux, which is however offset by their higher spectral cutoffs (around 100 GeV), where the MAGIC collection area is already relatively large. The result of this is that we still expect millisecond pulsar detection times of a few hours with MAGIC. Since most canonical pulsars are expected to show a cutoff at or well below 30 GeV, a new technique is proposed to detect γ-rays within the G to 10 GeV range, using the central ∼ 0.4 degree region of the camera. Effective areas from 50 to G500 m² are found, without interfering with the standard operational mode. When observing pulsars, timing parameter are required to perform a periodicity search. If contemporary radio parameters are not available, we have to extrapolate archival radio parameters to the observation time in question. Such an extrapolation must then be accurate enough to avoid significant pulse smearing due to the intrinsic pulsar timing noise and glitches. But sometimes, the optical emission can be used to derive timing parameters. The used of a IACT camera central pixel to detect the optical pulsed emission is discussed. This method was tested with the HEGRA CT1 telescope and the application of this technique to MAGIC is also discussed