Study of the High Energy Gamma-ray Emission from the Crab Pulsar with the MAGIC telescope and Fermi-LAT

TL;DR

This paper investigates the high energy gamma-ray spectrum of the Crab pulsar using MAGIC telescope and Fermi-LAT data to distinguish between inner and outer magnetosphere emission models based on the spectral cut-off shape.

Contribution

It provides the first detailed analysis of the Crab pulsar's spectrum around the cut-off energy using ground-based and satellite data, testing pulsar emission models.

Findings

Measured the gamma-ray spectrum around the cut-off energy.

Compared ground-based MAGIC data with Fermi-LAT results.

Supported the outer magnetosphere emission scenario.

Abstract

My thesis deals with a fundamental question of high energy gamma-ray astronomy. Namely, I studied the cut-off shape of the Crab pulsar spectrum to distinguish between the leading scenarios for the pulsar models. Pulsars are celestial objects, which emit periodic pulsed electromagnetic radiation (pulsation) from radio to high energy gamma-rays. Two major scenarios evolved in past 40 years to explain the pulsation mechanism: the inner magnetosphere scenario and the outer magnetosphere scenario. Both scenarios predict a high energy cut-off in the gamma-ray energy spectrum, but with different cut-off sharpness. An exponential cut-off is expected for the outer magnetosphere scenario while a super-exponential cut-off is predicted for the inner magnetosphere scenario. Therefore, one of the best ways to confirm or rule out these scenarios is to measure the energy spectrum of a pulsar at around the cut-off energy, i.e., at energies between a few GeV and a few tens of GeV. All past attempts (>10) to measure pulsars with ground-based instruments have failed while satellite-borne detectors had a too small area to study detailed spectra in the GeV domain. In this thesis, the gamma-ray emission at around the cut-off energy from the Crab pulsar is studied with the MAGIC telescope. The public data of the satellite-borne gamma-ray detector, Fermi-LAT, are also analyzed in order to discuss the MAGIC observation results in comparison with the adjacent energy band.