Study of high energy cosmic ray acceleration in Tycho SNR with VERITAS

Abstract

Supernova Remnants (SNRs) are broadly accepted as the main accelerators of Galactic cosmic rays (GCRs) with energies up to the knee region. Recent measurements of pion bumps in IC 443 and W 44 by Fermi-LAT show indirect evidence of the acceleration of hadronic particles in SNRs. But, whether SNRs are the powerhouses for GCR acceleration all the way up to the knee region still remains an unsolved question. Tycho is a promising target for this study because it has been widely studied in multi-wavelength observations from IR to TeV and it is a young type Ia SNR located in a relatively clean environment. Though recently developed models generally agree on the likely hadronic origin of the gamma-ray emission from Tycho, the details of the models vary considerably because the current data in the GeV-TeV range are weakly constraining. Since the initial detection, VERITAS has increased its data size by more than 40%. We also recently upgraded the telescope cameras and the analysis packages, which will allow us to extend the measurements toward both lower and higher energies. In this talk, I present updates on the VHE gamma-ray measurements of Tycho with VERITAS, focusing on the interpretation of the additional data in the context of hadronic GCR acceleration models.