Latest view of CTA 1 with VERITAS
Alisha Chromey
TL;DR
This study provides a deeper VERITAS examination of CTA 1, a middle-aged composite SNR+PWN, to probe leptonic transport and electron escape in a spatially resolved VHE source. By combining observations from 2010–2011 and 2023–2024 for a total exposure of $118.6\ \mathrm{h}$ and applying VEGAS with the Image Template Method, the authors derive energy-dependent morphology and a broadband VHE spectrum. The emitted VHE radiation appears extended and consistent with leptonic PWN models, characterized by a power-law with $\Gamma \approx 2.2$ and a flux above $1\ \mathrm{TeV}$; this corroborates the PWN origin and tightens constraints on electron propagation within PWNe. The results lay groundwork for detailed broadband modeling and comparative studies of PWN evolution across different evolutionary stages, with broad implications for cosmic-ray electron transport in SNR environments.
Abstract
CTA 1 is a shell-type supernova remnant (SNR) with a central pulsar wind nebula (PWN), visible at very-high-energy (VHE) from 50 GeV to 100 TeV from a moderately extended emission region. While general consensus concludes the VHE emission originates from relativistic leptons accelerated by the PWN and undergoing inverse Compton scattering, questions remain about electron escape and propagation, as well as the evolutionary stage of this particular PWN. CTA 1 is on the cusp of middle age (~13 kyr) and spatially resolvable at energies visible to imaging atmospheric Cherenkov telescopes (IACTs), such as the Very Energetic Radiation Imaging Telescope Array System (VERITAS) (PSF < 0.1 deg). Therefore, this remnant is an excellent candidate to study lepton propagation and escape between different PWN evolutionary stages. Since the initial VERITAS publication on CTA 1 in 2013, VERITAS has performed new observations, adding to a total exposure of about 120 hours. We have analyzed the entire VERITAS CTA 1 dataset to date and report results.