Orbit Mode observations of Crab and Mrk 421

TL;DR

This paper introduces and analyzes the orbit mode for IACT gamma-ray observations, where the target continuously rotates around the camera center, potentially improving background estimation and reducing dead-time.

Contribution

The paper presents the implementation and analysis of the new orbit observation mode for VERITAS, demonstrating its potential advantages over traditional wobble mode.

Findings

Orbit mode may improve cosmic ray background estimation.

Orbit mode reduces detector dead-time between runs.

Successful observations of Crab Nebula and Mrk 421 using orbit mode.

Abstract

The canonical observation mode for IACT gamma-ray observations employs four discrete pointings in the cardinal directions (the "wobble" mode). For the VERITAS Observatory, the target source is offset by 0.5-0.7 degrees from the camera center, and the observation lasts 20 minutes. During January/February of 2011, the VERITAS Observatory tested a new "orbit" observation mode, where the target source is continuously rotated around the camera center at a fixed radial offset and constant angular velocity. This mode of observation may help better estimate the cosmic ray background across the field of view, and will also reduce detector dead-time between the discrete 20 minute runs. In winter 2011, orbit mode observations where taken on the Crab Nebula and Mrk 421. In this paper we present the analysis of these observations, and describe the potential applications of orbit mode observations for diffuse (extended) sources as well as GRBs.