Timing Calibration of the NuSTAR X-Ray Telescope
Matteo Bachetti, Craig B. Markwardt, Brian W. Grefenstette, Eric V. Gotthelf, Lucien Kuiper, Didier Barret, W. Rick Cook, Andrew Davis, Felix Fürst, Karl Forster, Fiona A. Harrison, Kristin K. Madsen, Hiromasa Miyasaka, Bryce Roberts, John A. Tomsick, Dominic J. Walton
Abstract
Abstract The Nuclear Spectroscopic Telescope Array (NuSTAR) mission is the first focusing X-ray telescope in the hard X-ray (3–79 keV) band. Among the phenomena that can be studied in this energy band, some require high time resolution and stability: rotation-powered and accreting millisecond pulsars, fast variability from black holes and neutron stars, X-ray bursts, and more. Moreover, a good alignment of the timestamps of X-ray photons to UTC is key for multi-instrument studies of fast astrophysical processes. In this paper, we describe the timing calibration of the NuSTAR mission. In particular, we present a method to correct the temperature-dependent frequency response of the on-board temperature-compensated crystal oscillator. Together with measurements of the spacecraft clock offsets obtained during downlinks passes, this allows a precise characterization of the behavior of the oscillator. The calibrated NuSTAR event timestamps for a typical observation are shown to be accurate to a precision of ∼65 μ s.