The WINTER Observatory: A One-degree InGaAs Survey Instrument to Study the Transient Infrared Sky

Abstract

The Wide-field Infrared Transient Explorer (WINTER) is a near-infrared time-domain survey instrument operating on a dedicated robotic 1 m telescope at Palomar Observatory. Since June of 2023, WINTER has surveyed the sky nightly to a median depth of JAB = 18.5 mag. The survey balances a variety of science programs, including searching for kilonovae from gravitational-wave alerts, blind surveys to study galactic and extragalactic transients and variables, and building up reference images of the near-infrared sky. WINTER also demonstrates large-format Indium Gallium Arsenide (InGaAs) sensors as a new technology for wide-field near-infrared astronomy without cryogenic optics or detectors. A novel tiled fly’s-eye optical design allows WINTER to couple six non-buttable InGaAs sensors into a wide-field near-infrared camera with minimal chip gaps. The instrument covers a >1 deg2 field of view with 1″ sampling. A filter exchanger enables observations in Y-, J-, or shortened-H-band filters (0.9–1.7 μm). This paper presents the design and performance of the WINTER observatory, including the novel optical system, InGaAs detector performance, robotic survey operations, and highlights from the first years of on-sky science.