Livermore Optical Transient Imaging System

The Livermore Optical Transient Imaging System (LOTIS) was a fully automated telescope built to swing quickly toward gamma-ray bursts (GRBs) and capture their optical light at the same time. Because GRBs can appear anywhere in the sky, are often hard to pinpoint, and vanish rapidly, the system needed to reposition in under ten seconds and cover a field of view larger than 15 degrees. To meet this speed requirement, LOTIS was linked via an Internet socket to the Gamma-ray Burst Coordinates Network, which processes satellite data—from missions like HETE-2 and the Swift Gamma-Ray Burst Mission—and relays burst coordinates in real time. Its optics consisted of four commercial telephoto lenses, each with an 11 cm aperture, paired with custom 2048 × 2048 CCD cameras, giving it a 17.6 × 17.6 degree view. Routine operations began in October 1996, with a limiting magnitude of about Mv 11.5. An upgrade in March 1998 added cooled cameras, pushing the sensitivity to roughly Mv 14. LOTIS remained active until at least 2001, but it never directly detected a GRB optical counterpart, though it did establish upper limits on their brightness. By 2001, the four cameras had been aligned with each other, and two had filters installed. Between GRB alerts, LOTIS systematically scanned the entire visible sky each night for new optical transients. It was later succeeded by Super-LOTIS, a robotic telescope with a larger mirror but a narrower field of view. Super-LOTIS, the second version of the system, was installed at the Steward Observatory on Kitt Peak. Like its predecessor, it was automated and designed to race to GRB locations for simultaneous optical measurements. The original LOTIS’s wide field of view limited it to studying only the brightest GRB afterglows, but later satellites—including HETE-2 and the BATSE detector on the Compton Gamma Ray Observatory—provided much more accurate coordinates. This allowed Super-LOTIS to use a Boller and Chivens 0.6 meter telescope, which had a much smaller field of view (initially 51 arcminutes by 51 arcminutes) but far deeper imaging. It operated in this mode from 2000 to 2003. After the Swift mission launched in 2004 and delivered even tighter error boxes, Super-LOTIS’s optics were modified again, giving it a 17 by 17 arcminute field at the secondary focus and a simultaneous visible/near-infrared camera.