Carl Akerlof

The First Data from the MACHO Experiment.

MAssive Compact Halo Objects such as brown dwarfs, Jupiters, and black holes are prime candidates to comprise the dark halo of our galaxy. Paczynski noted that objects (dubbed MACHOS) with masses in the range 10{sup {minus}6} M{circle_dot} < M {approx_lt} 100M{circle_dot} can be detected via gravitational microlensing of stars in the Magellanic Clouds with the caveat that only about one in 10{sup 6} stars will be lensed at any given time. Our group has recently begun a search for microlensing using a refurbished 1.27 meter telescope at the Mount Stromlo Observatory in Australia. Since the summer of 1992, we have been imaging up to 10{sup 7} stars a night in the Large Magellanic Cloud using our large format two-color 3.4 {times} 10{sup 7} pixel CCD camera. Here I report on our first results based on an analysis of {approximately}10{sup 6} of these stars. Although this is not enough data to make definitive statements about the nature of the dark matter, we are able to conclude that the rate of variable star background events is not larger than the expected MACHO signal.

The ROTSE detection of early optical light from GRB 990123

An overview is given of the Robotic Optical Transient Search Experiment, a ground-based observational astronomy project intended to detect visible radiation from gamma-ray bursts. The major result of the project was the detection of an early bright optical transient from a GRB. (AIP)

Gamma ray burst optical counterpart search experiment (GROCSE)

GROCSE (Gamma-Ray Optical Counterpart Search Experiments) is a system of automated telescopes that search for simultaneous optical activity associated with gamma ray bursts in response to real-time burst notifications provided by the BATSE/BACODINE network. The first generation system, GROCSE 1, is sensitive down to Mv {approximately} 8.5 and requires an average of 12 seconds to obtain the first images of the gamma ray burst error box defined by the BACODINE trigger. The collaboration is now constructing a second generation system which has a 4 second slewing time and can reach Mv {approximately} 14 with a 5 second exposure. GROCSE 2 consists of 4 cameras on a single mount. Each camera views the night sky through a commercial Canon lens (f/1.8, focal length 200 mm) and utilizes a 2K x 2K Loral CCD. Light weight and low noise custom readout electronics were designed and fabricated for these CCDs. The total field of view of the 4 cameras is 17.6 x 17.6 {degree}. GROCSE II will be operated by the end of 1995. In this paper, the authors present an overview of the GROCSE system and the results of measurements with a GROCSE 2 prototype unit.