Rapid photometry of supernova 1987A: a 2.14 ms pulsar?

We have monitored Supernova 1987A in optical/near-infrared bands using vari ous high-speed photometers from a few weeks following its birth until early 1996 in order to search for a pulsar remnant. While we have found no clear evidence of any pulsar of constant intensity and stable timing, we have fo und emission with a complex period modulation near the frequency of 467.5 H z - a 2.14 ms pulsar candidate. We first detected this signal in data taken on the remnant at the Las Campanas Observatory (LCO) 2.5-m Dupont telescop e during 14-16 Feb. 1992 UT. We detected further signals near the 2.14 ms p eriod on numerous occasions over the next four years in data taken with a v ariety of telescopes, data systems and detectors, at a number of ground- an d space-based observatories. In particular, an effort during mid-1993 to mo nitor this signal with the U. of Tasmania 1-m telescope, when SN1987A was i naccessible to nearly all other observing sites due to high airmass, clearl y detected the 2.14 ms signal in the first three nights' observations. The sequence of detections of this signal from Feb. '92 through August '93, pri or to its apparent subsequent fading, is highly improbable (<10(-10) for an y noise source). In addition, the frequency of the signals followed a consi stent and predictable spin-down (similar to 2-3 x 10(-10) Hz/s) over the se veral year timespan ('92-'96). We also find evidence in data, again taken b y more than one telescope and recording system, for modulation of the 2.14 ms period with a similar to 1,000 s period which complicates its detection. The 1,000 s modulation was clearly detected in the first two observations with the U. Tas. 1-m during mid-1993. The characteristics of the 2.14 ms si gnature and its similar to 1,000 s modulation are consistent with precessio n and spindown via gravitational radiation of a neutron star with an effect ive non-axisymmetric oblateness of similar to 10(-6). The implied luminosit y of the gravitational radiation exceeds the spindown luminosity of the Cra b Nebula pulsar by an order of magnitude. Due to the nature of the 2.14 ms signature and its modulation, and the analysis techniques necessary for det ection, it is difficult to determine the overall probability that all aspec ts of the signal are real, though it has remained consistent with an astrop hysical origin throughout the several year timespan of our study. (C) 2000 Elsevier Science B.V. All rights reserved.