Rapid photometry of supernova 1987A: a 2.14 ms pulsar?
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Middleditch, J and Kristian, JA and Kunkel, WE and Hill, KM and Watson, RD and Lucinio, R and Imamura, JN and Steiman-Cameron, TY and Shearer, A and Butler, R and Redfern, M and Danks, AC, Rapid photometry of supernova 1987A: a 2.14 ms pulsar?, New Astronomy, 5, (5) pp. 243-283. ISSN 1384-1092 (2000) [Refereed Article]
We have monitored Supernova 1987A in optical/near-infrared bands using various 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 found emission with a complex period modulation near the frequency of 467.5 Hz - 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 telescope during 14-16 Feb. 1992 UT. We detected further signals near the 2.14 ms period on numerous occasions over the next four years in data taken with a variety of telescopes, data systems and detectors, at a number of ground- and space-based observatories. In particular, an effort during mid-1993 to monitor this signal with the U. of Tasmania 1-m telescope, when SN1987A was inaccessible to nearly all other observing sites due to high airmass, clearly 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, prior to its apparent subsequent fading, is highly improbable ( < 10 -10 for any noise source). In addition, the frequency of the signals followed a consistent and predictable spin-down (~2-3×10 -10 Hz/s) over the several year timespan ('92-'96). We also find evidence in data, again taken by more than one telescope and recording system, for modulation of the 2.14 ms period with a ~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 signature and its ~1,000 s modulation are consistent with precession and spindown via gravitational radiation of a neutron star with an effective non-axisymmetric oblateness of ~10 -6 . The implied luminosity of the gravitational radiation exceeds the spindown luminosity of the Crab 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 detection, it is difficult to determine the overall probability that all aspects of the signal are real, though it has remained consistent with an astrophysical origin throughout the several year timespan of our study. © Elsevier Science B.V.
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