The 1997 outburst of AO 0235+164: Evidence for a microlensing event?

We present: multiwavelength observations of AO 0235+164 made during a 5 mag outburst in 1997. Detection of the outburst at the observatory of the Sout h Eastern Association for Research in Astronomy prompted a concerted effort by several observatories to monitor the source in the R band. We present V -, R-, and I-band photometry, as well as contemporaneous 850 mu m and X-ray measurements. We also use radio measurements from the University of Michig an's World Wide Web site in our analysis. We find that the source varies ne arly simultaneously over 6 decades in frequency during this outburst and ex amine the possibility that the outburst was a result of a microlensing even t. The duration of the outburst was on the order of 800 days, and the maxim um luminosity was approximately 9.86 x 10(47) ergs s(-1) (assuming no relat ivistic beaming). We also analyze the long-term optical light curve and fin d that, although there is still no evidence for periodicity, the variations are interesting: the timescales between pairs of outbursts are remarkably similar. We suggest that the multifrequency behavior of the 1997 outburst i s consistent with microlensing scenarios, while observations of previous ou tbursts suggest they were not consistent with gravitational microlensing.