  We present multiwavelength observations of the BL Lacertae object Markarian
501 (Mrk 501) in 1997 between April 8 and April 19. Evidence of correlated
variability is seen in very high energy (VHE, E > 350 GeV) gamma-ray
observations taken with the Whipple Observatory gamma-ray telescope, data from
the Oriented Scintillation Spectrometer Experiment of the Compton Gamma-Ray
Observatory, and quicklook results from the All-Sky Monitor of the Rossi X-ray
Timing Explorer while the Energetic Gamma-Ray Experiment Telescope did not
detect Mrk 501. Short term optical correlations are not conclusive but the
U-band flux observed with the 1.2m telescope of the Whipple Observatory was 10%
higher than in March. The average energy output of Mrk 501 appears to peak in
the 2 keV to 100 keV range suggesting an extension of the synchrotron emission
to at least 100 keV, the highest observed in a blazar and ~100 times higher
than that seen in the other TeV-emitting BL Lac object, Mrk 421. The VHE
gamma-ray flux observed during this period is the highest ever detected from
this object. The VHE gamma-ray energy output is somewhat lower than the 2-100
keV range but the variability amplitude is larger. The correlations seen here
do not require relativistic beaming of the emission unless the VHE spectrum
extends to >5 TeV.
