  For the purpose of investigating the differential rotation of the solar
corona, we analyzed ultraviolet (UV) spectral line observations acquired on
both the east and west limbs at 1.7 $R_{\odot}$ by SOHO/UVCS during the solar
minimum preceding solar cycle 23. To obtain a reliable and statistically robust
picture of the rotational profile, we used a set of simultaneous 400-day long
spectral line intensities of five different spectral lines: O VI 1032 A, O VI
1037 A, Si XII 499 A, Si XII 521 A, and H I 1216 A, which are routinely
observed by UVCS. The data were analyzed by means of two different techniques:
the generalized Lomb-Scargle periodogram (GLS) and a multivariate data-adaptive
technique called multichannel singular spectrum analysis (MSSA). Among many
other positive outcomes, this latter method is unique in its ability to
recognize common oscillatory modes between the five time series observed at
both limbs. The latitudinal rotation profile obtained in this work emphasizes
that the low-latitude region of the UV corona (about $\pm 20^{\circ}$ from the
solar equator) exhibits differential rotation, while the higher-latitude
structures do rotate quasi-rigidly. The differential rotation rate of the solar
corona as evinced at low-latitudes is consistent with the rotational profile of
the near-surface convective zone of the Sun, suggesting that the rotation of
the corona at 1.7 $R_{\odot}$ is linked to intermediate-scale magnetic bipole
structures anchored near 0.99 $R_{\odot}$. The quasi-rigid rotation rate found
at mid and high latitudes is instead attributed to the influence of large-scale
coronal structures linked to the rigidly rotating coronal holes. We further
suggest that the methodology presented in this paper could represent a
milestone for future investigations on differential rotation rates when dealing
with simultaneous multiwavelength data.
