Anisotropy in the Microwave Sky at 90 GHz: Results From Python III

The third year of observations with the Python microwave background experiment densely sample a ${5.5}^o\times {22}^o$ region of sky that includes the fields measured during the first two years of observations with this instrument. The sky is sampled in two multipole bands centered at $l \approx 92$and$l \approx 177$. These two data sets are analyzed to place limits on fluctuations in the microwave sky at 90 GHz. Interpreting the observed fluctuations as anisotropy in the cosmic microwave background we find flat band power estimates of $\delta T_l\equiv \sqrt{l(l+1)C_l/2\pi }% =54_{-12}^{+14}\mu K$at$l=92_{-24}^{+37}$and$\delta T_l=58_{-13}^{+15}\mu K$at$l=177_{-58}^{+66}$. Combining the entire three year set of Python observations, we find that the angular power spectrum of fluctuations has a spectral index $m=.02_{-.16}^{+.18}$ and an amplitude $% \delta T_{l_e}=53_{-11}^{+13}\mu K$at$l_e=145_{-74}^{+59}$forthefunctionalform$\delta T_l=\delta T_{l_e}(l/l_e)^m$. The stated uncertainties in the amplitudes and spectral index represent 1$\sigma$ confidence intervals in the likelihood added in quadrature with a 20% calibration uncertainty and an estimate of the effects introduced due to imperfect overlap of the beams on the sky. The limits of $l$ are determined from the full width at half maximum of the window functions.