Anisotropy in the cosmic microwave background at degree angular scales: Python V results

Observations of the microwave sky using the Python telescope in its fifth s eason of operation at the Amundsen-Scott South Pole Station in Antarctica a re presented. The system consists of a 0.75 m off-axis telescope instrument ed with a HEMT amplifier-based radiometer having continuum sensitivity from 37 to 45 GHz in two frequency bands. With a 0.degrees 91 x 1.degrees 02 be am, the instrument fully sampled 598 deg(2) of sky, including fields measur ed during the previous four seasons of Python observations. Interpreting th e observed fluctuations as anisotropy in the cosmic microwave background, w e place constraints on the angular power spectrum of fluctuations in eight multipole bands up to l similar to 260. The observed spectrum is consistent with both the COBE experiment and previous Python results. There is no sig nificant contamination from known foregrounds. The results show a discernib le rise in the angular power spectrum from large (l similar to 40) to small (l similar to 200) angular scales. The shape of the observed power spectru m is not a simple linear rise, but has a sharply increasing slope starting at l similar to 150.