Evidence of Primordial Non-Gaussianity (<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mi>f</mml:mi><mml:mi>NL</mml:mi></mml:msub></mml:math>) in the Wilkinson Microwave Anisotropy Probe 3-Year Data at<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mn>2.8</mml:mn><mml:mi>σ</mml:mi></mml:math>

We present evidence for primordial non-Gaussianity of the local type (fNL) in the temperature anisotropy of the cosmic microwave background. Analyzing the bispectrum of the Wilkinson Microwave Anisotropy Probe 3-year data up to lmax=750 we find 27<fNL<147 (95% C.L.). This amounts to a rejection of fNL=0 at 2.8sigma, disfavoring canonical single-field slow-roll inflation. The signal is robust to variations in lmax, frequency and masks. No known foreground, instrument systematic, or secondary anisotropy explains it. We explore the impact of several analysis choices on the quoted significance and find 2.5sigma to be conservative.