THE radio-2mm spectral index of the Crab Nebula measured with GISMO

Abstract

We present results of 2mm observations of the Crab Nebula, obtained using the Goddard-IRAM Superconducting 2 Millimeter Observer (GISMO) bolometer camera on the IRAM 30 m telescope. Additional 3.3mm observations with the MUSTANG bolometer array on the Green Bank Telescope are also presented. The integrated 2mm flux density of the Crab Nebula provides no evidence for the emergence of a second synchrotron component that has been proposed. It is consistent with the radio power-law spectrum, extrapolated up to a break frequency of log (νb[GHz]) = 2.84 0.29 or νb = ∼ 695 +651- 336GHz. The Crab Nebula is well resolved by the 167 beam (FWHM) of GISMO. Comparison to radio data at comparable spatial resolution enables us to confirm significant spatial variation of the spectral index between 21cm and 2mm. The main effect is a spectral flattening in the inner region of the Crab Nebula, correlated with the toroidal structure at the center of the nebula that is prominent in the near-IR through X-ray regime. © 2011. The American Astronomical Society. All rights reserved.