Spitzer Space TelescopeInfrared Imaging and Spectroscopy of the Crab Nebula

We present 3.6, 4.5, 5.8, 8.0, 24, and 70 micron images of the Crab Nebulaobtained with the Spitzer Space Telescope IRAC and MIPS cameras, Low- andHigh-resolution Spitzer IRS spectra of selected positions within the nebula,and a near-infrared ground-based image made in the light of [Fe II]1.644micron. The 8.0 micron image, made with a bandpass that includes [Ar II]7.0micron, resembles the general morphology of visible H-alpha and near-IR [Fe II]line emission, while the 3.6 and 4.5 micron images are dominated by continuumsynchrotron emission. The 24 micron and 70 micron images show enhanced emissionthat may be due to line emission or the presence of a small amount of warm dustin the nebula on the order of less than 1% of a solar mass. The ratio of the3.6 and 4.5 micron images reveals a spatial variation in the synchrotron powerlaw index ranging from approximately 0.3 to 0.8 across the nebula. Combiningthis information with optical and X-ray synchrotron images, we derive abroadband spectrum that reflects the superposition of the flatter spectrum jetand torus with the steeper diffuse nebula, and suggestions of the expectedpileup of relativistic electrons just before the exponential cutoff in theX-ray. The pulsar, and the associated equatorial toroid and polar jetstructures seen in Chandra and HST images (Hester et al. 2002) can beidentified in all of the IRAC images. We present the IR photometry of thepulsar. The forbidden lines identified in the high resolution IR spectra areall double due to Doppler shifts from the front and back of the expandingnebula and give an expansion velocity of approximately 1264 km/s.Comment: 21 pages, 4 tables, 16 figure