/ 01 07 54 0 v 2 2 8 Ju l 2 00 1 Accepted for publication in ApJ . X - Ray Synchrotron Emission from 10 – 100 TeV Cosmic - Ray Electrons in the Supernova Remnant SN 1006

We present the results of a joint spectral analysis of RXTE PCA, ASCA SIS, and ROSAT PSPC data of the supernova remnant SN 1006. This work represents the first attempt to model both the thermal and nonthermal X-ray emission over the entire X-ray energy band. The thermal flux is described by a nonequilibrium ionization model with an electron temperature kT e = 0.6 keV, an ionization timescale n 0 t = 9 × 10 9 cm −3 s, and a relative elemental abundance of silicon that is 10–18 times larger than the solar abundance. The nonthermal X-ray spectrum is described by a broken power law model with low-and high-energy photon indices Γ 1 = 2.1 and Γ 2 = 3.0, respectively. Since the nonthermal X-ray spectrum steepens with increasing energy, the results of the present analysis corroborate previous claims that the nonthermal X-ray emission is produced by synchrotron radiation. We argue that the magnetic field strength is significantly larger than previous estimates of about 10 µG and arbitrarily use a value of 40 µG to estimate the parameters of the cosmic-ray electron, proton, and helium spectra of the remnant. The results for the ratio of the number densities of protons and electrons (R = 160 at 1 GeV), the total energy in cosmic rays (E cr = 1 × 10 50 ergs), and the spectral index of the electrons at 1 GeV (Γ e = 2.14 ± 0.12) are consistent with the hypothesis that Galactic cosmic rays are accelerated predominantly in the shocks of supernova remnants. Yet, the remnant may or may not accelerate nuclei to energies as high as the energy of the " knee, " depending on the reason why the maximum energy of the electrons is only 10 TeV. – 2 –