RXTE, ROSAT, AND ASCA OBSERVATIONS OF G347.3-0.5 (RX J1713.7-3946): PROBING COSMIC-RAY ACCELERATION BY A GALACTIC SHELL-TYPE SUPERNOVA REMNANT

摘要

We present an analysis of the X-ray spectrum of the Galactic shell-type supernova remnant (SNR) G347.3-0.5 (RX J1713.7-3946). This SNR is a member of a growing class of dynamically young, shell-type SNRs that emit nonthermal X-rays from specific regions on their outer shells. By performing a joint spectral analysis of data from observations made of G347.3-0.5 using the ROSAT PSPC, the ASCA GIS, and the RXTE PCA, we have fitted the spectra of particular regions of this SNR (including the bright northwestern and southwestern rims, the northeast rim, and the interior diffuse emission) over the approximate energy range of 0.5-30 keV. We find that fits to the spectra of this SNR over this energy range using the SRCUT model were superior to a simple power-law model or the SRESC model. We also find that the inclusion of a thermal model with the SRCUT model helps to improve the fit to the observed X-ray spectrum: this represents the first detection of thermal X-ray emission from G347.3-0.5. Thermal emission appears to be more clearly associated with the diffuse emission in the interior of the SNR than with the bright X-ray-emitting rims. A weak emission feature seen near 6.4 keV in the RXTE PCA spectrum most likely originates from diffuse X-ray emission from the surrounding Galactic ridge rather than from G347.3-0.5 itself. We have analyzed our RXTE PCA data to search for pulsations from a recently discovered radio pulsar (PSR J1713-3949) which may be associated with G347.3-0.5, and we do not detect any X-ray pulsations at the measured radio period of 392 ms. Using the best-fit parameters obtained from the SRCUT model, we estimate the maximum energy of cosmic-ray electrons accelerated by the rims of G347.3-0.5 to be 36-48 TeV (assuming a magnetic field strength of B = 10 μG). We present a broadband (radio to γ-ray) photon energy-flux spectrum for the northwestern rim of G347.3-0.5, where we have fitted the spectrum using a more sophisticated synchrotron-inverse Compton model with a variable magnetic field strength. Our fit derived from this model yields a maximum energy of only 8.8_(-3.4)~(+4.1) TeV for the accelerated cosmic-ray electrons and a much greater magnetic field strength of 150_(-80)~(+250) μG; however, our derived ratio of volumes for TeV emission and X-ray emission based on this fit, V_(TeV)/V_(X-ray) ≈ 1000, is too large to be physically acceptable. We argue that neither nonthermal bremsstrahlung nor neutral pion particle decay can adequately explain the TeV emission from this rim, and therefore the physical process responsible for this emission at this site is currently uncertain. Finally, we compare the gross properties of G347.3-0.5 with other SNRs known to possess X-ray spectra dominated by nonthermal emission.