ASCA and RXTE observations of non-thermal X-ray emission from galactic supernova remnants: G156.2+5.7

Abstract

We are conducting a survey of Galactic shell-type supernova remnants (SNRs) known or suspected to possess non-thermal components to their X-ray emission using new and archived observations made with such X-ray satellites as ROSAT, ASCA, RXTE, Chandra and XMM-Newton. This research is intended to probe the phenomenon of cosmic-ray acceleration by Galactic SNRs and estimate the maximum energy of cosmic-ray electrons accelerated by these sources. To illustrate this work, we examine the X-ray spectrum of the northwestern rim of an SNR suspected to have a non-thermal component to its X-ray emission, G156.2+5.7 (RX J04591+5147), over the energy range ≈0.7–12.0 keV using observations made by the ASCA GIS and the RXTE PCA. We compare fits made to the non-thermal component using two models, a simple power law and SRCUT. Both models give acceptable fits: the photon index derived from the fit made with the power law model ( Γ=2.0 +0.2 −0.5) is comparable to values obtained for the bright rims of other SNRs with hard X-ray spectra. Using the SRCUT model, we derive a value of 2.42 +0.24 −0.23×10 17 Hz for the cutoff frequency ν cutoff: based on this value and assuming a mean magnetic field strength of 14 μG, we estimate the cutoff energy E cutoff of cosmic-ray electrons accelerated by G156.2+5.7 to be ≈32 TeV. This energy value is well short of the “knee” feature of the cosmic-ray spectrum.