The synchrotron X-ray “ stripes ” discovered in Tycho ’ s supernova remnant ( SNR ) have been attracting attention since they may be evidence for proton acceleration up to PeV .
We analyzed Chandra data taken in 2003 , 2007 , 2009 , and 2015 for imaging and spectroscopy of the stripes in the southwestern region of the SNR .
Comparing images obtained at different epochs , we find that time variability of synchrotron X-rays is not limited to two structures previously reported but is more common in the region .
Spectral analysis of nine bright stripes reveals not only their time variabilities but also a strong anti-correlation between the surface brightness and photon indices .
The spectra of the nine stripes have photon indices of \Gamma = 2.1 – 2.6 and are significantly harder than those of the outer rim of the SNR in the same region with \Gamma = 2.7 – 2.9 .
Based on these findings , we indicate that the magnetic field is substantially amplified , and suggest that particle acceleration through a stochastic process may be at work in the stripes .