Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userTemporal and Spatial Variation of Synchrotron X-ray Stripes in Tychos Supernova Remnant
127
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
The synchrotron X-ray stripes discovered in Tychos 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.
rate research
Read More
Analyzing Chandra data of Tychos supernova remnant (SNR) taken in 2000, 2003, 2007, 2009, and 2015, we search for time variable features of synchrotron X-rays in the southwestern part of the SNR, where stripe structures of hard X-ray emission were previous found. By comparing X-ray images obtained at each epoch, we discover a knot-like structure in the northernmost part of the stripe region became brighter particularly in 2015. We also find a bright filamentary structure gradually became fainter and narrower as it moved outward. Our spectral analysis reveal that not only the nonthermal X-ray flux but also the photon indices of the knot-like structure change from year to year. During the period from 2000 to 2015, the small knot shows brightening of $sim 70%$ and hardening of $Delta Gamma sim 0.45$. The time variability can be explained if the magnetic field is amplified to $sim 100~mathrm{mu G}$ and/or if magnetic turbulence significantly changes with time.
High-resolution Chandra observations of Tychos SNR have revealed several sets of quasi-steady, high-emissivity, nearly-parallel X-ray stripes in some localized regions of the SNR. These stripes are most likely the result of cosmic-ray (CR) generated magnetic turbulence at the SNR blast wave. However, for the amazingly regular pattern of these stripes to appear requires the simultaneous action of a number of shock-plasma phenomena and is not predicted by most models of magnetic field amplification. A consistent explanation of these stripes yields information on the complex nonlinear plasma processes connecting efficient CR acceleration and magnetic field fluctuations in strong collisionless shocks. The nonlinear diffusive shock acceleration (NL-DSA) model described here, which includes magnetic field amplification from a cosmic-ray current driven instability, does predict stripes consistent with the synchrotron emission observations of Tychos SNR. We argue that the local ambient mean magnetic field geometry determines the orientation of the stripes and therefore it can be reconstructed with the high resolution X-ray imaging. The estimated maximum energy of the CR protons responsible for the stripes is $sim 10^{15}$,eV. Furthermore, the model predicts that a specific X-ray polarization pattern, with a polarized fraction ~ 50%, accompanies the stripes, which can be tested with future X-ray polarimeter missions.
We present X-ray proper-motion measurements of the forward shock and reverse-shocked ejecta in Tychos supernova remnant, based on three sets of archival Chandra data taken in 2000, 2003, and 2007. We find that the proper motion of the edge of the remnant (i.e., the forward shock and protruding ejecta knots) varies from 0.20 yr^{-1} (expansion index m=0.33, where R = t^m) to 0.40 yr^{-1} (m=0.65) with azimuthal angle in 2000-2007 measurements, and 0.14 yr^{-1} (m=0.26) to 0.40 yr^{-1} (m=0.65) in 2003-2007 measurements. The azimuthal variation of the proper motion and the average expansion index of ~0.5 are consistent with those derived from radio observations. We also find proper motion and expansion index of the reverse-shocked ejecta to be 0.21-0.31 yr^{-1} and 0.43-0.64, respectively. From a comparison of the measured m-value with Type Ia supernova evolutionary models, we find a pre-shock ambient density around the remnant of <~0.2 cm^{-3}.
Recent rapid development of deep learning algorithms, which can implicitly capture structures in high-dimensional data, opens a new chapter in astronomical data analysis. We report here a new implementation of deep learning techniques for X-ray analysis. We apply a variational autoencoder (VAE) using a deep neural network for spatio-spectral analysis of data obtained by Chandra X-ray Observatory from Tychos supernova remnant (SNR). We established an unsupervised learning method combining the VAE and a Gaussian mixture model (GMM), where the dimensions of the observed spectral data are reduced by the VAE, and clustering in feature space is performed by the GMM. We found that some characteristic spatial structures, such as the iron knot on the eastern rim, can be automatically recognised by this method, which uses only spectral properties. This result shows that unsupervised machine learning can be useful for extracting characteristic spatial structures from spectral information in observational data (without detailed spectral analysis), which would reduce human-intensive preprocessing costs for understanding fine structures in diffuse astronomical objects, e.g., SNRs or clusters of galaxies. Such data-driven analysis can be used to select regions from which to extract spectra for detailed analysis and help us make the best use of the large amount of spectral data available currently and arriving in the coming decades.
We present newly obtained X-ray and radio observations of Tychos supernova remnant using {it Chandra} and the Karl G. Jansky Very Large Array in 2015 and 2013/14, respectively. When combined with earlier epoch observations by these instruments, we now have time baselines for expansion measurements of the remnant of 12-15 year in the X-rays and 30 year in the radio. The remnants large angular size allows for proper motion measurements at many locations around the periphery of the blast wave. We find, consistent with earlier measurements, a clear gradient in the expansion velocity of the remnant, despite its round shape. The proper motions on the western and southwestern sides of the remnant are about a factor of two higher than those in the east and northeast. We showed in an earlier work that this is related to an offset of the explosion site from the geometric center of the remnant due to a density gradient in the ISM, and using our refined measurements reported here, we find that this offset is $sim 23$ towards the northeast. An explosion center offset in such a circular remnant has implications for searches for progenitor companions in other remnants.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
