In September, Dmitry Prokhorov started to work on X-ray polarimetry in the group led by Jacco Vink at the University of Amsterdam (UvA). Dmitry will analyze data from the Imaging X-ray Polarimetry Explorer for performing a polarimetric study of supernova remnants to characterize particle acceleration at their shock fronts.
As of October, Emanuele Greco joined UvA as a member of the SHARP team. He will deal with non-thermal emission due to synchrotron radiation in supernova remnants by analyzing observations collected in the X-ray energy band. In particular, he will look for spectral signatures of jittering radiation in young remnants such as Cassiopeia A, Tycho and SN 1006.
The Mach number is one of the most important parameters of collisionless shocks. The accuracy of its observational determination is compromised by several complications. Incomplete measurements of plasma parameters significantly contribute to the uncertainty, along with the errors of the normal determination. A set of CLUSTER observed shocks is analyzed using several methods for finding the shock normal and to circumvent the shortcomings of the plasma data. A relation between the maximum magnetic compression and the Alfvénic Mach number is established. It is proposed as a proxy for the Mach number estimate when measurements are incomplete.
Theoretical proxy for the Mach number.
Full article: Gedalin, M., Russell, C. T., Dimmock, A. P. (2021). Shock Mach number estimates using incomplete measurements.Journal of Geophysical Research: Space Physics, 126, doi: 10.1029/2021JA029519
In August, Andreas Johlander joined IRF as a member of the SHARP team. He will work on improving our understanding of how particles behave during shock rippling and nonstationarity. In addition, he will investigate the characteristics of waves and instabilities as well as their roles in regulating the macroscopic properties of the shock front.
Andrew Dimmock gave a presentation entitled “An MMS bow shock database using machine learning: EU H2020 SHARP project” at the summer GEM virtual workshop (https://gemworkshop.org/) in the focus group “Particle Heating and Thermalization in Collisionless Shocks in the MMS Era”. The presentation provided details of the identification of terrestrial bow shocks using machine learning classification of the ion phase space distribution functions and the SHARP project. An overview of the SHARP terrestrial database was presented, as well as quick look plots, and the online functionality available to the wider community.
Since 1996 the blast wave driven by SN 1987A has been interacting with the dense circumstellar material, which provides us with a unique opportunity to study the early evolution of a newborn supernova remnant (SNR). Based on the XMM-Newton RGS and EPIC-pn X-ray observations from 2007 to 2019, we investigated the post-impact evolution of the X-ray-emitting gas in SNR 1987A. The hot plasma is represented by two nonequilibrium ionization components with temperatures of ~0.6 keV and ~2.5 keV. The low-temperature plasma has a density ~2400 cm−3, which is likely dominated by the lower-density gas inside the equatorial ring (ER). The high-temperature plasma with a density ~550 cm−3 could be dominated by the H ii region and the high-latitude material beyond the ring. In the last few years, the emission measure of the low-temperature plasma has been decreasing, indicating that the blast wave has left the main ER. But the blast wave is still propagating into the high-latitude gas, resulting in the steady increase of the high-temperature emission measure. Meanwhile, the average abundances of N, O, Ne, and Mg are found to be declining, which may reflect the different chemical compositions between the two plasma components. We also detected Fe K lines in most of the observations, showing increasing flux and centroid energy. We interpret the Fe K lines as originating from a third hot component, which may come from the reflected shock heated gas or originate from Fe-rich ejecta clumps shocked by the reverse shock.
EPIC-pn images of SNR 1987A region. The source and background extraction regions used for the spectral analysis are denoted by red and white circles, respectively.
Full article: Lei Sun et al (2021), The Post-impact Evolution of the X-Ray-emitting Gas in SNR 1987A as Viewed by XMM-Newton, The Astrophysical Journal, 916(1), doi: 10.3847/1538-4357/ac033d
The distribution and kinematics of the circumstellar medium (CSM) around a supernova remnant (SNR) tell us useful information about the explosion of its natal supernova (SN). Kepler’s SNR, the remnant of SN 1604, is widely regarded to be of Type Ia origin. Its shock is moving through a dense, asymmetric CSM. The presence of this dense gas suggests that its parent progenitor system consisted of a white dwarf and an asymptotic giant branch (AGB) star. In this paper, we analyze a new and long observation with the reflection grating spectrometers on board the XMM-Newton satellite, spatially resolving the remnant emission in the cross-dispersion direction. We find that the CSM component is blueshifted with velocities in the general range 0–500 km s−1. We also derive information on the central bar structure and find that the northwest half is blueshifted, while the southeast half is redshifted. Our result is consistent with a picture proposed by previous studies, in which a “runaway” AGB star moved to the north-northwest and toward us in the line of sight, although it is acceptable for both single- and core-degenerate scenarios for the progenitor system.
Full article: Tomoaki Kasuga et al (2021), Spatially Resolved RGS Analysis of Kepler’s Supernova Remnant, The Astrophysical Journal, 915(1), doi: 10.3847/1538-4357/abff4f
Observations in the heliosphere show that magnetized collisionless shocks are very efficient at ion heating. Ion heating is a nonadiabatic process and the temperature downstream of the shock is not proportional to the upstream temperature. Directly transmitted ions may be responsible for most of the downstream temperature. We determine the gyrophase-dependent distribution of directly transmitted ions just behind the magnetic jump, the gyrotropic distribution farther behind the shock, and establish the relation with the magnetic compression and the maximum overshoot magnetic field. These relations may be used as proxies for estimating the shock Mach number when reliable measurements of density are not available.
Dependence of the magnetic compression at the overshoot on the Mach number MA for various cross-shock potentials.
Full article: Michael Gedalin (2021), Shock Heating of Directly Transmitted Ions, The Astrophysical Journal, 912(2), doi: 10.3847/1538-4357/abf1e2
