Nonthermal X-ray emission from young Supernova Remnants

The cosmic-ray spectrum up to the knee ($E\sim 10^{15}$ eV) is attributed to acceleration processes taking place at the blastwaves which bound supernova remnants. Theoretical predictions give a similar estimate for the maximum energy which can be reached at supernova remnant shocks by particle acceleration. Electrons with energies of the order $\sim 10^{15}$ eV should give a nonthermal X-ray component in young supernova remnants. Recent observations of SN1006 and G347.3-0.5 confirm this prediction. We present a method which uses hydrodynamical simulations to describe the evolution of a young remnant. These results are combined with an algorithm which simultaneously calculates the associated particle acceleration. We use the test particle approximation, which means that the back-reaction on the dynamics of the remnant by the energetic particles is neglected. We present synchrotron maps in the X-ray domain, and present spectra of the energies of the electrons in the supernova remnant. Some of our results can be compared directly with earlier semi-analytical work on this subject by Reynolds [1].Comment: 4 pages, 2 figures, contribution proceedings of poster presented at the 11th Annual Astrophysics Conference in Maryland, to appear in Young Supernova Remnants, ed. by S. S. Holt and U. Hwang (AIP

New Constraints on the Structure and Evolution of the Pulsar Wind Nebula 3C 58

We present an investigation of the spectral and spatial structure of the X-ray emission from 3C 58 based on a 350 ks observation with the Chandra X-ray Observatory. This deep image, obtained as part of the Chandra Large Project program, reveals new information on nearly all spatial scales in the pulsar wind nebula (PWN). On the smallest scales we derive an improved limit of T < 1.02 X 10^6 K for blackbody emission from the entire surface of the central neutron star (NS), confirming the need for rapid, nonstandard cooling in the stellar interior. Furthermore, we show that the data are consistent with emission from a light element atmosphere with a similar temperature. Surrounding the NS, a toroidal structure with a jet is resolved, consistent with earlier measurements and indicative of an east-west orientation for the projected rotation axis of the pulsar. A complex of loop-like X-ray filaments fills the nebula interior, and corresponds well with structures seen in the radio band. Several of the structures coincide with optical filaments as well. The emission from the interior of the PWN, including the pulsar, jet, and filaments, is primarily nonthermal in nature. The power law index steepens with radius, but appears to also show small azimuthal variations. The outermost regions of the nebula require a thermal emission component, confirming the presence of an ejecta-rich swept up shell.Comment: 12 pages, 9 figures. Accepted for Publication in ApJ. Fixed several incorrect east/west designations and revised treatment of column density. The latter results in minor changes to some derived spectral parameter

Chandra and XMM Observations of the Composite Supernova Remnant G327.1-1.1

We present new X-ray imaging and spectroscopy of a composite supernova remnant G327.1-1.1 using the Chandra and XMM-Newton X-ray observatories. G327.1-1.1 has an unusual morphology consisting of a symmetric radio shell and an off center nonthermal component that indicates the presence of a pulsar wind nebula (PWN). Radio observations show a narrow finger of emission extending from the PWN structure towards the northwest. X-ray studies with ASCA, ROSAT, and BeppoSAX revealed elongated extended emission and a compact source at the tip of the finger that may be coincident with the actual pulsar. The high resolution Chandra observations provide new insight into the structure of the inner region of the remnant. The images show a compact source embedded in a cometary structure, from which a trail of X-ray emission extends in the southeast direction. The Chandra images also reveal two prong-like structures that appear to originate from the vicinity of the compact source and extend into a large bubble that is oriented in the north-west direction, opposite from the bright radio PWN. The emission from the entire radio shell is detected in the XMM data and can be characterized by a thermal plasma model with a temperature of 0.3 keV, which we use to estimate the physical properties of the remnant. The peculiar morphology of G327.1-1.1 may be explained by the emission from a moving pulsar and a relic PWN that has been disrupted by the reverse shock.Comment: 12 pages, 10 figures, 4 table

Improvements in air quality in the Netherlands during the corona lockdown based on observations and model simulations

The lockdown measures in response to the SARS-CoV-2 virus outbreak in 2020 have resulted in reductions in emissions of air pollutants and corresponding ambient concentrations. In the Netherlands, the most stringent lockdown measures were in effect from March to May 2020. These measures coincided with a period of unusual meteorological conditions with wind from the north-east and clear-sky conditions, which complicates the quantification of the effect of the lockdown measures on the air quality. Here we quantify the lockdown effects on the concentrations of nitrogen oxides (NOx and NO2), particulate matter (PM10 and PM2.5) and ozone (O3) in the Netherlands, by analyzing observations and simulations with the atmospheric chemistry-transport model EMEP/MSC-W in its EMEP4NL configuration, after eliminating the effects of meteorological conditions during the lockdown. Based on statistical analyses with a Random Forest method, we estimate that the lockdown reduced observed NO2 concentrations by 30% (95% confidence interval 25–35%), 26% (21–32%), and 18% (10–25%) for traffic, urban, and rural background locations, respectively. Slightly smaller reductions of 8–28% are found with the EMEP4NL simulations for urban and regional background locations based on estimates in reductions in economic activity and emissions of traffic and industry in the Netherlands and other European countries. Reductions in observed PM2.5 concentrations of about 20% (10–25%) are found for all locations, which is somewhat larger than the estimates of 5–16% based on the model simulations. A comparison of the calculated NO2 traffic contributions with observations shows a substantial drop of about 35% in traffic contributions during the lockdown period, which is similar to the estimated reductions in mobility data as reported by Apple and Google. Since the largest health effects related to air pollution in the Netherlands are associated with exposure to PM10 and PM2.5, the lockdown measures in spring of 2020 have temporarily improved the air quality in the Netherlands. The concentrations of the most health relevant compounds have only been reduced by about 10–25%