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Register a new userCompleting the X-ray view of the recently discovered supernova remnant G53.41+0.03
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Vladim\\'ir Dom\\v{c}ek
Publication date
2021
fields
Physics
and research's language is
English
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Aims: We present a detailed X-ray study of the recently discovered supernova remnant (SNR) G53.41+0.03 that follows up and further expands on the previous, limited analysis of archival data covering a small portion of the SNR. Methods: With the new dedicated 70ks XMM-Newton observation we investigate the morphological structure of the SNR in X-rays, search for a presence of a young neutron star and characterise the plasma conditions in the selected regions by means of spectral fitting. Results: The first full view of SNR G53.41+0.03 shows an X-ray emission region well aligned with the reported half-shell radio morphology. We find three distinct regions of the remnant that vary in brightness and hardness of the spectra, and are all best characterised by a hot plasma model in a non-equilibrium ionisation state. Of the three regions, the brightest one contains the most mature plasma, with ionisation age $tau approx 4times10^{10}$s cm$^{-3}$ (where $tau = n_e t$), a lower electron temperature of kT$_mathrm{e} approx 1$ keV and the highest estimated gas density of n$_mathrm{H}approx 0.87$ cm$^{-3}$. The second, fainter but spectrally harder, region reveals a younger plasma ($tau approx 1.7times10^{10}$s cm$^{-3}$) with higher temperature (kT$_mathrm{e} approx 2$ keV) and two to three times lower density (n$_mathrm{H}approx 0.34$ cm$^{-3}$). The third region is very faint, but we identify spectroscopically the presence of a hot plasma.Employing several methods for age estimation, we find the remnant to be $t approx 1000-5000$ yrs old, confirming the earlier reports of a relatively young age. The environment of the remnant also contains a number of point sources, of which most are expected to be positioned in the foreground. Of the two point sources in the geometrical centre of the remnant one is consistent with the characteristics of a young neutron star.
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NuSTAR observed G1.9+0.3, the youngest known supernova remnant in the Milky Way, for 350 ks and detected emission up to $sim$30 keV. The remnants X-ray morphology does not change significantly across the energy range from 3 to 20 keV. A combined fit between NuSTAR and CHANDRA shows that the spectrum steepens with energy. The spectral shape can be well fitted with synchrotron emission from a power-law electron energy distribution with an exponential cutoff with no additional features. It can also be described by a purely phenomenological model such as a broken power-law or a power-law with an exponential cutoff, though these descriptions lack physical motivation. Using a fixed radio flux at 1 GHz of 1.17 Jy for the synchrotron model, we get a column density of N$_{rm H}$ = $(7.23pm0.07) times 10^{22}$ cm$^{-2}$, a spectral index of $alpha=0.633pm0.003$, and a roll-off frequency of $ u_{rm rolloff}=(3.07pm0.18) times 10^{17}$ Hz. This can be explained by particle acceleration, to a maximum energy set by the finite remnant age, in a magnetic field of about 10 $mu$G, for which our roll-off implies a maximum energy of about 100 TeV for both electrons and ions. Much higher magnetic-field strengths would produce an electron spectrum that was cut off by radiative losses, giving a much higher roll-off frequency that is independent of magnetic-field strength. In this case, ions could be accelerated to much higher energies. A search for $^{44}$Ti emission in the 67.9 keV line results in an upper limit of $1.5 times 10^{-5}$ $,mathrm{ph},mathrm{cm}^{-2},mathrm{s}^{-1}$ assuming a line width of 4.0 keV (1 sigma).
The Cosmic Ray (CR) physics has entered a new era driven by high precision measurements coming from direct detection (especially AMS-02 and PAMELA) and also from gamma-ray observations (Fermi-LAT). In this review we focus our attention on how such data impact the understanding of the supernova remnant paradigm for the origin of CRs. In particular we discuss advancement in the field concerning the three main stages of the CR life: the acceleration process, the escape from the sources and the propagation throughout the Galaxy. We show how the new data reveal a phenomenology richest than previously thought that could even challenge the current understanding of CR origin.
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}.
G21.5-0.9 is a plerionic supernova remnant (SNR) used as a calibration target for the Chandra X-ray telescope. The first observations found an extended halo surrounding the bright central pulsar wind nebula (PWN). A 2005 study discovered that this halo is limb-brightened and suggested the halo to be the missing SNR shell. In 2010 the spectrum of the limb-brightened shell was found to be dominated by non-thermal X-rays. In this study, we combine 15 years of Chandra observations comprising over 1~Msec of exposure time (796.1~ks with the Advanced CCD Imaging Spectrometer (ACIS) and 306.1~ks with the High Resolution Camera (HRC)) to provide the deepest-to-date imaging and spectroscopic study. The emission from the limb is primarily non-thermal and is described by a power-law model with a photon index $Gamma = 2.22 , (2.04-2.34)$, plus a weak thermal component characterized by a temperature $kT = 0.37, (0.20-0.64)$ keV and a low ionization timescale of $n_{e}t < 2.95 times 10^{10}$ cm$^{-3}$s. The northern knot located in the halo is best fitted with a two-component power-law + non-equilibrium ionization thermal model characterized by a temperature of 0.14 keV and an enhanced abundance of silicon, confirming its nature as ejecta. We revisit the spatially resolved spectral study of the PWN and find that its radial spectral profile can be explained by diffusion models. The best fit diffusion coefficient is $D sim 2.1times 10^{27}rm cm^2/s$ assuming a magnetic field $B =130 mu G$, which is consistent with recent 3D MHD simulation results.
We present an analysis of archival Chandra observations of the mixed-morphology remnant 3C400.2. We analysed spectra of different parts of the remnant to observe if the plasma properties provide hints on the origin of the mixed-morphology class. These remnants often show overionization, which is a sign of rapid cooling of the thermal plasma, and super-solar abundances of elements which is a sign of ejecta emission. Our analysis shows that the thermal emission of 3C400.2 can be well explained by a two component non-equilibrium ionization model, of which one component is underionized, has a high temperature ($kT approx 3.9$ keV) and super-solar abundances, while the other component has a much lower temperature ($kT approx 0.14$ keV), solar abundances and shows signs of overionization. The temperature structure, abundance values and density contrast between the different model components suggest that the hot component comes from ejecta plasma, while the cooler component has an interstellar matter origin. This seems to be the first instance of an overionized plasma found in the outer regions of a supernova remnant, whereas the ejecta component of the inner region is underionized. In addition, the non-ionization equilibrium plasma component associated with the ejecta is confined to the central, brighter parts of the remnant, whereas the cooler component is present mostly in the outer regions. Therefore our data can most naturally be explained by an evolutionary scenario in which the outer parts of the remnant are cooling rapidly due to having swept up high density ISM, while the inner parts are very hot and cooling inefficiently due to low density of the plasma. This is also known as the relic X-ray scenario.
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