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Register a new userKinematics of Supernova Remnants: Status of X-Ray Observations
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Daniel Dewey
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A supernova (SN) explosion drives stellar debris into the circumstellar material (CSM) filling a region on a scale of parsecs with X-ray emitting plasma. The velocities involved in supernova remnants (SNRs), thousands of km/s, can be directly measured with medium and high-resolution X-ray spectrometers and add an important dimension to our understanding of the last stages of the progenitor, the explosion mechanism, and the physics of strong shocks. After touching on the ingredients of SNR kinematics, I present a summary of the still-growing measurement results from SNR X-ray observations. Given the advances in 2D/3D hydrodynamics, data analysis techniques, and especially X-ray instrumentation, it is clear that our view of SNRs will continue to deepen in the decades ahead.
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We searched for X-ray supernova remnants (SNRs) in the starburst region of M82, using archival data from the Chandra X-ray Observatory with a total effective exposure time of 620 ks with an X-ray spectroscopic selection. Strong line-emission from Fe xxv at 6.7 keV is a characteristic spectral feature of hot, shocked gas of young SNRs and distinctive among the discrete sources in the region populated by X-ray binaries. We selected candidates using narrow-band imaging aimed at the line excess and identified six (and possibly a seventh) X-ray SNRs. Two previously known examples were recovered by our selection. Five of them have radio counterparts, including the radio supernova SN2008iz, which was discovered as a radio transient in 2008. It shows a hard X-ray spectrum with a blueshifted Fe K feature with v ~ -2700 km/s, both of which suggest its youth. The 4-8 keV luminosities of the selected SNRs are in the range of (0.3-3)e38 erg/s. We made a crude estimate of the supernova rate, assuming that more luminous SNRs are younger, and found 0.06 (0.03-0.13) /yr, in agreement with the supernova rates estimated by radio observations and the generally believed star formation rate of M82, although the validity of the assumption is questionable. A sum of the Fe xxv luminosity originating from the selected X-ray SNRs consists of half of the total Fe xxv luminosity observed in the central region of M82. We briefly discuss its implications for starburst winds and the Fe xxv emission in more luminous starburst galaxies.
The unprecedented spatial and spectral resolutions of Chandra have revolutionized our view of the X-ray emission from supernova remnants. The excellent data sets accumulated on young, ejecta dominated objects like Cas A or Tycho present a unique opportunity to study at the same time the chemical and physical structure of the explosion debris and the characteristics of the circumstellar medium sculpted by the progenitor before the explosion. Supernova remnants can thus put strong constraints on fundamental aspects of both supernova explosion physics and stellar evolution scenarios for supernova progenitors. This view of the supernova phenomenon is completely independent of, and complementary to, the study of distant extragalactic supernovae at optical wavelengths. The calibration of these two techniques has recently become possible thanks to the detection and spectroscopic follow-up of supernova light echoes. In this paper, I will review the most relevant results on supernova remnants obtained during the first decade of Chandra, and the impact that these results have had on open issues in supernova research.
We consider anisotropic diffusion of Galactic cosmic rays in the Galactic magnetic field, using the Jansson-Farrar model for the field. In this paper we investigate the influence of source position on the cosmic ray flux at Earth in two ways: [1] by considering the contribution from cosmic ray sources located in different intervals in Galacto-centric radius, and [2] by considering the contribution from a number of specific and individual close-by supernova remnants. Our calculation is performed by using a fully three-dimensional stochastic method. This method is based on the numerical solution of a set of stochastic differential equations, equivalent to Ito formulation, that describes the propagation of the Galactic cosmic rays.
Supernova remnants are beautiful astronomical objects that are also of high scientific interest, because they provide insights into supernova explosion mechanisms, and because they are the likely sources of Galactic cosmic rays. X-ray observations are an important means to study these objects.And in particular the advances made in X-ray imaging spectroscopy over the last two decades has greatly increased our knowledge about supernova remnants. It has made it possible to map the products of fresh nucleosynthesis, and resulted in the identification of regions near shock fronts that emit X-ray synchrotron radiation. In this text all the relevant aspects of X-ray emission from supernova remnants are reviewed and put into the context of supernova explosion properties and the physics and evolution of supernova remnants. The first half of this review has a more tutorial style and discusses the basics of supernova remnant physics and thermal and non-thermal X-ray emission. The second half offers a review of the recent advances.The topics addressed there are core collapse and thermonuclear supernova remnants, SN 1987A, mature supernova remnants, mixed-morphology remnants, including a discussion of the recent finding of overionization in some of them, and finally X-ray synchrotron radiation and its consequences for particle acceleration and magnetic fields.
During an [O III] survey for planetary nebulae, we identified a region in Sagittarius containing several candidate Supernova Remnants and obtained deep optical narrow-band images and spectra to explore their nature. The images of the unstudied area have been obtained in the light of Halpha+[N II], [S II] and [O III]. The resulting mosaic covers an area of 1.4x1.0 deg^2 where filamentary and diffuse emission was discovered, suggesting the existence of more than one supernova remnants (SNRs) in the area. Deep long slit spectra were also taken of eight different regions. Both the flux calibrated images and the spectra show that the emission from the filamentary structures originates from shock-heated gas, while the photo-ionization mechanism is responsible for the diffuse emission. Part of the optical emission is found to be correlated with the radio at 4850 MHz suggesting their association, while the WISE infrared emission found in the area at 12 and 22 micron marginally correlates with the optical. The presence of the [O III] emission line in one of the candidate SNRs suggests shock velocities into the interstellar clouds between 120 and 200 km/s, while the absence in the other indicates slower shock velocities. For all candidate remnants the [S II] 6716/6731 ratio indicates electron densities below 240 cm^{-3}, while the Halpha emission has been measured to be between 0.6 to 41x10^{-17} erg/s/cm^2/arcsec^2. The existence of eight pulsars within 1.5deg away from the center of the candidate SNRs also supports the scenario of many SNRs in the area as well as that the detected optical emission could be part of a number of supernovae explosions.
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