Non thermal X-ray radiation from superfast ejecta in SN 1006

Supernova remnants, which are nebulae produced by explosion of supernovae and undergoing rapid expansion, typically serve as intense sources of high-energy radiation, particularly in the form of X-ray emissions. This radiation can be of two different types: thermal and non-thermal. Thermal radiation is emitted by dense material and is contingent upon the temperature of the emitting gas. To emit X-rays, the temperature must be on the order of millions of degrees. Non-thermal emission, on the other hand, is generated by physical processes involving particles at extremely high energy, or it can result from electronic transitions in highly ionized atoms.

An alternative mechanism for the production of non-thermal X-ray radiation is associated with the presence of high-velocity ejecta, fragments of exploded stars expelled by the supernova, moving at speeds exceeding thousands of kilometers per second through dense material. These fragments can generate bow shocks in the surrounding gas, where particles may be accelerated to relativistic energies. Such accelerated particles can ionize gas atoms, leading to the emission of X-ray photons.


In order to comprehend the mechanisms behind the production of non-thermal X-ray radiation, numerous supernova remnants have been studied in recent years, with some investigations led by astronomers from our observatory. Among these remnants, SN 1006 holds particular significance. It originated from a type Ia supernova, the progenitor of which is an accreting white dwarf in a binary system, and it exploded in the 1006. Therefore, it is a relatively young supernova remnant, situated in a rather peculiar position—7200 light years away from us and 1800 light years distant from the Galactic plane. In the case of SN 1006, the non-thermal X-ray emission emanates from two lobes positioned in a specular manner in the south-west and north-east, where the acceleration of electrons by the shock is more efficient.


Given its unique characteristics, it is not surprising that SN 1006 has become observed in X-rays using the most powerful telescopes available. A team of researchers, led by the astronomer R. Giuffrida (University of Palermo and INAF – Astronomical Observatory of Palermo), analyzed observations obtained from NASA satellites Chandra and NuSTAR, as well as the ESA satellite XM/Newton, to unravel the origin of the non-thermal X-ray radiation from SN 1006.

The study particularly concentrates on a bright X-ray knot, also visible in infrared, situated in the south-east, approximately 6 light years in front of the expanding shock. Analysis of the X-ray images revealed that a significant portion of the non-thermal radiation emanates from highly ionized atoms of neon, silicon, and iron. This emission is inconsistent with being produced by relativistic particles. The most plausible hypothesis, supported by physical models, suggests that it is emitted by a superfast fragments of the exploded star, with a mass of a thousandth of the solar mass, traveling ahead of the shock and interacting with the dense surrounding gas.

Non-thermal emission from high-velocity ejecta has been previously identified in other remnants, such as IC 443, but this marks the first detection from a type Ia remnant with Fe/Si/Ne-rich ejecta. The study’s findings are described in the article titled “Indication of a fast ejecta fragment in the atomic cloud interacting with the southwestern limb of SN 1006,” recently published in the journal Astronomy and Astrophysics. Coauthors include M. Miceli (University of Palermo) and F. Bocchino and S. Orlando (INAF – Astronomical Observatory of Palermo).


The cover figure (click here to view it in its entirety) displays four images of the X-ray knot analyzed in this study. The top-left panel presents an image captured by Chandra in 2003. The white line indicates the direction of the center of SN 1006. The top-right panel exhibits a Chandra image obtained in 2012, with the 2003 position marked. In the bottom panels, there are images acquired with XMM/Newton in 2004 and 2010.


Mario Giuseppe Guarcello  ( follow mariospiegacose) ( mariospiegacose) ( follow mariospiegacose)

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