Astronomy researchers from the University of Michigan have used the Nuclear Spectroscopic Telescope Array (NuSTAR) to resolve the non-thermal, hard X-ray emission at >8keV from the two limbs of the historical supernova remnant SN1006, which exploded more than 1,000 years ago. Their findings have recently been published in The Astrophysical Journal.

Supernova remnants are produced in the explosion at the end of the lifetime of a star. Within those supernova remnants, charged particles can be accelerated to relativistic speeds. Those particles are an essential ingredient of galactic cosmic rays, and they radiate non-thermal emission in a broad energy range via different mechanisms.

The research performed by Dr. Jiangtao Li and an international team including UM astronomers, was in an effort to resolve the non-thermal emission features of supernova remnants and study the shape of the non-thermal spectrum in a broad energy range to better understand how cosmic rays are produced.

The SN1006 Supernova Remnant is one of the best cases for the study of cosmic rays and their non-thermal emission from radio to gamma rays. This is due to the fact that SN1006 is located in a clean, high-Galactic latitude environment with a well-constrained magnetic field and surrounding interstellar medium structures. In the past, broad-band non-thermal emissions have been detected from the two limbs of SN1006. However, due to the presence of soft X-ray thermal emission and the complicated shape of the synchrotron emission spectrum predicted by different models, the synchrotron emission has not been well understood with only radio and soft X-ray observations.

The NuSTAR observations made by Dr. Li and colleagues for the first time extends the energy coverage of the spatially-resolved synchrotron emission features to >8keV to study SN1006. Their beautiful NuSTAR image of SN1006 shows how non-thermal emission from cosmic rays appears in hard X-ray. The similar morphology in radio and hard X-ray, as well as the shape of the broad-band non-thermal emission spectrum, indicate that the non-thermal emissions over nine orders of magnitude in wavelength, from radio to hard X-ray, are produced by the same cosmic ray electron population with the same emission mechanism. In addition, their research also demonstrates how spatially-resolved observations at higher energy is critical to characterizing the shape of the synchrotron emission.

Jiangtao Li:

RIGHT: tricolor images of SN1006—red: VLA 1.37GHz radio image; green and blue: XMM-Newton 0.3–2 keV and 2–8 keV images. The two white boxes roughly outline the FOV of the NuSTAR observations. LEFT: NuSTAR tricolor (red: 3–10 keV; green: 10–20 keV; blue: 20–30 keV) images of the NE and SW limbs from the two white boxes in right image.