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We present ∼400 ks NuSTAR observations of the northeast (NE) and southwest (SW) nonthermal limbs of the Galactic SNR SN1006. We discovered three sources with X-ray emission detected at ≳50 keV. Two of them are identified as background active galactic nuclei. We extract the NuSTAR spectra from a few regions along the nonthermal limbs and jointly analyze them with the XMM-Newton spectra and the radio data. The broadband radio/X-ray spectra can be well described with a synchrotron emission model from a single population of CR electrons with a power-law energy distribution and an exponential cutoff. The power-law index of the electron particle distribution function (PDF) is ≈1.88–1.95 for both the NE and SW limbs, and we do not find significant evidence for a variation of this index at different energy (curvature). There are significant spatial variations of the synchrotron emission parameters. The highest energy electrons are accelerated in regions with the lowest expansion velocity, which is opposite to what has been found in Tycho’s supernova remnant. In addition to a gradual steepening of synchrotron emission from the center of the nonthermal limbs to larger azimuthal angles, we also find that both the emission spectrum and the PDF are significantly flatter in three regions in the SW limb where the shock encounters a higher density ambient medium. The NE limb also shows significantly higher cutoff energy in the PDF than the SW limb. By comparing with the roughly symmetric TeV emission and largely asymmetric GeV emission from the two nonthermal limbs, we conclude that the asymmetry in the ambient medium and magnetic fields may have largely modified the acceleration and emission of CR leptons. [ABSTRACT FROM AUTHOR]

We report our independent GeV γ-ray study of the young shell-type supernova remnant (SNR) Kes 73, which harbors a central magnetar, and CO-line millimeter observations toward the SNR. Using 7.6 years of Fermi-LAT observation data, we detected an extended γ-ray source (“source A”) with centroid on the west of the SNR, with a significance of 21σ in 0.1–300 GeV and an error circle of 5.′4 in angular radius. The γ-ray spectrum cannot be reproduced by a pure leptonic emission or a pure emission from the magnetar, and thus a hadronic emission component is needed. The CO-line observations reveal a molecular cloud (MC) at VLSR ∼ 90 km s−1, which demonstrates morphological correspondence with the western boundary of the SNR brightened in multiwavelength. The 12CO (J = 2 − 1)/12CO (J = 1 − 0) ratio in the left (blue) wing 85–88 km s−1 is prominently elevated to ∼1.1 along the northwestern boundary, providing kinematic evidence of the SNR-MC interaction. This SNR-MC association yields a kinematic distance 9 kpc to Kes 73. The MC is shown to be capable of accounting for the hadronic γ-ray emission component. The γ-ray spectrum can be interpreted with a pure hadronic emission or a magnetar+hadronic hybrid emission. In the case of pure hadronic emission, the spectral index of the protons is 2.4, very similar to that of the radio-emitting electrons, essentially consistent with the diffusive shock acceleration theory. In the case of magnetar+hadronic hybrid emission, a magnetic field decay rate ≳1036 erg s−1 is needed to power the magnetar’s curvature radiation. [ABSTRACT FROM AUTHOR]