The Hard X-Ray View of the Young Supernova Remnant G1.9+0.3

Abstract

NuSTAR observed G1.9+0.3, the youngest known supernova remnant in the Milky Way, for 350 ks and detected emission up to ∼30 keV. The remnant's 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 powerlaw 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 H = (7.23 ± 0.07) × 10 22 cm −2 , a spectral index of α = 0.633 ± 0.003, and a roll-off frequency of ν rolloff = (3.07 ± 0.18) × 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 µG, 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 × 10 −5 ph cm −2 s −1 assuming a line width of 4.0 keV (1 sigma). Subject headings: supernova remnants -X-rays: individual (G1.9+0.3)

Energy distribution of relativistic electrons in the young supernova remnant G1.9+0.3

“…We use the same source regions for Chandra observations. The results of our study of the the spatial distribution of X-rays appeared quite similar the one reported by (Zoglauer et al 2015). Therefore, in this paper we do not discuss the morphology of the source but focus on the study of spectral features of radiation.…”

“…The combined Chandra and NuSTAR data sets have been claimed to be best described by the so-called srcut model (Reynolds 2008) or by the power-law function with an exponential cutoff. The characteristic cutoff energies in these two fits have been found around 3 keV and 15 keV, respectively (Zoglauer et al 2015).…”

“…The detailed study of the NuS-TAR data, combined with the Chandra observations at lower energies, have been comprehensively analysed by Zoglauer et al (2015). In particular, it was found that the source can be resolved into two bright limbs with similar spectral features.…”

“…ms tral shape of synchrotron radiation in the cutoff region. Such a study has been conducted by the team of the NuSTAR collaboration (Zoglauer et al 2015). However, some conclusions and statements of that paper seem to us rather confusing and, to a certain extent, misleading.…”

“…The X-ray observations with the Chandra and NuSTAR satellites (Reynolds et al 2009;Zoglauer et al 2015) cover a rather broad energy interval which is crucial for the study of the spec-A&A proofs: manuscript no. ms tral shape of synchrotron radiation in the cutoff region.…”