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THE HARD X-RAY VIEW OF THE YOUNG SUPERNOVA REMNANT G1.9+0.3

2014; IOP Publishing; Volume: 798; Issue: 2 Linguagem: Inglês

10.1088/0004-637x/798/2/98

1538-4357

Andreas Zoglauer, Stephen P. Reynolds, Hongjun An, Steven E. Boggs, Finn E. Christensen, William W. Craig, Chris L. Fryer, Brian W. Grefenstette, Fiona A. Harrison, Charles J. Hailey, Roman Krivonos, Kristin K. Madsen, H. Miyasaka, Daniel Stern, William W. Zhang,

Astrophysical Phenomena and Observations

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 power law 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 NH = (7.23 ± 0.07) × 1022 cm−2, a spectral index of α = 0.633 ± 0.003, and a roll-off frequency of νrolloff = (3.07 ± 0.18) × 1017 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 44Ti emission in the 67.9 keV line results in an upper limit of 1.5 × 10−5 photons cm−2 s−1 assuming a line width of 4.0 keV (1 sigma).