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X-RAY SPECTRAL VARIATIONS IN THE YOUNGEST GALACTIC SUPERNOVA REMNANT G1.9+0.3

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Stephen P. Reynolds1, Kazimierz J. Borkowski1, David A. Green2, Una Hwang3, Ilana Harrus3 and Robert Petre3

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The discovery of the youngest Galactic supernova remnant (SNR) G1.9+0.3 has allowed a look at a stage of SNR evolution never before observed. We analyze the 50 ks Chandra observation with particular regard to spectral variations. The very high column density (NH ~ 6 × 1022 cm–2) implies that dust scattering is important, and we use a simple scattering model in our spectral analysis. The integrated X-ray spectrum of G1.9+0.3 is well described by synchrotron emission from a power-law electron distribution with an exponential cutoff. Using our measured radio flux and including scattering effects, we find a rolloff frequency of 5.4(3.0, 10.2) × 1017 Hz (hνroll = 2.2 keV). Including scattering in a two-region model gives lower values of νroll by over a factor of 2. Dividing G1.9+0.3 into six regions, we find a systematic pattern in which spectra are hardest (highest νroll) in the bright southeast and northwest limbs of the shell. They steepen as one moves around the shell or into the interior. The extensions beyond the bright parts of the shell have the hardest spectra of all. We interpret the results in terms of dependence of shock acceleration properties on the obliquity angle θBn between the shock velocity and a fairly uniform upstream magnetic field. This interpretation probably requires a Type Ia event. If electron acceleration is limited by synchrotron losses, the spectral variations require obliquity-dependence of the acceleration rate independent of the magnetic-field strength.


Keywords

ISM: individual (G1.9+0.3); supernova remnants; X-rays: ISM


PACS

98.58.Mj Supernova remnants

98.58.Ay Physical properties (abundances, electron density, magnetic fields, scintillation, scattering, kinematics, dynamics, turbulence, etc.)

98.62.En Electric and magnetic fields

95.85.Nv X-ray

98.62.Ai Origin, formation, evolution, age, and star formation

98.62.Gq Galactic halos

Subjects

Astrophysics and astroparticles

Dates

Issue 2 (2009 April 20)

Received 2008 December 23, accepted for publication 2009 March 10

Published 2009 March 30



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