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Title:
ROSAT Observations of the Composite Supernova Remnant G326.3-1.8
Authors:
Kassim, Namir E.; Hertz, Paul; Weiler, Kurt W.
Publication:
Astrophysical Journal v.419, p.733 (ApJ Homepage)
Publication Date:
12/1993
Origin:
APJ; KNUDSEN
ApJ Keywords:
ISM: SUPERNOVA REMNANTS, ISM: INDIVIDUAL ALPHANUMERIC: SNR G326.3-1.8, X-RAYS: INTERSTELLAR
DOI:
10.1086/173523
Bibliographic Code:
1993ApJ...419..733K

Abstract

We have observed X-ray emission from the radio-defined composite (shell plus filled-center plerion) Galactic supernova remnant (SNR) G326.3 -1.8 with the ROSAT position sensitive proportional counter (PSPC). The data are best fitted by a single-component, thermal line spectrum with temperature kT = 0.56±0.04 keV, hydrogen column density NH = 8.9±0.3 × 1021 cm-2, and unabsorbed X-ray flux Fχ0 = 3.9±0.5 × 10-10 ergs cm-2 s-1 (0.1-2.4 keV). The standard Sedov analysis with an assumed initial kinetic energy ɛ0 = 1051 ergs gives a radius R ≃ 20 pc, distance D ≃ 3.7 kpc, age t ≃ 1.0 × 104 yr, X-ray luminosity Lχ ≃ 6.1 × 103 ergs s-1 (0.1-2.4 keV), and an ambient interstellar medium (ISM) density n0 ≃ 0.1 cm-3.

The derived distance falls within the range of a variety of previous but poor and uncertain distance estimates and is consistent with the only reliable lower limit of D ≥ 1.5 kpc. Evidence exists in the literature from both optical and radio studies that would place the SNR significantly further than this lower limit. Higher quality radio H I absorption measurements are warranted to confirm our distance determination. Since D scales only weakly with ɛ0 (D ∝ ɛ02/5, this result, along with other recent ROSAT studies of SNRs, implies that improved distance estimates may be established for the large number of extended shell-type SNRs with very poor distance estimates which fall within ROSAT's all-sky survey.

No X-ray analog to the plerionic radio emission appears on our ROSAT image, but our exposure is not sufficient to establish a stringent limit on any filled-center nonthermal X-ray emission. An indistinguishable nonthermal component with spectral index -0.5 ≤ α ≤ -4 (S ∝ ν+α) could be present with a luminosity comparable to or exceeding that of the detected thermal component, particularly in light of the significant absorption that our results indicate must exist toward this distant source. A deeper X-ray exposure is required to set more meaningful limits on any plerionic X-ray emission.

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