Chandra ACIS Survey of M33 (ChASeM33): X-Ray Imaging Spectroscopy of M33SNR 21, the Brightest X-Ray Supernova Remnant in M33

Abstract

We present and interpret new X-ray data for M33SNR 21, the brightest X-ray supernova remnant (SNR) in M33. The SNR is in seen projection against (and appears to be interacting with) the bright H II region NGC 592. Data for this source were obtained as part of the Chandra ACIS Survey of M33 (ChASeM33) Very Large Project. The nearly on-axis Chandra data resolve the SNR into a ~5'' diameter (20 pc at our assumed M33 distance of 817 ± 58 kpc) slightly elliptical shell. The shell is brighter in the east, which suggests that it is encountering higher density material in that direction. The optical emission is coextensive with the X-ray shell in the north, but extends well beyond the X-ray rim in the southwest. Modeling the X-ray spectrum with an absorbed sedov model yields a shock temperature of 0.46img1.gif keV, with an ionization timescale of net = 2.1img2.gif × 1012 cm-3 s and half-solar abundances (0.45img3.gif). Assuming Sedov dynamics gives an average preshock H density of 1.7 ± 0.3 cm-3. The dynamical age estimate is 6500 ± 600 yr, while the best-fit net value and derived ne gives 8200 ± 1700 yr; the weighted mean of the age estimates is 6700 ± 600 yr. We estimate an X-ray luminosity (0.25-4.5 keV) of (1.2 ± 0.2) × 1037 ergs s-1 (absorbed), and (1.7 ± 0.3) × 1037 ergs s-1 (unabsorbed), in good agreement with the recent XMM-Newton determination. No significant excess hard emission was detected; the luminosity lesssim1.2 × 1035 ergs s-1 (2-8 keV) for any hard point source.