Chandra ACIS Survey of M33 (ChASeM33):: X-ray imaging spectroscopy of M33SNR 21, the brightest X-ray supernova remnant in M33

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 similar to 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 0.46(-0.02)(+0.01) with an ionization timescale of n(e)t = 2.1(-0.3)(+0.2) cm(-3) s and half-solar abundances (0. 45- (+0.12)(0.09)). 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); 10(37) ergs s(-1) ( absorbed), and (1.7 +/- 0.3) x 10(37) ergs s(-1) ( unabsorbed), in good agreement with the recent XMM- Newton determination. No significant excess hard emission was detected; the luminosity less than or similar to 1.2 x 10(35) ergs s(-1) (2-8 keV) for any hard point source.