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 \sim 5 \arcsec diameter ( 20 pc at our assumed M33 distance of 817 \pm 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 with X-ray spectrum with an absorbed sedov model yields a shock temperature of 0.46 ^ { +0.01 } _ { -0.02 } \mathrm { keV } , an ionization timescale of n _ { \mathrm { e } } t = 2.1 ^ { +0.2 } _ { -0.3 } \times 10 ^ { 12 } \mathrm { cm } ^ { -3 } \mathrm { s } , and half-solar abundances ( 0.45 ^ { +0.12 } _ { -0.09 } ) .
Assuming Sedov dynamics gives an average preshock H density of 1.7 \pm 0.3 \mathrm { cm } ^ { -3 } .
The dynamical age estimate is 6500 \pm 600 \mathrm { yr } , while the best fit n _ { \mathit { e } } t value and derived n _ { \mathit { e } } gives 8200 \pm 1700 \mathrm { yr } ; the weighted mean of the age estimates is 7600 \pm 600 \mathrm { yr } .
We estimate an X-ray luminosity ( 0.25-4.5 keV ) of ( 1.2 \pm 0.2 ) \times 10 ^ { 37 } \mathrm { ergs } \mathrm { s } ^ { -1 } ( absorbed ) , and ( 1.7 \pm 0.3 ) \times 10 ^ { 37 } \mathrm { ergs } \mathrm { s } ^ { -1 } ( unabsorbed ) , in good agreement with the recent XMM-Newton determination .
No significant excess hard emission was detected ; the luminosity \leq 1.2 \times 10 ^ { 35 } \mathrm { ergs } \mathrm { s } ^ { -1 } ( 2-8 keV ) for any hard point source .