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Chandra ACIS Survey of M33 (ChASeM33): X-ray Imaging and Spectroscopy of the Bright SNR M33SNR21
T.J. Gaetz, R.J. Edgar, P.P. Plucinsky, M. Sasaki (SAO), P. Ghavamian, W. P. Blair (Johns Hopkins) B. Williams (U. Washington), K.S. Long (STScI), P.F. Winkler (Middlebury College), J.P. Hughes (Rutgers) T. Pannuti (Spitzer Sci. Center), M. Avillez (U. Evora, U. Wien), D. Breitscherdt (U. Wien), and R.P. Kirshner (Harvard U.)

Introduction

M33SNR 21 Analysis
We combined the nearly on-axis and off-axis Chandra data to obtain a total of 10000 counts from the remnant. We fit with an absorbed nonequilibrium ionization model in xspec (vsedov); the resulting remnant proper ties (assuming a Sedov model) are listed in the table. The remnant is 20 pc in diameter and 6000­9000 yr old. Its likely association with the H I I region suggests that it is the remnant of a Type II explosion. The mean abundances are low, consistent with what would be expected for M33. We searched for enhanced abundances by fitting the bright eastern por tion and the faint remainder of the remnant, but did not find any significant differences in abundances.

Multiwavelength studies of nearby galaxies are effective at providing statistically interesting samples of many classes of objects. M33, a late type Sc spiral at 817 ± 58 kpc [1] (but see [2]) and relatively face on (i = 55 ± 1 , [3]) is a key galaxy for such studies. At that distance, 1 = 4pc, and at least some supernova remnants (SNRs) can be resolved. We present new X-ray data for M33SNR 21, the brightest M33 X-ray supernova remnant, obtained as par t of the ChASeM33 [4]. 200 ks of nearly on-axis data shows the remnant to be 5 in diameter, and a slightly elliptical shell which is much brighter on the eastern side than the rest of the remnant, suggestive of a strong density gradient.
M33 NGC592

M33SNR 21 Proper ties
2.68 в 2.47 10.2 в 9.5 9.85 ± 0.8 Ts 0.46 ± 0.02 ne ,s t0 (2.2 ± 0.02) в 1012 Z 0.5 vs 610 ± 10 n0 1.6 ± 0.2 t0 6500 ± 500 9100 ± 1800 MSU 240 ± 66 E0 (1.3 ± 0.4) в 1051 LX 1.05 ± 0.2) в 1037 R
s

NGC592

H [S II] [O III] KPNO

M33SNR 21

NGC592 & M33SNR 21
M33SNR 21 appears in projection against the giant H I I region NGC 592 (see figure). NGC 592 is 4 в 106 yr old [5], and dominated by a pair of bright cores. Optical emission (high [S I I]/H ratio) characteristic of SNRs was found for M33SNR 21, in addition to nonthermal radio emission [7]. Density-sensitive [S I I] line ratios show gas density ne 270 cm-3 [7], suppor ting the idea that the SNR is associated with the H I I region.
M33SNR21 Chandra 0.35-4 keV M33SNR21 Chandra 0.35-4 keV

pc pc keV cm-3 s Z km s-1 cm-3 yr yr M erg erg s-1

radii postshock temperature ionization scale abundances shock velocity preshock density expansion age ionization age swept-up mass explosion energy 0.5­5.0 keV

Discussion
M33SNR 21 appears to be interacting with denser gas on the eastern par t. This suggests comparison to the LMC remnant N23, which also shows which show strong X-ray and optical enhancements, and evidence for interacting with denser gas. N23 has diameter 16 pc, and the ambient density variation is more than a factor of 10 around the remnant [8]. The abundances of O, and Ne (possibly Mg) are enhanced in one region. Assuming a Sedov model using the long radius (12 pc) toward the low density side, they obtain n 0.25cm-3 and an age of 4600 yr. In contrast to N23 in which the bright X-ray and optical emission appear on the same side of the remnant, in M33SNR 21, the bright X-ray optical emission appears to be anticorrelated. The shor t axis of the M33SNR 21 X-ray axis runs through the brightest par t of the remnant, and the optical emission extends well beyond the X-ray rim in the southwest. The reasons for this complex mor phology are not yet clear, but may be fur ther evidence of interaction with a complex environment.
REFERENCES
[1] [2] [3] [4] [5] [6] [7] [8] Freedman, W.L., et al. 2001, ApJ, 553, 47 Bonanos et al. 2006, astroph/0606279 Zaritsky, D., et al. 1989, AJ, 97, 97 Ghavamian, P., et al. 2005, AJ, 130, 539 Sasaki, M., et al. 2006, in preparation Pellerin, A. 2006, AJ, 131, 849 Gordon, S.M., et al. 1993, ApJ, 418, 743 Hughes, J.P., et al. 2006, ApJ, 645505, L117

1/4" pixels, 3 pixel smoothing M33SNR21 KPNO

Lucy-Richardson deconvolution H [S II] [O III]

M33SNR21 H [S II] KPNO [O III]

Acknowledgments
This work was suppor ted by NASA Chandra award number G06-7073A and by NASA contract NAS8-03060.