Supernova Remnants in the ChASeM33 X-ray Survey of

M33Knox S. Long, William P. Blair, P. Frank Winkler,

and the ChASeM33 team

• SNRs in nearby galaxies identified primarily from [SII]:Ha ratios > 0.4. HII regions ~ 0.1

• Before this work, ~100 optical SNRs in M33• 98 from [S II]: Ha imagery (Gordon et al 1998)• 53 have radio fluxes (Gordon et al 1999)

• Before Chandra and XMM, few SNRs detected in X-rays outside Galaxy and MCs. In M33:• 10 counterparts with ROSAT (Long et al.1996) • 22 with Chandra (Ghavamian et al. 2005)• 12 (+13 candidates) with XMM (Misanovic et al 2006)

Background X-ray H [S II] v

ChASeM33

Basics ACIS-I 7 bore sight pointings totaling 1.4Ms Minimum depth of ~ 200 ksec, 400

ksec typical.

Highlights 662 point sources Two eclipsing binaries Unusual giant HII region IC 133

dominated by non-thermal emission

Sensitive to SNRs At M33, 20 pc = 5” LX > ~2 1034 erg s-1.”

H images of Southern Arm

Optical SNRs in M33’s southern spiral arm on Chandra image

Imaging of Bright SNRs

Spectroscopy of Bright SNRs

• 7 SNRs with enough counts for spectral analysis

• M33 SNR 21 is ISM- dominated expanding into dense molecular cloud (Gaetz et al 2007)

• M33 SNR 31 has a spectrum resembling the core-collapse object E0102 in the SMC

Finding X-ray SNRs

• Approach – Use optical SNRs as the starting point• 137 optical SNR and SNR candidates after our re-inspection of the available

interference imaging (LGGS and new Schmidt images• Want accurate fluxes, but the basic difficulties are:

• Many point sources need to be excluded from background regions• Chandra point source response function varies across field

• Solution - Use Patrick Broos’ AcisExtract S/W • The Procedure

• Pass 1 - Carry out standard extraction treating all as point sources• Expanding point source region files of SNRs to account for SNR size• Pass 2 – Re-process the SNRs only• Check and repeat Pass 2 as necessary

X-ray H [S II] v

Finding X-ray SNRs - Results

• 82 of 137 SNRs > 2

• 61 (of 96) GKL SNRs

• 21 other SNR candidates also detected

• Chance probability low

SNRs have soft X-ray spectra

S=0.35-1.2 keV, M=1.2-2.6 keV; Total=0.35-8 keV

Luminosity Function

Mostly Middle-Aged SNRs

• Median diameters

• All= 44 pc• Detected = 38

(32) pc; • Undetected =

54 pc

Sample, >2 , >3

Simple Interpretation

• Middle age SNRs dominate detections (and sample)

• Lx at a single diameter is highly variable

• Very large objects are always faint

• 60%is detected; 40% is not

• Lx ~ n2 R3

• (0.35-2 keV) • ~ constant for kT>0.3 keV• drops rapidly for kT<0.3 keV

• T inversely proportional to M• M(Mo) = 83 T(keV)-1 E51

• Implications • Small diameter objects are faint• Large diameter( Rmax ~ n1/3) are faint• Lx of intermediate diameter objects

strongly dependent on density (n2)

Just the Facts It’s the environment, stupid!

Would your favorite SNR have been detected?

At the distance of M33, we should have detected• Most of the bright SNRs in the Galaxy and Magellanic Clouds• Most historical SNe - the Crab Nebula, Tycho, Cas A, & Kepler

Radio: No objects as bright as Crab; one possible PWN, coincident with slightly extended, non-thermal radio source

X-ray: No bright sources (>4 1035 erg s-1) that are thermal except stars or known SNRs

Are X-ray properties correlated with other properties?

• Extreme X-ray SNRs are extreme in most respects• High Lx objects tend to

be high LH objects• High Lx objects are

generally to be radio detected

• Converse is often not true• High LH objects often not

X-ray detected• High radio flux objects

often not X-ray detected

The M33 SNR sample

Summary

• ChASeM33 enabled the sensitive study of SNRs in M33 we had hoped• Individual SNRs can be studied

• The sample of SNRs brighter than LX ~4 1035 ergs s-1 is complete

• X-ray SNRs in M33 with LX> 2 1034 ergs s-1 now total 82• Given that many SNRs are near the luminosity limit, a

factor of 2 or 3 in sensitivity would likely reveal the rest.• There are large variations of properties at a given

size.• Need to understand local environment to extract class

properties of SNRs