Strange Galactic Supernova Remnants

1. Strange Galactic Supernova Remnants Anant Tanna Physics IV 2007 Supervisor: Prof. Bryan Gaensler G357.7-0.1 (the Tornado) & G350.1-0.3 in X-rays

2. Supernova Remnants (SNRs) • Formed from supernova explosion (~1044 J) shockwave sweeping up interstellar medium (ISM). • Important because: • Nucleosynthesis generates the heaviest elements. • Heat up ISM, putting energy into the Galaxy. • Shocks can trigger star formation. • Accelerate cosmic rays. • Reveal structure of ISM.

3. Supernova Remnants • Common types: • Shell-like and Crab-like. • SNR has three phases: • Free expansion. • Adiabatic phase. • Radiative phase. • Eventually disperses into ISM.

4. Adiabatic Phase • Total remnant energy taken as constant. • Phase begins when hot reverse shock fills interior. • Age found from: (1) • Remnant radius determined by the cooler forward shock is given by. (2)

5. XMM-Newton • Lower spatial and spectral resolution than Chandra, but: • Three X-ray telescopes, each with a CCD camera, forming the EPIC instruments PN, MOS1 and MOS2. • Chandra has maximum collecting area of 800 cm2, XMM has 4500 cm2. • Observations: • Each camera produces an event list used to make images and extract spectra. • Spectra analysed using XSPEC.

6. G350.1-0.3 • Bright! Four regions in X-rays, but region 2 has no radio counterpart. • Is it a part of this complex object? • Spectra extraction was easy.

7. Ar Ca Fe Mg Si S G350.1-0.3 Spectra • Clearly thermal spectrum (right). • Spectral fit for region 1: • Absorbed NEI  OK. • Tested absorbed VNEI  improved fit, except for Fe line. • Added VNEI for Fe only  improved fit. • Added NEI  cooler forward shock identified and fit improved. • χ2/ν ~ 1.5. Upper (PN) spectrum has ~46000 counts. All three spectra binned at 100 counts per channel.

8. G350.1-0.3 Spectra G350.1-0.3 Spectra • Same model applied to other three regions, giving χ2/ν values of 1.2, 1.1 and 1.4 for regions 2 to 4. • Interstellar absorption agreed for regions 1, 3 and 4 at 3.6 x 1022 cm-2, but region 2 is more absorbed 4.6 x 1022 cm-2 for this model. • Region 2 spectrum (right) clearly different, but power law doesn’t fit absorbed black body gives excellent fit.

9. Plasma temperature and ionisation timescale for the reverse shock varied between regions. Plasma temperature and ionisation timescale for the forward shock agreed for regions 1, 3 and 4. Plasma temp. = 0.31 keV (~3.1 million K) τ = 4.2 x 1013 s cm-3. Can now derive age of remnant and supernova explosion energy! G350.1-0.3 Spectra G350.1-0.3 Spectra (1) (2) • Distance to G350.1-0.3 is 4.5-11 kpc  R = 1.3-3.1 pc. • Equation 1  t = 990-2360 yr.  n = 563-1340 cm-3  n0 = 141-336 cm-3. • Finally, equation 2 implies that Esn is between 4.4 x 1043 and 2.5 x 1044 J.

10. The Tornado • Faint, extended X-ray component coincident with Head. • Extracting spectra required detailed background subtraction (tedious). • Fitting spectra: • Absorbed blackbody  poor fit. • Absorbed power law  photon index of ~6. • Absorbed NEI  good fit with χ2/ν ~ 1.0. Strong absorbing column, nH ~5.1 x 1022 cm-2.

11. Si S NEI Model and Tornado Spectrum • NEI has two very important parameters: • Plasma temperature, • Ionisation timescale τ = t x n (in s cm-3) • This spectrum gives τ < 9 x 1012 indicating the detected plasma has not equilibrated. • 2nd absorbed NEI added to find cooler forward shock (ie. τ > ~9 x 1012) but was not detected (absorbed)  can’t derive Esn. This spectrum has ~1800 counts, binned at 30 counts per channel.

12. The Tornado Head is almost certainly a thermal SNR. Tail, not detected in X-rays, requires further work to be explained. G350.1-0.3 A very bright, very young thermal SNR. The bright point source in region 2 is a possible neutron star. Conclusions • These results are not just important for the ecology of the Milky Way, but suggest that: • Simple shell-like SNRs may not be the norm, and • Complex objects like these may better represent how SNRs interact with the ISM.