Strange Galactic Supernova Remnants G 357 7 0

Strange Galactic Supernova Remnants G 357. 7 -0. 1 (the Tornado) & G 350. 1 -0. 3 in X-rays Anant Tanna Physics IV 2007 Supervisor: Prof. Bryan Gaensler

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.

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

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)

XMM-Newton • Lower spatial and spectral resolution than Chandra, but: – Three X-ray telescopes, each with a CCD camera, forming the EPIC instruments PN, MOS 1 and MOS 2. – Chandra has maximum collecting area of 800 cm 2, XMM has 4500 cm 2. • Observations: – Each camera produces an event list used to make images and extract spectra. • Spectra analysed using XSPEC.

G 350. 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.

G 350. 1 -0. 3 Spectra • Clearly thermal spectrum (right). • Spectral fit for region 1: Ar Fe – 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. Ca Mg Si S Upper (PN) spectrum has ~46000 counts. All three spectra binned at 100 counts per channel.

G 350. 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.

G 350. 1 -0. 3 Spectra • 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 ke. V (~3. 1 million K) – τ = 4. 2 x 1013 s cm-3. • Can now derive age of remnant and supernova explosion energy! (1) (2) • Distance to G 350. 1 -0. 3 is 4. 511 kpc R = 1. 3 -3. 1 pc. • Equation 1 t = 990 -2360 yr. n = 563 -1340 cm-3 n 0 = 141 -336 cm-3. • Finally, equation 2 implies that Esn is between 4. 4 x 1043 and 2. 5 x 1044 J.

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, n. H ~5. 1 x 1022 cm-2.

NEI Model and Tornado Spectrum • NEI has two very important parameters: – – Plasma temperature, Ionisation timescale Si S τ = t x n (in s cm-3) • • This spectrum gives τ < 9 x 1012 indicating the detected plasma has not equilibrated. 2 nd 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.

Conclusions G 350. 1 -0. 3 • A very bright, very young thermal SNR. • The bright point source in region 2 is a possible neutron star. The Tornado • Head is almost certainly a thermal SNR. • Tail, not detected in X -rays, requires further work to be explained. 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.