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

Supernova Remnants (SNRs) Formed from supernova explosion (~10 44 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: Remnant radius determined by the cooler forward shock is given by. (1) (2)

XMM-Newton –Three X-ray telescopes, each with a CCD camera, forming the EPIC instruments PN, MOS1 and MOS2. –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. Lower spatial and spectral resolution than Chandra, but:

G 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.

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. –χ 2 / ν ~ 1.5. G Spectra Mg Si S Ar Ca Fe Upper (PN) spectrum has ~46000 counts. All three spectra binned at 100 counts per channel.

G Spectra Same model applied to other three regions, giving χ 2 / 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 cm -2, but region 2 is more absorbed 4.6 x cm -2 for this model. Region 2 spectrum (right) clearly different, but power law doesn’t fit  absorbed black body gives excellent fit. G 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 keV (~3.1 million K) –τ = 4.2 x s cm -3. Can now derive age of remnant and supernova explosion energy! G Spectra (1) (2) Distance to G is kpc  R = pc. Equation 1  t = yr.  n = cm -3  n 0 = cm -3. Finally, equation 2 implies that E sn is between 4.4 x and 2.5 x 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 χ 2 / ν ~ 1.0. Strong absorbing column, n H ~5.1 x cm -2.

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 indicating the detected plasma has not equilibrated. 2 nd absorbed NEI added to find cooler forward shock (ie. τ > ~9 x ) but was not detected (absorbed)  can’t derive E sn. Si S This spectrum has ~1800 counts, binned at 30 counts per channel.

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