Strange Galactic Supernova Remnants

G357.7-0.1 (the Tornado) & G350.1-0.3 in X-rays

Anant TannaPhysics 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:

• 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 cm2, XMM has 4500 cm2.

• 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:

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.

• 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.

G350.1-0.3 Spectra

Mg Si

S

ArCa

Fe

Upper (PN) spectrum has ~46000 counts. All three spectra binned at 100 counts per channel.

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.

G350.1-0.3 Spectra

G350.1-0.3 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 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

(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.

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.

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.

Si S

This spectrum has ~1800 counts, binned at 30 counts per channel.

ConclusionsThe 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.

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.