strange galactic supernova remnants
DESCRIPTION
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. Supernova Remnants (SNRs). Formed from supernova explosion (~10 44 J) shockwave sweeping up interstellar medium (ISM). Important because: - PowerPoint PPT PresentationTRANSCRIPT
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.