Chapter 1 Flashcards
What gives rise to x-ray emission?
change in momentum of high energy particle excitation blackbody radiation electronic transitions non-thermal emission nuclear reactions
Where is a possible site of particle acceleration?
Supernova remnant located on the galactic disc expanding into the interstellar medium
What are cosmic ray particles made of?
Predominantly protons but include heavier stable nuclei
What happens when cosmic rays interact with the Earth’s atmosphere?
They create new particles detected by the Earth
What do the radio emissions of supernova remnants show?
They are highly polarised and their spectra are of power law form
How are supernova expansions measured?
the velocity of the expanding gas cloud using Doppler shift of spectral lines is measured
What is the first phase of the expansion of a supernova?
FREE EXPANSION
the blast wave expands into the interstellar medium and gains mass
To conserve momentum it must slow down, ending free expansions at t1 (mass swept up = ejected mass)
What is the second phase of the expansion of a supernova?
DECELERATION (Sedov-Taylor phase)
As the spherical blast wave sweeps up cold ISM, mass swept up . ejected mass and the expansion slows down
(lasts 1000 to 30,000 yrs)
What is a shock front?
The expanding SNR gas cloud enters ISM and due to the lack of time for gradual pressure readjustment, the SNR gas pushes in front of it a growing layer of compressed interstellar gas
(like a snow plough)
What does the shock front move faster than?
The expanding SN gas and leaves compressed gas behind it
What happens during the third phase of supernova expansion?
The outer edges of the remnant decelerate first so material expanding behind it start to run in to the outer shells, heating them up to 10^6K (Thermal bremsstrahlung x-rays)
This phase ends when temperature falls and ion recombination leads to significant radiative energy losses. Shell has less KE
Where do galactic radio emissions come from?
The gas, not from stars in galaxies which is evident from I(v) vs (v/MHz) graph which shows a linear relationship from 10MHz to 100MHz
What do accelerating charges lead to?
Photons being released
Loss of energy from a charge caused by a moving charge due to an accelerated charge and a pulse of radiation propagating outwards at c
Where is the maximum radio emission?
Perpendicular to the direction of acceleration
What is the frequency at which the most energy is being emitted?
The inverse of the pulse duration (1/deltat)
