Searching for Solar Shocks

Including a brief history of

X-ray astronomy

H. Hudson, SPRC/UCSD/ISAS

Beautiful Chandra shock(E0102-72)

How X-ray astronomy began

• September 21, 1859 (Carrington)

• Kew Gardens - magnetic effects

• The proper conservatism of L. Kelvin of Largs

Latent discoveries

• X-rays (Roentgen, 1895)

• The ionosphere (Heaviside, 1902)

• Collisionless shock waves - ?

• “Space weather” - ??

Oliver Heaviside• Maxwell’s equations

• Laplace transforms

• The Heaviside function

• Telegraph equation - Pupin Laboratory

• Heavy opposition to quaternions

• T.S. Eliot, Cats, “Journey to the Heaviside Layer”

• Not the father of X-ray astronomy (due credit to B. Rossi, of course)

• “Why should I refuse a good dinner simply because I don't understand the digestive processes involved.”

We’re in a golden era of coronal observation

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are needed to see this picture.

The dynamic corona

The boundary between Photosphere and corona

• Density plummets precipitously

• Collisionality diminishes

• Radiation decouples

• Plasma beta drops drastically

Height in corona

T

B

∞0

T.R.

Solar shock: Type II burst

A Type II burst is the same thing as a “slow drift”burst - perhaps discovered by early military radars;explained by J. P. Wild and Y. Uchida

Time

Wav

elen

gth

IIIII

(rec

all

-2 ~

ne)

Meter-waves and soft X-rays

• Megahertz vs Exahertz

• Radiative transfer vs direct view

• Magnetic effects vs Bremsstrahlung

• Inherent fuzziness vs sharp resolution

• But - by 1998, we’d seen Types I, III, IV and others

But not the simplest and most obvious: Type II!

X-ray observation of a global wave

• Wave propagation tells us about coronal structure

• The innermost (earliest) motions tell us about the flare process itself

Moreton-Ramsey waveand EIT wave

Why didn’t SXT discover “SXT waves”?

• SXT views the whole corona

• Fast-mode MHD waves must involve compressional heating

• SXT response increases monotonically with temperature

• So… why did it take 8 years and the competitive example of EIT?

Factors abetting wave detectionin soft X-rays

• The wave needn’t be shocked

• The SXT response strongly favors detection of a temperature increase (adiabatic law)

Sensitivity estimation

Ri (n,Te) =const £ n2e £ Si (Te),

@(ln(Ri ))@(ln(Te))

= ¢ i (Te) = 3 +d(ln(Si ))d(ln(Te))

,

SXT and TRACE responses

Courtesy N. V. Nitta

Factors reducing sensitivity

• Poor CCD dynamic range (AEC)

• Limited SXT telemetry(“Velocity filter”)

• Photon counting statistics

• Scattering from grazing-incidence mirror

• Flare mode

May 6, 1998

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FOV 10 arc min

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FOV 5 arc min

Gas pressure in flare loops

SOHO/ EIT

Uchida’s 1968 model

S.W.

Uchida

A.R.

OK, so what caused the wave?

• In principle we can see it all in soft X-rays

• The earliest manifestation of the wave is within 20,000 km of the flare core

• But… it is significantly displaced from the soft X-ray core of the flare

Mysteries of lowplasma

• Everything seems to expand (cf. Aly)

• The Virial Theorem looks goofy too

Implosion conjecture

• At low , the coronal energy is purely B2/8• During a flare, there’s no time for energy

transport through the photosphere

• Therefore, some field lines must shorten

Isomagnetobars

Closed field linesOpen field lines

How low-implosions must work

MHD Virial TheoremZR>R0B28ºdV=R0ZR=R018º(B2r°B2¡°B2µ°p)dV+ZR>R0[ΩGM0r°3p]dV

The end, thanks

The end, thanks