RHESSI OBSERVATIONS OF THE 2005 JANUARY 20

SOLAR FLARE

Gerald Share1,2, Ronald Murphy2, David Smith3, Gordon Hurford4,

Allan Tylka2, and Robert Lin4

1 UMD, 2NRL,3UCSC, 4UCB

Supported by NASA SEC-GI & SR&T

SUMMARY

RHESSI has observed two distinct components of particle acceleration in the 2005 January 20th solar

flare.

There is a ‘normal’ impulsive component beginning at ~06:42 UT, peaking at ~06:47 UT,

lasting about 10 minutes, evidenced by bremsstrahlung and nuclear-line radiation

interacting at a footpoint with an ion power-law index of ~-3.

A separate component began with a sharp 1-2 min peak at ~06:46 UT, with a spectrum dominated by

pion-decay radiation; emission lasted for ~2 hours. No information as yet on how compact this

source is.

The GLE event commenced at 06:48 UT and was observed at energies >4 GeV. An ~5 min-wide

peak was observed at ~06:53 UT.

Spectral Accumulations

RHESSI observation of the 2005 January 20

SEPs

Spectrum dominated by a strong continuum (bremsstrahlung & pi-decay) extending to high

energies. Line features are relatively weak, consistent with a hard accelerated-particle

spectrum.

…. Bremsstrahlung

___ Narrow Nuclear

- - - Broad Nuclear

-decay

Calculated gamma-ray spectra vs flare-accelerated particle power-law index.

RHESSI gamma-ray time line in January 20 flare

Neutron-capture line fluxes agree with calculations for an accelerated-particle spectrum following a power-law with

index ~3.

250-500 keV 250 – 500 keV 2215-2231keV

RMC 4-9 RMC 6+9 RMC6+9

12 arcsec 35 arcsec 35 arcsec

35 arcsecond resolution cannot distinguish the footpoints

20 January 2005 06:44 - 06:56

128 x 128 arcsec

20 January 2005 06:44-06:56

TRACE 1600A at 06:52:30 UT250 – 500 keV 30, 50, 70, 90% contours 2215-2231 keV centroid 1- error circle

Comparison of Imaged and Spatially-Integrated Neutron-

Capture Line Counts

Demonstrates that particles producing a bulk of the neutron-capture line emission are primarily confined

in magnetic loops.

There appears to be a second high-energy component revealed above 10 MeV that can be fit by a pion-decay spectrum. Its time profile is

different: sharp peak and long tail. This high-energy radiation produces instrumental annihilation line radiation that contributes to

the solar flux in panel 4.

CORONAS (Kuznetsov et al. 2005/6) also observed this high-energy component with a

time profile similar to that observed by RHESSI.

0,01 0,1 1 10 10010-5

10-3

10-1

101

103

SPRN

IAIB

SONG

20 January, 2005

F, sm

-2 s

-1 MeV

-1

Eγ, MeV

06:43:30 – 06:45:10 UT

06:45:10 – 06:47:25 UT

The CORONAS spectra at the peak in the decay phase are consistent with a pion-decay origin.

Good agreement between corrected 511 keV flux and calculation for PL index =3. Nuclear-line flux appears to be produced by one population of accelerated ions interacting in a footpoint while the ‘pion’ and >20 MeV flux is dominated by a second higher-energy

particle component.

The high-energy photon emission observed by RHESSI extends up to two hours after the sharp

peak.

>20 MeV

There is weak 2.223 MeV line emission after 08:00 UT

suggesting that the high-energy emission is from ion interactions.

South Pole neutron monitor flux increased within about 2 min after high-energy gamma-ray peak. The neutron monitor and Milagro rates have relatively narrow peaks

at ~06:53 UT

Hi-E gamma peak

SUMMARY

RHESSI has observed two distinct components of particle acceleration in the 2005 January 20th solar

flare.

There is a ‘normal’ impulsive component beginning at ~06:42 UT, peaking at ~06:47 UT,

lasting about 10 minutes, evidenced by bremsstrahlung and nuclear-line radiation

interacting at a footpoint with an ion power-law index of ~-3.

A separate component began with a sharp 1-2 min peak at ~06:46 UT, with a spectrum dominated by

pion-decay radiation; emission lasted for ~2 hours. No information as yet on how compact this

source is.

The GLE event commenced at 06:48 UT and was observed at energies >4 GeV. An ~5 min-wide

peak was observed at ~06:53 UT.

Comparison of accelerated particles interacting at the Sun and observed in space (Mewaldt, priv. comm. 2005)

Total number of protons >30 MeV:

Solar flare impulsive component: (2.8 ± 0.8) x 1032

Solar flare high-energy component: 0.7 x 1032

Event integrated SEPs: 210 x 1032

Power-law spectral index:

Solar flare impulsive component: 3.0 ± 0.05

Solar flare high-energy component: <2.3

Event integrated SEPs: 2.15

Narrow peaks in the Milagro and Climax NM data (Ryan et al. 2005) appear similar to the high-energy gamma-ray peak. Does the GLE event also have an extended high-

energy component?

Extended emission > 4 GV?

The Tibet Yangbaging neutron monitor also observed such an extended tail. Could some of the counts be due to solar

neutrons?