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?