Comparison between Microwave and Hard X-ray Spectral Indices of Temporally and Spatially Resolved Non-Thermal Sources

1
Comparison between Microwave and Hard X-ray
Spectral Indices of Temporally and Spatially
Resolved Non-Thermal Sources
Nobeyama Symposium 2004.10.26-29 Kiyosato

• Kiyohara, J., Takasaki, H., Narukage, N. (Kyoto
  Univ.), Masuda, S. (STE Lab., Nagoya Univ.),
• Nakajima, H. (NRO/NAOJ)
• Yokoyama, T. (Univ. Tokyo)

2
Introduction

• Non-thermal emission of flares are frequently
  observed simultaneously by microwave and hard
  X-rays.
• The time profiles of these frequencies are
  similar with each other. (Kundu 1961) These
  observations suggest that the electrons emitting
  microwave and HXRs belong to the same population
  in each event.
• However, it is observed that the indices of the
  power-law fit to the distribution functions in
  microwave and HXRs differ (Kundu et al 1994.
  Silva et al. 1999 Raulin et al. 1998).
• In order to study this, we analyzed simultaneous
  observations of flares by NoRH, NoRP, and
  Yohkoh/HXT. The advantage of these observations
  is that they are spatially and temporally
  resolved.

3
Data

• Instruments
• Yohkoh Hard X-ray Telescope (HXT)
• Nobeyama Radioheliograph (NoRH)
• Nobeyama Radio Polarimeters (NoRP)
• Event Selection
• gt 30 cts/s/SC in M2-band of HXT
• (source size)/(beam size) gt4 in NoRH image
• 15 events analyzed in total

4
Power-law indices

• Power-law index in HXR spectrum
• Assume the thick-target model
• Electron index dx
• Power-law index in microwave spectrum
• Observed NoRP spectrum is fitted by the
  broken-power-law model.
• Taking the intensity ratio in different frequency
  obtained by NoRH
• Only optically-thin part (high-frequency part)
• Using Dulk痴 (1985) fitting function
• Electron index dm

5
Group 1
20
HXT H-band

• 8 of 15 events
• Impulsive ( lt 10min.)
• Power-law indices have similar values at the HXR
  peak
• Spatially compact in microwave

NoRP 17GHz
600
8
dx
dm
2
0144
0152
29-Oct-2000
6
Group 2
25
HXT H-band

• 3 of 15 events
• Gradual ( gt 10 min.)
• Power-law indices show little change temporally
• Relatively large scale in microwave

3000
NoRP 35GHz
8
dx
dm
2
0320
0344
03-Apr-2001
7
Group 3
60
HXT H-band

• 4 of 15 events

1000
NoRP 17GHz
8
dx
dm
2
0538
0543
28-Nov-1998
8
2000-11-25 event
HXR
NoRH spectral index
NoRH 34GHz Intensity
Soft
Hard

• The HXR source is located at the part where the
  microwave spectrum is softer.

9
HXR vs Microwave

• The HXR sources seem to be located at the part
  where the microwave spectrum is softer in general.

10
Summary Discussion

• Power-law indices, dm and dx of electron
  distribution functions are derived from the
  microwave and hard X-rays spectra, respectively,
  in the impulsive phase of the selected events as
  functions of time and position.
• We found
• The selected events are categorized in three
  types by the temporal behavior of the delta.
• The microwave spectrum near the footpoints is
  softer than that near the looptop.
• Hard X-ray sources seem to be located at the area
  where such softer microwave spectra are seen.
• The previous studies show by using
  spatially-unresolved data that dx is generally
  larger than dm. Our findings, however, suggest
  that the previous results are because of the
  relatively weighted signal of microwave from the
  loop top which is emitted by trapped electrons.
  There still remains a possibility that the
  electron power indices have a single value from
  hard X-ray emitting energy around 100keV up to
  microwave emitting energy, which is believed to
  be gt 0.3 MeV.