RHESSI Investigations of the Neupert Effect in Solar Flares

Brian R. Dennis

AAS/SPD Meeting

6 June 2002

The Neupert Effect

• The time integral of the hard X-ray emission closely matches the temporal variation of the soft X-ray emission.

• Implies that accelerated electrons that produce the hard X-rays also heat the plasma that produces the soft X-rays.

SXR:HXR Ratio vs. Flare SizeA. Veronig et al. A&A, in press (2002)

RHESSI Contribution

• RHESSI observes both the soft X-rays (down to ~3 keV) and the hard X-rays with the same detectors.

• RHESSI also provides 2 arcsecond imaging capability in both soft and hard X-rays.

• RHESSI’s temporal resolution for images is 2 s for a complete set of spatial Fourier components.

• The spatially integrated time resolution is limited only by counting statistics.

RHESSI’s Limitations

• Suffers pulse pile up when the rates exceed ~10,000 counts per detector per second.

• Shutters moved into FOV when dead time reaches ~10%. Limits lower energy response below ~10 keV.

• K-escape photons contaminate low energy counts with higher energy emission.

RHESSI/GOES Comparison

10 April 2002

GOES 10 1 - 8 Å

Time derivative GOES 1 - 8 Å

RHESSI Light Curves6 – 12 keV12 – 25 keV25 – 50 keV50 – 100 keV

RHESSI Images

6 – 12 keV

25 - 50 keV

12 – 25 keV

50 – 100 keV

10 April 200219:02:34 – 19:03:03 UT

X1.5 Flare on 21 April 20022650 + 0043 0151 0238 GO8 5 XRA 1-8A X1.5 6.0E-01 9906

X1.5 Flare on 21 April 2002

21 April 2002

GOES 1 - 8 Å

Time derivative GOES 1 - 8 Å

RHESSI Light Curves25 – 50 keV50 – 100 keV

X1.5 Flare on 21 April 2002

Start of X1.5 Flare on 21 April 2002TRACE images at 195 Å, RHESSI 12 – 25 keV contours

00:42:50 – 00:43:10 UT 00:48:54 – 00:49:14 UT

Start of X1.5 Flare on 21 April 2002TRACE images at 195 Å, RHESSI 12 – 25 keV contours

X1.5 Flare on 21 April 2002TRACE 195Å images and RHESSI contours at times of hard X-ray peaks

12-25 keV 50 – 100 keV

01:15:43 – 01:16:03 UT 01:23:27 – 01:23:47 UT

Conclusions

• Neupert Effect is alive and well.

• Fraction of flare energy in accelerated electrons– Increases with flare size on average– Decreases with time during 21 April X flare

• Additional heating mechanism is required