1. RHESSI Investigations of the Neupert Effect in Solar Flares Brian R. Dennis AAS/SPD Meeting 6 June 2002

2. 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.

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

4. 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.

5. 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.

6. RHESSI/GOES Comparison

7. 10 April 2002 GOES 10 1 - 8 Å Time derivative GOES 1 - 8 Å RHESSI Light Curves 6 – 12 keV 12 – 25 keV 25 – 50 keV 50 – 100 keV

8. RHESSI Images 6 – 12 keV 25 - 50 keV 12 – 25 keV 50 – 100 keV 10 April 2002 19:02:34 – 19:03:03 UT

9. X1.5 Flare on 21 April 2002 2650 + 0043 0151 0238 GO8 5 XRA 1-8A X1.5 6.0E-01 9906

10. X1.5 Flare on 21 April 2002

11. 21 April 2002 GOES 1 - 8 Å Time derivative GOES 1 - 8 Å RHESSI Light Curves 25 – 50 keV 50 – 100 keV

12. X1.5 Flare on 21 April 2002

13. Start of X1.5 Flare on 21 April 2002 TRACE images at 195 Å, RHESSI 12 – 25 keV contours 00:42:50 – 00:43:10 UT00:48:54 – 00:49:14 UT

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

15. X1.5 Flare on 21 April 2002 TRACE 195 Å images and RHESSI contours at times of hard X-ray peaks 12-25 keV 50 – 100 keV 01:15:43 – 01:16:03 UT01:23:27 – 01:23:47 UT

16. 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