Relationship between plasma temperature and HXR intensity from INTEGRAL

Transcription

1 Relationship between plasma temperature and HXR intensity from INTEGRAL Alexei Struminsky and Ivan Zimovets Space Research Institute, Moscow, Russia RHESSI workshop, Genova, September 4, 09

2 INTRODUCTION What is a nature of flare plasma heating? Are accelerated electrons one of the main sources of heating? If the electron acceleration occurs during some time interval and the flare plasma heating is a process with negligible inertion, then a relation between the instant energy of electrons (HXR intensity) and the thermal plasma energy (SXR intensity) should exist. We observed this relation during pre-flare and impulsive phases of the 06 December 6 solar flare. Moreover the electron acceleration and plasma heating was a system with positive feed back.this relation was destroyed after the electrons density reached values of about 9 cm -3 due to plasma expansion and heating. Discussing a relation between thermal (SXR) and non-thermal emission it is general referring to the Neupert effect (1968), but the Neupert effect is not valid for more than 50% of gradual flares (see Veronig et al., 05 and references therein).

3 INSTRUMENTS AND METHODS The Anti-coincidence system of the Spectrometer on INTEGRAL () records primary and secondary gamma rays with energies >0 kev (the HXR intensity) with high statistical accuracy ( orbit period 72 hours, more than 85% of the orbit are out of the radiation belts). Solar radio data are from (ftp://ftp.ngdc.noaa.gov/stp/solar_data/solar_radio/). The lowest frequency available is 245 MHz. It is generated by non-thermal electrons propagating in plasma with electron density of ~ -9 cm -3 at heights of ~ 4-5 км. The temperature of flare plasma was estimated from 3 sec data of GOES-11 ( using the standard GOES Solar Soft Ware package. The onset of a microwave burst at 15.4 GHz from the tables of NOAA solar events was assumed as a zero time (i.e. appearance of ~ MeV electrons).

4 Plasma temperature and HXR intensity 24 temperature Temperature, 6 К count rate, Temperature, 6 К temperature 00 0 count rate, min since 1838 UT, 06/12/ min since 1838 UT, 06/12/06

5 The pre-flare phase HXR increase started 5 min before the SXR onset, close to the temperature minimum. Electrons were accelerated before the GOES onset and possibly were a trigger of the event. The temperature increase started at -8 min, but a balance between electron acceleration and plasma heating was observed during [-4,+4] min. The temperature is proportional to the HXR intensity. Temperature, 6 К temperature count rate, min since 1838 UT, 06/12/06

6 The impulsive phase Temperature, 6 К temperature 245 МГц count rate, 00 0 The temperature is proportional to the logarithm of HXR intensity with delay of 0.4 min. This relation is destroyed after 18:46 UT (+8 min ). Sharp peaks of radio emission at 245 МГц possibly indicates density in the interaction region and beginning of new physical processes! Plasma cooling is more effective than heating! min since 1838 UT, 06/12/06

7 & RHESSI The RHESSIsensitivity within kev is not enough for pre-flare phase measurements. Similar rise of count rates of >150 kev ( ) and 6-12 kev (RHESSI) till +4 min, a discrepancy is observed later, when the spectrum becomes harder. Relative intensity of non-thermal 6-12 kev photons is lower in the impulsive phase due to harder spectrum in comparison with preflare phase. count rate, 00 0 >150 kev RHESSI, 6-12 kev count rate, RHESSI RHESSI, kev min since 1838 UT, 06/12/06

8 RHESSI spectra

9 DISCUSSION Temperature, 6 K Temperature 6-12 kev kev 245 MHz min since 0023 UT, 23/07/ count rate, RHESSI The normalized temperature curve is above the RHESSI 6-12 kev time profile (semi-logarithmic scale) at 00:27 00:31 UT (from +4 till +8 мин). Heating conditions are different in the pre-flare and impulsive phases for changing spectra of non-thermal electrons (the first phase transition?). Conditions of heating and electron acceleration have changed next time after 00:29 UT(the second phase transition?) observations of resonance peaks at 245 MHz (+6 min). The CME lift-off occurred at 00:27 UT ± 2 min (Riener et al., 07) ending of the impusive phase and beginning of the posteruptive phase.

10 DISCUSSION The pre-flare phase was not observed by. The RHESSI observations started only at :35 UT, so we do not have any information on non-thermal emission of lower energies and, therefore, on nature of heating till this moment. The impulsive phase started close to zero time. The temperature was proportional to the logarithm of HXR intensity with delay of 0.4 min during the interval [+1, +2] min. The resonance peak at 245 MHz was observed at :27:30 UT (+2.5 min) A separation of heating and acceleration processes started much more earlier than in the events of 02 July 23 and 06 December 6. Temperature, 6 K Temperature 245 MHz min since 25 UT, 05/12/06 0 counts,

11 DISCUSSION RHESSI, 6-12 kev counts, 0 temperature, out of scale counts, RHESSI RHESSI, kev min since :25 UT, 05/12/06

12 CONCLUSIONS Several acceleration episodes of particle acceleration and plasma heating occurred during pre-flare, impulsive and post-eruptive phases of the 06 December 6 event. The plasma temperature was proportional to the logarithm of HXR intensity ( count rate, >150 kev) with 0.4 min time delay during the impulsive phase. This dependence corresponds to the linear proportionality of the temperature to the HXR intensity for small values of time and temperature that has been observed during the pre-flare phase. Non-thermal electrons were the main source of plasma heating during the pre-flare and impulsive phases, moreover particle acceleration and plasma heating were a system with positive feed back. This proportionality was destroyed, when the plasma density in the interaction region reached values of about 9 cm -3, when considerable electron fluxes were not able to heat expanding plasma. These conclusions are applicable to the impulsive phase of the 06 December 5 event as well as the pre-flare and impulsive phases of the 02 July 23 event.