High energy solar neutron and gamma ray emissions from the Sun: from first ground level event to CORONAS-F indications

S.N. Kuznetsov (1), K. Kudela (2)

1 Skobeltsyn Institute of Nuclear Physics, Moscow State University,Moscow, Russia

2 Institute of Experimental Physics, Slovak Academy of Sciences, Watsonova 47, 04001, Kosice, Slovakia (kkudela@kosice.upjs.sk)

COST 724, Sofia, Bulgaria, May 22, 2007

Abstract.

A short review of earlier observations of high energy neutrons and gamma rays from the Sun on satellites and on the ground, with specific emphasis on contribution of IEP SAS Košice to that study is presented.

Second part illustrates measurements of solar gamma rays and neutrons on russian satellite CORONAS-F during period August 2001 – December 2005. High energy neutral emissions from the Sun in four solar flares, namely August 25, 2001, October 28, 2003, November 4, 2003 and January 20, 2005 are discussed.

1. Introduction. Short survey of earlier observations. IEP SAS contribution to the study. Ground based. a. Before June 3, 1982.

First detection of solar neutron signal at Earth’s orbit proposed long time ago in the paper (Bierman et al. 1953) was done on June 21, 1980 [(Chupp et al. 1982). Before that the presence of neutrons at the sites of solar flares was reported by the observation of 2.23 MeV neutron capture gamma-ray line (Chupp et al. 1973). Basic considerations about production of solar neutrons are e.g. in papers (Lingenfelter and Ramaty, 1967).

b. Event June 3, 1982. The solar neutron response, observed for the first time at the surface of Earth, was reported from NM at Jungfraujoch with 1min time resolution (Debrunner et al, 1983) in time coincidence with gamma ray spectrometer on SMM which recorded an extremely intense ray line flare with the onset at ~1140 UT with the the counting rates at the high energy channels remained high, which is characteristic for a flux of high energy solar neutrons at the satellite (Chupp, personnal communication, 1982).

Lomnický Štít 5 min counting rate. Although LŠ NM had at that time only 5 min resolution, its measurement (883 g.cm-2, excess 2.7±0.3 % in 1145-1150 UT, Efimov et al, 1983) confirmed clearly, with relatively high statistical accuracy, the increase at Jungfraujoch (745 g.cm-2, excess 3.9±0.6 %). The increase from the same event was reported in the data of Rome NM (Iucci et al. 1984). Protons produced by the decay of solar neutrons were reported from the same flare also by the satellite measurements (Evenson et al, 1983).

Balloons and satellites.

Gamma and hard X ray from the Sun was measured earlier on satellites e.g. OSO-7, SMM, CGRO, YOHKOH, GAMMA, GRANAT and others (e.g. Chupp et al, 1982; 1993 and references therein). At present hard electromagnetic spectral range is observed on satellites by RHESSI (Lin et al. 2002; Smith et al. 2002 and other) and INTEGRAL.

IEP. Started from balloon experiment (Dubinský et al, 1977), continued on low altitude polar orbiting satellite IK-17. Pulse shape discrimination separating the responses from neutrons and gamma rays (Michaeli et al, 1983; Gusev et al, 1989) was used with detector systém described in paper (Efimov et al. 1983). Although no solar neutrons were observed during the IK-17 mission, profile of albedo neutrons and gamma rays 1-30 MeV was obtained (Dubinský et al. 1982).

Continuation at CORONAS-I launched in Russia in March 1994. SONG (SOlar Neutron and Gamma) decsribed in paper (Baláž et al, 1994), a joint experiment SINP MSU and IEP SAS. CsI(Tl) crystal with anticoincidence shielding. Gamma 0.1-100 MeV and neutrons 1-60 MeV have been detected. Detailed maps of -ray flux were obtained and two components (1) that due to interactions of primary CR with residual atmosphere and (2) due to bremsstrahlung by high energy magnetospheric electrons, were identified (Bučík et al, 2000).

2. SONG experiment on CORONAS-F satellite.

CORONAS-F launched on July 31, 2001, in Russia: 50721 km, i=82.5o, T=94.5 min. Oriented towards the Sun. One of the instruments of SKL (or SCR, Solar Cosmic Rays) coordinated by SINP MSU is SONG, an improved version of SONG on CORONAS-I (description in paper Kuznetsov et al, 1995), joint SINP MSU and IEP SAS.

Review plots – light curves of counting rate of different energy channels are at http://space.saske.sk/projects/songm/data.php?lang=1

CsI(Tl) in active plastic shielding.

Hard X and 0.03 - 200 MeV (12 energy channel analyzer, S = 270 cm2), n 3 – 100 MeV (PSD of n/, S = 38 cm2), e ( 5 channels 8 – 100 MeV, S = 620 cm2), high energies (p > 75 MeV + e > 55 MeV; p 100 – 200 MeV). Aug. 2001 – Dec. 2005. More details in (Kuznetsov et al, 2003a,b, 2004).

Capable to observe hard X and of solar origin outside the radiation belts or not shadowed by Earth. The background is due to local -ray (interactions of CR with instrument, satellite body, atmosphere).

Increases due to bremstrahlung by relativistic electrons of radiation belts are skipped from the flare emission analysis. Evolution of the energy thresholds during the flight.

SONG on CORONAS-F

3. Solar flare measurements by SONG on CORONAS-F.Table. Solar gamma-ray flares detected by SONG (CORONAS-F) from August, 2001 to September, 2005 with observed emissions above 6 MeV

N Datedd/mm/yy

UT of flare according SXR data (GOES), hh:mm

SXR class GOES

Flare coordinates

AR UT of flare according HXR SONG data , hh:mm

Emax (channel) SONG, MeV

Gamma fluencies (>500 keV сm-2)

1 25/08/01 16:23-16:45-17:04 X5.3 S17E34 9591 16:29-16:39 60-100 7150

2 11/12/01 07:58-08:14-08:08 X2.8 N16E41 9733 08:04-08:08 7-15 78

3 20/05/02 15:21-15:27-15:31 X2.1 S21E65 9961 15:25-15:29 7.7-16.5 87

4 28/10/03 09:51-11:10-11:24 Х17.2 S16E08 0486 11:02-11:13 150-300 >9200

5 29/10/03 20:37-20:49-21:01 X10.0 S15W02 0486 20:40-20:55 6-10 1270

6 04/11/03 19:29-19:53-20:06 X28 S19W83 0486 19:40-19:57 150-300 >8100

7 20/01/05 06:36-07:01-07:26 X7.1 N14W61 0720 09:44-09:56 90-150 3620

Event on August 25, 2001.

Gamma rays up to > 60 MeV well above the background. Before launch of HESSI. The event is not accompanied by any significant charged particle flux.

SONG, August 25, 2001. The index of power law spectra in energy at time of maximum flux ~ -2.8±0.1.

The event as one with highest energy emission of clear signal in n channels detected in coincidence with the ground based observations by neutron monitor in proper local time (Watanabe et al, 2003).

Event on October 28, 2003

Counting rate of rays at various energy channels by SONG during the solar flare on October 28, 2003. Time in seconds.The units in #/(cm2.s.MeV).

Hard energy spectra after 600 s

SONG on CORONAS-F observed increase on n channels 15 – 100 MeV above the background from ~ 1104 UT on October 28, 2003 (lower panel). The time coincidence with the onset on Tsumeb station (upper panel, copied from Watanabe et al, 2006) is seen. The onset on Lomnický Štít is few minutes after that on Tsumeb and it corresponds to high energy protons.

Event on November 4, 2003.

According to Watanabe et al (2006) the largest flux of high energy n from flares in 23rd cycle was on November 4, 2003. SONG on CORONAS-F observed - ray increase up to 60 – 100 MeV above the background. Also n signal was seen clearly.

Different n, profile.

Difference in NM profiles at different local times

Event on January 20, 2005.

SONG observed high-energy -ray emission attributed to º decay implying ion acceleration up to 200 MeV. Evolution of energy spectra in time.

Summary.

SONG on CORONAS-F observed -ray >6 MeV in 7 solar flares from August 2001 – September 2005. The most intensive flares were observed on August 25, 2001, October 28, and November 4, 2003 (at least up to 60 MeV, n channels 15-100 MeV).

SONG extends the spectra to high energies, in addition to RHESSI and INTEGRAL.

Increases at n channels for 3 events are accompanied by simultaneous NM increases in the proper local time confirming solar n events reported by (Watanabe et al, 2005).

In addition to space probe and satellite studies, continuous measurements on the ground, especially at high mountains are important for understanding the solar n spectra at high energies. New solar n detector described in papers (Tsuchiya et al, 2001; Flückiger et al, 2001) is valuable to measure energy of incident n and their arrival direction. In cycle 23 there were observed 16 remarkable solar n events by the worldwide network of solar n telescopes and NMs (Flückiger et al, 2005). Also the new ground based detectors as described recently e.g. by (Chilingaryan et al, 2007) may improve the knowledge about solar n production near the Sun.

Acknowledgement.

This work was supported by the Slovak Research and Development Agency under the contract No. APVV-51-053805

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