Cliver, E W

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29th International Cosmic Ray Conference Pune (2005) 1, 5356Solar Flare Nuclear Gamma Rays and Energetic Particles in Space,1980-1989E.W. Cliver , W.T. Vestrandand D.V. Reames(a) Air Force Research Laboratory, AFRL/VSBXS, 29 Randolph Rd, Hanscom AFB, MA 01731-3010 USA(b) Los Alamos National Laboratory, NIS-2, MS D436, Los Alamos, NM 87545 USA(c) NASA Goddard Space Flight Center, Code 661, Greenbelt, MD 20771 USAPresenter: E.W. Cliver (edward.cliver@hanscom.af.mil), usa-cliver-E-abs1-sh11-posterFrom February 1980 - November 1989, 52 solar gamma-ray-line (GRL; 4-8 MeV) flares	were recordedby the Gamma Ray Spectrometer (GRS) on the Solar Maximum Mission. During the same interval, 121  10MeV solar energetic proton (SEP) events with front side flare associations were observed. In general, when aGRL flare occurred during a time that the SEP background was not already elevated due to an earlier protonevent, a new SEP event was observed near Earth (17 of 18 cases for western hemisphere flares; 29/33 overall).GRS observed the associated flare for 50 of the 121 SEP events. Of these 50 flares, 17 had detectable gamma-ray lines. Gamma-ray-fluences and SEP peak fluxes are poorly correlated; the 24 SEP events associated withwestern hemisphere flares for which only an upper limit flare GRL fluencecm could be determinedhad peak  10 MeV fluxes that spanned more than three orders of magnitude. The ratio of interacting (GRLproducing) to interplanetary protons (SEPs) is inversely proportional to flare time scale. In general, GRL flaresare more impulsive than SEP flares; the median e-folding decay times of the associated 1-8 A˚ bursts are 14minutes and 24 minutes, respectively. These results substantiate those in Cliver et al. (ApJ 343, 953, 1989),that were based in large part on GRL fluences or upper limits inferred from proxy (microwave, X-ray) data.1. IntroductionPrompt gamma-ray-line emission is formed during flares when accelerated protons bombard and excite C, N,and O nuclei in the solar atmosphere. These excited nuclei decay to their ground states by emitting 4-8 MeVgamma rays. The 4-8 MeV de-excitation lines provide direct information on the protons accelerated duringflares for comparative analysis with the solar energetic protons subsequently observed in space. We have pre-viously [1] reported a comparison of solar flare nuclear GRL fluences and the peak fluxes of associated  10MeV proton events at 1 AU for the period from February 1980 - January 1985, corresponding to the first fiveyears of the Solar Maximum Mission (SMM). We found that these two parameters were poorly correlated, pri-marily because of a subset of large SEP events for which the associated flares lacked detectable GRL emission.In addition, we noted that the ratio of interacting (gamma-ray-producing) to interplanetary  10 MeV protonsvaried with flare time scale, with the ratio decreasing with flare duration. Our earlier study was based in part onproxy gamma-ray data that we used to compensate for the  50% effective duty cycle of the Gamma Ray Spec-trometer [GRS; 2] on SMM. In a scatter plot of SEP event peak flux vs. GRL fluence of the associated flare in[1], 31 of 52 GRL fluences (or upper limits) were based on microwave or hard X-ray data. Here we extend ouranalysis through the end of the SMM lifetime in November 1989. This extended time interval includes the riseto maximum of cycle 22 and enables us to test our previous results without the use of proxy data.2. AnalysisProton data were obtained by the Goddard Space Flight Center experiments on ISEE-3 and IMP 8. Gamma raydata were taken from the SMM atlas [3]. During the  10-yr SMM lifetime, GRS observed 52	above54 E.W. Cliver, W.T. Vestrand and D.V. Reames4-8 MeV background fluctuations) GRL flares. During the same interval 121 9-12 MeV SEP events (with peakfluxes10  pr cm  s  sr  MeV  ) that could be reliably linked to solar flares were observed. In generalwhen a GRL flare occurs, it is followed by a SEP event at 1 AU. Of the 33 cases when a GRL flare occurredwhen the SEP background was not high due to a previous event (that might mask a fresh SEP injection), in29 an associated  10 MeV SEP event was observed (17 of 18 cases for western hemisphere flares). GRSobserved the associated flare for 50 of the 121 SEP events. Of these 50 flares, 17 had detectable gamma-raylines. Figure 1 contains a scatter plot of peak fluxes of all western hemisphere SEP events vs. 4-8 MeV GRLfluences, or upper limit values, for their associated disk flares. In all there are 35 such SEP events, of whichonly 11 were associated with flares with detectable GRL emission. [In some cases the GRL observations weretruncated at the beginning or the end of the event because of SMM eclipse as it orbited the Earth; we includedthese events if it appeared from the microwave burst timing that the bulk of the line emission was recorded.]In the figure it can be seen that  10 MeV SEP peak flux and the flare 4-8 MeV GRL fluence are not wellcorrelated; in particular, the SEP peak flux spans more than three orders of magnitude for the 24 source flaresfor which no GRL emission was recorded above the somewhat arbitrary background upper limit fluence of 1cm  (see [4]). Since smaller SEP events tend to be associated with shorter flares, integrating background forall upper limit cases will cause data points associated with small SEP events to shift to the left relative to thoselinked to larger SEP events. We note, however, that 12 of the 24 SEP events with upper limit GRL fluences,Figure 1. Scatter plot of peak interplanetary proton ux near 10 MeV vs. the associated are 4-8 MeV GRL uence (or anupper limit) for well-connected (W00-W90) SEP ares occurring from February 1980 to November 1989.Solar Flare Nuclear ... 55including the two largest SEP events of this group (20 July 1981 and 9 December 1981), lacked detectable 300keV emission, the nominal lower energy for gamma ray continuum. If we only consider the 10 SEP events inFigure 1 that were associated with flares withGRL emission, we obtain a correlation with r  = 0.6.As noted in [1] and evidenced in Figure 1, large SEP events, having peak  10 MeV fluxes ﬀ 10 pr cm  s sr  MeV  , can originate in solar eruptions unaccompanied by detectable GRL emission. An example of anevent of this type is shown in Figure 2. On 23 March 1989, a moderate ﬀ 300 keV gamma ray continuum burstwithout a 4-8 MeV counterpart was followed by a SEP event at 1 AU that extended to ﬀ 100 MeV.In our previous study [1], we found that the ratio of the number of interacting protons to the number of in-terplanetary protons was inversely proportional to the flare time scale ( ﬁ ) as given by the e-folding time ofthe flare 1-8 A˚ burst, measured from the peak. This analysis is repeated in Figure 3 for all events in Figure1. For the expanded data set, and without the use of proxy data, our earlier finding is confirmed. In general,SEP-associated flares have longer time scales (median ﬁ = 24 minutes) than GRL-flares ( ﬁ = 14 minutes).3. Discussion: The current flares vs. shocks debateHow to interpret these results? The lack of correlation between SEP peak flux and GRL line fluence is con-sistent with the current view [5, 6] that the bulk of the  10 MeV protons observed in space is not acceleratedin a flare but rather at a coronal/interplanetary shock. While big SEP events have been observed without de-tectable GRL emission [Figure 2], such SEP events are invariably accompanied by coronal mass ejections [7]and strong shocks [8]. The fact that nearly 90% (29/33) of GRL flares (from anywhere on the disk) werefollowed by protons at Earth admits the possibility that for some large SEP events, solar and interplanetaryprotons originate in a common acceleration process in a flare. Alternatively, this association may reflect theFigure 2. GRS X-ray/ ﬂ -ray data and GOES proton data for the 23 March 1989 SEP event.56 E.W. Cliver, W.T. Vestrand and D.V. ReamesFigure 3. Ratio of solar to interplanetary protons vs. are time scale.Big Flare Syndrome (median GRL flare 1-8 A˚ X-ray class = X2). The case for a direct flare contribution tolarge SEP events will require comparisons of GRL and SEP spectra, composition, and timing, as well as SEPcharge state measurements. The inverse correlation in Figure 3 might be due to a narrower SEP “cone of emis-sion” for more impulsive flares. However, flare time scale has also been related to e/p ratio [10, 11, 12], Fe/Oratio [13], and electron spectra [14], and its role in SEP physics remains unclear.References[1] E.W. Cliver et al., Astrophys. J. 343, 953 (1989).[2] D.J.Forrest et al., Solar Phys. 65, 15 (1980).[3] W.T. Vestrand et al., Astrophys. J. (Suppl. Ser.) 120, 409 (1999).[4] D.J. Forrest, in Positron-Electron Pairs in Astrophysics, (New York: AIP), 3 (1983).[5] D.V. Reames, Space Sci. Rev. 90, 413 (1999).[6] A.J. Tylka et al., Astrophys. J. 625, 474 (2005).[7] S.W. Kahler et al., J. Geophys. Res. 89, 9683 (1984).[8] E.W. Cliver, S.W. Kahler, and D.V. Reames, Astrophys. J. 605, 902 (2004).[9] S.W. Kahler, J. Geophys. Res. 87, 3439 (1982).[10] G.E. Kocharov, G.A. Kovaltsov, and L.G. Kocharov, Proc. 18th Int. Cosmic Ray Conf., 4, 105 (1983).[11] H.V. Cane, R.E McGuire, and T.T. von Rosenvinge, Astrophys. J. 301, 448 (1986).[12] M.B. Kallenrode, E.W. Cliver, and G. Wibberenz, Astrophys. J. 391, 370 (1992).[13] N.V. Nitta, E.W. Cliver, and A.J. Tylka, Astrophys. J. (Lett.) 586, L103 (2003).[14] D. Moses et al., Astrophys. J. 346, 523 (1989).

Solar Flare Nuclear Gamma Rays and Energetic Particles in Space, 1980-198

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