Abstract
Near solar maximum, hard X-ray microflares with peak 20 keV fluxes of ≳10−2 (cm2 s keV)−1, more than ten times smaller than for typical flares and subflares, can occur at the rate of about once every five minutes. We report here on a search for hard X-ray microflares made on a long duration balloon flight in February 1987 near solar minimum, at a time when no active regions were on the Sun. No microflares were observed over a total observing time of 16.5 hours spread over three days, implying a statistical upper limit to their rate of occurrence about a factor often lower than observed near solar maximum. Thus hard X-ray microflaring appears to be an active region phenomenon, and apparently not associated with flaring of soft X-ray bright points.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
References
Datlowe, D. W., Elcan, M. J., and Hudson, H. S.: 1974, Solar Phys. 39, 155.
Davis, J. M.: 1983, Solar Phys. 88, 337.
Davis, J. M., Golub, L., and Krieger, A. S.: 1977, Astrophys. J. 214, L141.
Dennis, B. R.: 1985, Solar Phys. 100, 465.
Dennis, B. R., Orwig, L. E., Kiplinger, A. L., Schwartz, R. A., Gibson, B. R., Kennard, G. S., Tolbert, A. K., Biesacker, D. A., Labow, G. J., and Shaver, A.: 1988, NASA Technical Memorandum 4036.
Duijveman, A., Hoyng, P., and Machado, M. E.: 1982, Solar Phys. 81, 137.
Golub, L., Davis, J. M., and Krieger, A. S.: 1979, Astrophys. J. 229, L145.
Golub, L., Krieger, A. S., Silk, J. K., Timothy, A. F., and Vaiana, G. S.: 1974, Astrophys. J. 189, L93.
Golub, L., Maxson, C., Rosner, R., Serio, R., and Vaiana, G. S.: 1980, Astrophys. J. 238, 343.
Kane, S. R., Crannell, C. J., Datlowe, D., Feldman, U., Gabriel, A., Hudson, H. S., Kundu, M. R., Matzler, C., Neidig, D., Petrosian, V., and Sheeley, N. R., Jr.: 1980, in P. A. Sturrock (ed.), Solar Flares, Associated UniversityPress, Boulder, Colorado, p. 187.
Kundu, M. R., Gergely, T. E., and Golub, L.: 1980, Astrophys. J. 236, L87.
Lally, V.: 1982, Proc. XXIV COSPAR Conf., Ottawa I, p. 1.4.
Lin, R. P. and Hudson, H. S.: 1971, Solar Phys. 17, 412.
Lin, R. P. and Hudson, H. S.: 1976, Solar Phys. 50, 153.
Lin, R. P., Schwarz, R. A., Pelling, R. M., and Hurley, K. C.: 1981, Astrophys. J. 251, L109.
Lin, R. P., Schwartz, R. A., Kane, S. R., Pelling, R. M., and Hurley, K. C.: 1984, Astrophys. J. 283, 421.
Lin, R. P., Curtis, D. W., Primbsch, J. H., Harvey, P. R., Levedahl, W. K., Smith, D. M., Pelling, R. M., Duttweiler, F., and Hurley, K.: 1987, Solar Phys. 113, 333.
Matteson, J. L., Nolan, P. L., Paciesas, W. S., and Pelling, R. M.: 1977, Space Sci. Instr. 3, 491.
Moore, R. L., Tang, F., Bohlin, J. D., and Golub, L.: 1977, Astrophys. J. 218, 286.
Nitta, N. and Kundu, M. R.: 1988, Solar Phys. 117, 37.
Parker, E. N.: 1983a, Astrophys. J. 264, 635.
Parker, E. N.: 1983b, Astrophys. J. 264, 642.
Porter, J. G., Moore, R. L., Reichmann, E. J., Engvold, O., and Harvey, K. L.: 1987, Astrophys. J. 323, 380.
Rosner, R., Tucker, W. H., and Vaiana, G. S.: 1978, Astrophys. J. 220, 643.
Rosner, R., Golub, L., Coppi, B., and Vaiana, G. S.: 1978, Astrophys. J. 222, 317.
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Lin, R.P., Hurley, K.C., Smith, D.M. et al. A search for hard X-ray microflares near solar minimum. Sol Phys 135, 57–64 (1991). https://doi.org/10.1007/BF00146698
Received:
Issue Date:
DOI: https://doi.org/10.1007/BF00146698