Geminga 是一顆沒有無線電波輻射但在X射線（X-ray）和伽馬射線（γ-ray）波段有觀測到以週期0.237秒自轉的波霎（pulsar）。我們使用ASCA和XMM人造衛星取得的數據來分析Geminga 在X射線波段的週期性行為，而我們選定探討的週期範圍為0.1秒到100秒之間。在分析過程中，我們使用H-test和epoch folding方法，以每一個間格為五分之一的傅立葉寬度（Fourier width）進行搜尋。如果我們能找到不是自轉的週期，也許能暗示中子星星震的存在或是說中子星表面存在波的傳遞。經過我們對此週期範圍的徹底搜尋，並未發現任何證據能說明星震的存在。最後，依據不同的觀測資料，對可能存在於中子星表面的波而言，我們給出3 倍標準差信心水準的能量通量（flux）上限：由1994、1999年ASCA的資料，得到3.5×10^-14 erg/cm^2/sec和1.9×10^-14 erg/cm^2/sec，分別為原來星體能量通量的12.4﹪和6.9﹪。從2002年XMM的數據，我們對不同能量範圍求得7.7×10^-13 erg/cm^2/sec（0.2-0.7 keV）和1.7×10^-14 erg/cm^2/sec（0.7-5.0keV），分別為原來波霎能量通量的1.3﹪和3.3﹪。

Geminga is a radio-quiet, rotation-powered pulsar with a 237-msec period observed in X-ray and gamma-ray bands. We conduct a periodicity search with its ASCA data and XMM-Newton data in the period range of 0.1 sec to 100 sec. The H-test and the method of epoch folding are employed with period search steps at one fifth of the corresponding Fourier widths. Periods other than the already known pulsar period, if found, may indicate the phenomenon of neutron star oscillations, which in a broad sense include waves on the stellar surface. We have found no evidence for such oscillations in our search. Upper limits to the pulsed component of these possible oscillations at the 3-sigma level inferred from the 1994 and 1999 ASCA data in 0.7-5 keV are 3.5x10^-14 erg/cm^2/sec and 1.9x10^-14 erg/cm^2/sec respectively, which are 12.4\% and 6.9\% of the source flux. 3-sigma upper limits inferred from 2002 XMM-Newton data in energy bands of 0.2-0.7 and 0.7-5 keV are 7.7x10^-13 erg/cm^2/sec and 1.7x10^-14 erg/cm^2/sec, which are 1.3\% and 3.3\% of the source flux respectively.

Bertch, D. L. et al. 1992, Nature, 357, 306
Bignami, G. F., Caraveo, P. A., & Lamb, R. C. 1983, ApJ, 272, L9
Bignami, G. F., Caraveo, P. A., & Paul, J. A. 1988, A\&A, 202, L1
Bignami, G. F. et al. 1987, ApJ, 319, 358
Boriakoff, V. 1976, ApJ, 208, L43
Buccheri, R. et al. 1998, The Many Faces of Neutron stars, 525-537, Kluwer Academic Publishers.
Caraveo, P. A. et al. 1996, ApJ, 461, L91
Caraveo, P. A. et al. 2003, Science, 301, 1345
Caraveo, P. A. et al. 2004, Mem. S.A.It. Vol. 75, 470
Carroll, B. W. & Ostlie, D. A. 1996, An Introduction to Modern Astrophysics, Addison Wesley.
Cheng, K. S., Gil, J. & Zhang, L. 1998, ApJ, 493, L35
Cheng, K. S. & Zhang, L. 1999, ApJ, 515, 337
Chukwude, A. E. 2003, A&A, 406, 667
Cordes, J. M. & Greenstein, G. 1981, ApJ, 245, 1060
Crawford, F. & Demianski, M. 2003, ApJ, 595, 1052
De Jager, O.C. et al. 1989, A&A, 221,180
Dodson, R. G., McCulloch, P. M. & Lewis, D. R. 2002, ApJ, 564, L85
Fichtel, C. E. et al. 1975, ApJ, 198, 163
Goldreich, P. & Julian, W. H., 1969, ApJ, 157, 869
Halpern, J. P. & Holt, S. S., 1992, Nature, 357, 222
Halpern, J. P. & Ruderman, M., 1993, ApJ, 415, 286
Halpern, J. P. & Tytler, D. 1988, ApJ, 330, 201
Halpern, J. P. & Wang, F. Y.-H. 1997, ApJ, 477, 905
Hobbs, G. et al. 2002, Mon. Not. R. Astron. Soc. 333, L7
Jackson, M. S. et al. 2002, ApJ, 578, 935
Leahy, D. A. 1987, A&A, 180, 275
Lewis, David A., Methods of Experimental Physics, Vol. 28, 349
Lyne, A. G. & Graham-Smith, F. 1998, Pulsar Astronomy, Cambridge University Press.
Lyne, A. G., Shemar, S. L. & Graham-Smith, F. 2000, Mon. Not. R. Astron. Soc. 315, 534
Malofeev, V. M. & Malov, O. I. 1997, Nature, 389, 697
Mattox, J. R., Halpern, J. P., and Caraveo, P. A. 1998, ApJ, 493, 891
Rankin, J. M., 1986, ApJ, 301, 901
Ruderman, M. A. & Sutherland, P. G. 1975, ApJ. 196, 51
Ruderman, M. A. 1970, Nature, 225, 619
Scott, D. M., Finger, M. H., and Wilson, C. A. 2003, Mon. Not. R. Astron. Soc. 344, 412
Str?er, L. et al. 2001, A&A, 365, L18
Thompson, D. J. et al. 1977, ApJ, 213, 252
Turner, M. J. L. et al. 2001, A&A, 365, L27
Wang, F. Y.-H., Ruderman, M., Halpern, J. P. & Zhu, T. 1998, ApJ, 498, 373
Wasaburo Unno et al. 1989, Nonradial Oscillations of Stars, University of Tokyo Press.