References

 
• Bradt, H., Rotshild, R., & Swank, J. 1993, A&AS, 97, 355 NASA ADS  
• Bleach, R., Boldt, E., Holt, S., et al. 1972, ApJ, 174, 101L NASA ADS  
• Dame, T. M., Ungerechts, H., Cohen, R. S., et al. 1987, ApJ, 322, 706 NASA ADS  
• Dickey, J., & Lockman, F. 1990, ARA&A, 28, 215 NASA ADS  
• Dogiel, V., Schoenfelder, V., & Strong, A. 2002, A&A, 382, 730 NASA ADS  
• Ebisawa, K., Maeda, Y., Kaneda, H., et al. 2001, Science, 293, 1633 NASA ADS  
• Green, D. 2001, http://www.mrao.cam.ac.uk/surveys/snrs/snrs.data.html  
• Grimm, H.-J., Gilfanov, M., & Sunyaev, R. 2002, A&A, 391, 923 NASA ADS  
• Iwan, D., Marshall, F., Boldt, E., et al. 1982, ApJ, 260, 111 NASA ADS  
• Kaneda, H., Makishima, K., Yamauchi, S., et al. 1997, ApJ, 491, 638 NASA ADS  
• Koyama, K., Makishima, K., Tanaka, Y., et al. 1986a, PASJ, 38, 121 NASA ADS  
• Koyama, K., Ikeuchi, S., & Tomisaka, K. 1986b, PASJ, 38, 503 NASA ADS  
• Liu, Q. Z., van Paradijs, J., & van den Heuvel, E. P. J. 2000, A&AS, 147, 25 NASA ADS  
• Lui, Q. Z., van Paradijs, J., & van den Heuvel, E. P. J. 2001, A&A, 368, 1021 NASA ADS  
• Markevitch, M., Sunyaev, R., & Pavlinsky, M. 1993, Nature, 364, 40 NASA ADS  
• Skibo, J., Johnson, W., Kurfess, J., et al. 1997, ApJ, 483, 95L  
• Sugizaki, M., Mitsuda, K., Kaneda, H., et al. 2001, ApJS, 134, 77 NASA ADS  
• Tanaka, Y., Miyaji, T., & Hasinger, G. 1999, Astron. Nahr., 320, 181 NASA ADS  
• Tanaka, Y. 2000, PASJ, 52, 25L NASA ADS  
• Tanuma, S., Yokoyama, T., Kudoh, T., et al. 1999, PASJ, 51, 161 NASA ADS  
• Townes, C. 1989, in IAU Symp., 136  
• Ueda, Y., Takahashi, T., Inoue, H., et al. 1999, ApJ, 518, 656 NASA ADS  
• Valinia, A., & Marshall, F. 1998, ApJ, 505, 134 NASA ADS  
• Voges, W., Aschenbach, B., Boller, Th., et al. 1999, A&A, 349, 389 NASA ADS  
• Warwick, R., Turner, M., Watson, M., et al. 1985, Nature, 317, 218 NASA ADS  
• Wood, K. S., Meekins, J. F., Yentis, D. J., et al. 1984, ApJS, 56, 507 NASA ADS  
• Worrall, D., Marshall, F., Boldt, E., et al. 1982, ApJ, 255, 111 NASA ADS  
• Yamasaki, N., Ohashi, T., Takahara, F., et al. 1997, ApJ, 481, 821 NASA ADS  
• Yamauchi, S., & Koyama, K. 1993, ApJ, 404, 620 NASA ADS

• If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
• You can define your own OpenURL resolver with your EDPS Account. In this case your choice will be given priority over that of your library.
• You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.