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D.-W. Kim, R. A. Cameron, J.J. Drake, N. Evans, P. Freeman, T.J. Gaetz, H. Ghosh, P.J. Green, F.R. Harnden, Jr., M. Karovska, V. Kashyap, P. Maksym, E.M. Schlegel, J.D. Silverman, H. Tananbaum, A. Vikhlinin, B. Wilkes (Harvard-Smithsonian CfA), ChaMP Collaboration
We present the first results of X-ray source properties obtained with the initial ChaMP (Chandra Multi-Wavelength Project) sample of 62 observations which have been uniformly reduced and analyzed with techniques specifically developed for the ChaMP and then validated by visual examination. Utilizing only good quality data (~700 sources out of ~4500 sources) with more than 20 counts in each energy band and off-axis distance < 400" (to avoid problems caused by incompleteness and the Eddington bias), we derive preliminary Log(N)-Log(S) relation in the soft (0.5-2 keV) and hard (2-8 keV) energy bands. The ChaMP data are consistent with previous results of ROSAT, ASCA and Chandra deep fields. In particular, our data nicely fill in the gap seen in the hard band between the Chandra deep field data and the previous ASCA data. We test whether there is any systematic difference in the source density in cluster and non-cluster fields and for field-to-field cosmic variation, both of which have been previously reported. We found no significant difference in either test within the statistics and flux level given by our sample. Also our data suggest a trend that on average the X-ray color hardens as the count rate decreases. However, since the hardening is confined to the softest X-ray color (0.3-0.9 keV), we conclude it is most likely due to absorption.
We gratefully acknowledge the financial support of NASA grant: AR1-2003X (Chandra).
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Bulletin of the American Astronomical Society,
© 2003. The American Astronomical Soceity.