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D.-W. Kim, H. Ghosh, R.A. Cameron, J. Drake, N.R. Evans, P. Freeman, T.J. Gaetz, P.J. Green, R.F. Harnden, M. Karovska, V. Kashyap, P. Maksym, A. Mossman, E.M. Schlegel, J.D. Silverman, H. Tananbaum, A. Vikhlinin, B.J. Wilkes (Harvard-Smithsonian CfA), ChaMP Collaboration
We present the first results of X-ray source properties obtained with the initial sample of the Chandra Multi-wavelength Project (ChaMP). 62 observations have been uniformly analyzed by specifically developed data reduction techniques and then validated by eye-examination. We have detected ~4000 sources in 62 fields. Using ~1000 sources of good quality (ie., near on-axis and with more than 20 counts to ensure completeness), we have derived LogN-LogS. In both soft (0.5-2 keV) and hard (2-8 keV) energy bands, our results are consistent with those previously reported. In particular, our data in the hard band nicely fill the gap between the Chandra deep field and ASCA data. Taking advantage of our wide area coverage, we search for field-to-field cosmic variation which was suggested in a few fields with clusters. We have compared LogN-LogS generated separately for fields containing X-ray clusters and those without. We have also searched for possible variation in individual fields by comparing the number of detected sources to the number of expected sources based on our LogN-LogS. We do not find any statistically significant variation, either individually or between cluster and non-cluster fields. In an X-ray color-color plot, most sources fall in the region characterized by photon index = 1.5-2 and N(H) = a few \times 1020 cm-2, indicating that they are typical AGNs. Also present are a considerable number of sources with peculiar X-ray colors (eg., highly absorbed, very hard, or very soft). We have confirmed the trend that on average the X-ray color becomes harder as the count rate decreases. It appears that this is mainly because of absorption rather than intrinsic spectral hardening.
We acknowledge the financial support of NASA grant AR1-2003X (Chandra).
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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.