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Description
The authors performed a Chandra X-ray observation of the X-ray bright E2 elliptical galaxy NGC 4649 (M 60). In addition to bright diffuse emission, they resolved 165 discrete sources, most of which are presumably low-mass X-ray binaries (LMXBs). As found in previous studies, the luminosity function of the resolved sources is well-fitted by a broken power law. In NGC 4697 and NGC 1553, the break luminosity was comparable to the Eddington luminosity of a 1.4 solar mass neutron star. One possible interpretation of this result is that those sources with luminosities above the break are accreting black holes and those below are mainly accreting neutron stars. The total X-ray spectrum of the resolved sources is well fitted by a hard power law. NGC 4649 was observed on 2000 April 20 on the ACIS-S3 CCD operated at a temperature of -120 C and with a frame time of 3.2 s. In addition to the S3 chip, the ACIS chips I2, I3, S1, S2, and S4 were also turned on for the duration of the observation. Although a number of serendipitous sources were seen on the other chips, the analysis of NGC 4649 in this paper was based on data from the S3 chip alone. The total exposure for the S3 chip was 36,780 s. The discrete X-ray source population on the ACIS S3 image was determined using a wavelet detection algorithm in the 0.3 - 10.0 keV band, and they were confirmed with a local cell detection method. The authors used the CIAO, WAVDETECT, and CELLDETECT programs. The high spatial resolution of Chandra implies that the sensitivity to point sources is not affected very strongly by the background. Thus, the source detection was done using the entire exposure of 36,780 s, including periods with background flares. The wavelet source detection significance threshold was set at 10<sup>-6</sup>, which implies that less than 1 false source (due to a statistical fluctuation in the background) would be detected in the entire S3 image. This significance threshold approximately corresponds to requiring that the source flux be determined to better than 3 sigma. This table was created by the HEASARC in April 2007 based on <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/ApJ/600/729">CDS catalog J/ApJ/600/729</a> file table1.dat. This is a service provided by NASA HEASARC .
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