We present a deep Chandra ACIS-I observation of the Arches and Quintuplet clusters at the Galactic Center. We detect several bright point-like sources that are clearly associated with the clusters. Some of the sources are positionally coincident with known radio sources with strong stellar winds. The sources have similar X-ray spectra, which are dominantly thermal and show an unusually strong 6...

We present results from four recent Chandra monitoring observations of the jet in 3C 273 using the ACIS detector, obtained between November 2003 and July 2004. We find that the X-ray emission comes in two components: unresolved knots that are smaller than the corresponding optically emitting knots and a broad channel that is about the same width as the optical interknot region. We compute the j...

GRO J2058+42 is a 195 s transient X-ray pulsar discovered in 1995 with BATSE. In 1996, RXTE located GRO J2058+42 to a 90% confidence error circle with a 4 radius. On 20 February 2004, the region including the error circle was observed with Chandra ACIS-I. No X-ray sources were detected within the error circle, however, 2 faint sources were detected in the ACIS-I field-of-view. We obtained optic...

The imaging atmospheric Cherenkov array H.E.S.S. recently discovered an extended source in the 0.4−10 TeV energy range, HESS J1303−631. We obtained a 5 ks observation with the ACIS-I array on the Chandra X-ray observatory that does not reveal an obvious compact or diffuse X-ray counterpart. Archival ROSAT images are also blank in this region. Although there are several radio pulsars within the ...

The excellent angular resolution, good energy resolution and broad energy band make Chandra ACIS the best instrument for studying the X-ray halos around some galactic X-ray point sources caused by the dust scattering of X-rays in the interstellar medium, but the direct images of bright sources obtained with ACIS usually suffer from severe pileup. Making use of the fact that an isotropic image c...

We present new X-ray observations of the nucleus, jet and extended emission of the nearby radio galaxy NGC 6251 using the Chandra/ACIS-S camera, together with a reanal-ysis of archival Chandra/ACIS-I and XMM-Newton/EPIC data. We find that the nuclear X-ray spectrum is well-fitted with an absorbed power-law, and that there is tentative, but not highly significant, evidence for Fe Kα emission. We...

IGR J17544-2619 belongs to a distinct group of at least seven fast X-ray transients that cannot readily be associated with nearby flare stars or pre-main sequence stars and most probably are X-ray binaries with wind accretion. Sofar, the nature of the accretor has been determined in only one case (SAX J1819.3-2525/V4641 Sgr). We carried out a 20 ks Chandra ACIS-S observation of IGR J17544-2619 ...

The goal of this study was to assess the performance characteristics of the Automated Cellular Imaging System (ACIS III) for HER2 immunohistochemical analysis. The study was performed on 187 biopsy slides from patients who underwent HER2 testing between January and February 2008. Three scoring methods by the ACIS III were compared with the manual score and fluorescence in situ hybridization (FI...

We present Chandra observations of the X–ray environment of a sample of 6 BL Lacertae objects. The improved sensitivity of the ACIS experiment allows us to separate the core X-ray emission from the contribution of diffuse emission from the host galaxy/cluster scales. Within the short (2–6 ks) ACIS exposures, we find evidence for diffuse X–ray emission in 3 sources (BL Lac, PKS 0548–322, and PKS...

On January 10 and 13, 2001, Venus was observed for the first time with an X–ray astronomy satellite. The observation, performed with the ACIS–I and LETG/ACIS–S instruments on Chandra, yielded data of high spatial, spectral, and temporal resolution. Venus is clearly detected as a half–lit crescent, with considerable brightening on the sunward limb. The morphology agrees well with that expected f...