* Astronomy

Title: Chandra Discovery of an Intermediate Polar in Baade's Window
Authors: JaeSub Hong (CfA), Maureen van den Berg (CfA), Silas Lay**** (Gemini), Jonathan E. Grindlay (CfA), Ping Zhao (CfA)

We have discovered an intermediate polar (IP) in the 100 ks Chandra observation of Baade's Window (BW), a low extinction region at ~ 4 deg south of the Galactic Center. The source exhibits large X-ray modulations at a period of 1028.4 s in the 0.3 - 8 keV band. The X-ray spectral fit with a power law model shows the integrated spectrum is intrinsically hard (photon index ~ 0.44) and moderately absorbed (NH22 ~ 0.15). Quantile analysis reveals that the modulations in the X-ray flux strongly correlate with spectral changes that are dominated by varying internal absorption. The X-ray spectrum of the source is heavily absorbed (NH22 > 1) during the faint phases, while the absorption is consistent with the field value during the bright phases. These X-ray properties are typical signatures of IPs. Images taken with the IMACS camera on the Magellan 6.5m telescope show a faint (V ~ 22), relatively blue object within the 2 sigma error circle of the Chandra source. If we assume a nominal range of absolute V magnitude for a cataclysmic variable (MV ~ 5.5-10.5) and the known reddening in the region, the source would likely be at a distance of 2-10 kpc. The corresponding average Lx would be 6 x 10^{31} - 10^{33} erg s^{-1} in the 2-8 keV band. Assuming the space density of IPs follows the stellar distribution, which is highly concentrated in the Galactic Bulge, the source is probably a relatively bright IP belonging to the Galactic Bulge X-ray population, the majority of which is now believed to be magnetic cataclysmic variables.

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