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J Choi, K. M. Leighly (OU), C. Matsumoto (Nagoya University)
Follow-up spectroscopy of VLA FIRST survey quasar candidates discovered the very bright quasar, PHL 1811 (z=0.192, B=14.4, R=14.1), in the South Galactic Cap; it is the second brightest quasar beyond z=0.1 after 3C 273. Strangely, this quasar was not detected in the ROSAT All Sky Survey. Follow-up BeppoSAX, then coordinated HST and Chandra observations showed that it is very X-ray weak. The inferred \alphaox from the HST and Chandra observations was -2.4 to -2.2. The X-ray spectrum was steep and the flux varied between two Chandra observations implying that the X-ray emitting region was not absorbed but rather the quasar is intrinsically X-ray weak, pointing to unusual and extreme conditions in the X-ray emitting corona.
We observed PHL 1811 with XMM-Newton on November 1, 2004. The two MOS and PN detectors yielded 1100 photons in the 0.2--5 keV band. The flux was comparable to the Chandra observations; the object is still X-ray weak. Assuming Galactic absorption column of 3.73 \times 1020\,\rm cm-2, we obtained a good fit with a power-law model. The photon index is 2.32 ±0.11, typical for a Narrow-line Seyfert 1 galaxy. The upper limit on absorption in the host galaxy is 4.6 \times 1020\, \rm cm-2 (90% confidence for one parameter of interest); there is no evidence of intrinsic absorption. We found no evidence of X-ray variability in the 30 ks observation. Using the OM UVM2 filter we found that the UV flux at 2310Å\/ is 2.52\times 10-14\,\rm erg\,cm-2\,s-1Å\/-1. This value is comparable to the flux obtained during the December 2001 HST observation.
PHL 1811 has now been observed in X-rays five times over period of 14 years. In each observation it is X-ray weak and there is no evidence for X-ray absorption. We conclude PHL 1811 is an unusual intrinsically X-ray weak quasar.
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Bulletin of the American Astronomical Society, 37 #2
© 2005. The American Astronomical Soceity.