ChandraObservations of X‐Ray–weak Narrow‐Line Seyfert 1 Galaxies

We present Chandra observations of 17 optically-selected, X-ray weaknarrow-line Seyfert 1 (NLS1) galaxies. These objects were optically identifiedby Williams et al. (2002) in the Sloan Digital Sky Survey Early Data Release,but were not found in the ROSAT All-Sky Survey (RASS) despite having opticalproperties similar to RASS-detected NLS1s. All objects in this sample weredetected by Chandra and exhibit a range of 0.5-2 keV photon indicesGamma=1.1-3.4. One object was not detected in the soft band, but has a best-fitGamma=0.25 over the full 0.5-8 keV range. These photon indices extend to valuesfar below what are normally observed in NLS1s. A composite X-ray spectrum ofthe hardest objects in this sample does not show any signs of absorption,although the data do not prohibit one or two of the objects from being highlyabsorbed. We also find a strong correlation between Gamma and L_1keV; this maybe due to differences in L_bol/L_Edd among the NLS1s in this sample. Suchvariations are seemingly in conflict with the current paradigm that NLS1saccrete near the Eddington limit. Most importantly, this sample shows thatstrong, ultrasoft X-ray emission is not a universal characteristic of NLS1s; infact, a substantial number may exhibit weak and/or low-Gamma X-ray emission.Comment: Minor changes, added section on X-ray weakness. 25 pages incl. 6 figures, 3 tables, accepted to Ap