2004/02/29 by Rik J. Williams, Smita Mathur, Richard W. Pogge · 4 citations
Physics and Astronomy · #Active galactic nucleus #Astronomical Objects #Astronomy and Astrophysical Research #Astrophysical Phenomena and Observations #Galaxies: Formation, Evolution, Phenomena #Galaxy #Photon #ROSAT #Range (aeronautics) #Sample (material) #Sky #astro-ph
paper · pdf · doi:10.1086/421768
published as Astrophys.J. 610 (2004) 737-744 · Minor changes, added section on X-ray weakness. 25 pages incl. 6 figures, 3 tables, accepted to ApJ
arxiv created 2004/04/22 · openalex publication_date 2004/07/22 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We present Chandra observations of 17 optically selected, X-ray-weak narrow-line Seyfert 1 (NLS1) galaxies. These objects were optically identified by Williams et al. in the Sloan Digital Sky Survey Early Data Release but were not found in the ROSAT All-Sky Survey (RASS) despite having optical properties similar to RASS-detected NLS1s. All objects in this sample were detected by Chandra and exhibit a range of 0.5-2 keV photon indices Γ = 1.1-3.4. One object was not detected in the soft band but has a best-fit Γ = 0.25 over the full 0.5-8 keV range. These photon indices extend to values far below those normally observed in NLS1s. A composite X-ray spectrum of the 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 highly absorbed. We also find a strong correlation between Γ and L 1 keV ; this may be due to differences in L bol / L Edd among the NLS1s in this sample. Such variations are seemingly in conflict with the current paradigm that NLS1s accrete near the Eddington limit. Most importantly, this sample shows that strong, ultrasoft X-ray emission is not a universal characteristic of NLS1s; in fact, a substantial number may exhibit weak and/or low-Γ X-ray emission.