XMMBSSAGN - XMM-Newton Bright Serendipitous Survey: AGN X-Ray Spectral Properties
From the individual analysis, the authors find that there seems to be an anticorrelation between the spectral index and the sources' hard X-ray luminosity, such that the average photon index for the higher luminosity sources (>1044 erg s-1) is significantly (>2 sigma) flatter than the average for the lower luminosity sources. They also find that the intrinsic column density distribution agrees with AGN unified schemes, although a number of exceptions are found (3% of the whole sample), which are much more common among optically classified type 2 AGN. The authors also find that the so-called "soft-excess", apart from the intrinsic absorption, constitutes the principal deviation from a power-law shape in AGN X-ray spectra and it clearly displays different characteristics, and likely a different origin, for unabsorbed and absorbed AGN. Regarding the shape of the average spectra, they find that it is best reproduced by a combination of an unabsorbed (absorbed) power law, a narrow Fe K-alpha emission line and a small (large) amount of reflection for unabsorbed (absorbed) sources.
The X-ray spectral properties of the AGN population in the XMM-Newton bright serendipitous survey. Corral A., Della Ceca R., Caccianiga A., Severgnini P., Brunner H., Carrera F.J., Page M.J., Schwope A.D. <Astron. Astrophys., 530, A42 (2011)> =2011A&A...530A..42C
The XMM-Newton Bright Serendipitous Survey source designation using the 'XBS' prexix (for XMM Bright Source) and the J2000.0 source coordinates, as recommended by the Dictionary of Nomenclature of Celestial Objects, viz. 'XBS JHHMMSS.s+DDMMSS'.
The Right Ascension of the X-ray source in the selected equinox. This was taken from the primary XBS paper (Della Ceca et al. 2004, A&A, 428, 383: HEASARC Browse table XMMBSS) where is was given in J2000.0 equatorial coordinates to a precision of 0.1 seconds of time.
The Declination of the X-ray source in the selected equinox. This was taken from the primary XBS paper (Della Ceca et al. 2004, A&A, 428, 383: HEASARC Browse table XMMBSS) where is was given in J2000.0 equatorial coordinates to a precision of 0.1 arcseconds.
The Galactic Longitude of the X-ray source.
The Galactic Latitude of the X-ray source.
The XMM-Newton observation identifier (ObsID) for the observation in which the source was found.
The filter for the pn camera which was in use during the observation in which the source was found: 'Thin', 'Med(ium)' or 'Thick'.
The filter for the MOS1 camera which was in use during the observation in which the source was found: 'Thin', 'Med(ium)' or 'Thick'.
The filter for the MOS2 camera which was in use during the observation in which the source was found: 'Thin', 'Med(ium)' or 'Thick'.
The Galactic column density, in H atoms cm-2, in the direction of the XMM-Newton pointing (from Dickey and Lockman 1990, ARA&A, 28, 215).
The resulting exposure time for the source, in seconds, for the pn camera after the high-background intervals were removed.
The resulting exposure time for the source, in seconds, for the MOS1 camera after the high-background intervals were removed.
The resulting exposure time for the source, in seconds, for the MOS2 camera after the high-background intervals were removed.
The total EPIC counts for the X-ray source, i.e., the sum of the available pn, MOS1 and MOS2 counts, in the 0.3 - 10.0 keV band.
The XBS sample to which the X-ray source belongs, 'BSS' or 'HBSS' or 'HBSS,BSS' (i.e., both). The XMM-Newton Bright Serendipitous Survey contains two highly overlapping, flux-limited samples in two different energy bands, namely the bright serendipitous survey sample ('BSS') and the hard bright serendipitous survey sample ('HBSS'). The source selection criteria for these samples are discussed in Della Ceca et al. (2004, A&A, 428, 383).
The simple absorbed power-law model gave a good fit for 263 of the 305 sources, but failed to reproduce the spectral shape for 41 sources. This flag parameter if set to 'p' for these latter sources, indicating a low-confidence fit for which the null hypothesis probability to distinguish between an acceptable and an unacceptable fit is <10%. The authors consider their best-fit model to be the simplest model for which this probability is >10%.
The classification (AGN, AGN1, AGN2 or BL Lac) of the source. This sample contains 305 sources that were classified as AGN based on dedicated optical spectroscopy. For 25 out of the 305 AGN, redshift and calssification information were reported for the first time in the reference paper (agn_class_flag = 'b'). 35 of these 305 sources are optically classified as 'elusive AGN' (agn_class_flag = 'e'), i.e., sources for which a classification cannot be derived solely from the optical spectroscopy, although the redshift could be measured. For these 35 sources, the type 1/2 classification was assigned on the basis of the absence/presence of a significant amount of intrinsic absorption in their X-ray spectra.
This flag parameter has the following non-blank values indicating the following notes (see agn_class parameter description for more details):
e = elusive AGN b = new optical identification
The redshift of the AGN.
The best-fit photon index (Gamma) of the X-ray spectrum of the source. As a starting point for the spectral modeling, the authors first considered a simple absorbed power-law model that took into account both the Galactic hydrogen column density along the line of sight and a possible intrinsic absorption at the source redshift (the XSPEC model: wabszwabszpo). In the X-ray spectral modeling, the authors made use of the redshifts obtained from the optical spectroscopy.
This flag parameter is set to 'f' to indicates that the value of the photon index was fixed in the spectral fit for the source. In some cases, the spectral quality did not allow the authors to constrain the power-law photon index (Gamma) and the intrinsic absorption at the same time. In other cases, the resulting photon index was ~1, much lower than the typical values for unabsorbed AGN. In those cases, the authors fixed Gamma to be 1.9, a common value for unabsorbed AGN.
This parameter is set to '<' if the corresponding parameter is an upper limit (90% confidence) rather than an actual value.
The intrinsic column density, in H atoms cm-2, derived from the best-fit spectral model.
The observed flux of the source in the 2 - 10 keV band, in erg s-1 cm-2, using the MOS2 calibration, and de-absorbed by the Galactic column density.
The intrinsic luminosity of the source in the 2 - 10 keV band, in erg s-1, using the MOS2 calibration.
The Chi-squared value of the best-fit simple absorbed power-law model for the source.
The number of degrees of freedom of the best-fit simple absorbed power-law model for the source.
The null hypothesis probability to distinguish between an acceptable and an unacceptable fit. The authors consider their best-fit model to be the simplest model for which this probability is >10%.
This parameter contains information indicating whether or not the simple absorbed power-law is considered their best-fit ('Y') or not ('N'). In the latter case, the appended number refers to the corresponding table in the reference paper in which the spectral parameters of an alternative better fit model are reported:
5 = unabsorbed AGN; 6 = black-body; 7 = ionized absorbed power law; 8 = power law plus reflected component; 9 = Leaky/Leaky+line; 10 = power law plus thermal component ; 11 = power law and absorption edges
The HEASARC Browse object classification, based on the value of the agn_class parameter.