J/MNRAS/308/233 RIXOS source sample X-ray spectra (Mittaz+, 1999)
X-ray spectra of the RIXOS source sample.
Mittaz J.P.D., Carrera F.J., Romero-Colmenero E., Mason K.O., Hasinger G.,
McMahon R., Andernach H., Bower R., Burgos-Martin J., Gonzalez-serrano J.I.,
Wonnacott D.
<Mon. Not. R. Astron. Soc. 308, 233 (1999)>
=1999MNRAS.308..233M 1999MNRAS.308..233M
ADC_Keywords: X-ray sources ; Redshifts
Keywords: surveys - galaxies: active - quasars: general - X-rays: galaxies -
X-rays: stars
Abstract:
We present results of an extensive study of the X-ray spectral
properties of sources detected in the RIXOS survey, which is a large,
nearly complete sample of objects detected serendipitously in ROSAT
PSPC fields down to a flux limit of 3x10-14erg/cm2/s (0.5-2keV).
We show that for X-ray surveys containing sources with low count rate,
such as RIXOS, spectral slopes estimated using simple hardness ratios
in the ROSAT band can be biased. Instead, we analyse three-colour
X-ray data using statistical techniques appropriate to the Poisson
regime which remove the effects of this bias. We also show that the
use of three-colour data enables some discrimination between thermal
and non-thermal spectra. We have then applied this technique to the
RIXOS survey to study the spectral properties of the sample.
For the AGN we find an average energy index of 1.05±0.05, with no
evidence for spectral evolution with redshift. Individual AGN are
shown to have a range of properties, including soft X-ray excesses and
intrinsic absorption. Narrow-emission-line galaxies (NLLGs) also seem
to fit to a power-law spectrum, which may indicate a non-thermal
origin for their X-ray emission. We infer that most of the clusters in
the sample have a bremsstrahlung temperature >3keV, although some
show evidence for a cooling flow. The stars deviate strongly from a
power-law model but fit to a thermal model. Finally, we have analysed
the whole RIXOS sample (extending the flux cut-off to the sensitivity
threshold of each individual observation) containing 1762 sources to
study the relationship between spectral slope and flux. We find that
the mean spectral slope of the sources hardens at lower fluxes, in
agreement with results from other samples. However, a study of the
individual sources demonstrates that the majority have relatively soft
spectra even at faint flux levels, and the hardening of the mean is
caused by the appearance of a population of very hard sources at the
lowest fluxes. This has implications for the nature of the soft X-ray
background.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 127 391 Table of X-ray data for the RIXOS sample
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See also:
J/MNRAS/311/456 : RIXOS source catalogue (Mason+, 2000)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- FID [110/305] Field identification number (1)
5- 7 I3 --- SRC Source identification number in
the field (1)
9- 13 F5.2 10+20cm-2 NH Hydrogen column density
15- 22 A8 "DD/MM/YY" Obs Observation date
24- 28 F5.2 ks Exp Exposure time of the field in ks.
30- 33 F4.2 arcmin Rad [0.3/0.9] Extraction radius for the
source counts
35- 40 F6.2 10-17W/m2 Fx0 Original flux (0.5-2keV), assuming an
absorbed power law of slope 1 (in units
of (10-14erg/cm2/s)
42- 45 I4 ct C1 Extracted total counts in band S1 (2)
47- 49 I3 ct C2 Extracted total counts in band H1 (2)
51- 54 I4 ct C3 Extracted total counts in band H2 (2)
56- 61 F6.2 ct B1 Estimated background counts within the
extraction circle for band S1 (2)
63- 67 F5.2 ct B2 Estimated background counts within the
extraction circle for band H1 (2)
69- 73 F5.2 ct B3 Estimated background counts within the
extraction circle for band H2 (2)
75- 80 F6.3 --- alpha Marginalized power-law slope α1D
82- 85 F4.2 --- E_alpha Error in alpha (upper limit)
87- 90 F4.2 --- e_alpha Error in alpha (lower limit)
92- 98 F7.3 0.1/keV/m2/s Norm2 Normalization of the best fit N2D
(in units of 10-5photon/keV/cm2/s)
99-103 F5.2 --- alpha2 Best-fitting slope α2D
105-110 F6.2 10-17W/m2 Fx2 Flux (0.5-2keV) determined from the
best-fitting data (2D) (10-14erg/cm2/s)
112-115 F4.2 10-17W/m2 e_Fx2 rms uncertainty on Fx2
117 A1 --- u_Type Uncertainty flag on Type
118-121 A4 --- Type Object type (3)
122 A1 --- u_z Uncertainty flag on z
123-127 F5.3 --- z ? Redshift (if applicable)
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Note (1): See Mason et al., 2000, Cat. J/MNRAS/311/456 for details.
'RIXOS FID-SRC' in Simbad.
Note (2): Band characteristics:
S1 = channels 8-41 (∼0.1-0.4keV)
H1 = channels 52-90 (∼0.5-0.9keV)
H2 = channels 91-201 (∼0.9-2.0keV)
Note (3): the types are:
AGN = Active Galaxy Nucleus
CLUS = Cluster of galaxies
DME = dMe star
GAL = galaxy
MERG = merging galaxies
NELG = emission-line galaxy
STAR = star
UNKN = unknown
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History:
* 27-Apr-2000: Prepared via OCR at CDS.
* 21-Nov-2013: OCR errors detected by H.Andernach and fixed for
sources 212-6, 217-5, 213-522, 257-28 and 266-20.
(End) James Marcout, Patricia Bauer [CDS] 27-Apr-2000