J/ApJ/766/14 Deep Chandra bulge field X-ray point sources (Morihana+, 2013)
X-ray point-source populations constituting the Galactic Ridge X-ray emission.
Morihana K., Tsujimoto M., Yoshida T., Ebisawa K.
<Astrophys. J., 766, 14 (2013)>
=2013ApJ...766...14M 2013ApJ...766...14M
ADC_Keywords: Galactic plane ; X-ray sources
Keywords: Galaxy: bulge; Galaxy: disk; X-rays: diffuse background
Abstract:
Apparently diffuse X-ray emission has been known to exist along the
central quarter of the Galactic Plane since the beginning of X-ray
astronomy; this is referred to as the Galactic Ridge X-ray emission
(GRXE). Recent deep X-ray observations have shown that numerous X-ray
point sources account for a large fraction of the GRXE in the hard
band (2-8keV). However, the nature of these sources is poorly
understood. Using the deepest X-ray observations made in the Chandra
bulge field, we present the result of a coherent photometric and
spectroscopic analysis of individual X-ray point sources for the
purpose of constraining their nature and deriving their fractional
contributions to the hard-band continuum and Fe K line emission of the
GRXE. Based on the X-ray color-color diagram, we divided the point
sources into three groups: A (hard), B (soft and broad spectrum), and
C (soft and peaked spectrum). The group A sources are further
decomposed spectrally into thermal and non-thermal sources with
different fractions in different flux ranges. From their X-ray
properties, we speculate that the group A non-thermal sources are
mostly active galactic nuclei and the thermal sources are mostly white
dwarf (WD) binaries such as magnetic and non-magnetic cataclysmic
variables (CVs), pre-CVs, and symbiotic stars, whereas the group B and
C sources are X-ray active stars in flares and quiescence,
respectively. In the log N-log S curve of the 2-8 keV band, the group
A non-thermal sources are dominant above ~10-14erg/cm2/s,
which is gradually taken over by Galactic sources in the fainter flux
ranges. The Fe Kα emission is mostly from the group A thermal
(WD binaries) and the group B (X-ray active stars) sources.
Description:
We retrieved 10 archived data of the Chandra bulge field (CBF) taken
with the Advanced CCD Imaging Spectrometer-I (ACIS-I; 0.5-8.0keV
energy band with a spectral resolution of ∼280eV for the full width at
half-maximum at 5.9keV) array on board Chandra. The observations were
carried out from 2008 May to August with a total exposure time of
∼900ks.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 128 2002 Chandra catalog: basic source properties
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See also:
B/chandra : The Chandra Archive Log (CXC, 1999-2014)
J/ApJS/210/18 : X-ray survey of the Galactic Bulge (CXOGBS) (Jonker+, 2014)
J/ApJS/194/18 : The Galactic Bulge Survey: X-ray observations (Jonker+, 2011)
J/ApJ/700/1702 : ChaMPlane deep galactic bulge survey. I. (van den Berg+, 2009)
J/ApJ/685/463 : ChaMPlane X-ray sources in the Galactic bulge (Koenig+, 2008)
J/A+A/468/353 : XMM-Newton Extended Survey of Taurus (Guedel+, 2007)
J/A+A/451/457 : X-ray properties of AGN in CDFS (Tozzi+, 2006)
J/ApJ/635/214 : Chandra X-ray sources and NIR identifications (Ebisawa+, 2005)
J/MNRAS/351/31 : XMM-Newton Galactic Plane Survey (XGPS) (Hands+, 2004)
J/ApJS/134/77 : ASCA Galactic Plane Survey X-ray sources (Sugizak+, 2001)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 4 I4 --- Seq [1/2002] Sequence number; sorted by RA
6- 23 A18 --- CXOU IAU designation (HHMMSS.ss+DDMMSS.s; J2000)
25- 34 F10.6 deg RAdeg [267.68/268.03] Right Ascension (J2000)
36- 45 F10.6 deg DEdeg [-29.74/-29.44] Declination (J2000)
47- 49 F3.1 arcsec ePos [0/0.5] Positional uncertainty
51- 54 F4.1 arcmin theta Off-axis angle θ
56- 61 F6.1 ct Cnet [5/6441] Estimated net 0.5-8 keV counts
63- 66 F4.1 ct e_Cnet [3/83] Uncertainty in CNet
68- 72 F5.1 ct Cbkg [1/503] Background 0.5-8 keV counts
74- 79 F6.1 ct Chard [0/4337] Estimated net hard 2-8 keV counts
81- 84 F4.2 --- PSF [0/1] Fraction of PSF in extraction region (1)
86- 89 F4.1 --- Sig [1/78] Photometric significance
91 A1 --- l_Pb [<] Limit flag on Pb
92- 95 F4.1 [-] Pb [-5/-2] Log probability of background only (2)
97 A1 --- f_Pb [g] Source anomalies (3)
99 A1 --- Var [a-c] Variability characterization (4)
101-105 F5.1 ks Exp [169/892] Effective exposure time (5)
107-109 F3.1 keV Emed [0.8/5.1] Background-corrected median photon
energy
111-117 E7.1 mW/m2 Fx Photometric 0.5-8 keV flux estimate; erg/s/cm2
119-123 F5.2 [-] q1 The q1 quantile value (hardness) (6)
125-128 F4.2 --- q2 The q2 quantile value (concentration) (6)
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Note (1): (at 1.497keV) enclosed within the extraction region. A reduced
PSF fraction (significantly below 90%) may indicate that the source is
in a crowded region.
Note (2): Probability that the extracted counts (0.5-8.0keV) are solely
from background.
Note (3):
g = fractional time that source was on a detector (FRACEXPO from mkarf)
is <0.9.
Note (4): Based on K-S statistic (0.5-8.0keV). Variability as follows:
a = no evidence for variability (0.05<PKS);
b = possibly variable (0.005<PKS<0.05);
c = definitely variable (PKS<0.005). No value is reported for sources
in chip gaps or on field edges.
Note (5): Approximate time the source would have to be observed on-axis to
obtain the reported number of counts.
Note (6): parameters indicating the spectral shape of each source.
If Ex represents the energy below which x% of photons reside in the
energy-sorted event list (percentile), we define (section 4.1.1):
Qx = (Ex-Emin)/(Emax-Emin) (Emin=0.5keV, Emax=8keV)
q1 = log10(Q50/(1-Q50))
which is >0 for hard X-ray, <0 for soft X-ray
q2 = 3Q25/Q75
indicates the degree of photon spectrum concentration:
q2>1 is less concentrated (broad spectrum),
q2<1 is more concentrated (narrow spectrum).
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 07-Nov-2014