J/ApJ/773/92 XMM survey of soft background. III. Galactic halo (Henley+, 2013)
An XMM-Newton survey of the soft X-ray background.
III. The Galactic halo X-ray emission.
Henley D.B., Shelton R.L.
<Astrophys. J., 773, 92 (2013)>
=2013ApJ...773...92H 2013ApJ...773...92H
ADC_Keywords: X-ray sources ; Interstellar medium ; Surveys
Keywords: Galaxy: halo; ISM: structure; X-rays: diffuse background; X-rays: ISM
Abstract:
We present measurements of the Galactic halo's X-ray emission for 110
XMM-Newton sight lines selected to minimize contamination from solar
wind charge exchange emission. We detect emission from few million
degree gas on ∼4/5 of our sight lines. The temperature is fairly
uniform (median = 2.22x106K, interquartile range = 0.63x106K),
while the emission measure and intrinsic 0.5-2.0keV surface brightness
vary by over an order of magnitude (~(0.4-7)x10-3cm-6pc and
~(0.5-7)x10-12erg/cm2/s deg-2, respectively, with median
detections of 1.9x10-3cm-6pc and 1.5x10-12erg/cm2/s deg-2,
respectively). The high-latitude sky contains a patchy distribution of
few million degree gas. This gas exhibits a general increase in
emission measure toward the inner Galaxy in the southern Galactic
hemisphere. However, there is no tendency for our observed emission
measures to decrease with increasing Galactic latitude, contrary to
what is expected for a disk-like halo morphology. The measured
temperatures, brightnesses, and spatial distributions of the gas can
be used to place constraints on models for the dominant heating
sources of the halo. We provide some discussion of such heating
sources, but defer comparisons between the observations and detailed
models to a later paper.
Description:
The observations that we analyze here are a subset of those analyzed
by HS12 (Henley+, 2012, J/ApJS/202/14), who extracted ∼0.1-1keV
diffuse soft X-ray background (SXRB) OVII and OVIII intensities from
1880 archival XMM-Newton observations spread across the sky.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 173 164 Observation details and spectral fit results
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See also:
B/xmm : XMM-Newton Observation Log (XMM-Newton Science Operation Center, 2012)
IX/41 : XMM-Newton Serendipitous Source Catalogue 2XMMi-DR3 (XMM-SSC, 2010)
VIII/76 : Leiden/Argentine/Bonn (LAB) Survey of Galactic HI (Kalberla+ 2005)
VI/62 : Photoelectric absorption cross-sections (Balucinska-Church+, 1992)
J/ApJS/202/14 : Diffuse OVII and OVIII emission from XMM (II) (Henley+, 2012)
J/ApJS/187/388 : A XMM-Newton survey of the SXRB (I) (Henley+, 2010)
J/A+A/493/339 : XMM-Newton serendipitous Survey. V. (Watson+, 2009)
J/A+A/393/425 : Spectral analysis of Lockman Hole (Mainieri+, 2002)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 6 F6.2 --- Seq [1/110] Sight line identification number (1)
8- 10 A3 --- f_Seq Flag(s) about sight line (2)
12- 21 I010 --- ObsID ? XMM-Newton observation ID (3)
23- 46 A24 --- Name Target name (4)
48- 54 F7.3 deg GLON Galactic longitude (XMM pointing direction)
56- 62 F7.3 deg GLAT Galactic latitude (XMM pointing direction)
64- 67 F4.1 ks Exp1 [5/91]? Usable MOS1 exposure time (5)
69- 71 I3 arcmin2 O1 ? Solid angle of the MOS1 detector (6)
73- 76 F4.1 ks Exp2 [5.2/91]? Usable MOS2 exposure time (5)
78- 80 I3 arcmin2 O2 ? Solid angle of the MOS2 detector (6)
82- 84 I3 ct/s/arcmin2 F/g [304/898]? R12 count rate (7)
86- 90 F5.3 10+20cm-2 NHI [0.6/5.8]? Hydrogen column density (8)
92- 95 F4.2 10+6K T [1.4/4.1]? Best-fit halo temperature (9)
96 A1 --- f_T [c] c: Temperature held fixed during
fitting (see Section 3.1.2)
98-101 F4.2 10+6K E_T [0.05/8.2]? 90% confidence statistical
upper error
103-106 F4.2 10+6K e_T ? 90% confidence statistical lower error
108-112 F5.2 10+6K EsT [0.05/12.3]? Systematic positive error (10)
114-117 F4.2 10+6K esT [0.05/0.8]? Systematic negative error (10)
119-122 F4.2 10-3/cm6.pc EM [0/6.8]? Emission measure (9)
124-128 F5.2 10-3/cm6.pc E_EM [0.1/31.3]? 90% confidence statistical
upper error
130-133 F4.2 10-3/cm6.pc e_EM ? 90% confidence statistical lower error
135-138 F4.2 10-3/cm6.pc EsEM [0/1.6]? Systematic positive error (10)
140-143 F4.2 10-3/cm6.pc esEM ? Systematic negative error (10)
145-151 F7.2 --- chi2 [104.5/2449]? χ2
153-156 I4 --- dof [104/3320]? Degrees of freedom
158 A1 --- l_S0.5-2 Limit flag on S0.5-2
160-163 F4.2 fW/m2/deg2 S0.5-2 [0.3/7.3]? Intrinsic 0.5-2keV surface
brightness of the halo
in 10-12erg/cm2/s/deg2 (11)
165-168 F4.2 fW/m2/deg2 E_S0.5-2 [0.1/9]? Positive error on S0.5-2 (12)
170-173 F4.2 fW/m2/deg2 e_S0.5-2 [0.1/2]? Negative error on S0.5-2 (12)
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Note (1): Our set of 163 observations includes a cluster of 28 observations near
(l,b)~(326°,-58°). These observations represent 27 different
sight lines, which we have numbered 103.1-103.27 (sight line 103.8
consists of two observations). In order to avoid oversampling this
region of the sky in our subsequent analysis, we treat these 27 sight
lines as a single sight line, whose halo temperature and emission
measure are found from the weighted means of the halo temperatures and
emission measures of the individual sight lines. We tabulate these
mean values as the results for sight line 103.
After grouping together observations of the same sight line, and
combining the results from sight lines 103.1 through 103.27, our set
of 163 observations yields 110 measurements of the halo's temperature
and emission measure. The locations of our sight lines on the sky are
shown in Figure 4.
Note (2): Flag as follows:
a = 10-6counts/s/arcmin2
b = 10-12erg/cm2/s/deg2
d = For these sight lines, the exclusion regions used to excise bright and/or
extended sources are different from those used in HS12 (see Section 2.2).
e = This sight line was analyzed with a 2T model (see Section 3.1.2). The
table contains the results for the cooler component. The parameters for
the hotter component are: T=(11.3+0.6-0.4 +0.4-0.3)x106K,
EM=(2.8+0.4-0.3 +0.6-0.3)x10-3cm-6pc.
f = The temperature and emission measure for this sight line are the weighted
means of the values for sight lines 103.1-103.27. The errors were
calculated using the combined statistical and systematic errors from the
individual sight lines' measurements. The surface brightness was
calculated using the mean temperature and emission measure, with the error
on the surface brightness derived from the error on the emission measure.
Note (3): Note that for some sight lines there is more than one XMM-Newton
observation.
Note (4): Name of the original target, in general taken from the FITS file
header. If the target name was abbreviated or truncated, we attempted
to get the full target name from SIMBAD. If the original target was
a bright X-ray source, it was excised from the data, in order for us
to measure the diffuse SXRB emission in the XMM-Newton field of view
(see Section 2.2).
Note (5): The usable MOS1/MOS2 exposure, after the exclusion of times affected
by soft proton flaring and times of high solar wind proton flux.
Note (6): The solid angle of the MOS1/MOS2 detector from which the SXRB spectrum
was extracted, after the exclusion of sources and unusable CCDs.
Note (7): The R12 count rate used to fix the normalization of the foreground
component of the spectral model (using data from Snowden et al.
2000ApJS..128..171S 2000ApJS..128..171S; see Section 3.1.1).
Note (8): The HI column density for the pointing direction (Kalberla et al.
2005, VIII/76).
Note (9): The best-fit halo temperature and emission measure
(EM=∫(n2edl)) for a 1T halo model.
Note (10): The estimated systematic error due to our assumed foreground and
extragalactic models (see Section 3.2).
Note (11): The intrinsic 0.5-2.0keV surface brightness of the halo, calculated
using the best-fit 1T model parameters.
Note (12): The error on the surface brightness is derived from the error on the
emission measure (the statistical and systematic errors have been
added in quadrature).
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History:
From electronic version of the journal
References:
Henley & Shelton. Paper I. 2010ApJS..187..388H 2010ApJS..187..388H Cat. J/ApJS/187/388
Henley & Shelton. Paper II. 2012ApJS..202...14H 2012ApJS..202...14H Cat. J/ApJS/202/14
(End) Emmanuelle Perret [CDS] 23-Feb-2015