J/ApJ/766/88 Chandra observations of X-ray binaries in Cen A (Burke+, 2013)
Spectral properties of X-ray binaries in Centaurus A.
Burke M.J., Raychaudhury S., Kraft R.P., Maccarone T.J., Brassington N.J.,
Hardcastle M.J., Kainulainen J., Woodley K.A., Goodger J.L., Sivakoff G.R.,
Forman W.R., Jones C., Murray S.S., Birkinshaw M., Croston J.H.,
Evans D.A., Gilfanov M., Jordan A., Sarazin C.L., Voss R., Worrall D.M.,
Zhang Z.
<Astrophys. J., 766, 88 (2013)>
=2013ApJ...766...88B 2013ApJ...766...88B
ADC_Keywords: Binaries, X-ray ; Galaxies, nearby
Keywords: black hole physics; galaxies: elliptical and lenticular, cD;
galaxies: individual (Centaurus A, NGC 5128);
X-rays: binaries; X-rays: galaxies
Abstract:
We present a spectral investigation of X-ray binaries (XBs) in
NGC 5128 (Cen A), using six 100ks Chandra observations taken over two
months in 2007. We divide our sample into thermally and non-thermally
dominated states based on the behavior of the fitted absorption column
NH, and present the spectral parameters of sources with
Lx≳2x1037erg/s. The majority of sources are consistent with being
neutron star low-mass X-ray binaries (NS LMXBs) and we identify three
transient black hole (BH) LMXB candidates coincident with the dust
lane, which is the remnant of a small late-type galaxy. Our results
also provide tentative support for the apparent "gap" in the mass
distribution of compact objects between ∼2-5M☉. We propose that
BH LMXBs are preferentially found in the dust lane, and suggest this
is because of the younger stellar population. The majority (∼70%-80%)
of potential Roche lobe filling donors in the Cen A halo are ≳12Gyr
old, while BH LMXBs require donors ≳1M☉ to produce the observed
peak luminosities. This requirement for more massive donors may also
explain recent results that claim a steepening of the X-ray luminosity
function with age at Lx≥5x1038erg/s for the XB population of
early-type galaxies; for older stellar populations, there are fewer
stars ≳1M☉, which are required to form the more luminous
sources.
Description:
Six 100ks Chandra observations (ObsID 7797, 7798, 7799, 7800, 8449 and
8490) of NGC 5128 were taken as part of the Cen A Very Large Project
(VLP) spanning the course of two months in 2007 (Jordan et al.
2007ApJ...671L.117J 2007ApJ...671L.117J).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 178 61 Basic Source Properties
table2.dat 201 53 Cen A Sources: Spectral fitting and State
Identification
table3.dat 80 41 Spectral fits using inferred dominant model
(0.5-8.0keV)
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See also:
B/chandra : The Chandra Archive Log (CXC, 1999-2014)
J/AJ/143/84 : New candidate globular clusters in NGC 5128 (Harris+, 2012)
J/A+A/533/A33 : LMXBs detected in nearby galaxies (Zhang+, 2011)
J/ApJS/192/10 : Chandra ACIS survey in 383 nearby galaxies. I. (Liu, 2011)
J/MNRAS/401/1965 : Globular clusters in M104 (Harris+, 2010)
J/ApJ/682/199 : Globulars with X-ray sources in NGC 5128 (Woodley+, 2008)
J/ApJ/654/186 : VI photometry of Cepheids in NGC 5128 (Ferrarese+, 2007)
J/A+A/447/71 : CHANDRA X-ray point sources in Cen A (NGC 5128) (Voss+, 2006)
J/ApJ/602/231 : Chandra X-ray point sources in nearby galaxies (Colbert+, 2004)
J/ApJ/600/716 : NGC 5128 Chandra X-ray point sources (Minniti+, 2004)
J/ApJ/560/675 : Chandra X-ray point sources in Cen A (Kraft+, 2001)
http://cxc.harvard.edu/ : Chandra X-Ray Observatory (CXC) home page
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 3 A3 --- ID Source identifier (S1 to S61)
5- 6 I2 h RAh [13] Hour of Right Ascension (J2000)
8- 9 I2 min RAm [25] Minute of Right Ascension (J2000)
11- 15 F5.2 s RAs Second of Right Ascension (J2000)
17 A1 --- DE- [-] Sign of the Declination (J2000)
18- 19 I2 deg DEd [42/43] Degree of Declination (J2000)
21- 22 I2 arcmin DEm Arcminute of Declination (J2000)
24- 27 F4.1 arcsec DEs Arcsecond of Declination (J2000)
29- 32 I4 ct C7797 ? Net 0.5-8 keV counts in ObsID 7797
34- 36 I3 ct e_C7797 ? Lower uncertainty limit on C7797
38- 40 I3 ct E_C7797 ? Upper uncertainty limit on C7797
42- 44 A3 --- f_C7797 Flag on C7797 (1)
46- 49 I4 ct C7798 ? Net 0.5-8 keV counts in ObsID 7798
51- 53 I3 ct e_C7798 ? Lower uncertainty limit on C7798
55- 57 I3 ct E_C7798 ? Upper uncertainty limit on C7798
59- 61 A3 --- f_C7798 Flag on C7798 (1)
63- 66 I4 ct C7799 ? Net 0.5-8 keV counts in ObsID 7799
68- 70 I3 ct e_C7799 ? Lower uncertainty limit on C7799
72- 74 I3 ct E_C7799 ? Upper uncertainty limit on C7799
76- 78 A3 --- f_C7799 Flag on C7799 (1)
80- 83 I4 ct C7800 ? Net 0.5-8 keV counts in ObsID 7800
85- 87 I3 ct e_C7800 ? Lower uncertainty limit on C7800
89- 91 I3 ct E_C7800 ? Upper uncertainty limit on C7800
93- 94 A2 --- f_C7800 Flag on C7800 (1)
96- 99 I4 ct C8449 Net 0.5-8 keV counts in ObsID 8449
101-103 I3 ct e_C8449 ? Lower uncertainty limit on C8449
105-107 I3 ct E_C8449 ? Upper uncertainty limit on C8449
109-110 A2 --- f_C8449 Flag on C8449 (1)
112-115 I4 ct C8490 Net 0.5-8 keV counts in ObsID 8490
117-119 I3 ct e_C8490 Lower uncertainty limit on C8490
121-123 I3 ct E_C8490 Upper uncertainty limit on C8490
125-126 I2 --- G-Lm Intra-observational variability (G-Lmax)
128-137 A10 --- Type Source classification (2)
140 A1 --- n_ID Additional flag (1)
142-178 A37 --- Note Additional notes (GC coincident numbers from
Woodley+, 2008, J/ApJ/682/199)
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Note (1): Note as follows:
N = Within 20" of the Cen A nucleus;
R = Source is coincident with read-out streak;
C = Source is coincident with chip-edge;
FoV = Source is outside of the field-of-view;
SC = Source confused;
GC = Coincident with globular cluster;
D = Coincident with dust lane;
NA = Not applicable.
Note (2): Classification as follows:
AGN = active galactic nucleus
BHC = black hole candidate
NSC = neutron star candidate
FG = foreground star
P = persistent
T- = transient
β NSC = S48 as a highly-magnetised neutron star candidate (β)
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 3 A3 --- ID Source identifier
5- 33 A29 --- ObsID Observation identifier(s)
35- 38 F4.2 10+22/cm2 NHPO Hydrogen column density of absorbed power
law model
41- 44 F4.2 10+22/cm2 e_NHPO Lower limit uncertainty in NHPO (1)
46- 49 F4.2 10+22/cm2 E_NHPO Upper limit uncertainty in NHPO (1)
51- 54 F4.2 --- SpIPO Spectral index of absorbed power law model
ΓPO
56- 59 F4.2 --- e_SpIPO Lower limit uncertainty in SpIPO (1)
61- 64 F4.2 --- E_SpIPO Upper limit uncertainty in SpIPO (1)
66- 71 F6.2 10+30W LxPO1 Minimal absorbed power law model 0.5-10keV
luminosity (in 1037erg/s)
73- 78 F6.2 10+30W e_LxPO1 Lower limit uncertainty in LxPO1 (1)
80- 85 F6.2 10+30W E_LxPO1 Upper limit uncertainty in LxPO1 (1)
87- 92 F6.2 10+30W LxPO2 ? Maximal absorbed power law model 0.5-10
keV luminosity (in 1037erg/s)
94- 98 F5.2 10+30W e_LxPO2 ? Lower limit uncertainty in LxPO2 (1)
100-105 F6.2 10+30W E_LxPO2 ? Upper limit uncertainty in LxPO2 (1)
107-111 F5.1 --- chi2PO The χ2 of the PO fit
113-115 I3 --- DoFPO Degrees of freedom of power law fit
117-120 F4.2 10+22/cm2 NHDBB ? Hydrogen column density of disk
blackbody model (2)
123-126 F4.2 10+22/cm2 e_NHDBB ? Lower limit uncertainty in NHDBB (1)
128-131 F4.2 10+22/cm2 E_NHDBB ? Upper limit uncertainty in NHDBB (1)
133-136 F4.2 keV kTDBB ? Temperature of disk blackbody model (2)
138-141 F4.2 keV e_kTDBB ? Lower limit uncertainty in kTDBB (1)
143-146 F4.2 keV E_kTDBB ? Upper limit uncertainty in kTDBB (1)
148-152 F5.2 10+30W LxDBB1 ? Minimal disk blackbody model 0.5-10 keV
luminosity (in 1037erg/s) (2)
154-157 F4.2 10+30W e_LxDBB1 ? Lower limit uncertainty in LxDBB1 (1)
159-162 F4.2 10+30W E_LxDBB1 ? Upper limit uncertainty in LxDBB1 (1)
164-168 F5.2 10+30W LxDBB2 ? Maximal disk blackbody model 0.5-10 keV
luminosity (in 1037erg/s) (2)
170-173 F4.2 10+30W e_LxDBB2 ? Lower limit uncertainty in LxDBB2 (1)
175-178 F4.2 10+30W E_LxDBB2 ? Upper limit uncertainty in LxDBB2 (1)
180-184 F5.1 --- chi2DBB ? The χ2 of the disk blackbody fit (2)
186-188 I3 --- DoFDBB ? Degrees of freedom of disk
blackbody fit (2)
190-201 A12 --- State Spectral state(s) (3)
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Note (1): The 95% confidence interval.
Note (2): Blanks for these values in S48 shows where no fit could be achieved.
(i.e. χ2/dof>2), which is discussed in section 4.3.
Note (3): The state column denotes the spectral states that a given set of
spectra are consistent with, based on the classification scheme
proposed by Brassington et al. (2010ApJ...725.1805B 2010ApJ...725.1805B):
* T indicates a thermally dominant state, P indicates power law dominant
state,
* M suggests that there is significant, unmodelled emission from
another component (>30-40%)
* N suggests a result was not-produced by the Brassington et al.
(2010ApJ...725.1805B 2010ApJ...725.1805B) simulations
* I indicates there is additional line-of-sight absorption, when both
simple models have NH significantly above the Galactic value.
* The extent to which a component dominates is indicated by the associated
number, i.e. 1 implies the state is almost completely dominated by
that component, while 2 indicates that there is some unmodelled
component also present. Instances of NHDBB=0.00-0.820.00 for
some fits are the result of not being able to constrain an upper-limit
in Xspec. We believe the source to be in the power law state at these
times, with NHPO consistent with the Galactic value. NA denotes
where no inference can be made regarding the state (see section 4.4).
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 3 A3 --- ID Source identifier (1)
5- 8 F4.2 10+22/cm2 NH [0.08/1.1] Hydrogen column density
10- 13 F4.2 10+22/cm2 e_NH Lower limit uncertainty in NH
15- 18 F4.2 10+22/cm2 E_NH Upper limit uncertainty in NH
20- 24 F5.3 keV kT ? Model DBB fit parameter (1)
26- 29 F4.2 keV e_kT ? Lower limit uncertainty in kT
31- 34 F4.2 keV E_kT ? Upper limit uncertainty in kT
36- 40 F5.3 --- Gam ? Model power_law parameter (1)
42- 45 F4.2 --- e_Gam ? Lower limit uncertainty in Gam
47- 50 F4.2 --- E_Gam ? Upper limit uncertainty in Gam
52- 56 F5.2 10+30W Lx1 [2.4/36.3] Minimal 0.5-10 keV luminosity
58- 61 F4.2 10+30W e_Lx1 Lower limit uncertainty in Lx1
63- 66 F4.2 10+30W E_Lx1 Upper limit uncertainty in Lx1
68- 72 F5.2 10+30W Lx2 ? Maximal 0.5-10 keV luminosity
74- 77 F4.2 10+30W e_Lx2 ? Lower limit uncertainty in Lx2
79- 82 F4.2 10+30W E_Lx2 ? Upper limit uncertainty in Lx2
84- 88 F5.1 --- chi2 Model χ2 of fit
90- 93 I4 --- DoF Degrees of Freedom
95- 96 A2 --- Note [D GC] Source coincidence (2)
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Note (1): The first 23 entries (S3-S45) are fit with a thermally dominant
(DBB = disk blackbody) model. The remaining 18 entries (S3-S59) are
fit with a power law dominant (PO) model. In both cases HH is forced
to be above the Galactic value to reach a better estimate of the
source luminosity.
Note (2): Note as follows:
GC = source is coincident with globular cluster;
D = source is in the vicinity of the dust lane.
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 12-Nov-2014