J/ApJ/738/129 XMM-Newton X-ray sources in NGC 6553 (Guillot+, 2011)
Discovery of a candidate quiescent low-mass X-ray binary in the globular
cluster NGC 6553.
Guillot S., Rutledge R.E., Brown E.F., Pavlov G.G., Zavlin V.E.
<Astrophys. J., 738, 129 (2011)>
=2011ApJ...738..129G 2011ApJ...738..129G (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, globular ; Binaries, X-ray ; Stellar distribution
Keywords: globular clusters: individual: NGC 6553 - stars: neutron -
X-rays: binaries
Abstract:
This paper reports the search for quiescent low-mass X-ray binaries
(qLMXBs) in the globular cluster (GC) NGC 6553 using an XMM-Newton
observation designed specifically for that purpose. We spectrally
identify one candidate qLMXB in the core of the cluster, based on the
consistency of the spectrum with a neutron star H-atmosphere model at
the distance of NGC 6553. Specifically, the best-fit radius found
using the three XMM European Photon Imaging Camera spectra is
RNS=6.3+2.3-0.8 km (for MNS=1.4 M☉) and the best-fit
temperature is kTeff=136+21-34 eV. Both physical parameters are
in accordance with typical values of previously identified qLMXBs in
GC and in the field, i.e., RNS∼5-20 km and kTeff=50-150 eV. A
power-law (PL) component with a photon index Γ=2.1+0.5-0.8 is
also required for the spectral fit and contributes ∼33% of the total
flux of the X-ray source. A detailed analysis supports the hypothesis
that the PL component originates from nearby sources in the core,
unresolved with XMM. The analysis of an archived Chandra observation
provides marginal additional support to the stated hypothesis.
Finally, a catalog of all the sources detected within the XMM field of
view is presented here.
Description:
NGC 6553 was observed with XMM-Newton on 2006 October 6 at 01:41:44 UT,
using the three EPIC cameras, for an exposure time of 20.4 ks, with
the medium filter. The Chandra X-ray Observatory observed the GC for
5.25 ks, on 2008 October 30 at 01:38:12 UT, with the ACIS-S detector
(Garmire et al. 2003, Proc. SPIE, 4851, 28) in VERY-FAINT mode.
Objects:
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RA (ICRS) DE Designation(s)
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18 09 15.68 -25 54 27.9 NGC 6553 = GCl 88
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 56 43 X-ray Sources Detected in the XMM Observation
of NGC 6553
table2.dat 93 43 Spectral Results of X-ray Sources in NGC 6553
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See also:
VII/195 : Globular Clusters in the Milky Way (Harris, 1996)
V/106 : Catalogue of X-ray binaries (Liu+ 2001)
IX/50 : XMM-Newton Serendipitous Source Catalogue 3XMM-DR6
(XMM-SSC, 2016)
J/A+A/331/70 : JKVI photometry of NGC 6553 stars (Guarnieri+ 1998)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 19 A19 --- Name Object name (XMMU JHHMMSS+DDMMSS)
21- 29 F9.5 deg RAdeg Right Ascension in decimal degrees (J2000)
31- 33 F3.1 arcsec e_RAdeg Uncertainty in RAdeg
35- 43 F9.5 deg DEdeg Declination in decimal degrees (J2000)
45- 47 F3.1 arcsec e_DEdeg Uncertainty in DEdeg
49- 53 F5.1 --- S/N Detection significance provided by wavdetect
55- 56 I2 --- ID [01/43] Source identifier
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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- 2 I2 --- ID [01/43] Source identifier
4- 8 F5.1 ct/ks pnRate Background subtracted count rates in
the 0.3-10 keV range
10- 12 F3.1 ct/ks e_pnRate Uncertainty in pnRate
13 A1 --- n_pnRate [a] Note on pnRate (1)
15- 18 F4.1 --- Gamma ? Best-fit photon index when a power law
(PL) model was used
19 A1 --- n_Gamma [)] Note on Gamma (2)
22- 24 F3.1 --- E_Gamma ? Upper limit uncertainty in Gamma
26- 28 F3.1 --- e_Gamma ? Lower limit uncertainty in Gamma
31- 35 F5.3 keV kTeff ? Best-fit effective temperature when a
thermal model was used
37- 41 F5.3 keV E_kTeff ? Upper limit uncertainty in kTeff
43- 47 F5.3 keV e_kTeff ? Lower limit uncertainty in kTeff
49- 52 F4.2 keV kTeff1 ? Best-fit effective temperature when a
thermal model was used
54- 57 F4.2 keV E_kTeff1 ? Upper limit uncertainty in kTeff1
59- 62 F4.2 keV e_kTeff1 ? Lower limit uncertainty in kTeff1
64- 68 F5.2 10-16W/m2 FX Unabsorbed X-ray flux in the band 0.5-10 keV
(10-13 erg/cm2/s) (3)
70- 73 F4.2 --- chi2 χ2 statistic of the fit
75- 77 I3 --- dof [3/115] Number of degrees of freedom
79- 82 F4.2 --- Prob [0/1] Null hypothesis probability
84- 93 A10 --- Model Model used (4)
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Note (1): Note as follows:
a = The MOS1/2 count rates are, respectively, 8.5±0.8 and
6.6±0.7 counts/ks in the 0.3-10 keV range.
Note (2): Note as follows:
) = Values were held fixed.
Note (3): Note that the flux is not corrected for the finite aperture in this
table. This energy range is different from that used for the spectrum
extraction (0.3-10 keV), for comparison purposes with previously
published work.
Note (4): Model as follows:
PL = Power law;
RS = Raymond-Smith plasma;
nsatmos = (McClintock et al. 2004ApJ...615..402M 2004ApJ...615..402M; Heinke et al.
2006ApJ...644.1090H 2006ApJ...644.1090H); nsatmos as been computed for the range
g=(0.63-6.3)x1014 cm/s2.
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History:
From electronic version of the journal
(End) Prepared by Tiphaine Pouvreau [CDS] 17-Aug-2017