J/ApJ/700/1702 ChaMPlane deep galactic bulge survey. I. (van den Berg+, 2009)
ChaMPlane deep galactic bulge survey.
I. Faint accretion-driven binaries in the limiting window.
van den Berg M., Hong J., Grindlay J.E.
<Astrophys. J., 700, 1702-1715 (2009)>
=2009ApJ...700.1702V 2009ApJ...700.1702V
ADC_Keywords: Binaries, cataclysmic ; X-ray sources ; Surveys ; Photometry, HST
Keywords: Galaxy: bulge - novae, cataclysmic variables - surveys -
X-rays: binaries
Abstract:
We have carried out a deep X-ray and optical survey with Chandra and
HST of low-extinction regions in the Galactic bulge. Here we present
the results of a search for low-luminosity (LX≲1034erg/s)
accreting binaries among the Chandra sources in the region closest to
the Galactic center, at an angular offset of 1.4°, that we have
named the Limiting Window (LW). Based on their blue optical colors,
excess Hα fluxes, and high X-ray-to-optical flux ratios, we
identify three likely accreting binaries; these are probably white
dwarfs accreting from low-mass companions (cataclysmic variables; CVs)
although we cannot exclude that they are quiescent neutron-star or
black-hole low-mass X-ray binaries. Distance estimates put these
systems farther than ≳2kpc. Based on their Hα-excess fluxes
and/or high X-ray-to-optical flux ratios, we find 22 candidate
accreting binaries; however, the properties of some can also be
explained if they are dMe stars or active galaxies.
Description:
As part of the Chandra Multi-wavelength Plane survey (ChaMPlane;
Grindlay et al. 2005ApJ...635..920G 2005ApJ...635..920G), we have carried out an X-ray and
optical survey of deep, near-simultaneous Chandra and HST pointings of
three low-extinction regions, or windows, in the Galactic bulge.
The Limiting Window (LW) was observed with the Chandra/ACIS-I aimpoint
placed at Galactic coordinates (l,b)= (0.10°,-1.43°). Due to
observatory constraints, the observation was split in three exposures:
ObsID 6362 (2005 August 19, 38ks), ObsID 5934 (2005 August 22, 41ks),
and ObsID 6365 (2005 October 25, 21ks).
We observed with HST the inner area of the ACIS field on the Advanced
Camera for Surveys (ACS). The observations (program GO-10353) were
carried out simultaneous with the first Chandra exposure (2005 Aug 19).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 31 100 Chandra sources in the ACS field of view
table3.dat 120 13 *Candidate accreting binaries in the LW selected
on optical colors
table4.dat 109 12 Candidate accreting binaries in the LW selected
on intrinsic X to optical flux ratio
table5.dat 119 21 *Other identifications of Chandra sources in the LW
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Note on table3.dat: Properties of our best candidate CVs (LW 1-4) and the more
marginal candidates (LW 5-13).
Note on table5.dat: Properties of the likely coronal source identifications
(LW26-43) discussed in Section 4.2.
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See also:
B/chandra : The Chandra Archive Log (CXC, 1999-)
B/hst : HST Archived Exposures Catalog (STScI, 2007)
I/315 : UCAC3 Catalogue (Zacharias+ 2009)
II/213 : OGLE Galactic Bulge periodic variables (Udalski+ 1996)
J/ApJ/685/463 : ChaMPlane X-ray sources in the Galactic bulge (Koenig+, 2008)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 15 A15 --- CXOPS Source name (HHMMSS.s+DDMMSS; J2000)
17 A1 --- f_CXOPS [a] Source partly in chip gap (1)
19 A1 --- l_SNRh [-] The source was not significantly detected
in the hard band
20- 23 F4.2 --- SNRh Hard (2-8keV) band signal-to-noise ratio
25- 26 A2 --- --- [LW]
28- 29 I2 --- LW [1/43]? LW identifier if in Limiting Window
31 I1 --- T [3,5]? table number (3+4 = accreting binary
candidates; 5 = other optical sources)
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Note (1): a = The 95% error radius of this source lies partly in the ACS
chip gap.
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Byte-by-byte Description of file: table3.dat table4.dat table5.dat
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Bytes Format Units Label Explanations
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1- 2 A2 --- --- [LW]
4- 5 I2 --- LW [1/43] Source name <[VHG2009] LW NN> in Simbad
6 A1 --- u_LW [b] Ambiguous identification (1)
8- 22 A15 --- CXOPS Chandra source name (HHMMSS.s+DDMMSS; J2000)
24- 26 I3 ct Cts Net source counts in the Bx band (0.3-8keV)
28- 29 I2 ct e_Cts Cts uncertainty
31- 34 F4.2 keV E50 ? Median energy E50 in the Bx band
36- 39 F4.2 keV e_E50 ? E50 uncertainty
41 I1 --- Gp [1,3] Quantile spectral group (4)
43- 44 I2 h RAh ? Optical hour of right ascension (J2000) (2)
46- 47 I2 min RAm ? Optical minute of right ascension (J2000)
49- 54 F6.3 s RAs ? Optical second of right ascension (J2000)
56 A1 --- DE- Optical sign of declination (J2000) (2)
57- 58 I2 deg DEd ? Optical degree of declination (J2000)
60- 61 I2 arcmin DEm ? Optical arcminute of declination (J2000)
63- 67 F5.2 arcsec DEs ? Optical arcsecond of declination (J2000)
69- 73 F5.2 mag R625 ? HST/ACS R-band magnitude (F625W) unless
flagged (not for table 4)
74 A1 --- f_R625 [a] Flag on R625 (3)
76- 80 F5.2 mag B435 ? HST/ACS B-band magnitude (F435W) (not for
table 4)
82- 86 F5.2 mag Ha ? Hα magnitude (not for table 4)
88- 92 F5.2 [-] logX/R Ratio of the observed (log(fX/fR)) X-ray
and optical fluxes (4)
94- 97 F4.2 [-] e_logX/R logX/R uncertainty (4)
98 A1 --- f_logX/R [acd] Flag on logX/R (3)
100-104 F5.2 [-] logX/Ru Ratio of the intrinsic (log(fX/fR)u)
X-ray and optical fluxes (4)
106-109 F4.2 [-] e_logX/Ru logX/Ru uncertainty (4)
110 A1 --- f_logX/Ru [acd] Flag on logX/Ru (3)
112-120 A9 --- Com Comment
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Note (1): The identification of the OGLE variable in the ACS image is
ambiguous; therefore we list both candidate optical counterparts.
Note (2): Optical positions are not given for table 4. Errors in the
absolute astrometry are ∼0.095".
Note (3): Flag as follows:
a = LW 26 and LW 27 are saturated in our ACS images. In Column R625 we give
the UCAC2 magnitude from Zacharias et al. (2004, Cat. I/289; obsoleted by
I/315) that is between V and R, and use it to compute the
X-ray-to-optical flux ratios.
c = The optical source is saturated in the F625W image; we assume
R625=Hα to compute the X-ray-to-optical flux ratios.
d = The optical source is not detected in the F625W and Hα images; we
use B435 to compute the X-ray-to-optical flux ratios.
Note (4): Fluxes are corrected for extinction using the group-specific
nH values below:
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Gp Model Parameter nH (1022atoms/cm2)
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1 MeKaL kT=1keV 0.76
2 power law Γ=1.28 0.76
3 power law Γ=1.21 1.95
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Quoted errors in the flux ratios only include a contribution from
errors in the X-ray counts, not from systematic errors.
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 10-Aug-2011