J/ApJS/181/605 Catalog of X-ray sources in NGC 4278 (Brassington+, 2009)
Deep Chandra monitoring observations of NGC 4278: catalog of source properties.
Brassington N.J., Fabbiano G., Kim D.-W., Zezas A., Zepf S., Kundu A.,
Angelini L., Davies R.L., Gallagher J., Kalogera V., Fragos T., King A.R.,
Pellegrini S., Trinchieri G.
<Astrophys. J. Suppl. Ser., 181, 605-626 (2009)>
=2009ApJS..181..605B 2009ApJS..181..605B
ADC_Keywords: X-ray sources ; Clusters, globular ; Spectroscopy ; Photometry
Keywords: galaxies: individual (NGC 4278) - X-rays: binaries - X-rays: galaxies
Abstract:
We present the properties of the discrete X-ray sources detected in
our monitoring program of the globular cluster (GC) rich elliptical
galaxy, NGC 4278, observed with Chandra ACIS-S in six separate
pointings, resulting in a co-added exposure of 458ks. From this deep
observation, 236 sources have been detected within the region
overlapped by all observations, 180 of which lie within the D25
ellipse of the galaxy. These 236 sources range in LX from
3.5x1036erg/s (with 3σ upper limit ≤1x1037erg/s) to
∼2x1040erg/s, including the central nuclear source which has been
classified as a LINER. From optical data, 39 X-ray sources have been
determined to be coincident with a GC, these sources tend to have high
X-ray luminosity, with 10 of these sources exhibiting
LX>1x1038erg/s. From X-ray source photometry, it has been
determined that the majority of the 236 point sources that have
well-constrained colors have values that are consistent with typical
low-mass X-ray binary spectra, with 29 of these sources expected to be
background objects from the log N-log S relation. There are 103
sources in this population that exhibit long-term variability,
indicating that they are accreting compact objects. Three of these
sources have been identified as transient candidates, with a further
three possible transients. Spectral variations have also been
identified in the majority of the source population, where a diverse
range of variability has been identified, indicating that there are
many different source classes located within this galaxy.
Description:
The six separate Chandra observations of NGC 4278 have been carried
out over a two-year baseline, with the first of these, a 37ks
pointing, being performed in 2005 February. This observation has been
followed by five deeper pointings, all carried out between 2006 March
and 2007 February, resulting in a total exposure time of 471ks.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 108 236 Master source list
table4.dat 167 236 Source counts, hardness ratios and color-color
values: coadded observation
table5.dat 167 236 Source counts, hardness ratios, color-color
values and variability: observation 1
table6.dat 167 236 Source counts, hardness ratios, color-color
values and variability: observation 2
table7.dat 169 236 Source counts, hardness ratios, color-color
values and variability: observation 3
table8.dat 167 236 Source counts, hardness ratios, color-color
values and variability: observation 4
table9.dat 167 236 Source counts, hardness ratios, color-color
values and variability: observation 5
table10.dat 167 236 Source counts, hardness ratios, color-color
values and variability: observation 6
table11.dat 46 45 Properties of optical sources that are
correlated with an X-ray point source
table12.dat 46 38 Properties of optical sources that have been
classified as "Excluded Matches": sources
detected between 0.6" and 3" of an X-ray point
source
table15.dat 105 236 Raw source and background counts from the
co-added observation
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See also:
B/chandra : The Chandra Archive Log (CXC, 1999-)
Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1 A1 --- q_[BFK2009] [gl] Quality of detection (1)
3- 5 I3 --- [BFK2009] Master identification number
7- 22 A16 --- CXOU The IAU name (JHHMMSS.s+DDMMSS)
24- 25 I2 h RAh Hour of Right Ascension (J2000)
27- 28 I2 min RAm Minute of Right Ascension (J2000)
30- 35 F6.3 s RAs Second of Right Ascension (J2000)
37 A1 --- DE- Sign of the Declination (J2000)
38- 39 I2 deg DEd Degree of Declination (J2000)
41- 42 I2 arcmin DEm Arcminute of Declination (J2000)
44- 48 F5.2 arcsec DEs Arcsecond of Declination (J2000)
50- 53 F4.2 arcsec Rad ? Source extraction radius
55- 58 F4.2 arcsec e_pos ? Position uncertainty (PU) (2)
60- 64 F5.1 --- S/N ? Signal-to-noise ratio
66- 69 F4.1 [10-7W] logLX Log 0.3-0.8 keV luminosity (3)
71- 74 F4.1 [10-7W] ulogLX ? The 3σ upper limit value of logLX
76- 78 A3 --- vLT Long-term variability (4)
80 A1 --- v1 Short-term variability: Bayesian block
analysis (5)
82 A1 --- v2 Short-term variability: Komogorov-Smirnov
test (5)
84- 89 A6 --- Ocorr Optical association (6)
91- 95 F5.1 arcsec Dist Distance from galaxy center
97 A1 --- n_Dist [b] Indicates Dist is within the D25
ellipse
99-108 A10 --- Flag Remarks (7)
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Note (1): Flag as follows:
g = source with S/N>3, in at least one observation (good)
l = source with S/N<3, in all observations (low)
Note (2): From section 2.2, equation 1
Note (3): Assuming D=16.1Mpc and in units of erg/s. For sources only
detected in a single observation, 1σ upper limits from the
co-added observation are quoted (with 3σ upper limits from the
detected observation in the next column).
Note (4): Long-term variability as follows:
N = non-variable source;
V = variable source;
TC = transient candidate;
PTC = possible transient.
Note (5): Short-term variability as follows:
N = non-variable in all observations;
V = variable in at least one observation;
P = possible variability in at least one observation.
Note (6): Optical association as follows:
GC = optical source is a confirmed globular cluster;
BG = optical source is a background object;
corr = match that has been defined as a correlation;
exmt = match between 0.6" and 3" in separation;
none = source inside the field of view of the HST observation, but has no
optical counterpart. All other sources are external to the HST FOV.
Note (7): Flags as follows:
X = source detected in a single observation only;
O1 = single overlapping sources;
O2 = complicated case of overlapping sources.
double? = possible double sources.
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Byte-by-byte Description of file: table[456789].dat table10.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- [BFK2009] Master identification number
6- 7 A2 --- f_Bct [≤ ] Limit flag on Bct (1)
9- 15 F7.1 ct Bct ? Net broad band (0.3-8keV) counts
17- 21 F5.1 ct e_Bct ? Error in Bct
23- 29 F7.1 ct S1ct ? Net soft 1 band (0.3-0.9keV) counts
31- 35 F5.1 ct e_S1ct ? Error in S1ct
37- 43 F7.1 ct S2ct ? Net soft 2 band (0.9-2.5keV) counts
45- 49 F5.1 ct e_S2ct ? Error in S2ct
51- 57 F7.1 ct Sct ? Net soft band (0.3-2.5keV) counts
59- 63 F5.1 ct e_Sct ? Error in Sct
65- 70 F6.1 ct Hct ? Net hard band (2.5-8keV) counts
72- 75 F4.1 ct e_Hct ? Error in NHct
77- 83 F7.1 ct Scct ? Net conventional soft band (0.5-2keV) counts
85- 89 F5.1 ct e_Scct ? Error in Scct
91- 96 F6.1 ct Hcct ? Net conventional hard band (2-8keV) counts
98-101 F4.1 ct e_Hcct ? Error in NHcct
103-107 F5.2 --- HR ? Hardness ratio (2)
109-112 F4.2 --- e_HR ? Lower limit uncertainty in HR
114-117 F4.2 --- E_HR ? Upper limit uncertainty in HR
119-123 F5.2 --- C21 ? The C21 X-ray color (3)
125-128 F4.2 --- e_C21 ? Lower limit uncertainty in C21
130-133 F4.2 --- E_C21 ? Upper limit uncertainty in C21
135-139 F5.2 --- C32 ? The C32 X-ray color (4)
141-144 F4.2 --- e_C32 ? Lower limit uncertainty in C32
146-149 F4.2 --- E_C32 ? Upper limit uncertainty in C32
151 A1 --- v1 ? Short-term variability: Bayesian block
analysis
153 A1 --- v2 ? Short-term variability: Komogorov-Smirnov
test
155-158 F4.1 --- Signif ? Significance of change (5)
161-162 A2 --- f_logLX [≤ ] Limit flag on LogLX (1)
164-167 F4.1 [10-7W] logLX ? Log 0.3-0.8keV luminosity (6)
169 A1 --- n_logLX [i ] Indicates infinite value (for table 7)
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Note (1): Upper limit values are at the 68% confidence level.
Note (2): Where HR = [(2-8keV)-(0.5-2keV)]/[((2-8keV)+(0.5-2keV)].
Note (3): Where C21 = log[(0.3-0.9keV)/(0.9-2.5keV)].
Note (4): Where C32 = log[(0.3-2.5keV)/(2.5-8keV)].
Note (5): In logLX between the previous observation and the current
observation respectively (equation 2:
signif=|LX1-LX2|/(σ12+σ22)0.5
where σn is the error value of the luminosity from that
individual observation, based on the Gehrels approximation, or, where
upper limits have been used, the standard deviation of the estimated
luminosity).
Note (6): Assuming D=16.1Mpc and in units of erg/s.
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Byte-by-byte Description of file: table11.dat table12.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- [BFK2009] X-ray source number
5- 9 F5.2 mag Vmag V-band magnitude
11- 14 F4.2 mag e_Vmag Uncertainty in Vmag
16- 20 F5.2 mag Imag I-band magnitude
22- 25 F4.2 mag e_Imag Uncertainty in Imag
27- 30 F4.2 mag V-I V-I color index
32- 35 F4.2 mag e_V-I Uncertainty in V-I color index
37- 40 F4.2 arcsec Sep Separation between the X-ray source and the
globular cluster (GC)
42- 46 F5.2 --- sep1 Error-relative separation (ratio between
separation and the combined position error)
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Byte-by-byte Description of file: table15.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- [BFK2009] Master identification number (1)
5- 11 F7.1 ct Bct ? Net broad band (0.3-8keV) counts
13- 19 F7.1 ct Braw ? Raw broad band (0.3-8keV) source counts
21- 25 F5.1 ct Bbg ? Raw broad band (0.3-8keV) background counts
27- 33 F7.1 ct S1raw ? Raw soft 1 band (0.3-0.9keV) source counts
35- 39 F5.1 ct S1bg ? Raw soft 1 band (0.3-0.9keV) background
counts
41- 47 F7.1 ct S2raw ? Raw soft 2 band (0.9-2.5keV) source counts
49- 53 F5.1 ct S2bg ? Raw soft 2 band (0.9-2.5keV) background
counts
55- 60 F6.1 ct Hraw ? Raw hard band (2.5-8keV) source counts
62- 65 F4.1 ct Hbg ? Raw hard band (2.5-8keV) background counts
67- 73 F7.1 ct Bcraw ? Raw conventional broad band (0.5-8keV)
source counts
75- 79 F5.1 ct Bcbg ? Raw conventional broad band (0.5-8keV)
background counts
81- 87 F7.1 ct Scraw ? Raw conventional soft band (0.5-2keV)
source counts
89- 93 F5.1 ct Scbg ? Raw conventional soft band (0.5-2keV)
background counts
95-100 F6.1 ct Hcraw ? Raw conventional hard band (2-8keV)
source counts
102-105 F4.1 ct Hcbg ? Raw conventional hard band (2-8keV)
background counts
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Note (1): In some instances background counts are very low. For these
sources standard aperture photometry results in negative net counts,
so, instead, the source cell determined by wavdetect has been used.
This results in a large area ratio between the background and source
regions and therefore a low background count value is derived.
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 05-Nov-2009