J/ApJ/796/105 Catalog of X-ray sources in the NARCS (Fornasini+, 2014)
The Norma arm region Chandra survey catalog: X-ray populations in the spiral arms. Fornasini F.M., Tomsick J.A., Bodaghee A., Krivonos R.A., An H., Rahoui F., Gotthelf E.V., Bauer F.E., Stern D. <Astrophys. J., 796, 105 (2014)> =2014ApJ...796..105F (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; X-ray sources ; Binaries, X-ray ; Photometry, CCD Keywords: binaries: general - catalogs - Galaxy: disk - novae, cataclysmic variables - X-rays: binaries - X-rays: stars Abstract: We present a catalog of 1415 X-ray sources identified in the Norma Arm Region Chandra Survey (NARCS), which covers a 2°x0.8° region in the direction of the Norma spiral arm to a depth of ∼20 ks. Of these sources, 1130 are point-like sources detected with ≥3σ confidence in at least one of three energy bands (0.5-10, 0.5-2, and 2-10 keV), five have extended emission, and the remainder are detected at low significance. Since most sources have too few counts to permit individual classification, they are divided into five spectral groups defined by their quantile properties. We analyze stacked spectra of X-ray sources within each group, in conjunction with their fluxes, variability, and infrared counterparts, to identify the dominant populations in our survey. We find that ∼50% of our sources are foreground sources located within 1-2 kpc, which is consistent with expectations from previous surveys. Approximately 20% of sources are likely located in the proximity of the Scutum-Crux and near Norma arm, while 30% are more distant, in the proximity of the far Norma arm or beyond. We argue that a mixture of magnetic and nonmagnetic cataclysmic variables dominates the Scutum-Crux and near Norma arms, while intermediate polars and high-mass stars (isolated or in binaries) dominate the far Norma arm. We also present the cumulative number count distribution for sources in our survey that are detected in the hard energy band. A population of very hard sources in the vicinity of the far Norma arm and active galactic nuclei dominate the hard X-ray emission down to fX∼10-14 erg/cm2/s, but the distribution curve flattens at fainter fluxes. We find good agreement between the observed distribution and predictions based on other surveys. Description: We performed Chandra ACIS-I observations in faint mode of a 2°x0.8° region of the Norma spiral arm in 2011 June. The ACIS-I consists of four 1024x1024 pixel CCDs, covering a 17'x17' field of view (Garmire et al. 2003SPIE.4851...28G). The on-axis spatial resolution of the ACIS-I is fully sampled by the 0.492"x0.492" CCD pixel but it increases greatly off-axis. The PSF increases in size and becomes more elliptical at large off-axis angles, such that at an off-axis angle of 10', the PSF has ellipticity ∼0.3 and semi-major axis ∼15' for an enclosed-count fraction (ECF) of 90% for 4.5 keV photons (Allen et al. 2004SPIE.5165..423A). The CCDs are sensitive to incident photons with energies in the 0.3-10.0 keV range, and have a resolution of about 50-300 eV. The time resolution of the CCDs, which is determined by the read-out time, is 3.2 s. Objects: ---------------------------------------------------------- RA (ICRS) DE Designation(s) ---------------------------------------------------------- 16 00 -50.0 Norma arm = NAME Norma Arm ---------------------------------------------------------- File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This fileil table3.dat 147 1415 Catalog of Point and Extended Sources: Detection and Localization table4.dat 142 1415 Catalog of Point and Extended Sources: Photometry table5.dat 60 1415 Catalog of Point and Extended Sources: Infrared Counterparts
See also: IX/45 : The Chandra Source Catalog, Release 1.1 (Evans+ 2012) II/348 : VISTA Variable in the Via Lactea Survey DR2 (Minniti+, 2017) J/ApJS/134/77 : ASCA Galactic Plane Survey faint X-ray sources (Sugizak+, 2001) J/ApJ/635/214 : Chandra X-ray sources and NIR identifications (Ebisawa+, 2005) Byte-by-byte Description of file: table3.dat
Bytes Format Units Label Explanations
1- 4 I4 --- NARCS [1/1415] NARCS catalog number 6- 20 A15 --- ID Chandra source identifier (CXOU JHHMMSS.s+DDMMSS in Simbad) 22- 29 A8 --- ObsID Observation identifier (1) 31- 40 F10.6 deg RAdeg Right Ascension in decimal degrees (J2000) (2) 42- 51 F10.6 deg DEdeg Declination in decimal degrees (J2000) (2) 53- 57 F5.2 arcsec PosUnc Positional uncertainty (3) 59- 71 A13 arcmin Off Offset angular separation of source and aim point 73- 78 F6.1 --- SigFB Full 0.5-10 keV band significance (4) 80- 84 F5.1 --- SigSB Soft 0.5-2 keV band significance (4) 86- 91 F6.1 --- SigHB Hard 2-10 keV band significance (4) 93-106 A14 arcsec Radius Radius of aperture source region (5) 108-120 A13 arcsec PSF Point spread function (6) 122-147 A26 --- Flag Source flag(s) (7)
Note (1): Observation(s) in which wavdetect detects the source. The format of ObsID numbers is 125XX, where the last two digits are those provided in the catalog. See Section 2.1 for details about wavdetect usage. Note (2): If the source is detected in multiple observations, the position reported is the weighted average of its positions in different observations. Note (3): For a source detected in a given observation, this uncertainty is equal to the quadrature sum of the 95% statistical uncertainty based on Equation (5) of Hong et al. (2005ApJ...635..907H) and the average systematic uncertainty of positions in that observation after astrometric refinement (see Column 5 in Table 2). For sources detected in multiple observations, the uncertainties associated with the source position in different observations were combined to provide the uncertainty of the weighted average of the source positions. Note (4): It is calculated by finding the probability that the source is a noise fluctuation using Equation (5) and using the Gaussian cumulative distribution function to determine the corresponding source significance. If the source is detected in multiple observations, the reported significance is the sum in quadrature of the source significance in individual observations. Note (5): For most sources, the aperture source region is defined as a circle with radius equal to the 90% ECF for 4.5 keV photons (see Column 12). For potentially extended sources, flagged with "e" (see Column 13), the radius is instead equal to the semi-major axis of the aperture region defined by wavdetect. In cases where two or more sources have overlapping circular regions, the regions are redefined as a circular core plus an annular pie sector following the guidelines in Table 6; in such cases, the radius provided in the catalog represents the outer radius of the pie sector. For sources detected in multiple observations, a semicolon-separated list of the aperture region radius used in different observations is provided; the order of radii matches the order of ObsIDs reported in Column 3. Note (6): PSF radius for 90% ECF for 4.5 keV photons at the detector location of the source. The PSF radius varies with detector position, generally increasing with increasing offset angle from the observation aim point. For sources detected in multiple observations, a semicolon-separated list of the PSF radius at the source detector position in different observations is provided; the order of PSF radii matches the order of ObsIDs reported in Column 3. Note (7): Flag as follows: m1, m2 or m3 = "modified"; in cases where the circular source aperture region overlaps with the aperture region of another source, the source region is modified to reduce overlapping. See Table 6 for details; nb = "near bright"; source near a very bright source which may be a spurious detection; nd = "not detected"; source is located where at least two observations overlap but it is only detected in one observation; s = "surrounding"; a possibly extended source that completely surrounds one or more point sources. The aperture regions of the surrounded sources are excluded from the aperture region of the source flagged with "s"; vl = "variable long"; source determined to be variable on long (hours-days) timescales. The photon flux in at least one energy band (full, soft, or hard) varies by ≥ 3σ between different observations; vp = "variable probable"; source is probably variable on short (second-hour) timescales. The K-S test finds the source light curve within a single observation to be inconsistent with a constant light curve at ≥95% confidence; vs = "variable short"; source is variable on short (second-hour) timescales. The K-S test finds the source light curve within a single observation to be inconsistent with a constant light curve at ≥3σ confidence.
Byte-by-byte Description of file: table4.dat
Bytes Format Units Label Explanations
1- 4 I4 --- NARCS [1/1415] NARCS catalog number 6- 10 I5 ct FBNet Net full 0.5-10 keV band source counts (1) 12- 14 I3 ct E_FBNet ? Upper 1σ error in FBNet 16- 18 I3 ct e_FBNet ? Lower 1σ error in FBNet 20- 22 I3 ct SBNet Net soft 0.5-2 keV band source counts (1) 24- 25 I2 ct E_SBNet ? Upper 1σ error in SBNet 27- 28 I2 ct e_SBNet ? Lower 1σ error in SBNet 30- 34 I5 ct HBNet Net hard 2-10 keV band source counts (1) 36- 38 I3 ct E_HBNet ? Upper 1σ error in HBNet 40- 42 I3 ct e_HBNet ? Lower 1σ error in HBNet 44- 50 F7.2 10-6/cm2/s fphFB Full 0.5-10 keV band photon flux (2) 52- 55 F4.2 10-6/cm2/s E_fphFB ? Upper 1σ error in fphFB 57- 60 F4.2 10-6/cm2/s e_fphFB ? Lower 1σ error in fphFB 62- 66 F5.2 10-6/cm2/s fphSB Soft 0.5-2 keV band photon flux (2) 68- 71 F4.2 10-6/cm2/s E_fphSB ? Upper 1σ error in fphSB 73- 76 F4.2 10-6/cm2/s e_fphSB ? Lower 1σ error in fphSB 78- 84 F7.2 10-6/cm2/s fphHB Hard 2-10 keV band photon flux (2) 86- 89 F4.2 10-6/cm2/s E_fphHB ? Upper 1σ error in fphHB 91- 94 F4.2 10-6/cm2/s e_fphHB ? Lower 1σ error in fphHB 96- 98 F3.1 keV E50 Median source energy (3) 100-102 F3.1 keV e_E50 The 1σ error in E50 104-106 F3.1 keV E25 Energy below which 25% of total source counts reside (3) 108-110 F3.1 keV e_E25 The 1σ error in E25 112-115 F4.1 keV E75 Energy below which 75% of total source counts reside (3) 117-119 F3.1 keV e_E75 The 1σ error in E75 121-126 F6.2 10-17W/m2 fXFB Full 0.5-10 keV band flux (4) 128-131 F4.2 10-17W/m2 E_fXFB ? Upper 1σ error in fXFB 133-136 F4.2 10-17W/m2 e_fXFB ? Lower 1σ error in fXFB 138-140 A3 --- PFlag Photometric flag (5) 142 A1 --- Q [ABCDE] Quantile group (6)
Note (1): Calculated as described in Section 2.2. For cases in which the estimated background counts in a source aperture region were determined to be greater than or equal to the total number of counts in the source region, then the catalog presents the 90% upper confidence limit to the net source counts based on the method described in Kraft, Burrows & Nousek (1991ApJ...374..344K); in such cases, the error columns are left blank. For sources detected in multiple observations, net counts from different observations were added together and errors combined in quadrature. Note (2): The photon flux was calculated by dividing the net counts by the exposure time and the mean effective area within the source region. For sources with zero or negative net counts, the catalog provides the 90% upper limit on the photon flux and leaves the error columns blank. For sources detected in multiple observations, the average photon fluxes are reported; if a source was found to be variable between observations (flagged as "vl") then its photon fluxes from individual observations were simply averaged, but otherwise its photon fluxes were weight-averaged. Note (3): It is determined from the total counts (not background corrected) in the source region. For sources detected in multiple observations, the simple average of the energies from individual observations is reported if a source is found to be variable between observations or the weighted-average is reported otherwise. Note (4): This estimate of the energy flux is calculated by multiplying the full band photon flux and the median energy of the source provided in the catalog. In cases where only an upper limit to the photon flux is available, the 90% upper limit to the energy flux is reported and the error columns are left blank. Note (5): If the photometric values provided for a source are 90% upper limits in the full, soft, or hard energy bands, this column displays an F, S, or H, respectively. Note (6): The spectral group defined using quantile diagrams to which the source belongs. Group as follows: A = The group A stacked spectrum is best fit by a two-temperature thermal plasma model. The column density associated with each temperature component is low (~<1021 cm-2), suggesting most sources in this group are foreground sources, located at a distance ~<1 kpc. B = Similar to group A, the group B stacked spectrum is also best-fit by a two-temperature thermal model with low hydrogen column densities. However, the temperature of the hotter component is significantly higher (kT∼7 keV) for the B sources than for the A sources. The origin of the low-temperature component may be low-mass X-ray active stars, ABs, and symbiotic binaries, the dominant sources in group A, while the high-temperature component is more typical of CVs. C = The group C stacked spectrum is best-fit by an absorbed power-law with Γ∼1.1 and NH=1.4x1022 cm-2, which suggests that these sources are located at a distance of 3-5 kpc, in the Scutum-Crux and near Norma spiral arms. The luminosities spanned by group C sources are LX=1031-1032.7 erg/s, assuming a distance of 4 kpc. Possible classes of X-ray sources present in this group are magnetic and nonmagnetic CVs, hard-spectrum symbiotic binaries, low-mass X-ray binaries (LMXBs), and HMXBs. D = The group D stacked spectrum has a very hard photon index (Γ∼0.7), a prominent Fe line, and a high NH, indicating that these sources typically lie on the far side of the Galaxy, near, in, or beyond the far Norma arm. The presence of this strong, non-redshifted Fe line suggests that many of the sources in this group must be Galactic; otherwise, if this group were dominated by AGNs, their spread in redshift would result in a smearing out of the Fe line. E = The group E stacked spectrum is best-fit by a two-temperature thermal model, making it significantly different from the group D power-law spectrum, even though some of the same classes of X-ray sources must be present in both groups D and E since they are not sharply separated in the quantile diagram. The photometric and spectral properties of group E are also consistent with symbiotic binaries. See Section 3 for details about quantile analysis and the spectral groups defined in this work.
Byte-by-byte Description of file: table5.dat
Bytes Format Units Label Explanations
1- 4 I4 --- NARCS [1/1415] NARCS catalog number 6- 17 A12 --- VVV VVV source identifier; if available (Minniti et al. 2010NewA...15..433M) 19- 28 F10.6 deg RAdeg ? Right Ascension in decimal degrees (J2000) 30- 39 F10.6 deg DEdeg ? Declination in decimal degrees (J2000) 41- 44 F4.2 arcsec Delta ? Angular separation between Chandra & VVV source 46- 53 E8.2 --- pnoise ? Probability VVV source is a noise fluctuation 55- 60 F6.4 --- Rel ? Reliability (1)
Note (1): Of the VVV counterpart calculated according to the method of Sutherland & Saunders (1992MNRAS.259..413S). The reliability depends on the distance between the X-ray and IR sources, the positional uncertainties of the X-ray and IR sources, and the spatial density of IR sources. The reliability is expressed as a fraction between zero and one; VVV sources with a higher reliability are more likely to be true IR counterparts to the Chandra sources.
History: From electronic version of the journal
(End) Prepared by [AAS], Tiphaine Pouvreau [CDS] 07-Aug-2017
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