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NARCSCAT - Norma Arm Region Chandra Survey Point & Extended Source Catalog

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Overview

This table contains the catalog of 1,415 X-ray sources identified in the Norma Arm Region Chandra Survey (NARCS), which covers a 2 degree x 0.8 degree region in the direction of the Norma spiral arm to a depth of ~ 20 ks. Of these sources, 1,130 are point-like sources detected with >= 3-sigma 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. The authors 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 this survey. They find that ~ 50% of their 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. The authors argue that a mixture of magnetic and non-magnetic 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. In the paper, they also present the cumulative number count distribution for sources in this 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 cm-2 s-1, but the distribution curve flattens at fainter fluxes. The authors find good agreement between the observed distribution and predictions based on other surveys.

Chandra ACIS-I observations were performed in faint mode of a 2 degree by 0.8 degree region of the Norma spiral arm in 2011 June. This field was subdivided into 27 pointings; Table 1 in the reference paper reports their coordinates and exposure times and Figure 1 (op. cit.) is a mosaic image of the survey. The observing strategy was to cover a wide area with relatively uniform flux sensitivity and good spatial resolution; therefore, the authors chose field centers spaced by 12 arcminutes, which provided roughly 70 arcminute2 of overlap on the outskirts of adjacent observations such that the additional exposure time in these overlapping regions partly made up for the worsening point-spread function (PSF) at large off-axis angles.


Catalog Bibcode

2014ApJ...796..105F

References

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 Hongjun, R.F.,
    Gotthelf E.V., Bauer F.E., Stern D.
   <Astrophys. J., 796, 105. (2014)>
   =2014ApJ...796..105F

Provenance

This table was created by the HEASARC in March 2015 based on electronic versions of Tables 3, 4 and 5 from the reference paper which were obtained from the ApJ web site.

Parameters

Source_Number
A uniquely identifying source number for each Chandra X-ray source in this catalog, in order on increasing J2000.0 Right Ascension.

Name
The standard (with the exception noted below) Chandra X-ray source designation recommended by the Dictionary of Nomenclature of Celestial Objects, viz., the 'CXOU' prefix for 'Chandra X-Ray Observatory, Unregistered' combined with the J2000 positional coordinates for the X-ray source, e.g., 'CXOU J163228.2-473755'. The X-ray sources numbered 172 and 173 have the same positions in this table, as #172 is an extended source surrounding the point source #173. So as to avoid having duplicate names for these 2 sources, the HEASARC has given them (unofficial) source suffixes of 'E' and 'P', respectively: thus, source #172 is now named 'CXOU J163447.8-473243E' and source #173 is now named 'CXOU J163447.8-473243P'.

ObsID_1
The Chandra observation identifier (ObsID) of a Chandra pointing in which wavdetect detected the source. The list of 27 Chandra pointings from which this catalog is derived is given in Table 1 of the reference paper. Since these pointings overlapped, a given source could be detected in more than pointing. See Section 2.1 of the reference paper for the details about wavdetect usage.

ObsID_2
The Chandra observation identifier (ObsID) of a Chandra pointing in which wavdetect detected the source. The list of 27 Chandra pointings from which this catalog is derived is given in Table 1 of the reference paper. Since these pointings overlapped, a given source could be detected in more than pointing. See Section 2.1 of the reference paper for the details about wavdetect usage.

ObsID_3
The Chandra observation identifier (ObsID) of a Chandra pointing in which wavdetect detected the source. The list of 27 Chandra pointings from which this catalog is derived is given in Table 1 of the reference paper. Since these pointings overlapped, a given source could be detected in more than pointing. See Section 2.1 of the reference paper for the details about wavdetect usage.

RA
The Right Ascension of the X-ray source in the selected equinox. This was given in J2000 decimal degrees to a precision of 10-6 degrees in the original table. If the source is detected in multiple observations, the position reported is the weighted average of its positions in different observations.

Dec
The Declination of the X-ray source in the selected equinox. This was given in J2000 decimal degrees to a precision of 10-6 degrees in the original table. If the source is detected in multiple observations, the position reported is the weighted average of its positions in different observations.

LII
The Galactic Longitude of the X-ray source.

BII
The Galactic Latitude of the X-ray source.

Error_Radius
The positional uncertainty of the source, in arcseconds. 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. (2005, ApJ, 635, 907) and the average systematic uncertainty of the positions in that observation after astrometric refinement (see Column 5 in Table 2 of the reference paper). 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.

Off_Axis_1
The offset angular separation of the source from the center of the aim point of the observation, in arcminutes, as specified by the corresponding ObsID, i.e., as given by the obsid_1 parameter value.

Off_Axis_2
The offset angular separation of the source from the center of the aim point of the observation, in arcminutes, as specified by the corresponding ObsID, i.e., as given by the obsid_2 parameter value.

Off_Axis_3
The offset angular separation of the source from the center of the aim point of the observation, in arcminutes, as specified by the corresponding ObsID, i.e., as given by the obsid_3 parameter value.

FB_Significance
The significance of the X-ray source in the full 0.5 - 10 keV band. It is calculated by finding the probability that the source is a noise fluctuation using Equation (5) of the reference paper 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 the individual observations.

SB_Significance
The significance of the X-ray source in the soft 0.5 - 2 keV band. It is calculated by finding the probability that the source is a noise fluctuation using Equation (5) of the reference paper 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 the individual observations.

HB_Significance
The significance of the X-ray source in the hard 2 - 10 keV band. It is calculated by finding the probability that the source is a noise fluctuation using Equation (5) of the reference paper 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 the individual observations.

Extraction_Radius_1
The radius of the aperture source region, in arcseconds, in the Chandra observation of the source specified in the obsid_1 parameter. For most sources, the aperture source region is defined as a circle with a radius equal to the 90% enclosed-count fraction (ECF) for 4.5 keV photons, i.e., the point-spread function (PSF) radius. For potentially extended sources, flagged with a value of 'e' in the corresponding source_flags parameter, 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 of the reference paper; in such cases, the radius provided in the catalog represents the outer radius of the pie sector.

Extraction_Radius_2
The radius of the aperture source region, in arcseconds, in the Chandra observation of the source specified in the obsid_2 parameter. For most sources, the aperture source region is defined as a circle with a radius equal to the 90% enclosed-count fraction (ECF) for 4.5 keV photons, i.e., the point-spread function (PSF) radius. For potentially extended sources, flagged with a value of 'e' in the corresponding source_flags parameter, 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 of the reference paper; in such cases, the radius provided in the catalog represents the outer radius of the pie sector.

Extraction_Radius_3
The radius of the aperture source region, in arcseconds, in the Chandra observation of the source specified in the obsid_3 parameter. For most sources, the aperture source region is defined as a circle with a radius equal to the 90% enclosed-count fraction (ECF) for 4.5 keV photons, i.e., the point-spread function (PSF) radius. For potentially extended sources, flagged with a value of 'e' in the corresponding source_flags parameter, 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 of the reference paper; in such cases, the radius provided in the catalog represents the outer radius of the pie sector.

PSF_Radius_1
The PSF radius for the 90% ECF for 4.5 keV photons at the detector location of the source, in arcseconds, in the Chandra observation of the source specified in the obsid_1 parameter. The PSF radius varies with detector position, generally increasing with increasing offset angle from the observation aim point.

PSF_Radius_2
The PSF radius for the 90% ECF for 4.5 keV photons at the detector location of the source, in arcseconds, in the Chandra observation of the source specified in the obsid_2 parameter. The PSF radius varies with detector position, generally increasing with increasing offset angle from the observation aim point

PSF_Radius_3
The PSF radius for the 90% ECF for 4.5 keV photons at the detector location of the source, in arcseconds, in the Chandra observation of the source specified in the obsid_3 parameter. The PSF radius varies with detector position, generally increasing with increasing offset angle from the observation aim point

Source_Flags_1
This parameter contains flags for the specified source in the Chandra observation of the source specified in the obsid_1 parameter, as follows:

     Flag    Meaning

     b       'blended': blended source that is unblended in another observation.
     c       'created': source noticed by eye but not detected by wavdetect. The
             source aperture region was created manually based on the visible
             position and extent of the source. The positional uncertainties
             calculated for such sources underestimate the true uncertainties,
             since the source is found by eye and not by wavdetect.
     e       'extended': possibly extended source. The semi-major axis of the
             smallest aperture region defined by wavdetect for such sources is
             larger than twice the PSF radius reported in the corresponding
             psf_radius_1 parameter. These sources are typically detected in
             images that have been binned by 4 x 4 or 8 x 8 pixels.
     id      'inspected duplicate': possible duplicate source flagged for manual
             inspection. A 'duplicate' source refers to a single source detected
             in multiple overlapping observations;sources were considered to be
             duplicates of one another if the distance between them was smaller
             than the quadrature sum of their positional uncertainties. Sources
             were flagged for manual inspection if (1) they were separated by
             a distance greater than the quadrature sum of their positional
             uncertainties but smaller than the simple sum of their positional
             uncertainties, or (2) they were separated by a distance smaller
             than the quadrature sum of their positional uncertainties but
             differed in a substantial way (e.g., one is flagged as possibly
             extended while another is not, one is found to have two duplicates
             by the distance criterion but these two duplicates of the first
             source are not found to be duplicates of one another by the distance
             criterion). Generally, if sources flagged with 'id' showed
             consistent photon fluxes and quantile parameters, they were
             determined to be true duplicates.
     m1, m2, 'modified': in cases where the circular source aperture region
      or m3  overlaps with the aperture region of another source, the source
             region is modified to reduce overlapping. See Table 6 of the
             reference paper 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 an 's' value.
     vl      'variable long': source determined to be variable on long (hours to
             days) timescales. The photon flux in at least one energy band (full,
              soft, or hard) varies by >= 3 sigma between different observations.
     vp      'variable probable': source is probably variable on short (second
             to hour) timescales. The K-S test finds the source light curve
             within a single observation to be inconsistent with a constant
             light curve at a 95% confidence level.
     vs      'variable short': source determined to be variable on short
             (seconds to hours) timescales. The K-S test finds the source
             light curve within a single observation to be inconsistent with a
             constant light curve at a >= 3-sigma confidence level.
  

Source_Flags_2
This parameter contains flags for the specified source in the Chandra observation of the source specified in the obsid_2 parameter, with the same possible values and meanings as given for the source_flags_1 parameter (see above).

Source_Flags_3
This parameter contains flags for the specified source in the Chandra observation of the source specified in the obsid_3 parameter, with the same possible values and meanings as given for the source_flags_1 parameter (see above).

FB_Counts_Limit
This parameter is set to '<' if the corresponding counts value is an upper limit rather than an actual detection in this band.

FB_Counts
The net source counts in the full 0.5-10 keV band, calculated as described in Section 2.2 of the reference paper.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 et al. (1991, ApJ, 374, 344); in such cases, the corresponding error parameters are left blank and the corresponding limit value set to '<'. For sources detected in multiple observations, the net counts from different observations were added together.

FB_Counts_Pos_Err
The upper 1-sigma error for the net full 0.5-10 keV band source counts. For sources detected in multiple observations, the errors are combined in quadrature.

FB_Counts_Neg_Err
The lower 1-sigma error for the net full 0.5-10 keV band source counts. For sources detected in multiple observations, the errors are combined in quadrature.

SB_Counts_Limit
This parameter is set to '<' if the corresponding counts value is an upper limit rather than an actual detection in this band.

SB_Counts
The net source counts in the soft 0.5-2 keV band, calculated as described in Section 2.2 of the reference paper.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 et al. (1991, ApJ, 374, 344); in such cases, the corresponding error parameters are left blank and the corresponding limit value set to '<'. For sources detected in multiple observations, the net counts from different observations were added together.

SB_Counts_Pos_Err
The upper 1-sigma error for the net soft 0.5-2 keV band source counts. For sources detected in multiple observations, the errors are combined in quadrature.

SB_Counts_Neg_Err
The lower 1-sigma error for the net soft 0.5-2 keV band source counts. For sources detected in multiple observations, the errors are combined in quadrature.

HB_Counts_Limit
This parameter is set to '<' if the corresponding counts value is an upper limit rather than an actual detection in this band.

HB_Counts
The net source counts in the hard 2-10 keV band, calculated as described in Section 2.2 of the reference paper.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 et al. (1991, ApJ, 374, 344); in such cases, the corresponding error parameters are left blank and the corresponding limit value set to '<'. For sources detected in multiple observations, the net counts from different observations were added together.

HB_Counts_Pos_Err
The upper 1-sigma error for the net hard 2-10 keV band source counts. For sources detected in multiple observations, the errors are combined in quadrature.

HB_Counts_Neg_Err
The lower 1-sigma error for the net hard 2-10 keV band source counts. For sources detected in multiple observations, the errors are combined in quadrature.

FB_Photon_Flux_Limit
This parameter is set to '<' if the corresponding photon flux value is an upper limit rather than an actual detection in this band.

FB_Photon_Flux
The photon flux of the Chandra source in the full 0.5-10 keV band, in photons cm-2 s-1. 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, the corresponding error parameters are left blank and the corresponding limit value is set to '<'. For sources detected in multiple observations, the average photon fluxes are reported; if a source was found to be variable between observations (flagged with a value of 'vl' in the source_flags parameter), then its photon fluxes from individual observations were simply averaged, but otherwise its photon fluxes were weight-averaged.

FB_Photon_Flux_Pos_Err
The upper 1-sigma error in the net full 0.5-10 keV band photon flux, in photons cm-2 s-1.

FB_Photon_Flux_Neg_Err
The lower 1-sigma error in the net full 0.5-10 keV band photon flux, in photons cm-2 s-1.

SB_Photon_Flux_Limit
This parameter is set to '<' if the corresponding photon flux value is an upper limit rather than an actual detection in this band.

SB_Photon_Flux
The photon flux of the Chandra source in the soft 0.5-2 keV band, in photons cm-2 s-1. 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, the corresponding error parameters are left blank and the corresponding limit value is set to '<'. For sources detected in multiple observations, the average photon fluxes are reported; if a source was found to be variable between observations (flagged with a value of 'vl' in the source_flags parameter), then its photon fluxes from individual observations were simply averaged, but otherwise its photon fluxes were weight-averaged.

SB_Photon_Flux_Pos_Err
The upper 1-sigma error in the net soft 0.5-2 keV band photon flux, in photons cm-2 s-1.

SB_Photon_Flux_Neg_Err
The lower 1-sigma error in the net soft 0.5-2 keV band photon flux, in photons cm-2 s-1.

HB_Photon_Flux_Limit
This parameter is set to '<' if the corresponding photon flux value is an upper limit rather than an actual detection in this band.

HB_Photon_Flux
The photon flux of the Chandra source in the hard 2-10 keV band, in photons cm-2 s-1. 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, the corresponding error parameters are left blank and the corresponding limit value is set to '<'. For sources detected in multiple observations, the average photon fluxes are reported; if a source was found to be variable between observations (flagged with a value of 'vl' in the source_flags parameter), then its photon fluxes from individual observations were simply averaged, but otherwise its photon fluxes were weight-averaged.

HB_Photon_Flux_Pos_Err
The upper 1-sigma error in the net hard 2-10 keV band photon flux, in photons cm-2 s-1

HB_Photon_Flux_Neg_Err
The lower 1-sigma error in the net hard 2-10 keV band photon flux, in photons cm-2 s-1.

Median_Energy
The median energy of the source, in keV. 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.

Median_Energy_Error
The 1-sigma error in the median source energy, in keV.

Q25_Energy
The energy below which 25% of the total source counts reside, in keV. 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.

Q25_Energy_Error
The 1-sigma error in the energy below which 25% of the total source counts reside, in keV.

Q75_Energy
The energy below which 75% of the total source counts reside, in keV. 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.

Q75_Energy_Error
The 1-sigma error in the energy below which 75% of the total source counts reside, in keV.

FB_Flux_Limit
This parameter is set to '<' if the corresponding full band flux value is an upper limit rather than an actual detection.

FB_Flux
The energy flux of the source in the full 0.5-10 keV band, in erg cm-2 s-1. 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 herein, the error parameter value is left blank, and the corresponding limit value is set to '<'.

FB_Flux_Pos_Err
The upper 1-sigma error in the net full band 0.5-10 keV band energy flux, in erg cm-2 s-1.

FB_Flux_Neg_Err
The lower 1-sigma error in the net full band 0.5-10 keV band energy flux, in erg cm-2 s-1.

Photometric_Flags
This parameter contains photometric flags which indicate the presence of non-detections in some of the energy bands. If the photometric values provided for a source are 90% upper limits in the full, soft, and/or hard energy bands, this column displays an 'F', 'S', and/or 'H', respectively.

Quantile_Group
The spectral group ('A', B', 'C', 'D' or 'E') defined using quantile diagrams to which the source belongs. See Section 3 (particularly Figure 8) of the reference paper for the full details about the quantile analysis and the significance of the spectral groups defined in this work.

VVV_Source
The source number of the nearest VISTA Variables in the Via Lactea (VVV: Minniti et al. 2010, NewA, 14, 433) Survey infrared source to the Chandra source position, if there is one within the 3-sigma uncertainty.

IR_RA
The Right Ascension of the infrared source counterpart in the selected equinox. This was given in J2000 decimal degrees to a precision of 10-6 degrees in the original table.

IR_Dec
The Declination of the infrared source counterpart in the selected equinox. This was given in J2000 decimal degrees to a precision of 10-6 degrees in the original table.

Xray_IR_Offset
The angular separation between the Chandra and VVV source positions, in arcseconds.

IR_Noise_Probability
The probability that the VVV infrared source counterpart is a noise fluctuation, as provided in the VVV Catalog.

IR_Match_Reliability
The reliability of the VVV counterpart calculated according to the method of Sutherland & Saunders (1992, MNRAS, 259, 413). The reliability depends on the angular 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.


Contact Person

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Last Modified: 17-Mar-2015