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IC10CXO - IC 10 Chandra X-ray Point Source Catalog

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Overview

The authors monitored the Cassiopeia dwarf galaxy (IC 10) in a series of 10 Chandra ACIS-S observations to capture its variable and transient X-ray source population, which is expected to be dominated by High Mass X-ray Binaries (HMXBs). They present a sample of 21 X-ray sources that are variable between observations at the 3-sigma level, from a catalog of 110 unique point sources (the HEASARC notes that there are actually 111 sources in the CDS version of the catalog from which this HEASARC table originates). The authors find four transients (flux variability ratio greater than 10) and a further eight objects with ratios >5. The observations span the years 2003-2010 and reach a limiting luminosity of >1035 erg/s, providing sensitivity to X-ray binaries in IC 10 as well as flare stars in the foreground Milky Way. The nature of the variable sources is investigated from light curves, X-ray spectra, energy quantiles, and optical counterparts. The purpose of this study is to discover the composition of the X-ray binary population in a young starburst environment. IC 10 provides a sharp contrast in stellar population age (<10 million years) when compared to the Magellanic Clouds (40-200 Myr) where most of the known HMXBs reside. The authors find 10 strong HMXB candidates, 2 probable background active galactic nuclei, 4 foreground flare-stars or active binaries, and 5 not yet classifiable sources. Complete classification of the sample requires optical spectroscopy for radial velocity analysis and deeper X-ray observations to obtain higher S/N spectra and search for pulsations. A catalog (contained in this HEASARC table) has been created and supporting data sets (the data used to create the light curves shown in Figures 3, 4 and 5 in the reference paper) are available at http://cdsarc.u-strasbg.fr/ftp/cats/J/ApJ/836/50/.

A monitoring series of 7x15 ks Chandra/ACIS observations, spaced at roughly six-week intervals was obtained during 2009-2010. A pair of very deep ACIS-S3 observations (2x45ks) made in 2006 November provided a reference data set for improved source positions and spectral information. The original Wang+ (2005, MNRAS, 362, 1065) Chandra (ACIS-S3) observation of 30 ks made in 2003 was also included in this analysis.

The complete listing of 10 Chandra observation identifiers (ObsIDs) comprising the data set is summarized in Table 1 of the reference paper, also shown here:

MJD    |Date         |ObsID|Flag|Exp.|RA(J2000)Dec(J2000)|Roll|Num. Sources
                                  ks  hh mm ss  dd mm ss  deg.

52710.7|2003 Mar 12  |03953|a   |28.9|00 20 25 +59 16 55|339.27|31
54041.8|2006 Nov 2   |07082|    |40.1|00 20 04 +59 16 45|223.70|48
54044.2|2006 Nov 5   |08458|    |40.5|00 20 04 +59 16 45|223.70|41
55140.7|2009 Nov 5   |11080|    |14.6|00 20 17 +59 17 56|226.53|19
55190.2|2009 Dec 25  |11081|    | 8.1|00 20 19 +59 18 02|286.15|24
55238.5|2010 Feb 11  |11082|    |14.7|00 20 23 +59 17 10|320.56|24
55290.6|2010 Apr 4   |11083|    |14.7|00 20 34 +59 19 01| 10.32|25
55337.8|2010 May 21  |11084|    |14.2|00 20 25 +59 20 16| 67.89|27
55397.5|2010 Jul 20  |11085|    |14.5|00 20 11 +59 19 13|121.25|22
55444.6|2010 Sep 5   |11086|    |14.7|00 20 15 +59 18 11|157.71|27
       |2006 Nov 2-5 |57082|b   |80.6|00 20 04 +59 16 45|223.70|63

Flag values as follows:

  a = ObsID 03953 used about half of the CCD area in subarray mode.
  b = Merged 2006 data set referred to as ObsID 57082 consists of the nearly
      contiguous ObsIDs 07082 and 08458, which had identical pointings.

Roll is the spacecraft roll angle, and Num. Sources is the number of unique point sources detected in each observation after combining wavdetect lists from the soft (S: 0.3-1.5 keV), broad (B: 0.3-8 keV) and hard (H: 2.5-8 keV) energy bands.


Catalog Bibcode

2017ApJ...836...50L

References

The X-ray binary population of the nearby dwarf starburst galaxy IC 10:
variable and transient X-ray sources.
    Laycock S., Cappallo R., Williams B.F., Prestwich A., Binder B.,
    Christodoulou D.M.
   <Astrophys. J., 836, 50-50 (2017)>
   =2017ApJ...836...50L    (SIMBAD/NED BibCode)

Provenance

This table was created by the HEASARC in November 2017 based upon the CDS Catalog J/ApJ/836/50 file table2.dat.

Parameters

Source_Number
A unique identification number for each X-ray source in this catalog.

Name
The standard Chandra source designation recommended by the CDS Dictionary of Nomenclature of Celestial Objects, using the prefix of 'CXOU' for 'Chandra X-ray Observatory, Unregistered' and the J2000.0 equatorial coordinates truncated to 0.1 seconds of time in RA and to 1 arcsecond in Dec.

Wang_Source_Numbers
A cross reference(s) to spatially coincident sources in the Wang et al. (2005, MNRAS, 362, 1065) catalog of IC 10 sources (available at the HEASARC as the IC10XMMCXO table), e.g., '11C' or '46X', where 'X' refers to the list list of XMM-Newton sources given in Table 1 of Wang et al. and 'C' refers to the list of Chandra sources given in Table 2 of Wang et al. Notice that in Simbad the former are named '[WWW2005] XP NN', where NN is the source number, and the latter are named '[WWW2005] XA NN'.

Best_Det_ID
The source identifier within the observation that provided the best detection, e.g., 'XS57082S3B_1', where digits 3-7 are the ObsID, 'S3' is the ACIS-S3 CCD and the 10th digit (S, B or H) refers to the band in which the source had the highest significance, soft (0.3-1.5 keV), broad (0.3-8 keV) and hard (2.5-8 keV), respectively.

RA
The Right Ascension of the Chandra source in the selected equinox after the astrometric correction described in the reference paper. The position was derived from the source detection with the smallest error circle. This was given in J2000.0 decimal degrees in the original table.

Dec
The Declination of the Chandra source in the selected equinox after the astrometric correction described in the reference paper. The position was derived from the source detection with the smallest error circle. This was given in J2000.0 decimal degrees in the original table.

LII
The Galactic Longitude of the Chandra source. The position was derived from the source detection with the smallest error circle

BII
The Galactic Latitude of the Chandra source. The position was derived from the source detection with the smallest error circle

Error_Radius
The positional uncertainty radius, in arcseconds, of the Chandra source at a 95% confidence level, as derived using the methodology described in Hong et al. (2005, ApJ, 635, 907).

Num_Pointings
The number of observations in which the source was in the field-of-view (FOV) of the Chandra ACIS S-3 detector.

Num_Detections
The number of observations in which the source was detected in the 0.3-8 keV (B) band.

Count_Rate
The average 0.3-8 keV (B-band) net count rate of the Chandra source, in ct s-1, as derived using the methodology described in Hong et al. (2005, ApJ, 635, 907). There are seven sources (source numbers 2, 4, 11, 59, 60, 61 and 62) for which no B-band count rates are given. These sources were presumably detected only in either the S or H band, but were not significant enough to count as detected in the B band.

Count_Rate_Error
The root-mean-squared error in the 0.3-8 keV band count rate of the Chandra source, in ct s-1, as derived using the methodology described in Hong et al. (2005, ApJ, 635, 907).

Min_Count_Rate
The minimum observed 0.3-8 keV (B-band) net count rate of the Chandra source (Rmin) among all of the observations in which it was in the field-of-view (FOV) of the Chandra ACIS S-3 detector, in ct s-1.

Min_Count_Rate_Error
The uncertainty in the minimum observed 0.3-8 keV (B-band) net count rate of the Chandra source (error[R_min_]) among all of the observations in which it was in the field-of-view (FOV) of the Chandra ACIS S-3 detector, in ct s-1.

Max_Count_Rate
The maximum observed 0.3-8 keV (B-band) net count rate of the Chandra source (Rmax) among all of the observations in which it was in the field-of-view (FOV) of the Chandra ACIS S-3 detector, in ct s-1.

Max_Count_Rate_Error
The uncertainty in the maximum observed 0.3-8 keV (B-band) net count rate of the Chandra source (error[R_max_]) among all of the observations in which it was in the field-of-view (FOV) of the Chandra ACIS S-3 detector, in ct s-1.

Count_Rate_Range
The range of the observed 0.3-8 keV (B-band) net count rate of the Chandra source among all of the observations in which it was in the field-of-view (FOV) of the Chandra ACIS S-3 detector, i.e., the maximum value minus the minimum value, in ct s-1.

Count_Rate_Ratio
The ratio of the maximum to the minimum observed 0.3-8 keV (B-band) net count rates of the Chandra source among all of the observations in which it was in the field-of-view (FOV) of the Chandra ACIS S-3 detector.

Var_Index
The variability ratio of the observed 0.3-8 keV (B-band) net count rate of the Chandra source among all of the observations in which it was in the field-of-view (FOV) of the Chandra ACIS S-3 detector. This is defined as (Rmax - Rmin)/sqrt(error[R_max_]2 + error[R_min_]2).

Net_Counts
The net counts in the 0.3-8 keV (B-band) for the Chandra source summed over all of the observations in which it was in the field-of-view (FOV) of the Chandra ACIS S-3 detector.

Total_Events
The total number of events in the 0.3-8 keV (B-band) in the extraction region of the Chandra source summed over all of the observations in which it was in the field-of-view (FOV) of the Chandra ACIS S-3 detector and there was a positive detection.

Median_Energy
The median energy of the events in the source extraction region, in keV, accumulated over all observations in which there were positive detections.

Median_Energy_Error
The standard deviation in the median energy of the events in the source extraction region, in keV.

Num_Bck_Events
The number of events in the background annulus region in the 0.3-8 keV (B-band) in the extraction region of the Chandra source summed over all of the observations in which it was in the field-of-view (FOV) of the Chandra ACIS S-3 detector and there were positive detections.

Median_Bck_Energy
The median energy of events in the background annulus region, in keV, accumulated over all observations in which there were positive detections.

Median_Bck_Energy_Error
The standard deviation in the median energy of the events in the background annulus region, in keV.

Slope_Quantile
The QDx Slope quantile for the spectrum of the Chandra source accumulated over all the observations. Energy quantiles (Hong et al. 2004, ApJ, 614, 508) were computed from the event lists for each unique source in the master catalog. Quantiles were computed for each observation and also for the combined event list, which provides the maximum number of counts and hence delivers better S/N values. In their analysis, the authors use two of the quantiles defined by Hong et al. (2004): the Slope quantile QDx, which is related to the steepness of the spectrum, and the Curvature quantile QDy, which is constructed from the ratio of the quartiles Q25/Q75. Full details are available in Hong et al. (2004).

Slope_Quantile_Neg_Err
The lower 1-sigma uncertainty in the QDx Slope quantile for the spectrum of the Chandra source accumulated over all the observations. A value of 1000. means that the parameter was unbounded in this direction. In the original CDS table, this quantity was always negative; the HEASARC has replaced these by their absolute values.

Slope_Quantile_Pos_Err
The upper 1-sigma uncertainty in the QDx Slope quantile for the spectrum of the Chandra source accumulated over all the observations. In the original CDS table, this quantity was sometimes negative; the HEASARC has replaced these by their absolute values.

Curve_Quantile
The QDy Curvature quantile for the spectrum of the Chandra source accumulated over all the observations. Energy quantiles (Hong et al. 2004, ApJ, 614, 508) were computed from the event lists for each unique source in the master catalog. Quantiles were computed for each observation and also for the combined event list, which provides the maximum number of counts and hence delivers better S/N values. In their analysis, the authors use two of the quantiles defined by Hong et al. (2004): the Slope quantile QDx, which is related to the steepness of the spectrum, and the Curvature quantile QDy, which is constructed from the ratio of the quartiles Q25/Q75. Full details are available in Hong et al. (2004).

Curve_Quantile_Neg_Err
The lower 1-sigma uncertainty in the QDy Curvature quantile for the spectrum of the Chandra source accumulated over all the observations. In the original CDS table, this quantity was always negative; the HEASARC has replaced these by their absolute values.

Curve_Quantile_Pos_Err
The upper 1-sigma uncertainty in the QDy Curvature quantile for the spectrum of the Chandra source accumulated over all the observations.

Source_Type
A candidate source classification based on the X-ray and optical properties of the source, coded as follows:

      T = Transient (Ma/Min Ratio > 10);
     TC = Transient Candidate;
      V = Variable;
      X = X-ray binary;
      S = Stellar Corona;
      A = AGN;
      U = unclassified.
  

Contact Person

Questions regarding the IC10CXO database table can be addressed to the HEASARC User Hotline.
Page Author: Browse Software Development Team
Last Modified: Tuesday, 07-Nov-2017 14:04:06 EST