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RCW49CXO - RCW 49 Chandra X-Ray Point Source Catalog

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Overview

This table contains the list of X-ray sources detected in a high-resolution X-ray imaging study of the stellar population in the Galactic massive star-forming region RCW 49 and its central OB association Westerlund 2. The authors obtained a ~ 40 ks X-ray image of a ~ 17' x 17' field using the Chandra X-Ray Observatory and deep NIR images using the Infrared Survey Facility in a concentric ~ 8.3' x 8.3' region. They detected 468 X-ray sources with a photometric significance >=1.0 and a 1% or less chance of being a background fluctuation, and identified optical, near-infrared (NIR), and Spitzer mid-infrared (MIR) counterparts for 379 of them. The unprecedented spatial resolution and sensitivity of the X-ray image, enhanced by optical and infrared imaging data, yielded the following results: (1) The central OB association Westerlund 2 is resolved for the first time in the X-ray band. X-ray emission is detected from all spectroscopically identified early-type stars in this region. (2) Most (~ 86%) X-ray sources with optical or infrared identifications are cluster members in comparison with a control field in the Galactic plane. (3) A loose constraint (2-5 kpc) for the distance to RCW 49 is derived from the mean X-ray luminosity of T Tauri stars. (4) The cluster X-ray population consists of low-mass pre-main-sequence and early-type stars as obtained from X-ray and NIR photometry. About 30 new OB star candidates are identified. (5) The authors estimate a cluster radius of 6' - 7' based on the X-ray surface number density profiles. (6) A large fraction (~ 90%) of cluster members are identified individually using complimentary X-ray and MIR excess emission. (7) The brightest five X-ray sources, two Wolf-Rayet stars and three O stars, have hard thermal spectra.

The X-ray observation of RCW 49 was carried out using the Advanced CCD Imaging Spectrometer (ACIS) on board the Chandra X-Ray Observatory from 2003 August 23 UT 18:20 to August 24 UT 4:54. Four imaging array (ACIS-I) chips covered a 17 by 17 arcminutes field centered at (R.A., Dec.) = (10h24m00.5s, -57d 45' 18") in the equinox J2000.0 for a 36.7 ks exposure. ACIS-I covers the 0.5 - 8.0 keV energy band with a spectral resolution of ~ 150 eV at 6 keV and a point-spread function (PSF) radius of ~ 0.5" within ~ 2' of the on-axis position, degrading to ~ 6" at a 10' off-axis angle. The data were taken with the very faint telemetry mode and the timed exposure CCD operation with a frame time of 3.2 s.

Sources with photometric significance of larger than 2 were fitted with an absorbed thin thermal plasma model. The abundance was fixed to be 0.3 times the solar value. Fits lacking uncertainties, fits with large uncertainties, and fits with frozen parameters should be viewed merely as splines to the data to obtain rough estimates of the X-ray luminosities: the listed parameter values are considered unreliable in such cases.

The authors also conducted NIR observations on 2004 December 25 and 28 using the Simultaneous three-color Infrared Imager for Unbiased Surveys (SIRIUS) mounted on the Cassegrain focus of the IRSF 1.4 m telescope at the South African Astronomical Observatory. SIRIUS is a NIR imager capable of obtaining simultaneous images in the J, H, and K_s bands. The instrument is equipped with three HAWAII arrays of 1024 by 1024 pixels. The pixel scale of 0.45" is an excellent match with the on-axis spatial resolution of Chandra. The authors covered 8.3 by 8.3 arcminute fields at two positions, one aimed at RCW 49 (10h24m01.9s, -57d 45' 31") and the other at a control region.


Catalog Bibcode

2007ApJ...665..719T

References

An X-ray Imaging Study of the Stellar Population in RCW 49
    Tsujimoto M., Feigelson E.D., Townsley L.K., Broos P.S., Getman K.V.,
    Wang J., Garmire G.P., Baba D., Nagayama T., Tamura M., Churchwell E.B
   <Ap. J. 665, 719 (2007)>
   = 2007ApJ...665..719T

Provenance

This table was created by the HEASARC in October 2007 based on the versions of Tables 1, 2, and 3 from the paper which were obtained from the electronic ApJ website.

Parameters

Source_Number
A running X-ray source number in order of increasing J2000.0 Right Ascension.

Alt_Name
An alternative name for the X-ray source using the '[TFT2002]' prefix (for Tsujimoto, Feigelson and Townsley, 2007) and the source number, as recommended by the CDS Dictionary of Nomenclature of Celestial Objects.

Name
The name for the X-ray source using the 'CXOU' prefix (for Chandra X-Ray Observatory, Unregistered) and the truncated J2000.0 coordinates (JHHMMSS.s+DDMMSS), in the standard way recommended by the CDS Dictionary of Nomenclature of Celestial Objects.

RA
The Right Ascension of the X-ray source in the selected equinox. This was given in J2000.0 decimal degrees to a precision of 10-5 degrees (0.036 arcseconds) in the original table. The X-ray positions given here include a correction for systematic errors in the Chandra aspect system to match the absolute astrometry of 2MASS using the closest ACIS-2MASS pairs.

Dec
The Declination of the X-ray source in the selected equinox. This was given in J2000.0 decimal degrees to a precision of 10-5 degrees (0.036 arcseconds) in the original table. The X-ray positions given here include a correction for systematic errors in the Chandra aspect system to match the absolute astrometry of 2MASS using the closest ACIS-2MASS pairs.

LII
The Galactic Longitude of the X-ray source.

BII
The Galactic Latitude of the X-ray source.

Error_Radius
The positional error of the X-ray source, in arcseconds, being the estimated standard deviation of the random component of the position error, {sqrt}[sigma_x2 + sigma_y2]. The single-axis position errors, sigma_x and sigma_y, are estimated from the single-axis standard deviations of the PSF inside the extraction region and the number of counts extracted.

Off_Axis
The off-axis angle of the X-ray source, in arcminutes.

Counts
The estimated net (i.e., background-subtracted) counts of the X-ray source in the total energy band (0.5 - 8 keV).

Counts_Error
The average of the upper and lower 1-sigma errors in the net total-band (0.5 - 8 keV) counts of the X-ray source. The errors were calculated using the Gehrels (1986, ApJ, 303, 336) approximation.

Bck_Counts
The background counts extracted locally in a region around the X-ray source, and scaled to the source extraction area, in the total energy band (0.5 - 8.0 keV).

HB_Counts
The estimated net (i.e., background-subtracted) counts of the X-ray source in the hard energy band (2 - 8 keV).

PSF_Fraction
The fraction of the PSF enclosed within the source extraction region (at 1.497 keV). A reduced PSF fraction (significantly below 0.9 or 90%) may indicate that the source is in a crowded region.

SNR
The X-ray source photometric significance in the total band.

Log_P_Null_Limit
This parameter is set to '<' to indicate that the corresponding value of log_p_null is an upper limit

Log_P_Null
The logarithmic probability that the extracted (0.5 - 8 keV) counts are solely from the background.

Source_Flag
This parameter contains flags that indicate the presence of the following source anomalies:

      g = fractional time that source was on a detector
          (FRACEXPO from mkarf) is < 0.9;
      e = source on field edge;
      p = source piled up;
      s = source on readout streak.
  

Var_Flag
This parameter contains flag values that contain X-ray source variability characterization based on the K-S statistic applied to the total-band counts, coded as follows (no value is reported for sources in chip gaps or on field edges):

      a = no evidence for variability (0.05 < P_KS);
      b = possibly variable (0.005 < P_KS < 0.05);
      c = definitely variable (P_KS < 0.005).
  

Exposure
The effective exposure time for the X-ray source, in seconds. This is the approximate time the source would have to be observed on-axis to obtain the reported number of counts.

Median_Energy
The background-corrected median photon energy, in keV, of the X-ray source counts in the total (0.5 - 8 keV) band.

Flux
The photometric 0.5 - 8 keV estimated flux of the X-ray source, in erg/s/cm2. See the discussion in Section 4.1.3 of the reference paper for more details.

Log_NH_Neg_Err
The lower 90%-confidence error in the value of log_nh derived from the spectral fit, in log(H-atoms/cm2). More significant digits are used for uncertainties <= 0.1 in order to avoid large rounding errors; for consistency, the same number of significant digits is used for both lower and upper uncertainties. Uncertainties are missing when XSPEC was unable to compute them or when their values were so large that the parameter is effectively unconstrained.

Log_NH
The log of the absorbing hydrogen column density derived from the spectral fit (see Overview), in H-atoms/cm2.

Log_NH_Pos_Err
The upper 90%-confidence error in the value of log_nh derived from the spectral fit, in log(H-atoms/cm2). More significant digits are used for uncertainties <= 0.1 in order to avoid large rounding errors; for consistency, the same number of significant digits is used for both lower and upper uncertainties. Uncertainties are missing when XSPEC was unable to compute them or when their values were so large that the parameter is effectively unconstrained.

APEC_kT_Neg_Err
The lower 90%-confidence error in the value of the APEC plasma temperature, apec_kt, derived from the spectral fit, in keV. More significant digits are used for uncertainties <= 0.1 in order to avoid large rounding errors; for consistency, the same number of significant digits is used for both lower and upper uncertainties. Uncertainties are missing when XSPEC was unable to compute them or when their values were so large that the parameter is effectively unconstrained.

APEC_kT
Plasma Temperature from Spectral Fit (keV)

APEC_kT_Pos_Err
The upper 90%-confidence error in the value of the APEC plasma temperature, apec_kt, derived from the spectral fit, in keV. More significant digits are used for uncertainties <= 0.1 in order to avoid large rounding errors; for consistency, the same number of significant digits is used for both lower and upper uncertainties. Uncertainties are missing when XSPEC was unable to compute them or when their values were so large that the parameter is effectively unconstrained.

Log_EM_Neg_Err
The lower 90%-confidence error in the value of the logarithm of the APEC emission measure log_em, in cm-3. More significant digits are used for uncertainties <= 0.1 in order to avoid large rounding errors; for consistency, the same number of significant digits is used for both lower and upper uncertainties. Uncertainties are missing when XSPEC was unable to compute them or when their values were so large that the parameter is effectively unconstrained.

Log_EM
The logarithm of the APEC emission measure, in cm-3, derived from the spectral fit, assuming a distance of 4.2 kpc.

Log_EM_Pos_Err
The upper 90%-confidence error in the value of the logarithm of the APEC emission measure log_em, in cm-3. More significant digits are used for uncertainties <= 0.1 in order to avoid large rounding errors; for consistency, the same number of significant digits is used for both lower and upper uncertainties. Uncertainties are missing when XSPEC was unable to compute them or when their values were so large that the parameter is effectively unconstrained.

Log_SB_Lx_Obs
The log of the observed soft-band (0.5 - 2 keV) luminosity of the X-ray source, in erg/s, derived assuming a distance of 4.2 kpc.

Log_HB_Lx_Obs
The log of the observed hard-band (2 - 8 keV) luminosity of the X-ray source, in erg/s, derived assuming a distance of 4.2 kpc.

Log_HB_Lx
The log of the absorption-corrected hard-band (2 - 8 keV) luminosity of the X-ray source, in erg/s, derived assuming a distance of 4.2 kpc.

Log_Lx_Obs
The log of the observed total-band (0.5 - 8 keV) luminosity of the X-ray source, in erg/s, derived assuming a distance of 4.2 kpc.

Log_Lx
The log of the absorption-corrected total-band (0.5 - 8 keV) luminosity of the X-ray source, in erg/s, derived assuming a distance of 4.2 kpc. Absorption-corrected luminosities are omitted when log NH > 22.5, since the soft-band emission is essentially unmeasurable in such cases.

NOMAD_Name
The Naval Observatory Merged Astrometric Database (NOMAD) identification of the optical/IR counterpart to the X-ray source. The HEASARC has added the prefix 'NOMAD1' to the numerical part of the name given in Table 3 of the reference paper to conform with the recommendations of the CDS Dictionary of Nomenclature of Celestial Objects.

TwoMASS_Name
The 2MASS identification of the optical/IR counterpart to the X-ray source. The HEASARC has added the standard prefix '2MASS J' to the numerical (position-based) part of the name given in Table 3 of the reference paper.

IRAC_ID
The GLIMPSE Infrared Array Camera (IRAC) identification of the optical/IR counterpart to the X-ray source based on the position of the object in galactic coordinates. GLIMPSE is a Legacy Program of the Spitzer Space Telescope to survey a ~ 220 square degrees region of the Galactic plane at four MIR bands ([3.6], [4.5], [5.8], and [8.0] micron) with a 1.6 - 1.9 arcseconds resolution using the IRAC.

NIR_Flag
This parameter flags the source of the NIR photometry of the counterpart to the X-ray source, where 'T' and 'S' indicate that the NIR photometry is from 2MASS and SIRIUS data (see Overview), respectively. NIR magnitudes are given only for good photometry; i.e., flags A, B, or C for 2MASS sources and the uncertainty of < 0.1 mag for SIRIUS sources.

Rmag
The R-band magnitude of the optical/IR counterpart to the X-ray source.

Jmag
The J-band magnitude of the optical/IR counterpart to the X-ray source.

Hmag
The H-band magnitude of the optical/IR counterpart to the X-ray source.

Ks_Mag
The K_s-band magnitude of the optical/IR counterpart to the X-ray source.

IRAC_3p6_um_Mag
The IRAC 3.6-micron band magnitude of the IR counterpart to the X-ray source.

IRAC_4p5_um_Mag
The IRAC 4.5-micron band magnitude of the IR counterpart to the X-ray source.

IRAC_5p8_um_Mag
The IRAC 5.8-micron band magnitude of the IR counterpart to the X-ray source.

IRAC_8p0_um_Mag
The IRAC 8.0-micron band magnitude of the IR counterpart to the X-ray source.

Comments
This parameter contains literature identifications and/or flags for the source. The identifications beginning 'MSP' are from Moffat et al. (1991, AJ, 102, 642) and those beginning 'BM' are from Belloni & Mereghetti (1994, A&A, 286, 935). There are 3 types of flags ('NE', 'ME', and `ET') which indicate the NIR excess sources identified in the NIR color-color diagram (Fig. 9a of the reference paper), MIR excess sources (Whitney et al. 2004, ApJS, 154, 315), and early-type star candidates that have a brighter K-band magnitude than a main-sequence B2V star in the NIR color-magnitude diagram (Fig 9b of the reference paper), respectively.


Contact Person

Questions regarding the RCW49CXO database table can be addressed to the HEASARC User Hotline.

Page Author: Browse Software Development Team
Last Modified: 5-Mar-2012