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GC47TUCCXO - 47 Tuc Globular Cluster Chandra X-Ray Point Source Catalog

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Overview

The authors have detected 300 X-ray sources within the half-mass radius (2.79') of the globular cluster 47 Tucanae in a deep (281 ks) Chandra exposure. They perform photometry and simple spectral fitting for our detected sources and construct luminosity functions, X-ray color-magnitude, and color-color diagrams. Eighty-seven X-ray sources show variability on timescales from hours to years. Thirty-one of the new X-ray sources are identified with chromospherically active binaries from the catalogs of Albrow and coworkers (2001, CDS Cat. <J/ApJ/559/1060>). The authors estimate that the total number of neutron stars in 47 Tuc is of order 300, reducing the discrepancy between theoretical neutron star retention rates and observed neutron star populations in globular clusters. The data used in this paper are from the 2000 and 2002 Chandra observations of the globular cluster 47 Tuc. The 2000 observations, initially described in Grindlay et al. (2001, Science 292, 2290), were performed with the ACIS-I CCD array at the telescope focus, while the 2002 observations placed the back-illuminated ACIS-S aim point at the focus for maximum low-energy sensitivity.

The authors combined the results from wavdetect source detection runs with a threshold probability of 1 x 10^-5, in two energy bands (0.5 - 2.0 keV and 0.5 - 6.0 keV for the 2000 observations, and (0.3 - 2.0 keV and 0.3 - 6.0 keV for the 2002 observations), to make independent source lists for the 2000 and 2002 observations, given in Tables 2 and 3 of the reference paper, which have been combined in the present HEASARC table. A total of 146 sources were detected in this way in the 2000 observations (entries with dataset_year = 2000), while 300 sources were detected in the 2002 observations (dataset_year = 2002). A total of 143 of the sources were clearly detected in both observations, while only three of the sources from the 2000 observations were not detected in the 2002 observations.


Catalog Bibcode

2005ApJ...625..796H

References

A deep Chandra survey of the globular cluster 47 Tucanae:
catalog of point sources.
    Heinke C.O., Grindlay J.E., Edmonds P.D., Cohn H.N., Lugger P.M.,
    Camilo F., Bogdanov S., Freire P.C.
   <Astrophys. J., 625, 796-824 (2005)>
   =2005ApJ...625..796H

Provenance

This table was created by the HEASARC in June 2007 based on CDS Catalog J/ApJ/625/796 files table2.dat, table3.dat, and (part of) table5.dat.

Parameters

Dataset_Year
The data in this table are derived from two separate Chandra sequences of observations, one set in 2000 (the data for which are listed in Table 3 of the reference paper), the second (longer) set in 2002 (listed in Table 2 of the reference paper). This HEASARC table combines the entries from both datasets into a single table, and, in order to distinguish entries, the HEASARC has created this parameter which, for a given X-ray sources, identifies the corresponding observation year.

Source_Number
The WAVDETECT (W) detection number of the X-ray source. Because of the iterative nature of source list construction over several papers (Grindlay et al. 2001, 2002; Edmonds et al. 2003a, 2003b), the W numbering scheme does not follow clear patterns and has holes (numbers that do not correspond to real sources within the chosen field).

Alt_Name_1
An alternative X-ray source designation as recommended by the CDS Dictionary of Nomenclature of Celestial Objects using the '[GHE2001] W' prefix as first used in Grindlay et al. (2001, Science, 292, 2290) and the X-ray (W) source number.

Name
The name for the X-ray source using the 'CXOGlb' prefix (for Chandra X-Ray Observatory, Globular Cluster) and the J2000.0 equatorial coordinates (JHHHMMSSs-DDMMSS), as registered with 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 coordinates to a precision of 0.001 seconds of time in the reference paper. The X-ray positions were aligned to the international celestial reference frame using the radio and/or HST optical follow-up positions of cleanly detected millisecond pulsars (MSPs) in the field of view.

RA_Error
The 1-sigma error (corresponding to the 68% confidence limits) in the Right Ascension of the X-ray source, in seconds of time.

Dec
The Declination of the X-ray source in the selected equinox. This was given in J2000.0 coordinates to a precision of 0.01 arcseconds in the reference paper. The X-ray positions were aligned to the international celestial reference frame using the radio and/or HST optical follow-up positions of cleanly detected millisecond pulsars (MSPs) in the field of view.

Dec_Error
The 1-sigma error (corresponding to the 68% confidence limits) in the Declination of the X-ray source, in arcseconds.

LII
The Galactic Longitude of the X-ray source.

BII
The Galactic Latitude of the X-ray source.

Radial_Distance
The radial distance of the X-ray source from the center of the 47 Tuc cluster (taken to be J2000.0 RA = 00h 24m 05.29s, Dec = -72d 04' 52.3" as in de Marchi et al. 1996, APJ, 468, L51), in arcseconds. This field is populated only for the 2002 dataset.

PSF_Fraction
The fraction of the 1.5 keV point-spread function (PSF) enclosed by the extraction region for the X-ray source.

Exposure
The exposure time for the X-ray source, in seconds (s). The HEASARC calculated the value of this parameter using the fractional exposure times given in Tables 3 and 5 of the reference paper (CDS tables table3.dat and table5.dat) and the nominal on-axis exposure times of 72155 and 281074 seconds for the 2000 and 2002 datasets, respectively.

Counts
The background-subtracted counts in the X-ray source in the 0.5 - 4.5 keV energy band.

Counts_Pos_Err
The upper limit 1-sigma (68% confidence) error in the background-subtracted 0.5 - 4.5 keV counts.

Counts_Neg_Err
The lower limit 1-sigma (68% confidence) error in the background-subtracted 0.5 - 4.5 keV counts.

SB1_Counts
The background-subtracted counts in the X-ray source in the 0.5 - 1.5 keV energy band.

SB1_Counts_Pos_Err
The upper limit 1-sigma (68% confidence) error in the background-subtracted 0.5 - 1.5 keV counts.

SB1_Counts_Neg_Err
The lower limit 1-sigma (68% confidence) error in the background-subtracted 0.5 - 1.5 keV counts

HB_Counts
The background-subtracted counts in the X-ray source in the 1.5 - 6.0 keV energy band.

HB_Counts_Pos_Err
The upper limit 1-sigma (68% confidence) error in the background-subtracted 1.5 - 6.0 keV counts.

HB_Counts_Neg_Err
The lower limit 1-sigma (68% confidence) error in the background-subtracted 1.5 - 6.0 keV counts.

Lx
The 0.5 - 6.0 keV luminosity of the X-ray source, in erg/s. Photon fluxes were computed from the recorded counts, effective apertures, exposure times, and effective area functions for each source. Assuming a 2 keV VMEKAL spectrum (a reasonable approximation for the average spectrum of the fainter X-ray sources; see Sections 5 and 7 of the reference paper), an absorbing column of 1.3 x 10^20 cm^-2, and a distance of 4.85 kpc, the authors derived conversion factors of 5.93 x 10^36 and 4.94 x 10^36 erg photon^-1 cm^2 to convert from photon flux to unabsorbed X-ray luminosity in the 0.5 - 6.0 and 0.5 - 2.5 keV energy bands, respectively. To recover the directly measured photon fluxes in photons cm^-2 s^-1, divide the quoted X-ray luminosities by these factors.

Lx_Pos_Err
The upper limit 1-sigma (68% confidence) error in the 0.5 - 6.0 keV luminosity, in erg/s.

Lx_Neg_Err
The lower limit 1-sigma (68% confidence) error in the 0.5 - 6.0 keV luminosity, in erg/s.

SB2_Lx
The 0.5 - 2.5 keV luminosity of the X-ray source, in erg/s. Photon fluxes were computed from the recorded counts, effective apertures, exposure times, and effective area functions for each source. Assuming a 2 keV VMEKAL spectrum (a reasonable approximation for the average spectrum of the fainter X-ray sources; see Sections 5 and 7 of the reference paper), an absorbing column of 1.3 x 10^20 cm^-2, and a distance of 4.85 kpc, the authors derived conversion factors of 5.93 x 10^36 and 4.94 x 10^36 erg photon^-1 cm^2 to convert from photon flux to unabsorbed X-ray luminosity in the 0.5 - 6.0 and 0.5 - 2.5 keV energy bands, respectively. To recover the directly measured photon fluxes in photons cm^-2 s^-1, divide the quoted X-ray luminosities by these factors.

SB2_Lx_Pos_Err
The upper limit 1-sigma (68% confidence) error in the 0.5 - 2.5 keV luminosity, in erg/s.

SB2_Lx_Neg_Err
The lower limit 1-sigma (68% confidence) error in the 0.5 - 2.5 keV luminosity, in erg/s.

Source_Type
The classification of the source, defined as follows:

      AB  = active binary
      CV  = cataclysmic variable
      qLX = quiescent low-mass X-ray binary containing where accretion onto
            a neutron star is stopped or greatly reduced
      AB  = an X-ray active binary consisting of normal stars in a tidally locked
            short-period binary, where the fast rotation rate drives increased
            coronal activity
      AGB = an AB from Albrow et al. (2001, CDS Cat. <J/ApJ/559/1060>) identified
            with an X-ray source in this work.
      MSP = millisecond radio pulsar
  

Source_Type_Flag
A value of '?' for this flag parameter indicates that there is some uncertainty in the source classification.

Alt_Name_2
A second alternative name for the source, defined as follows:

      AKO 9         = Auriere et al. (1989A&A...214..113A);
      ROSAT X #     = Verbunt & Hasinger (1998A&A...336..895V);
      MSP lettering = Camilo et al. (2000ApJ...535..975C),
                      Freire et al. (2001MNRAS.326..901F), and
                      Edmonds et al. (2002ApJ...564L..17E, 2002ApJ...579..741E)
  

Note_Flags
This flag parameter contains notes indicating variability or confusion, as follows:

      Y  = 99.9% confidence variability on years timescale;
      D  = 99.9% confidence variability on days timescale;
      H  = 99.9% confidence variability on hours timescale;
      D? = 99% confidence variability on days timescale;
      H? = 99% confidence variability on hours timescale;
      t  = not detected in the 2002 data; 2 of these may be spurious detections;
      c  = source may suffer from confusion;
      m  = source identified manually, rather than by WAVDETECT.
  

Class
The HEASARC Browse object classification, based on the value of the source_type parameter.


Contact Person

Questions regarding the GC47TUCCXO database table can be addressed to the HEASARC User Hotline.

Page Author: Browse Software Development Team
Last Modified: 19-Jun-2007