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M81CXO2 - M 81 Chandra X-Ray Point Source Catalog

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Overview

This table contains the source table from an analysis of 15 Chandra ACIS observations of the nearby spiral galaxy M81 taken over the course of six weeks in 2005 May-July. Each observation reaches a sensitivity of ~1037 erg s-1. With these observations and one previous deeper Chandra observation (the properties of which are described in Table 1 and Section 2 of the reference paper), the authors have compiled a master source list of 265 point sources, extracted and fitted their spectra, and differentiated basic populations of sources through their colors. They also carried out variability analyses of individual point sources and of X-ray luminosity functions (XLFs) in multiple regions of M81 on timescales of days, months, and years. They find that, despite measuring significant variability in a considerable fraction of sources, snapshot observations provide a consistent determination of the XLF of M81. They also fit the XLFs for multiple regions of M81 and, using common parameterizations, compare these luminosity functions to those of two other spiral galaxies, M31 and the Milky Way.

This table contains the 265 point sources at or above the 99.9% probability level of being real according to AE's PROB_NO_SOURCE statistic (the "master" source list), and 11 additional "borderline" sources which have 99.0-99.9% probability of being real according to AE's PROB_NO_SOURCE statistic, for a total of 276 sources whose properties were described in Tables 3 and 4 of the reference paper. The 265 "master" sources have source numbers from 1 to 265 while the 11 "borderline" sources have source numbers beginning with 'B', e.g., they have source numbers 'B1' to 'B11'. Note that only coordinates are listed for 3 sources in the master source list (source numbers 234, 241 and 262) and 2 sources in the borderline source list (B8 and B9) because they were only in the field of view (on chip) of one observation (ObsID 735). Six additional sources near the center of M81 which were found using maximum likelihood image reconstruction are not included in either the master or borderline source lists contained herein but their positions are listed in table 2 of the reference paper.


Catalog Bibcode

2011ApJ...735...26S

References

Luminosity Functions and Point-Source Properties from Multiple Chandra
Observations of M81.
   Sell P.H., Pooley D., Zezas A., Heinz S., Homan, J., Lewin W.H.G.
   <Astrophys. J. 735, 26 (2011)>
   =2011ApJ...735...26S

Provenance

This table was created by the HEASARC in August 2011 based on electronic versions of Tables 3 and 4 from the reference paper which were obtained from the ApJ web site.

Parameters

Source_Number
A unique source number for each point source. The 265 "master" sources have source numbers from 1 to 265 while the 11 "borderline" sources have source numbers beginning with 'B', e.g., they have source numbers 'B1' to 'B11'

Alt_Name
An alternative source designation in the style recommended by the Dictionary of Nomenclature of Celestial Objects, which was created by the HEASARC using the prefix '[SPZ2011]' for Sell, Pooley, Zezas (2011) and the source number value.

Name
The primary source designation in the style recommended by the Dictionary of Nomenclature of Celestial Objects, which was created by the HEASARC using the prefix 'CXOU' for Chandra X-ray Observatory, Unregistered and the J2000.0 Right Ascension and Declination truncated to 0.1 seconds of time in RA and 1 arcsecond in Declination.

RA
The Right Ascension of the Chandra X-ray source in the selected equinox. This was given in J2000.0 decimal degrees to a precision of 10-6 degrees in the original table.

Dec
The Declination of the Chandra X-ray source in the selected equinox. This was given in J2000.0 decimal degrees to a precision of 10-6 degrees in the original table.

LII
The Galactic Longitude of the Chandra X-ray source.

BII
The Galactic Latitude of the Chandra X-ray source.

Off_Axis
The average off-axis angle on the sky between the source and the aimpoint of the observation in the merged observation, in arcminutes.

Raw_FB_Counts
The total source counts in the 0.5-6.0 keV energy range, referring to the number of counts extracted in all of the source regions in observations with ObsIDs 5935 to 5949.

Bck_FB_Counts
The number of background counts in the 0.5-6.0 keV energy range expected in the source region, based on the nearby annular merged background extraction.

SB_Counts
The net background-subtracted source counts in the soft (0.5-1 keV) energy band.

SB_Counts_Neg_Err
The lower uncertainty in the source soft-band counts using the Gehrels (1986, ApJ, 303, 336) formulation.

SB_Counts_Pos_Err
The upper uncertainty in the source soft-band counts using the Gehrels (1986, ApJ, 303, 336) formulation.

MB_Counts
The net background-subtracted source counts in the medium (1-2 keV) energy band.

MB_Counts_Neg_Err
The lower uncertainty in the source medium-band counts using the Gehrels (1986, ApJ, 303, 336) formulation.

MB_Counts_Pos_Err
The upper uncertainty in the source medium-band counts using the Gehrels (1986, ApJ, 303, 336) formulation.

HB_Counts
The net background-subtracted source counts in the hard (2-8 keV) energy band.

HB_Counts_Neg_Err
The lower uncertainty in the source hard-band counts using the Gehrels (1986, ApJ, 303, 336) formulation.

HB_Counts_Pos_Err
The upper uncertainty in the source hard-band counts using the Gehrels (1986, ApJ, 303, 336) formulation.

PSF_Fraction
The average fraction of the point-spread function (PSF) enclosed by the source extraction region, in percent.

Source_Flag
This flag parameter for the variability statistics is set to 'OC' for sources that were off the chip, and to 'NA' (for "not applicable/available") for those cases for which the source was only on the chips for one of the ObsIDs 5935-5949 or is off the ObsID 735 chips.

Var_Stat_1
The variability significance statistic as defined in equation (1) of the reference paper comparing the source fluxes between each of the individual ObsID 5935 to 5949, which thus probes the short-term variability on days to weeks timescales.

Var_Obsid_Nums
The ObsIDs of the two observations corresponding to the short-term variability statistic, e.g., '5935.5936' if the ObsIDs were 5935 and 5936.

Var_Stat_2
The variability significance statistic as defined in equation (1) of the reference paper comparing the source fluxes in the merged observation of the ObsIDs 5935 to 5949 with that of the source flux in ObsID 735, which thus probes the long-term variability on a 5-year timescale.

Spectral_Model
The type of model used for fitting the X-ray source spectrum, where 'plaw' means power law and 'bbod' means black body (see Section 3.3 of the reference paper for more details).

Spectral_Model_Flag
This flag parameter when set to non-blank values indicates the following notes on the spectral model used to fit the X-ray source spectrum:

      a = Sherpa's JD pileup model (Davis 2001, ApJ, 562, 575) was used in
          addition to the power-law fit.
      b = See Swartz et al. (2003, ApJS, 144, 213) for model parameters.
  

Spectral_Shape
The spectral shape parameter value for the best-fit model to the X-ray source spectrum: Gamma, the power-law photon index, if the spectral_model is 'plaw', or kT, the blackbody temperature, in keV, if the spectral_model is 'bbod'.

Spectral_Shape_Neg_Err
The lower uncertainty in the value of the spectral shape parameter, Gamma or kT. A value of 9.99 indicates that this parameter was frozen during the spectral fitting. A null value of this error parameter indicates that one of the following conditions apply:

     (1) in the case of source 62, the model is too complicated to be listed
         fully in the table, or
     (2) Sherpa failed to find the confidence interval, or
     (3) the source has zero flux so that the value of the spectral shape
         parameter (photon index or kT) is not defined.
  

Spectral_Shape_Pos_Err
The upper uncertainty in the value of the spectral shape parameter, Gamma or kT. A value of 9.99 indicates that this parameter was frozen during the spectral fitting. A null value of this error parameter indicates that one of the following conditions apply:

     (1) in the case of source 62, the model is too complicated to be listed
         fully in the table, or
     (2) Sherpa failed to find the confidence interval, or
     (3) the source has zero flux so that the value of the spectral shape
         parameter (photon index or kT) is not defined.
  

Spectral_Norm
The spectral model normalization, in units of photons keV-1 cm-2 s-1 at 1 keV for the power-law model and L39/(D_10)2, where L39 is the source luminosity in units of 1039 erg s-1 and D_10 is the distance to the source in units of 10 kpc, for the blackbody model.

Spectral_Norm_Neg_Err
The lower uncertainty in the value of the model normalization (q.v.). A value of 9.99 indicates that this parameter was frozen during the spectral fitting. A null value of this error parameter indicates that one of the following conditions apply:

     (1) in the case of source 62, the model is too complicated to be listed
         fully in the table, or
     (2) Sherpa failed to find the confidence interval, or
     (3) the source has zero flux so that the value of the spectral shape
         parameter (photon index or kT) is not defined.
  

Spectral_Norm_Pos_Err
The upper uncertainty in the value of the model normalization (q.v.). A value of 9.99 indicates that this parameter was frozen during the spectral fitting. A null value of this error parameter indicates that one of the following conditions apply:

     (1) in the case of source 62, the model is too complicated to be listed
         fully in the table, or
     (2) Sherpa failed to find the confidence interval, or
     (3) the source has zero flux so that the value of the spectral shape
         parameter (photon index or kT) is not defined.
  

NH
The best-fit column density NH for the source, which includes galactic foreground and intrinsic source absorption, in atoms cm-2. A value of 4.0E20 cm-2 indicates that the best-fit is on the galactic foreground minimum column density (in such a case the lower bound will then be null).

NH_Neg_Err
The lower uncertainty in the value of the best-fit column density NH for the source, in atoms cm-2. A value of 9.99 indicates that this parameter was frozen during the spectral fitting. A null value of this error parameter indicates that one of the following conditions apply:

     (1) in the case of source 62, the model is too complicated to be listed
         fully in the table, or
     (2) Sherpa failed to find the confidence interval, or
     (3) the source has zero flux so that the value of the spectral shape
         parameter (photon index or kT) is not defined.
  

NH_Pos_Err
The upper uncertainty in the value of the best-fit column density NH for the source, in atoms cm-2. A value of 9.99 indicates that this parameter was frozen durng the spectral fitting. A null value of this error parameter indicates that one of the following conditions apply:

     (1) in the case of source 62, the model is too complicated to be listed
         fully in the table, or
     (2) Sherpa failed to find the confidence interval, or
     (3) the source has zero flux so that the value of the spectral shape
         parameter (photon index or kT) is not defined.
  

Best_Fit_C_Stat
The total best-fit C-statistic for the source and background models together.

Best_Fit_DoF
The number of degrees of freedom of the best-fit spectral model for the source and background models together.

Lx
The 0.5-8 keV luminosity of the X-ray source, in erg/s, calculated from the best-fit model

Lx_Neg_Err
The lower uncertainty in the 0.5-8 keV luminosity of the X-ray source, in erg/s. The uncertainties are estimated by scaling the luminosity by the uncertainty in the counts, which was calculated from the 90% Bayesian confidence intervals, (Kraft et al. 1991, ApJ, 374, 344). A value of 9.99 indicates that this parameter was frozen during the spectral fitting. A null value of this error parameter indicates that one of the following conditions apply:

     (1) in the case of source 62, the model is too complicated to be listed
         fully in the table, or
     (2) Sherpa failed to find the confidence interval, or
     (3) the source has zero flux so that the value of the spectral shape
         parameter (photon index or kT) is not defined.
  

Lx_Pos_Err
The upper uncertainty in the 0.5-8 keV luminosity of the X-ray source, in erg/s. The uncertainties are estimated by scaling the luminosity by the uncertainty in the counts, which was calculated from the 90% Bayesian confidence intervals, (Kraft et al. 1991, ApJ, 374, 344). A value of 9.99 indicates that this parameter was frozen during the spectral fitting. A null value of this error parameter indicates that one of the following conditions apply:

     (1) in the case of source 62, the model is too complicated to be listed
         fully in the table, or
     (2) Sherpa failed to find the confidence interval, or
     (3) the source has zero flux so that the value of the spectral shape
         parameter (photon index or kT) is not defined.
  

Comments
Some comments concerning source extraction, coded as follows:

     'RS ObsID' indicates that the source was on the readout streak in the
                specified ObsID;
     'POC ObsID' indicates that the source was partially off of the chip in
                the specified ObsID;
     'S#" indicates the Swartz et al. (2003, ApJS, 144, 213) source number
                (#) that this source is matched to;
     'VC #' indicates that the source was very close to another source
                in this table whose source number is #.
  

Contact Person

Questions regarding the M81CXO2 database table can be addressed to the HEASARC User Hotline.

Page Author: Browse Software Development Team
Last Modified: 4-Aug-2011