NGC4278CXO - NGC 4278 Chandra X-Ray Point Source Catalog

Overview

This table lists some of the properties of the discrete X-ray sources detected in the authors' monitoring program of the globular cluster (GC)-rich elliptical galaxy, NGC 4278, observed with Chandra ACIS-S in six separate pointings, resulting in a co-added exposure of 458 ks. From this deep observation, 236 sources have been detected within the region overlapped by all observations, 180 of which lie within the D₂₅ ellipse angular diameter of the galaxy. These 236 sources range in X-ray luminosity L_X from 3.5 x 10³⁶ erg s^-1 (with 3-sigma upper limit <= 1 x 10³⁷ erg s^-1) to ~2 x 10⁴⁰ erg s^-1, including the central nuclear source which has been classified as a LINER. From optical data, 39 X-ray sources have been determined to be coincident with a GC, these sources tend to have high X-ray luminosity, with 10 of these sources exhibiting L_X > 1 x 10³⁸ erg s^-1. From X-ray source photometry, it has been determined that the majority of the 236 point sources that have well-constrained colors have values that are consistent with typical low-mass X-ray binary spectra, with 29 of the sources expected to be background objects from the log N-log S relation. There are 103 sources in this population that exhibit long-term variability, indicating that they are accreting compact objects. Three of these sources have been identified as transient candidates, with a further three possible transients. Spectral variations have also been identified in the majority of the source population, where a diverse range of variability has been identified, indicating that there are many different source classes located within this galaxy.

This HEASARC table contains the master source list (Table 3 of the reference paper) and the X-ray properties of the sources in the co-added observations (Table 4 of the reference paper), but not the X-ray properties of the sources in the 6 individual observations (Tables 5-10 of the reference paper).

The details of the six individual pointings used in this study, e.g., the Chandra ObsIDs, dates, exposure times and cleaned exposure times, are given in Table 1 of the reference paper, and repeated here:

Obs. No.OBSID	Date	        Exposure (s)	  Cleaned Exposure (s)
1	 4741	2005 Feb 3	37462.0	           37264.5
2	 7077	2006 Mar 16	110303.8	  107736.7
3	 7078	2006 Jul 25	51433.2	           48076.2
4	 7079	2006 Oct 24	105071.7	  102504.6
5	 7081	2007 Feb 20	110724.0	  107564.5
6	 7080	2007 Apr 20	55824.8	           54837.5
Total Co-added          	470819.5	  457984.0

Notes. The pointing OBSID 7181 was taken before OBSID 7080, so to maintain the time sequence of the exposures these observation numbers have been labeled as above in the reference paper.

The details of the energy bands and X-ray colors used in this study are given in Table 2 of the reference paper, and repeated here:

Band/Color	        Energy Range/Definition

Broad (B)	        0.3-8 keV
Soft (S)	        0.3-2.5 keV
Hard (H)	        2.5-8 keV
Soft 1 (S1)	        0.3-0.9 keV
Soft 2 (S2)	        0.9-2.5 keV
Conventional broad (Bc)	0.5-8 keV
Conventional soft (Sc)	0.5-2 keV
Conventional hard (Hc)	2-8 keV
Hardness ratio HR	(Hc-Sc)/(Hc+Sc)
X-ray color C21    	-log(S2) + log(S1) = log(S1/S2)
X-ray color C32 	-log(H) + log(S2) = log(S2/H)

Catalog Bibcode

2009ApJS..181..605B

References

Deep Chandra Monitoring Observations of NGC 4278: Catalog of Source Properties
    Brassington N.J., Fabbiano G., Kim D.-W., Zezas A., Zepf S., Kundu A.,
    Angelini L., Davies R.L., Gallagher J., Kalogera V., Fragos T., King A.R.,
    Pellegrini S., Trinchieri G.
    <Astrophys. J. Suppl. 181, 605-626 (2009)>
    =2009ApJS..181..605B

Provenance

This table was created by the HEASARC in April 2009 based on machine-readable versions of Tables 3 and 4 from the reference paper which were obtained from the ApJ web site.

Parameters

Source_Flag
This flag parameter [gl] indicates the quality (signal-to-noise ratio, S/N) of the X-ray source: 'g' means that S/N > 3 in at least one of the 6 individual observations, while 'l' means that S/N < 3 an all of the observations.

Source_Number
A sequential identification number ("master ID") which uniquely identifies each X-ray source in the catalog.

Alt_Name
The alternative name for the X-ray source using the'[BFK2009]' prefix that the HEASARC anticipates will be recommended by the CDS Dictionary of Astronomical Nomenclature for these sources, and the X-ray source number.

Name
The name of the Chandra X-ray source using the 'CXOU J' prefix (Chandra X-ray Observatory, Unregistered) and the J2000 coordinates of the source in the standard JHHMMSS.s+DDMMSS format, e.g., 'CXOU J122023.6+291614'.

RA
The Right Ascension of the X-ray source in the selected equinox. This was given in J2000 coordinates and to a precision of 0.001 seconds of time in the original table.

Dec
The Declination of the X-ray source in the selected equinox. This was given in J2000 coordinates and to a precision of 0.01 arcseconds in the original table.

LII
The Galactic Longitude of the X-ray source.

BII
The Galactic Latitude of the X-ray source.

Extraction_Radius
The X-ray source extraction radius, in arcseconds. The extraction radius for each source was chosen to be the 95% encircled energy radius at 1.5 keV (which varies as a function of the off-axis angle), with a minimum of 3" near the aim point.

Error_Radius
The X-ray source positional uncertainty, in arcseconds. The formulae which the authors used to calculate this parameter is given in Section 2.2 of the reference paper (their Equation 1).

SNR
The signal-to-noise ratio, S/N, of the co-added X-ray source in the broad band (0.3-8.0 keV).

Longterm_Var_Flag
This flag parameter provides information about the long-term variability of the X-ray source, i.e., whether the luminosities of the source in the individual observations differed, indicating if the source was, on these timescales, non-variable (N), variable (V), a transient candidate (TC) or a possible transient candidate (PTC). In all other cases (which have blank values), the source was only detected in the combined observation, providing insufficient information to investigate long-term variability.

Shortterm_BB_Flag
This flag parameter provides information about the short-term variability of the source as indicated from Bayesian block (BB) analysis, where 'V' indicates that the source is variable within at least one observation and 'N' indicates that it has been found to be non-variable in all six observations (see Section 2.4 of the reference paper for further information). In all other cases (which have blank values), there were insufficient counts to investigate the short-term variability of the source.

Shortterm_Ks_Flag
This flag parameter provides information about the short-term variability of the source is indicated from the Kolmogorov-Smirnov (K-S) test, where 'V' indicates that the source is variable in at least one observation, 'N' indicates that it has been found to be non-variable in all six observations, and 'P' indicates that the source is a possible variable source (see Section 2.4 for further information). In all other cases, there were insufficient counts to investigate the short-term variability.

Optical_Corr_Flag
This flag provides information indicating any optical association for the X-ray source, as follows:

     GC = optical source is a confirmed globular cluster;
     BG = optical source is a background object;
   corr = match that has been defined as a correlation;
   exmt = excluded match between 0.6" and 3" in separation;
   none = source inside the field of view of the HST observation, but has no
          optical counterpart;
        = The X-ray source is external to the HST FOV.

Center_Offset
The angular distance of the X-ray source from the galaxy center, in arcseconds.

D25_Flag
This flag parameter is set to 'b' to indicate that the distance of the X-ray source from the galaxy center is within the D₂₅ ellipse, i.e., is less than 120".

Xray_Detect_Flag
This flag parameter provides information about those X-ray sources for which there are complications in the detection, as follows:

        X = source detected in a single observation only;
       O1 = single overlapping sources;
       O2 = complicated case of overlapping sources.
  double? = possible double sources.

FB_Counts_Limit
This flag parameter is set to '<' if the value of the corresponding parameter is an upper limit rather than an actual value.

FB_Counts
The net counts in the X-ray source in the B (broad) band (0.3-8 keV).

FB_Counts_Error
The uncertainty in the corresponding counts parameter.

SB1_Counts
The net counts in the X-ray source in the S1 band (0.3-0.9 keV).

SB1_Counts_Error
The uncertainty in the corresponding counts parameter.

SB2_Counts
The net counts in the X-ray source in the S2 band (0.9-2.5 keV).

SB2_Counts_Error
The uncertainty in the corresponding counts parameter.

SB12_Counts
The net counts in the X-ray source in the soft (S1+S2) band (0.3-2.5 keV).

SB12_Counts_Error
The uncertainty in the corresponding counts parameter.

HB1_Counts
The net counts in the X-ray source in the H (hard) band (2.5-8 keV).

HB1_Counts_Error
The uncertainty in the corresponding counts parameter.

SB_Counts
The net counts in the X-ray source in the conventional soft band (Sc: 0.5-2.0 keV).

SB_Counts_Error
The uncertainty in the corresponding counts parameter.

HB_Counts
The net counts in the X-ray source in the conventional hard band (Hc: 2-8 keV).

HB_Counts_Error
The uncertainty in the corresponding counts parameter.

Hardness_Ratio
The X-ray source hardness ratio HR calculated from the counts in the conventional hard and soft bands in the standard way: HR = (Hc-Sc)/(Hc+Sc).

Hardness_Ratio_Neg_Err
The lower (negative) uncertainty in the hardness ratio HR.

Hardness_Ratio_Pos_Err
The upper (positive) uncertainty in the hardness ratio HR.

C21_Color
The X-ray color C21 of the X-ray source, calculated using: C21 = -log(S2) + log(S1) = log(S1/S2).

C21_Color_Neg_Err
The lower (negative) uncertainty in the C21 X-ray color.

C21_Color_Pos_Err
The upper (positive) uncertainty in the C21 X-ray color.

C32_Color
The X-ray color C32 of the X-ray source, calculated using: C32 = -log(H) + log(S2) = log(S2/H).

C32_Color_Neg_Err
The lower (negative) uncertainty in the C32 X-ray color.

C32_Color_Pos_Err
The upper (positive) uncertainty in the C32 X-ray color.

Log_Lx_Limit
This flag parameter is set to '<' if the value of the corresponding parameter is an upper limit rather than an actual value.

Log_Lx
The logarithm of the broad-band (0.3-8.0 keV) X-ray luminosity of the source in the co-added observation, in erg s^-1, assuming a distance to the source of 16.1 Mpc. Where sources were not detected in the co-added observation, the upper limit is given here. The X-ray luminosity was calculated with an energy conversion factor (ECF) corresponding to an assumed power-law spectral shape, with a spectral index Gamma = 1.7 and a Galactic column density N_H = 1.76 x 10²⁰ cm^-2.

Log_Lx_Single
The 3-sigma upper limit to the value of the logarithm of the broad-band (0.3-8.0 keV) X-ray luminosity of the source in the single observation in which it was detected, in erg s^-1, assuming a distance to the source of 16.1 Mpc. The X-ray luminosity was calculated with an energy conversion factor (ECF) corresponding to an assumed power-law spectral shape, with a spectral index Gamma = 1.7 and a Galactic column density N_H = 1.76 x 10²⁰ cm^-2.

Contact Person

Questions regarding the NGC4278CXO database table can be addressed to the HEASARC Help Desk.

Page Author: Browse Software Development Team
Last Modified: Monday, 16-Sep-2024 17:32:00 EDT