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NGC3115CXO - NGC 3115 Chandra X-Ray Point Source Catalog

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Overview

This table contains some of the results from an in-depth study of low-mass X-ray binaries (LMXBs) detected in the nearby lenticular galaxy NGC 3115 using the Megasecond Chandra X-ray Visionary Project observation (total exposure time 1.1 Ms). In total the authors found 136 candidate LMXBs in the field and 49 in globular clusters (GCs) above 2-sigma detection, with 0.3-8 keV luminosity LX ~ 1036 - 1039 erg s-1. Other than 13 transient candidates, the sources overall have less long-term variability at higher luminosity, at least at LX >~ 2 x 1037 erg s-1. In order to identify the nature and spectral state of these sources, the authors compared their collective spectral properties based on single-component models (a simple power law or a multicolor disk) with the spectral evolution seen in representative Galactic LMXBs. The authors found that in the LX vs. photon index GammaPL and LX versus disk temperature kTMCD plots, most of their sources fall on a narrow track in which the spectral shape hardens with increasing luminosity below LX ~ 7 x 1037 erg s-1, but is relatively constant (GammaPL ~ 1.5 or kTMCD ~ 1.5 keV) above this luminosity, which is similar to the spectral evolution of Galactic neutron star (NS) LMXBs in the soft state in the Chandra bandpass. Therefore, the authors identified the track as the NS LMXB soft-state track and suggested sources with LX <~ 1037 erg s-1 as atolls in the soft state and those with LX >~ 1037 erg s-1 as Z sources. Ten other sources (five are transients) displayed significantly softer spectra and are probably black hole X-ray binaries in the thermal state. One of them (a persistent source) is in a metal-poor GC.

The 11 Chandra observations of NGC 3115 are listed in Table 1 of the reference paper. They were made during three epochs: one in 2001,two in 2010, and nine in 2012. All observations used the imaging array of the AXAF CCD Imaging Spectrometer (ACIS).

This table contains the properties of the 482 detected point sources in the merged and single Chandra ACIS observations of NGC 3115 above a 2-sigma threshold and after eliminating a number of spurious sources associated with bright streaks on the ACIS-S1 chip and (in one case) on a CCD edge. 469 of these sources (indicated by values of obs_flag = '0') have a single entry in this table, based on their properties as derived from all of the available Chandra data for that position. There are 13 transient sources (having obs_flag = 'h') for which an additional entry is provided referring to their properties in the "high state", and based on the combination of their high-state observations, as shown in Figures 3(a) - 3(d) in the reference paper. For source number 198, there is a second additional entry provided referring to its properties in the "low state", and based on the combination of its low-state observations, as shown in Figure 3(c) in the reference paper. Thus, there are 496 entries (rows) in this table, i.e., 482 + 13 + 1.


Catalog Bibcode

2015ApJ...808...19L

References

The Megasecond Chandra X-Ray Visionary Project Observation of NGC 3115.
II. Properties of Point Sources.

    Lin D., Irwin J.A., Wong K., Jennings Z.G., Homan J., Romanowsky A.J.,
    Strader J., Sivakoff G.R., Brodie J.P., Remillard R.A.
   <Astrophys. J., 808, 19 (2015)>
   =2015ApJ...808...19L

Provenance

This table was created by the HEASARC in August 2015 based on the union of the machine-readable versions of Table 3 (the master source catalog) and Table 4 (the source counts, fluxes and hardness ratios in the merged observations) that were obtained from the ApJ web site. It does not contain the source counts and fluxes in the individual observations which were given in Table 5 of the reference paper.

snr

The signal-to-noise ratio of the Chandra source detection in the broad band (0.5 - 7.0 keV), i.e., the 0.5-7 keV net counts divided by the error in the counts, in the observation(s) in which the source was detected.

Parameters

Source_Number
A unique master source identification for each source in this catalog (but not for each row in this table). Most (469) of the 482 sources have a single row of data (entries having obs_flag = '0') in this table corresponding to all of the available X-ray data. There are 13 transient sources (entries having obs_flag = 'h') for which, as well as the entry describing the properties based on all available X-ray data, there is an additional entry provided referring to their properties in the "high state", and based on the combination of their high-state observations, as shown in Figures 3 (a) - 3(d) in the reference paper. For source number 198, there is a second additional entry provided referring to its properties in the "low state", and based on the combination of its low-state observations, as shown in Figure 3 (c) in the reference paper. There are thus 496 entries (rows) in this table, i.e., 482 + 13 + 1. Thus, the combination of source_number and obs_flag uniquely specifies a row in this table.

Name
The standard J2000.0 position-based "unregistered"d Chandra source designation, e.g., 'CXOU J100513.7-074416'. The HEASARC discovered that the positionally very close sources numbered 55 and 58 had the same name of 'CXOU J100513.9-074306'. To make these names unique the HEASARC has added suffixes of 'a' and 'b' to these two names, so that source number 55 is named 'CXOU J100513.9-074306a', and source number 58 is named 'CXOU J100513.9-074306b'.

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 (0.0036 arcseconds) 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 (0.0036 arcseconds) in the original table

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

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

Error_Radius
The 1-sigma statistical positional uncertainty, in units of arcseconds, in the X-ray source position, based on Equation (12) of Kim et al. (2007, ApJS, 169, 401). The HEASARC has calculated this parameter by multiplying the positional uncertainty in each coordinate which was given in the original table by 20.5.

Angular_Radius
The angular separation of the Chandra X-ray source from the galaxy's center, in arcminutes.

Scaled_Radius
The angular separation of the Chandra X-ray source from the galaxy's center, in terms of multiples of the elliptical radius of the D25 isophotal ellipse in the direction from the galaxy center to the source. The D25 region of NGC 3115 has a semi-major axis of a = 3.62 arcminutes (10.2 kpc), a semi-minor axis of b = 1.23 arcminutes (3.5 kpc), and a position angle of 40 degrees (de Vaucouleurs et al. 1991, 3rd Reference Catalog of Bright Galaxies, RC3).

PSF_50pc_Radius
The radius of the circle enclosing 50% of the point spread function at 2.3 keV at the location of the X-ray source, in arcseconds.

PSF_90pc_Radius
The radius of the circle enclosing 90% of the point spread function at 2.3 keV at the location of the X-ray source, in arcseconds.

ObsID
The Chandra ObsID (observation identification number) in which the Chandra source was detected: if the source properties are based on merged Chandra observations, this i set to 0.

BB_SNR
Signal-to-Noise Ratio

Long_Term_Var_Factor
The long-term flux variation factor, Vvar, of the Chandra source in the 0.5-7.0 keV band. The authors defined the long-term flux variability as Vvar = Fmax /Fmin, where Fmax and Fmin are the maximum and minimum 0.5-7.0 fluxes of a unique source among the single observations. The authors only used detections with the flux above twice the error (sigma) when calculating Fmax (if no detections above 2 sigma,the one with the highest significance was used as Fmax); they used 2 sigma as the flux for detections with flux less than 2 sigma when calculating Fmin.

Long_Term_Var_Sig
The significance, Svar, of the long-term flux variation of the Chandra source as defined in equation (1) of the reference paper, viz.,

       Svar = (Fmax - Fmin)/sqrt(sigma_max2 + sigma_min2)
  
where Fmax and Fmin are the maximum and minimum 0.5-7.0 fluxes of a unique source among the single observations, with the corresponding errors sigmamax and sigmamin, respectively. The authors only used detections with the flux above twice the error (sigma) when calculating Fmax (if no detections above 2 sigma,the one with the highest significance was used as Fmax); they used 2 sigma as the flux for detections with flux less than 2 sigma when calculating Fmin.

Lx_BB_Max
The 0.5-7 keV luminosity of the Chandra source based on the maximum observed X-ray flux, assuming a source distance of 9.7 Mpc, in units of erg/s. The conversions from the count rates to the fluxes were based on the response files and assumed an absorbed power-law spectral shape with GammaPL = 1.7 and a Galactic absorption NH = 4.32 x 1020 cm-2 (Kalberla et al. 2005, A&A, 440, 775).

Lx_BB_Max_Neg_Err
The negative error in the 0.5-7 keV luminosity of the Chandra source based on the maximum observed X-ray flux, assuming a source distance of 9.7 Mpc, in units of erg/s, at the 68% confidence level.

Lx_BB_Max_Pos_Err
The positive error in the 0.5-7 keV luminosity of the Chandra source based on the maximum observed X-ray flux, assuming a source distance of 9.7 Mpc, in units of erg/s, at the 68% confidence level.

ObsID_Max
The Chandra observation identification (ObsID) of the observation in which the maximum 0.5-7 keV luminosity of the specified source was measured.

Lx_BB_Min
The 0.5-7 keV luminosity of the Chandra source based on the minimum observed X-ray flux, assuming a source distance of 9.7 Mpc, in units of erg/s. The conversions from the count rates to the fluxes were based on the response files and assumed an absorbed power-law spectral shape with GammaPL = 1.7 and a Galactic absorption NH = 4.32 x 1020 cm-2 (Kalberla et al. 2005, A&A, 440, 775).

Lx_BB_Min_Neg_Err
The negative error in the 0.5-7 keV luminosity of the Chandra source based on the minimum observed X-ray flux, assuming a source distance of 9.7 Mpc, in units of erg/s, at the 68% confidence level.

Lx_BB_Min_Pos_Err
The positive error in the 0.5-7 keV luminosity of the Chandra source based on the minimum observed X-ray flux, assuming a source distance of 9.7 Mpc, in units of erg/s, at the 68% confidence level.

ObsID_Min
The Chandra observation identification (ObsID) of the observation in which the minimum 0.5-7 keV luminosity of the specified source was measured.

Short_Term_Var_Index
The maximum short-term variability of the Chandra source as quantified using the Gregory-Loredo algorithm (Gregory and Loredo 1992, ApJ, 398, 146) as implemented by the CIAO tool 'glvary' (Evans et al. 2010, ApJS, 189, 37). This splits the events into multiple time bins and looks for significant deviations. The variation of the effective area with time was taken into account and was obtained by another CIAO tool, 'dither_region'. The different degrees of confidence are indicated by the "variability index" parameter which spans values within the range [0, 10] and is larger for a variability of higher confidence: sources with indices of 6-10 are definitely variable.

Source_Type
The estimated source type. The sources within D25 (i.e., with a value of the scaled_radius parameter less than 1.0) are expected to be dominated by LMXBs and are thus assumed to be such objects, except those with non-GC optical counterparts, which the authors identify as AGNs. The LMXBs identified in this way are expected to be contaminated by some AGNs, because the optical images which were used are not very deep. Sources outside D25 should be dominated by AGNs, because the authors only expect 1.5 field LMXBs above 4 x 1036 erg s-1 based on the IR light in the Ks band outside D25 (Lin et al. 2015, ApJ, 808, 20: Paper III). Therefore, they assumed all sources outside D25 to be AGNs, except those coincident with GCs, the supersoft X-ray source (SSS), S109, three coronally active stars in our Galaxy (which are coincident with stars and show soft X-ray spectra and possible stellar flares), two galaxies (due to hot gas emission in galaxies; which are coincident with galaxies in the optical images and show soft X-ray spectra), and BHC S179 (see Sections 3.2 and 3.3.2 of the reference paper; this source is slightly outside D25 but is also identified as a field LMXB, considering its possible transient nature and soft spectra). In total, there are 136 candidate field LMXBs and 49 candidate GC LMXBs (Table 2). The 13 transients and 10 BH X-ray binary candidates (BHCs) are also indicated in the source type. The acronyms used have the following significance:

      BH = black hole X-ray binary;
      GC = low-mass X-ray binary in a (candidate) globular cluster; those not
           designated as BH are most likely neutron star LMXBs;
       F = low-mass X-ray binary in the field;  those not designated as BH are
           most likely neutron star LMXBs;
     SSS = supersoft X-ray source;
     AGN = background active galactic nucleus;
    Star = coronally active star in our Galaxy;
       G = hot gas emission in a galaxy.
  

Obs_Flag
This flag parameter indicates in which type of observation the specified source parameters were derived, as follows:

      0 = combination of all observations in which the source is covered;
      h = combination of observations in the high state (for the 13
          transients in Figure 3 a-d of the reference paper);
      l = combination of observations in the low state (for source 198
          only, referred to Figure 3c of the reference paper).
  

Exposure
The total exposure time, in seconds, of the observation(s) from which the specified source parameters were derived. This was converted by the HEASARC from the kilosecond units given in the original table.

BB_Counts
The Chandra source counts in the broad band (0.5-7.0 keV) in the merged observation (if obs_flag = '0'), or for the high-state (if obs_flag = 'h') or the low-state (if obs_flag = 'l') observations.

BB_Counts_Neg_Err
The negative error in the corresponding parameter value at the 68% confidence level.

BB_Counts_Pos_Err
The positive error in the corresponding parameter value at the 68% confidence level.

BB_Flux
The flux of the Chandra source in the broad band (0.5-7.0 keV), in erg cm-2 s-1. The conversions from the count rates to the fluxes were based on the response files and assumed an absorbed power-law spectral shape with GammaPL = 1.7 and a Galactic absorption NH = 4.32 x 1020 cm-2 (Kalberla et al. 2005, A&A, 440, 775).

BB_Flux_Neg_Err
The negative error in the corresponding parameter value at the 68% confidence level.

BB_Flux_Pos_Err
The positive error in the corresponding parameter value at the 68% confidence level.

USB_Counts
The Chandra source counts in the ultra-soft band (0.2-0.5 keV) in the merged observation (if obs_flag = '0'), or for the high-state (if obs_flag = 'h') or the low-state (if obs_flag = 'l') observations.

USB_Counts_Neg_Err
The negative error in the corresponding parameter value at the 68% confidence level.

USB_Counts_Pos_Err
The positive error in the corresponding parameter value at the 68% confidence level.

USB_Flux
The flux of the Chandra source in the ultra-soft band (0.2-0.5 keV), in erg cm-2 s-1. The conversions from the count rates to the fluxes were based on the response files and assumed an absorbed power-law spectral shape with GammaPL = 1.7 and a Galactic absorption NH = 4.32 x 1020 cm-2 (Kalberla et al. 2005, A&A, 440, 775).

USB_Flux_Neg_Err
The negative error in the corresponding parameter value at the 68% confidence level.

USB_Flux_Pos_Err
The positive error in the corresponding parameter value at the 68% confidence level.

SB_Counts
The Chandra source counts in the soft band (0.5-1.2 keV) in the merged observation (if obs_flag = '0'), or for the high-state (if obs_flag = 'h') or the low-state (if obs_flag = 'l') observations.

SB_Counts_Neg_Err
The negative error in the corresponding parameter value at the 68% confidence level.

SB_Counts_Pos_Err
The positive error in the corresponding parameter value at the 68% confidence level.

SB_Flux
The flux of the Chandra source in the soft band (0.5-1.2 keV), in erg cm-2 s-1. The conversions from the count rates to the fluxes were based on the response files and assumed an absorbed power-law spectral shape with GammaPL = 1.7 and a Galactic absorption NH = 4.32 x 1020 cm-2 (Kalberla et al. 2005, A&A, 440, 775).

SB_Flux_Neg_Err
The negative error in the corresponding parameter value at the 68% confidence level.

SB_Flux_Pos_Err
The positive error in the corresponding parameter value at the 68% confidence level.

MB_Counts
The Chandra source counts in the medium band (1.2-2.0 keV) in the merged observation (if obs_flag = '0'), or for the high-state (if obs_flag = 'h') or the low-state (if obs_flag = 'l') observations.

MB_Counts_Neg_Err
The negative error in the corresponding parameter value at the 68% confidence level.

MB_Counts_Pos_Err
The positive error in the corresponding parameter value at the 68% confidence level.

MB_Flux
The flux of the Chandra source in the medium band (1.2-2.0 keV), in erg cm-2 s-1. The conversions from the count rates to the fluxes were based on the response files and assumed an absorbed power-law spectral shape with GammaPL = 1.7 and a Galactic absorption NH = 4.32 x 1020 cm-2 (Kalberla et al. 2005, A&A, 440, 775).

MB_Flux_Neg_Err
The negative error in the corresponding parameter value at the 68% confidence level.

MB_Flux_Pos_Err
The positive error in the corresponding parameter value at the 68% confidence level.

HB_Counts
The Chandra source counts in the hard band (2.0-7.0 keV) in the merged observation (if obs_flag = '0'), or for the high-state (if obs_flag = 'h') or the low-state (if obs_flag = 'l') observations.

HB_Counts_Neg_Err
The negative error in the corresponding parameter value at the 68% confidence level.

HB_Counts_Pos_Err
The positive error in the corresponding parameter value at the 68% confidence level.

HB_Flux
The flux of the Chandra source in the hard band (2.0-7.0 keV), in erg cm-2 s-1. The conversions from the count rates to the fluxes were based on the response files and assumed an absorbed power-law spectral shape with GammaPL = 1.7 and a Galactic absorption NH = 4.32 x 1020 cm-2 (Kalberla et al. 2005, A&A, 440, 775).

HB_Flux_Neg_Err
The negative error in the corresponding parameter value at the 68% confidence level.

HB_Flux_Pos_Err
The positive error in the corresponding parameter value at the 68% confidence level.

Hardness_Ratio_1
The hardness ratio HR1, where HR1 is defined as (H-S)/(H+S), and S and H are the energy fluxes in the 0.5-1.2 keV and the 1.2-2.0 keV bands, respectively.

Hardness_Ratio_1_Neg_Err
The negative error in the corresponding parameter value at the 68% confidence level.

Hardness_Ratio_1_Pos_Err
The positive error in the corresponding parameter value at the 68% confidence level.

Hardness_Ratio_2
The hardness ratio HR2, where HR2 is defined as (H-S)/(H+S), and S and H are the energy fluxes in the 1.2-2.0 keV and the 2.0-7.0 keV bands, respectively.

Hardness_Ratio_2_Neg_Err
The negative error in the corresponding parameter value at the 68% confidence level.

Hardness_Ratio_2_Pos_Err
The positive error in the corresponding parameter value at the 68% confidence level.

Hardness_Ratio_3
The hardness ratio HR3, where HR3 is defined as (H-S)/(H+S), and S and H are the energy fluxes in the 0.5-2.0 keV and the 2.0-7.0 keV bands, respectively.

Hardness_Ratio_3_Neg_Err
The negative error in the corresponding parameter value at the 68% confidence level.

Hardness_Ratio_3_Pos_Err
The positive error in the corresponding parameter value at the 68% confidence level.

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


Contact Person

Questions regarding the NGC3115CXO database table can be addressed to the HEASARC User Hotline.

Page Author: Browse Software Development Team
Last Modified: 18-Aug-2015