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NGC1600CXO - NGC 1600 Chandra X-Ray Discrete Source Catalog

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Overview

The authors observed the X-ray-bright E3 galaxy NGC 1600 and nearby members of the NGC 1600 group with the Chandra X-Ray Observatory ACIS-S3 to study their X-ray properties. NGC 1600 is the brightest member of the NGC 1600 group; NGC 1601 (1.6 arcminutes away) and NGC 1603 (2.5 arcminutes away) are the two nearest galaxies, both of which are non-interacting members. The authors adopted the 2MASS Point Source Catalog position of J2000.0 RA = 04h 31m 39.87s, Dec = -05o 05' 10.5" as the location of the center of the NGC 1600 galaxy.

Unresolved emission dominates the Chandra observation; however, some of the emission is resolved into 71 sources, most of which are low-mass X-ray binaries associated with NGC 1600. Twenty-one of the sources have LX > 2 x 1039 ergs/s (0.3-10.0 keV; assuming they are at the distance of NGC 1600 of 59.98 Mpc), marking them as ultraluminous X-ray point source (ULX) candidates. NGC 1600 may have the largest number of ULX candidates in an early-type galaxy to date; however, cosmic variance in the number of background active galactic nuclei cannot be ruled out. The spectrum and luminosity function (LF) of the resolved sources are more consistent with sources found in other early-type galaxies than with sources found in star-forming regions of galaxies. The source LF and the spectrum of the unresolved emission both indicate that there are a large number of unresolved point sources. The authors propose that these sources are associated with globular clusters (GCs) and that NGC 1600 has a large GC specific frequency. Observations of the GC population in NGC 1600 would be very useful for testing this prediction.

NGC 1600 was observed in two intervals on 2002 September 18-19 (ObsID 4283) and 2002 September 20 (ObsID 4371) with live exposures of 26,783 and 26,752 s, respectively. The first observation showed clear evidence of a major background "flare" in the first 20% of the observation. The second observation had some small fluctuations greater than 20% from the mean rate. After these were filtered, observations 4283 and 4371 had flare-free exposure times of 21,562 and 23,616 s, respectively. This table lists all 71 discrete sources detected by wavdetect over the 0.3-6 keV energy range in the combination of the two observations. The first 3 sources (source numbers 1, 2 and 3) are clearly extended according to the authors. The authors expect 11 +/- 2 foreground/background sources to be present based on the source counts in Brandt et al. (2000, AJ, 119, 2349) and Mushotzky et al. (2000, Nature, 404, 459).

The authors determined the observed X-ray hardness ratios for the sources, using the same techniques that they have used previously. They define three hardness ratios as H21 = (M-S)/(M+S), H31 = (H-S)/(H+S), and H32 = (H-M)/(H+M), where S,M, and H are the total counts in the soft (0.3-1 keV), medium (1-2 keV) and hard (2-6 keV) respectively. From their previous definitions, they have reduced the hard band from 2-10 to 2-6 keV: since the 6-10 keV range is dominated by background photons for most sources, this should increase the S/N of the hardness ratio techniques. The hardness ratios measure observed counts, which are affected by Galactic absorption and quantum efficiency (QE) degradation in the Chandra ACIS detectors. In order to compare with other galaxies, it is useful to correct the hardness ratios for these two soft X-ray absorption effects. Therefore, the authors have calculated the intrinsic hardness ratios, denoted by a superscript 0, using a correction factor in each band appropriate to the best-fit spectrum of the resolved sources, and these are what are quoted in this table.


Catalog Bibcode

2004ApJ...617..262S

References

Chandra observations of diffuse gas and luminous X-ray sources around the
X-ray-bright elliptical galaxy NGC 1600.
    Sivakoff G.R., Sarazin C.L., Carlin J.L.
   <Astrophys. J., 617, 262-280 (2004)>
   =2004ApJ...617..262S

Provenance

This table was created by the HEASARC in May 2018 based on CDS Catalog J/ApJ/617/262/ file table1.dat, the list of detected discrete X-ray sources in the Chandra observation of the NGC 1600 group.

Parameters

Source_Number
A unique sequential identification number for each X-ray source in the catalog in order of increasing radial distance d from the center of the NGC 1600 galaxy.

Name
The name of the Chandra source using the "CXOU" prefix (for Chandra X-ray Observatory Unregistered source) and the J2000.0 coordinates of the source in the recommended "JHHMMSS.s+DDMMSS" format used for Chandra sources.

RA
The Right Ascension of the Chandra X-ray source in the selected equinox. This parameter was given in J2000.0 equatorial coordinates to a precision of 0.01 seconds of time in the original table. All listed positions include astrometry corrections based on optical/IR counterparts (see Section 4.2 of the reference paper); the overall absolute astrometric errors are probably ~0.5" near the field center, with larger errors farther out.

Dec
The Declination of the Chandra X-ray source in the selected equinox. This parameter was given in J2000.0 equatorial coordinates to a precision of 0.1 arcseconds in the original table. All listed positions include astrometry corrections based on optical/IR counterparts (see Section 4.2 of the reference paper); the overall absolute astrometric errors are probably ~0.5" near the field center, with larger errors farther out.

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

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

Radial_Distance
The projected radial distance of the Chandra X-ray source from the enter of NGC 1600, in arcminutes (converted by the HEASARC from the arcsecond units used in the original table).

Semi_Major_Distance
The semi-major distance of the Chandra X-ray source from the enter of NGC 1600, in arcminutes (converted by the HEASARC from the arcsecond units used in the original table).

Count_Rate
The wavdetect count rate of the Chandra X-ray source in the 0.3-6 keV band, in counts per second. The fluxes were corrected for exposure and the instrument point-spread function (PSF).

Count_Rate_Error
the 1-sigma error in the wavdetect count rate of the Chandra X-ray source in the 0.3-6 keV band, in counts per second.

SNR
The signal-to-noise ratio (S/N) for the count rate of the Chandra X-ray source.

Lx
The X-lay luminosity of the Chandra source in the 0.3-10.0 keV band, in erg/s. To convert the source count rates into unabsorbed X-ray luminosities, the authors used the adopted Chandra X-ray spectrum (see Section 6.1, Table 2, row [3] of the reference paper) of the resolved sources to convert 0.3-6 keV count rates into 0.3-10 keV fluxes. They then assumed each source was at the distance of NGC 1600, 59.98 Mpc, yielding a conversion factor of 4.12 x 1042 erg/s. The X-ray luminosities range roughly from 2.8 x 1038 to 4.8 x 1040 ergs/s. Since sources 33 and 50 are likely foreground stars, their luminosities are probably considerable overestimates.

Hardness_Ratio21
The intrinsic hardness ratio HR210 of the Chandra X-ray source (see Overview above for more details).

Hardness_Ratio21_Pos_Err
The positive 1-sigma error in the intrinsic hardness ratio HR210 of the Chandra X-ray source (see Overview above for more details).

Hardness_Ratio21_Neg_Err
The negative 1-sigma error in the intrinsic hardness ratio HR210 of the Chandra X-ray source (see Overview above for more details).

Hardness_Ratio31
The intrinsic hardness ratio HR310 of the Chandra X-ray source (see Overview above for more details).

Hardness_Ratio31_Pos_Err
The positive 1-sigma error in the intrinsic hardness ratio HR310 of the Chandra X-ray source (see Overview above for more details).

Hardness_Ratio31_Neg_Err
The negative 1-sigma error in the intrinsic hardness ratio HR310 of the Chandra X-ray source (see Overview above for more details).

Hardness_Ratio32
The intrinsic hardness ratio HR320 of the Chandra X-ray source (see Overview above for more details).

Hardness_Ratio32_Pos_Err
The positive 1-sigma error in the intrinsic hardness ratio HR320 of the Chandra X-ray source (see Overview above for more details).

Hardness_Ratio32_Neg_Err
The negative 1-sigma error in the intrinsic hardness ratio HR320 of the Chandra X-ray source (see Overview above for more details).

Source_Flags
This parameter contains comments concerning the specified Chandra X-ray source, coded as follows:

      a = Sources near the center may be confused with nearby sources, making
          their positions, fluxes, and extents uncertain.
      b = Source is noticeably more extended than PSF.
      c = Source is at the edge of the S3 detector, and flux is uncertain because
          of large exposure correction.
      d = Possible optical counterpart.
      e = Source may be variable.
      f = Source is part of analysis sample.
  

Contact Person

Questions regarding the NGC1600CXO database table can be addressed to the HEASARC User Hotline.
Page Author: Browse Software Development Team
Last Modified: Wednesday, 30-May-2018 13:06:27 EDT