AKNEPDFCXO - Akari North Ecliptic Pole Deep Field Chandra X-Ray Point Source Catalog

Overview

This table contains results from the 300-ks Chandra survey in the AKARI North Ecliptic Pole (NEP) deep field. This field has a unique set of 9-band infrared photometry covering 2-24 micron from the AKARI Infrared Camera, including mid-infrared (MIR) bands not covered by Spitzer. The survey is one of the deepest ever achieved at ~15 micron, and is by far the widest among those with similar depths in the MIR. This makes this field unique for the MIR-selection of AGN at z ~1. The authors have designed a source detection procedure, which performs joint Maximum Likelihood PSF fits on all of their 15 mosaicked Chandra pointings covering an area of 0.34 square degrees. The procedure has been highly optimized and tested by simulations. A point source catalog with photometry and Bayesian-based 90%-confidence upper limits in the 0.5-7, 0.5-2, 2-7, 2-4, and 4-7 keV bands has been produced. The catalog contains 457 X-ray sources and the spurious fraction is estimated to be ~1.7%. Sensitivity and 90%-confidence upper flux limits maps in all bands are provided as well.

In their study, the authors searched for optical MIR counterparts in the central 0.25 square degrees, where deep Subaru Suprime-Cam multi-band images exist. Among the 377 X-ray sources detected therein, ~80% have optical counterparts and ~60% also have AKARI mid-IR counterparts. The authors cross-matched their X-ray sources with MIR-selected AGN from Hanami et al. (2012, PASJ, 64, 70). Around 30% of all AGN that have MID-IR SEDs purely explainable by AGN activity are strong Compton-thick AGN candidates.

The source catalog contained in this table uses an internal threshold of ML = 9.5 which corresponds to ML_empir ~12 (see Sect. 4.3.3 of the reference paper for more details). In total, 457 sources are detected, of which 377 objects fall in the deep Subaru imaging region (shown in Figure 1 of the reference paper). This catalog is designed to identify X-ray emitting objects in the Chandra/AKARI NEP deep field. Together with the optimized cross-identification procedure, the clear advantage of the catalog is the very high reliability, while the catalog sacrifices completeness for objects with low counts (see Figure 9 in the paper). Only ~1.7% of the objects listed in the source catalog are expected to be spurious source detections.

The two sources that have an ML-threshold in the 0.5-7 keV band below 9.5 originate from a 0.5-7 keV single-band source detection run. To quote similar ML values for all objects, the authors list the total 0.5-7 keV ML values from the joint 3-energy band source detection run. The listed counts, count rates, fluxes, and the corresponding uncertainties in the 0.5-7 keV band are taken from the single-band detection run.

Considering the uncertainty in the astrometric calibration, all sources should be considered as possible X-ray counterparts that are within a radius of r_match = sqrt(sigma_total²+sigma_astro²), with sigma_total = 5 * sqrt(sigma_sys²+sigma_stat²) and sigma_sys = 0.1 arcseconds and sigma_astro = 0.2 arcseconds (astrometric uncertainty).

The authors also created a low-probability source catalog (not contained in this present HEASARC table): they caution that, due to the significant number of spurious sources in the low-probability catalog, it should NOT be used to select X-ray sources or to increase the sample size of X-ray-selected objects. It can be of interest if the scientific goal requires one to EXCLUDE potential X-ray emitting objects from a sample with a high completeness, since, using this strategy, one accepts those objects that are excluded are not associated with an X-ray-emitting object. The low-probability source catalog (available at http://cdsarc.u-strasbg.fr/ftp/cats/J_MNRAS/446/911/ as the files lowpscat.dat.gz and lowpscat.fits) has a lower maximum likelihood threshold than the main source catalog (an internal threshold of ML = 5, corresponding to ML_empir ~9.5). This catalog contains 626 detected sources, of which 506 are located within the deep Subaru imaging region. Based on their simulated data, the authors conclude that 19% of all the low-probability source catalog entries are false detections. Considering only the deep Subaru imaging area the spurious source fraction drops to 15%.

When using information from this catalog, please cite the reference paper: Krumpe et al. (2015, MNRAS, 446, 911).

Catalog Bibcode

2015MNRAS.446..911K

References

.Chandra survey in the AKARI North Ecliptic Pole Deep Field.
I. X-ray data, point-like source catalogue, sensitivity maps, and number counts.
    Krumpe M., Miyaji T., Brunner H., Hanami H., Ishigaki T., Takagi T.,
    Markowitz A.G., Goto T., Malkan M.A., Matsuhara H., Pearson C., Ueda Y.,
    Wada T.
   <Mon. Not. R. Astron. Soc., 446, 911-931 (2015)>
   =2015MNRAS.446..911K

Provenance

This table was created by the HEASARC in August 2015 based on CDS table J/MNRAS/446/911 files mainscat.dat, the main source catalog. Some of the values for the name parameter in the HEASARC's implementation of this table were corrected in April 2018.

Parameters

Source_Number
A unique master source identification number for each source in this catalog.

Name
The standard J2000.0 position-based "unregistered" Chandra source designation, e.g., 'CXOU J175517.4+663226'. This was created by the HEASARC based on the positions given, since names were not specified for these sources in the original table.

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^-5 degrees (0.036 arcseconds) in the original table. The positional information of the Chandra X-ray source is based on the primary source catalog (three energy band images covering 0.5-7 keV), unless the source is only detected in the soft (0.5-2 keV) or the hard (2-7 keV) energy band.

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^-5 degrees (0.036 arcseconds) in the original table. The positional information of the Chandra X-ray source is based on the primary source catalog (three energy band images covering 0.5-7 keV), unless the source is only detected in the soft (0.5-2 keV) or the hard (2-7 keV) energy band.

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 error of the source position, in arcseconds. This was calculated by combining the 1-sigma statistical uncertainties on the RA. and Dec values in quadrature. The values for this parameter do not include the additional systematic uncertainty to optimize the source detection (Section 4.3.1 of the reference paper), nor do they contain the uncertainty of the astrometric calibration of the Chandra data to the Subaru/Suprime-Cam reference frame in the AKARI NEP Deep Field (Section 5.1 of the reference paper). To determine the counterparts of these X-ray sources in other wavelength regimes, the authors recommend using the procedure given in Section 5.2 of the reference paper.

FB_Counts
The total-band (0.5-7 keV) Chandra source counts. The emldetect routine (described in Section 4.2 of the reference paper) corrects automatically all counts, count errors, rates, rate errors, fluxes, and flux errors for the PSF fraction size. Thus, these values do not correspond only to the used 80% PSF fraction size, but represent the true (intrinsic) quantities.

FB_Counts_Error
The 1-sigma uncertainty in the corresponding parameter value, in the same units.

FB_Count_Rate
The total-band (0.5-7 keV) vignetting-corrected Chandra source count rate, in counts s^-1. The emldetect routine (described in Section 4.2 of the reference paper) corrects automatically all counts, count errors, rates, rate errors, fluxes, and flux errors for the PSF fraction size. Thus, these values do not correspond only to the used 80% PSF fraction size, but represent the true (intrinsic) quantities.

FB_Count_Rate_Error
The 1-sigma uncertainty in the corresponding parameter value, in the same units.

FB_Flux_Limit
This limit flag parameter is set to '<' if the corresponding parameter value is a 90% upper limit rather than a detection.

FB_Flux
The total-band (0.5-7 keV) Chandra source flux (corrected for Galactic absorption), in erg cm^-2 s^-1. If a source is not detected in an energy band (internal ML-threshold in this energy band below 9.5), the associated limit parameter is set to '<', the associated error parameter is set to null, and this flux value is set to the upper 90% limit (see Section 5.4 in the reference paper).

The emldetect routine (described in Section 4.2 of the reference paper) corrects automatically all counts, count errors, rates, rate errors, fluxes, and flux errors for the PSF fraction size. Thus, these values do not correspond only to the used 80% PSF fraction size, but represent the true (intrinsic) quantities. Single energy conversion factors ECFs are used to convert observed count rates into observed fluxes (corrected for Galactic absorption), based on the instrumental response and an assumed spectral property of the X-ray source. All ECFs consider the Galactic column density for the AKARI NEP Deep Field of N_H, Gal_ = 4.0 x 10²⁰ cm^-2 and a power-law spectrum with a photon index of 1.4. The authors also consider the time-dependent degradation of the CCD response at low energies by using the time-averaged calibration files from Chandra Cycle 12. Depending on the energy band used, ObsIDs 10443 and 11999 from Cycle 10 have an up to 8% higher sensitivity. To correctly account for this fact and use single ECFs for all observations based on Cycle 12 only, the authors multiplied the exposure maps of these observations by the corresponding correction factors.In other words, they normalized the Cycle 10 exposure maps to Cycle 12. The ECFs used for the 0.5-2, 2-4, 4-7, 2-7, 0.5-7 keV energy bands are 1.523, 0.704, 0.344, 0.509, and 0.849, respectively (count rates to fluxes, in units of 10^-11 erg s^-1 cm^-2). One limitation of using a single ECF is that the flux is only correct if each object has the same spectral shape as assumed for the ECF calculation.

FB_Flux_Error
The 1-sigma uncertainty in the corresponding parameter value, in the same units.

FB_Max_Likelihood
The internal maximum likelihood ML = -ln(P) of the source detection in the specified band, derived from emldetect (see Section 4.3.3 and the Appendix of the reference paper for the interpretation of these values).

SB_Counts
The soft-band (0.5-2 keV) Chandra source counts. The emldetect routine (described in Section 4.2 of the reference paper) corrects automatically all counts, count errors, rates, rate errors, fluxes, and flux errors for the PSF fraction size. Thus, these values do not correspond only to the used 80% PSF fraction size, but represent the true (intrinsic) quantities

SB_Counts_Error
The 1-sigma uncertainty in the corresponding parameter value, in the same units.

SB_Count_Rate
The soft-band (0.5-2 keV) vignetting-corrected Chandra source count rate, in counts s^-1. The emldetect routine (described in Section 4.2 of the reference paper) corrects automatically all counts, count errors, rates, rate errors, fluxes, and flux errors for the PSF fraction size. Thus, these values do not correspond only to the used 80% PSF fraction size, but represent the true (intrinsic) quantities.

SB_Count_Rate_Error
The 1-sigma uncertainty in the corresponding parameter value, in the same units.

SB_Flux_Limit
This limit flag parameter is set to '<' if the corresponding parameter value is a 90% upper limit rather than a detection.

SB_Flux
The soft-band (0.5-2 keV) Chandra source flux (corrected for Galactic absorption), in erg cm^-2 s^-1. If a source is not detected in an energy band (internal ML-threshold in this energy band below 9.5), the associated limit parameter is set to '<', the associated error parameter is set to null, and this flux value is set to the upper 90% limit (see Section 5.4 in the reference paper).

SB_Flux_Error
The 1-sigma uncertainty in the corresponding parameter value, in the same units.

SB_Max_Likelihood
The internal maximum likelihood ML = -ln(P) of the source detection in the specified band, derived from emldetect (see Section 4.3.3 and the Appendix of the reference paper for the interpretation of these values).

HB_Counts
The hard-band (2-7 keV) Chandra source counts. The emldetect routine (described in Section 4.2 of the reference paper) corrects automatically all counts, count errors, rates, rate errors, fluxes, and flux errors for the PSF fraction size. Thus, these values do not correspond only to the used 80% PSF fraction size, but represent the true (intrinsic) quantities

HB_Counts_Error
The 1-sigma uncertainty in the corresponding parameter value, in the same units.

HB_Count_Rate
The hard-band (2-7 keV) vignetting-corrected Chandra source count rate, in counts s^-1. The emldetect routine (described in Section 4.2 of the reference paper) corrects automatically all counts, count errors, rates, rate errors, fluxes, and flux errors for the PSF fraction size. Thus, these values do not correspond only to the used 80% PSF fraction size, but represent the true (intrinsic) quantities.

HB_Count_Rate_Error
The 1-sigma uncertainty in the corresponding parameter value, in the same units.

HB_Flux_Limit
This limit flag parameter is set to '<' if the corresponding parameter value is a 90% upper limit rather than a detection.

HB_Flux
The hard-band (2-7 keV) Chandra source flux (corrected for Galactic absorption), in erg cm^-2 s^-1. If a source is not detected in an energy band (internal ML-threshold in this energy band below 9.5), the associated limit parameter is set to '<', the associated error parameter is set to null, and this flux value is set to the upper 90% limit (see Section 5.4 in the reference paper).

HB_Flux_Error
The 1-sigma uncertainty in the corresponding parameter value, in the same units.

HB_Max_Likelihood
The internal maximum likelihood ML = -ln(P) of the source detection in the specified band, derived from emldetect (see Section 4.3.3 and the Appendix of the reference paper for the interpretation of these values).

B24_Counts
The 'medium-hard'-band (2-4 keV) Chandra source counts. The emldetect routine (described in Section 4.2 of the reference paper) corrects automatically all counts, count errors, rates, rate errors, fluxes, and flux errors for the PSF fraction size. Thus, these values do not correspond only to the used 80% PSF fraction size, but represent the true (intrinsic) quantities

B24_Counts_Error
The 1-sigma uncertainty in the corresponding parameter value, in the same units.

B24_Count_Rate
The 'medium-hard'-band (2-4 keV) vignetting-corrected Chandra source count rate, in counts s^-1. The emldetect routine (described in Section 4.2 of the reference paper) corrects automatically all counts, count errors, rates, rate errors, fluxes, and flux errors for the PSF fraction size. Thus, these values do not correspond only to the used 80% PSF fraction size, but represent the true (intrinsic) quantities.

B24_Count_Rate_Error
The 1-sigma uncertainty in the corresponding parameter value, in the same units.

B24_Flux_Limit
This limit flag parameter is set to '<' if the corresponding parameter value is a 90% upper limit rather than a detection.

B24_Flux
The 'medium-hard'-band (2-4 keV) Chandra source flux (corrected for Galactic absorption), in erg cm^-2 s^-1. If a source is not detected in an energy band (internal ML-threshold in this energy band below 9.5), the associated limit parameter is set to '<', the associated error parameter is set to null, and this flux value is set to the upper 90% limit (see Section 5.4 in the reference paper).

B24_Flux_Error
The 1-sigma uncertainty in the corresponding parameter value, in the same units.

B24_Max_Likelihood
The internal maximum likelihood ML = -ln(P) of the source detection in the specified band, derived from emldetect (see Section 4.3.3 and the Appendix of the reference paper for the interpretation of these values).

B47_Counts
The ultrahard-band (4-7 keV) Chandra source counts. The emldetect routine (described in Section 4.2 of the reference paper) corrects automatically all counts, count errors, rates, rate errors, fluxes, and flux errors for the PSF fraction size. Thus, these values do not correspond only to the used 80% PSF fraction size, but represent the true (intrinsic) quantities

B47_Counts_Error
The 1-sigma uncertainty in the corresponding parameter value, in the same units.

B47_Count_Rate
The ultrahard-band (4-7 keV) vignetting-corrected Chandra source count rate, in counts s^-1. The emldetect routine (described in Section 4.2 of the reference paper) corrects automatically all counts, count errors, rates, rate errors, fluxes, and flux errors for the PSF fraction size. Thus, these values do not correspond only to the used 80% PSF fraction size, but represent the true (intrinsic) quantities.

B47_Count_Rate_Error
The 1-sigma uncertainty in the corresponding parameter value, in the same units.

B47_Flux_Limit
This limit flag parameter is set to '<' if the corresponding parameter value is a 90% upper limit rather than a detection.

B47_Flux
The ultrahard-band (4-7 keV) Chandra source flux (corrected for Galactic absorption), in erg cm^-2 s^-1. If a source is not detected in an energy band (internal ML-threshold in this energy band below 9.5), the associated limit parameter is set to '<', the associated error parameter is set to null, and this flux value is set to the upper 90% limit (see Section 5.4 in the reference paper).

B47_Flux_Error
The 1-sigma uncertainty in the corresponding parameter value, in the same units.

B47_Max_Likelihood
The internal maximum likelihood ML = -ln(P) of the source detection in the specified band, derived from emldetect (see Section 4.3.3 and the Appendix of the reference paper for the interpretation of these values).

Hardness_Ratio_SH
The hardness ratio between the 0.5-2 keV and 2-7 keV energy bands. This is equivalent to a color index in the optical, and is the simplest way to characterize an X-ray spectrum. The count rates in two energy bands are used to compute the hardness ratio HR = (RATE_B - RATE_A)/(RATE_A + RATE_B), where band A is the low-energy and band B the high-energy band. The authors use the count rate, instead of the source counts, for two reasons. First, the count rate is one of the parameters that is fitted by the emldetect software, and is therefore a direct output. Secondly, the count rate is corrected for vignetting, while the source counts are not. In the case that a hardness ratio and/or its uncertainties are undefined (count rates in both bands are zero), a null value is given in the table for these quantities.

Hardness_Ratio_SH_Error
The 1-sigma uncertainty in the corresponding parameter value, in the same units.

Hardness_Ratio_SM
The hardness ratio between the 0.5-2 keV and 2-4 keV energy bands. This is equivalent to a color index in the optical, and is the simplest way to characterize an X-ray spectrum. The count rates in two energy bands are used to compute the hardness ratio HR = (RATE_B - RATE_A)/(RATE_A + RATE_B), where band A is the low-energy and band B the high-energy band. The authors use the count rate, instead of the source counts, for two reasons. First, the count rate is one of the parameters that is fitted by the emldetect software, and is therefore a direct output. Secondly, the count rate is corrected for vignetting, while the source counts are not. In the case that a hardness ratio and/or its uncertainties are undefined (count rates in both bands are zero), a null value is given in the table for these quantities.

Hardness_Ratio_SM_Error
The 1-sigma uncertainty in the corresponding parameter value, in the same units.

Hardness_Ratio_MU
The hardness ratio between the 2-4 keV and 4-7 keV energy bands. This is equivalent to a color index in the optical, and is the simplest way to characterize an X-ray spectrum. The count rates in two energy bands are used to compute the hardness ratio HR = (RATE_B - RATE_A)/(RATE_A + RATE_B), where band A is the low-energy and band B the high-energy band. The authors use the count rate, instead of the source counts, for two reasons. First, the count rate is one of the parameters that is fitted by the emldetect software, and is therefore a direct output. Secondly, the count rate is corrected for vignetting, while the source counts are not. In the case that a hardness ratio and/or its uncertainties are undefined (count rates in both bands are zero), a null value is given in the table for these quantities.

Hardness_Ratio_MU_Error
The 1-sigma uncertainty in the corresponding parameter value, in the same units.

SSC_Area_Flag
This flag parameters is to 1 to indicate that the source falls within the Deep Subaru/Suprime-Cam imaging region, else is set to 0.

Contact Person

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

Page Author: Browse Software Development Team
Last Modified: Monday, 16-Sep-2024 17:24:13 EDT