Browse
this table...

NGC2024CXO - NGC 2024 Chandra X-Ray Point Source Catalog

HEASARC
Archive

Overview

The NGC 2024 Chandra X-Ray Point Source Catalog contains the results of a sensitive 76 ks Chandra observation of the young stellar cluster in NGC 2024, lying at a distance of ~415 pc in the Orion B giant molecular cloud. Previous infrared observations have shown that this remarkable cluster contains several hundred embedded young stars, most of which are still surrounded by circumstellar disks. Thus, it presents a rare opportunity to study X-ray activity in a large sample of optically invisible protostars and classical T Tauri stars (CTTSs) undergoing accretion. Chandra detected 283 X-ray sources, of which 248 were identified with counterparts at other wavelengths, mostly in the near-infrared. Astrometric registration of Chandra images against the Two Micron All Sky Survey (2MASS) resulted in positional offsets of ~0.25" near field center, yielding high confidence identifications of infrared counterparts. The Chandra detections are characterized by hard, heavily absorbed spectra and spectular variability. Spectral analysis of more than 100 of the brightest X-ray sources yields a mean V-band extinction of ~10.5 magnitudes and typical plasma energies <kT> ~ 3 keV. Chandra detected all but one of a sample of 27 classical T Tauri stars (CTTSs) identified from previous near- and mid-infrared photometry, and their X-ray and bolometric luminosities are correlated. IRS 2b, which is thought to be a massive embedded late O or early B star that may be the ionizing source of NGC 2024, is detected as an X-ray source. Seven millimeter-bright cores (FIR 1-7) in NGC 2024 that may be protostellar were not detected, with the possible exception of faint emission near the unusual core FIR 4.

Catalog Bibcode

2003ApJ...598..375S

References

A deep Chandra X-ray observation of the embedded young cluster in NGC 2024.
    Skinner S., Gagne M., Belzer E.
   <Astrophys. J., 598, 375-391 (2003)>
   =2003ApJ...598..375S

Provenance

Theis table was created by the HEASARC in January 2007 based on CDS table J/ApJ/598/375/table1.dat.

Parameters

Source_Number
A running source number in order of increasing J2000.0 Right Ascension.

Notes_Flag
This parameter has a value of 'Y' if there is a note about this source available in the notes file (at CDS) ftp://cdsarc.u-strasbg.fr/pub/cats/J/ApJ/598/375/notes.dat , and a value of 'f' if a flare or other obvious variability was seen in the source light curve.

Name
The X-ray source name based on the truncated J2000 coordinates (JHHMMSS.s-DDMMSS) and using the 'CXOU' prefix for unregistered Chandra X-ray sources recommended by the CDS Dictionary of Nomenclature of Celestial Objects.

Alt_Name
An alternate name for the X-ray source, based on the [SGB2003]' prefix (for Skinner, Gagne and Belzer 2003) and the source number, as recommended by the CDS Dictionary of Nomenclature of Celestial Objects.

RA
The Right Ascension of the X-ray source in the selected equinox. This was given in J2000.0 coordinates to a precision of 0.01 seconds of time in the original table. An astrometric correction was applied to the original X-ray J2000.0 positions to register them to the 2MASS J2000.0 positional reference frame.

Dec
The Declination of the X-ray source in the selected equinox. This was given in J2000.0 coordinates to a precision of 0.1 arcseconds in the original table. An astrometric correction was applied to the original X-ray J2000.0 positions to register them to the 2MASS J2000.0 positional reference frame.

LII
The Galactic Longitude of the X-ray source.

BII
The Galactic Latitude of the X-ray source.

Counts
The net (total - background) counts of the X-ray source in the 0.5 - 7 keV range. Source counts were measured in PSF-corrected, 95%-encircled energy regions except for the brightest sources, where 99%-encircled energy regions were used.Smaller regions were used for some closely-spaced sources.

Counts_Error
The uncertainty in the net counts of the X-ray source using the Gehrels formula (1986, ApJ, 303, 336).

Ks_Var_Statistic
The Kolmogorov-Smirnov (K-S) variability statistic; sources with a value of the K-S statistic > 1.7 are considered to be variable (see Section 3.2 of the published paper for more details).

Mean_Photon_Energy
The mean photon energy, in keV, of the X-ray source as determined from source events in the 0.5 - 7 keV range.

NH
The Hydrogen absorption column density, n_H, in atoms/cm^2, as determined from spectral fits with 1-T VAPEC optically thin plasma models using a fixed iron abundance Fe = 0.3 solar (given for sources with >= 90 counts).

NH_Pos_Err
The upper 90% confidence error in the derived n_H value, in atoms/cm^2. An upper or lower 90% confidence error of +0.0 or -0.0 is quoted when the error calculation algorithm did not converge and no valid 90% confidence error was obtained.

NH_Neg_Err
The lower 90% confidence error in the derived n_H value, in atoms/cm^2. An upper or lower 90% confidence error of +0.0 or -0.0 is quoted when the error calculation algorithm did not converge and no valid 90% confidence error was obtained.

Te_Plasma
The time-averaged characteristic plasma temperature, kT, in keV, as determined from spectral fits with 1-T VAPEC optically thin plasma models using a fixed iron abundance Fe = 0.3 solar (given for sources with >= 90 counts). Note that no value of kT is listed for the X-ray source number 5 as the 1T model gave a high but uncertain temperature kT >= 4 keV for this source.

Te_Plasma_Pos_Err
The upper 90% confidence error in the derived kT value. An upper or lower 90% confidence error of +0.0 or -0.0 is quoted when the error calculation algorithm did not converge and no valid 90% confidence error was obtained.

Te_Plasma_Neg_Err
The lower 90% confidence error in the derived kT value. An upper or lower 90% confidence error of +0.0 or -0.0 is quoted when the error calculation algorithm did not converge and no valid 90% confidence error was obtained.

Flux
The absorbed flux of the X-ray source in the 0.5 - 7 keV range as determined from the source event list (see Section 3.3 of the published paper for more details), in units of erg/cm^2^/s.

Log_Lx
The log of the 0.5 - 7 keV unabsorbed luminosity of the X-ray source, in erg/s, for an assumed distance of 415 pc, determined from spectral fits of the brighter sources where an estimate of n_H and kT are available.

Log_Lx_Var_Flag
This parameter is set to 'v' if the source varied during the Chandra observation.

Ctrpart_Name
Candidate IR, optical, or radio identifications for the X-ray source from 2MASS, SIMBAD, and/or the following other references:

   B89-NN  = Barnes et al. (1989ApJ...342..883B), [BCB89] IRS NN in Simbad
   B-NN    = Beck et al. (2003ApJ...583..358B), Cl* NGC 2024 BSC NN in Simbad
   HLL-NNN = Haisch, Lada & Lada (2000AJ....120.1396H),
             Cl* NGC 2024 HLL NNN in Simbad
   HLP-NNN = Haisch et al. (2001AJ....121.1512H), Cl* NGC 2024 HLP NNN
   M-NNN   = Meyer (1996, Ph.D. thesis, Univ. Massachusetts, Amherst).
   V-NN    = Radio identifications from 3.6 cm VLA observations of Rodriguez
             et al. (2003ApJ...598.1100R), [RGR2003] VLA NN in Simbad
   HHMMSSss-DDMMSSs = IR identifications found in the all-sky release
             of the 2MASS Point Source Catalog (<II/246>) are listed by
             their coordinates (e.g. 05411324-0153306).
  

Contact Person

Questions regarding the NGC2024CXO database table can be addressed to the HEASARC User Hotline.

Page Author: Browse Software Development Team
Last Modified: 23-Jan-2007