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NGC2403CXO - NGC 2403 Central 3-kpc Region Chandra Source Catalog

HEASARC
Archive

Overview

Archival Chandra observations are used to study the X-ray emission associated with star formation in the central region of the nearby (D = 3.2 Mpc, 1 arcminute = 1 kpc) SAB(s)cd galaxy NGC 2403. The distribution of X-ray emission is compared to the morphology visible at other wavelengths using complementary Spitzer, Galaxy Evolution Explorer, and ground-based H-alpha imagery. In general, the brightest X-ray emission is associated with H II regions and to other star-forming structures, but is more pervasive, existing also in regions devoid of strong H-alpha and UV emission.

NGC 2403 was observed in full-frame mode with the Chandra ACIS-S on four occasions for a total of ~ 180 ks, on 2001 Apr 17, 2004 Aug 13, 2004 Oct 03 and 2004 Dec 22. The source-finding tool described by Tennant (2006, AJ, 132, 1372) was applied to all 4 individual data sets and to the merged data set in order to search for discrete X-ray sources. The search was limited to the cnetral 6' x 6' (6 kpc x 6 kpc) region and to events within the full Chandra energy range 0.3-8.0 keV. Fifty eight point sources were detected in the merged data set with a signal-to-noise ratio (S/N) above 2.8 and with a minimum of 5 sigma above background uncertainty (corresponding to a detection limit of 8-10 counts for a typical on-axis source). These sources were listed in Table 2 of the reference paper and and are contained in the present HEASARC table. They can be selected by specifying source_type = 'Point Source'.

The X-ray data were also examined to see if there was emission from known SNRs and H II regions after masking out the afore-mentioned X-ray point sources (see Section 2.1 of the reference paper for full details). Events falling within the areas defined by 24 optically identified SNRs that were imaged on the S3 chip in the first three observations were used to construct a composite spectrum. This stacked spectrum was fit by an absorbed 1-T APEC model with the hydrogen column density as a free parameter in XSPEC which was then used to translate the observed net count rates into X-ray luminosities. Only 4 or 5 of these SNRs are likely to be 'truely' detected X-ray sources. The SNRs can be selected in the present HEASARC table by specifying source_type ='SNR'.

A similar procedure was used to search the X-ray data for the presence of X-ray emission at the locations of 47 H II regions in NGC 2403. Events falling within the areas defined by 47 H II regiuons that were imaged on the S3 chip in the first three observations were used to construct a composite spectrum. This stacked spectrum was fit by an absorbed 2-T APEC model with the hydrogen column density as a free parameter in XSPEC which was then used to translate the observed net count rates into X-ray luminosities. Only the most X-ray-luminous H II regions are likely to be 'truely' detected X-ray sources. The H II regions can be selected in the present HEASARC table by specifying source_type ='HII Region'.


Catalog Bibcode

2010AJ....139.1066Y

References

An X-ray view of star formation in the central 3 kpc of NGC 2403.
    Yukita M., Swartz D.A., Tennant A.F., Soria R.
   <Astron. J., 139, 1066-1088 (2010)>
   =2010AJ....139.1066Y

Provenance

This table was created by the HEASARC in June 2012 based on CDS Catalog J/AJ/139/1066 files table2.dat, table5.dat and table7.dat.

Parameters

Name
The name of the source. For the 58 detected X-ray point sources, the HEASARC has constructed names using the usual CDS convention for unregistered Chandra sources, viz., 'CXOU JHHMMSS.s+DDMMSS', using the truncated J2000.0 equatorial coordinates. For the 24 SNRs for which X-ray information was extracted (only a few being detected), the HEASARC has constructed names extending the CDS convention for objects in a given class mentioned in this paper, viz., '[YST2010] SF JHHMMSS.s+DDMMSS' for the star formation regions listed in Tables 9 and 10 of the reference paper: thus, for the SNRs, the HEASARC-constructed names are of the form '[YST2010] SNR JHHMMSS.s+DDMMSS', where the prefix stands for 'Yukita, Swartz, Tennant 2010 supernova remnant' and the remainder is the truncated J2000.0 equatorial coordinates. For the 47 H II regions for which X-ray information was extracted (only a few being detected), the HEASARC has again constructed names extending the CDS convention for objects in a given class discussed in this paper, viz., '[YST2010] HII JHHMMSS.s+DDMMSS', where the prefix stands for 'Yukita, Swartz, Tennant 2010 H II region' and the remainder is the truncated J2000.0 equatorial coordinates.

RA
The Right Ascension of the object in the selected equinox. This was given in J2000.0 equatorial coordinates to a precision of 0.1 seconds of time in the original table.

Dec
The Declination of the object in the selected equinox. This was given in J2000.0 equatorial coordinates to a precision of 0.1 arcseconds in the original table

LII
The Galactic Longitude of the source.

BII
The Galactic Latitude of the source.

Count_Rate
The net (background-subtracted) count rate of the source for the ACIS-S3 chip, in the 0.5-2.0 keV band, in counts per second.

Count_Rate_Error
The uncertainty in the net (background-subtracted) count rate of the source for the ACIS-S3 chip, in the 0.5-2.0 keV band, in counts per second.

Lx
The X-ray luminosity of the source in the 0.5-2.0 keV band, in erg/s, assuming a distance to NGC 2403 of 3.2 Mpc and a flux calculated from the observed net X-ray count rate assuming a spectral model based on the best-fit model in XSPEC to the stacked spectra for the object class as given by the source_type parameter. For the detected X-ray point sources, this was an absorbed thermal bremsstrahlung model with the hydrogen column density as a free parameter (see Table 3 of the reference paper). For the SNRs, this was an absorbed one-temperature MEKAL model with the hydrogen column density as a free parameter (see Table 4 of the reference paper). For the H II regions, this was an absorbed two-temperature MEKAL model with the hydrogen column density as a free parameter (see Table 6 of the reference paper).

Lx_Error
The uncertainty in the X-ray luminosity of the source in the 0.5-2.0 keV band, in erg/s.

L_Halpha
The H-Alpha luminosity of the source, in erg/s. This is given only for the SNRs and the H II regions.

Var_Flag
The variability flag for the source. This is given only for the X-ray point sources. If the flux from a source during one observation deviated from its average over the other available observations by > 3 sigma, then it was flagged as a long-term variable and designated by the letter 'L' in this parameter. (Because of differences in spacecraft roll and target aim point, not all sources were within the FOV during all four observations). Short-term variability during individual observations was checked by binning the source light curve (event arrival times) for each observation using 2-ks temporal bins. The shape of the light curve was compared to a constant using the Chi-squared statistic to check for variability. Short-term variability is indicated by the letter 'S'.

Source_Type
This HEASARC-created parameter indicates the source classification, which is essentially in which table in the reference paper the source was listed: hence, (X-ray) 'Point Source' for Table 2 objects, 'SNR' for Table 5 objects and 'HII Region' for Table 7 objects.


Contact Person

Questions regarding the NGC2403CXO database table can be addressed to the HEASARC User Hotline.

Page Author: Browse Software Development Team
Last Modified: 20-Jun-2012