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IPCULTSOFT - Einstein IPC Ultrasoft Sources Catalog

HEASARC
Archive

Overview

A survey of the entire Einstein IPC database (a total of 5934 sources) has been carried out in order to select objects with strong components of ultrasoft X-ray emission (i.e., emission below 0.5 keV). The selection criteria were based on ratios of counts within three broad energy bands (i.e., X-ray "colors"). A total of 516 objects have been selected, with 202 (39%) having been identified through correlations with other databases. Of the currently identified objects, 45% are active galactic nuclei, 28% are stellar objects, 6% are "normal" galaxies and galaxy clusters, and the remaining 21% are "nonstellar" Galactic objects such as cataclysmic variables, pulsars, and white dwarfs.

The selection of sources for this survey was based on the analysis of counts in three broad energy bands defined as C1=0.16-0.56 keV, C2=0.56-1.08 keV, and C3= 1.08-3.5 keV. Ratios of these three bands constituted X-ray 'colors' which in turn were used to estimate the shape of the spectrum over the IPC bandpass. Based on models of X-ray spectra folded through the IPC response function, the following criteria were determined for the selection of ultrasoft sources: C1>0 and R1=C2/C1<0.36. These criteria guarantee an intrinsically soft X-ray spectrum that can be modeled by blackbody temperatures kT<50 keV, power-law spectral indices of >=2, or thermal plasma temperatures T<1 MK (million K). Details of the data analysis can be found in the Thompson et al. (1998) reference.


Catalog Bibcode

1998AJ....115.2587T

References

Thompson R.J., Jr., Shelton R.G., and Arning C.A. 1998, Astronomical Journal, 115, 2587.

Provenance

This database was created by the HEASARC in April 1999 based on tables provided by the catalog authors to the CDS/ADC.

Parameters

Sequence_Num
The Einstein IPC observation sequence number.

Source_Num
Object source number in field

RA
The right ascension of the X-ray source in the selected equinox (notice that the co-ordinates in the original input table were in J2000).

Dec
The declination of the X-ray source in the selected equinox (notice that the co-ordinates in the original input table were in J2000).

LII
The galactic longitude of the X-ray source.

BII
The galactic latitude of the X-ray source.

Count_Rate
The backround-subtracted count rate of the X-ray source in the 0.2 to 4.0 keV passband in units of counts per second. The counts for each source were extracted from within a circular region of 3 arcminutes radius centered on the catalog position of the source. Background subtraction was carried out with a background estimate based on counts within a source-centered annulus with an inner radius of 5 arcminutes and an outer radius of 6 arcminutes. This extraction procedure is consistent with the original Rev 1b extraction procedure.

Count_Rate_Error
The uncertainty in the count rate in units of counts per second.

SNR
The signal-to-noise ratio of the X-ray source.

Rib_Edge_Code
The Einstein IPC RECO or rib and edge code.

Name
The name or type of the optical counterpart to the X-ray source.

C1_Counts
The number of counts in the C1 low (0.16-0.56 keV) energy band, equivalent to PI (pulse-invariant) bins 2 and 3. The counts for each source were extracted from within a circular region of 3 arcminutes radius centered on the catalog position of the source. Background subtraction was carried out with a background estimate based on counts within a source-centered annulus with an inner radius of 5 arcminutes and an outer radius of 6 arcminutes. This extraction procedure is consistent with the original Rev 1b extraction procedure.

C1_Counts_Error
The rms uncertainty in the C1 counts.

C2_Counts
The number of counts in the C2 medium (0.56-1.08 keV) energy band, equivalent to PI (pulse-invariant) bins 4 and 5. The counts for each source were extracted from within a circular region of 3 arcminutes radius centered on the catalog position of the source. Background subtraction was carried out with a background estimate based on counts within a source-centered annulus with an inner radius of 5 arcminutes and an outer radius of 6 arcminutes. This extraction procedure is consistent with the original Rev 1b extraction procedure.

C2_Counts_Error
The rms uncertainty in the C2 counts.

C3_Counts
The number of counts in the C3 high (1.08-3.5 keV) energy band, equivalent to PI (pulse-invariant) bins 6 to 10. The counts for each source were extracted from within a circular region of 3 arcminutes radius centered on the catalog position of the source. Background subtraction was carried out with a background estimate based on counts within a source-centered annulus with an inner radius of 5 arcminutes and an outer radius of 6 arcminutes. This extraction procedure is consistent with the original Rev 1b extraction procedure.

C3_Counts_Error
The rms uncertainty in the C3 counts.


Contact Person

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

Page Author: Browse Software Development Team
Last Modified: 8-Nov-2004