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EMSS - Einstein Catalog IPC EMSS Survey

HEASARC
Archive

Overview

This database table contains information from the Einstein Extended Medium Sensitivity Survey (EMSS) which consists of 835 serendipitous X-ray sources detected at or above 4 times the rms level in 1435 IPC fields with their centers located away from the galactic plane. Their limiting sensitivities range from ~5*10E-14 to ~3*10-12 ergs cm-3 s-1 in the 0.3-3.5keV band. A total area of 778 square degrees of the high galactic latitude sky (|b|>20) has been covered. The analysis has been performed using data from the Rev 1 processing system at the CfA. The resulting EMSS catalog is a flux-limited and homogeneous sample of astronomical objects that can be used for statistical studies. Additional information is available from the HEASARC.

Catalog Bibcodes

1990ApJS...72..567G
1991ApJS...76..813S

References

The published articles: Gioia et al. 1990, Stocke et al. 1991.

Parameters

Background_Count
The background counts.

BII
The Galactic Longitude of the object.

Class
The BROWSE object classification. The classification is based on the 'Type' parameter, if one is available.

Comments
This parameter contains miscellaneous information about the object.

Count_Rate
The corrected IPC count rate in units of counts/second. The count rate is derived from the net counts given in Net Counts (which are then corrected for vignetting, mirror scattering, and point response function scattering) and the livetime given in the Exposure field, which has already been corrected for instrumental dead time.

Dec
The Declination of the object. The listed position is that of the centroid of the X-ray source.

Dec_Offset
The offset in position the X-ray centroid and the proposed optical counterpart in arcseconds of Dec. Negative offsets indicate directions west and south of the X-ray centroids. Most of the offsets were measured automatically on the POSS or SRC J plates. They are accurate to +/- 5". For the SAO stars we have used the equinox 1950, epoch 1980 positions from the SAO catalog. When the optical counterpart is a radio source (Column <fr>), the VLA radio position is used (+/-1"). If more than one optical object is visible on the POSS within 10" of the offset position listed in this column, the identity of the optical counterpart is clarified with a note in the Note field. When the optical counterpart is a cluster of galaxies, the optical offset refers to the brightest cluster member.

Dec_Rad
The Declination, given in radians.

Exposure
Also known as the live-time, the parameter contains the exposure time of the IPC observation, corrected for instrumental dead time. It is given in seconds.

Ext_Flag
The Ext_Flag column is flagged with an asterisk ('*') if extended counts from Net Ext Count were used to calculate the X-ray flux.

Flux_6_cm
The radio flux or 5 sigma upper limit in mJy at 5 GHz for the optical counterpart and mostly comes from VLA observations. When a cluster of galaxies is the X-ray counterpart, radio emission from any cluster galaxy within the cluster is listed here.

Hydrogen_Density
The hydrogen column density along the line of sight to the IPC field target determined using the HI survey of Stark et al. (1989), in units of 10^21 atoms/cm^2. For regions of sky not surveyed by Stark et al. (south of declination -42 degrees), the surveys of Heiles and Cleary (1979) and Cleary, Heiles, and Haslam (1979) have been used.

LII
The Galactic Latitude of the object.

Name
The source name; denoted by MS, followed by right ascension in hours, minutes, and truncated fraction of minutes, then declination in degrees and arcminutes (i.e. MS0013.4+1558).

Net_Count_Error
The error on the net counts, computed as the square root of the total observed counts in the detection cell.

Net_Counts
The uncorrected net counts in the 0.2-3.5 keV band. No correction has been applied to the counts.

Net_Ext_Count
The net extended counts. For IPC sources, counts were computed manually to include all counts belonging to the source. For sources resolved by the IPC, the observed counts have been computed manually within a region centered on the source and with a size evaluated case by case so as to contain all the counts belonging to the source itself. Background counts for these sources have been computed within this same area from the background map produced by the REV.1 processing. In these cases only the vignetting and mirror scattering corrections have been applied.

Note
This column is flagged with an 'n' if a note on the source is present at the end of the table. Please request the references from the HEASARC, due to the size of the list.

Pos_Error
The positional uncertainty, in arcseconds, the error associated with the position (90% confidence error circle radius). A positional uncertainty of 4" indicates sources detected also by the HRI. In these cases the coordinates of the source come from the HRI.

RA
The Right Ascension of the object. The listed position is that of the centroid of the X-ray source.

RA_Offset
The offset in position between the X-ray centroid and the proposed optical counterpart in arcseconds of RA. Negative offsets indicate directions west and south of the X-ray centroids. Most of the offsets were measured automatically on the POSS or SRC J plates. They are accurate to +/- 5". For the SAO stars we have used the equinox 1950, epoch 1980 positions from the SAO catalog. When the optical counterpart is a radio source (Column <fr>), the VLA radio position is used (+/-1"). If more than one optical object is visible on the POSS within 10" of the offset position listed in this column, the identity of the optical counterpart is clarified with a note in the Note field. When the optical counterpart is a cluster of galaxies, the optical offset refers to the brightest cluster member.

RA_Rad
The Right Ascension, given in radians.

Radio_Flag
Marked with a less than sign (<) if the radio flux is an upper limit.

Redshift
If the counterpart is extragalactic the redshift is listed (+/- 0.003).

Seq_Num
The sequence number of the observation, a unique numeric identifier for each observation which was allocated sequentially at the time of proposal submission. It is an internal index used to key on all references to an observation.

Sig_Noise
This parameter gives the signal-to-noise ratio.

Type
The proposed identification or classification of the X-ray source.

Type_Ref
This parameter gives the reference for identification or classification. Identifications come from either our own spectroscopic work (EMSS in the 2nd line) or from other authors' work as indicated in the id_ref column. References to other authors are given when the proposed identification has been published even if additional spectroscopic observations may have been obtained. Please request the references from the HEASARC, due to the volume of the list.

Vmag
Photographic magnitude. Some entries are from photoelectric aperture photometry or from CCD photometry with the Whipple Observatory 24 inch. These are typically accurate to 0.01 mag. Other entries are from the literature or are estimated magnitudes (+/- 0.5 mag) from the STScI digitized sky survey plates. A value of 0.0 indicates that the source is still unidentified, so there is no magnitude listed. Please consult the HEASARC for more information.

Xray_Flux
This parameter contains the X-ray flux in the 0.3-3.5keV band, in units of 10^-13 erg/cm^2/s.

Xray_Flux_Error
This parameter contains the one-sigma error on the X-ray flux in the 0.3-3.5keV band. The error on the x-ray flux is from photon counting statistics only and is computed as the square root of the total observed counts in the detection cell.

Xv_Flux
The logarithm of the ratio of the X-ray flux to optical flux, calculated from the observed X-ray and visible fluxes using the expression:

            log(fx_fv) = log fx + V/2.5 +5.37      (Maccacaro et al. 1988).
  
These values are used to determine whether the optical counterpart is plausible. For this reason the X-ray flux used for this computation is not the value in the X-ray flux field, but rather the X-ray flux computed prior to assigning an optical identification class to each source.

Contact Person

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

Page Author: Browse Software Development Team
Last Modified: 21-Mar-2006