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IPC: Help

IPC - Einstein IPC Sources Catalog


Overview

This database contains information on sources detected with the Einstein Observatory Image Proportional Counter (IPC), assembled for the Einstein Observatory Catalog (EOSCAT) of IPC X-ray Sources (2E) and containing over 4000 unique sources (with 6539 separate detections) which were detected with the IPC at a level of significance greater than 3.5 sigma in the broad band (0.2-3.5 keV).

This database also contains the list of 277 sources which are known not to have been included in the Einstein Observatory Source Catalog (flagged by supplement = 'Y' in this database). Those which were not detected during the standard Rev1B processing were typically discovered upon visual inspection of the contour diagrams in the Catalog. Others were detected with Rev1B standard processing but left out of the Catalog because of short exposure times or other reasons listed in the "missed_code" field. 258 of these 277 additional sources have no valid signal to noise ratio (SNR) estimate (values of 0.0), while 3 others have SNR values of 3.2 and 3.3, notice.

This IPC database is based on NASA Astrophysics Data System (ADS) tables that were created in 1991 and 1993 and were themselves derived from tables provided by Dr. D. E. Harris of the Center for Astrophysics at Harvard-Smithsonian. The HEASARC has a similar catalog in its database called EINSTEIN2E which comprises a more recent version of the IPC source list as archived at the NASA Astronomical Data Center (ADC) and the Center for Astronomical Data at Strasbourg (CDS). EINSTEIN2E has 868 fewer detections than the IPC catalog, notice, for reasons that the HEASARC is unsure of, but that may imply that some of the detections in IPC are not reliable. We have retained the IPC database for reasons of completeness, but caution that detections listed here which have no counterpart in the EINSTEIN2E Catalog should be treated with caution.


References

The Einstein IPC Source List From EOSCAT (ADS Creation Date: 26-Dec-1990;
    ADS Last Revision Date: 04-Nov-1993), D.E. Harris, CfA
The EOSCAT List of Missed IPC Sources (ADS Creation Date: 26-Oct-1990;
    ADS Last Revision Date: 17-Sep-1991), D.E. Harris, CfA

Provenance

This IPC database was recreated by the HEASARC in December 2000 to replace a previous version in which we discovered some transcription errors. It is based on NASA Astrophysics Data System (ADS) tables that were created in 1991 and 1993 and were themselves derived from tables provided by Dr. D. E. Harris of the Center for Astrophysics at Harvard-Smithsonian:
The Einstein IPC Source List From EOSCAT (ADS Creation Date: 26-Dec-1990;
    ADS Last Revision Date: 04-Nov-1993), D.E. Harris, CfA
The EOSCAT List of Missed IPC Sources (ADS Creation Date: 26-Oct-1990;
    ADS Last Revision Date: 17-Sep-1991), D.E. Harris, CfA

Parameters

Name
The designation derived from the B1950 right ascension and declination, with the prefix '2E'. This field was not in the original tables but was created by the HEASARC in accordance with the Dictionary of Astronomical Nomenclature recommendations for this catalog.

RA
The right ascension of the X-ray source. This was provided in B1950 equatorial coordinates in the originating tables.

Dec
The declination of the X-ray source. This was provided in B1950 equatorial coordinates in the originating tables.

LII
The galactic latitude of the X-ray source.

BII
The galactic longitude of the X-ray source.

Sequence_Num
The Einstein Observatory sequence number. The Einstein sequence number or ESN is a two to five digit number which uniquely identifies an Einstein observation. These numbers were assigned at the time of proposal submission.

Rev1b_Num
The one or two digit Rev 1B source number is the source number from standard processing and is given so that users may compare previous results. This field was not supplied with the addition to the IPC.

EOSCAT_Num
The EOSCAT source number is a one or two digit number which numbers the sources in each field. It should be noted that the catalog source number might not be the same as the Rev 1B source number (rev1b_num) from standard processing due to selection criteria. This field was not supplied with the addition to the IPC.

Global_Designation
The one to four digit global source number in the catalog. This is a running serial number (between 1 and 4809 inclusive) which uniquely identifies each separate source in the catalog. The catalog numbers are ordered by increasing right ascension and decreasing declination for identical right ascensions, and were assigned after multiple source detections (caused by multiple observations of the same area of sky) and were identified and "matched" to form a single source. This field was not supplied with the addition to the IPC.

Broad_RA_Rad
The right ascension in radians measured in the broad band. For multiple-detection sources, the position used is that of the detection with the largest signal-to-noise ratio and with Rib Edge Code=0. If no detection has Rib Edge Code=0, then the position is that of the source with the largest signal-to-noise ratio. This field was not supplied with the addition to the IPC (in that list source positions were directly given in equatorial coordinates).

Broad_Dec_Rad
The declination in radians measured in the broad band. For multiple-detection sources, the position used is that of the detection with the largest signal-to-noise ratio and with Rib Edge Code=0. If no detection has Rib Edge Code=0, then the position is that of the source with the largest signal-to-noise ratio. This field was not supplied with the addition to the IPC (in that list source positions were directly given in equatorial coordinates).

Error_Radius
The 90% confidence level error circle radius in arcseconds. The error has been corrected with variable systematic error. In Rev 1B, the systematic contribution was 30 arcsec, but we have used a value which depends on the distance between the source and the field center:


                    Table 5.3  Systematic Positional Errors

         Distance from Field Center (arcmin)      Systematic Error (arcsec)

                      < 5                                 25
                     5-15                                 37
                      > 5                                 47
  

This variation of uncertainty with distance from the field center is based on measurements of the observed positions of known sources. The listed uncertainty in position does not include a contribution to account for large errors which occur for sources detected near the field edge or rib shadows. Consequently, users should note that for sources for which the value of rib_edge_codes (reco) is not zero the uncertainty of the source position may be underestimated. This field was not supplied with the addition to the IPC.

Rflag
This flag marks when a source is underneath the ribs. The symbol "R" in this column indicates that the source is under a rib, thus the flux is a lower limit. If the source is not under a rib, this is blank. This field was not supplied with the addition to the IPC.

Count_Rate
The corrected count rate in the broad band in counts per second. The corrected count rates listed in the EOSCAT may differ slightly from those in the standard Rev 1B processing. This field was not supplied with the addition to the IPC (although some X-Ray sources in the addition do have values for a parameter called the intensity which appears to be essentially the same as the count_rate, albeit with a different detect cell size).

The count rate was caculated in the following way. For the detect cell (2.4 arcmin on each side) placed at the source position, the net counts (total minus background) are found. The background is determined by a frame around the detect cell (Ldetect) or from the background map (Mdetect), as mirror scattering and the point response function (PRF) and divided by the effective exposure to obtain the corrected count rate. The scattering correction (always equal to 1.18 for the broad energy band) recovers source counts scattered out of the detect cell as a result of large-angle mirror scattering. The PRF correction (1.13 for the chosen size of the detect cell) arises because source counts are distributed outside the detect cell by the IPC PRF. The effective exposure is the product of the live time, the relative exposure, and the vignetting correction. Relative exposure represents the fraction of the total live time during which the detect cell was exposed. The vignetting correction represents the loss of telescope area off-axis; it is normalized to 1.0 on-axis and decreases off-axis. Note that this is the inverse of the vignetting correction used in Rev 1B. Since the rib shadows may obscure part of a detect cell, the count rate when reco is nonzero underestimates the true count rate.

Count_Rate_Error
The error in the corrected count rate in the broad band, in counts per second. The corrected count rate listed in the EOSCAT may differ slightly from those in the standard Rev 1B processing. The error assigned to the count rate is calculated by taking the square root of the total number of counts (source plus background) in the box defined to measure the count rate, with the same corrections as for the count rate, and then dividing by the live time.

Net_Count
The net counts in a source in the broad band. The net counts in the detect cell is one of the most basic source quantities and is given so that the user may judge the reliability of the source parameters before any corrections are applied. This field was not supplied with the addition to the IPC.

Background_Count
The background counts in the broad band. The background counts in the detect cell is one of the most basic source quantities and is given so that the user may judge the reliability of the source parameters before any corrections are applied. This field was not supplied with the addition to the IPC.

SNR
The signal-to-noise ratio in the broad band. The signal-to-noise ratio of the source detection is the ratio of the net source counts to the estimated 1 sigma error of this quantity. The detection signal-to-noise ratio is set to 0.0 for those additional sources (with parameter supplement = 'Y') that were omitted from the original EOSCAT because the exposure time was less than 300 seconds or the source was below the 25% relative exposure cutoff.

Size_Corr
The size correction factor, or the ratio of counts contained within the 3-sigma contour to the counts within the 2.4 by 2.4 arcminute detection box, the latter value corrected for the point response function and mirror scattering, in the smoothed (with a Gaussian of 32 arcseconds sigma) and background-subtracted X-ray map. This parameter was developed to adjust the intensities for extended sources, since Rev 1B did not attempt to provide estimates of count rates or fluxes of extended sources. It serves to correct all intensity measurements (optimized for point sources) of resolved sources for the X-ray brightness which is outside of the detection box. This field was not supplied with the addition to the IPC.

Total_Net_Count
The sum of the net counts included within the 3-sigma contour of the smoothed map used for the contour diagrams generated for this catalog and used to calculate the size_corr parameter. This field was not supplied with the addition to the IPC.

Integration_Area
The number of 24"x24" pixels within a 3-sigma contour; this information was used in the calculation of the size_corr parameter. This field was not supplied with the addition to the IPC.

Rib_Edge_Codes
The ribs and edges code (RECO) is a numeric flag set to nonzero values to indicate that the detection cell (and/or frame defined for "local detect") falls near or on a rib shadow or detector edge. The code is formed by concatenating a pair of two-digit numbers: the first (thousands and hundreds columns) gives the number (up to 16) of frame subcells potentially shadowed by the ribs or masked-field edge; the second (tens and units columns) gives the number of subcells (up to 09) within the detect box which are potentially shadowed. This field was not supplied with the addition to the IPC.

Off_Axis
The angular separation between the optical axis (the telescope pointing direction) and the source position, in arcminutes. This field was not supplied with the addition to the IPC.

Detect_Method
The source detect method. The entry will be an "L" if the source was detected by the "Ldetect" or local detect method. Ldetect compares counts in the detect cell with counts in surrounding cells. The entry will be an "M" if the source was detected by the "Mdetect" or map detect method. Mdetect compares the counts in a detect cell with the counts in the background map in the same cell. This field was not supplied with the addition to the IPC.

Source_Flags
This parameter contains flags that are indicators that particular conditions apply or contain more information for the given source. Their meaning, and the number of occurrences in the catalog are given below:

     Flag     Meaning                                               Occurrences
     --------------------------------------------------------------------------
       A      Additional detection(s) occurred in other field(s)           1826
       B      Probably should be paired with another detection,              20
              but separation exceeded cutoff and thus not assigned
              an "A" flag
       E      Intensity corrected for source near the exposure cutoff at    122
              the field edge
       H      A hardness ratio is available (see below)                    3998
       I      Source detected by Ldetect near field edge; intensity          46
              adjusted to remove redundant exposure correction
  
This field was not supplied with the addition to the IPC.

Source_ID
This contains a code describing the source identification from the literature. No attempt was made to evaluate the accuracy or relevance of published identifications. This field was not supplied with the addition to the IPC.

The source identification codes are defined as follows:

            AGN             Active galactic nucleus
            BL              BL Lac object
            CLG             Cluster (or group) of galaxies
            CV              Cataclysmic variable
            G               Galaxy
            GLB             Globular cluster
            P               Pulsar
            Q               Quasar
            RS              Radio source
            S               Star
            SNR             Supernova remnant
            SY              Seyfert galaxy
            N               Nonspecific indicator for separations <100 arcsec
            NNN             Nonspecific indicator for separations between 100
                             and 150 arcsec
  

The non-specific indicator 'N' was adopted for the following three situations:

         a) the reference does not contain an optical identification
         b) there is more than one reference and there is disagreement as to the
            optical type
         c) the optical class cannot be categorized as one of the common types,
            e.g., the Galactic center, gamma-ray burster, nebula, and so on.
  

The symbol "NNN" is used if an identification entry exists between 100 and 150 arcsec from the source and there is no identification entry from the source position. It is often the case that the published paper is actually dealing with a different (but adjacent) source. Please note that this flag means only that there is an identification within the specified separation.

Hardness_Ratio
The maximum likelihood hardness ratio.The hardness ratio (HR) for a source is defined as: HR = [counts(hard) - counts(soft)]/ [counts(hard) + counts(soft)], where the hard band covers 0.81-3.5 keV and the soft band covers 0.16-0.81 keV.

Because the hardness ratio and error that were provided on the Einstein IPC Rev 1B printouts are incorrect for many sources, the hardness ratios have been recalculated using a maximum likelihood (ML) approach. THE HARDNESS RATIOS WERE CORRECTED IN OCTOBER 1993. This field was not supplied with the addition to the IPC.

The standard Rev1B method (a source-centered 5'-6' radii annulus) was used to estimate the background counts. The use of an annulus rather than the MDETECT background map formally invalidates the simplifying assumption of negligible error in the background expectation values, but in practice we expect the effects of this to be minor.

For those sources for which a hardness ratio could not be calculated, the columns for hardness ratio and uncertainties contain a value of 9.99. About 1300 of the sources without hardness ratios have non-zero RECO values making their spectra highly uncertain and their ratios unreliable. For another ~100 sources, computational conditions preclude obtaining confidence intervals, indicating that the value of the ratio itself is essentially indeterminate.

Plus_Uncert
The plus uncertainty for the hardness ratio. This field was not supplied with the addition to the IPC.

For those sources for which a hardness ratio could not be calculated, the columns for hardness ratio and uncertainties contain a value of 9.99. About 1300 of the sources without hardness ratios have non-zero RECO values making their spectra highly uncertain and their ratios unreliable. For another ~100 sources, computational conditions preclude obtaining confidence intervals, indicating that the value of the ratio itself is essentially indeterminate.

Minus_Uncert
The minus uncertainty for the hardness ratio. This field was not supplied with the addition to the IPC.

For those sources for which a hardness ratio could not be calculated, the columns for hardness ratio and uncertainties contain a value of 9.99. About 1300 of the sources without hardness ratios have non-zero RECO values making their spectra highly uncertain and their ratios unreliable. For another ~100 sources, computational conditions preclude obtaining confidence intervals, indicating that the value of the ratio itself is essentially indeterminate.

Rel_Correction
The exposure relative to the field center where the observation "livetime" is defined. Normally, this factor approximates the vignetting, but for observations with segments at different roll angles, it is a combination of the exposure factor and vignetting. This field was not supplied with the addition to the IPC.

Missed_Code
A one-letter code giving the reason the source was not included. This field was supplied with the addition to the IPC only. The following codes are defined:

      C:  Source is below the 25% cutoff in relative exposure
      E:  Source is close to the edge of the field
      L:  M detect was not run and L detect failed (probably an extended source)
      R:  Source is close to a rib shadow
      T:  Source lies in a region with <300 seconds exposure time
  

Intensity
The corrected count rates are given in this field for clusters which are contained in the compendium being prepared by Jones and Forman. These intensities refer to the count rate contained within a 0.5 Mpc (H=50 km/s) of the cluster center unless a different radius is stated in the comments. This field was supplied with the addition to the IPC only.

Contours
The number of contours plotted in the book version. The first contour is three sigma above background (at the field center), and subsequent contours increase by factors of two. This field was supplied with the addition to the IPC only.

Comments
Comments on added sources. This field gives comments such as source name, radius in which the intensity was calculated, and whether the source is extended. This field was supplied with the addition to the IPC only.

Supplement
Supplement flag. If 'Y', then the source was added from the EOSCAT List of Missed IPC Sources.

Class
BROWSE classification type. The classification is based on the 'source_id' parameter, if one is available.


Contact Person

Questions regarding the IPC database table can be addressed to the HEASARC User Hotline.
If you have any problems, please consult the help page or mail ledas-help@star.le.ac.uk
 
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