EXOHGLS - EXOSAT/CMA High Galactic Latitude Survey
A survey of serendipitous source performed in the very soft X-ray band
(0.05-2.0 keV) using the EXOSAT imaging telescopes is presented. The survey
covers 783 square degrees of high galactic latitude sky and includes 210
serendipitous sources which define a complete (flux-limited) sample. An
extensive program of optical and radio observatories together with
cross-correlations with catalogs of known objects lead to the identification
of 200 of the 210 detected sources. The 10 remaining objects have been
preliminarily classified on the basis of their X-ray to optical flux ratios,
thus making the sample essentially fully identified. Twenty-three additional
serendipitous sources which did not satisfy the requirements for inclusion in
the complete sample were also identified during the optical observations
program. The complete sample has been used to study the logN-logS relation and
the average spectral slope of AGN. It is found that the logN-logS slope is
consistent with that of the Einstein Extended Medium Sensitivity Survey (EMSS)
and with the "Euclidean" value of 1.5. The normalization of the logN-logS
is a strong function of the assumed spectral slope of AGN. Consistency with
the results of the EMSS implies that the average (energy) slope of
extragalactic sources in the soft X-ray band is very steep (alpha ~ 1.5). An
analysis of the association between AGN detection and Galactic NH also shows
that alpha is steep and inconsistent with the canonical value of 0.7. The
survey was particularly successful in detecting nearby Galactic soft X-ray
emitters and includes a significantly higher percentage of stars than the
Einstein EMSS, five White Dwarfs, and three previously unknown AM Her type
The sample of sources in this cataogue has been selected from the CMA
database, which it has been generated using a standard processing
on the LE data.
The source detection algorithm used a sliding cell method. The size of the
search cell is such as to maximize the sensitivity across the field of view.
For more information about the LE processing see the documentation in the
Giommi, P., Tagliaferri, G., Beuermann, K.,Branduardi-Raymont, G., Brissenden,
R., Graser, U., Mason, K.O., Mittaz, J.D.P., Murdin, P., Pooley, G., "The
EXOSAT High Galactic Latitude Survey," Astrophysical Journal, Part 1, vol. 378,
Sept. 1, 1991, p. 77-92.
For each entry is available an image and a lightcurve.
The data products were created in a binary format during the post-operational
phase at the EXOSAT Observatory using a standard automatic analysis.
HEASARC converted the images and lightcurves in FITS format.
The images are in linearized detector coordinates and de-blurred
(to account for fluctuations of the pointing position which were quite small).
The lightcurves are background subtracted and a time resolution of 2^n
seconds, where n was optimized such that the average number of counts per bin
To convert LE count rates to fluxes, do the following:
* log in to the `legacy.gsfc.nasa.gov` anonymous ftp area
* go to `caldb/data/exosat/cma/cpf`
* copy the `.rmf` file for the filter instrument combination you need
* start XSPEC, then:
model wabs po (or whatever your model is)
10000 (or whatever your exposure is)
flux 0.1 2.5
The `fakeit` and `flux` commands will give the flux and count rate for the
model you have specified.
* 7 = 3000 (thin) lexan
The EXOHGLS catalog name of the EXOSAT target/field.
The name of the EXOSAT target/field. There are many serendipitous sources
in the EXOSAT LE images, and in some cases the name given here will
reflect the original target name and not the actual source name.
Source order number
Source Classification. Type 'class' at the browse prompt for more info.
Source not identified as the class filed set to 'uniden'.
The RA is the Right Ascension of the detected source.
The Dec is the Declination of the detected source.
The galactic longitude of the source.
The galactic latitude of the source.
Counting rate from the Al/P filter, if available from an observation of
the same source made within one day. `AL count rate error` gives
the error on the Al/P counting rate.
Al-Par Count Rate Error
Counting rate from the boron filter, if available (see the `AL count rate`
description). `BO count rate error` gives the error on boron counting rate.
Boron Count Rate Error
For imaging instruments, the X pixels coordinate of the source in the detector
is given by the parameter `X pixels`.
The X value ranges between -1024 and 1023.
For imaging instruments, the Y pixels coordinate of the source in the detector
is given by the parameter `Y pixels`.
The Y value ranges between -1024 and 1023.
The file_image parameter contains the file name of the associated image.
Rates buffer indentifier (first letter)
Gives the time resolution of the associated data product lightcurve in
seconds. The time resolution was 2^n seconds, where n was optimized such
that the average number of counts per bin is 0.3.
The `time` of the observation refers to the start time. This is listed as
yr.day, where yr is the last two digits of the year and day is the day of
the year e.g., day 300 of 1984 is 84.300. All times are stored internally as
a short history file key (SHF), which is the number of seconds before or
after 1 January 1980 at 00:00 hrs UT. Times are accurate to the nearest
12-micron IRAS Flux
MJD key for buffer creation
The instrument paramater records which of the two telescope+detector combination,
LE1+CMA1 or LE2+CMA2, were used in the observation to detect the source.
The values are L1, for the combination LE1+CMA1, and L2, for the combination
Some observation were carried out with an OBC program that sets
a 'diamond' filter. This filter electronically screened out the outer part
of the field of view. The resulting image, which is shaped as a diamond,
covers only a fraction of the 2 X 2 deg.
If the diamond filter wa s in used than the DIAMOND_FILTER paramater is set to 1
otherwise its value is 0.
ROSAT Id (spare)
The filter numbers are
* 6 = al/p
* 8 = boron
* 2 = PPL
* 3 = 4000 (thick) lexan
Distance from xpix=15, ypix=15
Observed Variance in TA1
expected variance in TA1
The `exposure` is the total on-source observation time in seconds. This
includes all dead time effects, interruptions in coverage, etc.
Dead Time Correction
Counting rate from the ME detector during this observation (warning: this may
not cover exactly the same time interval), it also covers the central field of
view and so will include all sources seen by the LE. `ME count rate error`
gives the error on the count rate.
ME Count Rate Error
25-micron IRAS Flux
60-micron IRAS Flux
The probability of the detection being due to random chance. Note, this is
not scaled for the independent number of search attempts in an image.
Archival Tape Number Where Files Are Stored
Principal Investigator Code
Proposal Type (HLX)
ME Quality Flag
File name of the associated background lightcurve. One background lightcurve
is associated to each image.
Redshift or HD Number of Counterpart
NH (10**19 cm-2) in the Galaxy
21 cm NH thru the galaxy H cm**-2 from Starke et al.
ME Count Rate in 3-6 keV Band
ME Count Rate Error in 3-6 keV Band
ME Count Rate in 1-3 keV Band
ME Count Rate Error in 1-3 keV Band
The 90-percent confidence uncertainty in arc seconds for the source position.
IPC Count Rate
IPC Count Rate Error
Radio Flux (mJy) at 5 GHz
detector deadtime correction factor
Flag for Radio Emission
Flag for Serendipitous Sources
Background Level (cts/s/sq.pixel)
The `count rate` and `count rate error` are the average counting rate (counts
per sec) over the observation and its associated one sigma uncertainty.
Error on Count Rate
Observed Variance in TA2
expected variance in TA2
100-micron IRAS Flux
Date of Last Record Update
Quality flag for the LE. This is a number between 1 and 5, where 5 is
excellent, and 1 means there may be a serious problem with the entry. A value
of 3 means that the entry should be checked. For example, all boron filter
entries have a qflag of 3, to warn of the problem with the psf for soft sources
observed with this filter.
File name of the source lightcurve.
Visual Quality of Detection
Point Source Flag
Questions regarding the EXOHGLS database table can be addressed to the
HEASARC User Hotline.
If you have any problems, please consult the help
page or mail firstname.lastname@example.org