EXOHGLS - EXOSAT/CMA High Galactic Latitude Survey

Overview

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 systems.

The sample of sources in this catalog 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 CMA database.

Catalog Bibcode

1991ApJ...378...77G

References

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.

Data Products

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 is 0.3.

Count Rate to Flux

To convert LE count rates to fluxes, do the following:

 * go to https://heasarc.gsfc.nasa.gov/FTP/caldb/data/exosat/cma/cpf/,
 * download the `.rmf` file for the filter instrument combination you need,
 * start XSPEC, then:

 model wabs po        (or whatever your model is)
 fakeit none
 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.

Parameters

Name
The EXOHGLS catalog name of the EXOSAT target/field.

Alt_Name
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.

ID_Number
Source order number

Class
Source Classification. Type 'class' at the browse prompt for more info. Source not identified as the class filed set to 'uniden'.

RA
The RA is the Right Ascension of the detected source.

Dec
The Dec is the Declination of the detected source.

LII
The galactic longitude of the source.

BII
The galactic latitude of the source.

Al_Count_Rate
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_Count_Rate_Error
Al-Par Count Rate Error

Bo_Count_Rate
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.

Bo_Count_Rate_Error
Boron Count Rate Error

X_Pixels
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.

Y_Pixels
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.

File_Image
The file_image parameter contains the file name of the associated image.

Lightcurve_Prefix
Rates buffer identifier (first letter)

Res_of_LC
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.

Time
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 second.

IRAS_Flux_1
12-micron IRAS Flux

Processed_Date
MJD key for buffer creation

Instrument
The instrument parameter 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 LE2+CMA2.

Diamond_Filter
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 was used, then the DIAMOND_FILTER parameter is set to 1. Otherwise, its value is 0.

ROSAT_ID
ROSAT Id (spare)

Filter
The filter numbers are

   * 7 = 3000 (thin) lexan

   * 6 = al/p

   * 8 = boron

   * 2 = PPL

   * 3 = 4000 (thick) lexan

Offset_Detection_Angle
Distance from xpix=15, ypix=15

Observed_Variance_TA1
Observed Variance in TA1

Expected_Variance_TA1
expected variance in TA1

Exposure_Time
The `exposure` is the total on-source observation time in seconds. This includes all dead time effects, interruptions in coverage, etc.

Old_Deadtime
Dead Time Correction

Sequence_Number
Sequence Number

ME_Count_Rate
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
ME Count Rate Error

IRAS_Flux_2
25-micron IRAS Flux

IRAS_Flux_3
60-micron IRAS Flux

Detection_Significance
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.

Tape_No
Archival Tape Number Where Files Are Stored

PI_Code
Principal Investigator Code

Proposal_Type
Proposal Type (HLX)

Qflag_ME
ME Quality Flag

File_Bglcurve
File name of the associated background lightcurve. One background lightcurve is associated to each image.

Redshift
Redshift or HD Number of Counterpart

Old_NH_21cm
NH (10**19 cm-2) in the Galaxy

NH_21cm
21 cm NH through the galaxy H cm**-2 from Starke et al.

ME_3_To_6_Count_Rate
ME Count Rate in 3-6 keV Band

ME_3_To_6_Count_Rate_Err
ME Count Rate Error in 3-6 keV Band

ME_1_To_3_Count_Rate
ME Count Rate in 1-3 keV Band

ME_1_To_3_Count_Rate_Err
ME Count Rate Error in 1-3 keV Band

Error_Radius
The 90-percent confidence uncertainty in arc seconds for the source position.

IPC_Count_Rate
IPC Count Rate

IPC_Count_Rate_Error
IPC Count Rate Error

Vmag
Visual Magnitude

Radio_5GHz_Flux
Radio Flux (mJy) at 5 GHz

Deadtime_Correction
detector deadtime correction factor

Radio_Flag
Flag for Radio Emission

Serendipity_Flag
Flag for Serendipitous Sources

Background_Per_Sqpix
Background Level (counts per square pixel)

Count_Rate
The `count rate` and `count rate error` are the average counting rate (counts per sec) over the observation and its associated one sigma uncertainty.

Count_Rate_Error
Error on Count Rate

Observed_Variance_TA2
Observed Variance in TA2

Expected_Variance_TA2
expected variance in TA2

IRAS_Flux_4
100-micron IRAS Flux

Last_Update
Date of Last Record Update

BV_Color
B-V Color

Qflag_LE
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.

UB_Color
U-B color

File_Lcurve
File name of the source lightcurve.

Quality_Check
Visual Quality of Detection

Point_Source_Flag
Point Source Flag

Contact Person

Questions regarding the EXOHGLS database table can be addressed to the HEASARC Help Desk.

Page Author: Browse Software Development Team
Last Modified: Monday, 16-Sep-2024 17:27:13 EDT