CMA - EXOSAT CMA Images/Lightcurves
An image was generated for each observation using a particular filter. A detection program was used to generate one database entry per source detected above a particular threshold. The CMA database contains a list of detected sources, details about those detections, plus the names of the files containing the associated image and lightcurves. Since many objects were observed many times, there are multiple entries per object.
De Korte P.A.J. et al., 1981, Sp. Sci. Rev., Vol. 30, p. 495. White N.E. and Peacock A.P. 1988, in X-ray Astronomy with EXOSAT, [eds. N.E. White and R. Pallivicini], Memoria S. A. It, p. 59.
The most frequent problems experienced are:
* Extended sources: Many extended sources will not have been detected and the count rates of those that are detected can be severely underestimated. This is due to the fact that the program used to detect sources was optimized for point-like sources. Users interested in studying extended sources should extract the relevant images (which are available online) and perform a more detailed analysis. * Confused sources: In a few cases sources were detected near a bright object. In these cases it is possible that the lightcurve of the fainter source is contaminated by photons from the brightest object. One such example is the quasar EXO1102.7+2523 which lies only 2.5 arc min from the bright AM Her-type object CW 1103+254. * Boron filter: A special Boron PSF was used to estimate the count rate of sources detected in this filter configuration. However, since the Boron PSF is a function of the source's spectral shape, it is impossible to apply the most appropriate PSF in an automatic process. This limitation leads to a possible underestimation of the count rate which can be as large as a factor of two for unabsorbed sources with very steep soft X-ray spectra. * Spurious sources: There are two kinds of spurious sources - those due to statistical fluctuation of the background and those due to the inability of the software to cope with unusual situations. In the latter case these are removed from the database as soon as they are recognized as such. These sources are found near bright objects in very short exposures ( <1000 seconds), in images where a diamond filter was used, or when a bright, extended source is present in the field of view (e.g., Cas A). The detection threshold of a source is a complicated function of exposure time, image background and position in the field of view. This threshold is set so that at most one spurious detection is expected in every 5 images. More than 3000 images were analyzed and about 600 spurious sources are expected to be present in the LE database across the full field of view. The vast majority of these will be outside the central 15 arc min radius of the detector. The reality of a source can be determined on the basis of additional information such as significance of detection, exposure time, background level, distance from the center, etc.
* 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) fakeit none 10000 (or whatever your exposure is) flux 0.1 2.5The `fakeit` and `flux` commands will give the flux and count rate for the model you have specified.
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
The galactic latitude of the source.
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
Source Classification. Type 'class' at the browse prompt for more info. Source not identified as the class filed set to 'uniden'.
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
Detector Deadtime Correction Factor
The Dec is the Declination of the detected source.
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.
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 in used than the DIAMOND_FILTER paramater is set to 1 otherwise its value is 0.
The 90-percent confidence uncertainty in arc seconds for the LE1 telescope.
Expected Variance in TA1
Expected Variance in TA2
The `exposure` is the total on-source observation time in seconds. This includes all dead time effects, interruptions in coverage, etc.
File Name of Background Light Curve
The file_image parameter contains the file name of the associated image.
File name of the source lightcurve.
The filter numbers are
* 7 = 3000 (thin) lexan * 6 = al/p * 8 = boron * 2 = PPL * 3 = 4000 (thick) lexan
Source Order Number
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 LE2+CMA2.
IPC Count Rate
IPC Count Rate Error
12-micron IRAS Flux
25-micron IRAS Flux
60-micron IRAS Flux
100-micron IRAS Flux
Date of Last Record Update
Rates Buffer Identifier (First Letter)
The galactic longitude of the source.
ME Count Rate in 1-3keV Band
ME Count Rate Error in 1-3keV Band
ME Count Rate in 3-6 keV Band
ME Count Rate Error in 3-6 keV Band
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
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.
21 cm NH thru the galaxy H cm**-2 from Starke et al.
Observed Variance in TA1
Observed Variance in TA2
Distance from xpix=15, ypix=15
Dead Time Correction
NH (10**19 cm-2) in the Galaxy
Pricipal Investigator Code
Point Source Flag
Date of Buffer Creation
Proposal Type (HLX etc.)
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.
ME Quality Flag
Visual Quality of Detection
The RA is the Right Ascension of the detected source.
Radio Flux (mJy) at 5 GHz
Flag for Radio Emission
Redshift or HD Number of Counterpart
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.
ROSAT ID (spare)
Flag for Serendipitous Sources
Archive Tape # Where Files Are Stored
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.
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.