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CMA - EXOSAT CMA Images/Lightcurves |
HEASARC Archive |
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.
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
Background_Per_Sqpix
Background Level
BII
The galactic latitude of the source.
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
BV_Color
B-V Color
Class
Source Classification. Type 'class' at the browse prompt for more info.
Source not identified as the class filed set to 'uniden'.
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
Deadtime_Correction_Fact
Detector Deadtime Correction Factor
Dec
The Dec is the Declination of the detected source.
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.
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 in used than the DIAMOND_FILTER paramater is set to 1 otherwise its value is 0.
Error_Radius
The 90-percent confidence uncertainty in arc seconds for the LE1 telescope.
Expected_Variance_Ta1
Expected Variance in TA1
Expected_Variance_Ta2
Expected Variance in TA2
Exposure_Time
The `exposure` is the total on-source observation time in seconds. This
includes all dead time effects, interruptions in coverage, etc.
File_Bglcurve
File Name of Background Light Curve
File_Image
The file_image parameter contains the file name of the associated image.
File_Lcurve
File name of the source lightcurve.
Filter
The filter numbers are
* 7 = 3000 (thin) lexan * 6 = al/p * 8 = boron * 2 = PPL * 3 = 4000 (thick) lexan
ID_Number
Source Order Number
Instrument
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
IPC_Count_Rate_Error
IPC Count Rate Error
IRAS_Flux_1
12-micron IRAS Flux
IRAS_Flux_2
25-micron IRAS Flux
IRAS_Flux_3
60-micron IRAS Flux
IRAS_Flux_4
100-micron IRAS Flux
Last_Update
Date of Last Record Update
Lightcurve_Prefix
Rates Buffer Identifier (First Letter)
LII
The galactic longitude of the source.
ME_1_To_3_Count_Rate
ME Count Rate in 1-3keV Band
ME_1_To_3_Count_Rate_Err
ME Count Rate Error in 1-3keV Band
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_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
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.
NH_21cm
21 cm NH thru the galaxy H cm**-2 from Starke et al.
Observed_Variance_Ta1
Observed Variance in TA1
Observed_Variance_Ta2
Observed Variance in TA2
Offset_Angle_Of_Detectio
Distance from xpix=15, ypix=15
Old_Deadtime
Dead Time Correction
Old_NH_21cm
NH (10**19 cm-2) in the Galaxy
PI_Code
Pricipal Investigator Code
Point_Source_Flag
Point Source Flag
Processed_Date
Date of Buffer Creation
Proposal_Type
Proposal Type (HLX etc.)
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.
Qflag_Me
ME Quality Flag
Quality_Check
Visual Quality of Detection
RA
The RA is the Right Ascension of the detected source.
Radio_5GHz_Flux
Radio Flux (mJy) at 5 GHz
Radio_Flag
Flag for Radio Emission
Redshift
Redshift or HD Number of Counterpart
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.
ROSAT_ID
ROSAT ID (spare)
Sequence_Number
Sequence Number
Serendipity_Flag
Flag for Serendipitous Sources
Tape_No
Archive Tape # Where Files Are Stored
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.
UB_Color
U-B Color
Vmag
V Magnitude
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.