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A2LCSCAN: Help

A2LCSCAN - HEAO 1 A2 Scanned Lightcurves


Overview

The A2 experiment was flown on the HEAO-1 satellite, from August, 1977 until January 1979.

The experiment consisted of six multi-layer, multi-anode collimated gas proportional counters. These were two LEDs (Low Energy Detectors), a MED (Medium Energy Detector), and three HEDs (High Energy Detectors). The first 6-months of mission were dedicated to an all-sky scan after which a pointing phase started.

This database table accesses the lightcurves available at HEASARC obtained from the A2 MED (small and large field of view) and HEDs (3 units, each with small and large field of view) detectors during the scanning phase.


Data Products

The MED and HEDs have two different field of views a small and a large, whose sizes are various combination of 3.0 X 1.5 degrees 3.0 x 3.0 degrees, 3.0 x 6.0 degrees (FWHM). The collimators were oriented so that the 3.0 degrees angular response was always perpendicular to the scan plane.

Lightcurves were extracted from the XRATE database. The lightcurves were accumulated using positions from an input catalog which merges the following catalogs: the HEAO 1 A3 MC LASS Catalog, HEAO 1 A2 Piccinotti Catalog, and the X-ray binaries catalog. These catalogs are available within Browse under the names A3, A2PIC, and XRBCAT, respectively.

Multiple lightcurves were accumulated for the same sky position, if this was viewed by the same detector in time intervals separated by more than 1 day. Each entry in the A2LCSCAN database has associated with it 4 lightcurves (in FITS format) extracted from the MED and HED3 small and large fields of view respectively. A single GIF file containing plots of the 4 lightcurves is also associated with each entry.

The lightcurves are background subtracted and collimator corrected,with an integration time of 5.12 seconds. Data were included only if the source position was within 15 % of the collimator response. The background applied was derived from the standard background values listed in the HEAO1-A2 data analysis system (LHEA June 1988) user guide.

Because of the large A2 FOV more than one source could be in the detector collimator. The database contains a flag "CONFUSED" to indicate that other sources may contribute to the total count rate and/or variability. The confusion flag was derived by cross correlating the A2 pointing position with source positions in the following catalogs: the HEAO 1 A3 MC LASS Catalog, HEAO 1 A2 Piccinotti Catalog, and the X-ray Binaries Catalog.


Parameters

Name
Name of the source as listed in the input catalog.

RA
Right Ascension as listed in the input catalog.

Dec
Declination as listed in the input catalog.

LII
The galactic longitude.

BII
The galactic latitude.

Meds_Count_Rate
Lightcurve average count rate from the MED-S detector. The count rate is background subtracted and obtained over the nominal MED energy range (1.5-20 keV).

Meds_Count_Rate_Error
Error on count rate from the MED-S detector.

Hd3s_Count_Rate
Lightcurve average count rate from the HED3-S detector. The count rate is background subtracted and obtained over the nominal HED3 energy range (2.5-60 keV).

Hd3s_Count_Rate_Error
Error on count rate from the HED3-S detector.

Start_Date
File start time given as DD/MM/YY HH:MM:SS.

Stop_Date
File stop time given as DD/MM/YY HH:MM:SS.

Time
File start time given as SHF (for browse) or MJD for W3browse

End_Time
File stop time given as SHF (for browse) or MJD for W3browse

Exposure
The 'exposure' parameter (given in seconds) corresponds to the effective exposure on source.

Telapse
The 'Telapse' parameter (given in seconds) corresponds to the time interval covered by the lightcurve (Stop - Start).

GIF_File
Root name for the GIF file showing the light curve of MED and HED-3 SFOVs

Meds_File
Root name for the MED-S lightcurve file obtained with the small field of view. This product is in FITS format.

Medl_File
Root name for the MED-L lightcurve file obtained with the small field of view. This product is in FITS format.

Hd3s_File
Root name for the HED3-S lightcurve file obtained with the small field of view. This product is in FITS format.

Hd3l_File
Root name for the HED3-S lightcurve file obtained with the small field of view. This product is in FITS format.

Confused
This parameter indicates if there was another (bright X-ray) source in the detector field of view. The parameter value is set to 1 if there is another source in the FOV otherwise is 0. The source confusion was determined by using positions that appear in the following catalogs: the HEAO 1 A3 MC LASS Catalog, HEAO 1 A2 Piccinotti Catalog, and the X-ray binaries catalog.

Detect
The input catalog to determine the positions includes a source flux estimate. Lightcurves were extracted for all the positions in the catalog even if the estimate flux was below the nominal HEAO1-A2 detection threshold (~1mCrab). Lightcurves within the A2LCSCAN database are from : 1-sources in which the estimated catalog flux is above the HEAO1-A2 threshold (~1mCrab), even if at the time of the HEAO1-A2 the lightcurve is consistent with no source detection (DETECT=0). 2-sources which the estimated catalog flux is below the HEAO1-A2 threshold (~1mCrab) but where the extracted lightcurve shows significant counts (DETECT=1).

Quality
A crude quality flag was assigned to each lightcurve to flag obvious problems. These flags are preliminary and do not account for all the potential problems. (10 = good, 5 and 4 acceptable).


Contact Person

Questions regarding the A2LCSCAN 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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