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OSO8ALC: Help

OSO8ALC - OSO8 A Detector Lightcurves


Overview

This database accesses the FITS lightcurves obtained from the A detector part of the GSFC Cosmic X-ray Spectroscopy experiment (GCXSE) on board OSO8. The Orbiting Solar Observatory-I (OSO-8) was launched on 21 June 1975 into a 550 km circular orbit at 33 degrees inclination. While the primary objectives of the mission were solar in nature, there were 3 detectors (the GCXSE detectors A, B and C) which had exclusively non-solar objectives. The energy band was 2-60 keV for the A and C detector and 2-20 keV for the B detector. The spacecraft structure consisted of a rotating cylindrical base section called the "wheel" and a non-spinning upper section called the "sail". The GCXSE detectors were mounted in the rotating wheel and their fields-of-view were either aligned to the spin axis (B and C) or at small angles to it (A), hence they always viewed the portion of the sky at right angles to the earth-sun line. The GCXSE detectors obtained data until late September 1978.

Data Products

The data products associated with the OSO8ALC database are lightcurves, in FITS and GIF format, extracted from data obtained by the A detector part the GCXS experiment. The A detector had a 5 degree radius field of view and was offset 5 degrees from the spin axis of the space craft. Thus, any source which had a scan angle (angle between the source position and the spin axis) of less then 10 degrees was in the field of view. The lightcurves were extracted using the "super A" dataset, which contains data superimposed from several spin rotations, by fitting the accumulations for several spin rotation with the positions of known sources. The known source positions were taken from the HEAO-1 A3 MC LASS Catalog. The super A data set did not contain time, but this was computed from the recorded sun position. The routine that compute time is accurate to within .010 days, but it can be off as much as 0.016 days. In the FITS lightcurve, the column named ERR_TIME contains the difference between the time linearly interpolated from sun positions given in The American Ephemeris and Nautical Almanac and the time computed by the software. The rates in the lightcurves (and within this database) are normalized for the effective area, therefore are in units of count/cm^2/s. In 90% of the lightcurves show sharp spikes in the rate. These tipically occur for scan angles (column named SCAN_ANG in the FITS lightcurves) less than 1 deg or greated than 9 and they are appear more frequently at the beginning and/or the end of a time interval. Data with a scan angle value within this range are considered suspect. The lightcurves do not contain the integration time. This corresponds to the number of superimposed spins. Each spin period was about 10 seconds.

Each database record points to a single lightcurve per source in FITS and GIF file. The files are named as oso8_gcsxe_HHMMpDDD.lc, where HHMM is the RA hours and minutes, DDD is the Dec in decimal degrees and the p value is n (for + or north ) or s (for - or south).


Parameters

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

RA
The Right Ascension of the source position as given in the input catalog.

Dec
The Declination of the source position as given in the input catalog.

LII
The galactic longitude of the pointing.

BII
The galactic latitude of the pointing.

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

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

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).

Npoints
Number of points in the lightcurve.

Count_Rate
The average lightcurve count rate in unit of count/cm^2/s.

Scatter_Rate
Standard deviation of the rate in unit of count/cm^2/s.

Max_Rate
The maximun rate in the lightcurves in unit of count/cm^2/s.

Filename
Root name of the lightcurve files. The complete name is 'Filename.lc' for the FITS file and 'Filename.gif' for the GIF file.


Contact Person

Questions regarding the OSO8ALC 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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