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IPCIMAGE: Help

IPCIMAGE - Einstein IPC Images


Overview

The IPCIMAGE database contains information from the Imaging Proportional Counter aboard HEAO 2, the Einstein Observatory. Einstein incorporated a high-resolution X-ray telescope and a focal plane assembly capable of positioning at its focus one of four instruments: a high-resolution imaging detector (HRI), a broader-field imaging proportional counter (IPC), a solid state spectrometer (SSS), and a Bragg crystal spectrometer (FPCS). Einstein (HEAO 2) was launched on November 13, 1978, and operated successfully until April 1981.

References

The Imaging Proportional Counter has been described by Gorenstein, et al. (TRANS. IEEE Nuc. Sci., NS-28 , 869, 1981), and by Giacconi, et al. (Ap.J. 230 , 540, 1979).

Description

The IPC is a gas-filled, position-sensitive imaging proportional counter. The nominal energy range of the imaging X-ray telescope is 0.15-4.5 keV. The mirror ceases to reflect X-rays above about 4.5 keV. Time resolution is 63 microseconds, and the data is processed into 32 energy channels. The IPC has a 75 X 75 arcmin FOV with a spatial resolution of 1 arcmin, a peak effective area of order 100 cm**2, and a sensitivity of 1 count per sec per UFU, or 1 count per sec per 4 x 10**-11 erg cm**-2 sec**-1. The energy resolution (E/delta E) of the IPC is 0.5 at 0.25 keV and >=1 at 1.5-4 keV. The background is 3 x 10**-3 cts arcmin**-2 sec**-1.

Data Products

This database contains the 4132 IPC FITS-format images that were produced by the Harvard CfA. The images have a 75 arcmin square FOV centered on the nominal target and contain x-ray photons in the range 0.2-3.5 keV. There are 3935 individual images and 197 merged images of fields in which multiple images were obtained within this database.

Parameters

Bscale
FITS keyword: BSCALE

Array elements are converted to integers, scaled to +/- 32767. This is done by finding the maximum and minimum (datamax and datamin) and using the equation:

                      BSCALE=(datamax-datamin)/(2*32767).
  

True_Pixel_Offset
FITS keyword: BZERO

`BZERO` is the offset to the true pixel values.

BZERO=(datamax-datamin)/2

The true pixel value is found using the scaled value TAPE in the following equations:

                      TAPE = (TRUE - BZERO)/BSCALE
                      TRUE = (TAPE*BSCALE) + BZERO
  

RA
FITS keyword: CRVAL1

The RA reference point value of the FITS image file. The right ascension (1950.0) in decimal degrees of the center of the image.

Dec
FITS keyword: CRVAL2

The DEC reference point value of the FITS image file. The declination (1950.0) in decimal degrees of the center of the image.

X_Pixels
FITS keyword: CRPIX1

Pixel coordinates of `RA` in image center of the FITS image file. The RA reference pixel location.

Y_Pixels
FITS keyword: CRPIX2

Pixel coordinates of `DEC` in image center of the FITS image file. The declination reference pixel location.

Delta_RA
FITS keyword: CDELT1

The RA increment along axis of the FITS image file.

Delta_Dec
FITS keyword: CDELT2

The DEC increment along axis of the FITS image file.

Rotation_RA
FITS keyword: CROTA1

RA rotation.

Rotation_Dec
FITS keyword: CROTA2

DEC rotation.

Peak_Intensity
FITS keyword: DATAMAX

True peak intensity within the FITS image file.

Minimum_Intensity
FITS keyword: DATAMIN

True minimum intensity within the FITS image file.

Three_Sigma_Level
FITS keyword: TSIGMA

Three sigma level at field center within the FITS image file.

Deep_Survey_Counts
FITS keyword: DSBKG

Total number of Deep Survey (DS) counts in background map within the FITS image file.

Bright_Earth_Counts
FITS keyword: BEBKG

Total number of Bright Earth (BE) counts in background map within the FITS image file.

Roll_Angle
FITS keyword: ROLL_ANG

The angle in degrees which measures the roll of the spacecraft about an axis pointing toward the field center. A positive value indicates a clockwise rotation of the detector's FOV.

Aspect
FITS keyword: BAD_ASP

Bad Aspect: 0 if observation is characterized by average roll angle, 1 otherwise. If 1, do not use roll angle.

Live_Time
FITS keyword: TIME_LIV

A measure of the effective exposure time for the field center. TIME_LIV is the total number of seconds during which the detectors were able to gather data, corrected for Earth occultation, SAA, bad aspect solution and detector dead time.

Object
FITS keyword: OBJECT

Object sequence number in the Einstein catalog.

Y_Offset_Avg
FITS keyword: AVGOFFY

Average translation offsets (in 8 arcsec pixels) from nominal pointing direction on y axis.

Z_Offset_Avg
FITS keyword: AVGOFFZ

Average translation offsets (in 8 arcsec pixels) from nominal pointing direction on z axis.

Y_Aspect_Soln
FITS keyword: RMSOFFY

Root mean square of instantaneous pointing offsets from average defined by `Y OFFSET AVG`. This is useful in assessing stability of pointing.

Z_Aspect_Soln
FITS keyword: RMSOFFZ

Root mean square of instantaneous pointing offsets from average defined by `Z OFFSET AVG`. This is useful in assessing stability of pointing.

Focal_Plane_Detector
FITS keyword: INSTRUME

Focal plane detector, always `IPC` in this catalog.

Observer
FITS keyword: OBSERVER

Party responsible for collecting this particular observation, where 0 = CFA, 1 = CAL, 2 = MIT, 3 = GSFC.

LII
FITS keyword: GALL

Galactic Longitude of field center of the FITS image file.

BII
FITS keyword: GALB

Galactic Latitude of field center of the FITS image file.

Time
FITS keyword: DATE_OBS

Observation start time.

End_Time
FITS keyword: DATE_STP

Observation stop time.

H_Column_Density
FITS keyword: NH

Column density of neutral hydrogen in atoms/cm**2 integrated along the line of sight through our galaxy in the direction of the target.

Title
FITS keyword: TITLE

Information on the nature of the target. Entries include catalog names (e.g., 4U0248-85) and observer's notes.

File_Creation_Date
FITS keyword: DATE

FITS image file creation date.

File_Image
File name of the FITS image file in the BROWSE database. These files are of the form `*hhmmDdd.*`. The leading * can be either `I` or `M`, `I` denoting "IPC" and `M` denoting "Merged". The letters `hhmm` denote the RA hour and minute. The `D` is either `N` or `S` for North or South and `dd` is the Declination in degrees. The trailing * can be `XI` for "X-ray Intensity" or `RE` for "Relative Exposure". Final letters such as A, B, C distinguish XI and RE files when the rest of the file name is not unique.

File_GIF
File name of the GIF file created from the FITS image file. The file names follow the format `**hhmmDdd.gif`. The leading * is a letter such A, B, C, etc., to distinguish the files when the rest of the file name is not unique. The second * is either `I` or `M`, I denoting "IPC" and `M` denoting "Merged". The letters `hhmm` denote the RA hour and minute. The `D` is either `N` or `S` for North or South, and `dd` is the Declination in degrees.


Contact Person

Questions regarding the IPCIMAGE 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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