blanksky_g#_#_v2.evt

caldb/data/asca/gis/bcf/bgd/94may

Current - But Warning (see below)

These files contain GIS background datasets. Each file is a superposition of 13 blank sky fields observed during the ASCA PV phase (1993 May - Nov). Since the GIS internal background increases as the magnetic cut-off rigidity (COR) decreases, the files are sorted by COR values (in units of MeV/c). Like the AO data, these background data were taken after the Spread Discriminator was turned on (1993 May 27).

The naming scheme used is:

blanksky_g$i$_$xxx$_v2.evt

where

• $i$ is the GIS sensor ($i$=2 or 3)
• $xxx$ is a character string denoting which values of the magnetic cut-off rigidity (COR) were used to construct the dataset The character string can either be all, indicating no filtering on COR has been made, or has the form $j$cor$k$, where
  • $j$ is the lower value of the magnetic cut-off rigidity (COR) used to construct the dataset ($j$ = 4, 6, 8, 10, 12, 14, or can be missing)
  • $k$ is the upper value of the magnetic cut-off rigidity (COR) used to construct the dataset ($k$ = 4, 6, 8, 10, 12, 14)

Further information regarding the construction and use of these dataset can be obtained from the README file in the above directory.

Ken Ebisawa (NASA/GSFC ASCA GOF) 1994 Apr 18.

(No OGIP multi-mission standard)

See above, and the README file in the above directory.

• Ken Ebisawa (ASCA GOF NASA/GSFC)
  The difference from old blank sky files, (Section 3.11.1):
  • Addition of the two more blank sky fields, then total exposure time increased from 300 ksec to 350 ksec.
  • RTI (Rise Time Invariance) column is correctly filled, thus particle background is efficiently removed with the gisclean command in XSELECT.
• In order to prevent the extraction of astrophysical information, all the X & Y values (sky pixel) are set to 1, and the TIME values are made constant. Furthermore, events are sorted in ascending order of DETX.
• Ken Ebisawa (ASCA GOF NASA/GSFC) 1994 Dec 14:
  • These background files include data taken during 1994 Mar when an onboard computer error caused the GIS3 PHA spectra to be quantized to 128 channels rather than the designed/expected 1024 channels. These GIS3 observations should not have been included prior to delivery of the calibration files. However their effect is considered likely to be insignificant since (1) the bad datasets will be "smoothed' using random numbers when converted from PHA to PI, (2) the bad data is only $\sim$7% of the total.