FILM Data Archive (Draft)
2001-06-28
H. Shibai, T. Nakagawa, K. Okumura, S. Makiuti
0. Executive Summary
FILM (Far-Infrared Line Mapper) is a focal-plane instrument of the IRTS (Infrared Telescope in Space),
and has four detector channels. The channel 2 and 4 are for the [CII] 158 micron and [OI] 63 micron line
measurement, respectively. The channel 1 and 3 are for 155 micron and 160 micron continuum emission
measurement, respectively.
At the first time (June 28, 2001), the intensity maps of 155 micron continuum emission and the [CII] 158
micron line emission are available for public. The basic parameters of the data are listed in Table 1.
Table 1. Basic parameters of the FILM archive data
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Data Number 1 2
Data 155 um Continuum [CII] Line
Band Center (cm-1) 64.4 63.4
(um) 155.3 157.7
Resolution (cm-1) 0.495 (0.155)
(um) 1.19 (0.386)
Resolving Power 130 (409)
Beam Size (FWHM) 8' x 13' <--
(scanning direction) x (cross-scanning direction)
System NEP (W Hz^-1/2) 1.8 x 10^-16 6.0 x 10^-17
Target Continuum [CII] Line
RMS Noise (in n In W m-2 sr-1) 2 x 10^-7 3.5 x 10^-9 (without stripe noise)
(in In MJy sr^-1) 10
Uncertainty in Zero Level
(in n In W m^-2 sr^-1) 6 x 10^-7 3 x 10^-10 (including stripe noise)
(in In MJy sr^-1) 30
Uncertainty in Intensity Scale -19% to +26%
Pixel Size 4' x 4' <--
Number of Pixel 192 x 192 192 x 192
Image Size 12.8 deg x 12.8 deg <--
Uncertainty in Map Position 4'-8' <--
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1. Data Products
1-1. Data Format
All data files are given in simple FITS format files and are drawn on gnomonic projection with
the galactic coordinate. The size of the images is 12.8 by 12.8 degrees with 4' pixels (192 x 192 pixels).
Synopsis files are available for short explanation of both data sets.
1-2. Continuum maps
Five kinds of files are available for each sky area.
A. film-155-ns/ssXX-raw.fits (ns/ssXX_filmc1_flux.fits)
Average intensity images at 155 micron in W m^-2 sr^-1. Color correction procedures did not carry out
for the data, because the FILM 155 micron observation was the narrow-band photometry.
B. film-155-ns/ssXX-err.fits (ns/ssXX_filmc1_error.fits)
Standard deviations of the mean of the pixel.
C. film-155-ns/ssXX-smp.fits (ns/ssXX_filmc1_no.fits)
The number of observations in pixel.
D. film-155-ns/ssXX-intp.fits (ns/ssXX_filmc1_flux_intp.fits)
Average intensity and interpolated intensity data. The index of the interpolation procedure is described
in files (E)
E. film-155-ns/ssXX-flug.fits (ns/ssXX_filmc1_flag_intp.fits)
The number of the interpolation index for the files (D). The indexes are as follows:
0: original average intensity.
1: linearly interpolated from the nearest non-bad pixels within 3x3 box.
2: non-linearly interpolated from the nearest non-bad pixels within 5x5 pixel circle.
3: non-linearly interpolated from the nearest non-bad pixels within 7x7 pixel circle.
1-3. [CII] 158 micron maps
(1) ??-??-??-raw.fits : [CII] line intensity map
(2) ??-??-??-err.fits : statistical error (1-sigma) map
(3) ??-??-??-smp.fits : map of sample number in a pixel
(4) ??-??-??-intp.fits : interpolated [CII] line intensity map
ex.) film-c2-ns01-raw.fits (ns=North-Scan, ss=South-Scan)-(Map Number)
2. Data Reduction
Responsivity of the Ge:Ga detector has always fluctuated mainly owing to hitting of cosmic ray. Signals
for the calibrator lamp have acquired at certain intervals during the observation and slow components of
responsivity fluctuations have been corrected by post flight analysis with those data. Most of fast
fluctuations components by cosmic ray have removed.
The IRTS/FILM has a cold shutter at an entrance aperture, and it was closed at certain intervals.
The zero flux level for the [CII] line intensity was decided by those data. The zero flux level might
be dominant uncertainty for estimation of high latitude [CII] line emission that is very weak.
The zero flux level was stable on the whole. An accuracy estimated from the uncertainty in decision
of the zero level is less than 3(-7) erg cm-2 s-1 sr-1 for the [CII] line intensity. On theother hand,
As for the data reduction of the ch1 (155 micron continuum), the details of the processing are described
in Okumura (1999).
3. Intensity Accuracy
3-1. Continuum maps
The absolute intensity calibration of the 155 micron data was based on the pre-launch test of the internal
calibration light. The uncertainty of the absolute intensity was estimated in the range from -19% to +26%.
The FILM has an internal calibrator lamp in order to calibrate and correct fluctuations of detector
responsivity. Absolute calibration has been made independently from preflight experiments.
The typical rms error was 2x10^-7 W m^-2 sr^-1 for the detector noise. In addition to this, there are
stripe patterns in the in-scan direction in each FITS image. They are caused by the correction error
for the change in the responsivity of FILM detectors, stressed Ge:Ga photoconductors.
3-2. [CII] 158 micron maps
However, calibrated [CII] line intensity of the IRTS/FILM is different from results of other observations at present.
We compared the independent observations of the IRTS/FILM and the balloon-borne telescope BICE (Nakagawa et al. 1998)
for objects near the Galactic plane. The [CII] line intensity from the IRTS/FILM is about 65 % to 85 % (depending
on intensity) compared to the BICE. It is also reported that the observation from the BICE is about 65 % compared
to the COBE/FIRAS (Nakagawa et al. 1998; Bennett et al. 1994).
The levels of detector noise (statistical) were almost steady during the observation. Noise equivalent line intensity
(1-sigma, 1/2sec integrated) is about 3.5(-6) erg cm-2 s-1 sr-1.
4. Position Accuracy
The pointing information was determined using a star sensor (STS) instrument on board IRTS by collaborating
with IPAC/NASA. The pointing accuracy obtained about within 1 arc-min. The position of the FILM was calculated
as the distance between itself and the center of the IRTS was 1 degree. Since the distance has an uncertainty,
a systematic pointing error may have crept into the FILM images within 4'-8'.
5. Time-Ordered Data
A time-ordered data set is available, too. Please contact to irts_admin@u.phys.nagoya-u.ac.jp
6. References
Bennett et al. 1994
Hiromoto, N. et al. 1992, Appl. Opt. 31, 460
Nakagawa et al. 1998;Okumura (1999)
Shibai, H. et al. 1994, ApJ 428, 377
Shibai, H. et al. 1996, proc. SPIE 2817, 267