The data obtained by the gamma ray satellite COS-B was processed, condensed and integrated together with the relevant mission and experiment parameters into the Final COS-B Database. The database contents and the access programs available with the database are outlined. The final sky coverage and a presentation of the large scale distribution of the observed Milky Way emission are given. The database is announced to be available through the European Space Agency

Bennett, K.

Bignami, G. F.

Bloemen, J. B. G. M.

Buccheri, R.

Caraveo, P. A.

Hermsen, W.

Kanbach, G.

Lebrun, F.

Mayer-Hasselwander, H. A.

Paul, J. A.

English

Mayer-Hasselwander, H.A.

Bignami, G.F.

Bloemen, J.B.G.M.

Caraveo, P.A.

Paul, J.A.

NARCIS 

The final COS-B database now publicly available

NASA Technical Reports Server

383
OG 9.3-8
THE FINAL COS-B DATABASE - NOW PUBLICLY AVAILABLE
H.A. Mayer-Hasselwander _, K. Bennett 6, G.F. Bignami z, 3.B.G.M. Bloemenla,
R. Buccheri s, P.A. Caraveo 2, W. Hermsen 1, G. Kanbach _ F. Lebrun s, 3.A.
Paul s, B. Sacco s, A.W. Strong _
The 'Caravane' Collaboration for the COS-B satellite:
1Laboratory for Space Research Leiden_ Leiden_ The Netherlands
2Istituto di Fisica Cosmica del CNR, Milano, Italy
Slstituto di Fisica Cosmica e Inlormatica del CNR9 Palerm% Italy
_Max Planck Institut f_ir Physik und Astrophysik_ Institut ftir Extraterrestrische
Physik9 Garching bei M_inchen_ Germany
SService d'Astrophysiqu% Centre d'Etudes Nucl6aires de Saclay9 France
6Space Science Departement of the European Space Agency9 ESTEC9 Noordwijk_
The Netherlands
aSterrewacht Leiden9 Huygens Laboratorium9 Leiden_ The Netherlands
ABSTRACT
The data obtained by the gamma-ray satellite COS-B have been pro-
cesseG condensed and integrated together with the relevant mission
and experiment parameters into the 'Final COS-B Database'. The
database contents and the access programs available with the data-
base are outlined. The final sky coverage and a presentation of the
large-scale distribution of the observed Milky-Way emission are gi-
ven. The database is anounced to be available through the European
Space Agency.
I. Introduction: Gamma-ray astronomy in the energy range from about 50 MeV
up to several GeV is based at present on the data obtained by only two suc-
cessful satellite experiments_ both using the sparkchamber technique: the first
flown in 1972-1973 on the SAS-2 satellite of NASA 9 the second flown on the
ESA satellite COS-B. SAS-2 operated _7 months and aquired about 8_000 gam-
ma-ray events (1)9 COS-B was in successful operation from August 1975 until
April 1982 and recorded about 210_000 gamma photons. A presentation of part
of the COS-B database was given by Mayer-Hasselwander et al. (2).
The two datasets differ in the following respects: a) The low orbit of
SAS-2 was well shielded by the earth's magnetic field against the cosmic-ray
flux_ ensuring a very low instrumental background level; the highly eccentric
orbit (due to practical constraints) of COS-B exposed the satellite to the full
cosmic-ray intensity_ inducing a comparatively high instrumental background
level_ which is variable with the solar l 1-year cycle, b) The COS-B experiment
was supplemented by an energy calorimeter_ providing good energy information
for each recorded photon, c) Due to the differences in experiment configuration
the low-energy threshold of SAS-2 was somewhat lower (_30 MeV)_ than for
COS-B (_-50 MeV). d) The COS-B experiment achieved a complete coverage of
the galactic ridge. Its long lifetime, allowing for repeated observations in
regions of special interest, enabled detailed analyses of the spatial distribution
and of possible time variations of the observed emission.
The databases of SAS-2 (3) and of COS-B will remain for several years
the only available gamma-ray survey data, and after the forthcoming experi-
ments GAMMA-1 and EGRET9 these databases will remain of interest e.g. in
the search for possible secular and periodic time variations of celestial gamma-
ray objects. Although considerable analysis effort already has been invested to
1
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exploit the data, certainly much more can be done by applying new methods or
by using the data together with upcoming new results in other ranges of the
electromagnetic spectrum. So it appeared to be mandatory to establish and to
make available the COS-B database in a way which will make possible future
analysis also by scientists not familiar with the experiment.
2. The COS-B experiment and mission: The European Space Agency's satellite
CO5-B was dedicated to gamma-ray astronomy in the energy range 50 MeV to
5 GeV and carried a single experiment: a sparkchamber telescope (4), developed
in collaboration by six European institutes. The experiment became operational
on August 17, 1975 and was switched of on April 25, 1982, when onboard re-
sources were exhausted. During this timespan 65 observations, mostly of a
month duration, were performed. The satellite was spin stabilized, with the
telescope axis along the spin axis and circular sky regions of about 40 degree
diameter were covered in each observation. The majority of the pointings were
distributed along the galactic equator, 15 observations were devoted to regions
at high (>20 °) galactic latitudes. Several regions of specific interest were re-
peatedly observed. The overall coverage of the sky is illustrated by Figure 1.
The highly eccentric polar orbit of COS-B with an apogee around
90,000 kin, chosen to maximize useful observation time while allowing real-time
data transmission, exposed the experiment to the solar modulated interplanetary
cosmic-ray flux. The unexpectedly long operational life of the experiment, spe-
cifically of the sparkchamber, was acompanied by a long-term degradation and
by short-term disturbances of its performance and consequently of the experi-
ment sensitivity. The instrumental background and its variation and the changes
in instruments sensitivity were thoroughly investigated. The corrections finally
adopted and incorporated in the final database were derived by the method
described in a subsequent paper (5). The possible impact of their statistical and
systematic uncertainties must be considered in any type of analysis. It is em-
phasized that the corrections are averages over complete periods.
3. The database content and organisation: The database consists of several
parts: A) the observation period, basic dataset, and individual gamma-ray event
information, B) the experiment sensitivily, energy dispersion and pointspread
functions as derived by accelerator and inflight calibrations, C) programs for
easy and efficient access of the database, which produce event lists and sky-
maps for selected data parameters and time intervals, D) binned skymaps of
the galactic disc.
Part A) consists of 3 files: the first one contains a list of the parameters
of the 65 observations, including background and sensitivity corrections for each
period; the second provides similar information for the 5,9g3 datasets which
correspond to the uninterrupted time intervals during original data recording;
the third contains 209,537 entries) one for each accepted gamma-ray event.
Part B) contains the instrument response functions. The sensitivity,
energy-dispersion and pointspread-function files are derived from prelaunch cali-
bration; the latter is also based on analysis of the brightest gamma-ray source)
the Vela pulsar.
In part C) a collection of Fortran-77 programs is provided, which should
allow for easy handling and efficient access of the database. Included are pro-
grams to move the database between tape and disc) to make event selections
on event parameters and time intervals, and to produce binned skymaps of
intensities, counts and exposures. Since these programs access the files in di-
rect access mode) the database has to reside on disc, requiring about 25 Mb of
disc space. The system was developed and used under various IBM operating
systems (360/OS) MVT, MVS; VM/370) CMS), but also after moderate adaption)
885
. OG 9,3-8
has been successfully used on a VAX computer,
Part D) contains an atlas in several energy bands of the Milky Way,
Figure 2 gives as an illustration a map of the galactic disc emission
( 150 MeV)_ produced by a maximum entropy algorithm (7) using the database,
A more detailed description of the gamma-ray data and instrument res-
ponse functions is in preparation (6). In view of the complexity of the data it
is recommended to consult or to collaborate with members of the *Caravane'
collaboration when detailed analysis of the data is undertaken. It is hoped_ that
the release of this uriique database will promote the full exploitation of the
data_ which appears mandatory in view of the enormous efforts in acquiring it.
The database is available on tape from the COS-B project scientist_ Dr.K.
Bennett9 at the Space Science Department of ESA.
References:
1. Fichtel, C.E. et al.: 1975, Astrophys. 3. 198,163
2. Mayer-Hasselwander, H.A. et al.: 1982, Astron. Astrophys. 105,164
3. Fichtel_ C.E. et al.: 19789 NASA Technical Memorandum 79650
4. Bignami_ G.F. et al.: 1975_ Space Science Instrum. 19245
5. Strong_ A.W. et al.: 1985_ Proc. XIX ICRC_ La 3olla
6. Mayer-Hasselwander9 H.A. et ai.: in prep. for Astron. Astrophys. Suppl.
7. Skilling_ 3. et al.: 1979_ Mon. Not. Roy. Astr. Soc. 187_14J
. 90°
+18o° -180°
-90°
Figure 1: Approximate sky exposure achieved by the COS-B experiment. The
contour levels are in 32 d steps_ the lowest being 8 d (the exposure time is
weighted with the inclination dependance of the sensitivity). The crosses indi-
cate the pointing directions of the 65 observation periods.
Figure 2: Preliminary 'maximum entropy' deconvolved map of the galactic
disk9 indicating the structure in the emission seen in the energy range 150 MeV
to 5 GeV, derived from the database described in this paper. An approximate-
ly logarithmic intensity scale was chosen to allow the display of structure in
both intense and weak emission regions. This presentation does not give accu-
rate absolute intensities.
260 24 0 220 2 0 0  1 8 0  160 140 120 100  0 
GALACTIC LONGITUDE 
00 


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