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The POKER experiment: A 10,800 cm2 MWPC's array payload for hard X-Ray Astronomy
Adv. Space Z?es. Vol.3, No.4, pp.87—90, 1983 Printed in Great Britain. All rights reserved.
0273—1177/83 $0.00 + .50 Copyright © COSPAR
THE POKER EXPERIMENT: A 10,800 cm2 MWPC’S ARRAY PAYLOAD FOR HARD X-RAY ASTRONOMY P. Ubertini*, A. Bazzano*, L. Boccaccini*, C. La Padula*, R. K. Manchanda**, M. Mastropietro*, R. Patriarca*, V. F. Polcaro* and G. Sabatino* *1stituto di Astrofisica Spaziale, CNR, Frascati, Italy *
*Tata Institute of Fundamental Research, Bombay, India
ABSTRACT In this paper the POKER—HXR81M hard X—Ray payload is described. The instrument, designed and built at the Istituto di Astrofisica Spaziale of Frascati, is a very large array of Multi— Wire Proportional Counters (MWPC) devoted to stratospheric observations of cosmic sources in the field of hard X—Ray Astronomy. The payload basically consists of four passively collimated MWPC’s having a geometric sensitive area of 2,700 cm2 each with an efficiency higher than 10% in the operative range 15—200 KeV (80% at 60 KeV) with a square field of view of 50 x 50 FWHM. The overall spectral resolution is 13% at 60 Key. The four MWPC’s are filled with a very pure gas mixture of Xenon—Argon—Isobuthane at high pressure (3 bars). This experiment has been successfully flown during summer 1981 from the Milo balloon facility (Sicily, Italy). The performances of the payload and the preliminary results obtained during the 17 hours flight are discussed. INTRODUCTION In the past decade a large number of single source observations and surveys have been carried out in the X—ray range by means of satellite and balloon born experiments [l—6J. On the contrary only few balloon observations have been performed in the .2—20 MeV range 7—9] . At higher energy (above 50 MeV) a better knowledge of the sky has been achieved with the two satellite missions SAS—2 [ 10] and COS—B [ 11] . In this way the sky is quite well known below 20 KeV and above 50 MeV while is less known in the hard X—Ray and soft—’~range. At that energy the only complete survey is the one performed by HEAO A—4 experiment that with the sensitivity at a level of 1/200 Crab has been able to obtain spectral information of about 100 sources [13] In order to have valuable data with higher sensitivity in this range a long term program was started at lAS since 1979 to perform a limited survey of the sky by means the use of a very large area array of Spectroscopic Proportional Counters (SPC), operating in the range 15—200 KeV. The first prototype payload was flown during the summer 1980 [12] and consisted of two SPC’s having a sensitivity area of 2,700 cm2 each. A second flight, with the experimental array in the final configuration, was performed during 21st July 1981 from the Milo Balloon base (Sicily, Italy). The experiment reached the ceiling altitude at 2.4 mbar and the flight lasted 17 hours. PAYLOAD DETAILS The sensitive element of this experiment is a modular SPC replicated in four identical units that have a geometric sensitive area of 2,700 cm2 each. This new kind of detector has been widely described elsewhere istics are: — Operative range: 15—200 KeV — Efficiency: 10% at 15 and 200 KeV and 80% at 60 KeV 87
F
14] and its main character-
88
— —
P. Ubertini at al.
Resolution: 13% at 60 Key over the whole detector —4 —2 —l —1 Residual instrumental background (at 38°and 3 mbar):3 x 10 ct cm s KeV (15—200 KeV).
The field of view of the detectors was limited by means of brass square cell collimators with an aperture of 50 x 50 FWIN. The four SPC’s were filled with a gas mixture having the same composition and pressure and were carefully calibrated in order to achieve the same spectral resolution and efficiency at different energies. The payload is shown in figure 1 in the pre—flight configuration.
~
~
Figure 1 The HXR81—POKER experiment: the SPC’s array (left) and the payload before the launch on the flight pad (right). FLIGHT PERFORMANCE AND RESULTS The sky region scanned by the experiment was: R.A.=O
4hOOm 17h00m and ~ = 210 ÷ 530• A smaller region within the same R.A. and declination contained between 27°÷48°has been observed with full detectors coverage. This region, corresponding to 3900 square degree, was divided 6 cm2 s. intoA 156 total fields, numbereach of of 14 sources, them 50 xalready 50~ The identified average coverage or detected of by eachother fieldexperwas 2iments, x iO in the soft and/or hard X—Ray range, were detected with a statistical significance higher then 4a. The preliminary results are summarized in table 1.
The POKER Experiment
~
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typ.
R.A.
D.c
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19 —54
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108—200 L.V
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0.L.ctlc,btery
16h56.. 35.42
7.008—4 8.75.-S
0.0 4.328—4
0.0 9.18—5
A0535+26 (off .t.t.)
O.t.ctlc,binary
05h35. 26.70
6.658—4 1.408—4
0.0 3.248—4
0.0 8.48—4
11k 421
RI. L.c obJ.ct
IlbOl. 38.00
1.508—3 1.658—4
6.538—4 2.168—4
0.0 1.18—4
11k 501
81. Loc obJ.ct
16h51
3.098—4
2.218—4 2.118—4
0.0 1.18—4
39.92
1.098—4
NCG 8—11—11
S.~f.rt
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05h58. 46.30
7.888—4
1.248—4
0.0 3.298—4
0.0 8.98—5
NOC 4151
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L2h07. 39.77
5.998-4 1.448—4
0.0 7.568—4
0.0 6.98—5
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0.0 1.628—4
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151,55. 27.24
7.008-4 2.008—4
9.770-4 4.815—4
2.18—4 1.38—4
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12h57. 28.20
5.678-4
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0.0
1.408—4
4.438—4
1.08—4
£b.tl
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2* 1215+30
Soyf.rt ~.t.xy N0C 4631 7
12h15. 30.7
5.998—4 3.05.—4
2.658—4 2.168—4
2.98—4 1.08—4
81310+371
5.yf.rt ~at.xy NOC 5005 7
131,10. 37.1
9.568—4
0.0
0.0
2.148—4
3.838—4
8.58—S
Not Ld.ntlfL.d
05h16
9.808-4
0.0
0.0
1.688-4
2.058—4
8.30—5
9.458—4
1.188—3
0.0
1.688—4
3.898—4
7.98—5
6.550-4
1.260-3
0.0
1.658—4
3.620—4
8.18—5
4U05t5~38
38.4
1118 0516+38 11180638+38 7111 2
Not ld.ntlft.d Not 1d.ntlfi.d
06b39. 38 14h20. 38
Table 1 Sources detected by the HXR81—POKER experiment. The three right columns shows the detected photons in three channel of energy. The lower number is the in value.
Furthermore 6 statistically significant excesses not corresponding to any known X—Ray emitter were also detected. A y—Ray burst was also observed by two SPC’s with a statistical significance of 24n. It lasted about 40 s and reached the maximum intensity at U.T. 13h 55m 435~ As can be seen from Table 1 the majority of the identified sources are extragalactic objects. JASR 3/4—4
90
P. Ubertini at al.
This is expected since the region observed by our experiment were mainly out of the galactic plane. The preliminary results above outlined confirm the ability of the new generation of sophisticated balloon borne payloads to be used to perform deep surveys in the hard X—Ray range (15—200 KeV). In this particular experiment 20 % of the northen sky has been observed during a single flight supplying us with a homogeneous set of data. This research was mainly supported by a dedicated Italian Space Plan grant. REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14.
R. Giacconi et al., Ap. J., Lett., 165, 127, 1971. R. Rothschild et.al., Sp. Sci. Instr., 43, 279, 1981. R. Giacconi et al., Ap. J., 280, 540, 1979. I. Kondo et al., Sp. Sc. Instr., 5, 211, 1981. E. Boldt et al., J. Wash. Acad. Sc., 71, n 1, 1981. C. Villa et al., Mon. Not. R. Astr. Soc., 176, 609, 1976. Baker et al., Nucl. Instr. & Meth., 158, 595, 1979. A.S. Jacobson et al., Nucl. Instr. & Meth., 127, 115, 1975. G.D. Walraden et al., Ap. J., 202, 502, 1975. B.N. Wanenburg et al., Ap. J., 243, 169, 1981. R.C. Hartman, Ap. J., 230, 597, 1979. P. Ubertini et al., Sp. Sc. Rev., 30, 381, 1981. J. Matteson, private communication, 1982. P. Ubertini et al., Sp. Sc. Instr., 5, 237, 1981.
0273—1177/83 $0.00 + .50 Copyright © COSPAR
THE POKER EXPERIMENT: A 10,800 cm2 MWPC’S ARRAY PAYLOAD FOR HARD X-RAY ASTRONOMY P. Ubertini*, A. Bazzano*, L. Boccaccini*, C. La Padula*, R. K. Manchanda**, M. Mastropietro*, R. Patriarca*, V. F. Polcaro* and G. Sabatino* *1stituto di Astrofisica Spaziale, CNR, Frascati, Italy *
*Tata Institute of Fundamental Research, Bombay, India
ABSTRACT In this paper the POKER—HXR81M hard X—Ray payload is described. The instrument, designed and built at the Istituto di Astrofisica Spaziale of Frascati, is a very large array of Multi— Wire Proportional Counters (MWPC) devoted to stratospheric observations of cosmic sources in the field of hard X—Ray Astronomy. The payload basically consists of four passively collimated MWPC’s having a geometric sensitive area of 2,700 cm2 each with an efficiency higher than 10% in the operative range 15—200 KeV (80% at 60 KeV) with a square field of view of 50 x 50 FWHM. The overall spectral resolution is 13% at 60 Key. The four MWPC’s are filled with a very pure gas mixture of Xenon—Argon—Isobuthane at high pressure (3 bars). This experiment has been successfully flown during summer 1981 from the Milo balloon facility (Sicily, Italy). The performances of the payload and the preliminary results obtained during the 17 hours flight are discussed. INTRODUCTION In the past decade a large number of single source observations and surveys have been carried out in the X—ray range by means of satellite and balloon born experiments [l—6J. On the contrary only few balloon observations have been performed in the .2—20 MeV range 7—9] . At higher energy (above 50 MeV) a better knowledge of the sky has been achieved with the two satellite missions SAS—2 [ 10] and COS—B [ 11] . In this way the sky is quite well known below 20 KeV and above 50 MeV while is less known in the hard X—Ray and soft—’~range. At that energy the only complete survey is the one performed by HEAO A—4 experiment that with the sensitivity at a level of 1/200 Crab has been able to obtain spectral information of about 100 sources [13] In order to have valuable data with higher sensitivity in this range a long term program was started at lAS since 1979 to perform a limited survey of the sky by means the use of a very large area array of Spectroscopic Proportional Counters (SPC), operating in the range 15—200 KeV. The first prototype payload was flown during the summer 1980 [12] and consisted of two SPC’s having a sensitivity area of 2,700 cm2 each. A second flight, with the experimental array in the final configuration, was performed during 21st July 1981 from the Milo Balloon base (Sicily, Italy). The experiment reached the ceiling altitude at 2.4 mbar and the flight lasted 17 hours. PAYLOAD DETAILS The sensitive element of this experiment is a modular SPC replicated in four identical units that have a geometric sensitive area of 2,700 cm2 each. This new kind of detector has been widely described elsewhere istics are: — Operative range: 15—200 KeV — Efficiency: 10% at 15 and 200 KeV and 80% at 60 KeV 87
F
14] and its main character-
88
— —
P. Ubertini at al.
Resolution: 13% at 60 Key over the whole detector —4 —2 —l —1 Residual instrumental background (at 38°and 3 mbar):3 x 10 ct cm s KeV (15—200 KeV).
The field of view of the detectors was limited by means of brass square cell collimators with an aperture of 50 x 50 FWIN. The four SPC’s were filled with a gas mixture having the same composition and pressure and were carefully calibrated in order to achieve the same spectral resolution and efficiency at different energies. The payload is shown in figure 1 in the pre—flight configuration.
~
~
Figure 1 The HXR81—POKER experiment: the SPC’s array (left) and the payload before the launch on the flight pad (right). FLIGHT PERFORMANCE AND RESULTS The sky region scanned by the experiment was: R.A.=O
4hOOm 17h00m and ~ = 210 ÷ 530• A smaller region within the same R.A. and declination contained between 27°÷48°has been observed with full detectors coverage. This region, corresponding to 3900 square degree, was divided 6 cm2 s. intoA 156 total fields, numbereach of of 14 sources, them 50 xalready 50~ The identified average coverage or detected of by eachother fieldexperwas 2iments, x iO in the soft and/or hard X—Ray range, were detected with a statistical significance higher then 4a. The preliminary results are summarized in table 1.
The POKER Experiment
~
na
Soouc.
typ.
R.A.
D.c
89
D.t.ct.d
ph/ce
•.c
—
19 —54
54—108 L.V
108—200 L.V
M.r ~ (ld—oa .t.t.)
0.L.ctlc,btery
16h56.. 35.42
7.008—4 8.75.-S
0.0 4.328—4
0.0 9.18—5
A0535+26 (off .t.t.)
O.t.ctlc,binary
05h35. 26.70
6.658—4 1.408—4
0.0 3.248—4
0.0 8.48—4
11k 421
RI. L.c obJ.ct
IlbOl. 38.00
1.508—3 1.658—4
6.538—4 2.168—4
0.0 1.18—4
11k 501
81. Loc obJ.ct
16h51
3.098—4
2.218—4 2.118—4
0.0 1.18—4
39.92
1.098—4
NCG 8—11—11
S.~f.rt
gat.xy
05h58. 46.30
7.888—4
1.248—4
0.0 3.298—4
0.0 8.98—5
NOC 4151
$syf.rt
g.t.zy
L2h07. 39.77
5.998-4 1.448—4
0.0 7.568—4
0.0 6.98—5
3 C 129
CLuat.r
of
041,46. 44.96
5.188—4 1.478—4
0.0 1.628—4
9.08—5 6.58—5
CL,at.r of
151,55. 27.24
7.008-4 2.008—4
9.770-4 4.815—4
2.18—4 1.38—4
Ct,aat.r of
12h57. 28.20
5.678-4
0.0
0.0
1.408—4
4.438—4
1.08—4
£b.tl
2142
Co..
g~tax1..
2* 1215+30
Soyf.rt ~.t.xy N0C 4631 7
12h15. 30.7
5.998—4 3.05.—4
2.658—4 2.168—4
2.98—4 1.08—4
81310+371
5.yf.rt ~at.xy NOC 5005 7
131,10. 37.1
9.568—4
0.0
0.0
2.148—4
3.838—4
8.58—S
Not Ld.ntlfL.d
05h16
9.808-4
0.0
0.0
1.688-4
2.058—4
8.30—5
9.458—4
1.188—3
0.0
1.688—4
3.898—4
7.98—5
6.550-4
1.260-3
0.0
1.658—4
3.620—4
8.18—5
4U05t5~38
38.4
1118 0516+38 11180638+38 7111 2
Not ld.ntlft.d Not 1d.ntlfi.d
06b39. 38 14h20. 38
Table 1 Sources detected by the HXR81—POKER experiment. The three right columns shows the detected photons in three channel of energy. The lower number is the in value.
Furthermore 6 statistically significant excesses not corresponding to any known X—Ray emitter were also detected. A y—Ray burst was also observed by two SPC’s with a statistical significance of 24n. It lasted about 40 s and reached the maximum intensity at U.T. 13h 55m 435~ As can be seen from Table 1 the majority of the identified sources are extragalactic objects. JASR 3/4—4
90
P. Ubertini at al.
This is expected since the region observed by our experiment were mainly out of the galactic plane. The preliminary results above outlined confirm the ability of the new generation of sophisticated balloon borne payloads to be used to perform deep surveys in the hard X—Ray range (15—200 KeV). In this particular experiment 20 % of the northen sky has been observed during a single flight supplying us with a homogeneous set of data. This research was mainly supported by a dedicated Italian Space Plan grant. REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14.
R. Giacconi et al., Ap. J., Lett., 165, 127, 1971. R. Rothschild et.al., Sp. Sci. Instr., 43, 279, 1981. R. Giacconi et al., Ap. J., 280, 540, 1979. I. Kondo et al., Sp. Sc. Instr., 5, 211, 1981. E. Boldt et al., J. Wash. Acad. Sc., 71, n 1, 1981. C. Villa et al., Mon. Not. R. Astr. Soc., 176, 609, 1976. Baker et al., Nucl. Instr. & Meth., 158, 595, 1979. A.S. Jacobson et al., Nucl. Instr. & Meth., 127, 115, 1975. G.D. Walraden et al., Ap. J., 202, 502, 1975. B.N. Wanenburg et al., Ap. J., 243, 169, 1981. R.C. Hartman, Ap. J., 230, 597, 1979. P. Ubertini et al., Sp. Sc. Rev., 30, 381, 1981. J. Matteson, private communication, 1982. P. Ubertini et al., Sp. Sc. Instr., 5, 237, 1981.