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A High Resolution Gamma-ray and Hard X-ray Spectrometer (HIREGS) for Long Duration Balloon Flights
Adv. Space Res. Vol. 21, No. 7, pp. 101%1018,1998 Q1998 COSPAR. Publishedby Elsevier Science Ltd. All rightsreserved Printedin GreatBritain 0273-l 171/98 $19.00 + 0.00 PlI: SO273-1177(97)0109&9
A HIGH RESOLUTION GAMMA-RAY AND HARD X-RAY SPECTROMETER (HIREGS) FOR LONG DURATION BALLOON FLIGHTS S.
E. Boggs*v**, R. P. Lin****, P. T. Feffer *,**, S. Slassi-Sennou*, S. McBride*, J. H. Primbsch*, K. Youssefi*, G. Zimmer*, C. Cork***, P. Luke***, N. Madden ***, D. Malone***, R. Pehl***, M. Pellingt, F. Cot&, G. Vedrennet *Space Sciences Laboratory, **Department of Physics, University of California, Berkeley, CA 94720, U.S.A. ***Lawrence Berkeley National Laboratory, University of California, Berkeley, CA 94720, U.S.A. 'Center for Astrophysics and Space Sciences, University of California, San Diego, CA 92093, U.S.A. SCentre d’Etude Spatiale des Rayonnements, 31029 Toulouse, France
The l?LRKiS gamma-ray sptrometer made a U-day Long Duration Balloon Flight (LDBFI from Antarctica in January 1995 to mnmxs of gamma-ray and hani X-my line and continuum omission. The s&&ii inslnuaent itself is discnssed, omeGalactic followed by a more exmive discussion of the chara~te&i~s of the instrument unique to LDBFs. The flight pezformance and Iweliminary results are briefly summarized. 01998 COSPAR. Published by Elsevier Science Ltd. lNTRODUCTION ciimmway and Hard x-ray Spectram~ (I-llmGS) has flown three long dllrstioll (lo-20 day) balloon ~ovsrAnnrctica.‘IhefirsttwoflightsinJ~1991andJannary1993werededicatedtosolarflare~a~~~at al. 1997). while the third Bight in January 1995, described here, observed Galactic gamma-ray sources. HIRBGS can detect photons from 20 keV to 18 MeV with one to several keV energy resolution and a full-width-at-half-maximum (FWHM) field-of-view of
The High lzeallltti
-24’. The large detector area (423 cm2), high energy resolution, and use of active shielding, combined with long dnmtion balloon !lights (LDBFs). make the instmment highly se&rive to the detection of astrophysical narrow gamma-ray lines. The HIRBGS mt is similar in design to its predecessor HBXAGONE (Matteson et al. 19X)), but its larger area and long-duration cap&&es make it podentiauy much more powerful. LDBFs over -tica dtning the austral summer have several advantages over conventional balloon flights. The high altitude wind pattern ovez Antiuctica allows circumpolar LDBFs lasting one to several weeks to be achieved. With the Snn always above the ho&on, 24 hour/day solar observations are possible and the balloon altitude remains relatively stable with little or no b&sting. At mid-latit@s t&e day-night cycling not only limits solar observations to -12 hours per day, but more importantly. it leads to a loss of balloon lift and the consequent drop in daytime altitnde. Even with ballasting, mid-la&u&. flights with llocmal anpnssarl;tsd balloons are limited to less than 8 week of -12 hour/day solar observations before the daytime al&de drops too low (Lin et nl. 1987). The third LDBF of HIRBGS in January 1995 was dedicated to observations of Galactic sources, and had several main scientific goals:measarementofther;hapeofthe511keVannihilati~lineandtbe1809keV26AlradioactivedecaylinefromtheG~~ centa ngio& measuxmat of the Galactic diffuse continuum radiation, and separation of point somce spectra with spec& intent to seapch for cyclotron lines from Vela X-l and GX301-2. Half of the observations concentrated on the Galactic Center region, and the ot4er half were shared between the Galactic Plane (1=335”), Vela X-l. and the X-ray transient GRO J1655-40. INSTRUMENTAnON The EIIREGSinsunment consists of an array of twelve 6.7sm diameter x 6.2-cm long n-type germanium (Ge) closedend coaxial detectors (Figure 1). which are cooled by three 50-liter liquid nitrogen (LN) dewars. Eight of the detectors are electrically separated into front and rear segments to improve the low energy background and flare perf ormance (Pelling et al. 1992). Thei detector army JASR z1:,-0
1015
1016
S. E. Boggs et al
’ BQO Bottom Shield Fig,, 1. Diagramsof the HIREGS instrumentshowingthe relative positions of the Ge detectors, the BGO shield, and CsJcollimator.Liquid nitrogen dewarsmaintainthe detectors at cryogenic temperatures. is surroundedby an active shield that reduces the gamma-raybackgroundby allowing the anticoincidenceof simultaneousdetector and shield events. The shield system consists of S-cm-thickBGG segments at the rear and sides and a lo-cm-thick drilled CsJ collimator on the front which determines the 24’ field-of-view (Figure 1). Additionalhard X-ray (&tIK&eV)passive collimators inserted in the CsJ collimator cover half of the detectors, limiting these fields of view to 3.7” x24’ FWHM, allowing separation of point source spectra from the diffuse Galactic continuum(Boggs et al. 1997).The detectors, LN dewars, shield, and collimator are held in a cradle structure that is. in turn supported within the balloon gondola (Figure 2). For a more detailed description of the scientific instrumentsee (Pelhng et al. 1992). LONG DURATIONBALLOONFLIGHT SPECJFJCJSSUES LDBFs place many requimments on the instrument,such as the need for large data storage capacity, solar power, thermal stability, cryogenics, and commuuications. Besides the hardwarerequirements,LDBFs pIace tight constraints on the preparation ached&x an LDBF launch fnxn Antarcticain December requires shipmentof the instrumentto Antarctica in August, and integration of the entire instrumenteven earlier, in June.
The main computer packagesthe data frames, and sendsthem to an Exabyte tape storage system and/or to the telemetry system. The main computer also controls instrumentcommamhngand housekeeping.The flight code was developed in C and assembly, and governs the computer’sprimary functions. The Exabyte tape drive can store up to 4.6 Gbytes. enough to hold all the data generated in a 3 week balloon flight. Also, there is a 44-MbyteRAM disk for temporary data storage, the contents of which can be rransmi#cdtotbegroundortoanairplaneoncanmand.ThisRAMbufferisstatifandhasbacLupbatseries,sotbedatais pmsezvedeven in the event of a power cycle.
Dam is stored in two formats, mfenud to as event data and m&flight data. The event data consists mostly of detailed information abcrrrteachdctrctorevcntandisstosedinthetapesystem.ThellndafliOhtdatacmmiaaprimarily30minutecaadwrsedspectrathat arc~~~~iothemain~raadstoacdinthe44Mbytetemporary~o~,fromwhichitcaabetelunctedddowntoa ground statiar or to an LC-130 aircraft that is flown nuder the balloon every few days. The underflight data serves as a backup in case the data tape is not recovered.
AU pointing isdeterminedrelative to the Sun and is controlled by the Gondola Control Unit (GCU). The GCU is an independent computer dedicated to pointing operations, the collection of housekeepingdata, and the aqnisition of GPS information. The GCU alao controls varicms power relays and can receive commands from the main computer as well as from the several telemetry command links. Under normal operation, however, a fully autonomousLDBF is governed by preprogrammedcemting
A High Resolution Gamma-Ray Spectrometer
1017
Electronics Bay--\
Fig. 2. The HIREGSgondola.
Power isprovided by a 8.1 n.3 solar anay. made up of crystalline silicon phoWs, amnged on two lateral pmelk that delivers uptolOOOwatrsabpowsravathedaratianoftheflight.AsetafpnssruizcdleadacidbaUcrieslocatedinthcclec~baycan power th iastrment fix several hours if the solar panelsare pointed away from the Sun.
commpnication~~fromtheiwnuuentismadeviasevdpth5. AllcamrrmnicationisroutedthroughtheSIP~which is provided by the NASA balloongmup. The line-of-sight(LOS) telemetry is available only while the balloon is withia range of a
1018
S. E. Boggs er al
gmmd stationor an underflying aircraft. The IIF link, however, can be used at any time to send commands to the lnstntment. The ARGOS satellites are used to transmit 64 bytes of housekeeping data from the balloon approximately every 15 minutes. And while the INMARSAT link is designed to both send and receive data and commands, its use is severely restricted because much of Antarctica is outside of the satellite’s view.
The gondola frame is -7 x 9 ft. wide x 7 ft. tall. Including the solar panels, it spans -17 ft., and including the tripod aud rotor assembly, above, and the SIP solar panels, below, it is -19 ft. tall. The weight of the instrument cradle assembly (with filled LN dewars) is 1542 lbs; that of the electronics bay, 790 lbs; the total weight of the gondola (excluding the SIP, SIP solar panels, and ballast) is 2785 lbs. PERFORMANCE IUREGS was launched 9 January 1995 for its third LDBF on a 29 million cubic foot balloon from McMurdo Station, Antarctica. The balloon circumnavigated the continent in 23 days (Figure 3). with a daily altitude excursion of 126,000119,000 ft (corresponding to an atmospheric depth of 4.5-6.0
Fig. 3. IBREGS was launched from McMurdo Station on 9 January 1995 and landed 23 days later within several hundred miles of McMurdo. The entire instrument and gondola were recovered. though some of the structure was destroyed during landing.
g cms2), and the average daily altitude maintained throughout the flight. All twelve detectors functioned well throughout the flight. A failure occurred in the Exabyte tape storage system early in the flight, so that all but the first day of data is in the “tmderflight” format. Two LC-130 flights were made to retrieve the underflight data. The pointing system performed well for the fast eight days of the flight, but then underwent a nonrecoverable failure, effectively ending the data collection. The balloon was cut down a few hundred miles northwest of McMmdo Station on 2 February 1995. The instrument was recovered on the first attempt with an LC130. A total of 24 hours of event data and 7 days of underflight data were recovered. The analysis of the data is still in progress, but prehminary results have been very promising. We have been able to separate point source spectra from the diffuse emission in the Galactic Center region, allowing us the best hard X-ray measurements of diffuse Galactic emission (Boggs et al. 1997). as weli as spectra of two point sources that were flaring near the Galactic Center: pulsar GX1+4. and the black hole transient GRO J1655-40. The 511 keV and 1809 keV narrow line analysis and the analysis of Vela X-l observations are currently underway. The scientitic results will be reported elsewhere.
the the the the
ACKNOWLEDGEMENTS This research was supported in part by NASA grant NAGW3816. We would like to thank the staff of the National Scientific Balloon Foundation and the Antarctic Support Associates for a successful balloon launch and recovery. The National Science Fotmdatlon Antarctic Program provided much support with krgistics and operations. The United States Navy provided two invahrable LC-130 underflights. REFERENCES Boggs, S. E.. cl 01.. “HIREGS Observations of the Galactic Center and Galactic Plane: Separation of the Diise Galactic Hard XRay Continuum from the Point Source Spectra,” Proc. 2nd INTEGRAL Workshop. ESA SP-382 (1997). Feffer et 01.. “Solar Energetic Ion and Electron Limbs from IIIREGS Observations,” Solar Phys. 171,419 (1997). Lin, R. P., et al., “A Long-Duratirm Balloon Payload for Hard X-Ray and Gamma-Ray Observations of the Sun,” Solar Phys. 113, 333 (1987). I&won. J., et al.. 21st Internur. Cosmic Ray Conf. (Adeluide), 2, 174 (1990).
Pelling. M., et al., “A High Resolution Gamma-Ray and Bard X-Ray Spectrometer (HIREGS) for Long Duration Balloon Flights,” Sot. Photo-Opt. Insfr. Engin. 1743,408 (1992).
A HIGH RESOLUTION GAMMA-RAY AND HARD X-RAY SPECTROMETER (HIREGS) FOR LONG DURATION BALLOON FLIGHTS S.
E. Boggs*v**, R. P. Lin****, P. T. Feffer *,**, S. Slassi-Sennou*, S. McBride*, J. H. Primbsch*, K. Youssefi*, G. Zimmer*, C. Cork***, P. Luke***, N. Madden ***, D. Malone***, R. Pehl***, M. Pellingt, F. Cot&, G. Vedrennet *Space Sciences Laboratory, **Department of Physics, University of California, Berkeley, CA 94720, U.S.A. ***Lawrence Berkeley National Laboratory, University of California, Berkeley, CA 94720, U.S.A. 'Center for Astrophysics and Space Sciences, University of California, San Diego, CA 92093, U.S.A. SCentre d’Etude Spatiale des Rayonnements, 31029 Toulouse, France
The l?LRKiS gamma-ray sptrometer made a U-day Long Duration Balloon Flight (LDBFI from Antarctica in January 1995 to mnmxs of gamma-ray and hani X-my line and continuum omission. The s&&ii inslnuaent itself is discnssed, omeGalactic followed by a more exmive discussion of the chara~te&i~s of the instrument unique to LDBFs. The flight pezformance and Iweliminary results are briefly summarized. 01998 COSPAR. Published by Elsevier Science Ltd. lNTRODUCTION ciimmway and Hard x-ray Spectram~ (I-llmGS) has flown three long dllrstioll (lo-20 day) balloon ~ovsrAnnrctica.‘IhefirsttwoflightsinJ~1991andJannary1993werededicatedtosolarflare~a~~~at al. 1997). while the third Bight in January 1995, described here, observed Galactic gamma-ray sources. HIRBGS can detect photons from 20 keV to 18 MeV with one to several keV energy resolution and a full-width-at-half-maximum (FWHM) field-of-view of
The High lzeallltti
-24’. The large detector area (423 cm2), high energy resolution, and use of active shielding, combined with long dnmtion balloon !lights (LDBFs). make the instmment highly se&rive to the detection of astrophysical narrow gamma-ray lines. The HIRBGS mt is similar in design to its predecessor HBXAGONE (Matteson et al. 19X)), but its larger area and long-duration cap&&es make it podentiauy much more powerful. LDBFs over -tica dtning the austral summer have several advantages over conventional balloon flights. The high altitude wind pattern ovez Antiuctica allows circumpolar LDBFs lasting one to several weeks to be achieved. With the Snn always above the ho&on, 24 hour/day solar observations are possible and the balloon altitude remains relatively stable with little or no b&sting. At mid-latit@s t&e day-night cycling not only limits solar observations to -12 hours per day, but more importantly. it leads to a loss of balloon lift and the consequent drop in daytime altitnde. Even with ballasting, mid-la&u&. flights with llocmal anpnssarl;tsd balloons are limited to less than 8 week of -12 hour/day solar observations before the daytime al&de drops too low (Lin et nl. 1987). The third LDBF of HIRBGS in January 1995 was dedicated to observations of Galactic sources, and had several main scientific goals:measarementofther;hapeofthe511keVannihilati~lineandtbe1809keV26AlradioactivedecaylinefromtheG~~ centa ngio& measuxmat of the Galactic diffuse continuum radiation, and separation of point somce spectra with spec& intent to seapch for cyclotron lines from Vela X-l and GX301-2. Half of the observations concentrated on the Galactic Center region, and the ot4er half were shared between the Galactic Plane (1=335”), Vela X-l. and the X-ray transient GRO J1655-40. INSTRUMENTAnON The EIIREGSinsunment consists of an array of twelve 6.7sm diameter x 6.2-cm long n-type germanium (Ge) closedend coaxial detectors (Figure 1). which are cooled by three 50-liter liquid nitrogen (LN) dewars. Eight of the detectors are electrically separated into front and rear segments to improve the low energy background and flare perf ormance (Pelling et al. 1992). Thei detector army JASR z1:,-0
1015
1016
S. E. Boggs et al
’ BQO Bottom Shield Fig,, 1. Diagramsof the HIREGS instrumentshowingthe relative positions of the Ge detectors, the BGO shield, and CsJcollimator.Liquid nitrogen dewarsmaintainthe detectors at cryogenic temperatures. is surroundedby an active shield that reduces the gamma-raybackgroundby allowing the anticoincidenceof simultaneousdetector and shield events. The shield system consists of S-cm-thickBGG segments at the rear and sides and a lo-cm-thick drilled CsJ collimator on the front which determines the 24’ field-of-view (Figure 1). Additionalhard X-ray (&tIK&eV)passive collimators inserted in the CsJ collimator cover half of the detectors, limiting these fields of view to 3.7” x24’ FWHM, allowing separation of point source spectra from the diffuse Galactic continuum(Boggs et al. 1997).The detectors, LN dewars, shield, and collimator are held in a cradle structure that is. in turn supported within the balloon gondola (Figure 2). For a more detailed description of the scientific instrumentsee (Pelhng et al. 1992). LONG DURATIONBALLOONFLIGHT SPECJFJCJSSUES LDBFs place many requimments on the instrument,such as the need for large data storage capacity, solar power, thermal stability, cryogenics, and commuuications. Besides the hardwarerequirements,LDBFs pIace tight constraints on the preparation ached&x an LDBF launch fnxn Antarcticain December requires shipmentof the instrumentto Antarctica in August, and integration of the entire instrumenteven earlier, in June.
The main computer packagesthe data frames, and sendsthem to an Exabyte tape storage system and/or to the telemetry system. The main computer also controls instrumentcommamhngand housekeeping.The flight code was developed in C and assembly, and governs the computer’sprimary functions. The Exabyte tape drive can store up to 4.6 Gbytes. enough to hold all the data generated in a 3 week balloon flight. Also, there is a 44-MbyteRAM disk for temporary data storage, the contents of which can be rransmi#cdtotbegroundortoanairplaneoncanmand.ThisRAMbufferisstatifandhasbacLupbatseries,sotbedatais pmsezvedeven in the event of a power cycle.
Dam is stored in two formats, mfenud to as event data and m&flight data. The event data consists mostly of detailed information abcrrrteachdctrctorevcntandisstosedinthetapesystem.ThellndafliOhtdatacmmiaaprimarily30minutecaadwrsedspectrathat arc~~~~iothemain~raadstoacdinthe44Mbytetemporary~o~,fromwhichitcaabetelunctedddowntoa ground statiar or to an LC-130 aircraft that is flown nuder the balloon every few days. The underflight data serves as a backup in case the data tape is not recovered.
AU pointing isdeterminedrelative to the Sun and is controlled by the Gondola Control Unit (GCU). The GCU is an independent computer dedicated to pointing operations, the collection of housekeepingdata, and the aqnisition of GPS information. The GCU alao controls varicms power relays and can receive commands from the main computer as well as from the several telemetry command links. Under normal operation, however, a fully autonomousLDBF is governed by preprogrammedcemting
A High Resolution Gamma-Ray Spectrometer
1017
Electronics Bay--\
Fig. 2. The HIREGSgondola.
Power isprovided by a 8.1 n.3 solar anay. made up of crystalline silicon phoWs, amnged on two lateral pmelk that delivers uptolOOOwatrsabpowsravathedaratianoftheflight.AsetafpnssruizcdleadacidbaUcrieslocatedinthcclec~baycan power th iastrment fix several hours if the solar panelsare pointed away from the Sun.
commpnication~~fromtheiwnuuentismadeviasevdpth5. AllcamrrmnicationisroutedthroughtheSIP~which is provided by the NASA balloongmup. The line-of-sight(LOS) telemetry is available only while the balloon is withia range of a
1018
S. E. Boggs er al
gmmd stationor an underflying aircraft. The IIF link, however, can be used at any time to send commands to the lnstntment. The ARGOS satellites are used to transmit 64 bytes of housekeeping data from the balloon approximately every 15 minutes. And while the INMARSAT link is designed to both send and receive data and commands, its use is severely restricted because much of Antarctica is outside of the satellite’s view.
The gondola frame is -7 x 9 ft. wide x 7 ft. tall. Including the solar panels, it spans -17 ft., and including the tripod aud rotor assembly, above, and the SIP solar panels, below, it is -19 ft. tall. The weight of the instrument cradle assembly (with filled LN dewars) is 1542 lbs; that of the electronics bay, 790 lbs; the total weight of the gondola (excluding the SIP, SIP solar panels, and ballast) is 2785 lbs. PERFORMANCE IUREGS was launched 9 January 1995 for its third LDBF on a 29 million cubic foot balloon from McMurdo Station, Antarctica. The balloon circumnavigated the continent in 23 days (Figure 3). with a daily altitude excursion of 126,000119,000 ft (corresponding to an atmospheric depth of 4.5-6.0
Fig. 3. IBREGS was launched from McMurdo Station on 9 January 1995 and landed 23 days later within several hundred miles of McMurdo. The entire instrument and gondola were recovered. though some of the structure was destroyed during landing.
g cms2), and the average daily altitude maintained throughout the flight. All twelve detectors functioned well throughout the flight. A failure occurred in the Exabyte tape storage system early in the flight, so that all but the first day of data is in the “tmderflight” format. Two LC-130 flights were made to retrieve the underflight data. The pointing system performed well for the fast eight days of the flight, but then underwent a nonrecoverable failure, effectively ending the data collection. The balloon was cut down a few hundred miles northwest of McMmdo Station on 2 February 1995. The instrument was recovered on the first attempt with an LC130. A total of 24 hours of event data and 7 days of underflight data were recovered. The analysis of the data is still in progress, but prehminary results have been very promising. We have been able to separate point source spectra from the diffuse emission in the Galactic Center region, allowing us the best hard X-ray measurements of diffuse Galactic emission (Boggs et al. 1997). as weli as spectra of two point sources that were flaring near the Galactic Center: pulsar GX1+4. and the black hole transient GRO J1655-40. The 511 keV and 1809 keV narrow line analysis and the analysis of Vela X-l observations are currently underway. The scientitic results will be reported elsewhere.
the the the the
ACKNOWLEDGEMENTS This research was supported in part by NASA grant NAGW3816. We would like to thank the staff of the National Scientific Balloon Foundation and the Antarctic Support Associates for a successful balloon launch and recovery. The National Science Fotmdatlon Antarctic Program provided much support with krgistics and operations. The United States Navy provided two invahrable LC-130 underflights. REFERENCES Boggs, S. E.. cl 01.. “HIREGS Observations of the Galactic Center and Galactic Plane: Separation of the Diise Galactic Hard XRay Continuum from the Point Source Spectra,” Proc. 2nd INTEGRAL Workshop. ESA SP-382 (1997). Feffer et 01.. “Solar Energetic Ion and Electron Limbs from IIIREGS Observations,” Solar Phys. 171,419 (1997). Lin, R. P., et al., “A Long-Duratirm Balloon Payload for Hard X-Ray and Gamma-Ray Observations of the Sun,” Solar Phys. 113, 333 (1987). I&won. J., et al.. 21st Internur. Cosmic Ray Conf. (Adeluide), 2, 174 (1990).
Pelling. M., et al., “A High Resolution Gamma-Ray and Bard X-Ray Spectrometer (HIREGS) for Long Duration Balloon Flights,” Sot. Photo-Opt. Insfr. Engin. 1743,408 (1992).