Seeon WS, May 2003

MEGA: A next generation project for Medium Energy Gamma-ray Astronomy

0.4 – 50 MeVThe MPE team (prototype development, system design and calibration): R. Andritschke, P. Bloser (now GSFC), G. Kanbach, F. Schopper (now HLL), V. Schönfelder, A. Zoglauer

the MEGA Collaboration (Institution and Contact, present status):

Europe:

MPE, Garching,D (G. Kanbach), GACE, Valencia, E (V. Reglero),

IASF, Bologna, I (G. DiCocco), CESR, Toulouse, F (J. Knödlseder)

U.S.A.:

UNH, (J.M. Ryan), GSFC (S.D. Hunter), NRL (J.D. Kurfess), Columbia U. (E. Aprile),

U of Alabama (W.S. Paciesas), IGPP-UCR (A. Zych), LANL (T.Vestrand),

Clemson U. (D. Hartmann)

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A Map of MEGA Sciencenon-thermal continuumγ-ray lines MeV

300

100

30

10

3

1

0.3

0.1

Unidentified EGRET/COMPTELsources

Spectral cut-off in Magnetars

Luminosity Maxima of EGRET/COMPTEL Blazars

non-thermal spectrain black-hole binaries

GRB spectralevolution; polarization

cosmic accelerators

stellar & solar nuclear reactions

galactic radioactivity 26Al; 60Fe

young SNR search 44Ti

511 keV: galactic map;Novae; solar flares

nucleosynthesis

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ACT

Generations of γ-ray Missions:1. COMPTEL ⇔ COS-B

2. MEGA (~t0+5) ⇔ EGRET

3. Advancd Compton⇔ GLAST

(ACT,~2012) (~2006)

Sensitivities

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Detection of Gamma RadiationCrossSection

Energy

Pair Creation (> 10 MeV)Photons completely converted to e+e-

Telescope:Tracking chambersto visualize the pairs

Photoeffect(< 100 keV)

Photons effectively blocked and stopped

Telescopes:

CollimatorsCoded Mask Systems

Compton Scattering (0.2-10 MeV)Photon Crossection MinimumScattered photons with long rangeTelescope:Compton Camera Coincidence System

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MEGA Schema: Detection via Compton and Pair Creation interactions

• Selective Trigger & good Background Rejection• Large and Sensitive• Sensitive to Polarization @ a few MeV• ‚Matched‘ Resolution (Angular and Energy)

Our (current) choice of technique:

Tracker: double sided Si strip detectors

Calorimeter: CsI/PIN diode pixel arrays

Scale of detector for Aeff ~ 100 cm2 ?

Aeff = (1-e-µd ) Ageom η

µ~ 0.1 cm-1 (>100 keV) in Si Ageom ~ 1300 cm2 (=36x36 cm2)η ~ 0.5

tracker depth ~ 1.7 cm of Si i.e. 34 layers of 500µm ; ~ 5 m2 Si

Seeon WS, May 2003

Prototype and Full-size Instrument

30 layers of Si strip detectors36 x 36 cm2 , 0.5 mm thick

CsI Calorimeter

10 layers of Si strip detectors18 x 18 cm2 , 0.5 mm thick

Seeon WS, May 2003

Prototype Aeff estimate :

Aeff = (1-e-µd ) Ageomη= 16 cm2 η

with η = 0.4 x 0.3

Aeff ~ 2 cm2

Tracker: 10 (+1) layers of Silicon stripdetectors (wafers 6x6cm2)

Calorimeter: 20 modules of pixellated CsI(Tl) ScintillatorsFill factor lower hemisphere ~ 40%

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Integration of Prototype Detector

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Detector, Electronics, and DAQ

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Task: select valid events according to their trigger patterns / initiate configurations and readout

Implementation: FPGA Xilinx-SpartanDesign: Robert Andritschke

Trigger receiver and formatter

combined triggers

Coincidence circuit:trig. pattern (2Mb RAM)

timing & r/ocontrol

start

modecontrol:init. ACS,RAM,windows,HK r/o

Event hold and readoutchip triggers

Coincidence Electronics

D1: fastD1:12D1:36 (=12x3)

D2: 8 D2: slowD2: 24

VMEDAQ

ACS: 1ACS: 4

clear/reset

absolute vetoexternal trig: 2

VMEBus clock

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Calibration MeasurementsExposures to radioactive sources in the laboratory (2001-2003)Subsystem calibrations Prototype measurements

Beam Calibration (April/May 2003) : High Intensity Gamma-Ray Source (HIGS) atDuke University, Durham, N.C.

Goals: • Calibrate response: efficiency,

energy, direction, polarization• extend calibrated energy range to ~ 50 MeV• verify M.C. models• test response to radiation from lower hemisphere

(atmospheric background)

... see reports by Zoglauer and Andritschke (this meeting)

Seeon WS, May 2003

Plans for a balloon flight

Balloon Flight: (Spring 2004?):

Goal:Fly the MEGA Prototype (including a veto shield to guard againstcharged particles) on a balloon flight at 38-40 km altitude for 20-30 hrs

Determine the response of MEGA to the natural radiation background at the edge of space

Plan:Proposal to NSBF for from Ft. Sumner, NM. Next flight opportunities: Spring turnaround 2004

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Pressure vessel for the MEGA Prototype, ACS & FEC

VME DAQ

Batteries & Telemetry,

(NSBF, Ft. Sumner, NM, Spring 2004 ?)Balloon &Parachute

DifferentialGPS:Timing &Attitude

Front EndControl

MEGA

ACS

TM & TC Battery

The MEGABALL* Balloon Flight

Total weight of payload ~ 400 kgNo active attitude controlAttitude measured with a differential GPS

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MEGABALL Balloon Payload

Anticoincidence Shield to vetocharged cosmic ray particles

ACS readout: WLS fibres collected at PMTs

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ACS Development

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Project Outlook and Technical AdvancesScheduled Activities:•Beam Calibration: April 2003•Balloon Flight: Spring 2004 •Continue Simulations and Background Modelling•Advance Software and Analysis Methods

Study advanced Detector designs:•D1 Tracker: use of larger Si Wafers•D2 Calorimeter: use Si-Drift Diodes to improve

threshold and energy resolutionstudy alternatives: CdTe, CdZnTe, Ge

proposal for a MEGA space mission: - Aug 2001, DLR German Kleinsatellit: second place - preparations for a new opportunity: MidEx?

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Design of a SatelliteDesign of a Satellite Instrument (Instrument (prepre--phase phase A A studystudy, 2001), 2001)

Technical data of the Instrument

Mass: 650 kgPower: 214 WChannels: 134120

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MEGA-Instrument

Solarpanels

Satellite Electronics

2 Gastanks

2 Radiators

3 Magnet Torquers

Interface to Launcher

S-Band Nadir Antenna and Thruster

MEGA MEGA SatelliteSatelliteSatellit

OrbitdataOrbitdata

Altitude: 550 km, circ.Orbital Time: > 5 yearsInclination: 0° (< 28.5o)Attitude: Zenith-ScanPosition: GPS,

Starsensors

Technical DataTechnical Data of of the Satellitethe Satellite

Mass: 950 kgDiameter: 200 cmLength: 235 cmPower: 350 WTelemetry: online, max. 150 kbit/s

(TDRSS - DAS)

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All Sky `Real-Time` MonitorMEGA Mission:To TDRSS-DAS Real Time Telemetry

Exposure Map2 years Mission

- Transient sources are detected in real time- Prompt follow-up observations- Homogeneous exposure with slight tilting of attitude

Seeon WS, May 2003

MEGA Sensitivity

MEGA SensitivityGEANT Simulations incl. Orbital Background

Continuum Narrow Lines

Angular Resolution 2.4° FWHM @ 2 MeV / Source Location: < 2 arcminEnergy resolution 3% FWHM @ 2 MeVPolarization 10% (Crab in 100 h)

Seeon WS, May 2003

Expectations for a MEGA Satellite in a ~3 year lifetime

1 (OSSE: 4 / 25)10 - 15Radiogalaxies / Seyfert Galaxies

4100Unidentified EGRET Sources

39 (total)~0.5 / dayGamma Ray Bursts

COMPTELMEGASource

01(+1987a, SMM)

5 / year2-3 / year

Novae (7Be, 22Na, e+ e_ Ann.)Supernovae Ia (56Ni , 56Co, 57Co)

1(+ 1?)5 ?young SNR (44Ti)

27depends on cycleSolar Flares: continuum and lines

10100Blazars

1 (Cyg X-1)1 (N Per 91)1?

555

Binary SystemsBinary Novae Micro-Blazars, Jet Sources

310Pulsars