1. DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE POLAR POLAR: A novel X-ray polarimeter Daniel Haas ISDC Versoix ECRS 2008 Kosice, Slovakia Outline GRBs and their Models Why POLAR & The Detection Concept POLAR Design Testbench & First Results POLAR EQM Outlook/Challenges & Conclusions

2. DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE POLAR Daniel Haas, ECRS ‘08, Kosice Page 2 Gamma Ray Bursts... Gamma ray bursts (GRB): flashes of gamma rays at random places in the sky and at random times Brightest events in the universe About 1 GRB/day observed

3. DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE POLAR Daniel Haas, ECRS ‘08, Kosice Page 3...Origin of GRBs... Not clear, different models From M.Lyutikov, 2003 See papers discussing various models: T.Piran, A.Dar & A. De Rujula, M.Lyutikov, D.Eichler, G.Ghisellini, D.Lazzatti, M.Medvedev, E.Rossi etc. P lin ~ 10-20%P lin = 0 - 100%P lin ~ 50%

4. DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE POLAR Daniel Haas, ECRS ‘08, Kosice Page 4...GRB Polarization... Polarized  ’s produced by: –Synchrotron radiation –Cyclotron emission –Bremsstrahlung –Compton Scattering –Magnetic photon splitting

5. DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE POLAR Daniel Haas, ECRS ‘08, Kosice Page 5...GRB Polarization - Measurements Polarization of the prompt γ-ray emission from the γ-ray burst of 6 December 2002 (RHESSI), Coburn, W; Boggs, S. E., Nature, 2003, 423, 415 (122 citations): P lin = 80 ± 20% (highly significant detection!) –Re-analysis of polarization in the γ-ray flux of GRB 021206, Rutledge, R. E.; Fox, D. B., MNRAS, 2004, 350, 1288 Statistical Uncertainty in the Re-Analysis of Polarization in GRB021206, Coburn, W; Boggs, S. E., 2003astro.ph.10515B –Gamma-Ray Burst Polarization: Limits from RHESSI Measurements, Wiggler, C. et al, ApJ, 2004, 613, 1088 Evidence of polarisation in the prompt γ-ray emission from GRB 930131 and GRB 960924 (BATSE/GRO), Willis, D. R. et al, 2005, A&A, 439, 245 Polarisation studies of the prompt γ-ray emission from GRB 041219a using the spectrometer aboard INTEGRAL, McGlynn, S., 2007, A&A, 466, 895 Large Uncertainty & Controversial, poor sample of events, Polarization should be added to priority programs for GRB’s

6. DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE POLAR Daniel Haas, ECRS ‘08, Kosice Page 6 Detection principle... Compton scattering: –photons tend to scatter at a right angle w.r.t. the initial polarization vector –  = azimuthal scatter angle –  = Compton scatter angle Klein-Nishina: Level of Polarization:

7. DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE POLAR Daniel Haas, ECRS ‘08, Kosice Page 7...Detection principle Use two largest energy deposits with E > 5 keV GRB position is known or reasonably estimated Analysing power:  100 =A 100 /B 100 (mod. factor) modulation amplitude for 100% polarization MC predicts clear modulation signal with period  Unpolarized photons create pattern with period  /2

8. DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE POLAR Daniel Haas, ECRS ‘08, Kosice Page 8 POLAR design... Requirements Compton polarimeter Simple, compact instrument: –relies on given burst position and spectrum –or provides a crude estimate in case of unique observation Dedicated for GRB observations only: –Large area –Large modulation factor –Large field of view Energy range for incoming photons: –50 keV - 500 keV Design 40x40 uniform scintillator array –Light, fast and low Z plastic –Scintillator size: 6x6x200 mm –Matching Hamamatsu MAPM8500 –A eff ~ 400 cm 2 –  100 ~ 35% –FoV ~ 1/3 of the sky –Passive shielding –Main electronics below detector

9. DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE POLAR Daniel Haas, ECRS ‘08, Kosice Page 9...POLAR design Electronics housing Passive Shielding 25 Detector Modules Module in Carbon Fiber 8x8 bars MAPM H8500

10. DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE POLAR Daniel Haas, ECRS ‘08, Kosice Page 10 Testbench... CAMAC/NIM readout of a prototype module Prototype Module and scintillator bar testing

11. DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE POLAR Daniel Haas, ECRS ‘08, Kosice Page 11...Testbench Demonstrator Electronics with one prototype target (custom made FPGA board with ASICS and place for 2 PMs) Photon polarizer from Cs 137 with NaI detector as scatterer (290 keV  -rays) Trigger Readout Signal Source Scatterer Detector (here only a 2nd NaI) 90 o

12. DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE POLAR Daniel Haas, ECRS ‘08, Kosice Page 12 First Results... Tests with L-shape of 8+8 bars Polarized photons (290 keV/60%) from Cs 137 after 90 o scatterer Coupling to MAPM H8500 (mod.fac x degree of polarization) Asymmetry up to 12 % confirms proof-of-principle

13. DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE POLAR Daniel Haas, ECRS ‘08, Kosice Page 13...First Results... Light collection studies Simulation predicts: –~45%  ’s reach PM –10-20% difference top/bottom –Surface quality essential Measurements confirm simulation –different wrapping tested –use Vikuiti (Alu-like, but even higher reflectivity very good surface quality

14. DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE POLAR Daniel Haas, ECRS ‘08, Kosice Page 14...First Results (MC) Minimal detectable polarization E=10 -5 erg/cm 2 –MDP 3  ~ 10% for strong bursts –Several measurements per year Modulation factor as function of energy and theta –events from the side are harder to detect than from the top –low energies are favored

15. DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE POLAR Daniel Haas, ECRS ‘08, Kosice Page 15 MAPM in TVT Frontend Design Module in Carbon Fiber 8x8 bars MAPM H8500 Assembly studies EQM

16. DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE POLAR Daniel Haas, ECRS ‘08, Kosice Page 16 Outlook & Challenges Demonstrator will be tested on Polarizer soon Preliminary qualification tests of EQM mechanics underway (vibration, thermal stress etc.) Beamtests at SLS by end 2008 (PSI Villigen/CH) and ESRF (Grenoble/F) by end 2009 Optical crosstalk on PM pads is high (~10%), Trigger/Online rejection has to take care of this Gain calibration of 1600 scintillator bars is difficult In-flight calibration still an issue Localisation of GRBs stand-alone is challenging –rough estimation seems feasible, more studies ongoing

17. DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE POLAR Daniel Haas, ECRS ‘08, Kosice Page 17 Conclusions Accurate and statistical meaningful polarization measurements of GRBs can: –constrain theoretical models –give crucial information about GRBs central engine POLAR - a compton hard X-ray GRB polarimeter may answer these questions: –compact 40x40 array of low Z scintillators (6x6x200 mm) coupled to Hamamatsu MAPM H8500 –MDP 3  ~ 10% for GRBs of ~ 10 5 erg/cm 2 –Tens of detections/year expected –Proof-of-principle on polarizer testbench –Demonstrator will be used in testbeams for further studies –EQM under design, to be ready by 2010

18. DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE POLAR Daniel Haas, ECRS ‘08, Kosice Page 18 The POLAR Collaboration Centre des Physique des Particules de Marseilles, (CPPM, France) Département de Physique Nucléaire et Corpusculaire (DPNC Genève, Switzerland) Institute of High Energy Physics (IHEP Beijing, China) INTEGRAL Science Data Centre (ISDC Versoix, Switzerland) Laboratoire d’Annecy de Physique des Particules (LAPP, France) Paul Scherrer Institut, (PSI Villigen, Switzerland) Andrzej Soltan Institute for Nuclear Studies (IPJ Warsaw, Poland)