The GAS Pixel Detector Yesterday, Today and Tomorrow

Transcription

1 The GAS Pixel Detector Yesterday, Today and Tomorrow Enrico Costa IAPS Roma/ ASI Roma On behalf of the GPD Collaboration

2 When all this started? Scientists devoting a sigificant amount of their time to X-Ray Polarimetry could be seen as a small company of drug addicts. For general admission the original pusher was Vitaly Ginzburg. Notwithstanding his numerous unsuccesses Bob Novick, a professor at Columbia University, is still the most succesful of the company. In Italy we started around 1985 at the Istituto di Astrofisica Spaziale of CNR in Frascati in collaboration with the Istituto Astronommico of the University of Rome. Myself and Marco Salvati made the first computation of sensivties for a scattering polarimeter, that would arrive to a proposal for XMM. When Marco moved from Frascati to Arcetri he passed the program to Giorgio Matt, who became a new addict of this drug.

3 Different techniques and implementations Traditionally (35 years ago!) only polarimeters based on Bragg diffraction aroud 45. A large number of detectors proposed with different energy range and sensitivity. None approved so far. Based on: Diffraction/Photoelectrc Effect/Compton Scattering Philosophy: Dispersive / Not Dispersive Strategy: Collimated / Focal Plane Band: Very Soft (<2keV)/ Soft (2-10 kev), /Medium (5-30 kev) / Hard (>20keV); Narrow band / Broad Band A polarimeter foreseen aboard HEAO-2/Einstein but removed later A polarimeter foreseen aboard AXAF/Chandra but removed later A polarimeter proposed aboard XMM and rejected

4 Pierre Auger and the cloud chamber Pierre Auger studied the physics of the photoelectrons ejected by X-rays in gases. Photons are absorbed and a photoelectron ejected. The photoelectron ionizes the gas and is scattered. From the first part of the track the absorption point and the photoelectron direction can be derived. We need a modern cloud chamber. The Gas Pixel Detector is a modern implementation of the cloud chamber with: 1. Electronic read-out 2. Prompt read-out 3. Self triggering But the technology for such an only arrived fter 75 years Alsatian Workshop on X-rayachievement Polarimetry

5 A photoelectric polarimetry All the first experiments of X-Ray Astronomy were performed with photoelectric detectors. Photoelectric detectors are local, easy to be collimated and suited to the jump to a focal plane. Bragg and Thomson polarimeters were hopeless mismatched with imagers and spectrometers. But Vitali Ginzburg was suggesting to try the way of photoelectric polarimetry. Attempts were performed at Columbia, GSPC and MSSC by means of wire chambers. They were unsuccesful and are poorly documented in literature. But are clearly stated in a review of 1973 by Bob Novick.

6 The first published attempt

7 The first modern imager of photoelectron track SPIE Vol.2010 X-Ray and Ultraviolet Polarimetry(1993)

8 SXRP ad Photoelectric Polarimetry When the design of the Stellar X-Ray Polarimeter was in an advanced status George Fraser found a modulation in the photocurrent of a cathode inpinged at grazing angles by Xrays, much higher than what predicted by usual transfer programs. Bob Novick convinced Rashid Sunyaev to add a photoelectric polarimer to the SXRP. The increase of sensitivity was fantastic. Further mesurements at Columbia and Livermore showed that the effect was a fake due to systematics out of control and the PEP was removed from SXRP. Impressed by the foreseen increase of sensitivity at IAS in Italy we started to think that maybe we should start to reconsder photoelectric polarimetry based on good old physics but on modern technology. By elementary considerations we went back to the gas.

9 The first Italian Photoelectric Polarimeter Astronomical x-ray polarimetry based on photoelectric effect with microgap detectors Paolo Soffitta (1), Enrico Costa (1), Giuseppe di Persio (1), Ennio Morelli (1), Alda Rubini (1), Ronaldo Bellazzini (2), Alessandro Brez (2), Renzo Raffo (2), Gloria Spandre (2), David Joy (3) ((1)Istituto di Astrofisica Spaziale del CNR Rome Italy, (2)INFN-Pisa, S. Piero a Grado (Pisa) Italy, (3) Science and Engineering Research Facility, University of Tennessee, Knoxville,USA) (Submitted on 8 Dec 2000) Pulished on Nuclear Instruments and Methods in Physics Research Section A, Volume 469, Issue 2, p , 2001.

10 Not yet a viable instrument but a significant step forward

11 The first break-through the GPD 2001 Photoelectric polarimetry is feasible! But still many limits: 1) Few pixels ( ) 2) Large pixels 200 m 3) High Noise (Front End Electronics far from the pixel) 4) Electronics much larger than the detector

12 The second Break Through: The ASIC Chip The ASIC chip acts as: Bottom of the detector Multi-anode pad and field former Front End Electronics Self-trigger Definition and fetch of a Region of Interest

13 The dominant technique for the future:the focal plane Photoelectric Polarimeter The photoelectric gas detectors are a modern implementation of the cloud chamber with self triggering and instataneous readout.

14 The first X-ray polarimeter approved after many years The Gravity and Extreme Magnetism Small Explorer Based on Time Projection ChamberTechnique, and 3 light telescopes (descooped to 2 in implementative phase). Built and assembled at GSFC. Jean Swank PI. GEMS would perform polarimetry of everything falling within o f.o.v. of 12 arcminutes Pre-selected (with other 5 candidates) on may 2008 Selected (with another candidates) on june 2009 Stopped on august 2013 for unacceptable cost and schedule growth Instead of re-starting the path to polarimetry acted as a stopper for 5 more years

15 We have a mission: IXPE Satellite ters e m 2 ~ 5.

16 Toward higher energies Simulations show that GPD can work effectively as polarimeters with Argon based mixtures, with a pressure up to 3 atm and an absorption gap of the order of 30 mm. We built 2 prototypes and had to face a problem of uniformity of electric field. In order to have more freedom to increase the thickness of the absorption gap we had to make larger electrodes. So we changed our design. Nowadays this larger body is also adopted for lower energies. 80 g 300 g A second prototype was built. Preliminary tests showed that it works consistently with simulations. But the functionality was degraded in a short time for a leak. But a GPD polarimeter from 6 to 30 kev is feasible Alsatian Workshop oneffective X-ray Polarimetry

17 A medium energy polarimeter for the focus of multilayer optics (or without optics for solar flares) The new prototype is compatible with 3cm absorption/drift gap and a filling with 3 Atm pressure of Ar/DME. It is effective from 5 to 30 kev. We name it MEP (Medium Energy Polarimeter). Photoelectrons from 22 kev photons

18 A high energy focal plane polarimeter Fabiani et al. ExA 2013 We are studing this configuration At Washington University of Saint Louis a balloon experiment in the focus of a multi-layer telescope, is ready.

19 Three polarimeters for different energies The High Energy Polarimeter is more tuned to multilayer optics with long focallength (8-10 m). The other two polarimeters can be suited for XTP.

20 Which polarimetry with extended energies Scientific goal Sources < 1keV 1-10 Acceleration phenomena PWN (but absorption) SNR no Jet (Microquasars) (but absorption) Jet (Blazars) WD (but absorption) difficult AMS no Emission in strong magnetic fields > 10 kev X-ray pulsator difficult (no cyclotron?) Magnetar (better) no Scattering in aspherical geometries Corona in XRB & AGNs difficult (difficult) X-ray reflection nebulae no (long exposure) Fundamental Physics QED (magnetar) (better) no GR (BH) no no difficult? difficult QG (Blazars) Axions (Blazars, Clusters)

21 Acceleration: SNR In SNR the high energy tails show a non thermal emission, in the front regions of the shock. This could also be singled out by polarimetry, depending on how much the magetic fields are ordered.

22 Cyclotron lines with 100 ks of observation with NHXM-MEP The extension of polarimetry to Hard X-Ray can allow for a detailed study of cyclotron lines. All detected lines are above 10 kev. Photoelectric polarimetry extended to higher energies (such as in NHXM) or good quality compton polarimetry can allow for a direct exploration of the cyclotron resonances. Here we need the high energy and not need the imaging, except for some complex fields.

23 Or the Sun Fabiani et al. 2012