the gas pixel detector yesterday, today and tomorrowawoxpol.u-strasbg.fr/all_talks/costa.pdf · the...

The GAS Pixel Detector Yesterday, Today and Tomorrow

Alsatian Workshop on X-ray Polarimetry - 20171113

Enrico CostaIAPS Roma/ ASI Roma

On behalf of the GPD Collaboration

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.

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 laterA polarimeter foreseen aboard AXAF/Chandra but removed laterA polarimeter proposed aboard XMM and rejected

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-out2. Prompt read-out3. Self triggeringBut the technology for such an achievement only arrived fter 75 years of developments

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.

The first published attempt


The first modern imager of photoelectron track


SPIE Vol.2010 X-Ray and Ultraviolet Polarimetry(1993)

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 X-rays, 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.

The first Italian Photoelectric Polarimeter


Astronomical x-ray polarimetry based on photoelectric effect with microgap detectorsPaolo 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. 164-184, 2001.

Not yet a viable instrument but a significant step forward


The first break-through the GPD 2001


Photoelectric polarimetry is feasible!

But still many limits: 1) Few pixels (500-1000) 2) Large pixels 20 m 3) High Noise (Front End Electronics far from the pixel) 4) 0�Electronics much larger than the detector

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

• 2003 - 2005

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.

The first X-ray polarimeter approved after many yearsThe Gravity and Extreme Magnetism Small Explorer


Pre-selected (with other 5 candidates) on may 2008Selected (with another candidates) on june 2009Stopped on august 2013 for unacceptable cost and schedule growth

Instead of re-starting the path to polarimetryacted as a stopper for 5 more years

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

~ 5.2 meters

We have a mission: IXPE Satellite

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 effective from 6 to 30 keV is feasible

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

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.

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.

Which polarimetry with extended energies

Scientific goal Sources < 1keV 1-10 > 10 keV

Acceleration phenomena

PWN yes (but absorption)

yes yes

SNR no yes yes

Jet (Microquasars) yes (but absorption)

yes yes

Jet (Blazars) yes yes yes

Emission in strong magnetic fields

WD yes (but absorption)

yes difficult

AMS no yes yes

X-ray pulsator difficult yes (no cyclotron ?)

yes

Magnetar yes (better) yes no

Scattering in aspherical geometries

Corona in XRB & AGNs

difficult yes yes (difficult)

X-ray reflection nebulae

no yes (long exposure)

yes

Fundamental Physics

QED (magnetar) yes (better) yes no

GR (BH) no yes no

QG (Blazars) difficult yes yes

Axions (Blazars, Clusters)

yes ? yes difficult

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.

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.

Or the Sun

Fabiani et al. 2012

the gas pixel detector yesterday, today and tomorrowawoxpol.u-strasbg.fr/all_talks/costa.pdf · the...

Documents