Transcript Polarimetria X

X-Ray Polarimetery: Science&Detecors
Enrico Costa
IAPS Roma
Enrico Costa, Paolo Soffitta, Fabio Muleri, Sergio Fabiani, …….
INFN Pisa
Ronaldo Bellazzini, Alessandro Brez, Luca Baldini, Gloria Spandre,
Massimo Miniuti, Michele Pinchera
UNIVERSITY of ROMA-3
Giorgio Matt, Stefano Bianchi
Collaboration for the optics
OSSERVATORIO ASTRONOMICO DI BRERA Milano
Gianpiero Tagliaferri, Giovanni Pareschi, Daniele Spiga
X-Ray Polarimetry:Science & Detectors - Beijing 21-2-14
Why Polarimetry? Digging in literature
Astrophysics
Acceleration phenomena:
• Pulsar wind nebulae
• μQSO
• Blazar and radiogalaxy
• Solar Flares
Emission in magnetic fields:
• Emission in strong magnetic fields: magnetic cataclysmic variables
• Emission in strong magnetic fields: accreting millisecond pulsars
• Emission in very strong magnetic fields: accreting X-ray pulsars
Scattering in aspherical situations
• X-ray binaries
• Radio-quiet AGN
• X-ray reflection nebulae
Fundamental Physics
Matter in Extreme Magnetic Fields: QED effects
Matter in Extreme Gravitational Fields: GR effects
Quantum Gravity
Search for axion-like particles
X-Ray Polarimetry:Science & Detectors - Beijing 21-2-14
Synchrotron: X-Rays vs other bands
Radio
Infrared
(VLA)
(Keck)
Optical
X-rays
(Palomar)
(Chandra)
In the Crab X-rays are emitted by synchrotron from freshely
accelerated electrons in magnetic fields.
X-Ray Polarimetry:Science & Detectors Beijing 21-2-14
Acceleration phenomena: μQSO
The polarization degree of the
SSC emission as a function of
the Lorentz factor of the
electrons θo is the angle
between the observer and the
magnetic field (from
Celotti&Matt, 1994).
The study of their time and energy-dependent
polarization properties (possibly combined with
simultaneous radio and optical polarization
measurements) can help shading light on jet
formation and evolution, and its relation to
accretion disk emission. These studies may also
be applicable to AGN (e.g. Mirabel 2007), but in
μQSO we have the possibility, thanks to the much
smaller time scales, to study their behavior over a
wide interval of accretion rates
X-Ray Polarimetry:Science & Detectors - Beijing 21-2-14
PWN The only polarized source already known known
Positive measurement: of Xray polarization of the Crab
Nebula without pulsar
contamination (by lunar
occultation, Weisskopf et
al., 1978).
P = 19.2 ± 1.0 %
 = 156.4o ± 1.4o
XEUSBut this is only the average measurement
structure is much more complex! To
p.s.f. The
perform separate polarimetry of details of
f.o.v.
PSR
NW jet
SE jet
Inner torus
Outer torus
the major structures we need imaging!
How turbulent is the field? How polarized is the PSR?
At much higher energies INTEGRAL finds
polarization oriented as the jet axix.
Morover we know from AGILE (confirmed by
Fermi) that the Crab (not the PSR) is varying
on the scale of days at E>100 MeV. These
corresponds to a physical region on the
arcsecond timescale!
Tavani et al. 2011
X-Ray Polarimetry:Science & Detectors - Beijing 21-2-14
Acceleration phenomena: Blazar and radiogalaxy
While the polarization angles of
synchrotron and SSC emission are
expected to be the same, and
perpendicular to the magnetic field
(Celotti & Matt 1994), in the external
photons model the IC polarization is
related to the jet axis (Begelman & Sikora
1987), and the polarization angle in the two
peaks needs no longer to be the same. In
both models, the polarization degree (see
Figure 2) is expected to be very high, up to
50% or more unless the electrons
responsible for the IC emission are hot
(see also Poutanen 1994).
X-Ray Polarimetry:Science & Detectors - Beijing 21-2-14
Acceleration: SNR
In SNR the high energy tails show a non
thermal emission, in the front regions of
the shock. This could also be singed out
by polarimetry, depending on how mch the
magetif fields are ordered.
X-Ray Polarimetry:Science & Detectors - Beijing 21-2-14
Another case of extended source: reflection nebulae
SgrB2 is a giant molecular cloud at 100pc
projected distance from SgrA
The spectrumof SgrB2 is pure reflection spectrum
Reflection of what?
No bright enough
source is there
The emission from
SgrB2 is extended and
brighter in the direction
of SgrA,Murakami 2001
Rashid Sunyaev suggested
that SgrB2 is reflecting the
emission from the Black Hole
in SgrA as it was a few
hundred years ago.
Integral Image of GC, Revnivtsev 2004
X-Ray Polarimetry:Science
& Detectors
Enrico Costa – X-Ray Polarimetry
– Tsinghua Global Vision
Lectures -– Beijing December 6 2011
When Our Galaxy was an AGN
Definitely imaging is needed
also in this case
X-Ray Polarimetry:Science & Detectors - Beijing 21-2-14
Emission in very strong magnetic fields: magnetic NS
Spectropolarimetry may constraint the accretion geometry.
Electron (in strong B) or proton (in extreme B) cyclotron lines
may
X-Ray Polarimetry:Science &
Enrico Costa – X-Ray Polarimetry
– Tsinghua
Global
Vision Lectures – Beijing December 6 2011
Meszaros
et
al. (1988)
Detectors
- Beijing
21-2-14
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
Enrico Costa – X-Ray Polarimetry – Tsinghua Global Vision Lectures – Beijing December 6 2011
The Spin of Black Holes:a 4th method
X-Ray Polarimetry:Science & Detectors - Beijing 21-2-14
Fundamental parameters
Unpolarized
Every polarimeter is composed of
an analyzer, a stage where an
interaction occurs, whose
outcome angle depends on
polarization,
and a detector of the products
of the interaction, capable to
measure their angular
distribution.
Polarized
X-Ray Polarimetry:Science & Detectors - Beijing 21-2-14
Fundamental parameters
Fit function:
Modulation:
Polarization:
=
is the modulation factor, i.e. the modulation
for 100% polarized radiation
X-Ray Polarimetry:Science & Detectors - Beijing 21-2-14
Basic Statistics
Martin C.Weisskopf, Ronald F. Elsner, Victoria M. Kaspi,
Stephen L. O’Dell,
George, G. Pavlov, and Brain D. Ramsey: X-Ray Polarimetry
and Its Potential Use for Understanding Neutron Stars
Minimum Detectable Polarization (99%):
If background is negligible:
To reach MDP=1% with µ=0.5:
Source detection:
Source spectral slope:
Source polarimetry:
= 736 103 ph
>10 ph
>100 ph (for continuum)
>100,000 ph
Polarimetry is a matter of number of photons
Long observations and/or large area are needed
X-Ray Polarimetry:Science & Detectors - Beijing 21-2-14
Which Detectors for X-ray Polarimetry
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
X-Ray Polarimetry:Science & Detectors - Beijing 21-2-14
Polarimetry by Diffraction at ~ 45°
Traditionally (35 years ago!) only polarimeters based on Bragg
diffraction aroud 45°. Rocketts, OSO-8
Bragg Diffraction at > 2 keV is nowadays overruled by photoelectric
polarimeters. At energies < 1 keV is still the only viable technique.
Due to thre need of rotation and of long dedicated pointing is a
typical application for a (very) small dedicated satellite.
Lightweight Asymmetry and
Magnetism Probe (~250eV)
(Tsinghua, Tongji, INAF, INFN)
Pulsars
To measure the geometry of B-field
To constrain the equation of state
Be able to identify “bare quark stars”
Jets in Blazars
—
To measure the B-field in the X-ray jet
Black hole binaries and AGNs
—
To measure the disk inclination and help constrain BH
spin
Also H.Marshall at MIT is working on proposals based on bragg diffraction
X-Ray Polarimetry:Science & Detectors - Beijing 21-2-14
The dominant technique in soft/medium range for
focal plane: the Photoelectric Polarimeter
X-Ray Polarimetry:Science & Detectors - Beijing 21-2-14
The same concept Two different implementations
The TPC has:
• is more sensitive, at last down to levels where the source exceeds
the backround (.2mCrab for GEMS)
• Can have an exit window for photons that have not been detected.
The GPD has:
• Imaging capability (80µm for parallel 80µm for parallel beam 100µm
for a typical X-ray optics)
• No need of rotation
• Better control of systematics
• More margin vs the background
• Low power (2W the GPD; 12W the BEE)
• It is light (GPD+Buffle+Filter Wheel+Mech.IF = 3.3 kg from IXO
study) and since is connected to the BEE with a flexi cable it can be
mounted on a sliding device
X-Ray Polarimetry:Science & Detectors - Beijing 21-2-14
OUR DETECTOR
X-Ray Polarimetry:Science & Detectors - Beijing 21-2-14
MORE RECENT EVOLUTION
For the ESA M3 proposal New Hard X-ray Mission (a competitor of
GRAVITAS) we prototyped a hard X-ray detector based on a thicker
absorption gap filled with Argon at higher pressure. We found some
irregularities in the electric field that would produce a distrotion of the
image and spurious polarization.
It was clear (not surprisingly) that to increase the thickness of the
detector we had to make larger electrodes. So we changed our design:
80 g
300 g
X-Ray Polarimetry:Science & Detectors - Beijing 21-2-14
GPD spatial resolution – Uniform drift field
He 20% – DME 70% 1 bar 1 cm
Titanium fluorescence @ 4.5 keV + Brem.
0.3 mm
0.3 mm
FWHM 82 mm
X-Ray Polarimetry:Science & Detectors Beijing 21-2-14
Modulation factor
2.6 keV
Energy
Modulation factor
2.6
26.68 +/- 0.42
4.5
42.75 +/- 0.24
6.4
52.44 +/- 0.31
X-Ray Polarimetry:Science & Detectors Beijing 21-2-14
Spurious modulation and energy resolution
125 kcounts:
Modulation factor:
~50%
Spurious modulation measured:
~0.54%
Spurious polarization measured: ~1%
MDP 99% with m=50% and 125 kc: ~ 2.3%
X-Ray Polarimetry:Science & Detectors Beijing 21-2-14
Last attempt: XIPE proposed as ESA SM
X-Ray Polarimetry:Science & Detectors - Beijing 21-2-14
2 JET-X telescopes
One of these telescopes is the
optics of Swift XRT.
Cannot image better qualification
X-Ray Polarimetry:Science & Detectors - Beijing 21-2-14
X-Ray Polarimetry:Science & Detectors - Beijing 21-2-14
XILPE after XIPE not selected
XIPE was submitted at the first AOO for an ESA small mission
Good evaluation by ESA from the feasibility and readiness. Weak only
from the budget point of view. An ecellent rating by Physics Science
Working Group. Rated 2d by Astrophysics Working Group
CHEOPS (exoplanets photometry) was selected
In response to the ESA-CAS announcement we propose XILPE: a Ligth
(=descooped) version of XIPE.
No solar polarimeters. One telescope only.
We hope to fit the (very tight) boundaries fixed by the
announcement.
To define the chinese contribution. A collaboration with Tsinghua
University is already active on detectors. Optics could be another
area of interest. A.o.b. is on the table.
X-Ray Polarimetry:Science & Detectors - Beijing 21-2-14
Test at PANTER facility
We tested the GPD with one JET-X telescope at Panter Facility of Max
Planck in Munich.
Results are very encouraging for the imaging.
For the search of systematics the statistic is still poor
With a CCD the resolution (HPW) is 16 arcseconds. The efficiency is the
same it was 10 years ago.
With a GPD the resolution (HPW) is 23 arcseconds. Exactly what
expected from the space resolution and the blurring due to the inclined
penetration in the detector. But it is measured not simulated!.
X-Ray Polarimetry:Science & Detectors - Beijing 21-2-14
The telescope performs as predicted
With a GPD the resolution (HPW) is 23 arcseconds. Exactly what
expected from the space resolution and the blurring due to the
inclined penetration in the detector.
But it is measured not simulated!.
X-Ray Polarimetry:Science & Detectors - Beijing 21-2-14
Off-axis performance
X-Ray Polarimetry:Science & Detectors - Beijing 21-2-14
Do we really need imaging? Extended Sources
Supernova Remnants Supernova Remnants (SNRs) are believed to be
the acceleration sites of cosmic rays up to 1015 eV. While the line
emission makes it possible to determine the state of ionization of its
thermal plasma, the lack, or the weakness, of emission lines is
generally believed to be due to acceleration mechanisms responsible
for the synchrotron emission or non thermal Bremsstrahlung.
Moreover, TeV emission from some SNRs supports the idea that in
some regions, electrons are energized at least up to TeV. Imaging
polarimetry in this regard is useful to localize the regions of shock
acceleration and to measure the strength and the orientation of the
magnetic field at these emission sites (Vink (2012)).
Probing the regions where thermal or nonthermal plasma is emitting in
X-rays is particularly important in SNRs like Cas A or Tycho (see e.g.
Araya and Cui(2010).
Pulsar Wind Nebulae Spatially resolved X-ray polarimetry allows the magnetic field orientation in the torus, in the jet
and at various distances from the pulsarto be determined. This makes it possible to evaluate the level of turbulence
and instabilities exploring the acceleration mechanism responsible for the observed particle distribution (Shibata et
al (2003); Volpi et al (2009)). XIPE reaches an MDP of 2% in 5 × 5 angularly resolved regions of the Crab Nebula in
105 s of observing time thanks to its imaging capability. The capability to resolve the surrounding nebula makes the
emission model to be derived and compared for example with those studied in optical band (Harding (2005)). A few
additional PWNs will be accessible to XIPE for comparative measurements (see fig. 1).
More extended sources are Galaxy Clusters that should be unpolarized by definition. Beside the search for nonthermal component present in a few (such as A2256), they could be a good screen to search for polarization
introduced by photon-axion conversion (Bassan,Mirizzi,Roncadelli 2010) in intergalactic magnetic fields.
X-Ray Polarimetry:Science & Detectors - Beijing 21-2-14
Angular resolved polarimetry of Crab
We simulated a long observation
of Crab with XIPE. We blurred
the Chandra image to account for
the limited resolution of XIPE.
The major features are still
visible. We computed the
sensitivity to the amount and
angle of polarization for different
selected regions of the nebula.
Fabiani et al. ApJ under
review.
X-Ray Polarimetry:Science & Detectors - Beijing 21-2-14
Angular resolved polarimetry of CAS-A
X-Ray Polarimetry:Science & Detectors - Beijing 21-2-14
With the equation of sensitivity we can scale from XIPE to XILPE
X-Ray Polarimetry:Science & Detectors - Beijing 21-2-14
A medium energy polarimeter for multilayer optics?
We built a first prototype of the so-called Medium
Energy Polarimeter (MEP). As mentioned before the first
attempt by only increasing the thickness and pressure
failed because of irregulariries in the electric field.
A second attempt was performed with the new design of
detector. The new prototype was well performing from
the point of view of uniformity, and of the energy
resolution but in a few weeks showed a decay of the
spectral performances, evidence of a leak.
Notwithstanding we could still measure a modulation in
response to a polarized beam not far from that
predicted.
We are confident that by repearing the detector it will
work nominally. Moreover the Monte Carlo simulations are
usually more reliable at higher energies.
Photoelectrons from 22 keV photons
The MEP with 3cm
absorption/drift gap and 3
Atm pressure of Ar/DME
mixture should be very
effective from 5 to 30 keV.
X-Ray Polarimetry:Science & Detectors - Beijing 21-2-14
A high energy focal plane polarimeter
Fabiani et al. ExA 2013
X-Ray Polarimetry:Science & Detectors - Beijing 21-2-14
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.
X-Ray Polarimetry:Science & Detectors - Beijing 21-2-14
How can we contribute to XTP?
An Xray optics 2-10 keV would improve the XIPE performance (MDP) as
the √ of the Area. With a focal of 4m the angular resolution would be
dominated by the telescope for HPW>30 arcseconds.
XTP area should be around 20 times XILPE area
The 2 available JET X telecopes with a LEP in the focus could be added
to XTP. The mass resource needed is aroiund 200 kg. If readiness is
important whatever already exists is specially wellcome.
We could also study the possibility to substitute the baseline window of
Be with a thin window so that the detectors would provide an extension
down to .15keV (images and spectra only not polarimetry below 1.5 keV)
MEP detectors could fit the focalplane of M/L telescopes. Of course the
competitivity of imaging requires an adequate resolution of the optics.
X-Ray Polarimetry:Science & Detectors - Beijing 21-2-14