1. Meeting agenda 10:00 10:10 Welcome : Enrico Costa Chair : Enrico Costa
10:10 10:50 Towards XIPE proposal for M4 : Paolo Soffitta
10:50 11:10 Telescopes for XIPE : Gianpiero Tagliaferri
11:10 11:30 Science with XIPE : Fabio Muleri
11:30 11:50 Coffee break
11:50 13:00 who is doing what : participants involved with deliverable
items or major activities can present their contribution,
their team and the expected status of endorsements
13:00 14:00 Lunch break
14:00 15:30 Discussion
XIPE vs other proposals IXPE, ESA-CAS ?
Structure of the team : Instrument team and science team ?
Contribution extra-ESA ?
15:30 16:00 Coffee break
16:00 17:00 Next actions for the proposal
Bus ? POLARIX phase A Study.
P/L ? POLARIX/XIPE
Science ? (Do we follow the scheme of XIPE ? (TBV))
Ground Segment ? (Ground Station, MOC, SOC, SDC).

2. Towards XIPE proposal for M4
P. Soffitta IAPS/INAF

3. A brief History of Polarimetry
First experiments born with X-ray Astronomy
Rocket flight on April 1969 to search for polarization n the Crab Nebula (Wolff, 1970).
Rocket flight on July 1969 to search for polarization in Sco X-1 (Angel et al., 1969).
Rocket flight on 1971 (larger version) in combination with a Bragg polarimeter.
Ariel 5,
OSO-8,

4. SXRP (Stellar X-ray Polarimeter)
A step forward in the sensitivity was done devising and building a polarimeter based on Bragg diffraction and Thomson scattering in the focus of a large X-ray telescope.
Photons coming from the SODART telescope are diffracted by a thin mosaic graphite crystal at 2.6 keV and 5.2 keV creating a secondary focus. The photons at E > 5 keV that do not satisfy the Bragg condition pass through and are diffused around by a lithium scatterer. 4 position sensitive proportional counters detect simultaneously the radiation. SXRP is in rotation around the telescope axis.
Bragg diffraction saves the images and is more sensitive at low flux, Thomson scattering provides better sensitivity at large fluxes but the image is lost.
4 x 100 cm2 imaging proportional counter
Composite window thickness :
150 m for Thomson scattered photons
50 m for Bragg diffracted photons, ø = 3.3 cm )
Graphite mosaic cristal (50 m thick)
Lithium scatterer 7 cm long and Ø = 3 cm encapsulated in 150 m thick beryllium case
Rotary motor for the ensamble detector/analyser at 1 rpm
T=105 s.
Kaaret et al., SPIE 1989, Soffitta et al., NIM A, 1998

5. The missions where the GPD was proposed either are waiting after a phase A completed or were not selected or evolved in missions without anymore a polarimeter on-board.
POLARIX (2008)
Costa et al., ExpAst 2010
IXO
NHXM
Bookbinder, SPIE, 2010
Tagliaferri et al, ExpAst 2010

6. Two approaches
The photons enters perpendicularly with respect to the readout plane.
The photons enter parallel with respect to the readout plane.

7. We therefore proposed XIPE the X-ray Imaging Polarimetry Explorer
GEMS
Three telescopes were des-cooped in two telescopes and eventually the mission was discontinued in 2012 by NASA for ‘programmatic’ reason
We therefore proposed XIPE the X-ray Imaging Polarimetry Explorer

8. Energy Range = 2-10 keV

9. ESA-Small mission results
High scientific level (first priority of the PSWG)
Too costly/complex for an ESA S-mission
Eventually CHEOPS was selected but with a large contribution of a Swiss Space Agency

10. M4-call Cost-Cap : 450 M€ CaC hard boundary
Suggested mission parameters : M_S/C < 800 kg
M_P/L < 300 kg
TRL > 5-6 (ISO scale)
In-orbit operation : < years
CaC target implies an ESA industrial contract in the range of ~ 200 M€ (e.c. 2014) for
the space segment, including any ESA provision of payload elements.
From ESA debriefing Procurement of ESA funded P/L items will be done by ESA
Launch Definition and preparation phase yrs, Spacecraft development yr
Proposal are subdue to strict and technical evaluation prior to scientific evaluation
LoE must explicitly state the availability of the proposed partner to support a study phase and to undertake the necessary step to secure the funding necessary for the development and implementation phase.

11. For the M4 call we propose an evolution of XIPE presented at the S-1 ESA call based on the design of POLARIX
JET-X mirrors are too heavy due to the old technology. New mirrors with much larger effective areas and lower weight are available.
Drop the solar GPD which add complexity to the project.
Simple payload.
Break-trough in performances.
Area 6 times the area of XIPE (S-1)
Area 4 times the area of POLARIX

12. Rely on studies done for POLARIX (Phase A completed on 2008).
Vega Fairing
Study by Thales Alenia Space, Turin

13. Main components of the focal plane instruments.
3 Gas Pixel Detector Filled with He-DME atm 1-cm
3 Back End Electronics
3 Filter Wheel
1 Control Electronics

14. Focal plane
U.Valencia/INTA (V. Reglero, L. Sabau-Graziati

15. Filter wheel Filter wheel : fully open and a
fully closed position (for internal background monitoring),
beryllium filter for bright-source count rate reduction,
a diaphragm position for obscuring a portion of the field-of-view,
three calibration sources’ positions. The calibration sources will be both polarized,
through Bragg diffraction, and unpolarized (two sources).
Polarized calibration source at 2.6 keV and 5.9 keV .
The filter wheel will be provided by MSSL (S. Zane)
and the calibration sources by IRAP (J.L. Atteja)

16. Detectors

17. Photoelectric effect β =v/c
Polarimetry based on photoelectric effect was tempted very long ago but it is now a mature technology.
An X-ray photon directed along the Z axis with the electric vector along the Y axis, is absorbed by an atom.
The photoelectron is ejected at an angle θ (the polar angle) with respect the incident photon direction and at an azimuthal angle φ with respect to the electric vector.
If the ejected electron is in ‘s’ state (as for the K–shell) the differential cross section depends on cos2 (φ), therefore it is preferentially emitted in the direction of the electric field.
Being the cross section always null for φ = 90o the modulation factor µ equals 1 for any polar angle.
Heitler W.,The Quantum Theory of Radiation
Costa, Nature, 2001
β =v/c
By measuring the angular distribution of the ejected photoelectrons (the modulation curve) it is possible to derive the X-ray polarization.
X-ray polarisation - a window about to open? Stockholm August 2014

18. X-ray polarimetry with a Gas Pixel Detector
A photon cross a Beryllium window and it is absorbed in the gas gap, the photoelectron produces a track. The track drifts toward the multiplication stage that is the GEM (Gas Electron Multiplier) which is a kapton foil metallized on both side and perforated by microscopic holes (30 um diameter, 50 um pitch) and it is then collected by the pixellated anode plane that is the upper layer of an ASIC chip.
GEM electric field
1-cm drift, 1-bar.
He-DME (20-80) 2-10 keV.
pixel
GEM
20 ns
X photon (E)
PCB
conversion
gain
collection
Costa et al., 2001, Bellazzini et al.2006, 2007
Polarization information is derived from the angular distribution of the emission direction of the tracks produced by the photoelectrons that brings memory of the X-ray polarization. The detector has a very good imaging capability.
8/26/2014
X-ray polarisation - a window about to open? Stockholm August 2014

19. 400 g detector, 1.4 kg electronics and box 5 W power consumption
A new prototype with an extended GEM for better drift field uniformity
Mixture filling
He 20% + DME 80% 1 bar
Gas cell thickness
1 cm
GEM
50 um pitch, 50 um thick, 88 x 88 mm
Electronics
NEW
Beryllium window
9 cm
Titanium Frame
OLD
400 g detector, 1.4 kg electronics and box 5 W power consumption
Same window, same ASIC with a larger GEM plane (larger guard ring).
X-ray polarisation - a window about to open? Stockholm August 2014
8/26/2014

20. Modulation curves and their analysis
2 keV 1st step
3.7 keV 2-step
Counts
Phi (Rad)
X-ray polarisation - a window about to open? Stockholm August 2014
8/26/2014

21. Modulation factor measurements and simulationsMC
8/26/2014
X-ray polarisation - a window about to open? Stockholm August 2014

22. GPD Energy Resolution Filling date: 4th November 2011 July 2014 2 keV
8/26/2014
X-ray polarisation - a window about to open? Stockholm August 2014

23. Images of collimated beams
2.3 keV
4.5 keV
2.3 keV
8.0 keV
300 mm shift
8/26/2014

24. XIPE proposed as ESA SM1 AOO
2 X-ray Telescopes From the JET-X Program
GPD detectors already sudied for XEUS and IXO Program
The standard bus of IRIDIUM Program
PANTER X-ray test facility.
Frontier Research in Astrophysics Mondello Marzo 2014

25. The imaging properties of the GPD.
Panter X-ray facility (MPE, Germany):
JET-X (Telescope, same as Swift, ~1mm/arcmin)
Focal Length (3.5 m)
JET-X HEW (4.5 keV, 4.5 keV) : 18’’
JET-X + GPD (HEW) : 23.2’’ (394 m )
Spiga et al., 2013, Fabiani et al. 2014
IAPS/INAF laboratory :
Very narrow pencil beam.
Detector shifts : 300 m.
Position resolution : 30 m (rms).
Half Energy Width : 93 m
Imaging properties driven by the optics.

26. GPD imaging performances @ PANTER
‘In’ and ‘out’ focus
PSF fitting
Fabiani et al., 2014
GPD imaging PANTER
8/26/2014
X-ray polarisation - a window about to open? Stockholm August 2014

27. Stability
Energy resolution
Modulation Factor

28. Frame size and pixel size

29. Back-End Electronics INFN-Pisa, R. Bellazzini
Distribute and filter the power supply required to the low voltage front-end electronics;
Supply the detector with all the high voltages needed (HV, PAS/Wroclaw, S. Gburek)
Manage the Front-End Electronics;
Digitally convert the analog output of the FEE (ADC function);
Store auxiliary information related to each event (e.g. X,Y coordinates of the ROI corner);
Time-tag the events with at least 8µs of resolution and 50µs of accuracy w.r.t. the Universal Time (UT);
Digitally perform some basic processing (pedestal calculation, suppression of not-fired pixels)
Temporarily store the converted data (both from ASIC and GEM);
Transmit to the PEB the science data to be processed;
Integrate some HK and Science Ratemeters related to the detectors activity (e.g. good event, rejected events, …);
Provide Instrument HK to the CE for active monitoring and telemetries purposes.
Implement the Peltier Driver for the detector temperature control .
INFN-Pisa, R. Bellazzini

30. Information passed from the GPD to the Back End Electronics
Digital information :
Coordinates of the opposite vertices of the frame that contains the track
Analogue information:
Analogue information of the charge content in each pixel.
A 5-Mhz clock is used to get the analogue data from the GPD
Expected Data rate from 1 GPD to BEE (for Crab) : 250 c/s x 700 pixels about200 kHz

31. Control Electronics
Three serial interface with the three instrument to:
configure the corresponding Back-End and Front-End unit;
manage the digital HK periodic acquisition
retrieve the science data
manage one multiplexed differential analog line to periodically acquire the analog HK of each instrument (voltages, currents, temperatures,…). We assume to acquire up to 16 (TBC) analog values (already conditioned inside the BE box);
manage three dedicated interrupts lines to trigger the science data retrieval of the already pre-processed data from the BEE;
manage one filter wheel for each detector (the presence of this wheel is TBC).
Drive one Peltier driver (inside the Back-End) for each instrument, to implement the detector thermal controls with an accuracy of 2°C;
Manage the non regulated primary power bus in order to carry out all the secondary voltages needed by the unit (LV, PAS/Wroclaw, S. Gburek)
manage one MIL-1553 A&B data interface with the spacecraft. This link is used to get TC from the Spacecraft and to send both Science and HK telemetry packets.
Manage the Pulse Per Second synchronization signal line in order to perform the event time-tagging with the required accuracy (50µs);

32. Data Format to Telemetry

33. Expected data rate Analysis on-board ? X-band ? Memory size.
For a bright source like the Crab the expected data rate is :
3 x 200 ev/s x 1 kbit/ev = bit/s
With S band we need about 10 passages to download 10 E4 s of Crab observation
Analysis on-board ?
X-band ?
Memory size.

34. Analysis on-board Studied for IXO (5000 c/s)
U. Tuebingen A. Santangelo, C. Tenzer

35. Mass at launch 925 kg.
P/L mass 335 kg (mirror module 285 kg).

36. See Gianpiero’s slides.
We can save weight with optics made with new technologies that provide much larger effective area with respect to JET-X.
See Gianpiero’s slides.

37. IAPS-Rome facility for the production of polarized X-rays.
Calibration issues : Stand alone calibration
IAPS-Rome facility for the production of polarized X-rays.
Close-up view of the polarizer and the Gas Pixel Detector
Facility at IASF-Rome/INAF
keV Crystal Line Bragg angle
ADP(101) CONT
PET(002) CONT
Rh(001) Mo Lα
Graphite CONT
Al(111) Ca Kα
CaF2(220) Ti Kα
LiF(002) Fe
Ge(333) Cu Kα
FLi(420) Au Lα
Fli(800) Mo Kα
Capillary plate (3 cm diameter)
Aluminum and Graphite crystals.
Spectrum of the orders of diffraction from the Ti X-ray tube and a PET crystal acquired with a Si-PiN detector by Amptek
PET
(Muleri et al., SPIE, 2008)
8/26/2014
X-ray polarisation - a window about to open? Stockholm August 2014

38. Calibration issues End to end calibration
End to end calibration at PANTER with polarized X-ray source
(KOH; Si, Graphite crystal) at energies around 2-3 keV
End to end calibration with un-polarized sources (difficult!).
End to end calibration of imaging properties and gain
At PANTER with add-on from Tsinghua University at higher energies ?
Vadim Panter will take care of end-to-end calibration.

39. Background issues
The diffused X-ray background is negligible at the flux level of sources for polarimetry.
The residual backgrounds in 30’’ PSF is 1.3E-6 c/s according to A. Bunner (Ap.J 1978) estimates (Ne-filled proportional counter).
Background issues and rejection techniques will be studied by M. Pearce (KTH, Stockholm)

40. XIPE and other missions of X-ray polarimetry
ESA-CAS
XIPE-Light telescope 2.1 m focal length 1 GPD
Call will be issued at the end of this year or at the beginning of next year
(Everybody is invited to participate : P.Is. G. Matt and Hua Feng
At NASA
At least three missions for this SMEX Call :
IXPE : Imaging X-ray Polarimetry Explorer (many of us are participating(MSFC, IAPS/INFN).)
GEMS : 2 TPC’s detectors and two optics (NASA/GSFC).
EXCALIBUR-Like : One Thomson polarimeter 1 NuSTar optics (U. Washington-S, Louis)
Wide Field Polarimeter for GRB : (U. New Hampshire, M. Mc Connel)
At JAXA
PolariS : hard-X-ray optics with Compton polarimeters

41. -Optics : ESA, OAB (Italy, G. Tagliaferri)
Who is doing what
-Optics : ESA, OAB (Italy, G. Tagliaferri)
-GPD : University of Helsinki (Finland, J. Huovelin), INFN-Pisa (Italy, R. Bellazzini)
-Gas filling optimization : Tsinghua University (China, Hua Feng)
-Filter Wheel : Mullard Space Science Laboratory (UK, S. Zane)
-Polarized and unpolarized X-ray source : IRAP (France, J.L. Atteja)
-Background issues : KTH (Sweden, M. Pearce)
-Back End Electronics : INFN-Pisa (Italy, R. Bellazzini)
-HV/LV : SRC/PAS (Poland, S. Gburek)
-Control Electronics + EGSE : Tuebingen University (Germany, A. Santangelo, C. Tenzer)
-Science Console : IAPS/INAF (Italy, F. Muleri)
-Focal plane mechanical structure : Valencia University/INTA (Spain, V. Reglero, L.Sabau-Graziati)
-GPD stand alone calibration : IAPS/INAF (F. Muleri) INFN-Pisa (R. Bellazzini)
-END to END calibration : PANTER (V. Burwitz) with contribution from China ? (Hua Feng)

42. Main components of the focal plane
ITEMS kg no. (to be multiplied by)
GPD :
FW :
BEE :
CE :
(1 item) POWER
GPD : 2 W (included Peltier with 1.4 W)
FW : 6 W (rarely activated: 0 in Stand-By)
BEE : W (included 70 % DC/DC efficiency)
CE : W in Stand-by [70 % DC/DC efficiency] + Memory Power Consumption
(for example for IXO (16 GB) the total CE power = W
for XIPE we foresee much less needed memory).

43. End