- Email: [email protected]
XIPE, the X-ray imaging polarimetry explorer: Opening a new window in the X-ray sky
Author’s Accepted Manuscript XIPE, the X-ray Imaging Polarimetry Explorer: opening a new window in the X-ray sky Paolo Soffitta
www.elsevier.com/locate/nima
PII: DOI: Reference:
S0168-9002(17)30209-7 http://dx.doi.org/10.1016/j.nima.2017.02.025 NIMA59655
To appear in: Nuclear Inst. and Methods in Physics Research, A Received date: 30 November 2016 Accepted date: 10 February 2017 Cite this article as: Paolo Soffitta, XIPE, the X-ray Imaging Polarimetry Explorer: opening a new window in the X-ray sky, Nuclear Inst. and Methods in Physics Research, A, http://dx.doi.org/10.1016/j.nima.2017.02.025 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
XIPE, the X-ray Imaging Polarimetry Explorer: opening a new window in the X-ray sky Paolo Soffitta for the XIPE collaboration✩ IAPS/INAF Via Fosso Del Cavaliere 100 00133 Roma
Abstract XIPE, the X-ray Imaging Polarimetry Explorer, is a candidate ESA fourth medium size mission, now in competitive phase A, aimed at time-spectrallyspatially-resolved X-ray polarimetry of a large number of celestial sources as a breakthrough in high energy astrophysics and fundamental physics. Its payload consists of three X-ray optics with a total effective area larger than one XMM mirror but with a low mass and of three Gas Pixel Detectors at their focus. The focal length is 4 meters and the whole satellite fits within the fairing of the Vega launcher without the need of an extendable bench. XIPE will be an observatory with 75% of the time devoted to a competitive guest observer program. Its consortium across Europe comprises Italy, Germany, Spain, United Kingdom, Switzerland, Poland, Sweden Until today, thanks to a dedicated experiment that dates back to the ’70, only the Crab Nebula showed a non-zero polarization with large significance [1] in X-rays. XIPE, with its innovative detector, promises to make significative measurements on hundreds of celestial sources. Keywords: X-ray, Polarimetry, Detectors, Optics 1. XIPE Payload XIPE instrumentation derives from the phase A for POLARIX [2]and XEUS/IXO [3]. More similar to POLARIX (see fig.1(a)), it comprises three new optics made with the technology of replication of nickel electroformed thin-shells. Thirty ✩ The
XIPE collaboration is shown in http://www.isdc.unige.ch/xipe/
Preprint submitted to Journal of LATEX Templates
February 16, 2017
5
shells feature a double-cone approximation of the Wolter-I profile with 300 mm of parabolic segment plus 300 mm of hyperbolic segment. The instrument is composed of three Detector Units (DUs) consisting of three gas Pixel Detectors, clocked at 120◦ , each one equipped with a Filters and Calibration Wheels (FCW) and a Back End Electronics Units (BEEs). Moreover one Instrument
10
Control Unit (ICU) serves the DUs and provide the data interface with the spacecraft. A fixed focal length of 4 meters allows for fitting XIPE into the fairing of the Vega launcher (see fig. 1(a)). Each GPD is filled with a mixture of He-DME (20 % - 80 %) at 1-bar with 1 cm of drift length, a result of the studies performed for finding the
15
optimal mixture/configuration in the classical energy band (2-10 keV). The GPD temperature is stabilized between 5◦ C and 25◦ C at the level of 1◦ C by a Peltier cooler. The FCW, on top of it, is equipped with a set of calibration sources including one with a known high polarization degree and some unpolarized sources to check the absence of spurious modulation. Further diaphragms and
20
filters allow for optimizing the observation. A closed position allows for safety and for gathering the internal background. The FCW features a total of 8 positions. The GPD and its performances as an imaging X-ray polarimeter. The detector consists of a [4, 5, 6] sealed gas cell 9 cm × 9 cm large but sensitive only in the
25
central 1.5 cm × 1.5 cm. Prior of the final assembly, an ASIC-CMOS, developed at this aim, is internally bonded to the KYOCERA package in turn soldered on the circuit printed board at INFN. Oxford Instrument Analytical Oy (Finland) glues the Gas Electron Multiplier (GEM) with its supporting frame on the KYOCERA package. The Gas Cell, mainly consisting of a MACOR spacer, is
30
assembled onto this package resulting in a clean operative environment. A 50 µm thick low radioactivity beryllium window is glued onto a titanium frame in turn glued onto the spacer. Finally the cell is baked, filled with the purified and controlled gas mixture and sealed. The top layer of the multi-layer ASIC is an hexagonally patterned (105400 pixels, 50 µm pitch) collection plane. Below
2
35
each pixel there is a complete analogue chain as a front-end electronics. A set of local (four pixels) triggers define the region of interest that includes the collected track. Only a fraction of pixels (600-800) are serially readout and A/D converted thus dramatically minimizing the dead-time fraction. Out of three generations of ASICs produced, the current ASIC is the latter and the first
40
self-triggered one. Three years of operation showed a modulation factor and an energy resolution basically constant with time. Long term space missions are therefore guaranteed. The modulation factor is found in agreement with the Monte Carlo expectations and a cut on 20 % of data independent on energy allows for the best sensitivity. The energy resolution is found compliant with
45
the requirement of 20 % (point source) and 25 % extended sources. Details on these performances are included in [7]. Thanks to the structure of the readout plane, and to the reconstruction algorithm for the evaluation of the impact point (and the emission direction that provides polarization) from the resolved track, the imaging capabilities (HEW) are at level of 90 µm. They were determined
50
either in laboratory with a narrow pencil beam [8] and at the PANTER X-ray test facility (see fig. 1(b) [9]) with a real X-ray optics showing that the main contribution is provided by the performance of the optics and not that of the detector. The second contribution for importance is provided by the inclined penetration of the photons in the 1-cm thick drift region, while the intrinsic
55
position resolution of the detector provides a negligible contribution. We note here that the GPD met the strict requirements for operating in high vacuum and in the clean environment of the PANTER X-ray test facility. Moreover the GPD undergone to environmental test (Vibration: random and sinusoidal, thermal and thermo-vacuum tests, survival with heavy Fe ions) allowing ESA
60
for assigning to the GPD a TRL of 6 during the IXO phase A. The XIPE foreseen performance are shown in table 1:
3
(a)
(b)
Figure 1: (a). XIPE in the Vega Launcher(b). Real images with the GPD at the focus of JET-X optics.
2. Astrophysical goal X-ray polarimetry allows for studying Black hole, Neutron stars and White Dwarf binaries in their different physical conditions, due to the possible variable 65
presence of jets, of coronae and of accretion disks. These studies permit to improve our knowledge on the geometry of the systems and the physical processes at work. In addition X-ray imaging polarimetry allows for meaningful studies of a much larger classes of sources. Indeed imaging provides the following benefits: (1) reduced background and the consequent smaller flux limit (allowing
70
for measuring polarization of AGNs and of the dim magnetars) with respect to other non imaging techniques. Background discrimination is possible due to the application of the background rejection techniques based on track morphologies. Furthermore imaging permits to measure the background during the observation; (2) Identification and measurement of possible multiple celestial sources
75
in the Field of View during observation of crowded regions; (3) Angularly resolved polarimetry for extended sources as shell-like Supernova Remnants and
4
Table 1: The characteristics of XIPE.
Polarization sensitivity
1.2 % MDP for 2x10−10 erg/s/cm2 (10 mCrab) in 300 ks
Spurious polarization
< 0.5 % (goal: < 0.1 %)
Angular resolution
< 26 arcsec
Focal length
4m
Field of view.
12.9 × 12.9 arcmin2
Spectral resolution
16 % @ 5.9 keV. Resolution 8 µs
Timing
Dead Time 180 µs
Stability
> 3 yr
Mirror wall materials
Electroformed NiCo
Mirror coating
Iridium plus Carbon
Energy range
2-8 keV
Background
1.7 10−5 c/s or 34 nCrab
Pulsar Wind Nebulae. This capability allows for mapping magnetic fields and for studying acceleration mechanisms at the emission site. Moreover studies of cluster of Galaxies could probe the possible existence of Axion-Like Particles. 80
One example where imaging is crucial, is the observation of X-rays from cold molecular clouds in the Galactic Center region. These clouds are emitting Xrays, perhaps, because they are scattering now the radiation coming from a past flare from Sgr A*. Sgr A*, a massive black hole in the Galactic Center, could have been, few hundreds years ago, a dim AGN and 106 brighter than today.
85
This region is crowded (see figure 2), moreover these targets are faint, extended and embedded in an X-ray emitting thermal plasma which dilutes polarization. Notwithstanding this, with the imaging capability of XIPE, is possible to measure the polarization angle that pinpoints to the origin of the illuminating radiation with sufficient accuracy for probing this hypothesis [10]. Moreover
5
90
the concurrent presence of different complexes of clouds, at different putative distances, allows for making a tomography of the Galactic Center region. In fact the true distance of these clouds from SgrA* can be determined by the measurement of the degree of polarization setting the time of this brightening.
Figure 2: The galactic center region as seen by the Chandra X-ray mission
3. Acknowledgement 95
PS acknowledges the ASI grants no. 2015-034-R.O. References [1] M. C. Weisskopf, E. H. Silver, H. L. Kestenbaum, K. S. Long, R. Novick, A precision measurement of the X-ray polarization of the Crab Nebula without pulsar contamination, ApJ220 (1978) L117. doi:10.1086/182648.
100
[2] E. Costa, R. Bellazzini, G. Tagliaferri, G. Matt, A. Argan, P. Attin`a, L. Baldini, S. Basso, A. Brez, O. Citterio, S. di Cosimo, V. Cotroneo, S. Fabiani, M. Feroci, A. Ferri, L. Latronico, F. Lazzarotto, M. Minuti, E. Morelli, F. Muleri, L. Nicolini, G. Pareschi, G. di Persio, M. Pinchera, M. Razzano, L. Reboa, A. Rubini, A. M. Salonico, C. Sgro’, P. Soffitta, G. Span-
105
dre, D. Spiga, A. Trois, POLARIX: a pathfinder mission of X-ray polarimetry, Experimental Astronomy 28 (2010) 137–183. arXiv:1105.0637, doi:10.1007/s10686-010-9194-1. 6
[3] R. Bellazzini, et al., A polarimeter for IXO, in: R. Bellazzini, E. Costa, G. Matt, G. Tagliaferri (Eds.), X-ray Polarimetry: A New Window in 110
Astrophysics by Ronaldo Bellazzini, Enrico Costa, Giorgio Matt and Gianpiero Tagliaferri. Cambridge University Press, 2010. ISBN: 9780521191845, 2010, p. 269. [4] E. Costa, P. Soffitta, R. Bellazzini, A. Brez, N. Lumb, G. Spandre, An efficient photoelectric X-ray polarimeter for the study of black holes and
115
neutron stars, Nature411 (2001) 662. arXiv:arXiv:astro-ph/0107486. [5] R. Bellazzini, G. Spandre, M. Minuti, L. Baldini, A. Brez, F. Cavalca, L. Latronico, N. Omodei, M. M. Massai, C. Sgro’, E. Costa, P. Soffitta, F. Krummenacher, R. de Oliveira, Direct reading of charge multipliers with a self-triggering CMOS analog chip with 105 k pixels at 50 µm pitch,
120
Nuclear Instruments and Methods in Physics Research A 566 (2006) 552. arXiv:arXiv:physics/0604114, doi:10.1016/j.nima.2006.07.036. [6] R. Bellazzini, G. Spandre, M. Minuti, L. Baldini, A. Brez, L. Latronico, N. Omodei, M. Razzano, M. M. Massai, M. Pesce-Rollins, C. Sgr´ o, E. Costa, P. Soffitta, H. Sipila, E. Lempinen, A sealed Gas
125
Pixel Detector for X-ray astronomy, Nuclear Instruments and Methods in Physics Research A 579 (2007) 853. arXiv:arXiv:astro-ph/0611512, doi:10.1016/j.nima.2007.05.304. [7] F. Muleri, P. Soffitta, L. Baldini, R. Bellazzini, A. Brez, E. Costa, N. Di Lalla, E. Del Monte, Y. Evangelista, L. Latronico, A. Manfreda, M. Minuti,
130
M. Pesce-Rollins, M. Pinchera, A. Rubini, C. Sgr`o, F. Spada, G. Spandre, Performance of the Gas Pixel Detector: an x-ray imaging polarimeter for upcoming missions of astrophysics, in: Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series, Vol. 9905 of Proc. SPIE, 2016, p. 99054G. doi:10.1117/12.2233206.
135
[8] P. Soffitta, F. Muleri, S. Fabiani, E. Costa, R. Bellazzini, A. Brez, M. Minuti, M. Pinchera, G. Spandre, Measurement of the position 7
resolution of the Gas Pixel Detector, Nuclear Instruments and Methods in Physics Research A 700 (2013) 99–105.
arXiv:1208.6330,
doi:10.1016/j.nima.2012.09.055. 140
[9] S. Fabiani, E. Costa, E. Del Monte, F. Muleri, P. Soffitta, A. Rubini, R. Bellazzini, A. Brez, L. de Ruvo, M. Minuti, M. Pinchera, C. Sgr´o, G. Spandre, D. Spiga, G. Tagliaferri, G. Pareschi, S. Basso, O. Citterio, V. Burwitz, W. Burkert, B. Menz, G. Hartner, The Imaging Properties of the Gas Pixel Detector as a Focal Plane Polarimeter, ApJS212 (2014) 25.
145
arXiv:1403.7200, doi:10.1088/0067-0049/212/2/25. [10] F. Marin, F. Muleri, P. Soffitta, V. Karas, D. Kunneriath, Reflection nebulae in the Galactic center: soft X-ray imaging polarimetry, A&A576 (2015) A19. arXiv:1502.04894, doi:10.1051/0004-6361/201425341.
8
www.elsevier.com/locate/nima
PII: DOI: Reference:
S0168-9002(17)30209-7 http://dx.doi.org/10.1016/j.nima.2017.02.025 NIMA59655
To appear in: Nuclear Inst. and Methods in Physics Research, A Received date: 30 November 2016 Accepted date: 10 February 2017 Cite this article as: Paolo Soffitta, XIPE, the X-ray Imaging Polarimetry Explorer: opening a new window in the X-ray sky, Nuclear Inst. and Methods in Physics Research, A, http://dx.doi.org/10.1016/j.nima.2017.02.025 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
XIPE, the X-ray Imaging Polarimetry Explorer: opening a new window in the X-ray sky Paolo Soffitta for the XIPE collaboration✩ IAPS/INAF Via Fosso Del Cavaliere 100 00133 Roma
Abstract XIPE, the X-ray Imaging Polarimetry Explorer, is a candidate ESA fourth medium size mission, now in competitive phase A, aimed at time-spectrallyspatially-resolved X-ray polarimetry of a large number of celestial sources as a breakthrough in high energy astrophysics and fundamental physics. Its payload consists of three X-ray optics with a total effective area larger than one XMM mirror but with a low mass and of three Gas Pixel Detectors at their focus. The focal length is 4 meters and the whole satellite fits within the fairing of the Vega launcher without the need of an extendable bench. XIPE will be an observatory with 75% of the time devoted to a competitive guest observer program. Its consortium across Europe comprises Italy, Germany, Spain, United Kingdom, Switzerland, Poland, Sweden Until today, thanks to a dedicated experiment that dates back to the ’70, only the Crab Nebula showed a non-zero polarization with large significance [1] in X-rays. XIPE, with its innovative detector, promises to make significative measurements on hundreds of celestial sources. Keywords: X-ray, Polarimetry, Detectors, Optics 1. XIPE Payload XIPE instrumentation derives from the phase A for POLARIX [2]and XEUS/IXO [3]. More similar to POLARIX (see fig.1(a)), it comprises three new optics made with the technology of replication of nickel electroformed thin-shells. Thirty ✩ The
XIPE collaboration is shown in http://www.isdc.unige.ch/xipe/
Preprint submitted to Journal of LATEX Templates
February 16, 2017
5
shells feature a double-cone approximation of the Wolter-I profile with 300 mm of parabolic segment plus 300 mm of hyperbolic segment. The instrument is composed of three Detector Units (DUs) consisting of three gas Pixel Detectors, clocked at 120◦ , each one equipped with a Filters and Calibration Wheels (FCW) and a Back End Electronics Units (BEEs). Moreover one Instrument
10
Control Unit (ICU) serves the DUs and provide the data interface with the spacecraft. A fixed focal length of 4 meters allows for fitting XIPE into the fairing of the Vega launcher (see fig. 1(a)). Each GPD is filled with a mixture of He-DME (20 % - 80 %) at 1-bar with 1 cm of drift length, a result of the studies performed for finding the
15
optimal mixture/configuration in the classical energy band (2-10 keV). The GPD temperature is stabilized between 5◦ C and 25◦ C at the level of 1◦ C by a Peltier cooler. The FCW, on top of it, is equipped with a set of calibration sources including one with a known high polarization degree and some unpolarized sources to check the absence of spurious modulation. Further diaphragms and
20
filters allow for optimizing the observation. A closed position allows for safety and for gathering the internal background. The FCW features a total of 8 positions. The GPD and its performances as an imaging X-ray polarimeter. The detector consists of a [4, 5, 6] sealed gas cell 9 cm × 9 cm large but sensitive only in the
25
central 1.5 cm × 1.5 cm. Prior of the final assembly, an ASIC-CMOS, developed at this aim, is internally bonded to the KYOCERA package in turn soldered on the circuit printed board at INFN. Oxford Instrument Analytical Oy (Finland) glues the Gas Electron Multiplier (GEM) with its supporting frame on the KYOCERA package. The Gas Cell, mainly consisting of a MACOR spacer, is
30
assembled onto this package resulting in a clean operative environment. A 50 µm thick low radioactivity beryllium window is glued onto a titanium frame in turn glued onto the spacer. Finally the cell is baked, filled with the purified and controlled gas mixture and sealed. The top layer of the multi-layer ASIC is an hexagonally patterned (105400 pixels, 50 µm pitch) collection plane. Below
2
35
each pixel there is a complete analogue chain as a front-end electronics. A set of local (four pixels) triggers define the region of interest that includes the collected track. Only a fraction of pixels (600-800) are serially readout and A/D converted thus dramatically minimizing the dead-time fraction. Out of three generations of ASICs produced, the current ASIC is the latter and the first
40
self-triggered one. Three years of operation showed a modulation factor and an energy resolution basically constant with time. Long term space missions are therefore guaranteed. The modulation factor is found in agreement with the Monte Carlo expectations and a cut on 20 % of data independent on energy allows for the best sensitivity. The energy resolution is found compliant with
45
the requirement of 20 % (point source) and 25 % extended sources. Details on these performances are included in [7]. Thanks to the structure of the readout plane, and to the reconstruction algorithm for the evaluation of the impact point (and the emission direction that provides polarization) from the resolved track, the imaging capabilities (HEW) are at level of 90 µm. They were determined
50
either in laboratory with a narrow pencil beam [8] and at the PANTER X-ray test facility (see fig. 1(b) [9]) with a real X-ray optics showing that the main contribution is provided by the performance of the optics and not that of the detector. The second contribution for importance is provided by the inclined penetration of the photons in the 1-cm thick drift region, while the intrinsic
55
position resolution of the detector provides a negligible contribution. We note here that the GPD met the strict requirements for operating in high vacuum and in the clean environment of the PANTER X-ray test facility. Moreover the GPD undergone to environmental test (Vibration: random and sinusoidal, thermal and thermo-vacuum tests, survival with heavy Fe ions) allowing ESA
60
for assigning to the GPD a TRL of 6 during the IXO phase A. The XIPE foreseen performance are shown in table 1:
3
(a)
(b)
Figure 1: (a). XIPE in the Vega Launcher(b). Real images with the GPD at the focus of JET-X optics.
2. Astrophysical goal X-ray polarimetry allows for studying Black hole, Neutron stars and White Dwarf binaries in their different physical conditions, due to the possible variable 65
presence of jets, of coronae and of accretion disks. These studies permit to improve our knowledge on the geometry of the systems and the physical processes at work. In addition X-ray imaging polarimetry allows for meaningful studies of a much larger classes of sources. Indeed imaging provides the following benefits: (1) reduced background and the consequent smaller flux limit (allowing
70
for measuring polarization of AGNs and of the dim magnetars) with respect to other non imaging techniques. Background discrimination is possible due to the application of the background rejection techniques based on track morphologies. Furthermore imaging permits to measure the background during the observation; (2) Identification and measurement of possible multiple celestial sources
75
in the Field of View during observation of crowded regions; (3) Angularly resolved polarimetry for extended sources as shell-like Supernova Remnants and
4
Table 1: The characteristics of XIPE.
Polarization sensitivity
1.2 % MDP for 2x10−10 erg/s/cm2 (10 mCrab) in 300 ks
Spurious polarization
< 0.5 % (goal: < 0.1 %)
Angular resolution
< 26 arcsec
Focal length
4m
Field of view.
12.9 × 12.9 arcmin2
Spectral resolution
16 % @ 5.9 keV. Resolution 8 µs
Timing
Dead Time 180 µs
Stability
> 3 yr
Mirror wall materials
Electroformed NiCo
Mirror coating
Iridium plus Carbon
Energy range
2-8 keV
Background
1.7 10−5 c/s or 34 nCrab
Pulsar Wind Nebulae. This capability allows for mapping magnetic fields and for studying acceleration mechanisms at the emission site. Moreover studies of cluster of Galaxies could probe the possible existence of Axion-Like Particles. 80
One example where imaging is crucial, is the observation of X-rays from cold molecular clouds in the Galactic Center region. These clouds are emitting Xrays, perhaps, because they are scattering now the radiation coming from a past flare from Sgr A*. Sgr A*, a massive black hole in the Galactic Center, could have been, few hundreds years ago, a dim AGN and 106 brighter than today.
85
This region is crowded (see figure 2), moreover these targets are faint, extended and embedded in an X-ray emitting thermal plasma which dilutes polarization. Notwithstanding this, with the imaging capability of XIPE, is possible to measure the polarization angle that pinpoints to the origin of the illuminating radiation with sufficient accuracy for probing this hypothesis [10]. Moreover
5
90
the concurrent presence of different complexes of clouds, at different putative distances, allows for making a tomography of the Galactic Center region. In fact the true distance of these clouds from SgrA* can be determined by the measurement of the degree of polarization setting the time of this brightening.
Figure 2: The galactic center region as seen by the Chandra X-ray mission
3. Acknowledgement 95
PS acknowledges the ASI grants no. 2015-034-R.O. References [1] M. C. Weisskopf, E. H. Silver, H. L. Kestenbaum, K. S. Long, R. Novick, A precision measurement of the X-ray polarization of the Crab Nebula without pulsar contamination, ApJ220 (1978) L117. doi:10.1086/182648.
100
[2] E. Costa, R. Bellazzini, G. Tagliaferri, G. Matt, A. Argan, P. Attin`a, L. Baldini, S. Basso, A. Brez, O. Citterio, S. di Cosimo, V. Cotroneo, S. Fabiani, M. Feroci, A. Ferri, L. Latronico, F. Lazzarotto, M. Minuti, E. Morelli, F. Muleri, L. Nicolini, G. Pareschi, G. di Persio, M. Pinchera, M. Razzano, L. Reboa, A. Rubini, A. M. Salonico, C. Sgro’, P. Soffitta, G. Span-
105
dre, D. Spiga, A. Trois, POLARIX: a pathfinder mission of X-ray polarimetry, Experimental Astronomy 28 (2010) 137–183. arXiv:1105.0637, doi:10.1007/s10686-010-9194-1. 6
[3] R. Bellazzini, et al., A polarimeter for IXO, in: R. Bellazzini, E. Costa, G. Matt, G. Tagliaferri (Eds.), X-ray Polarimetry: A New Window in 110
Astrophysics by Ronaldo Bellazzini, Enrico Costa, Giorgio Matt and Gianpiero Tagliaferri. Cambridge University Press, 2010. ISBN: 9780521191845, 2010, p. 269. [4] E. Costa, P. Soffitta, R. Bellazzini, A. Brez, N. Lumb, G. Spandre, An efficient photoelectric X-ray polarimeter for the study of black holes and
115
neutron stars, Nature411 (2001) 662. arXiv:arXiv:astro-ph/0107486. [5] R. Bellazzini, G. Spandre, M. Minuti, L. Baldini, A. Brez, F. Cavalca, L. Latronico, N. Omodei, M. M. Massai, C. Sgro’, E. Costa, P. Soffitta, F. Krummenacher, R. de Oliveira, Direct reading of charge multipliers with a self-triggering CMOS analog chip with 105 k pixels at 50 µm pitch,
120
Nuclear Instruments and Methods in Physics Research A 566 (2006) 552. arXiv:arXiv:physics/0604114, doi:10.1016/j.nima.2006.07.036. [6] R. Bellazzini, G. Spandre, M. Minuti, L. Baldini, A. Brez, L. Latronico, N. Omodei, M. Razzano, M. M. Massai, M. Pesce-Rollins, C. Sgr´ o, E. Costa, P. Soffitta, H. Sipila, E. Lempinen, A sealed Gas
125
Pixel Detector for X-ray astronomy, Nuclear Instruments and Methods in Physics Research A 579 (2007) 853. arXiv:arXiv:astro-ph/0611512, doi:10.1016/j.nima.2007.05.304. [7] F. Muleri, P. Soffitta, L. Baldini, R. Bellazzini, A. Brez, E. Costa, N. Di Lalla, E. Del Monte, Y. Evangelista, L. Latronico, A. Manfreda, M. Minuti,
130
M. Pesce-Rollins, M. Pinchera, A. Rubini, C. Sgr`o, F. Spada, G. Spandre, Performance of the Gas Pixel Detector: an x-ray imaging polarimeter for upcoming missions of astrophysics, in: Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series, Vol. 9905 of Proc. SPIE, 2016, p. 99054G. doi:10.1117/12.2233206.
135
[8] P. Soffitta, F. Muleri, S. Fabiani, E. Costa, R. Bellazzini, A. Brez, M. Minuti, M. Pinchera, G. Spandre, Measurement of the position 7
resolution of the Gas Pixel Detector, Nuclear Instruments and Methods in Physics Research A 700 (2013) 99–105.
arXiv:1208.6330,
doi:10.1016/j.nima.2012.09.055. 140
[9] S. Fabiani, E. Costa, E. Del Monte, F. Muleri, P. Soffitta, A. Rubini, R. Bellazzini, A. Brez, L. de Ruvo, M. Minuti, M. Pinchera, C. Sgr´o, G. Spandre, D. Spiga, G. Tagliaferri, G. Pareschi, S. Basso, O. Citterio, V. Burwitz, W. Burkert, B. Menz, G. Hartner, The Imaging Properties of the Gas Pixel Detector as a Focal Plane Polarimeter, ApJS212 (2014) 25.
145
arXiv:1403.7200, doi:10.1088/0067-0049/212/2/25. [10] F. Marin, F. Muleri, P. Soffitta, V. Karas, D. Kunneriath, Reflection nebulae in the Galactic center: soft X-ray imaging polarimetry, A&A576 (2015) A19. arXiv:1502.04894, doi:10.1051/0004-6361/201425341.
8