The Gas Pixel Detetcor for the IXPE mission

Manfreda, Alberto

doi:10.1088/1748-0221/15/04/c04049

Cited by 4 publications

(3 citation statements)

References 12 publications

(12 reference statements)

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“…It is the first-ever satellite that measures spatial, temporal, and energy-resolved polarimetric data in a soft X-ray band of 2-8 keV. The satellite consists of three telescopes, each composed of a focusing Mirror Module Assembly and a Gas Pixel Detector unit at the focus to image the short photoelectric tracks produced as a result of X-ray absorption (Manfreda 2020;Baldini et al 2021;Di Marco et al 2022;Weisskopf et al 2022). IXPE observed the black hole X-ray binary 4U 1630-47 from 2022 August 23 to September 2 for ∼460 ks.…”

Section: Observation and Data Analysismentioning

confidence: 99%

Detection of X-Ray Polarized Emission and Accretion-disk Winds with IXPE and NICER in the Black Hole X-Ray Binary 4U 1630−47

Rawat

Garg

Méndez

2023

ApJL

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We detect a high level of polarization in the X-ray emission of the black hole binary 4U 1630–47 in an observation with the Imaging X-ray Polarimetry Explorer. The 2–8 keV polarization degree is 8% at a position angle of 18°, with the polarization degree increasing significantly with energy, from ∼6% at ∼2 keV to ∼11% at ∼8 keV. The continuum emission in the spectrum of simultaneous observations with the Neutron Star Interior Composition Explorer (NICER) is well described with only a thermal disk spectrum, with stringent upper limits to any Comptonized emission from the corona. Together with the lack of significant variability in the Fourier power spectrum, this suggests that the source was in the high soft state at the time of these observations. The NICER spectrum reveals the presence of several absorption lines in the 6–9 keV band that we fit with two ionized absorbers, providing evidence of the presence of a strong disk wind, which supports the idea that the source was in the soft state. Previous measurements of X-ray polarization in other sources in harder states were associated with the corona or the jet in those systems. Given that the corona is significantly absent in this observation of 4U 1630–47, and that the jet in black hole binaries is quenched in the high soft state, we speculate that in this observation of 4U 1630–47, the polarization likely arises from the direct and reflected radiation of the accretion disk in this source.

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Section: Observation and Data Analysismentioning

confidence: 99%

Detection of X-Ray Polarized Emission and Accretion-disk Winds with IXPE and NICER in the Black Hole X-Ray Binary 4U 1630−47

Rawat

Garg

Méndez

2023

ApJL

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“…The acquired information is passed to the Detector Service Unit to be further transmitted to the ground stations. Each DU has a gas pixel detector to detect X-ray photons in the range of 2-8 keV and image their resulting short photoelectric tracks (Manfreda 2020 ;Baldini et al 2021 ;Di Marco et al 2022 ;Weisskopf et al 2022 ). We analysed the IXPE data using the PYTHON based software IXPEOBSSIM 30.2.2 1 (Baldini et al 2022 ).…”

Section: O B S E Rvat I O N a N D Data A Na Ly S I Smentioning

confidence: 99%

Spectropolarimetric study of 4U 1630−47 in steep power-law state with IXPE and NICER

Rawat,

Garg,

Méndez

2023

Monthly Notices of the Royal Astronomical Society

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We probe the spectropolarimetric properties of the black-hole binary source 4U 1630−47 in the steep power law state. We detect a significant polarization fraction of ∼7 % at a polarization angle of ∼21 ○. The 2-12 keV NICER spectrum can be fitted with a combination of a thermal and a Comptonization component, the latter characterized by a spectral index, Γ ∼2.1, along with a reflection feature at ∼7.0 keV. In the 2–8 keV band, the degree of polarization of 4U 1630−47 in the steep power law state is 4.4 σ different from the value previously measured in the high soft state. In the steep power law state, the polarization fraction increases as a function of energy but exhibits an overall drop in each energy band compared to that of the high soft state. We propose that the decrease in the polarization fraction in the steep power law state could be attributed to the presence of a corona. The observed polarization properties in both states can be explained by the self-irradiation of the disk around a Kerr black hole, likely influenced by the frame-dragging effect.

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“…The example track image in Figure 2 shows this: the part with the greatest charge density (the Bragg peak) actually forms last, while the part with the real polarimetric information forms first and has got less charge. For this reason the reconstruction algorithm that is used to determine polarization (Bellazzini et al 2003;Fabiani & Muleri 2014;Manfreda 2020) actually identifies the Bragg peak first and only at the second step reconstructs the original direction. From the charge barycenter (only considering the first part of the track) the position is also computed, so that each event detected has a position associated to it even if the track is larger than the single pixels.…”

Section: Introductionmentioning

confidence: 99%

Equalizing the Pixel Response of the Imaging Photoelectric Polarimeter Onboard the IXPE Mission

Rankin

Muleri

Marco

et al. 2023

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The Gas Pixel Detector is a gas detector, sensitive to the polarization of X-rays, currently flying onboard the Imaging X-ray Polarimetry Explorer (IXPE)—the first observatory dedicated to X-ray polarimetry. It detects X-rays and their polarization by imaging the ionization tracks generated by photoelectrons absorbed in the sensitive volume, and then reconstructing the initial direction of the photoelectrons. The primary ionization charge is multiplied and ultimately collected on a finely pixellated ASIC specifically developed for X-ray polarimetry. The signal of individual pixels is processed independently and gain variations can be substantial, of the order of 20%. Such variations need to be equalized to correctly reconstruct the track shape, and therefore its polarization direction. The method to do such equalization is presented here and is based on the comparison between the mean charge of a pixel with respect to the other pixels for equivalent events. The method is shown to finely equalize the response of the detectors onboard IXPE, allowing a better track reconstruction and energy resolution, and can in principle be applied to any imaging detector based on tracks.

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The Gas Pixel Detetcor for the IXPE mission

Cited by 4 publications

References 12 publications

Detection of X-Ray Polarized Emission and Accretion-disk Winds with IXPE and NICER in the Black Hole X-Ray Binary 4U 1630−47

Detection of X-Ray Polarized Emission and Accretion-disk Winds with IXPE and NICER in the Black Hole X-Ray Binary 4U 1630−47

Spectropolarimetric study of 4U 1630−47 in steep power-law state with IXPE and NICER

Equalizing the Pixel Response of the Imaging Photoelectric Polarimeter Onboard the IXPE Mission

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