Abstract The Advanced X-ray Astrophysics Facility (AXAF) is the x-ray component of NASA's Great Observatories. Tobe launched in late 1998, AXAF will provide unprecedented capabilities for high-resolution imaging, spectrometricimaging, and high-resolution dispersive spectroscopy, over the x-ray band from about 0.1 keV to 10 keV. Withthese capabilities, AXAF observations will address many of the outstanding questions in astronomy, astrophysics,and cosmology.Keywords: space missions, x-ray astronomy, x-ray optics, x-ray instrumentation, x-ray spectroscopy 1 INTRODUCTION In late 1998, the Advanced X-ray Astrophysics Facility (AXAF) will join the Hubble Space Telescope (HST)and the Compton Gamma-Ray Observatory (CGRO) as one of NASA's Great Observatories. As the mostsensitive high-resolution x-ray observatory yet planned, AXAF will be a unique scientific facility for use by thegeneral astronomical community. AXAF will provide exceptional capabilities (§5) for x-ray imaging, spectrometricimaging, and dispersive spectroscopy over the energy range 0.1 keV to 10 keV. In very broad terms, the scientificobjectives of AXAF are these:1. To determine the nature of celestial objects and phenomena.2. To understand the physical processes occurring in cosmic sources.3. To investigate the history, evolution, and structure of the universe.312 / SPIE Vol. 2515 0-8194-I874-9/95/$6.00

X-Ray Astronomy

High-energy astronomy

X-ray telescope

Spectral resolution

X-Ray Spectroscopy

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Highly Significant Detection of X-Ray Polarization from the Brightest Accreting Neutron Star Sco X-1

arXiv (Cornell University) (2023)

Fabio La Monaca Alessandro Di Marco Juri Poutanen Matteo Bachetti S. Motta

The Imaging X-ray Polarimetry Explorer (IXPE) measured with high significance the X-ray polarization of the brightest Z-source Scorpius X-1, resulting in the nominal 2-8 keV energy band in a polarization degree of 1.0(0.2)% and a polarization angle of 8(6){\deg} at 90% of confidence level. This observation was strictly simultaneous with observations performed by NICER, NuSTAR, and Insight-HXMT, which allowed for a precise characterization of its broad-band spectrum from soft to hard X-rays. The source has been observed mainly in its soft state, with short periods of flaring. We also observed low-frequency quasi-periodic oscillations. From a spectro-polarimetric analysis, we associate a polarization to the accretion disk at <3.2% at 90% of confidence level, compatible with expectations for an electron-scattering dominated optically thick atmosphere at the Sco X-1 inclination of 44{\deg}; for the higher-energy Comptonized component, we obtain a polarization of 1.3(0.4)%, in agreement with expectations for a slab of Thomson optical depth of ~7 and an electron temperature of ~3 keV. A polarization rotation with respect to previous observations by OSO-8 and PolarLight, and also with respect to the radio-jet position angle, is observed. This result may indicate a variation of the polarization with the source state that can be related to relativistic precession or to a change in the corona geometry with the accretion flow.

Position angle

Thomson scattering

10.48550/arxiv.2311.06359

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Magnetic Structures and Turbulence in SN 1006 Revealed with Imaging X-Ray Polarimetry

The Astrophysical Journal (2023)

Ping Zhou Dmitry Prokhorov Riccardo Ferrazzoli Yi-Jung Yang Patrick Slane

Abstract Young supernova remnants strongly modify the surrounding magnetic fields, which in turn play an essential role in accelerating cosmic rays (CRs). The X-ray polarization measurements probe magnetic field morphology and turbulence at the immediate acceleration site. We report the X-ray polarization distribution in the northeastern shell of SN 1006 from a 1 Ms observation with the Imaging X-ray Polarimetry Explorer. We found an average polarization degree of 22.4% ± 3.5% and an average polarization angle of −45.°4 ± 4.°5 (measured on the plane of the sky from north to east). The X-ray polarization angle distribution reveals that the magnetic fields immediately behind the shock in the northeastern shell of SN 1006 are nearly parallel to the shock normal or radially distributed, similar to that in the radio observations, and consistent with the quasi-parallel CR acceleration scenario. The X-ray emission is marginally more polarized than that in the radio band. The X-ray polarization degree of SN 1006 is much larger than that in Cas A and Tycho, together with the relatively tenuous and smooth ambient medium of the remnant, favoring that CR-induced instabilities set the magnetic turbulence in SN 1006, and CR acceleration is environment-dependent.

Degree of polarization

10.3847/1538-4357/acf3e6

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Citations (9)

Studying geometry of the ultraluminous X-ray pulsar Swift J0243.6+6124 using X-ray and optical polarimetry

Astronomy and Astrophysics (2024)

Juri Poutanen Sergey S. Tsygankov Victor Doroshenko Sofia V. Forsblom Peter Jenke

Discovery of pulsations from a number of ultra-luminous X-ray (ULX) sources proved that accretion onto neutron stars can produce luminosities exceeding the Eddington limit by several orders of magnitude. The conditions necessary to achieve such high luminosities as well as the exact geometry of the accretion flow in the neutron star vicinity are, however, a matter of debate. The pulse phase-resolved polarization measurements that became possible with the launch of the Imaging X-ray Polarimetry Explorer (IXPE) can be used to determine the pulsar geometry and its orientation relative to the orbital plane. They provide an avenue to test different theoretical models of ULX pulsars. In this paper we present the results of three IXPE observations of the first Galactic ULX pulsar Swift J0243.6+6124 during its 2023 outburst. We find strong variations in the polarization characteristics with the pulsar phase. The average polarization degree increases from about 5% to 15% as the flux dropped by a factor of three in the course of the outburst. The polarization angle (PA) as a function of the pulsar phase shows two peaks in the first two observations, but changes to a characteristic sawtooth pattern in the remaining data set. This is not consistent with a simple rotating vector model. Assuming the existence of an additional constant polarized component, we were able to fit the three observations with a common rotating vector model and obtain constraints on the pulsar geometry. In particular, we find the pulsar angular momentum inclination with respect to the line of sight of i p = 15°–40°, the magnetic obliquity of θ p = 60°–80°, and the pulsar spin position angle of χ p ≈ −50°, which significantly differs from the constant component PA of about 10°. Combining these X-ray measurements with the optical PA, we find evidence for at least a 30° misalignment between the pulsar angular momentum and the binary orbital axis.

Swift

10.1051/0004-6361/202450696

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Toward large-area sub-arcsecond x-ray telescopes

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE (2014)

Stephen L. O’Dell Thomas L. Aldcroft Ryan Allured Carolyn Atkins D. N. Burrows

The future of x-ray astronomy depends upon development of x-ray telescopes with larger aperture areas (≈ 3 m²) and fine angular resolution (≈ 1″). Combined with the special requirements of nested grazing-incidence optics, the mass and envelope constraints of space-borne telescopes render such advances technologically and programmatically challenging. Achieving this goal will require precision fabrication, alignment, mounting, and assembly of large areas (≈ 600 m²) of lightweight (≈ 1 kg/m²areal density) high-quality mirrors at an acceptable cost (≈ 1 M$/m²of mirror surface area). This paper reviews relevant technological and programmatic issues, as well as possible approaches for addressing these issues—including active (in-space adjustable) alignment and figure correction.

X-ray telescope

X-ray optics

Aperture (computer memory)

X-Ray Astronomy

Active optics

10.1117/12.2061882

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Characterization of the optical and X-ray properties of the north-western wisps in the Crab nebula

Monthly Notices of the Royal Astronomical Society (2013)

T. Schweizer N. Bucciantini W. Idec K. Nilsson Allyn F. Tennant

We have studied the wisps to the north-west of the Crab pulsar as part of a multiwavelength campaign in the visible and in X-rays. Optical observations were obtained using the Nordic Optical Telescope in La Palma and X-ray observations were made with the Chandra X-ray Observatory. The observing campaign took place from 2010 October until 2012 September. About once per year we observe wisps forming and peeling off from (or near) the region commonly associated with the termination shock of the pulsar wind. We find that the exact locations of the north-western wisps in the optical and in X-rays are similar but not coincident, with X-ray wisps preferentially located closer to the pulsar. This suggests that the optical and X-ray wisps are not produced by the same particle distribution. Our measurements and their implications are interpreted in terms of a Doppler-boosted ring model that has its origin in magnetohydrodynamic (MHD) modelling. While the Doppler boosting factors inferred from the X-ray wisps are consistent with current MHD simulations of pulsar wind nebulae, the optical boosting factors are not, and typically exceed values from MHD simulations by about a factor of 3.

Crab Nebula

Characterization

10.1093/mnras/stt995

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Citations (41)

Chandra X‐ray Observatory

Martin C. Weisskopf

Abstract The Chandra X‐ray Observatory (originally called the Advanced X‐ray Astrophysics Facility—AXAF) is the X‐ray component of NASA's “Great Observatory” Program. Chandra is a NASA facility that provides scientific data to the international astronomical community in response to scientific proposals for using it. The Observatory is the product of the efforts of many organizations in the United States and Europe. The Great Observatories also include the Hubble Space Telescope for space‐based observations of astronomical objects primarily in the visible portion of the electromagnetic spectrum, the now defunct Compton Gamma‐Ray Observatory that was designed to observe gamma‐ray emission from astronomical objects, and the soon‐to‐be‐launched Space Infrared Telescope Facility (SIRTF). The Chandra X‐ray Observatory (hereafter CXO) is sensitive to X rays in the energy range from below 0.1 to above 10.0 keV, corresponding to wavelengths from 12 to 0.12 nanometers. The relationships among the various parts of the electromagnetic spectrum, sorted by characteristic temperature and the corresponding wavelength are illustrated in this article. X‐ray astronomy is an extremely important field because it has been found that all categories of astronomical objects (or a subset thereof), from comets to quasars, emit X‐rays. Thus learning how and why these objects produce X‐rays are fundamental to our understanding of the way astronomical systems work. This, together with the large amounts of energy required to produce X‐rays, makes their study interesting and exciting. A second reason that the field is so important is that the vast bulk of the matter in the Universe that we can directly observe through the electromagnetic radiation that it emits is in the very hot (temperatures of millions of degrees) X‐ray emitting gas that fills the space between galaxies in clusters of galaxies, the largest collections of matter in the Universe. The CXO is the prime method of gaining new information about the X‐ray emission seen in the Universe. The CXO was named in honor of the late Indian‐American Nobel laureate, Subrahmanyan Chandrasekhar, nicknamed “Chandra” which means “moon” or “luminous” in Sanskrit. He was one of the foremost astrophysicists of the twentieth century and, in 1983, was awarded the Nobel prize for his studies of the physical processes important to the structure and evolution of stars. The observatory and its instrumentation are discussed. Scientific results are detailed CXO's role in solving the mystery of gamma ray bursts is also discussed.

Electromagnetic spectrum

X-Ray Astronomy

Space observatory

Spitzer Space Telescope

10.1002/0471263869.sst072

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Optimizing X-Ray Optical Prescriptions for Wide-Field Applications

Ronald F. Elsner Stephen L. O’Dell Brian D. Ramsey Martin C. Weisskopf

X-ray telescopes with spatial resolution optimized over the field of view (FOV) are of special interest for missions, such as WFXT, focused on moderately deep and deep surveys of the x-ray sky, and for solar x-ray observations. Here we report on the present status of an on-going study of the properties of Wolter I and polynominal grazing incidence designs with a view to gain a deeper insight into their properties and simply the design process. With these goals in mind, we present some results in the complementary topics of (1) properties of Wolter I x-ray optics and polynominal x-ray optic ray tracing. Of crucial importance for the design of wide-field x-ray optics is the optimization criteria. Here we have adopted the minimization of a merit function, M, which measures the spatial resolution averaged over the FOV: M= ((integral of d phi) between the limits of 0 and 2 pi) (integral of d theta theta w(theta) sigma square (theta,phi) between the limits of 0 and theta(sub FOV)) (integral of d phi between the limits of 0 and phi/4) (Integral of d theta theta w(theta) between the limits of 0 and theta(sub FOV) where w(theta(sub 1) is a weighting function and Merit function: sigma-square (theta, phi) = summation of (x,y,z) [ - (exp 2)] is the spatial variance for a point source on the sky at polar and azimuthal off-axis angles (theta,phi).

Square (algebra)

Geometrical optics

Field of view

Sigma

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Off-axis effects on the performance of a scattering polarimeter at the focus of an x-ray telescope

Optical Engineering (1990)

Ronald F. Elsner Martin C. Weisskopf P. Kaaret R. Novick Eric Silver

Scattering from bound electrons in a suitable material placed at the focus of an X-ray telescope can be exploited to measure the linear polarization of radiation emitted from cosmic X-ray sources. Among the factors that affect the performance of such an instrument is a spurious polarization signal from unpolarized sources that lie within the field of view but are offset from the telescope pointing direction. This paper presents the results of analytical and Monte Carlo studies of this effect and provides means of evaluating its impact on realistic polarimeters for X-ray astronomy.

Polarimeter

X-ray optics

10.1117/12.55662

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Citations (10)

Search for Periodic Pulsation in Four Globular Cluster X-Ray Sources

Bulletin of the American Astronomical Society (1981)

D. A. Leahy W. Darbro Ronald F. Elsner S. Naranan Martin C. Weisskopf

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