| 11. |
- Aharonian, Felix, et al.
(författare)
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Solar abundance ratios of the iron-peak elements in the Perseus cluster
- 2017
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 551:7681, s. 478-
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Tidskriftsartikel (refereegranskat)abstract
- The metal abundance of the hot plasma that permeates galaxy clusters represents the accumulation of heavy elements produced by billions of supernovae(1). Therefore, X-ray spectroscopy of the intracluster medium provides an opportunity to investigate the nature of supernova explosions integrated over cosmic time. In particular, the abundance of the iron-peak elements (chromium, manganese, iron and nickel) is key to understanding how the progenitors of typical type Ia supernovae evolve and explode(2-6). Recent X-ray studies of the intracluster medium found that the abundance ratios of these elements differ substantially from those seen in the Sun(7-11), suggesting differences between the nature of type Ia supernovae in the clusters and in the Milky Way. However, because the K-shell transition lines of chromium and manganese are weak and those of iron and nickel are very close in photon energy, highresolution spectroscopy is required for an accurate determination of the abundances of these elements. Here we report observations of the Perseus cluster, with statistically significant detections of the resonance emission from chromium, manganese and nickel. Our measurements, combined with the latest atomic models, reveal that these elements have near-solar abundance ratios with respect to iron, in contrast to previous claims. Comparison between our results and modern nucleosynthesis calculations(12-14) disfavours the hypothesis that type Ia supernova progenitors are exclusively white dwarfs with masses well below the Chandrasekhar limit (about 1.4 times the mass of the Sun). The observed abundance pattern of the iron-peak elements can be explained by taking into account a combination of near-and sub-Chandrasekhar-mass type Ia supernova systems, adding to the mounting evidence that both progenitor types make a substantial contribution to cosmic chemical enrichment(5,15,16).
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| 12. |
- Aharonian, Felix, et al.
(författare)
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Temperature structure in the Perseus cluster core observed with Hitomi
- 2018
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Ingår i: Publications of the Astronomical Society of Japan. - : Oxford University Press (OUP). - 0004-6264 .- 2053-051X. ; 70:2
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Tidskriftsartikel (refereegranskat)abstract
- The present paper explains the temperature structure of X-ray emitting plasma in the core of the Perseus cluster based on 1.8-20.0 keV data obtained with the Soft X-ray Spectrometer (SXS) on board the Hitomi Observatory. A series of four observations was carried out, with a total effective exposure time of 338 ks that covered a central region of similar to 7' in diameter. SXS was operated with an energy resolution of similar to 5 eV (full width at half maximum) at 5.9 keV. Not only fine structures of K-shell lines in He-like ions, but also transitions from higher principal quantum numbers were clearly resolved from Si through Fe. That enabled us to perform temperature diagnostics using the line ratios of Si, S, Ar, Ca, and Fe, and to provide the first direct measurement of the excitation temperature and ionization temperature in the Perseus cluster. The observed spectrum is roughly reproduced by a single-temperature thermal plasma model in collisional ionization equilibrium, but detailed line-ratio diagnostics reveal slight deviations from this approximation. In particular, the data exhibit an apparent trend of increasing ionization temperature with the atomic mass, as well as small differences between the ionization and excitation temperatures for Fe, the only element for which both temperatures could be measured. The best-fit two-temperature models suggest a combination of 3 and 5 keV gas, which is consistent with the idea that the observed small deviations from a single-temperature approximation are due to the effects of projecting the known radial temperature gradient in the cluster core along the line of sight. A comparison with the Chandra/ACIS and the XMM-Newton/RGS results, on the other hand, suggests that additional lower-temperature components are present in the intracluster medium (ICM), but not detectable with Hitomi/SXS giving its 1.8-20 keV energy band.
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| 13. |
- Axelsson, Magnus, et al.
(författare)
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An imperfect double : probing the physical origin of the low-frequency quasi-periodic oscillation and its harmonic in black hole binaries
- 2014
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 438:1, s. 657-662
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Tidskriftsartikel (refereegranskat)abstract
- We extract the spectra of the strong low-frequency quasi-periodic oscillation (QPO) and its harmonic during the rising phase of an outburst in the black hole binary XTE J1550-564. We compare these frequency-resolved spectra to the time-averaged spectrum and the spectrum of the rapid (<0.1 s) variability. The spectrum of the time-averaged emission can be described by a disc, a Compton upscattered tail and its reflection. The QPO spectrum is very similar to the spectrum of the most rapid variability, implying it arises in the innermost regions of the flow. It contains little detectable disc, and its Compton spectrum is generally harder and shows less reflection than in the time-averaged emission. The harmonic likewise contains little detectable disc component, but has a Compton spectrum which is systematically softer than the QPO, softer even than the Compton tail in the time-averaged emission. We interpret these results in the context of the truncated disc model, where the inner disc is replaced by a hot flow. The QPO can arise in this picture from vertical (Lense-Thirring) precession of the entire hot inner flow, and its harmonic can be produced by the angular dependence of Compton scattering within the hot flow. We extend these models to include stratification of the hot flow, so that it is softer (lower optical depth) at larger radii closer to the truncated disc, and harder (higher optical depth) in the innermost parts of the flow where the rapid variability is produced. The different optical depth with radius gives rise to different angular dependence of the Comptonized emission, weighting the fundamental to the inner parts of the hot flow, and the harmonic to the outer. This is the first model which can explain both the spectrum of the QPO, and its harmonic, in a self consistent geometry.
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| 14. |
- Axelsson, Magnus, et al.
(författare)
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Breaking the spectral degeneracies in black hole binaries with fast timing data : the hard state of Cygnus X-1
- 2018
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 480:1, s. 751-758
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Tidskriftsartikel (refereegranskat)abstract
- The spectra of black hole binaries in the low/hard state are complex, with evidence formultiple different Comptonization regions contributing to the hard X-rays in addition to a cool disc component. We show this explicitly for some of the best RXTE data from Cyg X-1, where the spectrum strongly requires (at least) two different Comptonization components in order to fit the continuum above 3 keV, where the disc does not contribute. However, it is difficult to constrain the physical properties of these Comptonization components uniquely using spectral data alone. Instead, we show that additional information from fast variability can break this degeneracy. Specifically, we use the observed variability power spectra in each energy channel to reconstruct the energy spectra of the variability on time-scales of similar to 10, 1, and 0.1 s. The two longer time-scale spectra have similar shapes, but the fastest component is dramatically harder, and has strong curvature indicating that its seed photons are not from the cool disc. We interpret this in the context of propagating fluctuations through a hot flow, where the outer regions are cooler and optically thick, so that they shield the inner region from the disc. The seed photons for the hot inner region are then from the cooler Comptonization region rather than the disc itself.
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| 15. |
- Axelsson, Magnus, et al.
(författare)
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Fast variability as a probe of the smallest regions around accreting black holes
- 2013
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 431:2, s. 1987-1994
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Tidskriftsartikel (refereegranskat)abstract
- We extract the spectra of the fastest variability (above 10 Hz) from the black hole XTE J1550-564 during a transition from hard to soft state on the rise to outburst. We confirm previous results that the rapid variability contains no significant disc component despite this being strongly present in the total spectrum of the softer observations. We model ionized reflection significantly better than previous work, and show that this is also suppressed in the rapid variability spectrum compared to the total emission. This is consistent with the fast variability having its origin in a hot inner flow close to the black hole rather than in the accretion disc or in a corona above it. However, the rapid variability spectrum is not simply the same as the total Comptonized emission. It is always significantly harder, by an amount which increases as the spectrum softens during the outburst. This adds to evidence from time lags that the Comptonization region is inhomogeneous, with harder spectra produced closest to the black hole, the same region which produces the fastest variability.
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| 16. |
- Axelsson, Magnus, 1978-
(författare)
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X-ray variability in Galactic high-mass black hole binaries
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The stars of the night sky can to the naked eye appear to be steady and unchanging, apart from the twinkling created by air moving in the atmosphere. However, when viewed in X-rays, the sky is far from constant, with detectable changes occurring on very short timescales.Black hole X-ray binaries are strong sources of X-rays. These systems contain a star and a black hole in orbit around each other. As matter from the companion star is accreted by the black hole, large amounts of gravitational energy are released, giving rise to strong X-ray emission. The accretion flow close to a black hole is characterized by strong gravity, high-energy radiation and variability on timescales down to milliseconds. These systems allow us to probe physics under conditions we cannot recreate in a laboratory, and provide some of the strongest observational indications of the existence of black holes. Temporal analysis is a powerful diagnostic of the geometry and physical processes of this environment.The bulk of this thesis concerns studies of the rapid variability of perhaps the most well-known of all black hole binaries: Cygnus X-1. By tapping into the large amount of archival data available, a systematic study of the variability, in the form of the power spectrum, is conducted. The results show that timing studies can indeed give valuable information on the emission mechanisms and accretion geometry. Tying characteristic frequencies to effects predicted by general relativity directly gives information about the parameters of the compact object. Using these results, the past evolution of the binary system is studied.In addition, results from temporal analysis of the possible black hole binary Cygnus X-3 are presented. The study of X-ray variability covers timescales from years to seconds, and shows that while temporal analysis provides clues to this complex system, it does not provide immediate insight into the accretion geometry, or the nature of the compact object
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| 17. |
- Hjalmarsdotter, Linnea, et al.
(författare)
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Limits on pair production and multizone Comptonization : the broad-band X/gamma-ray spectrum of XTE J1550-564 revisited
- 2016
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 456:4, s. 4354-4363
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Tidskriftsartikel (refereegranskat)abstract
- At high luminosities black hole binaries show spectra with a strong disc component accompanied by an equally strong tail where at least some of the electrons are non-thermal. We reanalyse the simultaneous ASCA-RXTE-OSSE data from the 1998 outburst of XTE J1550-564, which span 0.7-1000 keV and remain the best data available of a black hole binary in this state. We reassess the importance of electron-positron pair production using a realistically high value of the source compactness for the first time. The lack of an observable annihilation line together with the observed gamma-ray flux beyond 511 keV constrains the maximum electron Lorentz factor to be <= 10, and the slope of the injected electrons to <= 2.5. We also use the fast (10-50 Hz) variability spectrum to constrain the spatial dependence of the electron heating and acceleration. We find that the spectrum of the fast variability is consistent with being fully thermal, so that the observed non-thermal emission is produced from further out in the flow.
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| 18. |
- Kawamura, Tenyo, et al.
(författare)
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A full spectral-timing model to map the accretion flow in black hole binaries : the low/hard state of MAXI J1820+070
- 2022
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 511:1, s. 536-552
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Tidskriftsartikel (refereegranskat)abstract
- The nature and geometry of the accretion flow in the low/hard state of black hole binaries is currently controversial. While most properties are generally explained in the truncated disc/hot inner flow model, the detection of a broad residual around the iron line argues for strong relativistic effects from an untruncated disc. Since spectral fitting alone is somewhat degenerate, we combine it with the additional information in the fast X-ray variability and perform a full spectral-timing analysis for NICER and NuSTAR data on a bright low/hard state of MAXI J1820+070. We model the variability with propagating mass accretion rate fluctuations by combining two separate current insights: that the hot flow is spectrally inhomogeneous, and that there is a discontinuous jump in viscous time-scale between the hot flow and variable disc. Our model naturally gives the double-humped shape of the power spectra, and the increasing high-frequency variability with energy in the second hump. Including reflection and reprocessing from a disc truncated at a few tens of gravitational radii quantitatively reproduces the switch in the lag-frequency spectra, from hard lagging soft at low frequencies (propagation through the variable flow) to the soft lagging hard at the high frequencies (reverberation from the hard X-ray continuum illuminating the disc). The viscous time-scale of the hot flow is derived from the model, and we show how this can be used to observationally test ideas about the origin of the jet.
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| 19. |
- Kawamura, Tenyo, et al.
(författare)
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MAXI J1820+070 X-ray spectral-timing reveals the nature of the accretion flow in black hole binaries
- 2023
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 519:3, s. 4434-4453
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Tidskriftsartikel (refereegranskat)abstract
- Black hole X-ray binaries display significant stochastic variability on short time-scales (0.01–100 s), with a complex pattern of lags in correlated variability seen in different energy bands. This behaviour is generally interpreted in a model where slow fluctuations stirred up at large radii propagate down through the accretion flow, modulating faster fluctuations generated at smaller radii. Coupling this scenario with radially stratified emission opens the way to measure the propagation time-scale from data, allowing direct tests of the accretion flow structure. We previously developed a model based on this picture and showed that it could fit the Neutron star Interior Composition Explorer (NICER; 0.5–10 keV) data from the brightest recent black hole transient, MAXI J1820+070. However, here we show it fails when extrapolated to higher energy variability data from the Insight-Hard X-ray Modulation Telescope(HXMT). We extend our model so that the spectrum emitted at each radius changes shape in response to fluctuations (pivoting) rather than just changing normalization. This gives the strong suppression of fractional variability as a function of energy seen in the data. The derived propagation time-scale is slower than predicted by a magnetically arrested disc (MAD), despite this system showing a strong jet. Our new model jointly fits the spectrum and variability up to 50 keV, though still cannot match all the data above this. Nonetheless, the good fit from 3 to 40 keV means the quasi-periodic oscillation (QPO) can most easily be explained as an extrinsic modulation of the flow, such as produced in the Lense–Thirring precession, rather than arising in an additional spectral-timing component such as the jet.
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| 20. |
- Middleton, Matthew J., et al.
(författare)
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Bright radio emission from an ultraluminous stellar-mass microquasar in M 31
- 2013
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 493:7431, s. 187-190
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Tidskriftsartikel (refereegranskat)abstract
- A subset of ultraluminous X-ray sources (those with luminosities of less than 10(40) erg s(-1); ref. 1) are thought to be powered by the accretion of gas onto black holes with masses of similar to 5-20M(circle dot), probably by means of an accretion disk(2,3). The X-ray and radio emission are coupled in such Galactic sources; the radio emission originates in a relativistic jet thought to be launched from the innermost regions near the black hole(4,5), with the most powerful emission occurring when the rate of infalling matter approaches a theoretical maximum (the Eddington limit). Only four such maximal sources are known in the Milky Way(6), and the absorption of soft X-rays in the interstellar medium hinders the determination of the causal sequence of events that leads to the ejection of the jet. Here we report radio and X-ray observations of a bright new X-ray source in the nearby galaxy M 31, whose peak luminosity exceeded 10(39) erg s(-1). The radio luminosity is extremely high and shows variability on a timescale of tens of minutes, arguing that the source is highly compact and powered by accretion close to the Eddington limit onto a black hole of stellar mass. Continued radio and X-ray monitoring of such sources should reveal the causal relationship between the accretion flow and the powerful jet emission.
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