The Impact of Accurate Extinction Measurements for X-Ray Spectral Models

Smith, Randall K.; Valencic, Lynne; Corrales, Lía

doi:10.3847/0004-637x/818/2/143

Cited by 42 publications

(48 citation statements)

References 31 publications

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“…Scattering on dust grains along the line of sight can have a significant impact on the observed X-ray spectra (Predehl & Schmitt 1995;Smith et al 2016). The main effect of dust scattering is to create a halo around the source, by removing flux from the line of sight.…”

Section: Dust Scatteringmentioning

confidence: 99%

A powerful flare from Sgr A* confirms the synchrotron nature of the X-ray emission

Ponti

George

Scaringi

et al. 2017

Monthly Notices of the Royal Astronomical Society

124

142

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We present the first fully simultaneous fits to the NIR and X-ray spectral slope (and its evolution) during a very bright flare from Sgr A ⋆ , the supermassive black hole at the Milky Way's center. Our study arises from ambitious multi-wavelength monitoring campaigns with XMMNewton, NuSTAR and SINFONI. The average multi-wavelength spectrum is well reproduced by a broken power-law with Γ N IR = 1.7 ± 0.1 and Γ X = 2.27 ± 0.12. The difference in spectral slopes (∆Γ = 0.57 ± 0.09) strongly supports synchrotron emission with a cooling break. The flare starts first in the NIR with a flat and bright NIR spectrum, while X-ray radiation is detected only after about 10 3 s, when a very steep X-ray spectrum (∆Γ = 1.8 ± 0.4) is observed. These measurements are consistent with synchrotron emission with a cooling break and they suggest that the high energy cut-off in the electron distribution (γ max ) induces an initial cut-off in the optical-UV band that evolves slowly into the X-ray band. The temporal and spectral evolution observed in all bright X-ray flares are also in line with a slow evolution of γ max . We also observe hints for a variation of the cooling break that might be induced by an evolution of the magnetic field (from B ∼ 30 ± 8 G to B ∼ 4.8 ± 1.7 G at the X-ray peak). Such drop of the magnetic field at the flare peak would be expected if the acceleration mechanism is tapping energy from the magnetic field, such as in magnetic reconnection. We conclude that synchrotron emission with a cooling break is a viable process for Sgr A ⋆ 's flaring emission.

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Section: Dust Scatteringmentioning

confidence: 99%

A powerful flare from Sgr A* confirms the synchrotron nature of the X-ray emission

Ponti

George

Scaringi

et al. 2017

Monthly Notices of the Royal Astronomical Society

124

142

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“…With the default parameter values, less than 5% of the dust-scattering halo is included in the source spectrum, affecting the spectrum overall by less than 1%. However, it has been shown that the diskshaped approximation vastly underestimates the true amount of the scattering halo recaptured within a typical source extraction radius; it is also heavily affected by the dust grain size and spatial distribution Smith et al 2016). Performing the full dust-scattering calculations is timeconsuming and provides many degenerate solutions.…”

Section: Fits To the Swift J1745407-290015 Spectrummentioning

confidence: 99%

“…Understanding the X-ray obscuration properties of the interstellar medium (ISM) is crucial for modeling accretion from compact objects and for learning about the material properties of dust Smith et al 2016). In GC studies, the ISM column obtained from fitting the X-ray continuum spectrum is often used to draw conclusions about where the compact object is in relation to SgrA * (e.g., Kennea et al 2013).…”

Section: Introductionmentioning

confidence: 99%

The Chandra Dust-scattering Halo of Galactic Center Transient Swift J174540.7–290015

Corrales

Mon

Haggard

et al. 2017

ApJ

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We report the detection of a dust-scattering halo around a recently discovered X-ray transient, Swift J174540.7-290015, which in early 2016 February underwent one of the brightest outbursts (F X ≈ 5 × 10 −10 erg cm −2 s −1 ) observed from a compact object in the Galactic Center field. We analyze four Chandra images that were taken as follow-up observations to Swift discoveries of new Galactic Center transients. After adjusting our spectral extraction for the effects of detector pile-up, we construct a point-spread function for each observation and compare it to the GC field before the outburst. We find residual surface brightness around Swift J174540.7-290015, which has a shape and temporal evolution consistent with the behavior expected from X-rays scattered by foreground dust. We examine the spectral properties of the source, which shows evidence that the object transitioned from a soft to hard spectral state as it faded below L X ∼10 36 ergs −1 . This behavior is consistent with the hypothesis that the object is a low-mass X-ray binary in the Galactic Center.

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“…Our dscat code 15 for the differential scattering cross section is based on the public 16 xscat package released by Smith et al (2016) that presents xspec table models of integrated scattering cross sections; that paper contains a detailed description of the methodology used in calculating dustscattering cross sections.…”

Section: Dscat: An Xspec Model For Differential Dust-scattering Crossmentioning

confidence: 99%

“…Following Smith et al (2016), we implemented four families of dust distributions as functions of grain size a: Mathis et al (1977, MRN77 hereafter) distribution, which consists of a combination of silicate and graphite grains, each following a distribution with a single slope of . The default values correspond to the parameter choices of the original MRN77 model.…”

Section: Dscat: An Xspec Model For Differential Dust-scattering Crossmentioning

confidence: 99%

A Joint Chandra and Swift View of the 2015 X-Ray Dust-Scattering Echo of V404 Cygni

Heinz

Corrales

Smith

et al. 2016

ApJ

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We present a combined analysis of the Chandra and Swift observations of the 2015 X-ray echo of V404 Cygni. Using a stacking analysis, we identify eight separate rings in the echo. We reconstruct the soft X-ray light curve of the 2015 June outburst using the high-resolution Chandra images and cross-correlations of the radial intensity profiles, indicating that about 70% of the outburst fluence occurred during the bright flare at the end of the outburst on MJD 57199.8. By deconvolving the intensity profiles with the reconstructed outburst light curve, we show that the rings correspond to eight separate dust concentrations with precise distance determinations. We further show that the column density of the clouds varies significantly across the field of view, with the centroid of most of the clouds shifted toward the Galactic plane, relative to the position of V404 Cyg, invalidating the assumption of uniform cloud column typically made in attempts to constrain dust properties from light echoes. We present a new XSPEC spectral dust-scattering model that calculates the differential dust-scattering cross section for a range of commonly used dust distributions and compositions and use it to jointly fit the entire set of Swift echo data. We find that a standard Mathis-Rumpl-Nordsieck model provides an adequate fit to the ensemble of echo data. The fit is improved by allowing steeper dust distributions, and models with simple silicate and graphite grains are preferred over models with more complex composition.

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The Impact of Accurate Extinction Measurements for X-Ray Spectral Models

Cited by 42 publications

References 31 publications

A powerful flare from Sgr A* confirms the synchrotron nature of the X-ray emission

A powerful flare from Sgr A* confirms the synchrotron nature of the X-ray emission

The Chandra Dust-scattering Halo of Galactic Center Transient Swift J174540.7–290015

A Joint Chandra and Swift View of the 2015 X-Ray Dust-Scattering Echo of V404 Cygni

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