Modelling the thermal X-ray emission around the Galactic centre from colliding Wolf-Rayet winds

AbstractWe compute the thermal X-ray emission from hydrodynamic simulations of the 30 Wolf-Rayet (WR) stars orbiting within a parsec of Sgr A*, with the aim of interpreting the Chandra X-ray observations of this region. The model well reproduces the spectral shape of the observations, indicating that the shocked WR winds are the dominant source of this thermal emission. The model X-ray flux is tied to the strength of the Sgr A* outflow, which clears out hot gas from the vicinity of Sgr A*. A moderate outflow best fits the present-day observations, even though this supermassive black hole (SMBH) outflow ended ~100 yr ago.

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Modelling the thermal X-ray emission around the Galactic centre from colliding Wolf-Rayet winds

Proceedings of the International Astronomical Union ◽

10.1017/s1743921316012308 ◽

2016 ◽

Vol 11 (S322) ◽

pp. 39-42

Author(s):

Christopher M. P. Russell ◽

Q. Daniel Wang ◽

Jorge Cuadra

Keyword(s):

Ambient Medium ◽

Galactic Centre ◽

Temperature Structure ◽

Massive Black Hole ◽

Large Reservoir ◽

Hydrodynamic Simulations ◽

X Ray ◽

Wind Speeds ◽

Hot Gas ◽

Sgr A

AbstractThe Galactic centre is a hotbed of astrophysical activity, with the injection of wind material from ~30 massive Wolf-Rayet (WR) stars orbiting within 12″ of the super-massive black hole (SMBH) playing an important role. Hydrodynamic simulations of such colliding and accreting winds produce a complex density and temperature structure of cold wind material shocking with the ambient medium, creating a large reservoir of hot, X-ray-emitting gas. This work aims to confront the 3Ms of Chandra X-ray Visionary Program (XVP) observations of this diffuse emission by computing the X-ray emission from these hydrodynamic simulations of the colliding WR winds, amid exploring a variety of SMBH feedback mechanisms. The major success of the model is that it reproduces the spectral shape from the 2″–5″ ring around the SMBH, where most of the stellar wind material that is ultimately captured by Sgr A* is shock-heated and thermalised. This naturally explains that the hot gas comes from colliding WR winds, and that the wind speeds of these stars are in general well constrained. The flux level of these spectra, as well as 12″×12″ images of 4–9 keV, show the X-ray flux is tied to the SMBH feedback strength; stronger feedback clears out more hot gas, thereby decreasing the thermal X-ray emission. The model in which Sgr A* produced an intermediate-strength outflow during the last few centuries best matches the observations to within about 10%, showing SMBH feedback is required to interpret the X-ray emission in this region.

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Glimpses of the past activity of Sgr A★ inferred from X-ray echoes in Sgr C

Astronomy and Astrophysics ◽

10.1051/0004-6361/201731864 ◽

2018 ◽

Vol 610 ◽

pp. A34 ◽

Cited By ~ 6

Author(s):

D. Chuard ◽

R. Terrier ◽

A. Goldwurm ◽

M. Clavel ◽

S. Soldi ◽

...

Keyword(s):

Monte Carlo ◽

Black Hole ◽

Monte Carlo Model ◽

Line Of Sight ◽

X Rays ◽

X Ray ◽

Supermassive Black Hole ◽

The Past ◽

Sgr A ◽

Past Activity

Context. For a decade now, evidence has accumulated that giant molecular clouds located within the central molecular zone of our Galaxy reflect X-rays coming from past outbursts of the Galactic supermassive black hole. However, the number of illuminating events as well as their ages and durations are still unresolved questions. Aims. We aim to reconstruct parts of the history of the supermassive black hole Sgr A★ by studying this reflection phenomenon in the molecular complex Sgr C and by determining the line-of-sight positions of its main bright substructures. Methods. Using observations made with the X-ray observatories XMM-Newton and Chandra and between 2000 and 2014, we investigated the variability of the reflected emission, which consists of a Fe Kα line at 6.4 keV and a Compton continuum. We carried out an imaging and a spectral analysis. We also used a Monte Carlo model of the reflected spectra to constrain the line-of-sight positions of the brightest clumps, and hence to assign an approximate date to the associated illuminating events. Results. We show that the Fe Kα emission from Sgr C exhibits significant variability in both space and time, which confirms its reflection origin. The most likely illuminating source is Sgr A★. On the one hand, we report two distinct variability timescales, as one clump undergoes a sudden rise and fall in about 2005, while two others vary smoothly throughout the whole 2000–2014 period. On the other hand, by fitting the Monte Carlo model to the data, we are able to place tight constraints on the 3D positions of the clumps. These two independent approaches provide a consistent picture of the past activity of Sgr A★, since the two slowly varying clumps are located on the same wavefront, while the third (rapidly varying) clump corresponds to a different wavefront, that is, to a different illuminating event. Conclusions. This work shows that Sgr A★ experienced at least two powerful outbursts in the past 300 yrs, and for the first time, we provide an estimation of their age. Extending this approach to other molecular complexes, such as Sgr A, will allow this two-event scenario to be tested further.

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Colliding winds in and around the stellar group IRS 13E at the galactic centre

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz3624 ◽

2019 ◽

Vol 492 (2) ◽

pp. 2481-2496 ◽

Cited By ~ 3

Author(s):

Q Daniel Wang ◽

Jun Li ◽

Christopher M P Russell ◽

Jorge Cuadra

Keyword(s):

Thermal Emission ◽

Ambient Medium ◽

Velocity Spread ◽

Galactic Centre ◽

X Ray ◽

Stellar Group ◽

Cool Gas ◽

Sgr A ◽

Colliding Winds ◽

Projected Distance

ABSTRACT IRS 13E is an enigmatic compact group of massive stars located in projection only 3.6 arcsec away from Sgr A*. This group has been suggested to be bounded by an intermediate-mass black hole (IMBH). We present a multiwavelength study of the group and its interplay with the environment. Based on Chandra observations, we find the X-ray spectrum of IRS 13E can be well characterized by an optically thin thermal plasma. The emission peaks between two strongly mass-losing Wolf–Rayet stars of the group. These properties can be reasonably well reproduced by simulated colliding winds of these two stars. However, this scenario underpredicts the X-ray intensity in outer regions. The residual emission likely results from the ram-pressure confinement of the IRS 13E group wind by the ambient medium and is apparently associated with a shell-like warm gas structure seen in Pa α and in ALMA observations. These latter observations also show strongly peaked thermal emission with unusually large velocity spread between the two stars. These results indicate that the group is colliding with the bar of the dense cool gas mini-spiral around Sgr A*. The extended X-ray morphology of IRS 13E and its association with the bar further suggest that the group is physically much farther away than the projected distance from Sgr A*. The presence of an IMBH, while favourable to keep the stars bound together, is not necessary to explain the observed stellar and gas properties of IRS 13E.

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The central cluster and X-ray emission from Sgr A*

Proceedings of the International Astronomical Union ◽

10.1017/s1743921307005388 ◽

2006 ◽

Vol 2 (S238) ◽

pp. 347-348

Author(s):

Robert F. Coker ◽

Julian M. Pittard

Keyword(s):

Black Hole ◽

Stellar Winds ◽

Solar Mass ◽

Hydrodynamic Simulations ◽

X Ray ◽

Central Cluster ◽

The Galaxy ◽

Early Type Stars ◽

Sgr A ◽

Hydrodynamic Data

AbstractAt the centre of the Milky Way is Sgr A*, a putative 3 million solar mass black hole with an observed luminosity that is orders of magnitude smaller than that expected from simple accretion theories. The number density of early-type stars is quite high near Sgr A*, so the ensemble of their stellar winds has a significant impact on the black hole's environment.We present results of 3D hydrodynamic simulations of the accretion of stellar winds onto Sgr A*. Using the LANL/SAIC code, RAGE, we model the central arc-second of the Galaxy, including the central cluster stars (the S-stars) with orbits and wind parameters that match observations. A significant fraction of the winds from the S stars becomes gravitationally bound to the black hole and thus could provide enough hot gas to produce the X-ray emission seen by Chandra. We perform radiative transfer calculations on the 3D hydrodynamic data cubes and present the resulting synthetic X-ray spectrum.

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Acceleration of particles up to PeV energies at the galactic centre

Proceedings of the International Astronomical Union ◽

10.1017/s1743921317002332 ◽

2016 ◽

Vol 12 (S324) ◽

pp. 317-321

Author(s):

Stefano Gabici ◽

Felix A. Aharonian ◽

Emmanuel Moulin ◽

Aion Viana

Keyword(s):

Black Hole ◽

High Energy ◽

Galactic Cosmic Rays ◽

Galactic Centre ◽

Acceleration Of Particles ◽

Supermassive Black Hole ◽

Centre Region ◽

Very High Energy ◽

Sgr A ◽

Very High

AbstractRecent very high energy observations of the galactic centre region performed by H.E.S.S. revealed the presence of a powerful PeVatron. This is the first of such objects detected, and its most plausible counterpart seems to be associated to Sgr A*, the supermassive black hole in the centre of our galaxy. The implications of this discovery will be discussed, in particular in the context of the problem of the origin of galactic cosmic rays.

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Dynamical constraints on a dark matter spike at the Galactic centre from stellar orbits

Astronomy and Astrophysics ◽

10.1051/0004-6361/201832652 ◽

2018 ◽

Vol 619 ◽

pp. A46 ◽

Cited By ~ 14

Author(s):

Thomas Lacroix

Keyword(s):

Black Hole ◽

Dark Matter ◽

Spectroscopic Data ◽

Galactic Centre ◽

Stellar Orbits ◽

Supermassive Black Hole ◽

Dynamical Constraints ◽

Sgr A

In this work I use astrometric and spectroscopic data on the S2 star at the Galactic centre (GC) up to 2016 to derive specific constraints on the size of a dark matter (DM) spike around the central supermassive black hole Sgr A*. These limits are the best direct constraints on a DM spike at the GC for non-annihilating dark matter and exclude a spike with radius greater than a few tens of parsecs for cuspy outer halos and a few hundred parsecs for cored outer halos.

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Scale-invariance of black hole accretion: modelling emission from a black hole X-ray binary with relativistic accretion flow simulations

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz2875 ◽

2019 ◽

Vol 490 (4) ◽

pp. 5353-5358

Author(s):

M Mościbrodzka

Keyword(s):

Black Hole ◽

Near Infrared ◽

Thermal Emission ◽

Broad Band ◽

Scale Invariant ◽

X Ray ◽

Accretion Flow ◽

Black Hole Accretion ◽

Sgr A ◽

Hole Accretion

ABSTRACT We model the non-thermal emission spectrum of the extremely sub-Eddington X-ray binary system A0620-00. It is believed that this non-thermal emission is produced by radiatively inefficient ‘quiescent’ accretion on to a stellar-mass black hole present in the system. We post-process general relativistic magnetohydrodynamics (GRMHD) simulations with multiwavelength, fully polarized, relativistic radiative transfer calculations to predict broad-band spectra and emission polarization levels for a range of electron models and accretion rates. We find that a model with strong coupling of electrons and ions in the accretion disc and accretion rate of only $\dot{M}=3\times 10^{-13} \, \rm [M_\odot \, yr^{-1}]$ is able to recover the observed X-ray spectral slope, as well as the excess of linear polarization detected in the source in the near-infrared (NIR)/optical bands. Our models constrain the spectral properties of a putative relativistic jet produced in this system. In addition, we show that the magnetized winds from our hot accretion flow carry away a small fraction of the orbital angular momentum of the binary, which is unable to explain the observed rapid orbital decay of the system. GRMHD simulations similar to the present ones are often used to explain emission from sub-Eddington supermassive black holes in Sgr A* or M87; the present simulations allow us to test whether some aspects of quiescent black hole accretion are scale-invariant.

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The origin of Keplerian megamaser disks

Proceedings of the International Astronomical Union ◽

10.1017/s1743921312007302 ◽

2012 ◽

Vol 8 (S287) ◽

pp. 354-355

Author(s):

Mark Wardle ◽

Farhad Yusef-Zadeh

Keyword(s):

Black Hole ◽

Molecular Clouds ◽

Active Galaxies ◽

Stellar Disk ◽

Galactic Centre ◽

Black Hole Mass ◽

Disk Radius ◽

Supermassive Black Hole ◽

Sgr A ◽

Pass Through

AbstractSeveral examples of thin, Keplerian, sub-parsec megamaser disks have been discovered in the nuclei of active galaxies and used to precisely determine the mass of their host black holes. We show that there is an empirical linear correlation between the disk radius and black hole mass and that such disks are naturally formed as molecular clouds pass through the galactic nucleus and temporarily engulf the central supermassive black hole. For initial cloud column densities below about 1023.5 cm−2 the disk is non-self gravitating, but for higher cloud columns the disk would fragment and produce a compact stellar disk similar to that observed around Sgr A* at the galactic centre.

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The effects of outbursts from Supermassive Black Holes: A close look at M87

Proceedings of the International Astronomical Union ◽

10.1017/s174392132000407x ◽

2019 ◽

Vol 15 (S359) ◽

pp. 99-107

Author(s):

C. Jones ◽

W. Forman

Keyword(s):

Black Holes ◽

Black Hole ◽

Fossil Record ◽

Virgo Cluster ◽

Supermassive Black Holes ◽

Article Title ◽

X Ray ◽

Hot Gas ◽

Supermassive Black Hole ◽

Evolution Of Galaxies

AbstractSupermassive black holes (SMBHs) play[-105pt]Kindly check and confirm the Article Title. fundamental roles in the evolution of galaxies, groups, and clusters. The fossil record of supermassive black hole outbursts is seen through the cavities and shocks that are imprinted on these gas-rich systems. For M87, the central galaxy in the Virgo cluster, deep Chandra observations illustrate the physics of AGN feedback in hot, gas-rich atmospheres and allow measurements of the age, duration, and power of the outburst from the supermassive black hole in M87 that produced the observed cavities and shocks in the hot X-ray atmosphere.

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