scholarly journals An X-ray survey of the central molecular zone: Variability of the Fe Kα emission line

2018 ◽  
Vol 612 ◽  
pp. A102 ◽  
Author(s):  
R. Terrier ◽  
M. Clavel ◽  
S. Soldi ◽  
A. Goldwurm ◽  
G. Ponti ◽  
...  
Keyword(s):  
Line Emission ◽  
Molecular Complexes ◽  
Massive Black Hole ◽  
X Ray ◽  
Open Questions ◽  
Long Duration ◽  
Sgr A ◽  
Thermal Diffuse ◽  
Archive Data ◽  
Do So

There is now abundant evidence that the luminosity of the Galactic super-massive black hole (SMBH) has not always been as low as it is nowadays. The observation of varying non-thermal diffuse X-ray emission in molecular complexes in the central 300 pc has been interpreted as delayed reflection of a past illumination by bright outbursts of the SMBH. The observation of different variability timescales of the reflected emission in the Sgr A molecular complex can be well explained if the X-ray emission of at least two distinct and relatively short events (i.e. about 10 yr or less) is currently propagating through the region. The number of such events or the presence of a long-duration illumination are open questions. Variability of the reflected emission all over of the central 300 pc, in particular in the 6.4 keV Fe Kα line, can bring strong constraints. To do so we performed a deep scan of the inner 300 pc with XMM-Newton in 2012. Together with all the archive data taken over the course of the mission, and in particular a similar albeit more shallow scan performed in 2000–2001, this allows for a detailed study of variability of the 6.4 keV line emission in the region, which we present here. We show that the overall 6.4 keV emission does not strongly vary on average, but variations are very pronounced on smaller scales. In particular, most regions showing bright reflection emission in 2000–2001 significantly decrease by 2012. We discuss those regions and present newly illuminated features. The absence of bright steady emission argues against the presence of an echo from an event of multi-centennial duration and most, if not all, of the emission can likely be explained by a limited number of relatively short (i.e. up to 10 yr) events.

scholarly journals Molecular gas in the immediate vicinity of Sgr A* seen with ALMA

2016 ◽  
Vol 11 (S322) ◽  
pp. 129-132
Author(s):  
Lydia Moser ◽  
Álvaro Sánchez-Monge ◽  
Andreas Eckart ◽  
Miguel A. Requena-Torres ◽  
Macarena García-Marin ◽  
...  
Keyword(s):  
Galactic Center ◽  
Line Emission ◽  
Molecular Gas ◽  
Future Studies ◽  
X Ray ◽  
Circumnuclear Disk ◽  
Sgr A ◽  
Central Parsec ◽  
Cloud Cores ◽  
Cold Core

AbstractWe report serendipitous detections of line emission with ALMA in band 3, 6, and 7 in the central parsec of the Galactic center at an up to now highest resolution (<0.7″). Among the highlights are the very first and highly resolved images of sub-mm molecular emission of CS, H13CO+, HC3N, SiO, SO, C2H, and CH3OH in the immediate vicinity (~1″ in projection) of Sgr A* and in the circumnuclear disk (CND). The central association (CA) of molecular clouds shows three times higher CS/X (X: any other observed molecule) luminosity ratios than the CND suggesting a combination of higher excitation - by a temperature gradient and/or IR-pumping - and abundance enhancement due to UV- and/or X-ray emission. We conclude that the CA is closer to the center than the CND is and could be an infalling clump consisting of denser cloud cores embedded in diffuse gas. Moreover, we identified further regions in and outside the CND that are ideally suited for future studies in the scope of hot/cold core and extreme PDR/XDR chemistry and consequent star formation in the central few parsecs.

scholarly journals Reprocessing of Uv and Line Emission in AGN Accretion Discs

1994 ◽  
Vol 159 ◽  
pp. 489-489
Author(s):  
Evlabia Rokaki ◽  
Catherine Boisson
Keyword(s):  
Black Hole ◽  
Accretion Rate ◽  
Line Emission ◽  
Line Spectrum ◽  
Physical Parameters ◽  
Spectral Features ◽  
Physical Processes ◽  
Massive Black Hole ◽  
X Ray ◽  
The Continuum

It is commonly admitted that AGN contain a massive black hole fuelled most likely by an accretion disc. Several spectral features of the AGN, as the continuum excess in the UV and the broad line spectrum, involving different physical processes of emission (thermal for the UV continuum, photoionisation for the line spectrum) have been proposed as signatures of the disc. Physical parameters of the nucleus (as the mass of the black hole, M, the disc inclination, i, and accretion rate, Ṁ) are better determined when these two spectral features are modelled simultaneously. Here, we present results from the disc modelling (see) of the UV and broad Hβ emission of the 22 Seyfert 1 galaxies in a complete AGN sample selected in a hard X-ray survey.

scholarly journals Impact of intrinsic polarization of Sgr A* historical flares on (polarization) properties of their X-ray echoes

2020 ◽  
Vol 498 (3) ◽  
pp. 4379-4385
Author(s):  
Ildar Khabibullin ◽  
Eugene Churazov ◽  
Rashid Sunyaev
Keyword(s):  
Primary Source ◽  
Molecular Complexes ◽  
Line Of Sight ◽  
Radiation Mechanisms ◽  
Intrinsic Polarization ◽  
X Ray ◽  
Relative Line ◽  
Sgr A ◽  
The Moment

ABSTRACT Reflection of X-ray emission on molecular clouds in the inner ∼100 pc of our Galaxy reveals that, despite being extremely quiet at the moment, our supermassive black hole Sgr A* should have experienced bright flares of X-ray emission in the recent past. Thanks to the improving characterization of the reflection signal, we are able to infer parameters of the most recent flare(s) (age, duration, and luminosity) and relative line-of-sight disposition of the brightest individual molecular complexes. We show that combining these data with measurements of polarization in the reflected X-ray continuum will not only justify Sgr A* as the primary source but also allow deriving intrinsic polarization properties of the flare emission. This will help to identify radiation mechanisms and underlying astrophysical phenomena behind them. For the currently brightest reflecting molecular complex, Sgr A, the required level of sensitivity might be already accessible with upcoming X-ray polarimeters.

scholarly journals Simulating the pericentre passage of the Galactic centre star S2

2018 ◽  
Vol 616 ◽  
pp. L8 ◽  
Author(s):  
M. Schartmann ◽  
A. Burkert ◽  
A. Ballone
Keyword(s):  
Power Law ◽  
Stellar Wind ◽  
Adaptive Mesh Refinement ◽  
Mass Loss Rate ◽  
Galactic Centre ◽  
Massive Black Hole ◽  
X Ray ◽  
Flow Models ◽  
Accretion Flow ◽  
Sgr A

Context. Our knowledge of the density distribution of the accretion flow around Sgr A* – the massive black hole (BH) at our Galactic centre (GC) – relies on two measurements only: one at a distance of a few Schwarzschild radii (Rs) and one at roughly 105 Rs, which are usually bridged by a power law, which is backed by magnetohydrodynamical simulations. The so-called S2 star reached its closest approach to the massive BH at around 1500 Rs in May 2018. It has been proposed that the interaction of its stellar wind with the high-density accretion flow at this distance from Sgr A* will lead to a detectable, month-long X-ray flare. Aims. Our goal is to verify whether or not the S2 star wind can be used as a diagnostic tool to infer the properties of the accretion flow towards Sgr A* at its pericentre (an unprobed distance regime), putting important constraints on BH accretion flow models. Methods. We run a series of three-dimensional adaptive mesh refinement simulations with the help of the RAMSES code which include the realistic treatment of the interaction of S2’s stellar wind with the accretion flow along its orbit and – apart from hydrodynamical and thermodynamical effects – include the tidal interaction with the massive BH. These are post-processed to derive the X-ray emission in the observable 2–10 keV window. Results. No significant excess of X-ray emission from Sgr A* is found for typical accretion flow models. A measurable excess is produced for a significantly increased density of the accretion flow. This can, however, be ruled out for standard power-law accretion flow models as in this case the thermal X-ray emission without the S2 wind interaction would already exceed the observed quiescent luminosity. Only a significant change of the wind parameters (increased mass loss rate and decreased wind velocity) might lead to an (marginally) observable X-ray flaring event. Conclusion. Even the detection of an (month-long) X-ray flare during the pericentre passage of the S2 star would not allow for strict constraints to be put on the accretion flow around Sgr A* due to the degeneracy caused by the dependence on multiple parameters (of the accretion flow model as well as the stellar wind).

scholarly journals X-raying molecular clouds with a short flare: probing statistics of gas density and velocity fields

2020 ◽  
Vol 495 (1) ◽  
pp. 1414-1432 ◽  
Author(s):  
I Khabibullin ◽  
E Churazov ◽  
R Sunyaev ◽  
C Federrath ◽  
D Seifried ◽  
...  
Keyword(s):  
Generation X ◽  
Line Emission ◽  
Future Generation ◽  
Effective Area ◽  
Velocity Fields ◽  
High Spectral Resolution ◽  
Gas Density ◽  
X Ray ◽  
Cloud Parameters ◽  
Sgr A

ABSTRACT We take advantage of a set of molecular cloud simulations to demonstrate a possibility to uncover statistical properties of the gas density and velocity fields using reflected emission of a short (with duration much less than the cloud’s light-crossing time) X-ray flare. Such a situation is relevant for the Central Molecular Zone (CMZ) of our Galaxy where several clouds get illuminated by an ∼110 yr-old flare from the supermassive black hole Sgr A* . Due to shortness of the flare (Δt ≲ 1.6 yr), only a thin slice (Δz ≲ 0.5 pc) of the molecular gas contributes to the X-ray reflection signal at any given moment, and its surface brightness effectively probes the local gas density. This allows reconstructing the density probability distribution function over a broad range of scales with virtually no influence of attenuation, chemo-dynamical biases, and projection effects. Such a measurement is key to understanding the structure and star formation potential of the clouds evolving under extreme conditions in the CMZ. For cloud parameters similar to the currently brightest in X-ray reflection molecular complex Sgr A, the sensitivity level of the best available data is sufficient only for marginal distinction between solenoidal and compressive forcing of turbulence. Future-generation X-ray observatories with large effective area and high spectral resolution will dramatically improve on that by minimizing systematic uncertainties due to contaminating signals. Furthermore, measurement of the iron fluorescent line centroid with sub-eV accuracy in combination with the data on molecular line emission will allow direct investigation of the gas velocity field.

scholarly journals ASCA Observations of 44I Bootis and VW Cephei

1998 ◽  
Vol 188 ◽  
pp. 226-227
Author(s):  
Chul-Sung Choi ◽  
Tadayasu Dotani
Keyword(s):  
Spectral Analysis ◽  
Light Curve ◽  
Plasma Model ◽  
X Ray ◽  
Long Duration ◽  
Orbital Phase ◽  
Different Temperatures ◽  
Archive Data ◽  
Peak Luminosity

We analyze X-ray archive data of the W UMa-type binaries 44i Boo and VW Cep, taken with ASCA on 1994 May 10 and 1993 November 5, respectively. By analyzing the light curve of VW Cep, we find a long-duration flare of ≈ 7.5 hrs with the peak luminosity of 1.2 × 1030 ergs s−1 (0.4-3.0 keV) for the assumed distance of 23.2 pc. We also find appreciable flux variations from the light curve of 44i Boo, and the variations are erratic and are not orbital phase dependent. From the spectral analysis of both data, we see that the spectra could be reproduced by the variable abundance plasma model with a combination of two different temperatures, kT = 0.64 – 0.65 keV and kT = 1.85 – 1.91 keV.

scholarly journals The Dark Mass Concentration at the Galactic Center

1997 ◽  
Vol 163 ◽  
pp. 637-646
Author(s):  
F. Melia
Keyword(s):  
Black Hole ◽  
Large Scale ◽  
Galactic Center ◽  
Line Emission ◽  
Concentrated Mass ◽  
Massive Black Hole ◽  
Central Mass ◽  
Kinematic Studies ◽  
Sgr A ◽  
Large Scale Flow

AbstractStellar kinematic studies indicate the presence of a concentrated central mass at just under 2 × 106M⊙, in close agreement with the mass deduced from gas velocities measured with the [Ne II] line. Although this mass is most likely a black hole, it may be dominated by a tightly concentrated cluster of stellar remnants. If Sgr A*, a point radio source coincident with this central mass, is a massive black hole embedded in a region with strong gaseous outflows, as suggested by the observation of He I, Brα and Brγ line emission, it is accreting from its environment via the Bondi-Hoyle process. We discuss the consequences of this activity, including the expected mass and angular momentum accretion rate onto the black hole, and the resulting observable characteristics. The latest infrared images of this region appear to rule out the possibility that this large scale flow settles down into a standard α-disk at small radii. We discuss some possible scenarios that might account for this, including strong advection in the disk or the presence of a massive, fossilized disk. Not all of the gas affected in this way by Sgr A*’s strong gravitational field becomes bound. Some of it is redirected into a focused flow that in turn interacts with other coherent gas structures near the black hole. We suggest that the mini-cavity (to the south-west of Sgr A*) may be formed as a result of this activity, and argue that the characteristics of the mini-cavity lend some observational support for the presence of a concentrated mass near Sgr A*. We show, however, that as far as the mini-cavity is concerned, this concentrated mass need not be in the form of a point mass, but may instead be a highly concentrated cluster of stellar remnants.

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

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.

scholarly journals Accretion of stellar winds onto Sgr A*

2006 ◽  
Vol 2 (S238) ◽  
pp. 191-194
Author(s):  
Jorge Cuadra ◽  
Sergei Nayakshin
Keyword(s):  
Black Hole ◽  
Numerical Study ◽  
Stellar Dynamics ◽  
Galactic Centre ◽  
Stellar Winds ◽  
Massive Black Hole ◽  
X Ray ◽  
3 Dimensional ◽  
Sgr A ◽  
Slow Wind

AbstractWe report a 3-dimensional numerical study of the accretion of stellar winds onto Sgr A*, the super-massive black hole at the centre of our Galaxy. Compared with previous investigations, we allow the stars to be on realistic orbits, include the recently discovered slow wind sources, and allow for optically thin radiative cooling. We first show the strong influence of the stellar dynamics on the accretion onto the central black hole. We then present more realistic simulations of Sgr A* accretion and find that the slow winds shock and rapidly cool, forming cold gas clumps and filaments that coexist with the hot X-ray emitting gas. The accretion rate in this case is highly variable on time-scales of tens to hundreds of years. Such variability can in principle lead to a strongly non-linear response through accretion flow physics not resolved here, making Sgr A* an important energy source for the Galactic centre.

Iron K-Line Emission from X-Ray Binaries

1988 ◽  
Vol 102 ◽  
pp. 47-50
Author(s):  
K. Masai ◽  
S. Hayakawa ◽  
F. Nagase
Keyword(s):  
Accretion Disk ◽  
Radiative Recombination ◽  
Characteristic Temperature ◽  
Line Emission ◽  
Ionization Front ◽  
Continuum Radiation ◽  
X Ray ◽  
Low Mass ◽  
X Ray Binaries

AbstractEmission mechanisms of the iron Kα-lines in X-ray binaries are discussed in relation with the characteristic temperature Txof continuum radiation thereof. The 6.7 keV line is ascribed to radiative recombination followed by cascades in a corona of ∼ 100 eV formed above the accretion disk. This mechanism is attained for Tx≲ 10 keV as observed for low mass X-ray binaries. The 6.4 keV line observed for binary X-ray pulsars with Tx&gt; 10 keV is likely due to fluorescence outside the He II ionization front.

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