X-RAY DIAGNOSTICS OF GIANT MOLECULAR CLOUDS IN THE GALACTIC CENTER REGION AND PAST ACTIVITY OF Sgr A*

AbstractThe history of supermassive black holes’ activity can be partly constrained by monitoring the diffuse X-ray emission possibly created by the echoes of past events propagating through the molecular clouds of their respective environments. In particular, using this method we have demonstrated that our Galaxy’s supermassive black hole, Sgr A⋆, has experienced multiple periods of higher activity in the last centuries, likely due to several short but very energetic events, and we now investigate the possibility of studying the past activity of other supermassive black holes by applying the same method to M31⋆. We set strong constraints on putative phase transitions of this more distant galactic nucleus but the existence of short events such as the ones observed in the Galactic center cannot be assessed with the upper limits we derived.

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X-ray emission from the giant molecular clouds in the Galactic Center region and the discovery of new X-ray sources

Astronomy and Astrophysics ◽

10.1051/0004-6361:20010503 ◽

2001 ◽

Vol 372 (2) ◽

pp. 651-662 ◽

Cited By ~ 14

Author(s):

L. Sidoli ◽

S. Mereghetti ◽

A. Treves ◽

A. N. Parmar ◽

R. Turolla ◽

...

Keyword(s):

Molecular Clouds ◽

Galactic Center ◽

Giant Molecular Clouds ◽

X Ray ◽

Center Region

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On the past activity of Sgr A*

Proceedings of the International Astronomical Union ◽

10.1017/s174392131400088x ◽

2013 ◽

Vol 9 (S303) ◽

pp. 333-343 ◽

Cited By ~ 1

Author(s):

G. Ponti ◽

M. R. Morris ◽

M. Clavel ◽

R. Terrier ◽

A. Goldwurm ◽

...

Keyword(s):

Strong Evidence ◽

Galactic Center ◽

Galactic Disk ◽

X Ray ◽

The Past ◽

Sgr A ◽

Past Activity

AbstractRecent X-ray emission events in the Galactic center would be expected to generate an X-ray reflection response within the surrounding clouds of the central molecular zone, in the Galactic disk and even, if powerful enough, in clouds outside our Galaxy. We review here the current constraints on Sgr A*'s past activity obtained through this method, with particular emphasis on the strong evidence that has been gathered for multiple X-ray flashes during the past few hundred years.

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Reflected X-ray Emissions on Giant Molecular Clouds— Evidence of the Past Activities of Sgr A

Proceedings of the Galactic Center Workshop 2002 ◽

10.1002/9783527617982.ch18 ◽

2007 ◽

pp. 125-131

Author(s):

Hiroshi Murakami ◽

Atsushi Senda ◽

Yoshitomo Maeda ◽

Katsuji Koyama

Keyword(s):

Molecular Clouds ◽

Giant Molecular Clouds ◽

X Ray ◽

The Past ◽

Sgr A

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Methanol masers in Galactic center region supernova remnants

Proceedings of the International Astronomical Union ◽

10.1017/s1743921314000441 ◽

2013 ◽

Vol 9 (S303) ◽

pp. 156-158

Author(s):

Y. M. Pihlström ◽

B. C. McEwen ◽

L. O. Sjouwerman

Keyword(s):

Molecular Clouds ◽

Supernova Remnants ◽

Galactic Center ◽

Cosmic Ray ◽

Large Array ◽

Very Large Array ◽

Center Region ◽

Cosmic Ray Acceleration ◽

Methanol Masers ◽

Sgr A

AbstractMethanol masers can be used to constrain densities and estimate kinematical distances to supernova remnants (SNRs), important parameters in cosmic ray acceleration models. With the goal of testing those models both for SNRs inside and outside the Galactic center (GC) region, we have used the Very Large Array to search for 36 GHz and 44 GHz methanol lines in Galactic SNRs. We report on the overall results of the maser search, and in particular the results of the GC SNR G1.4–0.1 in which more than 40 masers were found. They may be due to interactions between the SNR and at least two separate molecular clouds. Methanol masers were also detected in W28 and in Sgr A East.

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Multiple accretion events as a trigger for Sagittarius A* activity

Proceedings of the International Astronomical Union ◽

10.1017/s1743921314000830 ◽

2013 ◽

Vol 9 (S303) ◽

pp. 320-321

Author(s):

D. Kunneriath ◽

B. Czerny ◽

V. Karas ◽

T. K. Das

Keyword(s):

Angular Momentum ◽

Molecular Clouds ◽

Galactic Center ◽

X Ray ◽

Supermassive Black Hole ◽

The Past ◽

Sagittarius A ◽

Enhanced Activity ◽

Show Evidence ◽

Sgr A

AbstractThe Galactic center supermassive black hole is surrounded by orbiting clouds of gas. These clumps of gas may collide with each other, losing angular momentum and plunging towards the center. Observations of X-ray reflection from molecular clouds surrounding the Galactic center show evidence for enhanced activity of Sagittarius A* during the past few hundred years. These observations enable us to place constraints on the nature of past accretion events responsible for this enhanced activity. We model the source intrinsic luminosity of Sgr A* using multiple accretion events occurring at various moments in time, characterized by a range of angular momentum We also applied our scheme to the case of G2 cloud in the Galactic center.

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NH3 Observations of the Sgr A Complex Region with the Nobeyama Millimeter Array

Symposium - International Astronomical Union ◽

10.1017/s0074180900186760 ◽

1989 ◽

Vol 136 ◽

pp. 371-377 ◽

Cited By ~ 2

Author(s):

S. K. Okumura ◽

M. Ishiguro ◽

E. B. Fomalont ◽

Y. Chikada ◽

T. Kasuga ◽

...

Keyword(s):

Strong Interaction ◽

Molecular Clouds ◽

Galactic Center ◽

Molecular Gas ◽

Kinetic Temperature ◽

Complex Region ◽

Physical Conditions ◽

Center Region ◽

Sgr A ◽

The Continuum

We report NH3 observations of the Sgr A complex region including Sgr A West and the 20 km/s and 50 km/s molecular clouds (M–0.13–0.08 and M–0.02–0.07) using the Nobeyama Millimeter Array and the 45m telescope. NH3(1,1) and (2,2) lines were simultaneously observed to estimate the kinetic temperature. Our results suggest strong interaction between the molecular clouds and the continuum sources in the Sgr A complex. The interaction with continuum sources might be an important factor in determining the physical conditions of molecular gas in the galactic center region.

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An X-ray survey of the central molecular zone: variability of the FeKα emission line

Proceedings of the International Astronomical Union ◽

10.1017/s1743921314000258 ◽

2013 ◽

Vol 9 (S303) ◽

pp. 94-96

Author(s):

Simona Soldi ◽

Maïca Clavel ◽

Andrea Goldwurm ◽

Mark R. Morris ◽

Gabriele Ponti ◽

...

Keyword(s):

Emission Line ◽

Molecular Clouds ◽

Galactic Center ◽

X Ray ◽

Preliminary Results ◽

Sgr A ◽

Flux Increase ◽

C Complex ◽

First Time

AbstractThe bulk of the FeKα emission detected in the central molecular zone (CMZ) is thought to be associated with reflection by the central molecular clouds of enhanced past emission from an external X-ray source, most likely Sgr A*. In order to follow the propagation of the reflected emission through the Galactic center (GC), we analyzed all XMM-Newton observations carried out from 2000 to 2012. Preliminary results indicate that while most of the regions that were bright at 6.4 keV in 2000–2001 have a significantly lower flux in 2012, a few other experienced a flux increase. We report for the first time a significant decrease of the FeKα emission in the Sgr C complex, supporting the reflection origin of the 6.4 keV emission detected in this region.

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