ASCA View of Our Galactic Center: Remains of Past Activities in X-Rays?

Koyama, K.; Maeda, Yoshitomo; Sonobe, Takashi; Takeshima, T.; Tanaka, Yasuo; Yamauchi, Shigeo

doi:10.1093/pasj/48.2.249

Cited by 445 publications

(598 citation statements)

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“…last publications of Inui et al, 2009;Ponti et al, 2010;Terrier et al, 2010;Nobukawa et al, 2011;Capelli et al, 2012;Ryu et al, 2013;Clavel et al, 2013, and references therein). This line emission was observed first in the direction of the cloud Srg B2 (Koyama et al, 1996). The subsequent observations of the line and X-ray continuum emission from this cloud found its prominent time variability whose time characteristic corresponded to the period for which the front of primary photons from Sgr A* crossed the cloud (see e.g.…”

Section: Introductionmentioning

confidence: 89%

On the origin of the 6.4keV line in the Galactic Center region

Dogiel

Chernyshov

Kiselev

et al. 2014

Astroparticle Physics

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We analyse the 6.4 keV iron line component produced in the Galactic Center (GC) region by cosmic rays in dense molecular clouds (MCs) and in the diffuse molecular gas. We showed that this component, in principle, can be seen in several years in the direction of the cloud Srg B2. If this emission is produced by low energy CRs which ionize the interstellar molecular gas the intensity of the line is quite small, < 1%. However, we cannot exclude that local sources of CRs or X-ray photons nearby the cloud may provide much higher intensity of the line from there. Production of the line emission from molecular clouds depends strongly on processes of CR penetration into them. We show that turbulent motions of neutral gas may generate strong magnetic fluctuations in the clouds which prevent free penetration of CRs into the clouds from outside. We provide a special analysis of the line production by high energy electrons. We concluded that these electrons hardly provide the diffuse 6.4 keV line emission from the GC because their density is depleted by ionization losses. We do not exclude that local sources of electrons may provide an excesses of the 6.4 keV line emission in some molecular clouds and even reproduce a relatively short time variations of the iron line emission. However, we doubt whether a single electron source provides the simultaneous short time variability of the iron line emission from clouds which are distant from each other on hundred pc as observed for the GC clouds. An alternative speculation is that local electron sources could also provide the necessary effect of the line variations in different clouds that are seen simultaneously by chance that seems, however, very unlikely.

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Section: Introductionmentioning

confidence: 89%

On the origin of the 6.4keV line in the Galactic Center region

Dogiel

Chernyshov

Kiselev

et al. 2014

Astroparticle Physics

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“…ASCA observations near to Sgr A* were made on three occasions:'93 Autumn, '94 Autumn & '97 Spring. The results of the former two observations have been already published in Koyama et al,(1996) and . In the SIS/ ASCA hard-band image (2-10 keY) during '93 Autumn observations, we found two bright spots within the inner 2 arcmin from Sgr A* .One named as the "hard source" is located 1'.3 away from Sgr A*.…”

Section: Introduction 8£ Observationsmentioning

confidence: 90%

ASCA Observations of the SgrA Region

Maeda

Koyama

Murakami

et al. 1998

Symp. - Int. Astron. Union

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“…In the XRN scenario, the Fe o emission is a consequence of the illumination of the GC molecular clouds by external X-ray sources, together with Thomson scattering and/or absorption of these X-rays by the gas and dust in the clouds [16]. Those authors propose that a past episode of bright X-ray emission from some source in the GC, possibly the central super-massive black hole, Sgr A * , could be the illuminating source.…”

Section: X-ray Reflection Nebula (Xrn)mentioning

confidence: 99%

Correlation between SiO and X-ray emission in the galactic center

Amo-Baladrón

Martı́n-Pintado

Morris

et al. 2008

J. Phys.: Conf. Ser.

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Abstract. We present emission maps (spatial resolution ∼40") of the Sgr A molecular cloud complex at the Galactic Center (GC) in the J=2→1 SiO line, observed with the IRAM-30m telescope at Pico Veleta. We have compared our SiO(2-1) data cube with CS(1-0) maps, and we have found a correlation between the SiO/CS intensity ratio and the equivalent width of the X-ray Fe line at 6.4 keV. We discuss the SiO abundance enhancement in the two most plausible scenarios for the origin of the Fe line, which is, at the moment, under debate: fluorescence in an X-ray Reflection Nebula (XRN), or impact by Low-Energy Cosmic Rays (LECRs) followed by electronic relaxation. Both could explain the enhancement in the SiO/CS intensity ratio with the intensity of the Fe line, but both scenarios present difficulties: the first one requires a population of very small grains to produce the enhancement in the SiO/CS intensity ratio, and the second needs higher column densities than the ones derived from observations in the region.

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ASCA View of Our Galactic Center: Remains of Past Activities in X-Rays?

Cited by 445 publications

References 0 publications

On the origin of the 6.4keV line in the Galactic Center region

On the origin of the 6.4keV line in the Galactic Center region

ASCA Observations of the SgrA Region

Correlation between SiO and X-ray emission in the galactic center

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