A Monte Carlo Study of the 6.4 [CLC]ke[/CLC]V Emission at the Galactic Center

Fromerth, Michael J.; Melia, Fulvio; Leahy, D. A.

doi:10.1086/318906

Cited by 9 publications

(10 citation statements)

References 19 publications

(37 reference statements)

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“…A cloud radiates via X-ray fluorescence when it is illuminated, either internally or externally, by a source of ∼ 8 keV X-rays or ∼ 30 keV CR ions or electrons. Now, a steady X-ray source embedded within the cloud produces an upper limit to the equivalent width of only ∼ 1 keV (see, e.g., Fabian 1977;Vainshtein & Sunyaev 1980;Fromerth, Melia & Leahy 2001). A number of authors have taken the large equivalent width of Sgr B2, then, as evidence for illumination by an external X-ray source located towards the actual GC, usually identified with Sgr A* (see Revnivtsev et al (2004) and references therein).…”

Section: X-ray Observations Of Sgr Bmentioning

confidence: 99%

The Cosmic Ray Distribution in Sagittarius B

Crocker

Jones

Protheroe

et al. 2007

ApJ

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The HESS instrument has observed a diffuse flux of ~ TeV gamma rays from a large solid angle around the Galactic center (GC). This emission is correlated with the distribution of gas in the region suggesting that the gamma rays originate in collisions between cosmic ray hadrons (CRHs) and ambient matter. Of particular interest, HESS has detected gamma rays from the Sagittarius (Sgr) B Molecular Cloud Complex. Prompted by the suggestion of a hadronic origin for the gamma rays, we have examined archival 330 and 74 MHz Very Large Array radio data and 843 MHz Sydney University Molonglo Sky Survey data covering Sgr B, looking for synchrotron emission from secondary electrons and positrons (expected to be created in the same interactions that supply the observed gamma rays). Intriguingly, we have uncovered non-thermal emission, but at a level exceeding expectation. Adding to the overall picture, recent observations by the Atacama Pathfinder Experiment telescope show that the cosmic ray ionization rate is ten times greater in the Sgr B2 region of Sgr B than the local value. Lastly, Sgr B2 is also a very bright X-ray source. We examine scenarios for the spectra of CRHs and/or primary electrons that would reconcile all these different data. We determine that (i) a hard (~ E^-2.2), high-energy (> TeV) population CRHs is unavoidably required by the HESS gamma ray data and (ii) the remaining broad-band, non-thermal phenomenology is explained either by a rather steep (~ E^-2.9) spectrum of primary electrons or a (~ E^-2.7) population of CRHs. No single, power-law population of either leptons or hadrons can explain the totality of broadband, non-thermal Sgr B phenomenology.Comment: 45 pages, 5 figures; Minor revisions - version accepted for publication in Ap

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Section: X-ray Observations Of Sgr Bmentioning

confidence: 99%

The Cosmic Ray Distribution in Sagittarius B

Crocker

Jones

Protheroe

et al. 2007

ApJ

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“…Multiple scattering is essential for modeling the Compton shoulder and scattered hard X-rays in such dense clouds. Another approach is adoption of Monte Carlo simulations to solve the problem of radiative transfer (Leahy & Creighton 1993;Fromerth et al 2001). In general, Monte Carlo simulations treat particle tracking by calculating the propagation and interactions of a photon in matter.…”

Section: Introductionmentioning

confidence: 99%

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

Odaka

Aharonian

Watanabe

et al. 2011

ApJ

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Strong iron fluorescence at 6.4 keV and hard-X-ray emissions from giant molecular clouds in the Galactic center region have been interpreted as reflections of a past outburst of the Sgr A* supermassive black hole. Careful treatment of multiple interactions of photons in a complicated geometry is essential to modeling the reprocessed emissions from the dense clouds. We develop a new calculation framework of X-ray reflection from molecular clouds based on Monte Carlo simulations for accurate interpretation of high-quality observational data. By utilizing this simulation framework, we present the first calculations of morphologies and spectra of the reflected X-ray emission for several realistic models of Sgr B2, which is the most massive molecular cloud in our Galaxy. The morphology of scattered hard X-rays above 20 keV is significantly different from that of iron fluorescence due to their large penetrating power into dense regions of the cloud, probing the structure of the cloud. High-resolution spectra provide quantitative evaluation of the iron line including its Compton shoulder to constrain the mass and the chemical composition of the cloud as well as the luminosity of the illuminating source. These predictions can be checked in the near future with future X-ray missions such as NuStar (hard X-rays) and ASTRO-H (both iron lines and hard X-rays).

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“…With this knowledge, we can address several outstanding issues pertaining to the influence of this explosion on the morphology of the Galactic center: Did the supernova shock clear out the region surrounding the black hole, effectively shutting down what would otherwise have been a high accretion rate onto the black hole? Could the supernova have caused a brief increase in the accretion rate onto Sgr A*, producing a spike in X-ray emissivity that irradiated the X-ray-fluorescing Sgr B2 and other nearby molecular clouds some 300 years ago (see, e.g., Sunyaev & Churazov 1998;Fromerth & Melia 2001)?…”

Section: Introductionmentioning

confidence: 99%

The X-Ray Ridge Surrounding Sagittarius A* at the Galactic Center

Rockefeller

Fryer

Baganoff

et al. 2005

ApJ

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We present the first detailed simulation of the interaction between the supernova explosion that produced Sgr A East and the wind-swept inner ∼ 2-pc region at the Galactic center. The passage of the supernova ejecta through this medium produces an X-ray ridge ∼ 9 ′′ to 15 ′′ to the NE of the supermassive black hole Sagittarius A* (Sgr A*). We show that the morphology and X-ray intensity of this feature match very well with recently obtained Chandra images, and we infer a supernova remnant age of less than 2, 000 years. This young age-a factor 3-4 lower than previous estimates-arises from our inclusion of stellar wind effects in the initial (pre-explosion) conditions in the medium. The supernova does not clear out the central ∼ 0.2-pc region around Sgr A* and does not significantly alter the accretion rate onto the central black hole upon passage through the Galactic center.

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A Monte Carlo Study of the 6.4 [CLC]ke[/CLC]V Emission at the Galactic Center

Cited by 9 publications

References 19 publications

The Cosmic Ray Distribution in Sagittarius B

The Cosmic Ray Distribution in Sagittarius B

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

The X-Ray Ridge Surrounding Sagittarius A* at the Galactic Center

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