A faint discrete source origin for the highly ionized iron emission from the Galactic Centre region

Wang, Q. Daniel; Gotthelf, E. V.; Lang, Cornelia

doi:10.1038/415148a

Cited by 187 publications

(210 citation statements)

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“…Heindl et al 1993, Wang et al 2002, extended diffuse X-ray emission (Koyama et al 2007), as well as over 9000 X-ray point sources (Muno et al 2009) some of which lie at the edge of the CMZ between l = 358.…”

Section: X-ray Ionizationmentioning

confidence: 99%

Ionized gas at the edge of the central molecular zone

Langer

Goldsmith

Pineda

et al. 2015

A&A

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Context. The edge of the central molecular zone (CMZ) is the location where massive dense molecular clouds with large internal velocity dispersions transition to the surrounding more quiescent and lower CO emissivity region of the Galaxy. Little is known about the ionized gas surrounding the molecular clouds and in the transition region. Aims. We determine the properties of the ionized gas at the edge of the CMZ near Sgr E using observations of N + and C + .Methods. We observed a small portion of the edge of the CMZ near Sgr E with spectrally resolved [C ii] 158 μm and [N ii] 205 μm fine structure lines at six positions with the GREAT instrument on SOFIA and in [C ii] using Herschel HIFI on-the-fly strip maps. We use the [N ii] spectra along with a radiative transfer model to calculate the electron density of the gas and the [C ii] maps to illuminate the morphology of the ionized gas and model the column density of CO-dark H 2 .Results. We detect two [C ii] and [N ii] velocity components, one along the line of sight to a CO molecular cloud at −207 km s −1 associated with Sgr E and the other at −174 km s −1 outside the edge of another CO cloud. From the [N ii] emission we find that the average electron density is in the range of ∼5 to 21 cm −3 for these features. This electron density is much higher than that of the disk's warm ionized medium, but is consistent with densities determined for bright diffuse H ii nebula. The column density of the CO-dark H 2 layer in the −207 km s −1 cloud is ∼1−2× 10 21 cm −2 in agreement with theoretical models. The CMZ extends further out in Galactic radius by ∼7 to 14 pc in ionized gas than it does in molecular gas traced by CO. Conclusions. The edge of the CMZ likely contains dense hot ionized gas surrounding the neutral molecular material. The high fractional abundance of N + and high electron density require an intense EUV field with a photon flux of order 10 6 to 10 7 photons cm −2 s −1 , and/or efficient proton charge exchange with nitrogen, at temperatures of order 10 4 K, and/or a large flux of X-rays. Sgr E is a region of massive star formation as indicated by the presence of numerous compact H ii regions. The massive stars are potential sources of the EUV radiation that ionizes and heat the gas. In addition, X-ray sources and the diffuse X-ray emission in the CMZ are candidates for ionizing nitrogen.

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Section: X-ray Ionizationmentioning

confidence: 99%

Ionized gas at the edge of the central molecular zone

Langer

Goldsmith

Pineda

et al. 2015

A&A

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“…Based on a recent high-resolution survey carried out with Chandra, Wang et al (2002) report on faint sources which might also be wind accreting sources, but mainly neutron star wind accretors (Pfahl et al 2002). Mass overflow rates from the low-mass companion stars are usually lower so that the gas is accumulated in a cool quiescent disk until an outburst is triggered.…”

Section: Introductionmentioning

confidence: 99%

Why soft X-ray transients can remain in the low/hard state during outburst

Meyer-Hofmeister

2004

A&A

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Abstract. In the canonical understanding of transient X-ray sources the accretion during quiescence occurs via a geometrically thin disk in the outer part and via an advection-dominated hot coronal flow/ADAF in the inner part. The inner part important for the radiation yields a hard spectrum. In most sources the luminosity increase during outburst causes a change over to a soft spectrum which can be understood as that of a multi-color black body disk reaching inward to the marginally stable orbit. A few transient sources do not display this transition to the soft state. We show that this can be understood as due to relatively low peak luminosities in outburst in systems with short orbital periods and therefore less mass accumulated in the then smaller accretion disk. This is in agreement with the observations which show that most likely short orbital period systems remain in the hard spectral state.

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“…Chandra has provided us with a new tool to probe the high-energy properties of the GC. Wang, Gotthelf, & Lang (2002) have carried out a systematic survey of a 2 × 0.8 square degree field, which consists of 30 overlapping Chandra ACIS-I observations (about 11 -12 ks exposure each) and covers the most active ridge around the GC (Fig. 1).…”

Section: The Milky Way Center As a Laboratory For High Energy Astrophmentioning

confidence: 99%