Discoveries of Diffuse Iron Line Sources from the Sgr B Region

Koyama, K.; Inui, Tomoyuki; Hyodo, Yoshiaki; Matsumoto, Hironori; Tsuru, Takeshi Go; Maeda, Yoshitomo; Murakami, Hiroshi; Yamauchi, Shigeo; Kissel, S.; Chan, Kai-Wing; Soong, Yang

doi:10.1093/pasj/59.sp1.s221

Cited by 79 publications

(65 citation statements)

References 21 publications

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“…The molecular complexes bright in the Fe fluorescent line are embedded in strong X-ray emission due to the presence along the line of sight of unresolved thermal X-ray emission. This thermal emission, which permeates the whole GC region can be characterised as a two-temperature plasma with typically kT 1 ≈ 1 keV and kT 2 ≈ 6.5 keV (Koyama et al 2007). For our purposes, everything but the 6.4-keV line emission is considered as background radiation.…”

Section: Resultsmentioning

confidence: 99%

The X-ray lightcurve of Sagittarius A* over the past 150 years inferred from Fe-Kαline reverberation in Galactic centre molecular clouds

Capelli

Warwick

Porquet

et al. 2012

A&A

108

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Context. The spatial distribution and variability of Fe-Kα emission from molecular clouds in the Galactic centre region may provide an important key to the understanding of the recent history of Sgr A*. A very plausible interpretation is that this variability represents an echo in the reflected radiation from the clouds of a past episode of high activity in Sgr A*. Aims. We examine the temporal and spectral properties of nine Fe-Kα bright molecular clouds (three of which newly studied) within about 30 pc of Sgr A*, in order to understand and constrain the primary energising source of the Fe fluorescence. Methods. We collected all the archival XMM-Newton observations targeted at Sgr A*. The variability of the Fe-Kα line at 6.4-keV in specific cloud regions was investigated by spectrally fitting the data derived from the EPIC MOS cameras, after subtracting a modelled background. We have also studied the reflection imprints in time-averaged pn-spectra of each cloud. This involved measuring the equivalent width (EW) of the 6.4 keV line with respect to the underlying scattered continuum and the optical depth of the Fe-K absorption edge at 7.1 keV, superimposed on this same continuum. Finally we stacked the MOS spectra from two extended regions in order to quantify the east-west asymmetry apparent in the low-surface brightness diffuse Fe-Kα line emission. Results. Significant Fe-Kα variability was detected, with a spatial and temporal pattern consistent with that reported in previous studies. The main breakthrough that sets our paper apart from earlier contributions on this topic is the direct measurement of the column density and the Fe abundance of the MCs in our sample. All the spectra were characterised by a high EW of the Fe-Kα line and the presence of absorption at the Fe-K edge, both of which serve as tracers of X-ray illumination. We used the EW measurements to infer the average Fe abundance within the clouds to be 1.6 ± 0.1 times solar. The cloud column densities derived from the spectral analysis were typically of the order of 10 23 cm −2 , which is significantly higher than previous estimates. This in turn has a significant impact on the inferred geometry and time delays within the cloud system. The measured cloud parameters were used to set constraints on the past activity of Sgr A* and to investigate whether a contribution to the Fe fluorescence by cosmic-ray bombardment is plausible. Conclusions. Past X-ray activity of Sgr A* is the most likely source of ionisation within the molecular clouds in the innermost 30 pc of the Galaxy. In this scenario, the X-ray luminosity required to excite these reflection nebulae is of the order of 10 37 -10 38 erg s −1 , significantly lower than that estimated for the Sgr B2 molecular cloud. Moreover, the inferred Sgr A* lightcurve over the past 150 years shows a long-term downwards trend punctuated by occasional counter-trend brightening episodes of at least 5 years duration. Finally, we found that a contribution to the Fe fluorescence by X-ray transient binaries...

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Section: Resultsmentioning

confidence: 99%

The X-ray lightcurve of Sagittarius A* over the past 150 years inferred from Fe-Kαline reverberation in Galactic centre molecular clouds

Capelli

Warwick

Porquet

et al. 2012

A&A

108

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“…For the dense cores studied here, N is of the order of 10 23 cm −2 . In the region associated with the Galactic center and encompassing a diameter of about 20 arcminutes, the total X-ray luminosity in the range 2 to 40 KeV (Muno et al 2004;Koyama et al 2007;Yuasa et al 2008;Dogiel et al 2010) is 6 × 10 36 erg s −1 , yielding an X-ray flux density of 2.0 × 10 −3 erg cm −2 s −1 . The gas cooling via gas-dust interaction can be expressed as (Tielens 2005), where T kin is the gas kinetic temperature and T d dust temperature.…”

Section: X-ray Heatingmentioning

confidence: 99%

The thermal state of molecular clouds in the Galactic center: evidence for non-photon-driven heating

Henkel

Menten

et al. 2013

A&A

143

226

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We used the Atacama Pathfinder Experiment (APEX) 12 m telescope to observe the J K A Kc = 3 03 → 2 02 , 3 22 → 2 21 , and 3 21 → 2 20 transitions of para-H 2 CO at 218 GHz simultaneously to determine kinetic temperatures of the dense gas in the central molecular zone (CMZ) of our Galaxy. The map extends over approximately 40 × 8 (∼100 × 20 pc 2 ) along the Galactic plane with a linear resolution of 1.2 pc. The strongest of the three lines, the H 2 CO (3 03 → 2 02 ) transition, is found to be widespread, and its emission shows a spatial distribution similar to ammonia. The relative abundance of para-H 2 CO is 0.5−1.2 × 10 −9 , which is consistent with results from lower frequency H 2 CO absorption lines. Derived gas kinetic temperatures for individual molecular clouds range from 50 K to values in excess of 100 K. While a systematic trend toward (decreasing) kinetic temperature versus (increasing) angular distance from the Galactic center (GC) is not found, the clouds with highest temperature (T kin > 100 K) are all located near the nucleus. For the molecular gas outside the dense clouds, the average kinetic temperature is 65 ± 10 K. The high temperatures of molecular clouds on large scales in the GC region may be driven by turbulent energy dissipation and/or cosmic-rays instead of photons. Such a non-photon-driven thermal state of the molecular gas provides an excellent template for the more distant vigorous starbursts found in ultraluminous infrared galaxies (ULIRGs).

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“…The thermal X-ray emitting plasma has two components, characterized by temperatures of 1 and 6 keV and corresponding electron density of 4.7 and 0.6 cm −3 , respectively. (Park et al 2005;Koyama et al 2007). A candidate neutron star CXOGC J174545.5-285829 (the cannonball) detected in X-ray and radio has also been associated with the remnant (Park et al 2005;Zhao et al 2013).…”

Section: Sgr a East Towermentioning

confidence: 99%

SGR A* and Its Environment: Low-Mass Star Formation, the Origin of X-Ray Gas and Collimated Outflow

Yusef‐Zadeh

Wardle

Schödel

et al. 2016

ApJ

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We present high-resolution multiwavelength radio continuum images of the region within 150″ of SgrA * , revealing a number of new extended features and stellar sources in this region. First, we detect a continuous 2″ east-west ridge of radio emission, linking SgrA * and a cluster of stars associated with IRS 13 N and IRS 13E. The ridge suggests that an outflow of east-west blob-like structures is emerging from SgrA * . In particular, we find arc-like radio structures within the ridge with morphologies suggestive of photoevaporative protoplanetary disks. We use infrared K s and L′ fluxes to show that the emission has similar characteristics to those of a protoplanetary disk irradiated by the intense radiation field at the Galactic center. This suggests that star formation has taken place within the S-cluster 2″ from SgrA * . We suggest that the diffuse X-ray emission associated with Sgr A * is due to an expanding hot wind produced by the mass loss from B-type main sequence stars, and/or the disks of photoevaporation of low mass young stellar objects (YSOs) at a rate of ∼10 −6  M yr −1 . The proposed model naturally reduces the inferred accretion rate and is an alternative to the inflow-outflow style models to explain the underluminous nature of Sgr A * . Second, on a scale of 5″ from Sgr A * , we detect new cometary radio and infrared sources at a position angle PA∼50°which is similar to that of two other cometary sources X3 and X7, all of which face Sgr A * . In addition, we detect a striking tower of radio emission at a PA∼50°-60°along the major axis of the Sgr A East supernova remnant shell on a scale of 150″ from Sgr A * . We suggest that the cometary sources and the tower feature are tracing interaction sites of a mildly relativistic jet from Sgr A * with the atmosphere of stars and the nonthermal Sgr A East shell at a PA∼50°-60°with´-, and opening angle 10°. Lastly, we suggest that the east-west ridge of radio emission traces an outflow that is potentially associated with past flaring activity from Sgr A * . The position angle of the outflow driven by flaring activity is close to −90°.

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Discoveries of Diffuse Iron Line Sources from the Sgr B Region

Cited by 79 publications

References 21 publications

The X-ray lightcurve of Sagittarius A* over the past 150 years inferred from Fe-Kαline reverberation in Galactic centre molecular clouds

The X-ray lightcurve of Sagittarius A* over the past 150 years inferred from Fe-Kαline reverberation in Galactic centre molecular clouds

The thermal state of molecular clouds in the Galactic center: evidence for non-photon-driven heating

SGR A* and Its Environment: Low-Mass Star Formation, the Origin of X-Ray Gas and Collimated Outflow

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