A Multiwavelength Study of Sgr A*: The Role of Near‐IR Flares in Production of X‐Ray, Soft γ‐Ray, and Submillimeter Emission

Yusef‐Zadeh, F.; Bushouse, H.; Dowell, C. D.; Wardle, Mark; Roberts, D. A.; Heinke, C. O.; Bower, Geoffrey C.; Vila-Vilaro, Baltasar; Shapiro, Stuart L.; Goldwurm, A.; Bélanger, G.

doi:10.1086/503287

Cited by 137 publications

(207 citation statements)

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“…The goal of the present model is to combine the description of an adiabatically expanding cloud with a synchrotron self-Compton formalism, as this is the most likely physical scenario to explain the delay between the sub-mm and the simultaneous near-IR and X-ray peaks. Thus, we use the definition of τ 0 as the optical depth corresponding to the frequency at which the flux density is a maximum (van der Laan 1966), rather than the definition of τ 0 as the optical depth at which the light curve for any particular frequency peaks (Yusef-Zadeh et al 2006b). This implies that τ 0 depends only on p by means of the condition…”

Section: Adiabatically Expanding Source Componentsmentioning

confidence: 99%

“…Finally, a model for R(t) is required to convert the dependence on radius into one of time: as in previous references (e.g. Yusef-Zadeh et al 2006b;Eckart et al 2008) we adopt a simple linear expansion at constant expansion speed v exp , such that R−R 0 = v exp (t−t 0 ). For t ≤ t 0 , we have made the assumption that the source has an optical depth equal to its frequency-dependent initial value τ ν at R = R 0 .…”

Section: Adiabatically Expanding Source Componentsmentioning

confidence: 99%

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Millimeter to X-ray flares from Sagittarius A*

Eckart

García-Marín

Vogel

et al. 2012

A&A

146

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Context. We report on new simultaneous observations and modeling of the millimeter, near-infrared, and X-ray flare emission of the source Sagittarius A* (SgrA*) associated with the super-massive (4 × 10 6 M ) black hole at the Galactic center. Aims. We study the applicability of the adiabatic synchrotron source expansion model and study physical processes giving rise to the variable emission of SgrA* from the radio to the X-ray domain. Methods. Our observations were carried out on 18 May 2009 using the NACO adaptive optics (AO) instrument at the European Southern Observatory's Very Large Telescope, the ACIS-I instrument aboard the Chandra X-ray Observatory, the LABOCA bolometer at the Atacama Pathfinder EXperiment (APEX), and the CARMA mm telescope array at Cedar Flat, California. Results. The X-ray flare had an excess 2−8 keV luminosity between 6 and 12×10 33 erg s −1 . The observations reveal flaring activity in all wavelength bands that can be modeled as the signal from an adiabatically expanding synchrotron self-Compton (SSC) component.Modeling of the light curves shows that the sub-mm follows the NIR emission with a delay of about three-quarters of an hour with an expansion velocity of about v exp ∼ 0.009c. We find source component sizes of around one Schwarzschild radius, flux densities of a few Janskys, and spectral indices α of about +1 (S (ν) ∝ ν −α ). At the start of the flare, the spectra of the two main components peak just short of 1 THz. To statistically explain the observed variability of the (sub-)mm spectrum of SgrA*, we use a sample of simultaneous NIR/X-ray flare peaks and model the flares using a synchrotron and SSC mechanism. Conclusions. These parameters suggest that either the adiabatically expanding source components have a bulk motion larger than v exp or the expanding material contributes to a corona or disk, confined to the immediate surroundings of SgrA*. For the bulk of the synchrotron and SSC models, we find synchrotron turnover frequencies in the range of 300−400 GHz. For the pure synchrotron models, this results in densities of relativistic particles of the order of 10 6.5 cm −3 and for the SSC models, the median densities are about one order of magnitude higher. However, to obtain a realistic description of the frequency-dependent variability amplitude of SgrA*, models with higher turnover frequencies and even higher densities are required.

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Section: Adiabatically Expanding Source Componentsmentioning

confidence: 99%

Section: Adiabatically Expanding Source Componentsmentioning

confidence: 99%

Millimeter to X-ray flares from Sagittarius A*

Eckart

García-Marín

Vogel

et al. 2012

A&A

146

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“…Compton scattering of longer-wavelength photons [9][10][11] . The minimum intrinsic brightness temperature derived from our 1.3-mm results is 2 × 10 10 K.…”

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confidence: 99%

“…Plans to increase the sensitivity of the VLBI array described here by factors of up to 10 are under way, and the addition of more VLBI stations will increase baseline coverage and the ability to model increasingly complex structures. At projected VLBI array sensitivities, Sgr A* will be detected on multiple baselines within 10-s timescales, allowing sensitive tests for timevariable structures such as those suggested by orbiting hotspot 18 and flaring models [9][10][11] . Columns are observation date, correlated flux density on the ARO/SMT-JCMT baseline, signal to noise ratio of the VLBI detection, delay and delay-rate residual to the correlator model, and the baseline length projected in the direction of Sgr A*.…”

mentioning

confidence: 99%

Event-horizon-scale structure in the supermassive black hole candidate at the Galactic Centre

Doeleman

Weintroub

Rogers

et al. 2008

Nature

776

726

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The cores of most galaxies are thought to harbour supermassive black holes, which power galactic nuclei by converting the gravitational energy of accreting matter into radiation 1 . Sagittarius A*, the compact source of radio, infrared and X-ray emission at the centre of the Milky Way, is the closest example of this phenomenon, with an estimated black hole mass that is 4 million times that of the Sun 2,3 . A long-standing astronomical goal is to resolve structures in the innermost accretion flow surrounding Sgr A* where strong gravitational fields will distort the appearance of radiation emitted near the black hole. Radio observations at wavelengths of 3.5 mm and 7 mm have detected intrinsic structure in Sgr A*, but the spatial resolution of observations at these wavelengths is limited by interstellar scattering 4-7 . Here we report observations at a wavelength of 1.3 mm that set a size

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“…Top panel of Figure 3 shows the variability of the spectral indices estimated between the flux at 90 and 102 GHz. Recently, the other radio IDVs of Sgr A * were reported by some investigators (e.g., VLA at cm-wavelengths [17]; OVRO mm-interferometer at 3-mm [18]; VLA & ATCA at 7-& 12-mm [19]; SMA at 880μm (340 GHz) [20]). The variation of Sgr A * has probably the period of a few hours according to periodicity analyses in these reports [18], and our NMA results are consistent with the results of those.…”

Section: Intraday Variationmentioning

confidence: 87%