Detection of Polarized Millimeter and Submillimeter Emission from Sagittarius A*

Aitken, D. K.; Greaves, J. S.; Chrysostomou, A.; Jenness, Tim; Holland, W. S.; Hough, J. H.; Pierce-Price, D.; Richer, J. S.

doi:10.1086/312685

Cited by 172 publications

(232 citation statements)

References 21 publications

Supporting

Mentioning

208

Contrasting

Order By: Relevance

“…7, we show the observed flux densities of SgrA* taken from the literature (blue) (Zylka et al 1995;Serabyn et al 1997;Pierce-Price et al 2000;Aitken et al 2000;Marrone et al 2003) compared to a combined model that consists of the fits given by Falcke et al (2000) and Marrone et al (2003) line). At frequencies above 100 GHz, we selected a model that is representative of the emission contributed through the models presented by Dexter et al (2010) (black dashed line).…”

Section: Modeling the Variable Spectrum Of Sgra*mentioning

confidence: 99%

Millimeter to X-ray flares from Sagittarius A*

Eckart

García-Marín

Vogel

et al. 2012

A&A

146

View full text Add to dashboard Cite

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.

show abstract

Section: Modeling the Variable Spectrum Of Sgra*mentioning

confidence: 99%

Millimeter to X-ray flares from Sagittarius A*

Eckart

García-Marín

Vogel

et al. 2012

A&A

146

View full text Add to dashboard Cite

show abstract

“…Otherwise, our calculations incorporate all relativistic effects including frame dragging, gravitational redshift, light bending, and Doppler boosting. We use a second-order geodesic solver similar to that introduced by Bromley, Chen, & Miller The high-frequency data points are from Aitken et al (2000), and the curves are from the magnetohydrodynamic model discussed in the text. The limit at 84 GHz is from Bower et al (1999).…”

Section: Calculation Of the Polarimetric Imagementioning

confidence: 99%

“…This allows us to consistently map a position angle from one frame to another, an essential feature for calculating radiative transfer for the ordinary and extraordinary waves that make multiple passes through the disk. Aitken et al (2000) provide specific constraints for the magnetohydrodynamic disk model and our relativistic calculations in terms of the total flux and polarization of Sgr A*. The polarization "flip" in the spectrum near a wavelength of 1 mm is a particularly important constraint.…”

Section: Calculation Of the Polarimetric Imagementioning

confidence: 99%

“…During this past year, considerable progress has been made in modeling the structure and physical attributes of the inner emitting region surrounding Sgr A*, taking into account several crucial new data, including millimeter/submillimeter polarization measurements (Aitken et al 2000) and Chandra's identification of an X-ray counterpart (Baganoff et al 2001). In their analysis, Melia, Liu, & Coker (2000 concluded that the submillimeter bump is probably produced by thermal synchrotron emission in a tight Keplerian flow within the inner ∼5r S .…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Polarimetric Imaging of the Massive Black Hole at the Galactic Center

Bromley

Melia

Liu

2001

The Astrophysical Journal

119

115

View full text Add to dashboard Cite

The radio source Sagittarius A* in the Galactic center emits a polarized spectrum at millimeter and submillimeter wavelengths that is strongly suggestive of relativistic disk accretion onto a massive black hole. We use the wellconstrained mass of Sgr A* and a magnetohydrodynamic model of the accretion flow to match both the total flux and polarization from this object. Our results demonstrate explicitly that the shift in the position angle of the polarization vector, seen at wavelengths near the peak of the millimeter to submillimeter emission from this source, is a signal of relativistic accretion flow in a strong gravitational field. We provide maps of the polarized emission to illustrate how the images of polarized intensity from the vicinity of the black hole would appear in upcoming observations with very long baseline radio interferometers (VLBIs). Our results suggest that near-term VLBI observations will be able to directly image the polarized Keplerian portion of the flow near the horizon of the black hole.

show abstract

“…The submillimeter "excess" emission seen in the spectrum of this source appears to be associated with radiation produced within the inner Keplerian region. This view is supported by the linear polarization observed in Sgr A* at millimeter and submillimeter wavelengths (Aitken et al 2000), which is difficult to reconcile with other geometries of the emitting region. Both the degree of polarization and the rotation (by about 90Њ) in the position angle appear to be consistent with a transition of the emitting region within the Keplerian flow from optically thick emission (at millimeter and longer wavelengths) to optically thin emission in the submillimeter range (Melia 1992a(Melia , 1994.…”

mentioning

confidence: 99%

Accretion Processes in the Nucleus of M31

Liu

Melia

2001

The Astrophysical Journal

View full text Add to dashboard Cite

The hypothesized supermassive black hole in the nucleus of M31 (M31*) has many features in common with Sgr A* at the Galactic center, yet they differ in several significant and important ways. Although M31* is probably 10 times heavier, its radio luminosity at 3.6 cm is only one-third that of Sgr A*. At the same time, M31* is apparently thousands of times more luminous in X-rays than its Galactic center counterpart. Thus, a comparative study of these objects can be valuable in helping us to understand the underlying physical basis for their activity. We show here that the accretion model being developed for Sgr A* comprises two branches of solutions, distinguished by the relative importance of cooling compared to compressional heating at the radius where r C the ambient gas is captured by the black hole. For typical conditions in the interstellar medium, the initial temperature [ K] sits on the unstable branch of the cooling function. Depending on the actual 6 7T(r ) ∼ 10 -10 C value of and the accretion rate, the plasma settles onto either a hot branch (attaining a temperature as high T(r ) C as 10 10 K or so at small radii) or a cold branch, in which T drops to ∼10 4 K. Sgr A* is presumably a "hot" black hole. We show here that Very Large Array, Hubble Space Telescope, and Chandra observations of M31* reveal it to be a member of the "cold" black hole family. We discuss several predicted features in the spectrum of M31* that may be testable by future multiwavelength observations, including the presence of a prominent UV spike (from hydrogen line emission) that would be absent on the hot branch.

show abstract

Detection of Polarized Millimeter and Submillimeter Emission from Sagittarius A*

Cited by 172 publications

References 21 publications

Millimeter to X-ray flares from Sagittarius A*

Millimeter to X-ray flares from Sagittarius A*

Polarimetric Imaging of the Massive Black Hole at the Galactic Center

Accretion Processes in the Nucleus of M31

Contact Info

Product

Resources

About