Chandra Spectral and Timing Analysis of Sgr A*'s Brightest X-Ray Flares

Haggard, Daryl; Nynka, Melania; Mon, Brayden; Hernandez, Noelia de la Cruz; Nowak, Michael A.; Heinke, C. O.; Neilsen, Joey; Dexter, Jason; Fragile, P. Chris; Baganoff, F. K.; Bower, Geoffrey C.; Corrales, Lía; Zelati, F. Coti; Degenaar, N.; Markoff, Sera; Morris, Mark; Ponti, G.; Rea, N.; Wilms, J.; Yusef‐Zadeh, F.

doi:10.3847/1538-4357/ab4a7f

Cited by 49 publications

(47 citation statements)

References 94 publications

(152 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Sgr A* shows large-amplitude "flares" simultaneously at near-infrared (NIR, Genzel et al 2003;Ghez et al 2004) and X-ray (Baganoff et al 2001) wavelengths. They originate from transiently heated electrons, likely as a result of magnetic reconnection or shocks (Markoff et al 2001) close to the black hole (Barrière et al 2014;Haggard et al 2019). The observed emission is due to synchrotron radiation at radio to NIR (and likely also X-ray, Dodds-Eden et al 2009) The flares can now be spatially resolved with the second generation VLT Interferometer beam combiner instrument GRAVITY.…”

Section: Introductionmentioning

confidence: 99%

A parameter survey of Sgr A* radiative models from GRMHD simulations with self-consistent electron heating

Dexter

Jiménez-Rosales

Ressler

et al. 2020

Monthly Notices of the Royal Astronomical Society

Self Cite

View full text Add to dashboard Cite

The Galactic center black hole candidate Sgr A* is the best target for studies of lowluminosity accretion physics, including with near-infrared and submillimeter wavelength long baseline interferometry experiments. Here we compare images and spectra generated from a parameter survey of general relativistic MHD simulations to a set of radio to near-infrared observations of Sgr A*. Our models span the limits of weak and strong magnetization and use a range of sub-grid prescriptions for electron heating. We find two classes of scenarios can explain the broad shape of the submillimeter spectral peak and the highly variable near-infrared flaring emission. Weakly magnetized "disk-jet" models where most of the emission is produced near the jet wall, consistent with past work, as well as strongly magnetized (magnetically arrested disk) models where hot electrons are present everywhere. Disk-jet models are strongly depolarized at submillimeter wavelengths as a result of strong Faraday rotation, inconsistent with observations of Sgr A*. We instead favor the strongly magnetized models, which provide a good description of the median and highly variable linear polarization signal. The same models can also explain the observed mean Faraday rotation measure and potentially the polarization signals seen recently in Sgr A* near-infrared flares.

show abstract

Section: Introductionmentioning

confidence: 99%

A parameter survey of Sgr A* radiative models from GRMHD simulations with self-consistent electron heating

Dexter

Jiménez-Rosales

Ressler

et al. 2020

Monthly Notices of the Royal Astronomical Society

Self Cite

View full text Add to dashboard Cite

show abstract

“…There is overwhelming evidence that the Galactic Centre harbours a massive black hole, Sagittarius A* (Sgr A*, Ghez et al Eisenhauer et al 2005;Macquart & Bower 2006;Marrone et al 2008;Eckart et al 2008a;Do et al 2009Do et al , 2019bWitzel et al 2018). The simultaneous, large amplitude variations ("flares") seen in the near-infrared (NIR) and X-ray (Yusef-Zadeh et al 2006;Eckart et al 2008b) are the result of transiently heated relativistic electrons near the black hole, which are likely heated in shocks or by magnetic reconnection (Markoff et al 2001;Yuan et al 2003; Barrière et al 2014;Haggard et al 2019).…”

Section: Introductionmentioning

confidence: 99%

Dynamically important magnetic fields near the event horizon of Sgr A*

Jiménez-Rosales¹,

Dexter²,

Widmann³

et al. 2020

A&A

View full text Add to dashboard Cite

We study the time-variable linear polarisation of Sgr A* during a bright near-infrared flare observed with the GRAVITY instrument on July 28, 2018. Motivated by the time evolution of both the observed astrometric and polarimetric signatures, we interpret the data in terms of the polarised emission of a compact region (“hotspot”) orbiting a black hole in a fixed, background magnetic field geometry. We calculated a grid of general relativistic ray-tracing models, created mock observations by simulating the instrumental response, and compared predicted polarimetric quantities directly to the measurements. We take into account an improved instrument calibration that now includes the instrument’s response as a function of time, and we explore a variety of idealised magnetic field configurations. We find that the linear polarisation angle rotates during the flare, which is consistent with previous results. The hotspot model can explain the observed evolution of the linear polarisation. In order to match the astrometric period of this flare, the near horizon magnetic field is required to have a significant poloidal component, which is associated with strong and dynamically important fields. The observed linear polarisation fraction of ≃30% is smaller than the one predicted by our model (≃50%). The emission is likely beam depolarised, indicating that the flaring emission region resolves the magnetic field structure close to the black hole.

show abstract

“…However, the maximum peak of NIR emission is ∼ 0.5 mJy, which is an order of magnitude lower than the observed flaring flux (Dodds-Eden et al 2011). Moreover, the X-ray luminosity lies below the value of 2 × 10 34 erg s −1 for the entire time period, which is still identified as an X-ray 'quiescent' state: the observed luminosities of the bright X-ray flares are > 10 35 erg s −1 (Haggard et al 2019). One possible reason is that our assumption of purely thermal electrons is not sufficient to produce NIR flares, since non-thermal electrons can be produced near the BH via relativistic magnetic reconnection (Werner et al 2016).…”

Section: Variabilitymentioning

confidence: 70%

Spectral and imaging properties of Sgr A* from high-resolution 3D GRMHD simulations with radiative cooling

Yoon

Chatterjee

Markoff

et al. 2020

Monthly Notices of the Royal Astronomical Society

Self Cite

View full text Add to dashboard Cite

The candidate supermassive black hole in the Galactic Centre, Sagittarius A* (Sgr A*), is known to be fed by a radiatively inefficient accretion flow (RIAF), inferred by its low accretion rate. Consequently, radiative cooling has in general been overlooked in the study of Sgr A*. However, the radiative properties of the plasma in RIAFs are poorly understood. In this work, using full 3D general-relativistic magneto-hydrodynamical simulations, we study the impact of radiative cooling on the dynamical evolution of the accreting plasma, presenting spectral energy distributions and synthetic sub-millimeter images generated from the accretion flow around Sgr A*. These simulations solve the approximated equations for radiative cooling processes self-consistently, including synchrotron, bremsstrahlung, and inverse Compton processes. We find that radiative cooling plays an increasingly important role in the dynamics of the accretion flow as the accretion rate increases: the mid-plane density grows and the infalling gas is less turbulent as cooling becomes stronger. The changes in the dynamical evolution become important when the accretion rate is larger than 10−8 M⊙ yr−1 ($\gtrsim 10^{-7} \dot{M}_{\rm Edd}$, where $\dot{M}_{\rm Edd}$ is the Eddington accretion rate). The resulting spectra in the cooled models also differ from those in the non-cooled models: the overall flux, including the peak values at the sub-mm and the far-UV, is slightly lower as a consequence of a decrease in the electron temperature. Our results suggest that radiative cooling should be carefully taken into account in modelling Sgr A* and other low-luminosity active galactic nuclei that have a mass accretion rate of $\dot{M} > 10^{-7}\, \dot{M}_{\rm Edd}$.

show abstract

Chandra Spectral and Timing Analysis of Sgr A*'s Brightest X-Ray Flares

Cited by 49 publications

References 94 publications

A parameter survey of Sgr A* radiative models from GRMHD simulations with self-consistent electron heating

A parameter survey of Sgr A* radiative models from GRMHD simulations with self-consistent electron heating

Dynamically important magnetic fields near the event horizon of Sgr A*

Spectral and imaging properties of Sgr A* from high-resolution 3D GRMHD simulations with radiative cooling

Contact Info

Product

Resources

About