A Nonthermal Bomb Explains the Near-infrared Superflare of Sgr A*

Gutiérrez, Eduardo Mario; Nemmen, Rodrigo; Cafardo, Fabio

doi:10.3847/2041-8213/ab7998

Cited by 24 publications

(27 citation statements)

References 32 publications

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“…Bright, coincident episodic X-ray and near-infrared flares are detected on roughly a daily basis coming from Sgr A * , the supermassive black hole in the center of our Galaxy (see e.g., Baganoff et al 2001;Genzel et al 2003;Marrone et al 2008;Meyer et al 2008;Neilsen et al 2013;Fazio et al 2018;Boyce et al 2019). The origin of these flares is generally associated with electron acceleration in a localized flaring region not larger 2008; Younsi & Wu 2015;Ball et al 2016;Li et al 2017;Gutiérrez et al 2020). If such a reconnection layer becomes thin enough it can be liable to the tearing instability, break up, and produce chains of plasmoids (Loureiro et al 2007) that interact, merge, grow, and are advected with the flow.…”

Section: Introductionmentioning

confidence: 96%

Magnetic Reconnection and Hot Spot Formation in Black Hole Accretion Disks

Ripperda

Bacchini

Philippov

2020

ApJ

167

147

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Hot spots, or plasmoids, forming due to magnetic reconnection in current sheets, are conjectured to power frequent X-ray and near-infrared flares from Sgr A * , the black hole in the center of our Galaxy. It is unclear how, where, and when current sheets form in black-hole accretion disks. We perform axisymmetric general-relativistic resistive magnetohydrodynamics simulations to model reconnection and plasmoid formation in a range of accretion flows. Current sheets and plasmoids are ubiquitous features which form regardless of the initial magnetic field in the disk, the magnetization in the quasisteady-state phase of accretion, and the spin of the black hole. Within 10 Schwarzschild radii from the event horizon, we observe plasmoids forming, after which they can merge, grow to macroscopic scales of the order of a few Schwarzschild radii, and are ultimately advected along the jet's sheath or into the disk. Large plasmoids are energized to relativistic temperatures via reconnection and contribute to the jet's limb-brightening. We find that only hot spots forming in magnetically arrested disks can potentially explain the energetics of Sgr A * flares. The flare period is determined by the reconnection rate, which we find to be between 0.01c and 0.03c in all cases, consistent with studies of reconnection in isolated Harris-type current sheets. We quantify magnetic dissipation and non-ideal electric fields which can efficiently inject non-thermal particles. We show that explicit resistivity allows for converged numerical solutions, such that the electromagnetic energy evolution and dissipation become independent of the grid scale for the extreme resolutions considered here.

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Section: Introductionmentioning

confidence: 96%

Magnetic Reconnection and Hot Spot Formation in Black Hole Accretion Disks

Ripperda

Bacchini

Philippov

2020

ApJ

167

147

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“…There is also significant observational evidence that supports the idea that particles are accelerated in HAFs: The steady radio emission from Sgr A* is thought to be produced by a population of nonthermal electrons within the HAF that feeds the central black hole (Yuan et al 2003;Liu & Wu 2013). Additionally, the multiwavelength flaring activity of this source is likely related to nonthermal activity in the flow (Yuan et al 2003Gutiérrez et al 2020;Dexter et al 2020). Recently, Inoue & Doi (2018) found evidence of nonthermal electron activity occurring in the corona of more luminous AGNs such as Seyfert I galaxies.…”

Section: Introductionmentioning

confidence: 96%

Nonthermal processes in hot accretion flows onto supermassive black holes: An inhomogeneous model

Gutiérrez

Vieyro

Romero

2021

A&A

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Context. Many low-redshift active galactic nuclei harbor a supermassive black hole accreting matter at low or medium rates. At such rates, the accretion flow usually consists of a cold optically thick disk, plus a hot, low density, collisionless corona. In the latter component, charged particles can be accelerated to high energies by various mechanisms. Aims. We aim to investigate, in detail, nonthermal processes in hot accretion flows onto supermassive black holes, covering a wide range of accretion rates and luminosities. Methods. We developed a model consisting of a thin Shakura-Sunyaev disk plus an inner hot accretion flow or corona, modeled as a radiatively inefficient accretion flow, where nonthermal processes take place. We solved the transport equations for relativistic particles and estimated the spectral energy distributions resulting from nonthermal interactions between the various particle species and the fields in the source. Results. We covered a variety of scenarios, from low accretion rates up to 10% of the Eddington limit, and identified the relevant cooling mechanisms in each case. The presence of hadrons in the hot flow is decisive for the spectral shape, giving rise to secondary particles and gamma-ray cascades. We applied our model to the source IC 4329A, confirming earlier results which showed evidence of nonthermal particles in the corona.

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“…Thus, the framework of a "windy" star is likely flawed. In Gutiérrez et al (2020), in which the PhD candidate is a coauthor, a completely different scenario is proposed-independent of an increase in the mass accretion rate. Analogously to a nonthermal bomb, we suggest that the flare was the result of particle acceleration to nonthermal energies, leading to an explosive event in the innermost parts of the accretion flow.…”

Section: Variability and Flaresmentioning

confidence: 99%

“…The first one is Gutiérrez et al (2020) (already mentioned in Section 1.3.3.3 and reproduced in the following pages), from which the doctoral candidate was a coauthor. The Article explains an unprecedented NIR flare from Sgr A * in May 2019 as the result of particle acceleration to nonthermal energies in the innermost parts of the accretion flow.…”

Section: Appendixmentioning

confidence: 99%

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Exploring Sagittarius A* in gamma-rays with Fermi LAT Telescope

Cafardo¹

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Sagittarius A * (Sgr A * )-the supermassive black hole (SMBH) in the center of our galaxy-has been identified in most of the electromagnetic spectrum, from radio to Xrays. Diffuse gamma-ray emission has been observed around Sgr A * and a gamma-ray point source has been detected coinciding with the SMBH's position, although there is still no definitive association between the two. In this work, we have used ∼11 years of Fermi Large Area Telescope (LAT) observations of the point source 4FGL J1745.6−2859 and performed a detailed analysis across four energy bands. Our goal is to elucidate the nature of the gamma-ray emission at the Galactic Center (GC) and whether it is associated with the SMBH. We find that the centroids of the emission approach Sgr A * 's location as the energy increases and they are spatially associated with gas-rich regions in the GC.Assuming that the gamma-ray point source is located at the GC, we estimate a luminosity of 2.61 × 10 36 erg s −1 in the 100 MeV to 500 GeV energy range. This is consistent with Sgr A * 's bolometric luminosity. Based on the point source properties, we ruled out several potential candidates for its nature and favor a cosmic ray origin accelerated by-or in the vicinity of-the SMBH. We also created light curves (LCs), with time bins as short as 15 days, in search of variability in the 4FGL J1745.6−2859 gamma-ray flux. In contrast with Sgr A * 's flaring behavior in longer wavelengths, we detect that its gamma-ray flux distribution is compatible with a Gaussian, representative of a normal random process, hinting that the gamma-ray emission mechanism differs substantially from the low-energy regime. Finally, 4FGL J1745.6−2859's spectral energy distribution (SED) shows a "piondecay bump" characteristic of gamma-ray hadronic emission. Its SED is also compatible with several hadronic models for Sgr A * 's gamma-ray emission. Our results indicate that the point source at the GC is indeed the gamma-ray counterpart of Sgr A * in the GeV range. The characteristics of this emission-its spatial coincidence with gas reservoirs, energetics, lack of variability and SED-suggest that hadronic processes are likely behind its origin.

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A Nonthermal Bomb Explains the Near-infrared Superflare of Sgr A*

Cited by 24 publications

References 32 publications

Magnetic Reconnection and Hot Spot Formation in Black Hole Accretion Disks

Magnetic Reconnection and Hot Spot Formation in Black Hole Accretion Disks

Nonthermal processes in hot accretion flows onto supermassive black holes: An inhomogeneous model

Exploring Sagittarius A* in gamma-rays with Fermi LAT Telescope

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