arXiv subjects

H. Bushouse

Publications and source records attributed to H. Bushouse.

At least 19 recordsLinked to original sources

arXiv2026

Observational Tests of Sgr A*'s State of the Accretion Flow

General relativistic magneto-hydrodynamic (GRMHD) simulations of the possibly magnetically arrested disk (MAD) of the accretion flow of Sgr A* predict short and long time variability, lumpiness in the flow, strong magnetic fields, reconnection driving flux eruptions and a jet aligned with its spin angular momentum. We carried out simultaneous multi-wavelength observations with the objective of placing some constraints on these predictions. Our analysis supports most of the predictions of the MAD picture of the flow. It is not clear if there is evidence for a jet, but this could be the result of confusion in the complex region surrounding Sgr A*. Also, the geometry of the magnetic fields, which accelerate particles to produce X-ray emission via inverse Compton Scattering (ICS), appears to be consistent with a hybrid state where the accretion flow is represented by MAD-like magnetic field strength and with Standard and Normal Evolution-like (SANE-like) magnetic field geometry.

astro-ph.GA↗

arXiv2025

Simultaneous JWST, NuSTAR, and VLA Monitoring of Sgr A*: A Unified Picture of the Variable IR, X-ray and Radio Emission

Flux variability is a fundamental channel of information from Sgr A* because of its direct probe of processes occurring within an accretion disk under strong gravity. We present simultaneous IR, X-ray and radio observations of Sgr A* on 2024 Apr 05 using JWST, NuSTAR, and VLA. We report the detection of a strong X-ray flare with a luminosity of $\sim5.2x10^{35}$ erg/s coincident with a bright near-IR flare, and a brightening in radio about an hour later. We investigate the candidate physical mechanisms for the X-ray flare emission and conclude that this can best be explained by inverse Compton scattering of near-IR flare radiation. We propose a dynamic scenario analogous to a coronal mass ejection in which a magnetic flux rope is ejected from Sgr A*'s inner accretion flow with a current sheet extending down from the rope to the bulk of the accretion flow. Reconnection within the sheet produces oppositely directed flows of accelerated particles moving upwards towards the rope and downwards towards the accretion flow. Infrared radiation from the approaching energetic electrons is enhanced by beaming and up-scattered by thermal electrons in the accretion flow to produce the strong X-ray flare. Meanwhile, the relativistic electrons moving in the opposite direction away from the disk experience weaker magnetic fields so radiate at longer wavelengths by feeding into the magnetic flux tube and adiabatically cooled during its subsequent expansion. This physical picture attempts to unify the origin of the variable emission from Sgr A* at IR, X-ray and radio/submm wavelengths.

astro-ph.HE↗

arXiv2025

Non-stop Variability of Sgr A* using JWST at 2.1 and 4.8 micron Wavelengths: Evidence for Distinct Populations of Faint and Bright Variable Emission

We present first results of JWST Cycle 1 and 2 observations of Sgr A* using NIRCam taken simultaneously at 2.1 and 4.8 micron for a total of ~48 hours over seven different epochs in 2023 and 2024. We find correlated variability at 2.1 and 4.8 micron in all epochs, continual short-time scale (a few seconds) variability and epoch-to-epoch variable emission implying long-term ( ~days to months) variability of Sgr A*. A highlight of this analysis is the evidence for sub-minute, horizon-scale time variability of Sgr A*, probing inner accretion disk size scales. The power spectra of the light curves in each observing epoch also indicate long-term variable emission. With continuous observations, JWST data suggest that the flux of Sgr A* is fluctuating constantly. The flux density correlation exhibits a distinct break in the slope at ~3 mJy at 2.1 micron. The analysis indicates two different processes contributing to the variability of Sgr A*. Brighter emission trends towards shallower spectral indices than the fainter emission. Cross correlation of the light curves indicates for the first time, a time delay of 3 - 40 sec in the 4.8 micron variability with respect to 2.1 micron. This phase shift leads to loops in plots of flux density vs spectral index as the emission rises and falls. Modeling suggests that the synchrotron emission from the evolving, age-stratified electron population reproduces the shape of the observed light curves with a direct estimate of the magnetic field strengths in the range between 40-90 G, and upper cutoff energy, E_c, between 420 and 720 MeV.

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arXiv2017

ALMA and VLA observations of emission from the environment of Sgr A*

We present 44 and 226 GHz observations of the Galactic center within 20$"$ of Sgr A*. Millimeter continuum emission at 226 GHz is detected from eight stars that have previously been identified at near-IR and radio wavelengths. We also detect a 5.8 mJy source at 226 GHz coincident with the magnetar SGR~J1745-29 located 2.39$"$ SE of Sgr A* and identify a new 2.5$"\times1.5"$ halo of mm emission centered on Sgr A*. The X-ray emission from this halo has been detected previously and is interpreted in terms of a radiatively inefficient accretion flow. The mm halo surrounds an EW linear feature which appears to arise from Sgr A* and coincides with the diffuse X-ray emission and a minimum in the near-IR extinction. We argue that the millimeter emission is produced by synchrotron emission from relativistic electrons in equipartition with a $\sim 1.5$mG magnetic field. The origin of these is unclear but its coexistence with hot gas supports scenarios in which the gas is produced by the interaction of winds either from the fast moving S-stars, the photo-evaporation of low-mass YSO disks or by a jet-driven outflow from Sgr A*. The spatial anti-correlation of the X-ray, radio and mm emission from the halo and the low near-IR extinction provides compelling evidence for an outflow sweeping up the interstellar material, creating a dust cavity within 2$"$ of Sgr A*. Finally, the radio and mm counterparts to eight near-IR identified stars within $\sim$10\arcs\ of Sgr A* provide accurate astrometry to determine the positional shift between the peak emission at 44 and 226 GHz.

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arXiv2016

Multiwavelength study of the flaring activity of Sgr A* in 2014 February-April

The supermassive black hole Sgr A* is located at the Milky Way center. We studied its flaring activity close to the DSO/G2 pericenter passage to constrain the physical properties and origin of the flares. Simultaneous/coordinated observations were made in 2014 Feb-Apr with XMM-Newton, HST/WFC3, VLT/SINFONI, VLA and CARMA. We detected 2 X-ray and 3 NIR flares on Mar. 10 and Apr. 2 with XMM-Newton and HST and 2 NIR flares on Apr. 3 and 4 with VLT. The Mar. 10 X-ray flare has a long rise and a rapid decay. Its NIR counterpart peaked 4320s before the X-ray peak implying a variation in the X-ray-to-NIR flux ratio. This flare may be a single flare where change in the flux ratio is explained by the adiabatic compression of a plasmon or 2 close flares with simultaneous X-ray/NIR peaks. We observed an increase in the rising radio flux density on Mar. 10 with the VLA. It could be the delayed emission from a NIR/X-ray flare preceding our observation. The Apr. 2 X-ray flare occurred for HST in the Earth occultation of Sgr A*. We thus only observed the start of its NIR counterpart. After the occultation, we observed the decay phase of a bright NIR flare with no X-ray counterpart. On Apr. 3, 2 CARMA flares were observed. The 1rst one may be the delayed emission of a VLT NIR flare. We thus observed 7 NIR flares whose 3 have an X-ray counterpart. We studied the physical parameters of the flaring region for each NIR flare but none of the possible radiative processes can be ruled out for the X-ray flares creation. Our X-ray flaring rate is consistent with those observed in the 2012 Chandra XVP campaign. No increase in the flaring activity was thus triggered close to the DSO/G2 pericenter passage. Moreover, higher X-ray flaring rates had already been observed with no increase in the quiescent level. There is thus no direct link between an X-ray flaring-rate increase and an accretion-rate change. (abridged)

astro-ph.HE↗

arXiv2016

Sgr A* and its Environment: Low Mass Star Formation, the Origin of X-ray Gas and Collimated Outflow

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 13N and IRS 13E. The ridge suggests that an outflow of east-west blob-like structures is emerging from Sgr A*. We also find arc-like features within the ridge with morphologies suggestive of photoevaporative protoplanetary disks. We use near-IR 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 YSOs at a rate ~10^{-6} solar mass per year. 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, we detect new cometary radio and nea-IR sources and a striking tower of radio emission suggesting that they 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$\sim50-60^\circ$ with ~10^{-7} solar mass per year, and opening angle 10 degrees.

astro-ph.GA↗

arXiv2015

Compact Radio Sources within 30" of Sgr A: Proper Motions, Stellar Winds and the Accretion Rate onto Sgr A

Recent broad-band 34 and 44 GHz radio continuum observations of the Galactic center have revealed 41 massive stars identified with near-IR counterparts, as well as 44 proplyd candidates within 30" of Sgr A*. Radio observations obtained in 2011 and 2014 have been used to derive proper motions of eight young stars near Sgr A*. The accuracy of proper motion estimates based on near-IR observations by Lu et al. and Paumard et al. have been investigated by using their proper motions to predict the 2014 epoch positions of near-IR stars and comparing the predicted positions with those of radio counterparts in the 2014 radio observations. Predicted positions from Lu et al. show an rms scatter of 6 mas relative to the radio positions, while those from Paumard et al. show rms residuals of 20 mas, which is mainly due to uncertainties in the IR-based proper motions. Under the assumption of homogeneous ionized winds, we also determine the mass-loss rates of 11 radio stars, finding rates that are on average $\sim$2 times smaller than those determined from model atmosphere calculations and near-IR data. Clumpiness of ionized winds would reduce the mass loss rate of WR and O stars by additional factors of 3 and 10, respectively. One important implication of this is a reduction in the expected mass accretion rate onto Sgr A* from stellar winds by nearly an order of magnitude to a value of few$\times10^{-7}$ \msol\ yr$^{-1}$. Finally, we present the positions of 318 compact 34.5 GHz radio sources within 30\arcs\ of Sgr A*. At least 45 of these have stellar counterparts in the near-IR $K_s$ (2.18 $μ$m) and $L'$ (3.8$μ$m) bands.

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arXiv2015

Monitoring the Dusty S-Cluster Object (DSO/G2) on its Orbit towards the Galactic Center Black Hole

We analyse and report in detail new near-infrared (1.45 - 2.45 microns) observations of the Dusty S-cluster Object (DSO/G2) during its approach to the black hole at the center of the Galaxy that were carried out with ESO VLT/SINFONI between February and September 2014. Before May 2014 we detect spatially compact Br-gamma and Pa-alpha line emission from the DSO at about 40mas east of SgrA*. The velocity of the source, measured from the red-shifted emission, is 2700+-60 km/s. No blue-shifted emission above the noise level is detected at the position of SgrA* or upstream the presumed orbit. After May we find spatially compact Br-gamma blue-shifted line emission from the DSO at about 30mas west of SgrA* at a velocity of -3320+-60 km/s and no indication for significant red-shifted emission. We do not detect any significant extension of velocity gradient across the source. We find a Br-gamma-line full width at half maximum of 50+-10 Angstroem before and 15+-10 Angstroem after the peribothron transit, i.e. no significant line broadening with respect to last year is observed. Br-gamma line maps show that the bulk of the line emission originates from a region of less than 20mas diameter. This is consistent with a very compact source on an elliptical orbit with a peribothron time passage in 2014.39+-0.14. For the moment, the flaring activity of the black hole in the near-infrared regime has not shown any statistically significant increment. Increased accretion activity of SgrA* may still be upcoming. We discuss details of a source model according to which the DSO is rather a young accreting star than a coreless gas and dust cloud.

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arXiv2014

The Discovery of Radio Stars within 10 arcseconds of Sgr A* at 7mm

Very Large Array observations of the Galactic Center at 7 mm have produced an image of the 30 arcseconds surrounding Sgr A* with a resolution of 82x42 milliarcseconds (mas). A comparison with IR images taken simultaneously with the Very Large Telescope (VLT) identifies 41 radio sources with L-band (3.8 microns) stellar counterparts. The well-known young, massive stars in the central Sgr A* cluster (e.g., IRS 16C, IRS 16NE, IRS 16SE2, IRS 16NW, IRS 16SW, AF, AFNW, IRS 34W and IRS 33E) are detected with peak flux densities between 0.2 and 1.3 mJy. The origin of the stellar radio emission in the central cluster is discussed in terms of ionized stellar winds with mass-loss rates in the range 0.8-5x10^{-5} solar mass per year. Radio emission from eight massive stars is used as a tool for registration between the radio and infrared frames with mas precision within a few arcseconds of Sgr A*. This is similar to the established technique of aligning SiO masers and evolved stars except that radio stars lie within a few arcseconds of Sgr A*. Our data show a scatter of ~6.5 mas in the positions of the eight radio sources that appear in both the L-band and 7 mm images. Lastly, we use the radio and IR data to argue that members of IRS 13N are Young Stellar Objects rather than dust clumps, supporting the hypothesis that recent star formation has occurred near Sgr A*.

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arXiv2013

ALMA Observations of the Galactic Center: SiO Outflows and High Mass Star Formation near Sgr A*

ALMA observations of the Galactic center with spatial resolution $2.61"\times0.97"$ resulted in the detection of 11 SiO (5-4) clumps of molecular gas within 0.6pc (15$"$) of Sgr A*, interior to the 2-pc circumnuclear molecular ring. The three SiO (5-4) clumps closest to Sgr A* show the largest central velocities, $\sim150$ \kms, and broadest asymmetric linewidths with full width zero intensity (FWZI) $\sim110-147$ \kms. The remaining clumps, distributed mainly to the NE of the ionized mini-spiral, have narrow FWZI ($\sim18-56$ \kms). Using CARMA SiO (2-1) data, LVG modeling of the the SiO line ratios for the broad velocity clumps, constrains the column density N(SiO) $\sim10^{14}$ cm$^{-2}$, and the H$_2$ gas density n$_{\rm H_2}=(3-9)\times10^5$ cm$^{-3}$ for an assumed kinetic temperature 100-200K. The SiO clumps are interpreted as highly embedded protostellar outflows, signifying an early stage of massive star formation near Sgr A* in the last $10^4-10^5$ years. Support for this interpretation is provided by the SiO (5-4) line luminosities and velocity widths which lie in the range measured for protostellar outflows in star forming regions in the Galaxy. Furthermore, SED modeling of stellar sources shows two YSO candidates near SiO clumps, supporting in-situ star formation near Sgr A*. We discuss the nature of star formation where the gravitational potential of the black hole dominates. In particular, we suggest that external radiative pressure exerted on self-shielded molecular clouds enhances the gas density, before the gas cloud become gravitationally unstable near Sgr A*. Alternatively, collisions between clumps in the ring may trigger gravitational collapse.

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arXiv2012

A Three Parsec-Scale Jet-Driven Outflow from Sgr A*

The compact radio source Sgr A* is coincident with a 4 million solar mass black hole at the dynamical center of the Galaxy and is surrounded by dense orbiting ionized and molecular gas. We present high resolution radio continuum images of the central 3' and report a faint continuous linear structure centered on Sgr A* with a PA~60 degrees. The extension of this feature appears to be terminated symmetrically by two linearly polarized structures at 8.4 GHz, ~75" from Sgr A*. A number of weak blobs of radio emission with X-ray counterparts are detected along the axis of the linear structure. The linear structure is best characterized by a mildly relativistic jet from Sgr A* with an outflow rate 10^-6 solar mass per year. The near and far-sides of the jet are interacting with orbiting ionized and molecular gas over the last 1-3 hundred years and are responsible for a 2" hole, the "minicavity", characterized by disturbed kinematics, enhanced FeII/III line emission, and diffuse X-ray gas. The estimated kinetic luminosity of the outflow is ~1.2x10^{41} erg/s, so the interaction with the bar may be responsible for the Galactic center X-ray flash inferred to be responsible for much of the fluorescent Fe Kalpha line emission from the inner 100pc of the Galaxy.

astro-ph.HE↗

arXiv2012

An Inverse Compton Scattering Origin of X-ray Flares from Sgr A*

The X-ray and near-IR emission from Sgr A* is dominated by flaring, while a quiescent component dominates the emission at radio and sub-mm wavelengths. The spectral energy distribution of the quiescent emission from Sgr A* peaks at sub-mm wavelengths and is modeled as synchrotron radiation from a thermal population of electrons in the accretion flow, with electron temperatures ranging up to $\sim 5-20$\,MeV. Here we investigate the mechanism by which X-ray flare emission is produced through the interaction of the quiescent and flaring components of Sgr A*. The X-ray flare emission has been interpreted as inverse Compton, self-synchrotron-Compton, or synchrotron emission. We present results of simultaneous X-ray and near-IR observations and show evidence that X-ray peak flare emission lags behind near-IR flare emission with a time delay ranging from a few to tens of minutes. Our Inverse Compton scattering modeling places constraints on the electron density and temperature distributions of the accretion flow and on the locations where flares are produced. In the context of this model, the strong X-ray counterparts to near-IR flares arising from the inner disk should show no significant time delay, whereas near-IR flares in the outer disk should show a broadened and delayed X-ray flare.

astro-ph.HE↗

arXiv2011

HST Observations of the Stellar Distribution Near Sgr A*

We present HST/NICMOS data to study the surface brightness distribution of stellar light within the inner 10" of Sgr A* at 1.4, 1.7 and 1.9 microns. We use these data to independently examine the surface brightness distribution that had been measured previously with NICMOS and to determine whether there is a drop in the surface density of stars very near Sgr A*. Our analysis confirms that a previously reported drop in the surface brightness within 0.8" of Sgr A* is an artifact of bright and massive stars near that radius. We also show that the surface brightness profile within 5" or ~0.2 pc of Sgr A* can be fitted with broken power laws. The power laws are consistent with previous measurements, in that the profile becomes shallower at small radii. For radii > 0.7" the slope is beta=-0.34\pm0.04 where Sigma is proportional to r^beta and becomes flatter at smaller radii with beta=-0.13\pm0.04. Modeling of the surface brightness profile gives a stellar density that increases roughly as r^-1 within the inner 1" of Sgr A*. This slope confirms earlier measurements in that it is not consistent with that expected from an old, dynamically-relaxed stellar cluster with a central supermassive black hole. Assuming that the diffuse emission is not contaminated by a faint population of young stars down to the 17.1 magnitude limit of our imaging data at 1.70$μ$, the shallow cusp profile is not consistent with a decline in stellar density in the inner arcsecond. In addition, converting our measured diffuse light profile to a stellar mass profile, with the assumption that the light is dominated by K0 dwarfs, the enclosed stellar mass within radius r < 0.1 pc of Sgr A* is ~ 3.2x10^4 M_solar (r/0.1 {pc})^2.1.

astro-ph.GA↗

arXiv2010

Massive Star Formation of the Sgr A East HII Regions Near the Galactic Center

A group of four compact HII regions associated with the well-known 50 km/s molecular cloud is the closest site of on-going star formation to the dynamical center of the Galaxy, at a projected distance of ~6 pc. We present a study of ionized gas based on the [NeII] (12.8 micron) line, as well as multi-frequency radio continuum, HST Pa alpha and Spitzer IRAC observations of the most compact member of the HII group, Sgr A East HII D. The radio continuum image at 6cm shows that this source breaks up into two equally bright ionized features, D1 and D2. The SED of the D source is consistent with it being due to a 25\pm3 solar mass, star with a luminosity of 8\pm3x10^4 solar luminosity. The inferred mass, effective temperature of the UV source and the ionization rate are compatible with a young O9-B0 star. The ionized features D1 and D2 are considered to be ionized by UV radiation collimated by an accretion disk. We consider that the central massive star photoevaporates its circumstellar disk on a timescale of 3x10^4 years giving a mass flux ~3x10^{-5} solar mass per yr and producing the ionized material in D1 and D2 expanding in an inhomogeneous medium. The ionized gas kinematics, as traced by the [Ne II] emission, is difficult to interpret, but it could be explained by the interaction of a bipolar jet with surrounding gas along with what appears to to be a conical wall of lower velocity gas. The other HII regions, Sgr A East A-C, have morphologies and kinematics that more closely resemble cometary flows seen in other compact HII regions, where gas moves along a paraboloidal surface formed by the interaction of a stellar wind with a molecular cloud.

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arXiv2010

Occultation of the Quiescent Emission from Sgr A* by IR Flares

We have investigated the nature of flare emission from Sgr A* during multi-wavelength observations of this source that took place in 2004, 2005 and 2006. We present evidence for dimming of submm and radio flux during the peak of near-IR flares. This suggests that the variability of Sgr A* across its wavelength spectrum is phenomenologically related. The model explaining this new behavior of flare activity could be consistent with adiabatically cooling plasma blobs that are expanding but also partially eclipsing the background quiescent emission from Sgr A*. When a flare is launched, the plasma blob is most compact and is brightest in the optically thin regime whereas the emission in radio/submm wavelengths has a higher opacity. Absorption in the observed light curve of Sgr A* at radio/submm flux is due to the combined effects of lower brightness temperature of plasma blobs with respect to the quiescent brightness temperature and high opacity of plasma blobs. This implies that plasma blobs are mainly placed in the magnetosphere of a disk-like flow or further out in the flow. The depth of the absorption being larger in submm than in radio wavelengths implies that the intrinsic size of the quiescent emission increases with increasing wavelength which is consistent with previous size measurements of Sgr A*. Lastly, we believe that occultation of the quiescent emission of Sgr A* at radio/submm by IR flares can be used as a powerful tool to identify flare activity at its earliest phase of its evolution.

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arXiv2010

The Size Evolution of Passive Galaxies: Observations from the Wide Field Camera 3 Early Release Science Program

We present results on the size evolution of passively evolving galaxies at 1 1.5. We identify 30 galaxies in ~40 square arcmin to H<25 mag. We supplement spectroscopic redshifts from the literature with photometric redshifts determined from the 15-band photometry from 0.22-8 micron. We determine effective radii from Sersic profile fits to the H-band image using an empirical PSF. We find that size evolution is a strong function of stellar mass, with the most massive (M* ~ 10^11 Msol) galaxies undergoing the most rapid evolution from z~2 to the present. Parameterizing the size evolution as (1+z)^{-alpha}, we find a tentative scaling between alpha and stellar mass of alpha ~ -1.8+1.4 log(M*/10^9 Msol). We briefly discuss the implications of this result for our understanding of the dynamical evolution of the red galaxies.

astro-ph.CO↗

arXiv2009

Simultaneous Multi-Wavelength Observations of Sgr A* during 2007 April 1-11

We report the detection of variable emission from Sgr A* in almost all wavelength bands (i.e. centimeter, millimeter, submillimeter, near-IR and X-rays) during a multi-wavelength observing campaign. Three new moderate flares are detected simultaneously in both near-IR and X-ray bands. The ratio of X-ray to near-IR flux in the flares is consistent with inverse Compton scattering of near-IR photons by submillimeter emitting relativistic particles which follow scaling relations obtained from size measurements of Sgr A*. We also find that the flare statistics in near-IR wavelengths is consistent with the probability of flare emission being inversely proportional to the flux. At millimeter wavelengths, the presence of flare emission at 43 GHz (7mm) using VLBA with milli-arcsecond spatial resolution indicates the first direct evidence that hourly time scale flares are localized within the inner 30$\times$70 Schwarzschild radii of Sgr A*. We also show several cross correlation plots between near-IR, millimeter and submillimeter light curves that collectively demonstrate the presence of time delays between the peaks of emission up to three hours. The evidence for time delays at millimeter and submillimeter wavelengths are consistent with the source of emission being optically thick initially followed by a transition to an optically thin regime. In particular, there is an intriguing correlation between the optically thin near-IR and X-ray flare and optically thick radio flare at 43 GHz that occurred on 2007 April 4. This would be the first evidence of a radio flare emission at 43 GHz delayed with respect to the near-IR and X-ray flare emission.

astro-ph.GA↗

arXiv2006

A Multi-Wavelength Study of Sgr A*: The Role of Near-IR Flares in Production of X-ray, Soft $γ$-ray and Sub-millimeter Emission

(abridged) We describe highlights of the results of two observing campaigns in 2004 to investigate the correlation of flare activity in Sgr A* in different wavelength regimes, using a total of nine ground and space-based telescopes. We report the detection of several new near-IR flares during the campaign based on {\it HST} observations. The level of near-IR flare activity can be as low as $\sim0.15$ mJy at 1.6 $μ$m and continuous up to about 40% of the total observing time. Using the NICMOS instrument on the {\it HST}, the {\it XMM-Newton} and CSO observatories, we also detect simultaneous bright X-ray and near-IR flare in which we observe for the first time correlated substructures as well as simultaneous submillimeter and near-IR flaring. X-ray emission is arising from the population of near-IR-synchrotron-emitting relativistic particles which scatter submillimeter seed photons within the inner 10 Schwarzschild radii of Sgr A* up to X-ray energies. In addition, using the inverse Compton scattering picture, we explain the high energy 20-120 keV emission from the direction toward Sgr A*, and the lack of one-to-one X-ray counterparts to near-IR flares, by the variation of the magnetic field and the spectral index distributions of this population of nonthermal particles. In this picture, the evidence for the variability of submillimeter emission during a near-IR flare is produced by the low-energy component of the population of particles emitting synchrotron near-IR emission. Based on the measurements of the duration of flares in near-IR and submillimeter wavelengths, we argue that the cooling could be due to adiabatic expansion with the implication that flare activity may drive an outflow.

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