Testing for periodicities in near-IR light curves of Sgr A*

Do, Tuan; Ghez, A. M.; Morris, Mark; Yelda, S.; Lu, Jessica R.; Hornstein, S. D.; Matthews, K.

doi:10.1088/1742-6596/131/1/012003

Cited by 3 publications

(5 citation statements)

References 30 publications

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“…We conservatively choose to eliminate all astrometric measurements that are known to be the blend of two sources from the orbital analysis; specifically, if the predicted positions of two known sources are separated by less than 60 mas and only one of them is detected, then that measurement is removed from our analysis. For S0-2 (K ¼ 14:2 mag), the eliminated data points are those made in 1998, due to confusion with S0-19 (K ¼ 15:6 mag), in 2002, due to overlap with Sgr A Ã YIR (K median ¼ 16:4 mag, but can be as bright as 14 mag; see Do et al 2008), and in 2007 May, due to superposition with S0-20 (K ¼ 15:9). The impact of these overlapping sources, in the first two cases, can be seen in the photometric measurements (see Fig.…”

Section: Image Analysis and Astrometrymentioning

confidence: 99%

“…However, it is important to caution that other mechanisms can give rise to such short periodicities, such as a standing wave pattern recently suggested by Tagger & Melia (2006). Furthermore, claims of a QPO in Sgr A Ã have been called into question; Do et al (2008) find that the near-IR temporal power spectrum of Sgr A Ã is statistically consistent with pure red noise, such as might be caused by disk instabilities or intermittent jet fluctuations, and Bélanger et al (2008) reach a similar conclusion for the X-rays variations.…”

Section: Tablementioning

confidence: 99%

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Measuring Distance and Properties of the Milky Way’s Central Supermassive Black Hole with Stellar Orbits

Ghez

Salim

Weinberg

et al. 2008

Astrophysical Journal

1,512

1,601

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We report new precision measurements of the properties of our Galaxy's supermassive black hole. Based on astrometric (1995Y2007) and radial velocity (RV; 2000Y2007) measurements from the W. M. Keck 10 m telescopes, a fully unconstrained Keplerian orbit for the short-period star S0-2 provides values for the distance (R 0 ) of 8:0 AE 0:6 kpc, the enclosed mass (M bh ) of 4:1 AE 0:6 ; 10 6 M , and the black hole's RV, which is consistent with zero with 30 km s À1 uncertainty. If the black hole is assumed to be at rest with respect to the Galaxy (e.g., has no massive companion to induce motion), we can further constrain the fit, obtaining R 0 ¼ 8:4 AE 0:4 kpc and M bh ¼ 4:5 AE 0:4 ; 10 6 M . More complex models constrain the extended dark mass distribution to be less than 3Y4 ; 10 5 M within 0.01 pc, $100 times higher than predictions from stellar and stellar remnant models. For all models, we identify transient astrometric shifts from source confusion (up to 5 times the astrometric error) and the assumptions regarding the black hole's radial motion as previously unrecognized limitations on orbital accuracy and the usefulness of fainter stars. Future astrometric and RV observations will remedy these effects. Our estimates of R 0 and the Galaxy's local rotation speed, which it is derived from combining R 0 with the apparent proper motion of Sgr A Ã , ( 0 ¼ 229 AE 18 km s À1 ), are compatible with measurements made using other methods. The increased black hole mass found in this study, compared to that determined using projected mass estimators, implies a longer period for the innermost stable orbit, longer resonant relaxation timescales for stars in the vicinity of the black hole and a better agreement with the M bh -relation.

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Section: Image Analysis and Astrometrymentioning

confidence: 99%

Section: Tablementioning

confidence: 99%

Measuring Distance and Properties of the Milky Way’s Central Supermassive Black Hole with Stellar Orbits

Ghez

Salim

Weinberg

et al. 2008

Astrophysical Journal

1,512

1,601

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“…The lack of any significant power between 17 and 20 minutes supports the results from an earlier analysis of HST data in 2004(Yusef-Zadeh et al 2006a). Recent analysis of data taken with the combined VLT and the Keck observations shows no significant power on short time scales (Do et al 2008;Meyer et al 2008).…”

Section: Nir Power Spectrum Analysismentioning

confidence: 99%

“…Another difficulty with the hot spot model is the lack of evidence for power on the quasi-periodicity in NIR light curve (Do et al 2008. Claims of quasi-periodic variations in the NIR lightcurves were the motivating observation for the hotspot model, but the most thorough analysis of NIR lightcurve variability have not shown evidence for significant quasi-periodic power (Do et al 2008;Meyer et al 2008). Furthermore, MHD simulations of accreting gas indicate that hot spots can last less than an orbital time scale before they disperse (Hawley & Balbus 2002).…”

Section: Adiabatic Expansion Of Hot Plasma Vs Hot Spot Modelmentioning

confidence: 99%

SIMULTANEOUS MULTI-WAVELENGTH OBSERVATIONS OF Sgr A* DURING 2007 APRIL 1-11

Yusef‐Zadeh

Bushouse²,

Wardle

et al. 2009

ApJ

105

129

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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 30×70 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. The time delay measurements support the expansion of hot self-absorbed synchrotron plasma blob and weaken the hot spot model of flare emission. In addition, a simultaneous fit to 43 and 84 GHz light curves, using an adiabatic expansion model of hot plasma, appears to support a power law rather than a relativistic Maxwellian distribution of particles.

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“…Multiple hot spots revolving around a black hole in an accretion disk in AGNs or galactic black holes can give rise to light curves in the X-ray and NIR regimes whose power spectral density (PSD) is described by a broken power law with a slope similar to that of red noise processes (Armitage & Reynolds 2003;Pecháček et al 2008;Do et al 2008). Simulations show that polarized light curves exhibit behaviour associated with lensing of hot spots orbiting around a SMBH (Zamaninasab et al 2010).…”

Section: Relativistic Spot/disk Modelling Of Nir Flaresmentioning

confidence: 99%

Coordinated NIR/mm observations of flare emission from Sagittarius A*

Kunneriath

Witzel²,

Eckart

et al. 2010

A&A

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Context. We report on a successful, simultaneous observation and modelling of the millimeter (mm) to near-infrared (NIR) flare emission of the Sgr A* counterpart associated with the supermassive (4 × 10 6 M ) black hole at the Galactic centre (GC). We present a mm/sub-mm light curve of Sgr A* with one of the highest quality continuous time coverages. Aims. We study and model the physical processes giving rise to the variable emission of Sgr A*. Methods. Our non-relativistic modelling is based on simultaneous observations carried out in May 2007 and 2008, using the NACO adaptive optics (AO) instrument at the ESO's VLT and the mm telescope arrays CARMA in California, ATCA in Australia, and the 30 m IRAM telescope in Spain. We emphasize the importance of multi-wavelength simultaneous fitting as a tool for imposing adequate constraints on the flare modelling. We present a new method for obtaining concatenated light curves of the compact mm-source Sgr A* from single dish telescopes and interferometers in the presence of significant flux density contributions from an extended and only partially resolved source. Results. The observations detect flaring activity in both the mm domain and the NIR. Inspection and modelling of the light curves show that in the case of the flare event on 17 May 2007, the mm emission follows the NIR flare emission with a delay of 1.5 ± 0.5 h. On 15 May 2007, the NIR flare emission is also followed by elevated mm-emission. We explain the flare emission delay by an adiabatic expansion of source components. For two other NIR flares, we can only provide an upper limit to any accompanying mmemission of about 0.2 Jy. The derived physical quantities that describe the flare emission give a source component expansion speed of v exp ∼ 0.005c−0.017c, source sizes of about one Schwarzschild radius, flux densities of a few Janskys, and spectral indices of α = 0.6 to 1.3. These source components peak in the THz regime. Conclusions. These parameters suggest that either the adiabatically expanding source components have a bulk motion greater than v exp or the expanding material contributes to a corona or disk, confined to the immediate surroundings of Sgr A*. Applying the flux density values or limits in the mm-and X-ray domain to the observed flare events constrains the turnover frequency of the synchrotron components that are on average not lower than about 1 THz, such that the optically thick peak flux densities at or below these turnover frequencies do not exceed, on average, about ∼1 Jy.

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Testing for periodicities in near-IR light curves of Sgr A*

Cited by 3 publications

References 30 publications

Measuring Distance and Properties of the Milky Way’s Central Supermassive Black Hole with Stellar Orbits

Measuring Distance and Properties of the Milky Way’s Central Supermassive Black Hole with Stellar Orbits

SIMULTANEOUS MULTI-WAVELENGTH OBSERVATIONS OF Sgr A* DURING 2007 APRIL 1-11

Coordinated NIR/mm observations of flare emission from Sagittarius A*

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