scholarly journals Near infrared variability of Sgr A* - spectral index measurements

2013 ◽  
Vol 9 (S303) ◽  
pp. 274-282 ◽  
Author(s):  
G. Witzel ◽  
M. Morris ◽  
A. Ghez ◽  
L. Meyer ◽  
E. Becklin ◽  
...  
Keyword(s):  
Spectral Index ◽  
Near Infrared ◽  
Time Lag ◽  
Time Variable ◽  
Time Variability ◽  
Data Set ◽  
Sagittarius A ◽  
State Process ◽  
Sgr A ◽  
High Cadence

AbstractWe discuss observations of Sagittarius A* with NACO@VLT in K-band and recent synchronous observations with NIRC2@Keck II and OSIRIS@Keck I in L′-band and H-band, respectively. The variability of Sagittarius A* in the near infrared is a continuous one-state process that can be described by a pure red-noise process having a timescale of a few hours. We describe this process and its properties in detail. Our newest observations with the Keck telescopes represent the first truly synchronous high cadence data set to test for time variability of the spectral index within the near infrared. We discovered a time-variable spectral index that might be interpreted as a time lag of the L′-band with respect to the H-band.

scholarly journals The near-infrared spectral index of Sagittarius A* derived fromKs- andH-band flare statistics

2011 ◽  
Vol 532 ◽  
pp. A26 ◽  
Author(s):  
M. Bremer ◽  
G. Witzel ◽  
A. Eckart ◽  
M. Zamaninasab ◽  
R. M. Buchholz ◽  
...  
Keyword(s):  
Spectral Index ◽  
Near Infrared ◽  
Sagittarius A ◽  
Infrared Spectral

scholarly journals The infrared K-band identification of the DSO/G2 source from VLT and Keck data

2013 ◽  
Vol 9 (S303) ◽  
pp. 269-273
Author(s):  
A. Eckart ◽  
M. Horrobin ◽  
S. Britzen ◽  
M. Zamaninasab ◽  
K. Mužić ◽  
...  
Keyword(s):  
Fast Moving ◽  
Near Infrared ◽  
Dust Cloud ◽  
Continuum Emission ◽  
Proper Motions ◽  
Infrared Excess ◽  
Sagittarius A ◽  
Band Emission ◽  
Sgr A ◽  
Data Result

AbstractA fast moving infrared excess source (G2) which is widely interpreted as a core-less gas and dust cloud approaches Sagittarius A* (Sgr A*) on a presumably elliptical orbit. VLT Ks-band and Keck K′-band data result in clear continuum identifications and proper motions of this ∼19m Dusty S-cluster Object (DSO). In 2002-2007 it is confused with the star S63, but free of confusion again since 2007. Its near-infrared (NIR) colors and a comparison to other sources in the field speak in favor of the DSO being an IR excess star with photospheric continuum emission at 2 microns than a core-less gas and dust cloud. We also find very compact L′-band emission (<0.1″) contrasted by the reported extended (0.03″ up to ∼0.2″ for the tail) Brγ emission. The presence of a star will change the expected accretion phenomena, since a stellar Roche lobe may retain a fraction of the material during and after the peri-bothron passage.

scholarly journals Search for time lag in intra-day variability of Sgr A*

2013 ◽  
Vol 9 (S303) ◽  
pp. 322-323
Author(s):  
A. Miyazaki ◽  
S. S. Lee ◽  
B. W. Sohn ◽  
T. Jung ◽  
M. Tsuboi ◽  
...  
Keyword(s):  
Black Hole ◽  
Galactic Center ◽  
Time Lag ◽  
Light Curves ◽  
Time Lags ◽  
Significant Time ◽  
Sagittarius A ◽  
Receiver System ◽  
Sgr A ◽  
Plasma Blobs

AbstractWe searched the time lag between the intra-day variables (IDVs) of Sagittarius A* at 22, 43, and 86 GHz bands using the Korean VLBI Network (KVN). The time lags between the IDV flare peaks at 22 and 43 GHz are reported, and they suggest that the flare emissions come from adiabatically expanding plasma blobs, ejected close to the Galactic center black hole. We searched the time lags between light curves at 90 and 102 GHz using the Nobeyama Millimeter Array, but could not find significant time lags. In order to detect the diversity of the time lags of Sgr A* flares, we performed observations of Sgr A* in the 22, 43, and 86 GHz bands using the KVN in the winter of 2013. Because the receiver system of KVN can observe Sgr A* in these three bands simultaneously, the KVN is very useful to detect the time lags of Sgr A* flares.

scholarly journals Event horizon scale emission models for Sagittarius A*

2013 ◽  
Vol 9 (S303) ◽  
pp. 298-302
Author(s):  
J. Dexter
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Event Horizon ◽  
Near Infrared ◽  
Sagittarius A ◽  
Long Baseline ◽  
Black Hole Accretion ◽  
Emission Models ◽  
Infrared Interferometry ◽  
Sgr A

AbstractVery long baseline interferometry observations at millimeter wavelengths have detected source structure in Sgr A* on event horizon scales. Near-infrared interferometry will achieve similar resolution in the next few years. These experiments provide an unprecedented opportunity to explore strong gravity around black holes, but interpreting the data requires physical modeling. I discuss the calculation of images, spectra, and light curves from relativistic MHD simulations of black hole accretion. The models provide an excellent description of current observations, and predict that we may be on the verge of detecting a black hole shadow, which would constitute the first direct evidence for the existence of black holes.

scholarly journals 10.5. Short-term variability of Sagittarius A∗ at millimeter wavelengths

1998 ◽  
Vol 184 ◽  
pp. 439-440
Author(s):  
T. Tsutsumi ◽  
T. Kawabata ◽  
A. Miyazaki ◽  
M. Tsuboi
Keyword(s):  
Monitoring Program ◽  
Time Variability ◽  
Very Large Array ◽  
Sagittarius A ◽  
Compact Component ◽  
Millimeter Wavelengths ◽  
Submillimeter Wavelengths ◽  
Extended Component ◽  
Sgr A ◽  
Millimeter And Submillimeter Wavelengths

Time variability of Sgr A∗ at cm wavelengths is well known phenomenon and has been studied by several authors (e.g. Lo 1989; Zhao et al. 1992). On the other hand, variability at millimeter wavelengths is not well established. Wright & Backer (1993) reported significant flux variations at λ = 3.4mm in a month during the decay of a flare observed by the Very Large Array in 1990. However others found no variability at millimeter and submillimeter wavelengths (Gwinn et al. 1991; Zylka et al. 1995). Emission from extended component surrounding Sgr A∗ is significant even at millimeter wavelengths (e.g. Tsuboi et al. 1988), thus it is important to observe with a narrower beam to isolate the compact component for accurate measurement of variability of Sgr A∗. Here we present some results from an on-going millimeter monitoring program of Sgr A∗ with the Nobeyama Millimeter Array (NMA).

scholarly journals Continuation of the X-ray monitoring of Sgr A*: the increase in bright flaring rate confirmed

2020 ◽  
Vol 636 ◽  
pp. A25
Author(s):  
E. Mossoux ◽  
B. Finociety ◽  
J.-M. Beckers ◽  
F. H. Vincent
Keyword(s):  
Black Hole ◽  
Near Infrared ◽  
Milky Way ◽  
Detection Efficiency ◽  
Previous Method ◽  
Arrival Times ◽  
X Ray ◽  
Sagittarius A ◽  
Block Algorithm ◽  
Sgr A

Context. The supermassive black hole Sagittarius A* (Sgr A*) is located at the dynamical center of the Milky Way. In a recent study of the X-ray flaring activity from Sgr A* using Chandra, XMM-Newton, and Swift observations from 1999 to 2015, it has been argued that the bright flaring rate has increased from 2014 August 31 while the faint flaring rate decreased from around 2013 August. Aims. We tested the persistence of these changes in the flaring rates with new X-ray observations of Sgr A* performed from 2016 to 2018 (total exposure of 1.4 Ms). Methods. We reprocessed the Chandra, XMM-Newton, and Swift observations from 2016 to 2018. We detected 9 flares in the Chandra data and 5 flares in the Swift data that we added to the set of 107 previously detected flares. We computed the intrinsic distribution of flare fluxes and durations corrected for the sensitivity bias using a new method that allowed us to take the error on the flare fluxes and durations into account. From this intrinsic distribution, we determined the average flare detection efficiency for each Chandra, XMM-Newton, and Swift observation. After correcting each observational exposure for this efficiency, we applied the Bayesian blocks algorithm on the concatenated flare arrival times. As in the above-mentioned study, we also searched for a flux and fluence threshold that might lead to a change in flaring rate. We improved the previous method by computing the average flare detection efficiencies for each flux and fluence range. Results. The Bayesian block algorithm did not detect any significant change in flaring rate of the 121 flares. However, we detected an increase by a factor of about three in the flaring rate of the most luminous and most energetic flares that have occurred since 2014 August 30. Conclusions. The X-ray activity of Sgr A* has increased for more than four years. Additional studies about the overall near-infrared and radio behavior of Sgr A* are required to draw strong results on the multiwavelength activity of the black hole.

scholarly journals Short-term variability of Sgr A*

2006 ◽  
Vol 2 (S238) ◽  
pp. 195-200
Author(s):  
M. R. Morris ◽  
S. D. Hornstein ◽  
A. M. Ghez ◽  
J. R. Lu ◽  
K. Matthews ◽  
...  
Keyword(s):  
Time Scale ◽  
Near Infrared ◽  
Accretion Rate ◽  
Outer Boundary ◽  
Radial Distance ◽  
Emission Region ◽  
Sagittarius A ◽  
Dynamical Time ◽  
Galactic Black Hole ◽  
Sgr A

AbstractObservations of Sgr A* over the past 4 years with the Keck Telescope in the near-infrared, coupled with millimeter and submillimeter observations, show that the 3.7×106M⊙Galactic Black Hole, Sagittarius A*, displays continuous variability at all these wavelengths, with the variability power concentrated on characteristic time scales of a few hours, and with a variability fraction that increases with wavelength. We review the observations indicating that the few-hour time scale for variability is reproduced at all accessible wavelengths. Interpreted as a dynamical time, this time scale corresponds to a radial distance of 2 AU, or ∼25 Schwarzschild radii. Searches for quasi-periodicities in the near-infrared data from the Keck Telescope have so far been negative. One interpretation of the character of these variations is that they result from a recurring disk instability, rather than from variations in the mass accretion rate flowing through the outer boundary of the emission region. However, neither a variable accretion rate nor a mechanism associated with a jet can presently be ruled out.

scholarly journals CONSTRAINING THE FLARING REGION FOR SAGITTARIUS A* BY 1.3MM VLBI MEASUREMENTS

2013 ◽  
Vol 23 ◽  
pp. 92-94
Author(s):  
LEI HUANG ◽  
ZHI-QIANG SHEN ◽  
FENG GAO
Keyword(s):  
Black Hole ◽  
Time Variable ◽  
Sagittarius A ◽  
Sgr A ◽  
East West

We introduce a simple and useful method to interpret the 2009 data by 1.3mm VLBI, which detected the time-variable emission of Sgr A*. The flaring region can be constrained to scale comparable to black hole shadow size in East-West direction. Constraint in North-South direction is relaxed due to lack of baseline, which can be improved in future observations.

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