Simultaneous NIR/sub-mm observation of flare emission from Sagittarius A*

Eckart, A.; Schödel, R.; García-Marín, M.; Witzel, G.; Weiß, A.; Baganoff, Frederick K.; Morris, Mark; Bertram, Thomas; Dovčiak, Michal; Duschl, W. J.; Karas, V.; König, S.; Krichbaum, T. P.; Krips, M.; Kunneriath, D.; Lu, Ru-Sen; Markoff, Sera; Mauerhan, Jon C.; Meyer, L.; Moultaka, J.; Mužić, K.; Najarro, F.; Pott, Jörg-Uwe; Schuster, K.; Sjouwerman, Loránt O.; Straubmeier, C.; Thum, C.; Vogel, S. N.; Wiesemeyer, H.; Zamaninasab, M.; Zensus, J. A.

doi:10.1051/0004-6361:200810924

Cited by 88 publications

(116 citation statements)

References 42 publications

(74 reference statements)

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“…Furthermore, expanding blob models, which are presented elsewhere in the literature, have the following problems: (i) some observations appear to require a redder spectral index in the NIR than allowed by our lower limit of β −0.5 (see e.g. models A and B of Table 4 in Eckart et al 2008); the spectral index is given there as α where S ν ∝ ν −α , so α = 1 − β; (ii) moreover, they require self-absorbed flare emission in the sub-mm, which can only occur for the electron densities and/or magnetic fields that are much higher than the typical values in the accretion flow around Sgr A* (Dodds-Eden et al 2010).…”

Section: Sed Models For An Nir/x-ray Flare With a Sub-mm Dipmentioning

confidence: 93%

“…The explanation put forward in Dodds-Eden et al (2010) was that a dip in millimeter emission may occur due to the loss in emissivity of mm-emitting electrons that would occur in a magnetic reconnection event, in which significant magnetic energy is lost in the inner regions of the accretion flow. Eckart et al (2008) report a bright NIR flare and a sub-mm signal in which the lowest sub-mm flux is also coincident with the highest NIR flux (between 5 h and 6 h UT). Yusef-Zadeh et al (2010) have recently noted an anticorrelation in NIR/X-ray emission with sub-mm/mm emission, as well in previously published data, extending the number of observed examples to six.…”

Section: Submillimeter and Correlation With Nirmentioning

confidence: 94%

“…Distinct outbursting events in the lightcurves, called flares, have been detected on different timescales from a few minutes to a few hours, observed in X-rays (e.g., Baganoff et al 2001Baganoff et al , 2003 and the NIR (e.g., Genzel et al 2003;Ghez et al 2004;Clénet et al 2005). These X-ray/NIR flares are also sometimes followed by a submm flare with a time delay of 100 min to a few hours (Eckart et al 2008;Yusef-Zadeh et al 2009;Trap et al 2011). Flares are strongly polarized at the highest flux levels (for a review, see Genzel et al 2010).…”

Section: Introductionmentioning

confidence: 99%

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Flares and variability from Sagittarius A*: five nights of simultaneous multi-wavelength observations

Haubois¹,

Dodds-Eden²,

Weiß³

et al. 2012

A&A

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Aims. We report on simultaneous observations and modeling of mid-infrared (MIR), near-infrared (NIR), and submillimeter (submm) emission of the source Sgr A* associated with the supermassive black hole at the center of our Galaxy. Our goal was to monitor the activity of Sgr A* at different wavelengths in order to constrain the emitting processes and gain insight into the nature of the close environment of Sgr A*. Methods. We used the MIR instrument VISIR in the BURST imaging mode, the adaptive optics assisted NIR camera NACO, and the sub-mm antenna APEX to monitor Sgr A* over several nights in July 2007. Results. The observations reveal remarkable variability in the NIR and sub-mm during the five nights of observation. No source was detected in the MIR, but we derived the lowest upper limit for a flare at 8.59 μm (22.4 mJy with A 8.59 μm = 1.6 ± 0.5). This observational constraint makes us discard the observed NIR emission as coming from a thermal component emitting at sub-mm frequencies. Moreover, comparison of the sub-mm and NIR variability shows that the highest NIR fluxes (flares) are coincident with the lowest sub-mm levels of our five-night campaign involving three flares. We explain this behavior by a loss of electrons to the system and/or by a decrease in the magnetic field, as might conceivably occur in scenarios involving fast outflows and/or magnetic reconnection.

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Section: Sed Models For An Nir/x-ray Flare With a Sub-mm Dipmentioning

confidence: 93%

Section: Submillimeter and Correlation With Nirmentioning

confidence: 94%

Section: Introductionmentioning

confidence: 99%

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Flares and variability from Sagittarius A*: five nights of simultaneous multi-wavelength observations

Haubois¹,

Dodds-Eden²,

Weiß³

et al. 2012

A&A

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“…We use 0.007c as a typical value close to the expansion speeds found for other SgrA* flare events for which adiabatic expansion models have been applied (see e.g. Eckart et al 2008bEckart et al , 2009Yusef-Zadeh et al 2008). As an example of such a calculation we show in Fig.…”

Section: Modeling the April 4 2007 Nir/x-ray Light Curvesmentioning

confidence: 99%

The extreme luminosity states of Sagittarius A*

Sabha

Witzel

Eckart

et al. 2010

A&A

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We discuss mm-wavelength radio, 2.2-11.8 μm NIR and 2-10 keV X-ray light curves of the super massive black hole (SMBH) counterpart of Sagittarius A* (SgrA*) near its lowest and highest observed luminosity states. We investigate the structure and brightness of the central S-star cluster harboring the SMBH to obtain reliable flux density estimates of SgrA* during its low luminosity phases. We then discuss the physical processes responsible for the brightest flare as well as the faintest flare or quiescent emission in the NIR and X-ray domain. To investigate the low state of SgrA* we use three independent methods to remove or strongly suppress the flux density contributions of stars in the central 2 diameter region around SgrA*. The three methods are: a) low-pass filtering the image; b) iterative identification and removal of individual stars; c) automatic point spread function (PSF) subtraction. For the lowest observed flux density state all 3 image reduction methods result in the detection of faint extended emission with a diameter of 0.5 -1.0 and centered on the position of SgrA*. We analyzed two datasets that cover the lowest luminosity states of SgrA* we observed to date. In one case we detect a faint K-band (2.2 μm) source of ∼4 mJy brightness (de-reddened with A K = 2.8) which we identify as SgrA* in its low state. In the other case no source brighter or equal to a de-reddened K-band flux density of ∼2 mJy was detected at that position. As physical emission mechanisms for SgrA* we discuss bremsstrahlung, thermal emission of a hypothetical optically thick disk, synchrotron and synchrotron self-Compton (SSC) emission, and in the case of a bright flare the associated radio response due to adiabatic expansion of the synchrotron radiation emitting source component. The luminosity during the low state can be interpreted as synchrotron emission from a continuous or even spotted accretion disk. For the high luminosity state SSC emission from THz peaked source components can fully account for the flux density variations observed in the NIR and X-ray domain. We conclude that at near-infrared wavelengths the SSC mechanism is responsible for all emission from the lowest to the brightest flare from SgrA*. For the bright flare event of 4 April 2007 that was covered from the radio to the X-ray domain, the SSC model combined with adiabatic expansion can explain the related peak luminosities and different widths of the flare profiles obtained in the NIR and X-ray regime as well as the non detection in the radio domain.

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“…One is flaring on an hourly timescale at multiple wavelengths (e.g., Baganoff et al 2001;Genzel et al 2003). Observations of Sgr A * have detected a time delay at submillimeter, millimeter, and radio wavelengths consistent with a scenario in which plasma blobs expand away from the disk, becoming visible at successive longer wavelengths as the optical depths become of order unity effects (Yusef-Zadeh et al 2006Eckart et al 2008;Marrone et al 2008;Brinkerink et al 2015). The other is a jet-driven outflow (e.g., Falcke & Markoff 2000).…”

Section: Introductionmentioning

confidence: 96%

SGR A* and Its Environment: Low-Mass Star Formation, the Origin of X-Ray Gas and Collimated Outflow

Yusef‐Zadeh

Wardle

Schödel

et al. 2016

ApJ

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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 13 N and IRS 13E. The ridge suggests that an outflow of east-west blob-like structures is emerging from SgrA * . In particular, we find arc-like radio structures within the ridge with morphologies suggestive of photoevaporative protoplanetary disks. We use infrared K s and L′ 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 young stellar objects (YSOs) at a rate of ∼10 −6  M yr −1 . 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, on a scale of 5″ from Sgr A * , we detect new cometary radio and infrared sources at a position angle PA∼50°which is similar to that of two other cometary sources X3 and X7, all of which face Sgr A * . In addition, we detect a striking tower of radio emission at a PA∼50°-60°along the major axis of the Sgr A East supernova remnant shell on a scale of 150″ from Sgr A * . We suggest that the cometary sources and the tower feature 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∼50°-60°with´-, and opening angle 10°. Lastly, we suggest that the east-west ridge of radio emission traces an outflow that is potentially associated with past flaring activity from Sgr A * . The position angle of the outflow driven by flaring activity is close to −90°.

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Simultaneous NIR/sub-mm observation of flare emission from Sagittarius A*

Cited by 88 publications

References 42 publications

Flares and variability from Sagittarius A*: five nights of simultaneous multi-wavelength observations

Flares and variability from Sagittarius A*: five nights of simultaneous multi-wavelength observations

The extreme luminosity states of Sagittarius A*

SGR A* and Its Environment: Low-Mass Star Formation, the Origin of X-Ray Gas and Collimated Outflow

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