Monitoring dusty sources in the vicinity of Sagittarius A*

Peißker, F.; Hosseini, S. Elaheh; Eckart, A.; Saalfeld, R.; Valencia-S., M.; Parsa, M.; Karas, V.

doi:10.1051/0004-6361/201935953

Cited by 32 publications

(55 citation statements)

References 80 publications

(223 reference statements)

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“…Indeed, the uppermost limit for the density n a < 1.87 × 10 9 cm −3 is well in the range for the number density of broad-line region (BLR) clouds n BLR ∼ 10 8 −10 11 cm −3 (Gaskell 2009). Although we do not expect the presence of BLR clouds in such a low-luminosity nucleus as Sgr A* (see, however, Bianchi et al, 2019 for the discovery of the compact BLR in the low-luminosity Seyfert galaxy NGC3147 with L/L Edd ∼ 10 −4 ), we cannot exclude the presence of denser gaseous-dusty structures, with which stars can occasionally interact, such as dust-enshrouded objects monitored in the S-cluster (Peißker et al 2020b;Ciurlo et al 2020). This is also supported by the multiphase medium of Sgr A* on the scale of one parsec (Moser et al 2017), which could also be A105, page 10 of 17 present on smaller scales due to for example thermal instability (Różańska et al 2017).…”

Section: Discussionmentioning

confidence: 84%

“…The dust component is expected to coexist to a certain extent in this hot environment, which is also manifested by the presence of L -band dusty sources in the central ∼0.04 pc, namely DSO/G2, G1, and several other dusty and bow-shock sources in the central arcsecond (Gillessen et al 2012;Valencia-S et al 2015;Witzel et al 2017). In particular, for the orbital solutions and radiative properties of the dust-enshrouded objects, see Peißker et al (2020b) and Ciurlo et al (2020). An increase in the ambient gas-and-dust density ratio along with the change in the orbital velocity are expected to lead to a larger local extinction around S2 due to the formation of a bow shock, and hence to a change in the NIR magnitudes and corresponding colour indices.…”

Section: Constraining the Slope And Density Of The Ambient Accretion mentioning

confidence: 99%

“…The detection and the monitoring of the dusty G2 source or the Dusty S-cluster Object (DSO; Gillessen et al 2012;Eckart et al 2013;Witzel et al 2014;Valencia-S et al 2015;Peißker et al 2020b;Ciurlo et al 2020) triggered an effort to predict and observe its potential interaction with the ambient environment. Narayan et al (2012) predicted the radio synchrotron emission from the DSO bow shock to be comparable to the quiescent radio emission of Sgr A*.…”

Section: Introductionmentioning

confidence: 99%

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Constraining the accretion flow density profile near Sgr A* using theL′-band emission of the S2 star

Hosseini

Eckart

Sabha

et al. 2020

A&A

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Context. The density of the ambient medium around a supermassive black hole (SMBH) and the way it varies with distance plays an important role in our understanding of the inflow-outflow mechanisms in the Galactic centre (GC). This dependence is often fitted by spherical power-law profiles based on observations in the X-ray, infrared (IR), submillimetre (submm), and radio domains. Aims. Nevertheless, the density profile is poorly constrained at the intermediate scales of 1000 Schwarzschild radii (R s). Here we independently constrain the spherical density profile using the stellar bow shock of the star S2 which orbits the SMBH at the GC with the pericentre distance of 14.4 mas (∼1500 R s). Methods. Assuming an elliptical orbit, we apply celestial mechanics and the theory of bow shocks that are at ram pressure equilibrium. We analyse the measured IR flux density and magnitudes of S2 in the L-band (3.8 micron) obtained over seven epochs in the years between 2004-2018. We put an upper limit on the emission from S2's associated putative bow shock and constrain the density profile of the ambient medium. Results. We detect no significant change in S2 flux density until the recent periapse in May 2018. The intrinsic flux variability of S2 is at the level of 2-3%. Based on the dust-extinction model, the upper limit on the number density at the S2 periapse is ∼1.87 × 10 9 cm −3 , which yields a density slope of at most 3.20. Using the synchrotron bow-shock emission, we obtain the ambient density of 1.01 × 10 5 cm −3 and a slope of 1.47. These values are consistent with a wide variety of media from hot accretion flows to potentially colder and denser media comparable in properties to broad-line-region clouds. However, a standard thin disc can be excluded at the distance of S2's pericentre. Conclusions. With the current photometry sensitivity of 0.01 mag, we are not able to make stringent constraints on the density of the ambient medium in the GC using S2-star observations. We can distinguish between hot accretion flows and thin, cold discs, where the latter can be excluded at the scale of the S2 periapse. Future observations of stars in the S cluster using instruments such as Mid-IR Extremely Large Telescope Imager and Spectrograph at Extremely Large Telescope with the photometric sensitivity of as much as 10 −3 mag will allow the GC medium to be probed at intermediate scales at densities as low as ∼700 cm −3 in case of non-thermal bow-shock emission. The new instrumentation, in combination with discoveries of stars with smaller pericentre distances, will help to independently constrain the density profile around Sagittarius A* (Sgr A*).

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Section: Discussionmentioning

confidence: 84%

Section: Constraining the Slope And Density Of The Ambient Accretion mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Constraining the accretion flow density profile near Sgr A* using theL′-band emission of the S2 star

Hosseini

Eckart

Sabha

et al. 2020

A&A

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“…As a final remark, it is worth mentioning that this method can be used for low-luminosity sources, such as the Galactic center. The immediate vicinity of Sgr A* contains several gaseous structures (Ciurlo et al 2020;Peißker et al 2020) whose nature is still uncertain; they are unresolved, and at least for the so-called G objects, they show emission properties of gas clouds, but their dynamical properties are typical of stellar objects. One of them, G2, is intrinsically linearly polarized (Shahzamanian et al 2016) in the infrared (K s band), with a polarized fraction higher than 20%, and a varying polarization angle as it approaches the position of Sgr A*.…”

Section: Resultsmentioning

confidence: 99%

Reverberation mapping of AGNs through continuum polarization

Lobos

Goosmann

Hameury

et al. 2020

A&A

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Context. The size and geometry of the broad-line region (BLR) in active galactic nuclei (AGNs) are among the main ingredients in determining the mass of the accreting black hole. Size and geometry can be constrained by determining the delay between the optical continuum and the flux reprocessed by the BLR, in particular, through the emission lines. Aims. We propose here that the delay between polarized and unpolarized light can also be used in much the same way to constrain the size of the BLR; we verify that meaningful results can be expected from observations using this technique. Methods. We used our code STOKES to simulate polarized radiative transfer. We determined the response of the environment of the central source (BLR, dust torus, and polar wind) to randomly generated fluctuations in the central source. We then calculated the cross correlation between the simulated polarized flux and the total flux to estimate the time delay that would be provided by observations using the same method. Results. The BLR is the main contributor to the delay between the polarized flux and the total flux. This delay is independent of the observation wavelength. Conclusions. This validates the use of polarized radiation in the optical/UV band to estimate the geometrical properties of the BLR in type I AGNs, in which the viewing angle is close to pole-on and the BLR is not obscured by the dust torus.

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“…From an observational point of view, the first light of the IR instrument GRAVITY 1 (Gravity Collaboration et al 2017) increased the capability of detecting faint objects (GRAVITY Collaboration et al 2021). In contrast, using publically available data that cover almost 20 years in combination with enhanced image analysing techniques like the smooth-subtract algorithm (for a description, consider Peißker et al 2020b) or the Lucy-Richardson algrorithm (Lucy 1974) resulted in the observation and detection of the short-period star S62 and S4711-S4715 (Peißker et al 2020a,d). While the observation of the S47xx stars suffer from close-by sources but also overall data impacts like the variable background or general weather conditions, the detection of S62 is robust and follows a clear Keplerian trajectory (Peißker et al 2020a).…”

Section: Introductionmentioning

confidence: 99%

Observation of the apoapsis of S62 in 2019 with NIRC2 and SINFONI

Peißker,

Eckart,

Ali

2021

Preprint

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Given the increased attention towards the detection of faint stars in the Galactic center, we would like to address the detectability of S62 in its apoapsis with SINFONI (VLT) and NIRC2 (KECK) in this work. Because of the nearby stars and the chance of confusion, we are using Lucy-Richardson deconvolved images to detect S62 on its Keplerian orbit around Sgr A* with a period of less than 10 years. We use the same dataset as for S62 to trace additionally the S-cluster star S29 at the expected position based on the orbital elements presented in this work. To verify the results of the filtering technique, we are analysing K-band continuum data of the same epoch independently observed with NIRC2/KECK. Based on the well-derived orbit of S62, we find the star in projection at the expected position in 2019.4 and 2019.5. By analyzing the SINFONI data of 2019.5, we confirm the 16.1 ± 0.2 mag for S62 that was formerly derived with NACO (VLT). We base our NACO imaging analysis on the robust data set that was previously used to investigate the Schwarzschild precision of S2. We also present a critical discussion of the elsewhere proposed linear trajectory of S62 and its disputed identification with a 19 mag star found with GRAVITY mounted at the VLT Interferometer.

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Monitoring dusty sources in the vicinity of Sagittarius A*

Cited by 32 publications

References 80 publications

Constraining the accretion flow density profile near Sgr A* using theL′-band emission of the S2 star

Constraining the accretion flow density profile near Sgr A* using theL′-band emission of the S2 star

Reverberation mapping of AGNs through continuum polarization

Observation of the apoapsis of S62 in 2019 with NIRC2 and SINFONI

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