We investigate an infrared-excess source called G2 or Dusty S-cluster Object (DSO), which moves on a highly eccentric orbit around the Galaxy’s central black hole, Sgr A*. We use, for the first time, ...near-infrared polarimetric imaging data to determine the nature and properties of the DSO and obtain an improved Ks-band identification of this source in median polarimetry images of different observing years. The source started to deviate from the stellar confusion in 2008, and it does not show any flux density variability over the years we analyzed it. We measured the polarization degree and angle of the DSO between 2008 and 2012 and conclude, based on the significance analysis on polarization parameters, that it is an intrinsically polarized source (> 20%) with a varying polarization angle as it approaches the position of Sgr A*. The DSO shows a near-infrared excess of Ks−L′ > 3 that remains compact close to the pericenter of its orbit. Its observed parameters and the significant polarization obtained in this work show that the DSO might be a dust-enshrouded young star, forming a bow shock as it approaches the super massive black hole. The significantly high measured polarization degree indicates that it has a non-spherical geometry, and it can be modeled as a combination of a bow shock with a bipolar wind of the star. We used a 3D radiative transfer model that can reproduce the observed properties of the source such as the total flux density and the polarization degree. We obtain that the change of the polarization angle can be due to an intrinsic change in the source structure. Accretion disk precession of the young star in the gravitational field of the black hole can lead to the change of the bipolar outflow and therefore the polarization angle variation. It might also be the result of the source interaction with the ambient medium.
On 2019/07/30.86853 UT, IceCube detected a high-energy astrophysical neutrino can-didate. The Flat Spectrum Radio Quasar PKS 1502+106 is located within the 50 percent uncertainty region of the event. ...Our analysis of 15 GHz Very Long Baseline Ar-ray (VLBA) and astrometric 8 GHz VLBA data, in a time span prior and after theIceCube event, reveals evidence for a radio ring structure which develops with time.Several arc-structures evolve perpendicular to the jet ridge line. We find evidence forprecession of a curved jet based on kinematic modelling and a periodicity analysis.An outflowing broad line region (BLR) based on the C IV line emission (Sloan Dig-ital Sky Survey, SDSS) is found. We attribute the atypical ring to an interaction ofthe precessing jet with the outflowing material.We discuss our findings in thecontext of a spine-sheath scenario where the ring reveals the sheath andits interaction with the surroundings (NLR clouds).We find that the radioemission is correlated with theγ-ray emission, with radio lagging theγ-rays. Basedon theγ-ray variability timescale, we constrain theγ-ray emission zone to the BLR(30-200rg) and within the jet launching region. We discuss that the outflowing BLRprovides the external radiation field forγ-ray production via external Compton scat-tering.The neutrino is most likely produced by proton-proton interactionin the blazar zone (beyond the BLR), enabled by episodic encounters ofthe jet with dense clouds, i.e. some molecular cloud in the NLR.
The S-star cluster in the Galactic center allows us to study the physics close to a supermassive black hole, including distinctive dynamical tests of general relativity. Our best estimates for the ...mass of and the distance to Sgr A* using the three stars with the shortest period (S2, S38, and S55/S0-102) and Newtonian models are MBH = (4.15 0.13 0.57) × 106 M and R0 = 8.19 0.11 0.34 kpc. Additionally, we aim at a new and practical method to investigate the relativistic orbits of stars in the gravitational field near Sgr A*. We use a first-order post-Newtonian approximation to calculate the stellar orbits with a broad range of periapse distance rp. We present a method that employs the changes in orbital elements derived from elliptical fits to different sections of the orbit. These changes are correlated with the relativistic parameter defined as rs/rp (with rs being the Schwarzschild radius) and can be used to derive from observational data. For S2 we find a value of = 0.00088 0.00080, which is consistent, within the uncertainty, with the expected value of = 0.00065 derived from MBH and the orbit of S2. We argue that the derived quantity is unlikely to be dominated by perturbing influences such as noise on the derived stellar positions, field rotation, and drifts in black hole mass.
Context. The neutrino event IceCube−170922A appears to originate from the BL Lac object TXS 0506+056. To understand the neutrino creation process and to localize the emission site, we studied the ...radio images of the jet at 15 GHz. Aims. Other BL Lac objects show properties similar to those of TXS 0506+056, such as multiwavelength variability or a curved jet. However, to date only TXS 0506+056 has been identified as neutrino emitter. The aim of this paper is to determine what makes the parsec-scale jet of TXS 0506+056 specific in this respect. Methods. We reanalyzed and remodeled 16 VLBA 15 GHz observations between 2009 and 2018. We thoroughly examined the jet kinematics and flux-density evolution of individual jet components during the time of enhanced neutrino activity between September 2014 and March 2015, and in particular before and after the neutrino event. Results. Our results suggest that the jet is very strongly curved and most likely observable under a special viewing angle of close to zero. We may observe the interaction between jet features that cross each other’s paths. We find subsequent flux-density flaring of six components passing the likely collision site. In addition, we find a strong indication for precession of the inner jet, and model a precession period of about 10 yr via the Lense-Thirring effect. We discuss an alternative scenario, which is the interpretation of observing the signature of two jets within TXS 0506+056, again hinting toward a collision of jetted material. We essentially suggest that the neutrino emission may result from the interaction of jetted material in combination with a special viewing angle and jet precession. Conclusions. We propose that the enhanced neutrino activity during the neutrino flare in 2014–2015 and the single EHE neutrino IceCube-170922A could have been generated by a cosmic collision within TXS 0506+056. Our findings seem capable of explaining the neutrino generation at the time of a low gamma-ray flux and also indicate that TXS 0506+056 might be an atypical blazar. It seems to be the first time that a potential collision of two jets on parsec scales has been reported and that the detection of a cosmic neutrino might be traced back to a cosmic jet-collision.
Context.
Several dusty infrared sources traced on their orbits around Sgr A* with SINFONI and NACO mounted at the VLT/Chile show near-infrared (NIR) excess and Doppler-shifted line emission. We ...investigate these sources in order to clarify their nature and compare their relationship to other observed NIR objects close to Sgr A*.
Aims.
Using SINFONI, we are able to determine the spectroscopic properties of the dusty infrared sources. Furthermore, we can extract spatial and velocity information of these objects. We are able to identify X7, X7.1, X8, G1, DSO/G2, D2, D23, D3, D3.1, D5, and D9 in the Doppler-shifted line maps of the SINFONI
H
+
K
data. From our
K
- and
L
′-band NACO data, we derive the related magnitudes of the brightest sources located west of Sgr A*.
Methods.
For determining the line of sight velocity information and to investigate single emission lines, we used the near-infrared integral field spectrograph SINFONI datasets between 2005 and 2015. For the kinematic analysis, we used NACO datasets from the years between 2002 and 2018. This study was done in the
H
,
K
s
, and
L
′ band. From the 3D SINFONI data-cubes, we extracted line maps in order to derive positional information for the sources. In the NACO images, we identified the dusty counterpart of the objects. When possible, we determined the Keplerian orbits and applied a photometric analysis.
Results.
The spectrum of the investigated objects show a Doppler-shifted Br
γ
and HeI line emission. For some objects west of Sgr A*, we additionally find FeIII line emission that can be clearly distinguished from the background. A one-component blackbody model fits the extracted near-infrared flux for the majority of the investigated objects, with the characteristic dust temperature of 500 K. The photometric derived
H
- and
K
S
-band magnitudes are between mag
H
> 22.5 and mag
k
= 18.1
+0.3
−0.8
for the dusty sources. For the
H
-band magnitudes we can provide an upper limit. For the bright dusty sources D2, D23, and D3, the Keplerian orbits are elliptical with a semi-major axis of
a
D2
= (749 ± 13) mas,
a
D23
= (879 ± 13), and
a
D3
= (880 ± 13) mas. For the DSO/G2, a single-temperature and a two-component blackbody model is fitted to the
H
-,
K
-,
L
′-, and
M
-band data, while the two-component model that consists of a star and an envelope fits its SED better than an originally proposed single-temperature dusty cloud.
Conclusions.
The spectroscopic analysis indicates that the investigated objects could be dust-embedded pre-main-sequence stars. The Doppler-shifted FeIII line can be spectroscopically identified in several sources that are located between 17:45:40.05 and 17:45:42.00 in Dec However, the sources with a DEC less than 17:45:40.05 show no FeIII emission. Therefore, these two groups show different spectroscopic features that could be explained by the interaction with a non-spherical outflow that originates at the position of Sgr A*. Following this, the hot bubble around Sgr A* consists out of isolated sources with FeIII line emission that can partially account for the previously detected FeIII distribution on larger scales.
Context. We find an extended source in the direct vicinity of Sgr A* with an approximate projected mean distance of 425 ± 26 mas. Its sky-projected elongated shape can be described by an averaged ...spatial extension of x = 110 ± 20 mas and y = 180 ± 20 mas. With this, the observed object points in the analyzed SINFONI data sets between 2006 and 2016 directly toward the supermassive black hole. We discuss different possible scenarios that could explain the detected blueshifted line emission source. Aims. Here we present a detailed and extensive analysis of the adaptive optics corrected SINFONI data between 2006 and 2016 with a spatial pixel scale of 0.″025 0 . ″ 025 $ 0_.^{\prime \prime }025 $ and a corresponding field of view of 0.″8 × 0.″8 0 . ″ 8 × 0 . ″ 8 $ 0_.^{\prime \prime }8 \times 0_.^{\prime \prime }8 $ per single data cube with the focus on the newly discovered source. We spectroscopically identify the source, which we name X8, in the blueshifted Brγ line maps. Additionally, an upper limit for the continuum magnitude can be derived from the close-by S-star S41. Methods. We applied the standard reduction procedure with the SINFONI/EsoRex pipeline for the analysis. We applied pre- and post-data correction in order to establish various calibration procedures. For the sharpened images, we used the Lucy–Richardson algorithm with a low iteration number. For the high-pass filtered images, we used the smooth-subtracting process in order to increase the signal-to-noise ratio. Results. We are able to detect the elongated line emission source in quantified data sets between 2006 and 2016. We find a lower limit for the infrared continuum magnitude of Ks ≳ 17.0 ± 0.1. The alignment of X8 toward Sgr A* can be detected in data sets that fulfill a sufficient number of observations with a defined quality level. A more detailed analysis of the results shows indications of a bipolar outflow source that might be associated with either a young stellar object, or with a post-AGB star or young planetary nebula. Conclusions. The near-infrared excess source X8 close to S24, S25, and S41 can be detected between 2006 and 2016. In addition to an apparent bow-shock morphology, the source shows clear signatures of a bipolar outflow that is consistent with both a young stellar object and a post-AGB star. If confirmed, this would be the closest ever detected bipolar outflow source to the supermassive black hole. Similar to the case of the DSO/G2 source and other dusty sources, it further supports the in situ star formation in the direct vicinity of Sgr A*. If X8 were a bow-shock source, it would be the third object of this type that can be found in projection in the mini-cavity. This scenario would support the idea that the cavity is created by a wind from Sgr A*.
Radio jet precession in M 81 von Fellenberg, S. D.; Janssen, M.; Davelaar, J. ...
Astronomy and astrophysics (Berlin),
04/2023, Letnik:
672
Journal Article
Recenzirano
Odprti dostop
We report four novel position angle measurements of the core region M 81* at 5 GHz and 8 GHz, which confirm the presence of sinusoidal jet precession in the M 81 jet region, as suggested by ...Martí-Vidal et al. (2011, A&A, 533, A111). The model makes three testable predictions regarding the evolution of the jet precession, which we test in our data with observations from 2017, 2018, and 2019. Our data confirm a precession period of ∼7 yr on top of a small linear drift. We further show that two 8 GHz observation are consistent with a precession period of ∼7 yr but show a different time lag with respect to the 5 GHz and 1.7 GHz observations. We do not find a periodic modulation of the light curve with the jet precession and therefore rule out a Doppler nature for the historic 1998–2002 flare. Our observations are consistent with either a binary black hole origin for the precession or the Lense-Thirring effect.
Abstract Quasiperiodic eruptions (QPEs) represent a novel class of extragalactic X-ray transients that are known to repeat at roughly regular intervals of a few hours to days. Their underlying ...physical mechanism is a topic of heated debate, with most models proposing that they originate either from instabilities within the inner accretion flow or from orbiting objects. At present, our knowledge of how QPEs evolve over an extended timescale of multiple years is limited, except for the unique QPE source GSN 069. In this study, we present results from strategically designed Swift observing programs spanning the past 3 yr, aimed at tracking eruptions from eRO-QPE1. Our main results are as follows: (1) the recurrence time of eruptions can vary from flare to flare and is in the range of 0.6–1.2 days; (2) there is no detectable secular trend in evolution of the recurrence times; (3) consistent with prior studies, their eruption profiles can have complex shapes; and (4) the peak flux of the eruptions has been declining over the past 3 yr, with the eruptions barely detected in the most recent Swift data set taken in 2023 June. This trend of weakening eruptions has been reported recently in GSN 069. However, because the background luminosity of eRO-QPE1 is below our detection limit, we cannot verify whether the weakening is correlated with the background luminosity (as is claimed to be the case for GSN 069). We discuss these findings within the context of various proposed QPE models.
OJ287 is the best candidate active galactic nucleus for hosting a supermassive binary black hole at very close separation, corresponding to the orbital period of the order of ~9 yr. We studied the ...pc-scale jet dynamics in 118 Very Long Baseline Array (VLBA) observations at 15 GHz covering the time between Apr. 1995 and Jan. 2017. To our knowledge, this is the first time, that the kinematics of the Blandford-Znajek jet (originating in the ergosphere of a rotating black hole) and jet sheath (originating from the accretion disk) are seen and traced in observations. We also find that the OJ287 radio jet is rotating and precessing. The jet dynamics as well as the flux-density light curves can be understood in terms of geometrical effects. A binary black hole model can explain the time scale of the precessing motion. Lense-Thirring precession of an accretion disc surrounding a single black hole is consistent with the time scale as well.
PDF
