scholarly journals Optically thin circumstellar medium in the β Lyr A system

2021 ◽  
Vol 645 ◽  
pp. A51
Author(s):  
M. Brož ◽  
D. Mourard ◽  
J. Budaj ◽  
P. Harmanec ◽  
H. Schmitt ◽  
...  
Keyword(s):  
Spectral Energy Distribution ◽  
Light Curves ◽  
High Resolution Spectroscopy ◽  
Spectral Energy ◽  
Thermodynamical Equilibrium ◽  
Doppler Tomography ◽  
Differential Interferometry ◽  
Robust Model ◽  
Free Parameters ◽  
Local Thermodynamical Equilibrium

The complex binary system β Lyr A has an extensive observational dataset: light curves (from far UV to far IR), interferometric squared visibility, closure phase, triple product measurements, spectral-energy distribution, high-resolution spectroscopy, differential visibility amplitude, and also a differential phase. In particular, we used spectra from the Ondřejov 2m telescope from 2013 to 2015 to measure the emission in Hα, He I, Si II, Ne I, or C II lines, and differential interferometry by CHARA/VEGA from the 2013 campaign to measure wavelength-dependent sizes across Hα and He I 6678. This allowed us to constrain not only optically thick objects (primary, secondary, accretion disc), but also optically thin objects (disc atmosphere, jets, shell). We extended our modelling tool, Pyshellspec (based on Shellspec; a 1D local thermodynamical equilibrium radiative transfer code), to include all new observables, to compute differential visibilities/phases, to perform a Doppler tomography, and to determine a joint χ2 metric. After an optimisation of 38 free parameters, we derived a robust model of the β Lyr A system. According to the model, the emission is formed in an extended atmosphere of the disc, two perpendicular jets expanding at ∼700 km s−1, and a symmetric shell with the radius ∼70 R⊙. The spectroscopy indicates a low abundance of carbon, 10−2 of the solar value. We also quantified systematic differences between datasets, and we discuss here alternative models with higher resolutions, additional asymmetries, or He-rich abundances.

scholarly journals A novel approach for the analysis of the geometry involved in determining light curves of pulsars

2019 ◽  
Vol 490 (1) ◽  
pp. 1437-1450
Author(s):  
Daniele Viganò ◽  
Diego F Torres
Keyword(s):  
Reference Frames ◽  
Spectral Energy Distribution ◽  
Light Curves ◽  
Spectral Energy ◽  
Radius Of Curvature ◽  
Rotational Axis ◽  
Magnetic Line ◽  
Pulsar Magnetosphere ◽  
Radiation Process ◽  
Novel Approach

ABSTRACT In this work, we introduce the use of the differential geometry Frenet–Serret equations to describe a magnetic line in a pulsar magnetosphere. These equations, which need to be solved numerically, fix the magnetic line in terms of their tangent, normal, and binormal vectors at each position, given assumptions on the radius of curvature and torsion. Once the representation of the magnetic line is defined, we provide the relevant set of transformations between reference frames; the ultimate aim is to express the map of the emission directions in the star corotating frame. In this frame, an emission map can be directly read as a light curve seen by observers located at a certain fixed angle with respect to the rotational axis. We provide a detailed step-by-step numerical recipe to obtain the emission map for a given emission process, and give a set of simplified benchmark tests. Key to our approach is that it offers a setting to achieve an effective description of the system’s geometry together with the radiation spectrum. This allows to compute multifrequency light curves produced by a specific radiation process (and not just geometry) in the pulsar magnetosphere, and intimately relates with averaged observables such as the spectral energy distribution.

scholarly journals The GRAVITY young stellar object survey

2020 ◽  
Vol 642 ◽  
pp. A162
Author(s):  
◽  
Y.-I. Bouarour ◽  
K. Perraut ◽  
F. Ménard ◽  
W. Brandner ◽  
...  
Keyword(s):  
Near Infrared ◽  
Gravity Data ◽  
Spectral Energy Distribution ◽  
Central Star ◽  
High Resolution Spectroscopy ◽  
Spectral Energy ◽  
Disk Model ◽  
Stellar Radius ◽  
Fundamental Parameters ◽  
Outer Disk

Context. Studies of the dust distribution, composition, and evolution of protoplanetary disks provide clues for understanding planet formation. However, little is known about the innermost regions of disks where telluric planets are expected to form. Aims. We aim constrain the geometry of the inner disk of the T Tauri star RY Lup by combining spectro-photometric data and interferometric observations in the near-infrared (NIR) collected at the Very Large Telescope Interferometer. We use PIONIER data from the ESO archive and GRAVITY data that were obtained in June 2017 with the four 8m telescopes. Methods. We use a parametric disk model and the 3D radiative transfer code MCFOST to reproduce the spectral energy distribution (SED) and match the interferometric observations. MCFOST produces synthetic SEDs and intensity maps at different wavelengths from which we compute the modeled interferometric visibilities and closure phases through Fourier transform. Results. To match the SED from the blue to the millimetric range, our model requires a stellar luminosity of 2.5 L⊙, higher than any previously determined values. Such a high value is needed to accommodate the circumstellar extinction caused by the highly inclined disk, which has been neglected in previous studies. While using an effective temperature of 4800 K determined through high-resolution spectroscopy, we derive a stellar radius of 2.29 R⊙. These revised fundamental parameters, when combined with the mass estimates available (in the range 1.3–1.5 M⊙), lead to an age of 0.5–2.0 Ma for RY Lup, in better agreement with the age of the Lupus association than previous determinations. Our disk model (that has a transition disk geometry) nicely reproduces the interferometric GRAVITY data and is in good agreement with the PIONIER ones. We derive an inner rim location at 0.12 au from the central star. This model corresponds to an inclination of the inner disk of 50°, which is in mild tension with previous determinations of a more inclined outer disk from SPHERE (70° in NIR) and ALMA (67 ± 5°) images, but consistent with the inclination determination from the ALMA CO spectra (55 ± 5°). Increasing the inclination of the inner disk to 70° leads to a higher line-of-sight extinction and therefore requires a higher stellar luminosity of 4.65 L⊙ to match the observed flux levels. This luminosity would translate to a stellar radius of 3.13 R⊙, leading to an age of 2–3 Ma, and a stellarmass of about 2 M⊙, in disagreement with the observed dynamical mass estimate of 1.3–1.5 M⊙. Critically, this high-inclination inner disk model also fails to reproduce the visibilities observed with GRAVITY. Conclusions. The inner dust disk, as traced by the GRAVITY data, is located at a radius in agreement with the dust sublimation radius. An ambiguity remains regarding the respective orientations of the inner and outer disk, coplanar and mildly misaligned, respectively.As our datasets are not contemporary and the star is strongly variable, a deeper investigation will require a dedicated multi-technique observing campaign.

scholarly journals NEW SPECTRAL ANALYSIS RESULTS WITHIN THE SCOPE OF EXTENDED MATTER RESEARCH IN THE AR LACERTAE ACTIVE BINARY SYSTEM

2021 ◽  
Vol 57 (1) ◽  
pp. 167-179
Author(s):  
O. Karakuş ◽  
F. Ekmekçi
Keyword(s):  
Spectral Analysis ◽  
High Resolution ◽  
Binary System ◽  
Energy Distribution ◽  
Spectral Energy Distribution ◽  
Photometric Data ◽  
Light Curves ◽  
Spectral Energy ◽  
Orbital Phase ◽  
Low Dispersion

Within the scope of extended matter research, we present new spectral analysis results of an active binary system, AR Lac. The low and high resolution spectra of this system, were taken during the period 2013-2016. The evaluation of low dispersion spectra together with the B, V, Rc, Ic and WISE photometric data showed that AR Lac has an excess radiation in the W2 band. In addition, the spectral energy distribution and the minima depth ratios of the light curves of this active binary system were studied to examine the flux contributions of the components of the system depending on wavelengths and on orbital phase. Furthermore, high resolution spectral analysis showed evidence of prominence-like structures and a possible extended matter around the cooler component of AR Lac.

scholarly journals The flux distribution of Sgr A*

2020 ◽  
Vol 638 ◽  
pp. A2 ◽  
Author(s):  
◽  
R. Abuter ◽  
A. Amorim ◽  
M. Bauböck ◽  
J. B. Berger ◽  
...  
Keyword(s):  
Flux Density ◽  
Power Law ◽  
Lognormal Distribution ◽  
Flux Distribution ◽  
Spectral Energy Distribution ◽  
Model Fitting ◽  
Light Curves ◽  
Spectral Energy ◽  
Noise Characteristics ◽  
Sgr A

The Galactic center black hole Sagittarius A* is a variable near-infrared (NIR) source that exhibits bright flux excursions called flares. When flux from Sgr A* is detected, the light curve has been shown to exhibit red noise characteristics and the distribution of flux densities is non-linear, non-Gaussian, and skewed to higher flux densities. However, the low-flux density turnover of the flux distribution is below the sensitivity of current single-aperture telescopes. For this reason, the median NIR flux has only been inferred indirectly from model fitting, but it has not been directly measured. In order to explore the lowest flux ranges, to measure the median flux density, and to test if the previously proposed flux distributions fit the data, we use the unprecedented resolution of the GRAVITY instrument at the VLTI. We obtain light curves using interferometric model fitting and coherent flux measurements. Our light curves are unconfused, overcoming the confusion limit of previous photometric studies. We analyze the light curves using standard statistical methods and obtain the flux distribution. We find that the flux distribution of Sgr A* turns over at a median flux density of (1.1 ± 0.3) mJy. We measure the percentiles of the flux distribution and use them to constrain the NIR K-band spectral energy distribution. Furthermore, we find that the flux distribution is intrinsically right-skewed to higher flux density in log space. Flux densities below 0.1 mJy are hardly ever observed. In consequence, a single powerlaw or lognormal distribution does not suffice to describe the observed flux distribution in its entirety. However, if one takes into account a power law component at high flux densities, a lognormal distribution can describe the lower end of the observed flux distribution. We confirm the rms–flux relation for Sgr A* and find it to be linear for all flux densities in our observation. We conclude that Sgr A* has two states: the bulk of the emission is generated in a lognormal process with a well-defined median flux density and this quiescent emission is supplemented by sporadic flares that create the observed power law extension of the flux distribution.

scholarly journals F-GAMMA: Multi-frequency radio monitoring ofFermiblazars

2019 ◽  
Vol 626 ◽  
pp. A60 ◽  
Author(s):  
E. Angelakis ◽  
L. Fuhrmann ◽  
I. Myserlis ◽  
J. A. Zensus ◽  
I. Nestoras ◽  
...  
Keyword(s):  
Gamma Ray ◽  
Spectral Energy Distribution ◽  
Light Curves ◽  
Spectral Energy ◽  
Limiting Factor ◽  
Diagnostic Study ◽  
Atmospheric Conditions ◽  
Spectral Evolution ◽  
Radio Monitoring ◽  
Data Products

Context. The advent of theFermigamma-ray space telescope with its superb sensitivity, energy range, and unprecedented capability to monitor the entire 4πsky within less than 2–3 h, introduced a new standard in time domain gamma-ray astronomy. Among several breakthroughs,Fermihas – for the first time – made it possible to investigate, with high cadence, the variability of the broadband spectral energy distribution (SED), especially for active galactic nuclei (AGN). This is necessary for understanding the emission and variability mechanisms in such systems. To explore this new avenue of extragalactic physics theFermi-GST AGN Multi-frequency Monitoring Alliance (F-GAMMA) programme undertook the task of conducting nearly monthly, broadband radio monitoring of selected blazars, which is the dominant population of the extragalactic gamma-ray sky, from January 2007 to January 2015. In this work we release all the multi-frequency light curves from 2.64 to 43 GHz and first order derivative data products after all necessary post-measurement corrections and quality checks.Aims. Along with the demanding task to provide the radio part of the broadband SED in monthly intervals, the F-GAMMA programme was also driven by a series of well-defined fundamental questions immediately relevant to blazar physics. On the basis of the monthly sampled radio SEDs, the F-GAMMA aimed at quantifying and understanding the possible multiband correlation and multi-frequency radio variability, spectral evolution and the associated emission, absorption and variability mechanisms. The location of the gamma-ray production site and the correspondence of structural evolution to radio variability have been among the fundamental aims of the programme. Finally, the programme sought to explore the characteristics and dynamics of the multi-frequency radio linear and circular polarisation.Methods. The F-GAMMA ran two main and tightly coordinated observing programmes. The Effelsberg 100 m telescope programme monitoring 2.64, 4.85, 8.35, 10.45, 14.6, 23.05, 32, and 43 GHz, and the IRAM 30 m telescope programme observing at 86.2, 142.3, and 228.9 GHz. The nominal cadence was one month for a total of roughly 60 blazars and targets of opportunity. In a less regular manner the F-GAMMA programme also ran an occasional monitoring with the APEX 12 m telescope at 345 GHz. We only present the Effelsberg dataset in this paper. The higher frequencies data are released elsewhere.Results. The current release includes 155 sources that have been observed at least once by the F-GAMMA programme. That is, the initial sample, the revised sample after the firstFermirelease, targets of opportunity, and sources observed in collaboration with a monitoring programme following up onPlancksatellite observations. For all these sources we release all the quality-checked Effelsberg multi-frequency light curves. The suite of post-measurement corrections and flagging and a thorough system diagnostic study and error analysis is discussed as an assessment of the data reliability. We also release data products such as flux density moments and spectral indices. The effective cadence after the quality flagging is around one radio SED every 1.3 months. The coherence of each radio SED is around 40 min.Conclusions. The released dataset includes more than 3 × 104measurements for some 155 sources over a broad range of frequencies from 2.64 GHz to 43 GHz obtained between 2007 and 2015. The median fractional error at the lowest frequencies (2.64–10.45 GHz) is below 2%. At the highest frequencies (14.6–43 GHz) with limiting factor of the atmospheric conditions, the errors range from 3% to 9%, respectively.

scholarly journals Spectroscopy of the first resolved strongly lensed Type Ia supernova iPTF16geu

2020 ◽  
Author(s):  
J Johansson ◽  
A Goobar ◽  
S H Price ◽  
A Sagués Carracedo ◽  
L Della Bruna ◽  
...  
Keyword(s):  
Time Delay ◽  
Hubble Space Telescope ◽  
Signal To Noise Ratio ◽  
Spectral Energy Distribution ◽  
Compact Objects ◽  
Light Curves ◽  
Host Galaxy ◽  
Spectral Energy ◽  
Type Ia Supernova ◽  
Type Ia

Abstract We report the results from spectroscopic observations of the multiple images of the strongly lensed Type Ia supernova (SN Ia), iPTF16geu, obtained with ground based telescopes and the Hubble Space Telescope (HST). From a single epoch of slitless spectroscopy with HST, we resolve spectra of individual lensed supernova images for the first time. This allows us to perform an independent measurement of the time-delay between the two brightest images, Δt = 1.4 ± 5.0 days, which is consistent with the time-delay measured from the light-curves. We also present measurements of narrow emission and absorption lines characterizing the interstellar medium in the SN Ia host galaxy at z = 0.4087, as well as in the foreground lensing galaxy at z = 0.2163. We detect strong Na id absorption in the host galaxy, indicating that iPTF16geu belongs to a subclass of SNe Ia displaying ”anomalously” large Na id column densities compared to dust extinction derived from light curves. For the lens galaxy, we refine the measurement of the velocity dispersion, σ = 129 ± 4 km s−1, which significantly constrains the lens model. We use ground-based spectroscopy, boosted by a factor ∼70 from lensing magnification, to study the properties of a high-z SN Ia with unprecedented signal-to-noise ratio. The spectral properties of the supernova, such as pseudo-Equivalent widths of several absorption features and velocities of the Si ii-line, indicate that iPTF16geu is a normal SN Ia. We do not detect any significant deviations of the SN spectral energy distribution from microlensing of the SN photosphere by stars and compact objects in the lensing galaxy.

scholarly journals Correlation between optical and γ-ray flux variations in bright flat spectrum radio quasars

2020 ◽  
Vol 498 (4) ◽  
pp. 5128-5148
Author(s):  
Bhoomika Rajput ◽  
C S Stalin ◽  
S Sahayanathan
Keyword(s):  
Spectral Energy Distribution ◽  
Broad Band ◽  
High Energy ◽  
Light Curves ◽  
Spectral Energy ◽  
Emission Model ◽  
Uv Emission ◽  
Spectrum Radio ◽  
Cross Correlation Analysis ◽  
Γ Ray

ABSTRACT Blazars are known to show flux variations over a range of energies from low-energy radio to high-energy γ-rays. Cross-correlation analysis of the optical and γ-ray light curves in blazars shows that flux variations are generally correlated in both bands, however, there are exceptions. We explored this optical–GeV connection in four flat spectrum radio quasars by a systematic investigation of their long-term optical and γ-ray light curves. On analysis of the four sources, namely 3C 273, 3C 279, PKS 1510−089, and CTA 102, we noticed different behaviours between the optical and GeV flux variations. We found instances when (i) the optical and GeV flux variations are closely correlated, (ii) there are optical flares without γ-ray counterparts, and (iii) γ-ray flares without optical counterparts. To understand these diverse behaviours, we carried out broad-band spectral energy distribution (SED) modelling of the sources at different epochs using a one-zone leptonic emission model. The optical–UV emission is found to be dominated by emission from the accretion disc in the sources PKS 1510−089, CTA 102, and 3C 273, while in 3C 279, the synchrotron radiation from the jet dominates the optical–UV emission. Our SED analysis indicates that (i) correlated optical and γ-ray flux variations are caused by changes in the bulk Lorentz factor (Γ), (ii) γ-ray flares without optical counterparts are due to increase in Γ and/or the electron energy density, and (iii) an optical flare without γ-ray counterpart is due to increase in the magnetic field strength.

Spectral energy distribution of blazars

2019 ◽  
Vol 15 (S356) ◽  
pp. 374-374
Author(s):  
Prospery Simpemba
Keyword(s):  
Energy Distribution ◽  
Gamma Ray ◽  
Spectral Energy Distribution ◽  
Distribution Patterns ◽  
Radio Galaxies ◽  
Light Curves ◽  
Spectral Energy ◽  
Range Data ◽  
Energy Distributions ◽  
X Ray

AbstractThis study focuses on spectral energy distributions and light-curves of blazars and radio galaxies, and the testing of the existing models with a view to appropriately predict a new model that will nearly accurately present the nature of the energy outflows of these super-massive bodies. Understanding blazar emission is very important as it relates more directly to the physics of the AGN’s central black hole. X-ray, radio and gamma-ray wavelength range data on blazars and radio galaxies from archived data has been collected and a detailed investigation of the spectral energy distribution patterns of the blazars and radio galaxies carried out so as to fit the data in the various models. The results of this investigation will be discussed in detail in this presentation.

scholarly journals The Crab nebula variability at short time-scales with the Cherenkov telescope array

2020 ◽  
Vol 501 (1) ◽  
pp. 337-346
Author(s):  
E Mestre ◽  
E de Oña Wilhelmi ◽  
D Khangulyan ◽  
R Zanin ◽  
F Acero ◽  
...  
Keyword(s):  
Gamma Ray ◽  
Crab Nebula ◽  
Spectral Energy Distribution ◽  
Spectral Energy ◽  
Telescope Array ◽  
Cherenkov Telescopes ◽  
Cherenkov Telescope ◽  
Emission Models ◽  
Short Time ◽  
The Crab Nebula

ABSTRACT Since 2009, several rapid and bright flares have been observed at high energies (>100 MeV) from the direction of the Crab nebula. Several hypotheses have been put forward to explain this phenomenon, but the origin is still unclear. The detection of counterparts at higher energies with the next generation of Cherenkov telescopes will be determinant to constrain the underlying emission mechanisms. We aim at studying the capability of the Cherenkov Telescope Array (CTA) to explore the physics behind the flares, by performing simulations of the Crab nebula spectral energy distribution, both in flaring and steady state, for different parameters related to the physical conditions in the nebula. In particular, we explore the data recorded by Fermi during two particular flares that occurred in 2011 and 2013. The expected GeV and TeV gamma-ray emission is derived using different radiation models. The resulting emission is convoluted with the CTA response and tested for detection, obtaining an exclusion region for the space of parameters that rule the different flare emission models. Our simulations show different scenarios that may be favourable for achieving the detection of the flares in Crab with CTA, in different regimes of energy. In particular, we find that observations with low sub-100 GeV energy threshold telescopes could provide the most model-constraining results.

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