scholarly journals Reverberation in Tidal Disruption Events: Dust Echoes, Coronal Emission Lines, Multi-wavelength Cross-correlations, and QPOs

2021 ◽  
Vol 217 (5) ◽  
Author(s):  
Sjoert van Velzen ◽  
Dheeraj R. Pasham ◽  
Stefanie Komossa ◽  
Lin Yan ◽  
Erin A. Kara
Keyword(s):  
Coronal Emission ◽  
Tidal Disruption ◽  
X Ray ◽  
Wide Range ◽  
Multi Wavelength ◽  
Nuclear Dust ◽  
Cross Correlations ◽  
Infrared Wavelengths ◽  
Observational Techniques ◽  
Infrared Instruments

AbstractStellar tidal disruption events (TDEs) are typically discovered by transient emission due to accretion or shocks of the stellar debris. Yet this luminous flare can be reprocessed by gas or dust that inhabits a galactic nucleus, resulting in multiple reverberation signals. Nuclear dust heated by the TDE will lead to an echo at infrared wavelengths (1-10 μm) and transient coronal lines in optical spectra of TDEs trace reverberation by gas that orbits the black hole. Both of these signal have been detected, here we review this rapidly developing field. We also review the results that have been extracted from TDEs with high-quality X-ray light curves: quasi periodic oscillations (QPOs), reverberation lags of fluorescence lines, and cross-correlations with emission at other wavelengths. The observational techniques that are covered in this review probe the emission from TDEs over a wide range of scales: from $\sim 1$ ∼ 1  light year to the innermost parts of the newly formed accretion disk. They provide insights into important properties of TDEs such as their bolometric output and the geometry of the accretion flow. While reverberation signals are not detected for every TDE, we anticipate they will become more commonplace when the next generation of X-ray and infrared instruments become operational.

X-ray Binary Transients in the Magellanic Clouds and the Milky Way

2017 ◽  
Vol 14 (S339) ◽  
pp. 236-240
Author(s):  
P. Charles ◽  
G. Anderson ◽  
D. Coppejans ◽  
M. Motsoaledi
Keyword(s):  
Continuous Monitoring ◽  
High Energy ◽  
X Ray ◽  
Wide Range ◽  
Multi Wavelength ◽  
Optical Wavelengths ◽  
Galactic Sources ◽  
Careful Management ◽  
Eruptive Behaviour

AbstractThe X-ray sky is dominated by luminous galactic sources, variable on time-scales from milliseconds to years. Their eruptive behaviour is now under continuous monitoring by MAXI, Swift, INTEGRAL and other high-energy missions, and representing a superb exemplar of time-domain astronomy. Understanding the astrophysics of such variability requires multi-wavelength follow-up studies from a suite of ground- and space-based facilities. As SALT is a 100% Q-scheduled telescope, one of its key scientific capabilities is related to Target-of-Opportunity (ToO) programmes, and there has been a dedicated SALT Large Programme on Transients in place since 2016, a significant fraction of which has been devoted to the follow-up of X-ray binary transients. This Workshop addressed questions of how such programmes should evolve once the era of MeerKAT and MeerLICHT begins in ∼2018-9 (as well as other huge surveys at optical wavelengths), identifying the range of facilities that would be needed, and the key science topics. There is a clear and growing need for responses to transients to be faster (within minutes if possible), and to be multi-wavelength (particularly in radio and X-ray). Furthermore, extended ongoing coverage of such events (days to weeks for the next ‘V404 Cyg’-type outburst) will be needed for maximum astrophysical return. That would require careful management and coordination of a wide range of ground- and space-based facilities, and optimising coverage against logistical constraints that are often conflicting.

A Dust-Enshrouded Tidal Disruption Event in a Luminous Infared Galaxy

2017 ◽  
Vol 14 (S339) ◽  
pp. 65-65
Author(s):  
S. Mattila
Keyword(s):  
Near Infrared ◽  
Infrared Galaxies ◽  
Tidal Disruption ◽  
Local Universe ◽  
X Ray ◽  
Luminous Infrared Galaxies ◽  
Supermassive Black Hole ◽  
Infrared Wavelengths ◽  
Infrared Monitoring ◽  
Disruption Event

AbstractThis paper presented the discovery of an energetic nuclear transient from near-infrared monitoring of nearby starburst and luminous infrared galaxies. The transient radiated at least 1.5E+52 erg in the infrared but remained elusive at optical and X-ray wavelengths. We interpret its properties as arising from a stellar tidal disruption event (TDE) close to a supermassive black hole. Much of its emission must have been reprocessed by dense gas and re-radiated at infrared wavelengths by dust, suggesting a way for reducing the tension between theoretical luminosity predictions and observations of TDEs. Such events are not detectable by optical, UV or soft X-ray observations, and might represent just the tip of the iceberg of a missed TDE population in the local Universe. That population could be more numerous at higher redshifts where luminous infrared galaxies are more common.

scholarly journals XMMSL2 J144605.0+685735: a slow tidal disruption event

2019 ◽  
Vol 630 ◽  
pp. A98 ◽  
Author(s):  
R. D. Saxton ◽  
A. M. Read ◽  
S. Komossa ◽  
P. Lira ◽  
K. D. Alexander ◽  
...  
Keyword(s):  
Stellar Population ◽  
X Rays ◽  
Time Data ◽  
Tidal Disruption ◽  
X Ray ◽  
Bolometric Luminosity ◽  
Uv Emission ◽  
The Galaxy ◽  
Multi Wavelength ◽  
Disruption Event

Aims. We investigate the evolution of X-ray selected tidal disruption events. Methods. New events are found in near real-time data from XMM-Newton slews, and are monitored by multi-wavelength facilities. Results. In August 2016, X-ray emission was detected from the galaxy XMMSL2 J144605.0+685735 (also known as 2MASX 14460522+6857311), that was 20 times higher than an upper limit from 25 years earlier. The X-ray flux was flat for ∼100 days and then fell by a factor of 100 over the following 500 days. The UV flux was stable for the first 400 days before fading by a magnitude, while the optical (U,B,V) bands were roughly constant for 850 days. Optically, the galaxy appears to be quiescent, at a distance of 127 ± 4 Mpc (z = 0.029 ± 0.001) with a spectrum consisting of a young stellar population of 1–5 Gyr in age, an older population, and a total stellar mass of ∼6 × 109 M⊙. The bolometric luminosity peaked at Lbol ∼ 1043 ergs s−1 with an X-ray spectrum that may be modelled by a power law of Γ ∼ 2.6 or Comptonisation of a low-temperature thermal component by thermal electrons. We consider a tidal disruption event to be the most likely cause of the flare. Radio emission was absent in this event down to < 10 μJy, which limits the total energy of a hypothetical off-axis jet to E <  5 × 1050 ergs. The independent behaviour of the optical, UV, and X-ray light curves challenges models where the UV emission is produced by reprocessing of thermal nuclear emission or by stream-stream collisions. We suggest that the observed UV emission may have been produced from a truncated accretion disc and the X-rays from Compton upscattering of these disc photons.

The SALT Transient Programme

2017 ◽  
Vol 14 (S339) ◽  
pp. 176-180
Author(s):  
D. A. H. Buckley
Keyword(s):  
Gamma Ray ◽  
Cataclysmic Variables ◽  
Gamma Ray Bursts ◽  
High Mass ◽  
Core Collapse ◽  
Tidal Disruption ◽  
X Ray ◽  
Wide Range ◽  
X Ray Binaries

AbstractThe SALT transient follow-up programme began in 2016 and will continue for 5 semesters (until 31 Oct 2018), with an expectation of renewal thereafter. It is currently the only SALT Large Science Programme, and was awarded ~250 ksec. per semester, with a significant fraction (60%) given for the highest priority target-of-opportunity time. The aim is to characterise and study transients across a wide range of classes, currently including (from closest to most distant) cataclysmic variables, novæ and other associated eruptive variables, low- and high-mass X-ray binaries, OGLE and Gaia transients (including tidal disruption events), super-luminous and unusual core-collapse supernovæ, kilonovæ and other candidate optical counterparts to gravitational-wave events, flaring blazars and AGN, and gamma-ray bursts. This programme currently involves four SALT partners, of which South Africa is the major contributor of time (74%) and resources and includes five institutions with over 30 co-investigators. This talk reviewed the nature of the programme and highlighted some of the results to date.

scholarly journals Stellar X-Ray Emission as an Indicator of Stellar Magnetic Activity

1983 ◽  
Vol 102 ◽  
pp. 165-186 ◽  
Author(s):  
G. S. Vaiana
Keyword(s):  
Dynamic Range ◽  
Magnetic Activity ◽  
Coronal Emission ◽  
X Ray ◽  
Surface Magnetic Field ◽  
Solar Observations ◽  
Wide Range ◽  
Field Activity ◽  
The Mean ◽  
Stellar Magnetic Activity

An overview of recent Einstein Observatory observations and theoretical modeling of stellar x-ray emission is presented, with particular emphasis upon the role such studies can play furthering our understanding of stellar magnetic activity. We argue that solar observations can be used to show that coronal emission is morphologically related to surface magnetic field activity; to establish a quantitative link between the observed soft x-ray flux and the mean surface (photospheric) magnetic flux; and, in sum, to demonstrate that soft x-ray emission is a sensitive diagnostic for the presence of surface magnetic fields, uncomplicated by radiative transfer effects and the resulting coupling to the underlying atmosphere (which may introduce unwanted correlations with spectral type and luminosity class). Recent analyses of stellar x-ray observations from the Einstein Observatory have focused on the interpretation of stellar coronal emission and possibly-related surface magnetic activity within the framework of our understanding of solar activity; including “loop” models of stellar coronae, observations of coronal emission variability on a wide range of time scales (which provide information on the morphology of the emitting plasma), and observations and modeling of low-resolution spectroscopic x-ray observations (which test the applicability of solar modeling). These recent results, which I review, all reenforce the argument that stellar coronal emission constitutes an excellent probe for studying stellar magnetic activity over a wide dynamic range, one which may prove to be uniquely suited to studying such activity in distant (and hence faint) sources.

scholarly journals Tidal Disruption Events

2021 ◽  
Vol 59 (1) ◽  
Author(s):  
Suvi Gezari
Keyword(s):  
Black Hole ◽  
Dynamic Range ◽  
Thermal Emission ◽  
Spatial Scales ◽  
Line Emission ◽  
Annual Review ◽  
Publication Date ◽  
Tidal Disruption ◽  
X Ray ◽  
Wide Range

The concept of stars being tidally ripped apart and consumed by a massive black hole (MBH) lurking in the center of a galaxy first captivated theorists in the late 1970s. The observational evidence for these rare but illuminating phenomena for probing otherwise dormant MBHs first emerged in archival searches of the soft X-ray ROSAT All-Sky Survey in the 1990s, but has recently accelerated with the increasing survey power in the optical time domain, with tidal disruption events (TDEs) now regarded as a class of optical nuclear transients with distinct spectroscopic features. Multiwavelength observations of TDEs have revealed panchromatic emission, probing a wide range of scales, from the innermost regions of the accretion flow to the surrounding circumnuclear medium. I review the current census of 56 TDEs reported in the literature, and their observed properties can be summarized as follows: ▪ The optical light curves follow a power-law decline from peak that scales with the inferred central black hole mass as expected for the fallback rate of the stellar debris, but the rise time does not. ▪ The UV-optical and soft X-ray thermal emission come from different spatial scales, and their intensity ratio has a large dynamic range and is highly variable, providing important clues as to what is powering the two components. ▪ They can be grouped into three spectral classes, and those with Bowen fluorescence line emission show a preference for a hotter and more compact line-emitting region, whereas those with only Heii emission lines are the rarest class. Expected final online publication date for the Annual Review of Astronomy and Astrophysics, Volume 59 is August 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Counterfeit Parts Recognition and Detection for Failure Analysts

2010 ◽  
Author(s):  
Katherine V. Whittington
Keyword(s):  
Thermal Cycle ◽  
Visual Inspection ◽  
Acoustic Microscopy ◽  
Scanning Acoustic Microscopy ◽  
3D Measurement ◽  
X Ray ◽  
Wide Range ◽  
Electronic Parts ◽  
Testing Awareness

Abstract The electronics supply chain is being increasingly infiltrated by non-authentic, counterfeit electronic parts, whose use poses a great risk to the integrity and quality of critical hardware. There is a wide range of counterfeit parts such as leads and body molds. The failure analyst has many tools that can be used to investigate counterfeit parts. The key is to follow an investigative path that makes sense for each scenario. External visual inspection is called for whenever the source of supply is questionable. Other methods include use of solvents, 3D measurement, X-ray fluorescence, C-mode scanning acoustic microscopy, thermal cycle testing, burn-in technique, and electrical testing. Awareness, vigilance, and effective investigations are the best defense against the threat of counterfeit parts.

scholarly journals The role of AGN activity in the building up of the BCG at z ∼ 1.6

2019 ◽  
Vol 15 (S356) ◽  
pp. 280-284
Author(s):  
Angela Bongiorno ◽  
Andrea Travascio
Keyword(s):  
Galaxy Cluster ◽  
Cluster Galaxy ◽  
X Ray ◽  
Groups Of Galaxies ◽  
Star Forming ◽  
The Core ◽  
The Galaxy ◽  
Multi Wavelength

AbstractXDCPJ0044.0-2033 is one of the most massive galaxy cluster at z ∼1.6, for which a wealth of multi-wavelength photometric and spectroscopic data have been collected during the last years. I have reported on the properties of the galaxy members in the very central region (∼ 70kpc × 70kpc) of the cluster, derived through deep HST photometry, SINFONI and KMOS IFU spectroscopy, together with Chandra X-ray, ALMA and JVLA radio data.In the core of the cluster, we have identified two groups of galaxies (Complex A and Complex B), seven of them confirmed to be cluster members, with signatures of ongoing merging. These galaxies show perturbed morphologies and, three of them show signs of AGN activity. In particular, two of them, located at the center of each complex, have been found to host luminous, obscured and highly accreting AGN (λ = 0.4−0.6) exhibiting broad Hα line. Moreover, a third optically obscured type-2 AGN, has been discovered through BPT diagram in Complex A. The AGN at the center of Complex B is detected in X-ray while the other two, and their companions, are spatially related to radio emission. The three AGN provide one of the closest AGN triple at z > 1 revealed so far with a minimum (maximum) projected distance of 10 kpc (40 kpc). The discovery of multiple AGN activity in a highly star-forming region associated to the crowded core of a galaxy cluster at z ∼ 1.6, suggests that these processes have a key role in shaping the nascent Brightest Cluster Galaxy, observed at the center of local clusters. According to our data, all galaxies in the core of XDCPJ0044.0-2033 could form a BCG of M* ∼ 1012Mȯ hosting a BH of 2 × 108−109Mȯ, in a time scale of the order of 2.5 Gyrs.

scholarly journals Adjustment models for multivariate geodetic time series with vector-autoregressive errors

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Boris Kargoll ◽  
Alexander Dorndorf ◽  
Mohammad Omidalizarandi ◽  
Jens-André Paffenholz ◽  
Hamza Alkhatib
Keyword(s):  
Least Squares Method ◽  
Functional Model ◽  
Expectation Maximization Algorithm ◽  
Two Dimensions ◽  
Vector Autoregressive ◽  
Wide Range ◽  
Engineering Geodesy ◽  
Cross Correlations ◽  
T Distribution ◽  
Multivariate T

Abstract In this contribution, a vector-autoregressive (VAR) process with multivariate t-distributed random deviations is incorporated into the Gauss-Helmert model (GHM), resulting in an innovative adjustment model. This model is versatile since it allows for a wide range of functional models, unknown forms of auto- and cross-correlations, and outlier patterns. Subsequently, a computationally convenient iteratively reweighted least squares method based on an expectation maximization algorithm is derived in order to estimate the parameters of the functional model, the unknown coefficients of the VAR process, the cofactor matrix, and the degree of freedom of the t-distribution. The proposed method is validated in terms of its estimation bias and convergence behavior by means of a Monte Carlo simulation based on a GHM of a circle in two dimensions. The methodology is applied in two different fields of application within engineering geodesy: In the first scenario, the offset and linear drift of a noisy accelerometer are estimated based on a Gauss-Markov model with VAR and multivariate t-distributed errors, as a special case of the proposed GHM. In the second scenario real laser tracker measurements with outliers are adjusted to estimate the parameters of a sphere employing the proposed GHM with VAR and multivariate t-distributed errors. For both scenarios the estimated parameters of the fitted VAR model and multivariate t-distribution are analyzed for evidence of auto- or cross-correlations and deviation from a normal distribution regarding the measurement noise.

scholarly journals Preparation of Synthetic Zeolites from Coal Fly Ash by Hydrothermal Synthesis

Materials ◽  
2021 ◽  
Vol 14 (5) ◽  
pp. 1267
Author(s):  
David Längauer ◽  
Vladimír Čablík ◽  
Slavomír Hredzák ◽  
Anton Zubrik ◽  
Marek Matik ◽  
...  
Keyword(s):  
Fly Ash ◽  
Coal Combustion ◽  
Power Plants ◽  
Coal Fly Ash ◽  
Thermal Power ◽  
Product Analysis ◽  
Coal Combustion Products ◽  
X Ray ◽  
Wide Range ◽  
Silica Alumina

Large amounts of coal combustion products (as solid products of thermal power plants) with different chemical and physical properties cause serious environmental problems. Even though coal fly ash is a coal combustion product, it has a wide range of applications (e.g., in construction, metallurgy, chemical production, reclamation etc.). One of its potential uses is in zeolitization to obtain a higher added value of the product. The aim of this paper is to produce a material with sufficient textural properties used, for example, for environmental purposes (an adsorbent) and/or storage material. In practice, the coal fly ash (No. 1 and No. 2) from Czech power plants was firstly characterized in detail (X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy with energy dispersive X-ray analysis (SEM-EDX), particle size measurement, and textural analysis), and then it was hydrothermally treated to synthetize zeolites. Different concentrations of NaOH, LiCl, Al2O3, and aqueous glass; different temperature effects (90–120 °C); and different process lengths (6–48 h) were studied. Furthermore, most of the experiments were supplemented with a crystallization phase that was run for 16 h at 50 °C. After qualitative product analysis (SEM-EDX, XRD, and textural analytics), quantitative XRD evaluation with an internal standard was used for zeolitization process evaluation. Sodalite (SOD), phillipsite (PHI), chabazite (CHA), faujasite-Na (FAU-Na), and faujasite-Ca (FAU-Ca) were obtained as the zeolite phases. The content of these zeolite phases ranged from 2.09 to 43.79%. The best conditions for the zeolite phase formation were as follows: 4 M NaOH, 4 mL 10% LiCl, liquid/solid ratio of 30:1, silica/alumina ratio change from 2:1 to 1:1, temperature of 120 °C, process time of 24 h, and a crystallization phase for 16 h at 50 °C.

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