scholarly journals Intrinsic and observed dual AGN fractions from major mergers

2019 ◽  
Vol 624 ◽  
pp. A86 ◽  
Author(s):  
J. M. Solanes ◽  
J. D. Perea ◽  
G. Valentí–Rojas ◽  
A. del Olmo ◽  
I. Márquez ◽  
...  
Keyword(s):  
Observational Studies ◽  
Maximum Level ◽  
Theoretical Studies ◽  
Activity Levels ◽  
Nuclear Activity ◽  
Bolometric Luminosity ◽  
Global Properties ◽  
Relative Separation ◽  
Order Of Magnitude ◽  
Optical Wavelengths

A suite of 432 collisionless simulations of bound pairs of spiral galaxies with mass ratios 1:1 and 3:1, and global properties consistent with the ΛCDM paradigm, is used to test the conjecture that major mergers fuel the dual AGN (DAGN) of the local volume. Our analysis was based on the premise that the essential aspects of this scenario can be captured by replacing the physics of the central black holes with restrictions on their relative separation in phase space. We introduce several estimates of the DAGN fraction and infer predictions for the activity levels and resolution limits usually involved in surveys of these systems, assessing their dependence on the parameters controlling the length of both mergers and nuclear activity. Given a set of constraints, we find that the values adopted for some of the latter factors often condition the outcomes from individual experiments. Still, the results do not, in general, reveal very tight correlations, the clearest effect being the tendency of the frequencies normalized to the merger time to anticorrelate with the orbital circularity. In agreement with other theoretical studies, our simulations predict intrinsic DAGN abundances that range from ∼ a few to 15% depending on the maximum level of nuclear activity achieved, the higher the bolometric luminosity, the lower the fraction. At the same time, we show that these probabilities are reduced by about an order of magnitude when they are filtered with the typical constraints applied by observational studies of the DAGN fraction at low redshift. Seen as a whole, our results prove that consideration of the most common limitations involved in the detection of close active pairs at optical wavelengths is sufficient alone to reconcile the intrinsic frequencies envisaged in a hierarchical universe with the small fractions of double-peaked narrow-line systems which are often reported at kpc-scales.

scholarly journals Discovery and follow-up of ASASSN-19dj: an X-ray and UV luminous TDE in an extreme post-starburst galaxy

2020 ◽  
Vol 500 (2) ◽  
pp. 1673-1696 ◽  
Author(s):  
Jason T Hinkle ◽  
T W-S Holoien ◽  
K Auchettl ◽  
B J Shappee ◽  
J M M Neustadt ◽  
...  
Keyword(s):  
Optical Emission ◽  
Starburst Galaxy ◽  
Late Time ◽  
X Rays ◽  
Tidal Disruption ◽  
X Ray ◽  
Bolometric Luminosity ◽  
Order Of Magnitude ◽  
High Cadence

ABSTRACT We present observations of ASASSN-19dj, a nearby tidal disruption event (TDE) discovered in the post-starburst galaxy KUG 0810+227 by the All-Sky Automated Survey for Supernovae (ASAS-SN) at a distance of d ≃ 98 Mpc. We observed ASASSN-19dj from −21 to 392 d relative to peak ultraviolet (UV)/optical emission using high-cadence, multiwavelength spectroscopy and photometry. From the ASAS-SN g-band data, we determine that the TDE began to brighten on 2019 February 6.8 and for the first 16 d the rise was consistent with a flux ∝t2 power law. ASASSN-19dj peaked in the UV/optical on 2019 March 6.5 (MJD = 58548.5) at a bolometric luminosity of L = (6.2 ± 0.2) × 1044 erg s−1. Initially remaining roughly constant in X-rays and slowly fading in the UV/optical, the X-ray flux increased by over an order of magnitude ∼225 d after peak, resulting from the expansion of the X-ray emitting region. The late-time X-ray emission is well fitted by a blackbody with an effective radius of ∼1 × 1012 cm and a temperature of ∼6 × 105 K. The X-ray hardness ratio becomes softer after brightening and then returns to a harder state as the X-rays fade. Analysis of Catalina Real-Time Transient Survey images reveals a nuclear outburst roughly 14.5 yr earlier with a smooth decline and a luminosity of LV ≥ 1.4 × 1043 erg s−1, although the nature of the flare is unknown. ASASSN-19dj occurred in the most extreme post-starburst galaxy yet to host a TDE, with Lick HδA = 7.67 ± 0.17 Å.

scholarly journals Nuclear Activity in Interacting Galaxies

1994 ◽  
Vol 159 ◽  
pp. 499-499
Author(s):  
Tapan K. Chatterjee
Keyword(s):  
Elliptical Galaxy ◽  
Research Work ◽  
Interacting Galaxies ◽  
Nuclear Activity ◽  
Reactivation Process ◽  
Order Of Magnitude ◽  
Orbital Periods ◽  
Binary Evolution ◽  
New Feature ◽  
Comparable Mass

Dynamical studies of galactic collisions, conducted previously (Chatterjee, 1992, 1993a, b), indicated that most of the mergers take place in two to three shrinking orbital periods. We extend this line of research work to study induced nuclear activity. We study the binary evolution of a spiral galaxy perturbed by a compact elliptical galaxy of comparable mass and find that each time the perturber penetrates the disk of the spiral, the disk is subjected to an appropriate perturbation, causing inflow of gas towards its nucleus due to loss of angular momentum; there it could activate an inert black hole (consistent with previous studies; e.g. Naguchi, 1988). However a new feature that we find is that repeated episodes of disk penetration by the perturber occur in gradually shorter timescales, causing an overlap of the activity timescale and the dynamical timescale. In fact if the elliptical is very compact and the spiral has a massive bulge, subsequent dynamical timescales reduce by more than an order of magnitude. This periodic increase in the activity of the nucleus is of a secular nature (in contrast to a reactivation process), and could lead to the evolution of the spiral along the following lines, Starburst → Seyfert 2 → Seyfert 1, as interpenetrations follow.

scholarly journals Study of spider pulsar binary eclipses and discovery of an eclipse mechanism transition

2020 ◽  
Vol 494 (2) ◽  
pp. 2948-2968 ◽  
Author(s):  
E J Polzin ◽  
R P Breton ◽  
B Bhattacharyya ◽  
D Scholte ◽  
C Sobey ◽  
...  
Keyword(s):  
Direct Evidence ◽  
Low Frequency ◽  
Line Of Sight ◽  
Observational Constraints ◽  
Main Body ◽  
Theoretical Studies ◽  
Wide Range ◽  
Order Of Magnitude ◽  
Mechanism Transition ◽  
Hubble Time

ABSTRACT We present a comparative study of the low-frequency eclipses of spider (compact and irradiating binary) PSRs B1957+20 and J1816+4510. Combining these data with those of three other eclipsing systems we study the frequency dependence of the eclipse duration. PSRs B1957+20 and J1816+4510 have similar orbital properties, but the companions to the pulsars have masses that differ by an order of magnitude. A dedicated campaign to simultaneously observe the pulsed and imaged continuum flux densities throughout the eclipses reveals many similarities between the excess material within the two binaries, irrespective of the companion star properties. The observations show that the pulsar fluxes are removed from the line of sight throughout the main body of the eclipses. For PSR J1816 + 4510, we present the first direct evidence of an eclipse mechanism that transitions from one that removes the pulsar flux from the line of sight to one that merely smears out pulsations, and claim that this is a consequence of scattering in a tail of material flowing behind the companion. Inferred mass-loss rates from the companion stars are found to be $\dot{M}_{\text{C}} \sim 10^{-12}$ and $\sim 2 \times 10^{-13}\,\mathrm{M}_\odot$ yr−1 for PSR B1957+20 and PSR J1816 + 4510, respectively; seemingly too low to evaporate the stars within Hubble time. Measurements of eclipse durations over a wide range of radio frequencies show a significant dependence of eclipse duration on frequency for all pulsars, with wider eclipses at lower frequencies. These results provide a marked improvement in the observational constraints available for theoretical studies of the eclipse mechanisms.

scholarly journals Mid-infrared evolution of η Carinae from 1968 to 2018

2019 ◽  
Vol 630 ◽  
pp. L6 ◽  
Author(s):  
A. Mehner ◽  
W.-J. de Wit ◽  
D. Asmus ◽  
P. W. Morris ◽  
C. Agliozzo ◽  
...  
Keyword(s):  
Spectral Energy Distribution ◽  
Circumstellar Dust ◽  
Spectral Energy ◽  
Short Term ◽  
Dust Extinction ◽  
Bolometric Luminosity ◽  
Very Large Telescope ◽  
Optical Wavelengths ◽  
The Mean

η Car is one of the most luminous and massive stars in our Galaxy and is the brightest mid-IR source in the sky outside our solar system. Since the late 1990s, the central source has dramatically brightened at UV and optical wavelengths. This might be explained by a decrease in circumstellar dust extinction. We aim to establish the mid-IR flux evolution and further our understanding of the star’s UV and optical brightening. Mid-IR images from 8−20 μm were obtained in 2018 with VISIR at the Very Large Telescope. Archival data from 2003 and 2005 were retrieved from the ESO Science Archive Facility, and historical records were collected from publications. We present mid-IR images of η Car with the highest angular resolution to date at the corresponding wavelengths (≥0.22″). We reconstruct the mid-IR evolution of the spectral energy distribution of the spatially integrated Homunculus nebula from 1968 to 2018 and find no long-term changes. The bolometric luminosity of η Car has been stable over the past five decades. We do not observe a long-term decrease in the mid-IR flux densities that could be associated with the brightening at UV and optical wavelengths, but circumstellar dust must be declining in our line of sight alone. Short-term flux variations within about 25% of the mean levels could be present.

scholarly journals Superflares on AB Doradus observed with TESS

2019 ◽  
Vol 628 ◽  
pp. A79 ◽  
Author(s):  
J. H. M. M. Schmitt ◽  
P. Ioannidis ◽  
J. Robrade ◽  
S. Czesla ◽  
P. C. Schneider
Keyword(s):  
Solar Flare ◽  
Total Solar Irradiance ◽  
Time Variable ◽  
Solar Neighborhood ◽  
Light Curves ◽  
Active Star ◽  
X Ray ◽  
Rotational Modulation ◽  
Order Of Magnitude ◽  
Optical Wavelengths

We present short-cadence data of the ultra-active star AB Dor measured by the Transiting Exoplanet Survey Satellite (TESS). In the TESS light curves of AB Dor, we found numerous flare events in addition to time-variable rotational modulation with an amplitude of up to 7%. We identified eight superflares (releasing more than 1034 erg) and studied their morphologies and energetics. We compared these flares to both the most energetic solar flare seen in total solar irradiance measurements as well as to a very energetic flare on AB Dor observed by XMM-Newton, the superflare nature of which we also demonstrate. The total energy of both the solar flare and the event on AB Dor emitted in the optical exceed their respective X-ray outputs possibly by an order of magnitude, suggesting that the dominant energy loss of such flares actually occurs at optical wavelengths. Superflares are found to take place on AB Dor at a rate of about one per week, and due to the star’s proximity and brightness can be studied in excruciating detail. Thus the TESS data offer a superb possibility to study the frequency and energetics of superflare events for stars in the solar neighborhood and at large.

Reference frames in astrometry

1988 ◽  
Vol 128 ◽  
pp. 25-32 ◽  
Author(s):  
Chr. de Vegt ◽  
K. J. Johnston
Keyword(s):  
Reference Frame ◽  
Present Status ◽  
Reference Frames ◽  
Order Of Magnitude ◽  
Optical Wavelengths ◽  
Near Future ◽  
Magnitude Increase ◽  
Fundamental Reference ◽  
Made In

Present and near future advances in astrometry at radio and optical wavelengths will allow at least an order of magnitude increase in the precision with which fundamental reference frames are defined compared with those available ten years ago. A brief review is given of the present status of fundamental celestial reference frames with a view towards defining the problems encountered in establishing a fundamental reference frame and methods of linking these reference frames. An estimate is made of the progress to be made in reference frames over the next ten years.

Evaluation of the Toxicological Risk Associated with the Use of Poly aery lamides in the Recovery of Nutrients from Food Processing Waste (II)

1995 ◽  
Vol 14 (1) ◽  
pp. 34-39 ◽  
Author(s):  
LeeAnn Schechter ◽  
Randy Deskin ◽  
Amy Essenfeld ◽  
Bruce Bernard ◽  
Marvin Friedman ◽  
...  
Keyword(s):  
Food Processing ◽  
Nutritive Value ◽  
Animal Feed ◽  
Analytical Data ◽  
Maximum Level ◽  
Full Scale ◽  
Processing Waste ◽  
Order Of Magnitude ◽  
Poultry Processing ◽  
Food Processing Waste

Experiments were conducted using radiolabeled acrylamide and liquid scintillation counting methods to determine how acrylamide monomer would partition during the solid/liquid separation and subsequent rendering of a poultry processing waste. Due to its nutritive value, the rendered solids from such a full-scale food processing waste operation could potentially be used as a component of animal feed. Previous studies were unable to directly measure acrylamide in the solids samples after separation. Based on the analytical data herein, ∼1% of the original radiolabel administered to the waste system was detected in the rendered solids. In a full-scale food processing waste operation, this would represent a maximum level of 0.3 ppb acrylamide in the final animal feed with more typical levels, reflecting industry use, being ∼0.05 ppb. These levels are an order of magnitude less than those calculated in the previous experiment, confirming the associated risk as de minimis.

Evaluation of Interfacial and Permeation Leaks in Gaskets and Compression Packing

2019 ◽  
Vol 5 (1) ◽  
Author(s):  
Ali Salah Omar Aweimer ◽  
Abdel-Hakim Bouzid
Keyword(s):  
Experimental Testing ◽  
Design Criterion ◽  
Leak Rate ◽  
Theoretical Studies ◽  
Reasonable Accuracy ◽  
Sealing Material ◽  
Order Of Magnitude ◽  
Global Concern ◽  
Bolted Flange ◽  
Experimental And Theoretical Studies

The quantities of leak rate through sealing systems are subjected to strict regulations because of the global concern on radiative materials. The maximum tolerated leak is becoming a design criterion in pressure vessel design codes, and the leak rate for an application under specific conditions is required to be estimated with reasonable accuracy. In this respect, experimental and theoretical studies are conducted to characterize gasket and packing materials to predict leakage. The amount of the total leak is the summation of the permeation leak through the sealing material and the interfacial leak generated between the sealing element and its mating surfaces. Unfortunately, existing models used to predict leakage do not separate these two types of leaks. This paper deals with a study based on experimental testing that quantifies the amount of these two types of leaks in bolted gasketed joints and packed stuffing boxes. It shows the contribution of interfacial leak for low and high contact surface stresses and the influence of the surface finish of 0.8 and 6.3 μm (32 and 250 μin) resulting from phonographic grooves in the case of a bolted flange joint. The results indicate that most leakage is interfacial, reaching 99% at the low stress while interfacial leak is of the same order of magnitude of permeation leak at high stresses reaching 10−6 and 10−8 mg/s in both packing and gaskets, respectively. Finally, particular focus is put on the technique of precompression to improve material sealing tightness.

Characterization of groundwater composition in Punjab state with special emphasis on uranium content, speciation and mobility

2014 ◽  
Vol 102 (3) ◽  
pp. 239-254
Author(s):  
Ajay Kumar ◽  
R. M. Tripathi ◽  
Sabyasachi Rout ◽  
Manish K. Mishra ◽  
P. M. Ravi ◽  
...  
Keyword(s):  
Uranium Content ◽  
Activity Levels ◽  
Secular Equilibrium ◽  
Deep Aquifer ◽  
Rock Interaction ◽  
Aquifer System ◽  
Weathering Processes ◽  
Ionic Concentrations ◽  
Parent Rocks ◽  
Order Of Magnitude

Abstract Groundwaters (borewell and handpump) were sampled from two districts (Bathinda and Mansa) of Punjab state and analyzed for their major ionic concentrations and uranium isotope compositions in order to assess the possible origins of the waters and water–rock interactions that occurred in the deep aquifer system. The major ionic concentrations of waters were plotted on a Piper diagram and grouped into four dominant hydrochemical facies as (Na+K)-SO4+Cl type (69% – 73%), (Ca+Mg)-SO4+Cl type (6% – 21%), (Ca+Mg)–HCO3 type (4% – 6%) and (Na+K)-HCO3 type (2% – 19%). It was observed that mobility of uranium in groundwater was very much influenced by TDS (total dissolved solids). To investigate the various mechanisms for deriving the elevated uranium concentrations in groundwater, 234U/238U activity ratios (ARs) were calculated using the determined activity levels of 234U and 238U. The mean ARs was found to be near unity (i.e. secular equilibrium) in the study regions confirmed that uranium in groundwaters was mainly resulted from its host/parent rocks through weathering processes. The concentration of HCO3 − in ground water showed one order of magnitude higher than the total dissolved SiO2 indicates that carbonate weathering was the dominant process due to major water–rock interaction. The uranium speciation in groundwaters was investigated by an equilibrium model calculation using MEDUSA (make equilibrium diagrams using sophisticated algorithms) under the influence of redox conditions and complexant concentration. At the observed range of pH values, the predominant redox speciation of uranium was observed as hydroxo-carbonato complexes of (UO2)2(CO3)(OH)3 − and hydroxyl complexes of UO2(OH)3 − which might be caused for increasing the solubility of uranium. Due to very low concentration of phosphate in groundwater, its effects on U(VI)-aqueous speciation was negligible.

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