scholarly journals MOMO. IV. The Complete Swift X-Ray and UV/Optical Light Curve and Characteristic Variability of the Blazar OJ 287 during the Last Two Decades

2021 ◽  
Vol 923 (1) ◽  
pp. 51
Author(s):  
S. Komossa ◽  
D. Grupe ◽  
L. C. Gallo ◽  
A. Gonzalez ◽  
S. Yao ◽  
...  
Keyword(s):  
Black Hole ◽  
Function Analysis ◽  
Data Sets ◽  
Flare Activity ◽  
Wave Band ◽  
X Rays ◽  
Single Wave ◽  
X Ray ◽  
Optical Light Curve ◽  
Blazar Oj 287

Abstract We have been carrying out a dense monitoring of the blazar OJ 287 with Swift since late 2015 as part of our project MOMO (Multiwavelength Observations and Modeling of OJ 287). This is the densest existing monitoring of OJ 287 involving X-ray/UV data. In this latest publication of a sequence, we characterize the multiwavelength variability of OJ 287 based on >4000 Swift single-wave-band data sets including archival data since 2005. A structure function analysis reveals a characteristic timescale of ∼5 days in the optical–UV at epochs of low-level activity and larger during outbursts. The discrete correlation function shows zero lag between optical and UV, with τ = 0 ± 1 day at the epoch of densest cadence. During outbursts (in 2016/17 and 2020) the X-rays follow the UV with near-zero lags. However, during quiescence, the delay is 7–18 days with X-rays leading or lagging, interpreted as due to a different X-ray component dominated by inverse Compton emission. Scaling relations are used to derive the characteristic length scales of the broad-line region and torus in OJ 287. A remarkable, symmetric UV–optical deep fade is identified in late 2017, lasting 2 months. We rule out occultation from the passage of a dusty cloud and a model where the secondary black hole deflects the jet between the primary and observer. We speculate about a temporary dispersion or jet swing event in the core or in a bright quasi-stationary jet feature. The deep fade reveals an additional, spatially distinct X-ray component. The epoch 2020.9–2021.1 was searched for precursor flare activity predicted by the binary black hole model of OJ 287.

scholarly journals Lower resolution Laue neutron data yield correct nanocluster formulations

2014 ◽  
Vol 70 (a1) ◽  
pp. C187-C187
Author(s):  
Alison Edwards
Keyword(s):  
Neutron Diffraction ◽  
Single Crystal ◽  
Diffraction Pattern ◽  
Precise Determination ◽  
Data Sets ◽  
X Rays ◽  
Low Resolution ◽  
Neutron Data ◽  
X Ray ◽  
Product Formulation

"The renaissance in Laue studies - at neutron sources - provides us with access to single crystal neutron diffraction data for synthetic compounds without requiring synthesis of prohibitively large amounts of compound or improbably large crystals. Such neutron diffraction studies provide vital data where proof of the presence or absence of hydrogen in particular locations is required and which cannot validly be proved by X-ray studies. Since the commissioning of KOALA at OPAL in 2009[1] we have obtained numerous data sets which demonstrate the vital importance of measuring data even where the extent of the diffraction pattern is at relatively low resolution - especially when compared to that obtainable for the same compound with X-rays. In the Laue experiment performed with a fixed radius detector, data reduction is only feasible for crystals in the ""goldilocks"" zone – where the unit cell is relatively large for the detector, a correspondingly low resolution diffraction pattern in which adjacent spots are less affected by overlap will yield more data against which a structure can be refined than a pattern of higher resolution – one where neighbouring spots overlap rendering both unusable (in our current methodology). Analogous application of powder neutron diffraction in such determinations is also considered. Single crystal neutron diffraction studies of several important compounds (up to 5KDa see figure below)[2] in which precise determination of hydride content by neutron diffraction was pivotal to the final formulation will be presented. The neutron data sets typically possess 20% or fewer unique data at substantially "lower resolution" than the corresponding X-ray data sets. Careful refinement clearly reveals chemical detail which is typically unexplored in related X-ray diffraction studies reporting high profile chemistry despite the synthetic route being one which hydride ought to be considered/excluded in product formulation."

scholarly journals The X-ray/UV ratio in active galactic nuclei: dispersion and variability

2018 ◽  
Vol 619 ◽  
pp. A95 ◽  
Author(s):  
E. Chiaraluce ◽  
F. Vagnetti ◽  
F. Tombesi ◽  
M. Paolillo
Keyword(s):  
Black Hole ◽  
Cosmological Parameters ◽  
Multivariate Regression Analysis ◽  
Physical Parameters ◽  
Distance Modulus ◽  
X Rays ◽  
Viewing Angle ◽  
Black Hole Mass ◽  
Intrinsic Variability ◽  
X Ray

Context. The well established negative correlation between the αOX spectral slope and the optical/ultraviolet (UV) luminosity, a by-product of the relation between X-rays and optical/UV luminosity, is affected by relatively large dispersion. The main contributors to this dispersion can be variability in the X-ray/UV ratio and/or changes in fundamental physical parameters. Aims. We want to quantify the contribution from variability within single sources (intra-source dispersion) and that from variations of other quantities different from source to source (inter-source dispersion). Methods. We use archival data from the XMM-Newton Serendipitous Source Catalog (XMMSSC) and from the XMM-OM Serendipitous Ultraviolet Source Survey (XMMOM-SUSS3). We select a sub-sample in order to decrease the dispersion of the relation due to the presence of radio-loud and broad absorption line objects, and that due to absorptions in both X-ray and optical/UV bands. We use the structure function (SF) to estimate the contribution from variability to the dispersion. We analyse the dependence of the residuals of the relation on various physical parameters in order to characterise the inter-source dispersion. Results. We find a total dispersion of σ ∼ 0.12 and find that intrinsic variability contributes 56% of the variance of the αOX − LUV relation. If we select only sources with a larger number of observational epochs (≥3) the dispersion of the relation decreases by approximately 15%. We find weak but significant dependencies of the residuals of the relation on black-hole mass and on Eddington ratio, which are also confirmed by a multivariate regression analysis of αOX as a function of UV luminosity and black-hole mass and/or Eddington ratio. We find a weak positive correlation of both the αOX index and the residuals of the αOX − LUV relation with inclination indicators, such as the full width at half maximum (Hβ) and the equivalent width (EW)[OIII], suggesting a weak increase of X-ray/UV ratio with the viewing angle. This suggests the development of new viewing angle indicators possibly applicable at higher redshifts. Moreover, our results suggest the possibility of selecting a sample of objects, based on their viewing angle and/or black-hole mass and Eddington ratio, for which the αOX − LUV relation is as tight as possible, in light of the use of the optical/UV – X-ray luminosity relation to build a distance modulus (DM)-z plane and estimate cosmological parameters.

Structural study of the X-ray-induced enzymatic reaction of octahaem cytochromecnitrite reductase

2015 ◽  
Vol 71 (5) ◽  
pp. 1087-1094 ◽  
Author(s):  
A. A. Trofimov ◽  
K. M. Polyakov ◽  
V. A. Lazarenko ◽  
A. N. Popov ◽  
T. V. Tikhonova ◽  
...  
Keyword(s):  
Nitrite Reductase ◽  
Catalytic Reaction ◽  
Active Sites ◽  
Enzymatic Reaction ◽  
Absorbed Dose ◽  
Free Form ◽  
Data Sets ◽  
X Rays ◽  
X Ray ◽  
Site Water

Octahaem cytochromecnitrite reductase from the bacteriumThioalkalivibrio nitratireducenscatalyzes the reduction of nitrite to ammonium and of sulfite to sulfide. The reducing properties of X-ray radiation and the high quality of the enzyme crystals allow study of the catalytic reaction of cytochromecnitrite reductase directly in a crystal of the enzyme, with the reaction being induced by X-rays. Series of diffraction data sets with increasing absorbed dose were collected from crystals of the free form of the enzyme and its complexes with nitrite and sulfite. The corresponding structures revealed gradual changes associated with the reduction of the catalytic haems by X-rays. In the case of the nitrite complex the conversion of the nitrite ions bound in the active sites to NO species was observed, which is the beginning of the catalytic reaction. For the free form, an increase in the distance between the oxygen ligand bound to the catalytic haem and the iron ion of the haem took place. In the case of the sulfite complex no enzymatic reaction was detected, but there were changes in the arrangement of the active-site water molecules that were presumably associated with a change in the protonation state of the sulfite ions.

scholarly journals Mass transfer on a nuclear timescale in models of supergiant and ultra-luminous X-ray binaries

2019 ◽  
Vol 628 ◽  
pp. A19 ◽  
Author(s):  
M. Quast ◽  
N. Langer ◽  
T. M. Tauris
Keyword(s):  
Mass Transfer ◽  
Black Hole ◽  
Neutron Star ◽  
Roche Lobe ◽  
High Mass ◽  
X Rays ◽  
X Ray ◽  
Mass Ratios ◽  
X Ray Binaries ◽  
Eddington Limit

Context. The origin and number of the Galactic supergiant X-ray binaries is currently not well understood. They consist of an evolved massive star and a neutron star or black-hole companion. X-rays are thought to be generated from the accretion of wind material donated by the supergiant, while mass transfer due to Roche-lobe overflow is mostly disregarded because the high mass ratios of these systems are thought to render this process unstable. Aims. We investigate how the proximity of supergiant donor stars to the Eddington limit, and their advanced evolutionary stage, may influence the evolution of massive and ultra-luminous X-ray binaries with supergiant donor stars (SGXBs and ULXs). Methods. We constructed models of massive stars with different internal hydrogen and helium gradients (H/He gradients) and different hydrogen-rich envelope masses, and exposed them to slow mass-loss to probe the response of the stellar radius. In addition, we computed the corresponding Roche-lobe overflow mass-transfer evolution with our detailed binary stellar evolution code, approximating the compact objects as point masses. Results. We find that a H/He gradient in the layers beneath the surface, as it is likely present in the well-studied donor stars of observed SGBXs, can enable mass transfer in SGXBs on a nuclear timescale with a black-hole or a neutron star accretor, even for mass ratios in excess of 20. In our binary evolution models, the donor stars rapidly decrease their thermal equilibrium radius and can therefore cope with the inevitably strong orbital contraction imposed by the high mass ratio. We find that the orbital period derivatives of our models agree well with empirical values. We argue that the SGXB phase may be preceded by a common-envelope evolution. The envelope inflation near the Eddington limit means that this mechanism more likely occurs at high metallicity. Conclusion. Our results open a new perspective for understanding that SGBXs are numerous in our Galaxy and are almost completely absent in the Small Magellanic Cloud. Our results may also offer a way to find more ULX systems, to detect mass transfer on nuclear timescales in ULX systems even with neutron star accretors, and shed new light on the origin of the strong B-field in these neutron stars.

scholarly journals X-ray Interferometry

2001 ◽  
Vol 205 ◽  
pp. 457-462
Author(s):  
Webster Cash
Keyword(s):  
Black Hole ◽  
Event Horizon ◽  
Surface Brightness ◽  
High Surface ◽  
X Rays ◽  
High Surface Brightness ◽  
X Ray

X-rays have tremendous potential for imaging at the highest angular resulution. The high surface brightness of many x-ray sources will reveal angular scales heretofore thought unreachable. The short wavelengths make instrumentation compact and baselines short. We discuss how practical x-ray interferometers can be built for astronomy using existing technology. We describe the Maxim Pathfinder and Maxim missions which will achieve 100 and 0.1 micro-arcsecond imaging respectively. The science to be tackled with resolution of up to one million times that of HST will be outlined, with emphasis on eventually imaging the event horizon of a black hole.

scholarly journals Glimpses of the past activity of Sgr A★ inferred from X-ray echoes in Sgr C

2018 ◽  
Vol 610 ◽  
pp. A34 ◽  
Author(s):  
D. Chuard ◽  
R. Terrier ◽  
A. Goldwurm ◽  
M. Clavel ◽  
S. Soldi ◽  
...  
Keyword(s):  
Monte Carlo ◽  
Black Hole ◽  
Monte Carlo Model ◽  
Line Of Sight ◽  
X Rays ◽  
X Ray ◽  
Supermassive Black Hole ◽  
The Past ◽  
Sgr A ◽  
Past Activity

Context. For a decade now, evidence has accumulated that giant molecular clouds located within the central molecular zone of our Galaxy reflect X-rays coming from past outbursts of the Galactic supermassive black hole. However, the number of illuminating events as well as their ages and durations are still unresolved questions. Aims. We aim to reconstruct parts of the history of the supermassive black hole Sgr A★ by studying this reflection phenomenon in the molecular complex Sgr C and by determining the line-of-sight positions of its main bright substructures. Methods. Using observations made with the X-ray observatories XMM-Newton and Chandra and between 2000 and 2014, we investigated the variability of the reflected emission, which consists of a Fe Kα line at 6.4 keV and a Compton continuum. We carried out an imaging and a spectral analysis. We also used a Monte Carlo model of the reflected spectra to constrain the line-of-sight positions of the brightest clumps, and hence to assign an approximate date to the associated illuminating events. Results. We show that the Fe Kα emission from Sgr C exhibits significant variability in both space and time, which confirms its reflection origin. The most likely illuminating source is Sgr A★. On the one hand, we report two distinct variability timescales, as one clump undergoes a sudden rise and fall in about 2005, while two others vary smoothly throughout the whole 2000–2014 period. On the other hand, by fitting the Monte Carlo model to the data, we are able to place tight constraints on the 3D positions of the clumps. These two independent approaches provide a consistent picture of the past activity of Sgr A★, since the two slowly varying clumps are located on the same wavefront, while the third (rapidly varying) clump corresponds to a different wavefront, that is, to a different illuminating event. Conclusions. This work shows that Sgr A★ experienced at least two powerful outbursts in the past 300 yrs, and for the first time, we provide an estimation of their age. Extending this approach to other molecular complexes, such as Sgr A, will allow this two-event scenario to be tested further.

scholarly journals X-rays from Photoionized Accretion Discs

1994 ◽  
Vol 159 ◽  
pp. 380-380
Author(s):  
G. Matt ◽  
A.C. Fabian ◽  
R.R. Ross
Keyword(s):  
Black Hole ◽  
Seyfert Galaxies ◽  
High Energy ◽  
Accretion Disc ◽  
Accretion Discs ◽  
X Rays ◽  
Central Black Hole ◽  
X Ray

The presence of iron lines and high energy excesses in the X-ray spectra of Seyfert galaxies has been firmly established by Ginga (e.g. Nandra & Pounds 1993 and references therein). These features are generally interpreted as signatures of the reprocessing of the primary X-rays by matter in the neighbourhood of the central black hole, probably distributed in an accretion disc (Lightman & White 1988, George & Fabian 1991, Matt, Perola & Piro 1991).

Exosat Observations of H2252−035: Pulse Phase and Orbital Phase Dependent Low Energy Absorption and Iron Line Emission

1987 ◽  
Vol 93 ◽  
pp. 281-292
Author(s):  
W. Pietsch ◽  
W. Voges ◽  
E. Kendziorra ◽  
M. Pakull
Keyword(s):  
Energy Absorption ◽  
Line Emission ◽  
Low Energy ◽  
Gas Absorption ◽  
X Rays ◽  
Medium Energy ◽  
Iron Line ◽  
X Ray ◽  
Low Energies ◽  
Optical Light Curve

AbstractThe 805 sec pulsing X-ray source H2252−035 has been observed for 7 h on September 14/15 and on September 17, 1983 in X-rays with the low energy telescope and the medium energy detectors of EXOSAT. While below 2 keV the semiamplitude of the 805 s pulses is ~ 100% in the 2.3–7.9 keV band it is only ~ 40%. X-ray dips that are more pronounced in low energies occur simultaneously with the orbital minimum of the optical light curve. The medium energy spectra during dips with respect to the non dip spectrum can be explained by just enhanced cold gas absorption of an additional absorbing column of 2 1022 cm−2. Model spectra for the 805 s minimum have to include a strong iron emission line at 6.55 keV with an equivalent width of 3 keV in addition to a reduced continuum intensity (radiating area) and enhanced low energy absorption.

scholarly journals Optical, X-ray, and γ-ray observations of the candidate transitional millisecond pulsar 4FGL J0427.8-6704

2020 ◽  
Vol 494 (3) ◽  
pp. 3912-3926
Author(s):  
M R Kennedy ◽  
R P Breton ◽  
C J Clark ◽  
V S Dhillon ◽  
M Kerr ◽  
...  
Keyword(s):  
Light Curve ◽  
Time Scales ◽  
Periodic Oscillation ◽  
Optical Data ◽  
Data Sets ◽  
Millisecond Pulsar ◽  
X Ray ◽  
State Classification ◽  
Optical Light Curve ◽  
Γ Ray

ABSTRACT We present an optical, X-ray, and γ-ray study of 1SXPS J042749.2-670434, an eclipsing X-ray binary that has an associated γ-ray counterpart, 4FGL J0427.8-6704. This association has led to the source being classified as a transitional millisecond pulsar (tMSP) in an accreting state. We analyse 10.5 yr of Fermi LAT data and detect a γ-ray eclipse at the same phase as optical and X-ray eclipses at the >5 σ level, a significant improvement on the 2.8 σ level of the previous detection. The confirmation of this eclipse solidifies the association between the X-ray source and the γ-ray source, strengthening the tMSP classification. However, analysis of several optical data sets and an X-ray observation do not reveal a change in the source’s median brightness over long time-scales or a bi-modality on short time-scales. Instead, the light curve is dominated by flickering, which has a correlation time of 2.6 min alongside a potential quasi-periodic oscillation at ∼21 min. The mass of the primary and secondary stars is constrained to be $M_1=1.43^{+0.33}_{-0.19}$ M⊙ and $M_2=0.3^{+0.17}_{-0.12}$ M⊙ through modelling of the optical light curve. While this is still consistent with a white dwarf primary, we favour the tMSP in a low accretion state classification due to the significance of the γ-ray eclipse detection.

scholarly journals Determination of crystallographic intensities from sparse data

IUCrJ ◽  
2015 ◽  
Vol 2 (1) ◽  
pp. 29-34 ◽  
Author(s):  
Kartik Ayyer ◽  
Hugh T. Philipp ◽  
Mark W. Tate ◽  
Jennifer L. Wierman ◽  
Veit Elser ◽  
...  
Keyword(s):  
Diffraction Data ◽  
Crystal Size ◽  
Three Dimensional ◽  
Sparse Data ◽  
Data Sets ◽  
X Rays ◽  
Diffraction Intensity ◽  
X Ray ◽  
Proof Of Principle

X-ray serial microcrystallography involves the collection and merging of frames of diffraction data from randomly oriented protein microcrystals. The number of diffracted X-rays in each frame is limited by radiation damage, and this number decreases with crystal size. The data in the frame are said to be sparse if too few X-rays are collected to determine the orientation of the microcrystal. It is commonly assumed that sparse crystal diffraction frames cannot be merged, thereby setting a lower limit to the size of microcrystals that may be merged with a given source fluence. TheEMCalgorithm [Loh & Elser (2009),Phys. Rev. E,80, 026705] has previously been applied to reconstruct structures from sparse noncrystalline data of objects with unknown orientations [Philippet al.(2012),Opt. Express,20, 13129–13137; Ayyeret al.(2014),Opt. Express,22, 2403–2413]. Here, it is shown that sparse data which cannot be oriented on a per-frame basis can be used effectively as crystallographic data. As a proof-of-principle, reconstruction of the three-dimensional diffraction intensity using sparse data frames from a 1.35 kDa molecule crystal is demonstrated. The results suggest that serial microcrystallography is, in principle, not limited by the fluence of the X-ray source, and collection of complete data sets should be feasible at, for instance, storage-ring X-ray sources.

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