A simple method to test for energy-dependent dispersion in high energy light curves of astrophysical sources

AbstractSince mid-2007 we have carried out a dedicated long-term monitoring programme at 15 GHz using the Owens Valley Radio Observatory 40 meter telescope (OVRO 40m). One of the main goals of this programme is to study the relation between the radio and gamma-ray emission in blazars and to use it as a tool to locate the site of high energy emission. Using this large sample of objects we are able to characterize the radio variability, and study the significance of correlations between the radio and gamma-ray bands. We find that the radio variability of many sources can be described using a simple power law power spectral density, and that when taking into account the red-noise characteristics of the light curves, cases with significant correlation are rare. We note that while significant correlations are found in few individual objects, radio variations are most often delayed with respect to the gamma-ray variations. This suggests that the gamma-ray emission originates upstream of the radio emission. Because strong flares in most known gamma-ray-loud blazars are infrequent, longer light curves are required to settle the issue of the strength of radio-gamma cross-correlations and establish confidently possible delays between the two. For this reason continuous multiwavelength monitoring over a longer time period is essential for statistical tests of jet emission models.

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Constraints on the density distribution of type Ia supernovae ejecta inferred from late-time light-curve flattening

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa690 ◽

2020 ◽

Vol 493 (4) ◽

pp. 5617-5624

Author(s):

Doron Kushnir ◽

Eli Waxman

Keyword(s):

Light Curve ◽

Weighted Average ◽

Far Infrared ◽

Average Density ◽

Light Curves ◽

Type Ia Supernovae ◽

Late Time ◽

Simple Method ◽

Type Ia ◽

Ia Supernovae

ABSTRACT The finite time, τdep, over which positrons from β+ decays of 56Co deposit energy in type Ia supernovae ejecta lead, in case the positrons are trapped, to a slower decay of the bolometric luminosity compared to an exponential decline. Significant light-curve flattening is obtained when the ejecta density drops below the value for which τdep equals the 56Co lifetime. We provide a simple method to accurately describe this ‘delayed deposition’ effect, which is straightforward to use for analysis of observed light curves. We find that the ejecta heating is dominated by delayed deposition typically from 600 to 1200 d, and only later by longer lived isotopes 57Co and 55Fe decay (assuming solar abundance). For the relatively narrow 56Ni velocity distributions of commonly studied explosion models, the modification of the light curve depends mainly on the 56Ni mass-weighted average density, 〈ρ〉t3. Accurate late-time bolometric light curves, which may be obtained with JWST far-infrared (far-IR) measurements, will thus enable to discriminate between explosion models by determining 〈ρ〉t3 (and the 57Co and 55Fe abundances). The flattening of light curves inferred from recent observations, which is uncertain due to the lack of far-IR data, is readily explained by delayed deposition in models with $\langle \rho \rangle t^{3} \approx 0.2\, \mathrm{M}_{\odot }\, (10^{4}\, \textrm{km}\, \textrm{s}^{-1})^{-3}$, and does not imply supersolar 57Co and 55Fe abundances.

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Ultrafast charge transfer dynamics in 2D Covalent Organic Frameworks/Re-complex hybrid photocatalyst for CO2 reduction: hot electrons vs. cold electrons

10.21203/rs.3.rs-448398/v1 ◽

2021 ◽

Author(s):

Qinying Pan ◽

Mohamed Abdellah ◽

Yuehan Cao ◽

Yang Liu ◽

Weihua Lin ◽

...

Keyword(s):

Excited State ◽

Charge Transfer ◽

Excitation Energy ◽

Co2 Reduction ◽

Underlying Mechanism ◽

High Energy ◽

Hot Electrons ◽

Covalent Organic Frameworks ◽

Energy Excitation ◽

Energy Dependent

Abstract Rhenium(I)-carbonyl-diimine complexes are promising photocatalysts for CO2 reduction. Covalent organic frameworks (COFs) can be perfect sensitizers to enhance the reduction activities. Here we investigated the excited state dynamics of COF (TpBpy) with 2,2'-bipyridine incorporating Re(CO)5Cl (Re-TpBpy) to rationalize the underlying mechanism. The time-dependent DFT calculation first clarified excited state structure of the hybrid catalyst. The studies from transient visible and infrared spectroscopies revealed the excitation energy-dependent photo-induced charge transfer pathways in Re-TpBpy. Under low energy excitation, the electrons at the LUMO level are quickly injected from Bpy into ReI center (1–2 ps) followed by backward recombination (13 ps). Under high energy excitation, the hot-electrons are first injected into the higher unoccupied level of ReI center (1–2 ps) and then slowly relax back to the HOMO in COF (24 ps). There also remains long-lived free electrons in the COF moiety. This explained the excitation energy-dependent CO2 reduction performance in our system.

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High-energy pulsar light curves in an offset polar cap B-field geometry

10.22323/1.275.0042 ◽

2017 ◽

Author(s):

Monica Barnard ◽

Christo Venter ◽

Alice Kust Harding

Keyword(s):

High Energy ◽

Light Curves ◽

Polar Cap ◽

Field Geometry

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European Energy Security and Sustainability

Sustainable Systems and Energy Management at the Regional Level ◽

10.4018/978-1-61350-344-7.ch003 ◽

2011 ◽

pp. 38-67

Author(s):

Anatoly Zhuplev ◽

Dmitry A. Shtykhno

Keyword(s):

Energy Security ◽

Oil And Gas ◽

Sustainable Energy ◽

High Energy ◽

Energy Sector ◽

Technology Investment ◽

Regional Energy ◽

Political Economic ◽

Energy Dependent ◽

The Eu

Europe’s economic wellbeing and growth are highly energy dependent and heavily reliant on Russian imports of oil and gas. European energy security, its alternatives, and implications are examined in this chapter with the view of sustainability and the EU-Russian energy dialog. With an asymmetric mutual political-economic interdependency with Russia, Europe’s exposure in oil and gas calls for sustainable energy solutions. Meantime, Russia, the key energy supplier in the European region, is also a major energy consumer whose economy is characterized by high energy intensity. Russian energy sector needs serious improvements in technology, investment, and management: failure to address these priorities erodes Russia’s reliability as major regional energy supplier. The chapter explores the dynamics of Russian energy sector and implications for European energy security and sustainability.

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X-ray spectra and light curves of cooling novae and a nova like

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3012 ◽

2020 ◽

Vol 499 (2) ◽

pp. 3006-3018

Author(s):

Bangzheng Sun ◽

Marina Orio ◽

Andrej Dobrotka ◽

Gerardo Juan Manuel Luna ◽

Sergey Shugarov ◽

...

Keyword(s):

Light Curve ◽

Accretion Rate ◽

High Energy ◽

Gravitational Energy ◽

Light Curves ◽

Clear Correlation ◽

X Rays ◽

High State ◽

X Ray ◽

Low X

ABSTRACT We present X-ray observations of novae V2491 Cyg and KT Eri about 9 yr post-outburst of the dwarf nova and post-nova candidate EY Cyg, and of a VY Scl variable. The first three objects were observed with XMM–Newton, KT Eri also with the Chandra ACIS-S camera, V794 Aql with the Chandra ACIS-S camera and High Energy Transmission Gratings. The two recent novae, similar in outburst amplitude and light curve, appear very different at quiescence. Assuming half of the gravitational energy is irradiated in X-rays, V2491 Cyg is accreting at $\dot{m}=1.4\times 10^{-9}{\!-\!}10^{-8}\,{\rm M}_\odot \,{\rm yr}^{-1}$, while for KT Eri, $\dot{m}\lt 2\times 10^{-10}{\rm M}_\odot \,{\rm yr}$. V2491 Cyg shows signatures of a magnetized WD, specifically of an intermediate polar. A periodicity of 39 min, detected in outburst, was still measured and is likely due to WD rotation. EY Cyg is accreting at $\dot{m}\sim 1.8\times 10^{-11}{\rm M}_\odot \,{\rm yr}^{-1}$, one magnitude lower than KT Eri, consistently with its U Gem outburst behaviour and its quiescent UV flux. The X-rays are modulated with the orbital period, despite the system’s low inclination, probably due to the X-ray flux of the secondary. A period of 81 min is also detected, suggesting that it may also be an intermediate polar. V794 Aql had low X-ray luminosity during an optically high state, about the same level as in a recent optically low state. Thus, we find no clear correlation between optical and X-ray luminosity: the accretion rate seems unstable and variable. The very hard X-ray spectrum indicates a massive WD.

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X-ray Spectral Evolution of High Energy Peaked Blazars

Galaxies ◽

10.3390/galaxies8030062 ◽

2020 ◽

Vol 8 (3) ◽

pp. 62

Author(s):

Haritma Gaur

Keyword(s):

High Energy ◽

Energy Interval ◽

Spectral Studies ◽

Parabolic Model ◽

Spectral Evolution ◽

Spectral Variability ◽

Spectral Parameters ◽

X Ray ◽

Wide Energy ◽

Energy Dependent

The synchrotron hump of the high energy peaked blazars generally lies in the 0.1–10 keV range and such sources show extreme flux and spectral variability in X-ray bands. Various spectral studies showed that the X-ray spectra of high energy peaked blazars are curved and better described by the log-parabolic model. The curvature is attributed to the energy dependent statistical acceleration mechanism. In this work, we review the X-ray spectral studies of high energy peaked blazars. It is found that the log-parabolic model well describes the spectra in a wide energy interval around the peak. The log-parabolic model provides the possibility of investigating the correlation between the spectral parameters derived from it. Therefore, we compiled the studies of correlations between the various parameters derived from the log-parabolic model and their implications to describe the variability mechanism of blazars.

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