Results 81 to 90 of about 50,261 (220)

The X-ray/UV ratio in active galactic nuclei: dispersion and variability [PDF]

Astronomy & Astrophysics, 2018
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 ...
Chiaraluce, E, Vagnetti, F, Tombesi, F, Paolillo, M   +3 more
openaire   +5 more sources

Constraining the Hydration of Clay Minerals and Abundances of Amorphous Phases in Gale Crater, Mars

Journal of Geophysical Research: Planets, Volume 131, Issue 5, May 2026.
Abstract Both water and organic matter are required for the development and persistence of life. Phyllosilicates (clay minerals) have high surface areas that easily sorb water and organic matter. The Curiosity rover has investigated several hundred meters of stratigraphy in Gale crater, including where clays were detected from orbit.
Sean Czarnecki, Craig Hardgrove, Liz Rampe, Patrick Gasda   +3 more
wiley   +1 more source

A Systematic Search for X-Ray Eclipse Events in Active Galactic Nuclei Observed by Swift

The Astrophysical Journal
The nuclear regions of active galactic nuclei (AGNs) likely host clumpy clouds that occasionally obscure the central X-ray source, causing eclipse events. These events offer a unique opportunity to study the properties and origins of such clouds. However,
Tianying Lian, Chichuan Jin, Weimin Yuan
doaj   +1 more source

Hydromagnesite Precipitation in an Ultramafic‐Hosted Alkaline Lake: Insights From Lake Salda for Jezero Crater, Mars

Journal of Geophysical Research: Planets, Volume 131, Issue 5, May 2026.
Abstract Lake Salda (SW Turkey) is one of the most compelling terrestrial analogs for Jezero Crater on Mars due to its highly alkaline, Mg‐rich waters and hydromagnesite‐forming microbialites. This study integrates hydrochemical measurements, saturation‐index modeling, SEM–TEM imaging, and X‐ray diffraction (XRD) analysis to disentangle the biotic and ...
Mirosław Słowakiewicz, Mario Borrelli, Gürçay Kıvanç Akyıldız, Marek Szczerba, Ezher Tagliasacchi, Edoardo Perri   +5 more
wiley   +1 more source

X-ray reflection spectra from ionized slabs [PDF]

, 1999
X-ray reflection spectra are an important component in the X-ray spectra of many active galactic nuclei and Galactic black hole candidates. It is likely that reflection takes place from highly ionized surfaces of the accretion disc in some cases.
A. C. Fabian, A. J. Young, Böttcher, Done, Ebisawa, Ebisawa, George, Gierliński, Guilbert, Laor, Laor, Lightman, Magdziarz, Matt, Matt, Nandra, Nandra, R. R. Ross, Ross, Ross, Ross, Ross, Shakura, Stern, Tanaka, Ueda, Życki, Życki, Życki, Życki   +29 more
core   +3 more sources

Spectrally Tunable 2D Material‐Based Infrared Photodetectors for Intelligent Optoelectronics

Advanced Functional Materials, Volume 36, Issue 27, 2 April 2026.
Intelligent optoelectronics through spectral engineering of 2D material‐based infrared photodetectors. Abstract The evolution of intelligent optoelectronic systems is driven by artificial intelligence (AI). However, their practical realization hinges on the ability to dynamically capture and process optical signals across a broad infrared (IR) spectrum.
Junheon Ha, Yingshan Ma, Yong Nam An, Sung‐Un An, Hyeon Hak Jung, Suvi‐Tuuli Varjamo, Jiwon Yoo, Junho Min, Hanvit Kim, Faisal Ahmed, Sang Hoon Chae, Young Min Song, Weiwei Cai, Tawfique Hasan, Zhipei Sun, Dong‐Ho Kang, Hyeon‐Jin Shin, Yunyun Dai, Hoon Hahn Yoon   +18 more
wiley   +1 more source

Identifying Compton-thick Active Galactic Nuclei with a Machine Learning Algorithm in Chandra Deep Field-South

The Astrophysical Journal
Compton-thick active galactic nuclei (CT-AGNs), which are defined by column density N _H ≥ 1.5 × 10 ^24 cm ^−2 , emit feeble X-ray radiation, even undetectable by X-ray instruments.
Rui Zhang, Xiaotong Guo, Qiusheng Gu, Guanwen Fang, Jun Xu, Hai-Cheng Feng, Yongyun Chen, Rui Li, Nan Ding, Hongtao Wang   +9 more
doaj   +1 more source

X-ray emission from active galactic nuclei [PDF]

It is often held that the X-ray emission from active galactic nuclei (AGN) arises from a region close to the central energy source. Thus X-ray observations may provide the best constraints on the central engine.
Mushotzky, R.
core   +1 more source

The nature of the infrared counterpart of IGR J19140+0951

, 2007
The INTEGRAL observatory has been (re-)discovering new X-ray sources since the beginning of nominal operations in early 2003. These sources include X-ray binaries, Active Galactic Nuclei, cataclysmic variables, etc.
Bird, Bodaghee, Bronfman, Charles, Corbet, Cox, D. C. Hannikainen, Hannikainen, Hannikainen, Hanson, Hanson, In 't Zand, J. Rodriguez, J. Schultz, Kuulkers, Lebrun, Liu, Lu, M. G. Rawlings, Nespoli, O. Vilhu, P. Muhli, Rawlings, Rodriguez, Rodriguez, Swank, Ubertini, Walter, Winkler   +28 more
core   +1 more source

X-ray reverberation in Active Galactic Nuclei

, 2015
Narrow Line Type-1 Seyfert active galaxies can exhibit a high degree of variability in the X-ray regime. This thesis examines that variability in the context of reverberation models, in which a flare in activity has an extended, energy dependent, response. A novel method is developed for estimating the response function in different energy bands.
openaire   +2 more sources