Extragalactic background light (EBL) plays an important role in cosmology since it traces the history of galaxy formation and evolution. Such diffuse radiation from near-UV to far-infrared wavelengths can interact with γ -rays from distant sources such as active galactic nuclei (AGNs), and is responsible for the high-energy absorption observed in their spectra. However, probing the EBL from γ -ray spectra of AGNs is not trivial due to internal processes that can mimic its effect. Such processes are usually taken into account in terms of curvature of the intrinsic spectrum. Hence, an improper choice of parametrization for the latter can seriously affect EBL reconstruction. In this paper, we propose a statistical approach that avoids a priori assumptions on the intrinsic spectral curvature and that, for each source, selects the best-fit model on a solid statistical basis. By combining the Fermi -LAT observations of 490 blazars, we determine the γ -ray-inferred level of EBL for various state-of-the-art EBL models. We discuss the EBL level obtained from the spectra of both BL Lacs and flat spectrum radio quasars (FSRQ) in order to investigate the impact of internal absorption in different classes of objects. We further scrutinize constraints on the EBL evolution from γ -ray observations by reconstructing the EBL level in four redshift ranges, up to z ∼ 2.5. The approach implemented in this paper, carefully addressing the question of the modeling of the intrinsic emission at the source, can serve as a solid stepping stone for studies of hundreds of high-quality spectra acquired by next-generation γ -ray instruments.
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Enhanced contrast and high-resolution patterning of PMMA on insulating substrates under ambient gases
To our knowledge, these are the first studies of molecules other than water for EBL in gaseous environments. Exposure of PMMA under helium yields higher sensitivity, contrast (12.5) and the highest resolution (25-nm half-pitch dense lines and spaces) demonstrated to date for EBL on insulating substrates in a gaseous environment.
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- Award ID(s):
- 2135666
- PAR ID:
- 10588009
- Publisher / Repository:
- The 67th International Conference on Electron, Ion, and Photon Beam Technology and Nanofabrication
- Date Published:
- Format(s):
- Medium: X
- Location:
- La Jolla, CA
- Sponsoring Org:
- National Science Foundation
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Abstract The extragalactic background light (EBL) contains all the radiation emitted by nuclear and accretion processes in stars and compact objects since the epoch of recombination. Measuring the EBL density directly is challenging, especially in the near-to-far-infrared wave band, mainly due to the zodiacal light foreground. Instead, gamma-ray astronomy offers the possibility to indirectly set limits on the EBL by studying the effects of gamma-ray absorption in the very high energy (VHE: >100 GeV) spectra of distant blazars. The High Altitude Water Cherenkov Gamma Ray Observatory (HAWC) is one of the few instruments sensitive to gamma rays with energies above 10 TeV. This offers the opportunity to probe the EBL in the near/mid-IR region: λ = 1–100 μ m. In this study, we fit physically motivated emission models to Fermi-LAT gigaelectronvolt data to extrapolate the intrinsic teraelectronvolt spectra of blazars. We then simulate a large number of absorbed spectra for different randomly generated EBL model shapes and calculate Bayesian credible bands in the EBL intensity space by comparing and testing the agreement between the absorbed spectra and HAWC extragalactic observations of two blazars. The resulting bands are in agreement with current EBL lower and upper limits, showing a downward trend toward higher wavelength values λ > 10 μ m also observed in previous measurements.more » « less
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The light emitted by all galaxies over the history of the Universe produces the extragalactic background light (EBL) at ultraviolet, optical, and infrared wavelengths. The EBL is a source of opacity for gamma rays via photon-photon interactions, leaving an imprint in the spectra of distant gamma-ray sources. We measured this attenuation using 739 active galaxies and one gamma-ray burst detected by the Fermi Large Area Telescope. This allowed us to reconstruct the evolution of the EBL and determine the star formation history of the Universe over 90% of cosmic time. Our star formation history is consistent with independent measurements from galaxy surveys, peaking at redshiftz~ 2. Upper limits of the EBL at the epoch of reionization suggest a turnover in the abundance of faint galaxies atz~ 6.more » « less
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null (Ed.)To prevent electron leakage in deep ultraviolet (UV) AlGaN light-emitting diodes (LEDs), Al-rich p-type AlxGa(1−x)N electron blocking layer (EBL) has been utilized. However, the conventional EBL can mitigate the electron overflow only up to some extent and adversely, holes are depleted in the EBL due to the formation of positive sheet polarization charges at the heterointerface of the last quantum barrier (QB)/EBL. Subsequently, the hole injection efficiency of the LED is severely limited. In this regard, we propose an EBL-free AlGaN deep UV LED structure using graded staircase quantum barriers (GSQBs) instead of conventional QBs without affecting the hole injection efficiency. The reported structure exhibits significantly reduced thermal velocity and mean free path of electrons in the active region, thus greatly confines the electrons over there and tremendously decreases the electron leakage into the p-region. Moreover, such specially designed QBs reduce the quantum-confined Stark effect in the active region, thereby improves the electron and hole wavefunctions overlap. As a result, both the internal quantum efficiency and output power of the GSQB structure are ~2.13 times higher than the conventional structure at 60 mA. Importantly, our proposed structure exhibits only ~20.68% efficiency droop during 0–60 mA injection current, which is significantly lower compared to the regular structure.more » « less
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Abstract In this paper, a light-emitting diode in the ultra-violet range (UV-LED) with multiple-quantum wells (MQWs) of InGaN/GaN is designed and analyzed through Technology Computer-Aided Design (TCAD) simulations. The polarization effects in III-nitride heterojunction and the effects of graded composition in the electron blocking layer (EBL) are exploited to enhance the performance of the proposed UV-LED. It is observed that the effect of graded composition in the EBL helps to enhance the electrical and optical performance of the LED, thereby enabling the achievement of some promising results. The simulation-based results demonstrated that superior internal efficiency and an inferior leakage current are achieved by using a graded Al composition in the EBL rather than a uniform composition. The reported results also confirm the remarkable improvement of the light output power by 17% at ∼100 mA when using the graded composition and also show a reduction in series resistance leading to more current. Graded Al composition in the EBL results in the enhancement of electroluminescence spectra (i.e., an increase in the peak of the spectral density).more » « less
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