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Contribution from normal and starburst galaxies to the extragalactic gamma-ray background (EgRB)

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Chinese Journal of Astronomy and Astrophysics 2009年第5期9卷 509-519页

作者： Debbijoy Bhattacharya parameswaran sreekumar Department of Physics Indian Institute of Science Space Astronomy & Instrumentation Division ISRO Satellite Centre

The extragalactic diffuse emission at γ-ray energies has interesting cosmological implications since these photons suffer little or no attenuation during their propagation from the site of origin. The emission could originate from either truly diffuse processes or from unresolved point sources such as AgNs, normal galaxies and starburst galaxies. Here, we examine the unresolved point source origin of the extragalactic γ-ray background emission from normal galaxies and starburst galaxies. γ-ray emission from normal galaxies is primarily coming from cosmic-ray interactions with interstellar matter and radiation （-90%） along with a small contribution from discrete point sources （-10%）. Starburst galaxies are expected to have enhanced supernovae activity which leads to higher cosmic-ray densities, making starburst galaxies sufficiently luminous atγ-ray energies to be detected by the current γ-ray mission （Fermi gamma-ray Space Telescope）.

关键词： galaxy general -- galaxies luminosity function -- galaxies starburst -- gamma-rays observations

Contribution from unresolved discrete sources to the extragalactic gamma-ray background(EgRB)

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Research in Astronomy and Astrophysics 2009年第11期9卷 1205-1214页

作者： Debbijoy Bhattacharya parameswaran sreekumar Reshmi Mukherjee Department of Physics Indian Institute of Science Space Astronomy & Instrumentation Division ISRO Satellite Centre Barnard College Columbia University

The origin of the extragalactic gamma-ray background （EgRB） is still an open question, even nearly forty years after its discovery. The emission could originate either from truly diffuse processes or from unresolved point sources. Although the majority of the 271 point sources detected by EgRET （Energetic gamma Ray Experiment Telescope） are unidentified, of the identified sources, blazars are the dominant candidates. Therefore, unresolved blazars may be considered the main contributor to the EgRB, and many studies have been carried out to understand their distribution, evolution and contribution to the EgRB. Considering that γ-ray emission comes mostly from jets of blazars and that the jet emission decreases rapidly with increasing jet to line-of-sight angle, it is not surprising that EgRET was not able to detect many large inclination angle active galactic nuclei （AgNs）. Though Fermi could only detect a few large inclination angle AgNs during the first three months of its survey, it is expected to detect many such sources in the near future. Since non-blazar AgNs are expected to have higher density as compared to blazars, these could also contribute significantly to the EgRB. In this paper, we discuss contributions from unresolved discrete sources including normal galaxies, starburst galaxies, blazars and off-axis AgNs to the EgRB.

关键词： galaxies active -- galaxies jets -- gamma-rays observations

Does black hole spin play a key role in the FSRQ/BL Lac dichotomy?

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Research in Astronomy and Astrophysics 2016年第4期16卷 7-14页

作者： Debbijoy Bhattacharya parameswaran sreekumar Banibrata Mukhopadhyay Ishan Tomar Manipal Centre for Natural Sciences Manipal UniversityManipal 576104India Indian Institute of Astrophysics Bangalore 560034India Astronomy and Astrophysics Programme Department of PhysicsIndian Institute of ScienceBangalore 560012India Space Astronomy group ISRO Satellite CentreKarthik NagarBangalore 560037India

Blazars are characterized by large intensity and spectral variations across the electromagnetic spectrum It is believed that jets emerging from them are almost aligned with the line-of-sight. The major- ity of identified extragalactic sources in γ-ray catalogs of EgRET and Fermi are blazars. Observationally, blazars can be divided into two classes： fiat spectrum radio quasars （FSRQs） and BL Lacs. BL Lacs usually exhibit lower γ-ray luminosity and harder power law spectra at γ-ray energies than FSRQs. We attempt to explain the high energy properties of FSRQs and BL Lacs from Fermi γ-ray space telescope observations. It was argued previously that the difference in accretion rates is mainly responsible for the large mismatch in observed luminosity in ＂7-ray. However, when intrinsic luminosities are derived by correcting for beaming effects, this difference in 7-ray luminosity between the two classes is significantly reduced. In order to ex- plain this difference in intrinsic luminosities, we propose that spin plays an important role in the luminosity distribution dichotomy of BL Lacs and FSRQs. As the outflow power of a blazar increases with increasing spin of a central black hole, we suggest that the spin plays a crucial role in making BL Lac sources low luminous and slow rotators compared to FSRQ sources.

关键词： BL Lacertae objects: general -- quasars: general -- galaxies: jets -- black hole physics --relativistic processes -- gravitation

Methionine sulfoxide reductase A: Structure, function and role in ocular pathology

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World Journal of Biological Chemistry 2011年第8期2卷 184-192页

作者： parameswaran g.sreekumar David R Hinton Ram Kannan Arnold and Mabel Beckman Macular Research Center Doheny Eye Institute Department of Pathology Keck School of Medicine of the University of Southern California

Methionine is a highly susceptible amino acid that can be oxidized to S and R diastereomeric forms of methionine sulfoxide by many of the reactive oxygen species generated in biological systems. Methionine sulfoxide reductases (Msrs) are thioredoxin-linked enzymes involved in the enzymatic conversion of methionine sulfoxide to methionine. Although MsrA and MsrB have the same function of methionine reduction, they differ in substrate specifi city, active site composition, subcellular localization, and evolution. MsrA has been localized in different ocular regions and is abundantly expressed in the retina and in retinal pigment epithelial (RPE) cells. MsrA protects cells from oxidative stress. Overexpression of MsrA increases resistance to cell death, while silencing or knocking down MsrA decreases cell survival; events that are mediated by mitochondria. MsrA participates in protein-protein interaction with several other cellular proteins. The interaction of MsrAwith α-crystallins is of utmost importance given the known functions of the latter in protein folding, neuroprotection, and cell survival. Oxidation of methionine residues in α-crystallins results in loss of chaperone function and possibly its antiapoptotic properties. Recent work from our laboratory has shown that MsrA is co-localized with αA and αB crystallins in the retinal samples of patients with age-related macular degen- eration. We have also found that chemically induced hypoxia regulates the expression of MsrA and MsrB2 in human RPE cells. Thus, MsrA is a critical enzyme that participates in cell and tissue protection, and its interaction with other proteins/growth factors may provide a target for therapeutic strategies to prevent degenerative diseases.

关键词： Methionine sulfoxide reductases Hypoxia Protein interaction α crystallins Neuroprotection