X-ray absorption and rapid variability of the dwarf Seyfert nucleus of NGC4395

We report the detection of an absorbed central X-ray source and its strong, rapid variability in NGC4395, the least luminous Seyfert nucleus known. The X-ray source exhibits a number of flares with factors of 3-4 flux changes during a half day ASCA observation. Such X-ray variability is in constrast to the behaviour of other low luminosity active galaxies. It provides further support for an accreting black hole model rather than an extreme stellar process in accounting for the nuclear activity of NGC4395. The soft X-ray emission below 3 keV is strongly attenuated by absorption. The energy spectrum in this absorption band shows a dramatic change in response to the variation in continuum luminosity. A variable warm absorber appears to be an explanation for the spectral change. The absorption-corrected 2-10 keV luminosity is 4e39 erg/s for a source distance of 2.6 Mpc, and at 1 keV is one order of magnitude above previous ROSAT estimates. Our X-ray results infer the nuclear source of NGC4395 to be a scaled-down version of higher luminosity Seyfert nuclei, with an intermediate mass (10^4-10^5 Msun) black hole, unlike the nearby low luminosity active galaxies in which underfed massive black holes are suspected to reside.Comment: 12 pages, accepted for publication in MNRA

The Distribution of Redshifts in New Samples of Quasi-stellar Objects

Two new samples of QSOs have been constructed from recent surveys to test the hypothesis that the redshift distribution of bright QSOs is periodic in $\log(1+z)$. The first of these comprises 57 different redshifts among all known close pairs or multiple QSOs, with image separations $\leq$ 10\arcsec, and the second consists of 39 QSOs selected through their X-ray emission and their proximity to bright comparatively nearby active galaxies. The redshift distributions of the samples are found to exhibit distinct peaks with a periodic separation of $\sim 0.089$ in $\log(1+z)$ identical to that claimed in earlier samples but now extended out to higher redshift peaks $z = 2.63, 3.45$ and 4.47, predicted by the formula but never seen before. The periodicity is also seen in a third sample, the 78 QSOs of the 3C and 3CR catalogues. It is present in these three datasets at an overall significance level $10^{-5}$ - $10^{-6}$, and appears not to be explicable by spectroscopic or similar selection effects. Possible interpretations are briefly discussed.Comment: submitted for publication in the Astronomical Journal, 15 figure

Chandra X-ray Observations of the Spiral Galaxy M81

A Chandra X-Ray Observatory ACIS-S imaging observation is used to study the population of X-ray sources in the nearby Sab galaxy M81 (NGC 3031). A total of 177 sources are detected with 124 located within the D25 isophote to a limiting X-ray luminosity of 3e36 ergs/cm2/s. Source positions, count rates, luminosities in the 0.3-8.0 keV band, limiting optical magnitudes, and potential counterpart identifications are tabulated. Spectral and timing analysis of the 36 brightest sources are reported including the low-luminosity active galactic nucleus, SN 1993J, and the Einstein-discovered ultra-luminous X-ray source X6.Comment: 27 pages, 17 figures, 2 tables, submitted to Ap

Control of the induction of type I interferon by Peste des petits ruminants virus.

Peste des petits ruminants virus (PPRV) is a morbillivirus that produces clinical disease in goats and sheep. We have studied the induction of interferon-β (IFN-β) following infection of cultured cells with wild-type and vaccine strains of PPRV, and the effects of such infection with PPRV on the induction of IFN-β through both MDA-5 and RIG-I mediated pathways. Using both reporter assays and direct measurement of IFN-β mRNA, we have found that PPRV infection induces IFN-β only weakly and transiently, and the virus can actively block the induction of IFN-β. We have also generated mutant PPRV that lack expression of either of the viral accessory proteins (V&C) to characterize the role of these proteins in IFN-β induction during virus infection. Both PPRV_ΔV and PPRV_ΔC were defective in growth in cell culture, although in different ways. While the PPRV V protein bound to MDA-5 and, to a lesser extent, RIG-I, and over-expression of the V protein inhibited both IFN-β induction pathways, PPRV lacking V protein expression can still block IFN-β induction. In contrast, PPRV C bound to neither MDA-5 nor RIG-I, but PPRV lacking C protein expression lost the ability to block both MDA-5 and RIG-I mediated activation of IFN-β. These results shed new light on the inhibition of the induction of IFN-β by PPRV

Pediatric Measles Vaccine Expressing a Dengue Antigen Induces Durable Serotype-specific Neutralizing Antibodies to Dengue Virus

Dengue disease is an increasing global health problem that threatens one-third of the world's population. Despite decades of efforts, no licensed vaccine against dengue is available. With the aim to develop an affordable vaccine that could be used in young populations living in tropical areas, we evaluated a new strategy based on the expression of a minimal dengue antigen by a vector derived from pediatric live-attenuated Schwarz measles vaccine (MV). As a proof-of-concept, we inserted into the MV vector a sequence encoding a minimal combined dengue antigen composed of the envelope domain III (EDIII) fused to the ectodomain of the membrane protein (ectoM) from DV serotype-1. Immunization of mice susceptible to MV resulted in a long-term production of DV1 serotype-specific neutralizing antibodies. The presence of ectoM was critical to the immunogenicity of inserted EDIII. The adjuvant capacity of ectoM correlated with its ability to promote the maturation of dendritic cells and the secretion of proinflammatory and antiviral cytokines and chemokines involved in adaptive immunity. The protective efficacy of this vaccine should be studied in non-human primates. A combined measles–dengue vaccine might provide a one-shot approach to immunize children against both diseases where they co-exist

Past, Present, and Future X-Ray and Gamma-Ray Missions

X- and -ray astronomy began in the early sixties of the last century with balloons flights, sounding rocket experiment and satellites. Long before space satellite detected X- and -rays emitted by cosmic sources, scientists had known that the Universe should be producing these photons. In this chapter we provided an overview of past and present missions that has made the X- and -ray astronomy an integral part of astronomical research, and prospects of future developments