| 1. |
- Abdo, A. A., et al.
(author)
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FERMI Large Area Telescope and multi-wavelength observations of the flaring activity of PKS 1510-089 between 2008 september and 2009 june
- 2010
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In: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 721:2, s. 1425-1447
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Journal article (peer-reviewed)abstract
- We report on the multi-wavelength observations of PKS 1510-089 (a flat spectrum radio quasar (FSRQ) at z = 0.361) during its high activity period between 2008 September and 2009 June. During this 11 month period, the source was characterized by a complex variability at optical, UV, and gamma-ray bands, on timescales down to 6-12 hr. The brightest gamma-ray isotropic luminosity, recorded on 2009 March 26, was similar or equal to 2 x 1048 erg s-1. The spectrum in the Fermi Large Area Telescope energy range shows a mild curvature described well by a log-parabolic law, and can be understood as due to the Klein-Nishina effect. The. -ray flux has a complex correlation with the other wavelengths. There is no correlation at all with the X-ray band, a weak correlation with the UV, and a significant correlation with the optical flux. The. -ray flux seems to lead the optical one by about 13 days. From the UV photometry, we estimated a black hole mass of similar or equal to 5.4 x 10(8)M(circle dot) and an accretion rate of similar or equal to 0.5M(circle dot) yr(-1). Although the power in the thermal and non-thermal outputs is smaller compared to the very luminous and distant FSRQs, PKS 1510-089 exhibits a quite large Compton dominance and a prominent big blue bump (BBB) as observed in the most powerful gamma-ray quasars. The BBB was still prominent during the historical maximum optical state in 2009 May, but the optical/ UV spectral index was softer than in the quiescent state. This seems to indicate that the BBB was not completely dominated by the synchrotron emission during the highest optical state. We model the broadband spectrum assuming a leptonic scenario in which the inverse Compton emission is dominated by the scattering of soft photons produced externally to the jet. The resulting model-dependent jet energetic content is compatible with a scenario in which the jet is powered by the accretion disk, with a total efficiency within the Kerr black hole limit.
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| 2. |
- Abdo, A. A., et al.
(author)
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Gamma-ray emission concurrent with the nova in the symbiotic binary V407 cygni
- 2010
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In: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 329:5993, s. 817-821
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Journal article (peer-reviewed)abstract
- Novae are thermonuclear explosions on a white dwarf surface fueled by mass accreted from a companion star. Current physical models posit that shocked expanding gas from the nova shell can produce x-ray emission, but emission at higher energies has not been widely expected. Here, we report the Fermi Large Area Telescope detection of variable γ-ray emission (0.1 to 10 billion electron volts) from the recently detected optical nova of the symbiotic star V407 Cygni. We propose that the material of the nova shell interacts with the dense ambient medium of the red giant primary and that particles can be accelerated effectively to produce π0 decay γ-rays from proton-proton interactions. Emission involving inverse Compton scattering of the red giant radiation is also considered and is not ruled out.
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| 3. |
- Ackermann, M., et al.
(author)
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THE THIRD CATALOG OF ACTIVE GALACTIC NUCLEI DETECTED BY THE FERMI LARGE AREA TELESCOPE
- 2015
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In: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 810:1
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Journal article (peer-reviewed)abstract
- The third catalog of active galactic nuclei (AGNs) detected by the Fermi-LAT (3LAC) is presented. It is based on the third Fermi-LAT catalog (3FGL) of sources detected between 100 MeV and 300 GeV with a Test Statistic greater than 25, between 2008 August 4 and 2012 July 31. The 3LAC includes 1591 AGNs located at high Galactic latitudes (vertical bar b vertical bar > 10 degrees), a 71% increase over the second catalog based on 2 years of data. There are 28 duplicate associations, thus 1563 of the 2192 high-latitude gamma-ray sources of the 3FGL catalog are AGNs. Most of them (98%) are blazars. About half of the newly detected blazars are of unknown type, i.e., they lack spectroscopic information of sufficient quality to determine the strength of their emission lines. Based on their gamma-ray spectral properties, these sources are evenly split between flat-spectrum radio quasars (FSRQs) and BL Lacs. The most abundant detected BL Lacs are of the high-synchrotron-peaked (HSP) type. About 50% of the BL Lacs have no measured redshifts. A few new rare outliers (HSP-FSRQs and high-luminosity HSP BL Lacs) are reported. The general properties of the 3LAC sample confirm previous findings from earlier catalogs. The fraction of 3LAC blazars in the total population of blazars listed in BZCAT remains non-negligible even at the faint ends of the BZCAT-blazar radio, optical, and X-ray flux distributions, which hints that even the faintest known blazars could eventually shine in gamma-rays at LAT-detection levels. The energy-flux distributions of the different blazar populations are in good agreement with extrapolation from earlier catalogs.
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| 4. |
- Abdo, A. A., et al.
(author)
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THE FIRST FERMI MULTIFREQUENCY CAMPAIGN ON BL LACERTAE : CHARACTERIZING THE LOW-ACTIVITY STATE OF THE EPONYMOUS BLAZAR
- 2011
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In: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 730:2, s. 101-
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Journal article (peer-reviewed)abstract
- We report on observations of BL Lacertae during the first 18 months of Fermi LAT science operations and present results from a 48 day multifrequency coordinated campaign from 2008 August 19 to 2008 October 7. The radio to gamma-ray behavior of BL Lac is unveiled during a low-activity state thanks to the coordinated observations of radio-band (Metsahovi and VLBA), near-IR/optical (Tuorla, Steward, OAGH, and MDM), and X-ray (RXTE and Swift) observatories. No variability was resolved in gamma rays during the campaign, and the brightness level was 15 times lower than the level of the 1997 EGRET outburst. Moderate and uncorrelated variability has been detected in UV and X-rays. The X-ray spectrum is found to be concave, indicating the transition region between the low- and high-energy components of the spectral energy distribution (SED). VLBA observation detected a synchrotron spectrum self-absorption turnover in the innermost part of the radio jet appearing to be elongated and inhomogeneous, and constrained the average magnetic field there to be less than 3 G. Over the following months, BL Lac appeared variable in gamma rays, showing flares (in 2009 April and 2010 January). There is no evidence for the correlation of gamma rays with the optical flux monitored from the ground in 18 months. The SED may be described by a single-zone or a two-zone synchrotron self-Compton (SSC) model, but a hybrid SSC plus external radiation Compton model seems to be preferred based on the observed variability and the fact that it provides a fit closest to equipartition.
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| 5. |
- Sokolovsky, K. V., et al.
(author)
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Two active states of the narrow-line gamma-ray-loud AGN GB 1310+487
- 2014
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 565
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Journal article (peer-reviewed)abstract
- Context. Previously unremarkable, the extragalactic radio source GB 1310+487 showed gamma-ray flare on 2009 November 18, reaching a daily flux of similar to 10(-6) photons cm(-2) s(-1) at energies E > 100 MeV and became one of the brightest GeV sources for about two weeks. Its optical spectrum shows strong forbidden-line emission while lacking broad permitted lines, which is not typical for a blazar. Instead, the spectrum resembles those of narrow emission-line galaxies. Aims. We investigate changes in the object's radio-to-GeV spectral energy distribution (SED) during and after the prominent gamma-ray flare with the aim of determining the nature of the object and of constraining the origin of the variable high-energy emission. Methods. The data collected by the Fermi and AGILE satellites at gamma-ray energies; Swift at X-ray and ultraviolet (UV); the Kanata, NOT, and Keck telescopes at optical; OAGH and WISE at infrared (IR); and IRAM 30m, OVRO 40m, Effelsberg 100 m, RATAN-600, and VLBA at radio are analyzed together to trace the SED evolution on timescales of months. Results. The gamma-ray/ radio-loud narrow-line active galactic nucleus (AGN) is located at redshift z = 0.638. It shines through an unrelated foreground galaxy at z = 0.500. The AGN light is probably amplified by gravitational lensing. The AGN SED shows a two-humped structure typical of blazars and gamma-ray-loud narrow-line Seyfert 1 galaxies, with the high-energy (inverse-Compton) emission dominating by more than an order of magnitude over the low-energy (synchrotron) emission during gamma-ray flares. The difference between the two SED humps is smaller during the low-activity state. Fermi observations reveal a strong correlation between the gamma-ray flux and spectral index, with the hardest spectrum observed during the brightest gamma-ray state. The gamma-ray flares occurred before and during a slow rising trend in the radio, but no direct association between gamma-ray and radio flares could be established. Conclusions. If the gamma-ray flux is a mixture of synchrotron self-Compton and external Compton emission, the observed GeV spectral variability may result from varying relative contributions of these two emission components. This explanation fits the observed changes in the overall IR to gamma-ray SED.
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| 6. |
- Shipitsyna, E, et al.
(author)
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Evaluation of six nucleic acid amplification tests used for diagnosis of Neisseria gonorrhoeae in Russia compared with an international strictly validated real-time porA pseudogene polymerase chain reaction
- 2009
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In: Journal of the European Academy of Dermatology and Venereology. - : Wiley. - 0926-9959 .- 1468-3083. ; 23:11, s. 1246-1253
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Journal article (peer-reviewed)abstract
- Background In Russia, laboratory diagnosis of gonorrhoea has been mainly based on microscopy only and, in some settings, relatively rare suboptimal culturing. In recent years, Russian developed and manufactured nucleic acid amplification tests (NAAT) have been implemented for routine diagnosis of Neisseria gonorrhoeae. However, these NAATs have never been validated to any international well-recognized diagnostic NAAT. Objective This study aims to evaluate the performance characteristics of six Russian NAATs for N. gonorrhoeae diagnostics. Materials and methods In total, 496 symptomatic patients were included. Five polymerase chain reaction (PCR) assays and one real-time nucleic acid sequence based amplification (NASBA) assay, developed by three Russian companies, were evaluated on urogenital samples, i.e. cervical and first voided urine (FVU) samples from females (n = 319), urethral and FVU samples from males (n = 127), and extragenital samples, i.e. rectal and pharyngeal samples, from 50 additional female patients with suspicion of gonorrhoea. As reference method, an international strictly validated real-time porA pseudogene PCR was applied. Results The prevalence of N. gonorrhoeae was 2.7% and 16% among the patients providing urogenital and extragenital samples, respectively. The Russian NAATs and the reference method displayed high level of concordance (99.4-100%). The sensitivities, specificities, positive predictive values and negative predictive values of the Russian tests in different specimens were 66.7-100%, 100%, 100%, and 99.4-100%, respectively. Conclusions Russian N. gonorrhoeae diagnostic NAATs comprise relatively good performance characteristics. However, larger studies are crucial and, beneficially, the Russian assays should also be evaluated to other international highly sensitive and specific, and ideally Food and Drug Administration approved, NAATs such as Aptima Combo 2 (Gen-Probe).Conflicts of interest None declared.
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| 7. |
- Shipitsyna, E, et al.
(author)
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First evaluation of polymerase chain reaction assays used for diagnosis of Mycoplasma genitalium in Russia
- 2009
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In: Journal of the European Academy of Dermatology and Venereology. - : Wiley. - 0926-9959 .- 1468-3083. ; 23:10, s. 1164-1172
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Journal article (peer-reviewed)abstract
- Background Diagnosis of Mycoplasma genitalium is entirely based on nucleic acid amplification tests (NAATs). In Russia, several M. genitalium polymerase chain reaction (PCR) assays have been developed; however, any evaluation of their performance has never been performed. Objective To assess the performance of five PCRs developed and currently used in Russia for diagnosis of M. genitalium. Materials and methods Vaginal swabs and first voided urine samples (FVUs) from 281 females and urethral swabs and FVUs from 125 males were analysed using three conventional PCRs and two real-time PCRs developed by three Russian companies. As reference tests, a real-time PCR targeting the MgPa adhesin gene was used; positive results were confirmed by two conventional PCRs targeting the 16S rRNA gene and MgPa gene, respectively. For evaluation of detection limits and analytical specificities, a blinded control panel consisting of dilutions of six strains of M. genitalium and 14 other Mycoplasma species was tested. Results The prevalence of M. genitalium was 2.5% among females and 9.6% among males. The highest sensitivity (71.4-100% in different specimens) was exhibited by one real-time PCRs. Conventional PCRs from two manufacturers failed to detect M. genitalium in any of the seven positive female FVUs. All tests had a 100% clinical specificity; however, one cross-reacted with Mycoplasma pneumoniae. Conclusions Only one of the five Russian PCRs displayed reasonable sensitivity for all specimen types, but the specificities of all assays were high. Accordingly, improvements regarding sensitivity of all the tests are needed. However, larger studies, including other populations, evaluating these assays are crucial.
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| 8. |
- Shipitsyna, Elena, et al.
(author)
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First evaluation of six nucleic acid amplification tests widely used in the diagnosis of Chlamydia trachomatis in Russia
- 2009
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In: Journal of the European Academy of Dermatology and Venereology. - : Wiley. - 0926-9959 .- 1468-3083. ; 23:3, s. 268-276
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Journal article (peer-reviewed)abstract
- Abstract Background In Russia, nationally developed nucleic acid amplification tests (NAATs), which have never been validated to international commercially available NAATs, are mainly used in the diagnosis of Chlamydia trachomatis infection. Objective To evaluate the performance characteristics of six NAATs widely used to diagnose C. trachomatis infection in Russia. Materials and methods In total, 446 consecutive symptomatic patients (319 females and 127 males) were included. Five polymerase chain reaction (PCR) assays and one real-time nucleic acid sequence-based amplification (NASBA) assay were evaluated on cervical and vaginal samples from females and on urethral and first voided urine samples from males. As reference methods, the Cobas Amplicor PCR, as the main 'gold standard' method, and LightMix 480HT PCR were used. Results The overall prevalence of C. trachomatis infection was 12.6%. The Russian NAATs and the reference methods displayed a high level of concordance (97.9% to 99.2%). In comparison with the reference methods, the sensitivities, specificities, positive predictive values and negative predictive values of the Russian tests in different specimens ranged from 86.1% to 100%, 99.1% to 100%, 92.3% to 100% and 98.2% to 100%, respectively. Conclusions According to the reference methods, C. trachomatis NAATs developed and used in Russia have relatively good performance characteristics for both invasive and non-invasive samples. However, larger studies that include symptomatic and asymptomatic patients as well as genital and extra-genital samples, and in comparison with other internationally well-recognized, validated, and ideally Food and Drug Administration-approved C. trachomatis NAATs performed strictly according to the manufacturer's instructions, need to be conducted. Conflicts of interest None declared.
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| 9. |
- Akyuz, A., et al.
(author)
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Long-term multiwavelength studies of high-redshift blazar 0836+710
- 2013
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 556
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Journal article (peer-reviewed)abstract
- Aims. The observation of gamma-ray flares from blazar 0836+710 in 2011, following a period of quiescence, offered an opportunity to study correlated activity at different wavelengths for a high-redshift (z = 2.218) active galactic nucleus.Methods. Optical and radio monitoring, plus Fermi-LAT gamma-ray monitoring provided 2008-2012 coverage, while Swift offered auxiliary optical, ultraviolet, and X-ray information. Other contemporaneous observations were used to construct a broad-band spectral energy distribution.Results. There is evidence of correlation but not a measurable lag between the optical and.-ray flaring emission. In contrast, there is no clear correlation between radio and gamma-ray activity, indicating radio emission regions that are unrelated to the parts of the jet that produce the gamma rays. The gamma-ray energy spectrum is unusual in showing a change of shape from a power law to a curved spectrum when going from the quiescent state to the active state.
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| 10. |
- Litvinov, Dmitry, et al.
(author)
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Probing the gravitational redshift with an Earth-orbiting satellite
- 2018
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In: Physics Letters, Section A: General, Atomic and Solid State Physics. - : Elsevier BV. - 0375-9601. ; 382:33, s. 2192-2198
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Journal article (peer-reviewed)abstract
- We present an approach to testing the gravitational redshift effect using the RadioAstron satellite. The experiment is based on a modification of the Gravity Probe A scheme of nonrelativistic Doppler compensation and benefits from the highly eccentric orbit and ultra-stable atomic hydrogen maser frequency standard of the RadioAstron satellite. Using the presented techniques we expect to reach an accuracy of the gravitational redshift test of order 10−5, a magnitude better than that of Gravity Probe A. Data processing is ongoing, our preliminary results agree with the validity of the Einstein Equivalence Principle.
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