Patients co-infected with HIV-1 and tuberculosis (TB) are at risk of developing TB-associated immune reconstitution inflammatory syndrome (TB-IRIS) following commencement of antiretroviral therapy ...(ART). TB-IRIS is characterized by transient but severe localized or systemic inflammatory reactions against
Mycobacterium tuberculosis
antigens. Here, we review the risk factors and clinical management of TB-IRIS, as well as the roles played by different aspects of the immune response in contributing to TB-IRIS pathogenesis.
In the favoured core-accretion model of formation of planetary systems, solid planetesimals accumulate to build up planetary cores, which then accrete nebular gas if they are sufficiently massive. ...Around M-dwarf stars (the most common stars in our Galaxy), this model favours the formation of Earth-mass (M⊕) to Neptune-mass planets with orbital radii of 1 to 10 astronomical units (au), which is consistent with the small number of gas giant planets known to orbit M-dwarf host stars. More than 170 extrasolar planets have been discovered with a wide range of masses and orbital periods, but planets of Neptune's mass or less have not hitherto been detected at separations of more than 0.15 au from normal stars. Here we report the discovery of a 5.5+5.5-2.7 M⊕ planetary companion at a separation of 2.6+1.5-0.6 au from a 0.22+0.21-0.11 M M-dwarf star, where M refers to a solar mass. (We propose to name it OGLE-2005-BLG-390Lb, indicating a planetary mass companion to the lens star of the microlensing event.) The mass is lower than that of GJ876d (ref. 5), although the error bars overlap. Our detection suggests that such cool, sub-Neptune-mass planets may be more common than gas giant planets, as predicted by the core accretion theory.
Abstract
In 2017, the Event Horizon Telescope (EHT) Collaboration succeeded in capturing the first direct image of the center of the M87 galaxy. The asymmetric ring morphology and size are consistent ...with theoretical expectations for a weakly accreting supermassive black hole of mass ∼6.5 × 10
9
M
⊙
. The EHTC also partnered with several international facilities in space and on the ground, to arrange an extensive, quasi-simultaneous multi-wavelength campaign. This Letter presents the results and analysis of this campaign, as well as the multi-wavelength data as a legacy data repository. We captured M87 in a historically low state, and the core flux dominates over HST-1 at high energies, making it possible to combine core flux constraints with the more spatially precise very long baseline interferometry data. We present the most complete simultaneous multi-wavelength spectrum of the active nucleus to date, and discuss the complexity and caveats of combining data from different spatial scales into one broadband spectrum. We apply two heuristic, isotropic leptonic single-zone models to provide insight into the basic source properties, but conclude that a structured jet is necessary to explain M87’s spectrum. We can exclude that the simultaneous
γ
-ray emission is produced via inverse Compton emission in the same region producing the EHT mm-band emission, and further conclude that the
γ
-rays can only be produced in the inner jets (inward of HST-1) if there are strongly particle-dominated regions. Direct synchrotron emission from accelerated protons and secondaries cannot yet be excluded.
We have studied the long-term (∼ years) temporal variability of the prototype supersoft X-ray source (SSS) CAL 83 in the Large Magellanic Cloud, using data from the massive compact halo object ...(MACHO) and Optical Gravitational Lensing Experiment (OGLE) projects. The CAL 83 light curve exhibits dramatic brightness changes of ∼1 mag on time-scales of ∼450 d, and spends typically ∼200 d in the optical low state. Combined with archival XMM-Newton X-ray observations these represent the most extensive X-ray/optical study to date of this system, and reveal in much greater detail that the X-ray light curve is anticorrelated with the optical behaviour. This is remarkably similar to the behaviour of the 'transient' SSS, RX J0513.9−6951, where the SSS outbursts recur on a time-scale of ∼168 d, and also anticorrelate with the optical flux. We performed simple blackbody fits to both high- and low-state X-ray spectra, and find that the blackbody temperature and luminosity decrease when the optical counterpart brightens. We interpret these long-term variations in terms of the limit cycle model of Hachisu and Kato, which provides further support for these systems containing massive (∼1.3 M) white dwarfs. In addition, we have refined their orbital periods in the MACHO and OGLE-III light curves to values of 1.047529(1) d and 0.762956(5) d for CAL 83 and RX J0513.9−6951, respectively.
We combine the decade-long photometry of the Be/X-ray binary system A0538-66 provided by the Massive astrophysical compact halo object (MACHO) and optical gravitational lensing experiment (OGLE) IV ...projects with high-resolution Southern African Large Telescope (SALT) spectroscopy to provide detailed constraints on the orbital parameters and system properties. The ~420 d superorbital modulation is present throughout, but has reduced in amplitude in recent years. The well-defined 16.6409 d orbital outbursts, which were a strong function of superorbital phase in the MACHO data (not occurring at all at superorbital maximum), are present throughout the OGLE IV coverage. However, their amplitude reduces during superorbital maximum. We have refined the orbital period and ephemeris of the optical outburst based on ~25 yr light curves to HJD = 2455674.48 plus or minus 0.03 + n*16.6409 plus or minus 0.0003d. Our SALT spectra reveal a B1 III star with vsin i of 285 kms super( -1) from which we have derived an orbital radial velocity curve which confirms the high eccentricity of e = 0.72 plus or minus 0.14. Furthermore, the mass function indicates that, unless the neutron star far exceeds the canonical 1.44 M..., the donor must be significantly undermassive for its spectral type. We discuss the implications of the geometry and our derived orbital solution on the observed behaviour of the system. (ProQuest: ... denotes formulae/symbols omitted.)
Very high-energy γ rays (VHE, E ≳ 100 GeV) propagating over cosmological distances can interact with the low-energy photons of the extragalactic background light (EBL) and produce electron-positron ...pairs. The transparency of the Universe to VHE γ rays is then directly related to the spectral energy distribution (SED) of the EBL. The observation of features in the VHE energy spectra of extragalactic sources allows the EBL to be measured, which otherwise is very difficult. An EBL model-independent measurement of the EBL SED with the H.E.S.S. array of Cherenkov telescopes is presented. It was obtained by extracting the EBL absorption signal from the reanalysis of high-quality spectra of blazars. From H.E.S.S. data alone the EBL signature is detected at a significance of 9.5σ, and the intensity of the EBL obtained in different spectral bands is presented together with the associated γ-ray horizon.
•EHBL nature of Mrk 501 is explored using observations in X-ray and gamma-ray energy bands.•Spectral features broadly support the EHBL behavior of the blazar Mrk 501.•Temporal characteristics during ...flaring states contradict the EHBL nature of Mrk 501.•EHBL nature of Mrk 501 is found to be a dynamic characteristic of the source.
Extremely High energy peaked BL Lac (EHBL) objects are a special class of blazars with peculiar observational properties at X-ray and γ–ray energies. The observations of these sources indicate hard X-ray and γ–ray spectra and absence of rapid flux variations in the multi-wavelength light curves. These observational features challenge the leptonic models for blazars due to unusually hard particle spectrum in the emission region of the blazar jet and provide a strong motivation for exploring alternative scenarios to interpret the broad-band emission from blazars. At present, only few TeV blazars have been observed as EHBL objects in the extragalactic Universe. Due to their hard γ–ray spectra and long term variability, the observations of EHBL type of blazars at different redshifts help in probing the cosmic magnetic field and extragalactic background light in the Universe. Such objects also provide astrophysical sites to explore the particle acceleration mechanisms like magnetic reconnection and second order Fermi acceleration. Therefore, it has become important to identify more objects as EHBL using the observations available in the literature. Recent studies on the blazar Mrk 501 indicate that this source may exhibit an EHBL behaviour. In this paper, we use long term observations of Mrk 501 to explore its nature. Two sets of data, related to low and high/flaring activity states of Mrk 501, have been presented and compared with the observed features of a few well known EHBL type of blazars. We find that the spectral features of the blazar Mrk 501 indicate an EHBL nature of the source. Whereas, the temporal characteristics with fast variability during the high activity state of the source in X-ray and γ–ray energy bands are not compatible with the behaviour of EHBL type of blazars. However, Mrk 501 can be considered as an EHBL candidate in its low emission state. We also discuss the implications of identifying more EHBL objects using present and future ground-based γ-ray observatories.
A very bright and fast varying gamma-ray flare has been detected from the blazar 3C 279 on June 16, 2015. We have studied the broadband spectral energy distribution of the source during the flaring ...episode and in the low activity state using a simple one zone leptonic model. We find that an electron energy distribution described by a broken power law can be used to reproduce the broadband emissions during the high and low activity states. The flux measurements at radio, infrared and optical frequencies are reproduced by the synchrotron emission resulting from the relativistic electrons in a jet magnetic field strength of 0.37 G. The gamma-ray emission from the blazar 3C 279 is attributed to the Comptonization of the IR seed photons from the dusty torus with a temperature of 870 K. The outburst from the source observed on June 16, 2015 can be ascribed to an efficient acceleration process associated with a sudden enhancement in the electron energy density in the emitting region with respect to the low activity state. The fast gamma-ray variability at a minute timescale implies that the emission during the flare originates from a more compact region and the size of the emission zone in the low activity state is found to be four times larger than that during the flare. We have also used the model parameters derived from the broadband spectral energy distribution modelling to investigate a few physical properties of the jet during the outburst.
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