Context. The high and very high energy spectrum of gamma-ray binaries has become a challenge for all theoretical explanations since the detection of powerful, persistent GeV emission from LS 5039 and ...LS I +61 303 by Fermi/LAT. The spectral cutoff at a few GeV indicates that the GeV component and the fainter, hard TeV emission above 100 GeV are not directly related. Aims. We explore the possible origins of these two emission components in the framework of a young, non-accreting pulsar orbiting the massive star, and initiating the non-thermal emission through the interaction of the stellar and pulsar winds. Methods. The pulsar/stellar wind interaction in a compact-orbit binary gives rise to two potential locations for particle acceleration: the shocks at the head-on collision of the winds and the termination shock caused by Coriolis forces on scales larger than the binary separation. We explore the suitability of these two locations to host the GeV and TeV emitters, respectively, through the study of their non-thermal emission along the orbit. We focus on the application of this model to LS 5039 given its well-determined stellar wind with respect to other gamma-ray binaries. Results. The application of the proposed model to LS 5039 indicates that these two potential emitter locations provide the necessary conditions for reproduction of the two-component high-energy gamma-ray spectrum of LS 5039. In addition, the ambient postshock conditions required at each of the locations are consistent with recent hydrodynamical simulations. Conclusions. The scenario based on the interaction of the stellar and pulsar winds is compatible with the GeV and TeV emission observed from gamma-ray binaries with unknown compact objects, such as LS 5039 and LS I +61 303.
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On the origin of γ-ray emission in η Carina Ohm, S; Zabalza, V; Hinton, J. A ...
Monthly notices of the Royal Astronomical Society. Letters,
05/2015, Volume:
449, Issue:
1
Journal Article
Peer reviewed
Open access
η Car is the only colliding-wind binary for which high-energy γ rays are detected. Although the physical conditions in the shock region change on time-scales of hours to days, the variability seen at ...GeV energies is weak and on significantly longer time-scales. The γ-ray spectrum exhibits two features that can be interpreted as emission from the shocks on either side of the contact discontinuity. Here, we report on the first time-dependent modelling of the non-thermal emission in η Car. We find that emission from primary electrons is likely not responsible for the γ-ray emission, but accelerated protons interacting with the dense wind material can explain the observations. In our model, efficient acceleration is required at both shocks, with the primary side acting as a hadron calorimeter, whilst on the companion side acceleration is limited by the flow time out of the system, resulting in changing acceleration conditions. The system therefore represents a unique laboratory for the exploration of hadronic particle acceleration in non-relativistic shocks.
This study aimed to evaluate the self-reported satisfaction of Spanish postmenopausal women currently treated for vulvovaginal atrophy (VVA) symptoms.
The CRETA (CRoss sectional European sTudy on ...Adherence) is a multicenter cross-sectional study conducted in 29 public and private hospitals in Spain, which enrolled postmenopausal women receiving treatment with ospemifene, local hormone therapy (HT) or vaginal moisturizers for VVA. After the prior informed consent of the patients, sociodemographic and treatment perception data were collected using a structured questionnaire.
Among 752 women who completed the survey, the satisfaction score was significantly higher for the group treated with ospemifene (mean 8.3 ± 1.4) compared with the local HT group (7.2 ± 1.7) and the vaginal moisturizer group (6.5 ± 2.1) according to a 10-point Likert scale (p < 0.0001). Compared to vaginal moisturizers and local HT, participants treated with ospemifene reported the highest adherence (96.7% vs. 70.2% and 78.6%, respectively) and the lowest number of missed doses in the last month (0.6 ± 1.3 standard deviation SD vs. 3.5 ± 4.3 SD and 2.0 ± 2.8 SD, respectively) (p < 0.0001). Ospemifene was significantly perceived as easy to use (83.9% vs. 44.9% and 58.6%, respectively; p < 0.0001), efficacious in reducing the time to relieve symptoms (17.1% vs. 7.0% and 6.7%, p = 0.0005 and p = 0.0006, respectively) and convenient for sexual life (53.1% vs. 25.6% and 42.3%, p < 0.0001 and p = 0.0234, respectively).
Among postmenopausal women with VVA, treatment with ospemifene has the most positive perceptions and the highest overall satisfaction level and could be an optimal therapeutic approach, maximizing patient adherence.
Context. The MAGIC collaboration recently reported correlated X-ray and very high-energy (VHE) gamma-ray emission from the gamma-ray binary LS I +61 303 during ~60% of one orbit. These observations ...suggest that the emission in these two bands has its origin in a single particle population. Aims. We aim at improving our understanding of the source behaviour by explaining the simultaneous X-ray and VHE data through a radiation model. Methods. We use a model based on a one zone population of relativistic leptonic particles at the position of the compact object and assume dominant adiabatic losses. The adiabatic cooling time scale is inferred from the X-ray fluxes. Results. The model can reproduce the spectra and light curves in the X-ray and VHE bands. Adiabatic losses could be the key ingredient to explain the X-ray and partially the VHE light curves. From the best-fit result we obtain a magnetic field of B ≃ 0.2 G, a minimum luminosity budget of ~2 × 1035 erg s-1 and a relatively high acceleration efficiency. In addition, our results seem to confirm that the GeV emission detected by Fermi does not come from the same parent particle population as the X-ray and VHE emission. Moreover, the Fermi spectrum poses a constraint on the hardness of the particle spectrum at lower energies. In the context of our scenario, more sensitive observations would allow us to constrain the inclination angle, which could determine the nature of the compact object.
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Gamma-ray-loud X-ray binaries are binary systems that show non-thermal broadband emission from radio to gamma rays. If the system comprises a massive star and a young non-accreting pulsar, their ...winds will collide producing broadband non-thermal emission, most likely originated in the shocked pulsar wind. Thermal X-ray emission is expected from the shocked stellar wind, but until now it has neither been detected nor studied in the context of gamma-ray binaries. We present a semi-analytic model of the thermal X-ray emission from the shocked stellar wind in pulsar gamma-ray binaries, and find that the thermal X-ray emission increases monotonically with the pulsar spin-down luminosity, reaching luminosities of the order of 1033 erg s--1. The lack of thermal features in the X-ray spectrum of gamma-ray binaries can then be used to constrain the properties of the pulsar and stellar winds. By fitting the observed X-ray spectra of gamma-ray binaries with a source model composed of an absorbed non-thermal power law and the computed thermal X-ray emission, we are able to derive upper limits on the spin-down luminosity of the putative pulsar. We applied this method to LS 5039, the only gamma-ray binary with a radial, powerful wind, and obtain an upper limit on the pulsar spin-down luminosity of ~6 X 1036 erg s--1. Given the energetic constraints from its high-energy gamma-ray emission, a non-thermal to spin-down luminosity ratio very close to unity may be required.
MWC 656 (=HD 215227) was recently discovered to be the first binary system composed of a Be star and a black hole (BH). We observed it with XMM-Newton, and detected a faint X-ray source compatible ...with the position of the optical star, thus proving it to be the first Be/BH X-ray binary. The spectrum analysis requires a model fit with two components, a blackbody plus a power law, with (ProQuest: Formulae and/or non-USASCII text omitted) keV and a photon index Gamma = 1.0 + or - 0.8, respectively. The non-thermal component dominates above Asymptotically = to0.8 keV. The obtained total flux is (ProQuest: Formulae and/or non-USASCII text omitted) erg cm super(-2) s super(-1). At a distance of 2.6 + or - 0.6 kpc the total flux translates into a luminosity L sub(x) = (3.7 + or - 1.7) x 10 super(31) erg s super(-1). Considering the estimated range of BH masses to be 3.8-6.9 M sub(middot in circle), this luminosity represents (6.7 + or - 4.4) x 10 super(-8)L sub( Edd), which is typical of stellar-mass BHs in quiescence. We discuss the origin of the two spectral components: the thermal component is associated with the hot wind of the Be star, whereas the power-law component is associated with emission from the vicinity of the BH. We also find that the position of MWC 656 in the radio versus X-ray luminosity diagram may be consistent with the radio/X-ray correlation observed in BH low-mass X-ray binaries. This suggests that this correlation might also be valid for BH high-mass X-ray binaries (HMXBs) with X-ray luminosities down to ~10 super(-8)L sub(Edd). MWC 656 will allow the accretion processes and the accretion/ejection coupling at very low luminosities for BH HMXBs to be studied.
Context. There are a number of very high energy sources in the Galaxy that remain unidentified. Multi-wavelength and variability studies, and catalogue searches, are powerful tools to identify the ...physical counterpart, given the uncertainty in the source location and extension. Aims. This work carries out a thorough multi-wavelength study of the unidentified, very high energy source HESS J1858+020 and its environs. Methods. We have performed Giant Metrewave Radio Telescope observations at 610 MHz and 1.4 GHz to obtain a deep, low-frequency radio image of the region surrounding HESS J1858+020. We analysed archival radio, infrared, and X-ray data as well. This observational information, combined with molecular data, catalogue sources, and a nearby Fermi gamma-ray detection of unidentified origin, are combined to explore possible counterparts to the very high energy source. Results. We provide with a deep radio image of a supernova remnant that might be related to the GeV and TeV emission in the region. We confirm the presence of an H ii region next to the supernova remnant and coincident with molecular emission. A potential region of star formation is also identified. We identify several radio and X-ray sources in the surroundings. Some of these sources are known planetary nebulae, whereas others may be non-thermal extended emitters and embedded young stellar objects. Three old, background Galactic pulsars also neighbour HESS J1858+020 along the line of sight. Conclusions. The region surrounding HESS J1858+020 is rich in molecular structures and non-thermal objects that may potentially be linked to this unidentified very high energy source. In particular, a supernova remnant interacting with nearby molecular clouds may be a good candidate, but a star forming region, or a non-thermal radio source of yet unclear nature, may also be behind the gamma-ray source. The neighbouring pulsars, despite being old and distant, cannot be discarded as candidates. Further observational studies are needed, however, to narrow the search for a counterpart to the HESS source.
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Context. MGRO J2019+37 is an unidentified extended source of very high energy gamma-rays originally reported by the Milagro Collaboration as the brightest TeV source in the Cygnus region. Its ...extended emission could be powered by either a single or several sources. The GeV pulsar AGL J2020.5+3653, discovered by AGILE and associated with PSR J2021+3651, could contribute to the emission from MGRO J2019+37. Aims. Our aim is to identify radio and near-infrared sources in the field of the extended TeV source MGRO J2019+37, and study potential counterparts to explain its emission. Methods. We surveyed a region of about 6 square degrees with the Giant Metrewave Radio Telescope (GMRT) at the frequency 610 MHz. We also observed the central square degree of this survey in the near-infrared -band using the 3.5 m telescope in Calar Alto. Archival X-ray observations of some specific fields are included. VLBI observations of an interesting radio source were performed. We explored possible scenarios to produce the multi-TeV emission from MGRO J2019+37 and studied which of the sources could be the main particle accelerator. Results. We present a catalogue of 362 radio sources detected with the GMRT in the field of MGRO J2019+37, and the results of a cross-correlation of this catalog with one obtained at near-infrared wavelengths, which contains sources, as well as with available X-ray observations of the region. Some peculiar sources inside the 1 uncertainty region of the TeV emission from MGRO J2019+37 are discussed in detail, including the pulsar PSR J2021+3651 and its pulsar wind nebula PWN G75.2+0.1, two new radio-jet sources, the H II region Sh 2-104 containing two star clusters, and the radio source NVSS J202032+363158. We also find that the hadronic scenario is the most likely in case of a single accelerator, and discuss the possible contribution from the sources mentioned above. Conclusions. Although the radio and GeV pulsar PSR J2021+3651 / AGL J2020.5+3653 and its associated pulsar wind nebula PWN G75.2+0.1 can contribute to the emission from MGRO J2019+37, extrapolation of the GeV spectrum does not explain the detected multi-TeV flux. Other sources discussed here could contribute to the emission of the Milagro source.
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Context. LS I +61 303 is a member of the select group of gamma-ray binaries: galactic binary systems that contain a massive star and a compact object, show a changing milliarcsecond morphology and a ...similar broad spectral energy distribution (SED) that peaks at MeV–TeV energies and is modulated by the orbital motion. The nature of the compact object is unclear in LS I +61 303, LS 5039 and HESS J0632+057, whereas PSR B1259–63 harbours a 47.74 ms radio pulsar. Aims. A scenario in which a young pulsar wind interacts with the stellar wind has been proposed to explain the very high energy (VHE, E > 100 GeV) gamma-ray emission detected from LS I +61 303, although no pulses have been reported from this system at any wavelength. We aim to find evidence of the pulsar nature of the compact object. Methods. We performed phased array observations with the Giant Metrewave Radio Telescope at 1280 MHz centred at phase 0.54. Simultaneous data from the multi-bit phased array back-end with a sampling time of tsamp = 128 μs and from the polarimeter back-end with tsamp = 256 μs where taken. Results. No pulses have been found in the data set, with a minimum detectable mean flux density of ~0.38 mJy at 8-σ level for the pulsed emission from a putative pulsar with period P > 2 ms and duty cycle D = 10% in the direction of LS I +61 303. Conclusions. The detection of posible radio pulsations will require deep and sensitive observations at frequencies ~0.5–5 GHz and orbital phases 0.6−0.7. However, it may be unfeasible to detect pulses if the putative pulsar is not beamed at the Earth or if there is a strong absorption within the binary system.
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Context. A short duration burst reminiscent of a soft gamma-ray repeater/anomalous X-ray pulsar behaviour was detected in the direction of LS I +61 303 by the Swift satellite. While the association ...with this well known gamma-ray binary is likely, a different origin cannot be excluded. Aims. We explore the error box of this unexpected flaring event and establish the radio, near-infrared and X-ray sources in our search for any peculiar alternative counterpart. Methods. We carried out a combined analysis of archive Very Large Array radio data of LS I +61 303 sensitive to both compact and extended emission. We also reanalysed previous near infrared observations with the 3.5 m telescope of the Centro Astronómico Hispano Alemán and X-ray observations with the Chandra satellite. Results. Our deep radio maps of the LS I +61 303 environment represent a significant advancement on previous work and 16 compact radio sources in the LS I +61 303 vicinity are detected. For some detections, we also identify near infrared and X-ray counterparts. Extended emission features in the field are also detected and confirmed. The possible connection of some of these sources with the observed flaring event is considered. Based on these data, we are unable to claim a clear association between the Swift-BAT flare and any of the sources reported here. However, this study represents the most sophisticated attempt to determine possible alternative counterparts other than LS I +61 303.
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