We report on the results of the extensive multi-wavelength campaign from optical to GeV γ-rays of the 2014 periastron passage of PSR B1259−63, which is a unique high-mass γ-ray emitting binary system ...with a young pulsar companion. Observations demonstrate the stable nature of the post-periastron GeV flare and prove the coincidence of the flare with the start of rapid decay of the Hα equivalent width, usually interpreted as a disruption of the Be stellar disc. Intensive X-ray observations reveal changes in the X-ray spectral behaviour happening at the moment of the GeV flare. We demonstrate that these changes can be naturally explained as a result of synchrotron cooling of monoenergetic relativistic electrons injected into the system during the GeV flare.
ABSTRACT
PSR B1259-63 is a gamma-ray binary system hosting a radio pulsar orbiting around an O9.5Ve star, LS 2883, with a period of ∼3.4 yr. The interaction of the pulsar wind with the LS 2883 ...outflow leads to unpulsed broad-band emission in the radio, X-rays, GeV, and TeV domains. While the radio, X-ray, and TeV light curves show rather similar behaviour, the GeV light curve appears very different with a huge outburst about a month after a periastron. The energy release during this outburst seems to significantly exceed the spin-down luminosity of the pulsar and both the GeV light curve and the energy release vary from one orbit to the next. In this paper, we present for the first time the results of optical observations of the system in 2017, and also reanalyse the available X-ray and GeV data. We present a new model in which the GeV data are explained as a combination of the bremsstrahlung and inverse Compton emission from the unshocked and weakly shocked electrons of the pulsar wind. The X-ray and TeV emission is produced by synchrotron and inverse Compton emission of energetic electrons accelerated on a strong shock arising due to stellar/pulsar winds collision. The brightness of the GeV flare is explained in our model as a beaming effect of the energy released in a cone oriented, during the time of the flare, in the direction of the observer.
SCO and BRICS in an emerging multipolar world order Malyshev, D. V.
Vestnik Moskovskogo universiteta. Seriâ 25. Meždunarodnye otnošeniâ i mirovaâ politika (Online),
09/2024, Letnik:
16, Številka:
2
Journal Article
Recenzirano
Odprti dostop
The year 2024 will be a milestone for the development of both the Shanghai Cooperation Organization (SCO) and BRICS, a unique negotiating format for rapidly growing economies. This year, Kazan will ...host the BRICS summit, and Astana has already held the SCO summit, which was marked by the adoption of a number of important initiatives. The assessment of the results and historical significance of these summits requires a special study, in this article we will look at the state in which both BRICS and SCO approached them, what problems they are currently facing and what prospects open up to them in the context of a global transformation of the IR system. The first section examines the main stages of the formation and current trends in the development of the SCO. The author emphasizes that in addition to addressing traditional challenges, the SCO member states are actively cooperating in countering new threats, such as separatism, drug trafficking, terrorism, and Islamic extremism. In this context, the SCO countries are particularly attentive to the rapidly changing situation in Afghanistan. The author concludes that although the SCO member countries have managed to create a solid legal framework and effective mechanisms of interaction, there are contradictions and even clashes between them on a number of issues. The second section identifies the stages of formation and current trends in the development of BRICS. The author notes that in the last few years, BRICS have been actively expanding both quantitatively by including more and more new countries in the association, and qualitatively, exploring new forms and areas of cooperation. In this regard, special attention is paid to the efforts to create a BRICS currency and to cooperation within the framework of the New Development Bank. According to the author, the SCO summits in Astana and BRICS in Kazan in 2024 should bring the development of these international structures, which embody hopes for the establishment of a new, fairer world order, to a qualitatively new level.
We report on broad multiwavelength observations of the 2010-2011 periastron passage of the γ-ray loud binary system PSR B1259−63. High-resolution interferometric radio observations establish extended ...radio emission trailing the position of the pulsar. Observations with the Fermi
Gamma-ray Space Telescope reveal GeV γ-ray flaring activity of the system, reaching the spin-down luminosity of the pulsar, around 30 d after periastron. There are no clear signatures of variability at radio, X-ray and TeV energies at the time of the GeV flare. Variability around periastron in the Hα emission line, can be interpreted as the gravitational interaction between the pulsar and the circumstellar disc. The equivalent width of the Hα grows from a few days before periastron until a few days later, and decreases again between 18 and 46 d after periastron. In near-infrared we observe the similar decrease of the equivalent width of Brγ line between the 40th and 117th day after the periastron. For the idealized disc, the variability of the Hα line represents the variability of the mass and size of the disc. We discuss possible physical relations between the state of the disc and GeV emission under assumption that GeV flare is directly related to the decrease of the disc size.
Abstract
We consider the class
G
(
S
n
) of orientation preserving Morse–Smale diffeomorphisms of the sphere
S
n
of dimension
n
> 3, assuming that invariant manifolds of different saddle periodic ...points have no intersection. For any diffeomorphism
f
∈
G
(
S
n
), we define a coloured graph Γ
f
that describes a mutual arrangement of invariant manifolds of saddle periodic points of the diffeomorphism
f
. We enrich the graph Γ
f
by an automorphism
P
f
induced by dynamics of
f
and define the isomorphism notion between two coloured graphs. The aim of the paper is to show that two diffeomorphisms
f
,
f
′ ∈
G
(
S
n
) are topologically conjugated if and only if the graphs Γ
f
, Γ
f
′ are isomorphic. Moreover, we establish the existence of a linear-time algorithm to distinguish coloured graphs of diffeomorphisms from the class
G
(
S
n
).
A matching of a graph is a set of its edges that pairwise do not have common vertices. An important parameter of graphs, which is used in mathematical chemistry, is the Hosoya index, defined as the ...number of their matchings. Previously, the problems of maximizing this index were considered and completely solved for
-vertex trees with two, three and four leaves for any sufficiently large
. In the present paper, a similar problem is completely solved for 5-leaved trees with
and for 6-leaved trees with
.
ABSTRACT
The gamma-ray binary 1FGL J1018.6-5856 consists of an O6V((f)) type star and an unknown compact object, and shows orbitally modulated emission from radio to very high energy gamma rays. The ...X-ray light curve shows a maximum around the same phase as the GeV emission, but also a secondary maximum between phases ϕ = 0.2 and 0.6. A clear solution to the binary system is important for understanding the emission mechanisms occurring within the system. In order to improve on the existing binary solution, we undertook radial velocity measurements of the optical companion using the Southern African Large Telescope, as well as analysed publicly available X-ray and GeV gamma-ray data. A search for periodicity in Fermi-LAT data found an orbital period of P = 16.5507 ± 0.0004 d. The best-fitting solution to the radial velocities, held at this new period, finds the system to be more eccentric than previous observations, e = 0.531 ± 0.033 with a longitude of periastron of 151.2 ± 5.1°, and a larger mass function f = 0.00432 ± 0.00077 M⊙. We propose that the peaks in the X-ray and gamma-ray light curves around phase 0 are due to the observation of the confined shock formed between the pulsar and stellar wind pointing towards the observer. The secondary increase or strong rapid variations of the X-ray flux at phases 0.25 to 0.75 is due to the interaction of multiple randomly oriented stellar wind clumps/pulsar wind interactions around apastron.
Abstract
Milky Way-sized galaxies harbor a population of unmerged dark matter subhalos, as shown from cosmological N-body simulations. These subhalos could shine in gamma-rays and be eventually ...detected as unidentified sources in gamma-ray surveys. From a thorough selection of unidentified Fermi-LAT Objects (UFOs), we observe four UFOs with H.E.S.S. and we search for very high-energy (VHE,
E
≥ 100 GeV) gamma-ray emission. Considering dark matter masses above a few hundred GeV, the observed UFOs could be identified as dark matter subhalos, given their hard gamma-ray spectra in the few-ten-to-hundred GeV energy range. Since no significant very-high-energy gamma-ray emission is detected in any of the four UFOs dataset nor in the combined one, we derive constraints on the product of the velocity-weighted annihilation cross-section 〈
συ
〉 by the J-factor for the dark matter models. We derive 95% CL upper limits on 〈
συ
〉
J
in
W
+
W
−
and τ
+
τ
−
annihilation channels for the TeV dark matter particles. Considering thermal WIMPs, we derive constraints on the J-factors from the H.E.S.S. observations. Assuming model-dependent predictions from cosmological N-body simulations on the J-factor distribution for Milky Way-sized galaxies, the dark matter models with masses greater than 0.3 TeV for the UFO emissions can be ruled out at high confidence level.
We consider the coloring problem for hereditary graph classes, i.e. classes of simple unlabeled graphs closed under deletion of vertices. For the family of the hereditary classes of graphs defined by ...forbidden induced subgraphs with at most four vertices, there are three classes with an open complexity of the problem. For the problem and the open three cases, we present approximation polynomial-time algorithms with performance guarantees.
Context. The evidence of line-like spectral features above 100 GeV, in particular at 130 GeV, which have been recently reported from some parts of the Galactic plane, poses serious challenges for any ...interpretation of this surprise discovery. It is generally believed that the unusually narrow profile of the spectral line cannot be explained by conventional processes in astrophysical objects, and, if real, is likely to be associated with dark matter. Aims. In this paper we argue that cold ultrarelativistic pulsar winds can be alternative sources of very narrow gamma-ray lines. Methods. We demonstrate that Comptonization of a cold ultrarelativistic electron-positron pulsar wind in the deep Klein-Nishina regime can readily provide very narrow (ΔE/E ≤ 0.2) distinct gamma-ray line features. To verify this prediction, we produced photon-count maps based on the Fermi LAT data in the energy interval 100 to 140 GeV. Results. We confirm earlier reports of the presence of marginal gamma-ray line-like signals from three regions of the Galactic plane. Although the maps show some structure inside these regions, unfortunately the limited photon statistics do not allow any firm conclusion in this regard. Conclusions. The confirmation of 130 GeV line emission by low-energy threshold atmospheric Cherenkov telescope systems, in particular by the new 28 m diameter dish of the H.E.S.S. array, would be crucial for resolving the spatial structure of the reported hotspots, and thus for distinguishing between the dark matter and pulsar origins of the “Fermi Lines”.
PDF
