ABSTRACT
LS I +61°303 is a rare representative of the gamma-ray binaries with a compact object known to be a pulsar. We report on the periodicity and spectral analysis of this source performed with ...more than 14 yr of Fermi/LAT data. The periodicity of LS I +61°303 is strongly energy dependent. Two periods P1 = 26.932 ± 0.004(stat) ± 0.008(syst) and P2 = 26.485 ± 0.004(stat) ± 0.007(syst) are detected only at E > 1 GeV and at E < 0.3 GeV correspondingly. Within 1σ (stat + syst) the periods are consistent with orbital (P2) and beat orbital/superorbital (P1) periods. We present the orbital light curves of the system in several energy bands and the results of the spectral analysis. We discuss the possible origin of the change in the variability pattern between 0.1 and 1 GeV energy.
We present the results of a comprehensive analysis of the X-ray pulsar X Persei over the period 1996-2011, encompassing the quite low state and subsequent strong outburst activity. Using data from ...the Rossi X-ray Timing Explorer (RXTE) and Swift, we detected several consecutive outbursts, during which the source luminosity increased by a factor of ∼5 up to L
X≃ 1.2 × 1035 erg s−1. Previously, the source has been observed in a high state only once. The source spectrum in a standard energy band (4-25 keV) is independent of the flux change and can be described by a model that includes both thermal and non-thermal components. With the help of data from the International Gamma-Ray Astrophysics Laboratory (Integral), we registered the highly significant cyclotron absorption line in the source spectrum and, for the first time, detected a significantly hard X-ray emission from the pulsar up to ∼160 keV. We also report drastic changes of the pulse period during the outburst activity: a long episode of spin-down was changed to spin-up with a rate of
yr−1, which is several times higher than previous rates of spin-up and spin-down. To search for a correlation between the X-ray and optical light curves, we took data from the international data base of the American Association of Variable Star Observers (AAVSO). We found no significant correlation between optical and X-ray fluxes at any time-lag from dozens of days to years.
ABSTRACT
PSR J2032+4127 is only the second known gamma-ray binary where it is confirmed that a young radio pulsar is in orbit around a Be-star. The interaction of the pulsar wind with the mass ...outflow from the companion leads to broad-band emission from radio up to TeV energies. In this paper we present results of optical monitoring of the 2017 periastron passage with the Nordic Optical Telescope. These observations are complemented by X-ray (Swift/XRT, NuSTAR) and GeV (Fermi/LAT) monitoring. Joint analysis of the evolution of the parameters of the H α line and the broad-band (X-ray to TeV) spectral shape allows us to propose a model linking the observed emission to the interaction of the pulsar and Be-star winds under the assumption of the inclined disc geometry. Our model allows the observed flux and spectral evolution of the system to be explained in a self-consistent way.
We report on the results of ~7.5 yr of the very high energy (10-600 GeV) observations of HESS J0632+057 with Fermi-Large Area Telescope. In the highest energy band, 200-600 GeV, the source is ...detected with the statistical significance ... at orbital phases 0.2-0.4 and 0.6-0.8 at which HESS J0632+057 is known to demonstrate enhanced emission in TeV energy band. The analysis did not reveal the emission from HESS J0632+057 at lower energies and different orbital phases. Using the upper limits on source's flux, we locate the break of the spectrum to >140...GeV and low-energy slope <1.6 (... statistical significance). (ProQuest: ... denotes formulae/symbols omitted.)
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.
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.
In the centre of our Galaxy lies a supermassive black hole, identified with the radio source Sagittarius A*. This black hole has an estimated mass of around 4 million solar masses. Although ...Sagittarius A* is quite dim in terms of total radiated energy, having a luminosity that is a factor of 10 super( 10) lower than its Eddington luminosity, there is now compelling evidence that this source was far brighter in the past. Evidence derived from the detection of reflected X-ray emission from the giant molecular clouds in the Galactic Centre region. However, the interpretation of the reflected emission spectra cannot be done correctly without detailed modelling of the reflection process. Attempts to do so can lead to an incorrect interpretation of the data. In this paper, we present the results of a Monte Carlo simulation code we developed in order to fully model the complex processes involved in the emerging reflection spectra. The simulated spectra can be compared to real data in order to derive model parameters and constrain the past activity of the black hole. In particular, we apply our code to observations of Sagittarius B2, in order to constrain the position and density of the cloud and the incident luminosity of the central source. The results of the code have been adapted to be used in XSPEC by a large community of astronomers.
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.
Context. For a decade now, evidence has accumulated that giant molecular clouds located within the central molecular zone of our Galaxy reflect X-rays coming from past outbursts of the Galactic ...supermassive black hole. However, the number of illuminating events as well as their ages and durations are still unresolved questions. Aims. We aim to reconstruct parts of the history of the supermassive black hole Sgr A★ by studying this reflection phenomenon in the molecular complex Sgr C and by determining the line-of-sight positions of its main bright substructures. Methods. Using observations made with the X-ray observatories XMM-Newton and Chandra and between 2000 and 2014, we investigated the variability of the reflected emission, which consists of a Fe Kα line at 6.4 keV and a Compton continuum. We carried out an imaging and a spectral analysis. We also used a Monte Carlo model of the reflected spectra to constrain the line-of-sight positions of the brightest clumps, and hence to assign an approximate date to the associated illuminating events. Results. We show that the Fe Kα emission from Sgr C exhibits significant variability in both space and time, which confirms its reflection origin. The most likely illuminating source is Sgr A★. On the one hand, we report two distinct variability timescales, as one clump undergoes a sudden rise and fall in about 2005, while two others vary smoothly throughout the whole 2000–2014 period. On the other hand, by fitting the Monte Carlo model to the data, we are able to place tight constraints on the 3D positions of the clumps. These two independent approaches provide a consistent picture of the past activity of Sgr A★, since the two slowly varying clumps are located on the same wavefront, while the third (rapidly varying) clump corresponds to a different wavefront, that is, to a different illuminating event. Conclusions. This work shows that Sgr A★ experienced at least two powerful outbursts in the past 300 yrs, and for the first time, we provide an estimation of their age. Extending this approach to other molecular complexes, such as Sgr A, will allow this two-event scenario to be tested further.
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.
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