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.
Abstract
LMC P3 is the most luminous gamma-ray binary discovered to date and the first detected outside of the Galaxy, with an orbital period of 10.301 d. We report on optical spectroscopic ...observations undertaken with the Southern African Large Telescope using the High Resolution Spectrograph. We find the binary is slightly eccentric, e = 0.40 ± 0.07, and place the time of periastron at HJD 2457412.13 ± 0.29. Stellar model fitting finds an effective temperature of $T_ {\rm eff} = 36351 \pm 53$ K. The mass function, f = 0.0010 ± 0.0004 M$\odot$, favours a neutron star compact object. The phases of superior and inferior conjunctions are 0.98 and 0.24, respectively (where phase 0 is at the Fermi-LAT maximum), close to the reported maxima in the GeV and TeV light curves.
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.
ABSTRACT
We report on results of spectropolarimetry of the afterglow of the long gamma-ray burst GRB 191221B, obtained with SALT/RSS and VLT/FORS2, as well as photometry from two telescopes in the ...MASTER Global Robotic Network, at the MASTER-SAAO (South Africa) and MASTER-OAFA (Argentina) stations. Prompt optical emission was detected by MASTER-SAAO 38 s after the alert, which dimmed from a magnitude (white-light) of ∼10–16.2 mag over a period of ∼10 ks, followed by a plateau phase lasting ∼10 ks and then a decline to ∼18 mag after 80 ks. The light curve shows complex structure, with four or five distinct breaks in the power-law decline rate. SALT/RSS linear spectropolarimetry of the afterglow began ∼2.9 h after the burst, during the early part of the plateau phase of the light curve. Absorption lines seen at ∼6010 and 5490 Å are identified with the Mg ii 2799 Å line from the host galaxy at z = 1.15 and an intervening system located at z = 0.96. The mean linear polarization measured over 3400–8000 Å was ∼1.5 per cent and the mean equatorial position angle (θ) was ∼65°. VLT/FORS2 spectropolarimetry was obtained ∼10 h post-burst, during a period of slow decline (α = −0.44), and the polarization was measured to be p = 1.2 per cent and θ = 60°. Two observations with the MeerKAT radio telescope, taken 30 and 444 d after the GRB trigger, detected radio emission from the host galaxy only. We interpret the light curve and polarization of this long GRB in terms of a slow-cooling forward shock.
ABSTRACT
PSR B1259-63 is a gamma-ray binary system with a radio pulsar orbiting an O9.5Ve star, LS 2883, with a period of ${\sim} 3.4$ yr. Close to the periastron the system is detected at all ...wavelengths, from radio to the TeV energies. The emission in this time period is believed to originate from the interaction of LS 2883 and pulsar’s outflows. The observations of four periastra passages taken in 2010–2021 show strong correlation of the radio and X-ray light curves with two peaks just before and after the periastron. The observations of the latest 2021 periastron passage reveal the presence of the 3rd X-ray peak and subsequent disappearance of radio/X-ray flux correlation. In this paper, we present the results of our optical, radio, and X-ray observational campaigns on PSR B1259-63 performed in 2021 accompanied with the analysis of the publicly available GeV Fermi/LAT data. We compare the properties of different periastron passages, discuss the obtained results and show that they can be explained in terms of the 2-zone emission model proposed by us previously.
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
The Fermi-LAT (Large Area Telescope) has detected more than 3000 sources in the GeV γ-ray regime. The majority are extragalactic and these sources are dominated by blazars. However, ...∼28 per cent of the sources in Fermi 3LAC are listed as blazar candidates of uncertain type (BCU). Increasing the number of classified Fermi-LAT sources is important for improving our understanding of extragalactic γ-ray sources and can be used to search for new very high energy sources. We report on the optical spectroscopy of seven selected unclassified BCU sources during 2014 and 2015 undertaken using the SAAO 1.9-m and Southern African Large Telescope (SALT). Based on the identified spectral lines, we have classified three of the sources as FSRQs and the remaining four as BL Lac objects, determining the redshift for four sources.
ABSTRACT
In this paper three-dimensional relativistic hydrodynamic simulations of AGN jets are presented to investigate the FR I/FR II dichotomy. Three simulations are presented which illustrates the ...difference in morphology for high/low Lorentz factor injection as well as a stratified background medium. Lorentz factors of 10 and 1.0014 were used for the high and low Lorentz factor cases, respectively. The hydrodynamic simulations show a division in the morphology of jets based on their initial injection luminosity. An additional simulation was set-up to investigate the evolution of the low Lorentz factor jet if the mass injection was lowered after a certain time. A synchrotron emission model was applied to these simulations to reproduce intensity maps at radio frequencies (1.5 GHz) which were compared to the observed emission structures of FR I/FR II radio galaxies. The effect of Doppler boosting on the intensity maps was also investigated for different polar angles. The intensity maps of both the high and low Lorentz factor cases reproduced emission structures that resemble those of FR II type radio galaxies with a dominant cocoon region containing time-dependent hotspots and filaments. An FR I like structure was, however, produced for the low Lorentz factor case if the mass injection rate was lowered after a set time period.
ABSTRACT
In this work, we present a multiwavelength study of the blazar 1ES 1218+304 using near simultaneous observations over 10 yr during the period 2008 September 1 to 2018 August 31 (MJD ...54710–58361). We have analysed data from Swift-UVOT, Swift-XRT, and Fermi-LAT to study the long term behaviour of 1ES 1218+304 in different energy bands over the last decade. We have also used the archival data from OVRO, MAXI, and Swift-BAT available during the above period. The near simultaneous data on 1ES 1218+304 suggest that the long term multiwavelength emission from the source is steady and does not show any significant change in the source activity. The optical/UV fluxes are found to be dominated by the host galaxy emission and can be modelled using the pegase code. However, the time averaged X-ray and γ-ray emissions from the source are reproduced using a single zone leptonic model with log-parabolic distribution for the radiating particles. The intrinsic very high energy γ-ray emission during a low activity state of the source is broadly consistent with the predictions of the leptonic model for blazars. We have investigated the physical properties of the jet and the mass of the supermassive black hole at the centre of the host galaxy using long term X-ray observations from the Swift-XRT which is in agreement with the value derived using blackbody approximation of the host galaxy. We also discuss the extreme nature of the source on the basis of X-ray and γ-ray observations.
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