Evidence of coupling between the thermal and nonthermal emission in the gamma-ray binary LS I +61 303

Paredes-Fortuny, X.; Ribó, M.; Bosch‐Ramon, V.; Casares, J.; Fors, O.; Núñez, J.

doi:10.1051/0004-6361/201425361

Cited by 26 publications

(36 citation statements)

References 24 publications

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“…These timescales are usually interpreted as the orbital and superorbital periods of the system (see, however, Massi & Jaron (2013); Massi, Jaron & Hovatta (2015)). The detection of similar periods has been recently reported in the optical (Zamanov et al 2013;Paredes-Fortuny et al 2015), X-ray (Chernyakova et al 2012;Li, Torres & Zhang 2014) and gamma-ray bands (Ackermann et al 2013;Jaron & Massi 2014).…”

Section: Introductionsupporting

confidence: 79%

Study of orbital and superorbital variability of LSI +61° 303 with X-ray data

Chernyakova

Babyk

Malyshev

et al. 2017

Monthly Notices of the Royal Astronomical Society

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LSI +61 • 303 is one of the few X-ray binaries with a Be star companion from which radio, X-rays and high-energy gamma-ray (GeV and TeV) emission have been observed. The nature of the high energy activity of the system is not yet fully understood, but it is widely believed that it is generated due to the interaction of the relativistic electrons leaving the compact object with the photons and non-relativistic wind of the Be star. The superorbital variability of the system has been observed in the radio, optical and X-ray domains and could be due to the cyclic change of the Be star disk size. In this paper we systematically review all publicly available data from Suzaku, XMM-Newton, Chandra and Swift observatories in order to measure the absorption profile of the circumstellar Be disk as a function of orbital and superorbital phases. We also discuss short-term variability of the system, found during the analysis and its implications for the understanding of the physical processes in this system.

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Section: Introductionsupporting

confidence: 79%

Study of orbital and superorbital variability of LSI +61° 303 with X-ray data

Chernyakova

Babyk

Malyshev

et al. 2017

Monthly Notices of the Royal Astronomical Society

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“…Moreover, Paredes-Fortuny et al (2015) discovered that the orbital phase shift also affects the variations in the equivalent width (EW) of the Hα emission line from LS I +61 • 303. The orbital phase shift (Sect.…”

Section: Discussionmentioning

confidence: 99%

Origin of the long-term modulation of radio emission of LS I +61°303

Massi

Torricelli‐Ciamponi

2016

A&A

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Context. One of the most unusual aspects of the X-ray binary LS I +61 • 303 is that at each orbit (P 1 = 26.4960 ± 0.0028 d) one radio outburst occurs whose amplitude is modulated with P long , a long-term period of more than 4 yr. It is still not clear whether the compact object of the system or the companion Be star is responsible for the long-term modulation. Aims. We study here the stability of P long . Such a stability is expected if P long is due to periodic (P 2 ) Doppler boosting of periodic (P 1 ) ejections from the accreting compact object of the system. On the contrary it is not expected if P long is related to variations in the mass loss of the companion Be star. Methods. We built a database of 36.8 yr of radio observations of LS I +61 • 303 covering more than 8 long-term cycles. We performed timing and correlation analysis. We also compared the results of the analyses with the theoretical predictions for a synchrotron emitting precessing (P 2 ) jet periodically (P 1 ) refilled with relativistic electrons.Results. In addition to the two dominant features at P 1 and P 2 , the timing analysis gives a feature at P long = 1628 ± 48 days. The determined value of P long agrees with the beat of the two dominant features, i.e. P beat = 1/(ν 1 − ν 2 ) = 1626 ± 68 d. Lomb-Scargle results of radio data and model data compare very well. The correlation coefficient of the radio data oscillates at multiples of P beat , as does the correlation coefficient of the model data. Conclusions. Cycles in varying Be stars change in length and disappear after 2-3 cycles following the well-studied case of the binary system ζ Tau. On the contrary, in LS I +61 • 303 the long-term period is quite stable and repeats itself over the available 8 cycles. The long-term modulation in LS I +61 • 303 accurately reflects the beat of periodical Doppler boosting (induced by precession) with the periodicity of the ejecta. The peak of the long-term modulation occurs at the coincidence of the maximum number of ejected particles with the maximum Doppler boosting of their emission; this coincidence occurs every 1 ν 1 −ν 2 and creates the long-term modulation observed in LS I +61 • 303.

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“…The first method finds the two physical periods directly, and the second method deals with the result of the beating. In addition to radio data, the periods P 1 and P 2 were also directly determined in the LombScargle spectrum of data at apastron for Fermi-LAT data (Jaron & Massi 2014) and X-ray data (D'Aì et al 2016), whereas the long-term modulation (Zamanov et al 2013) and orbital shift (Paredes-Fortuny et al 2015) were found in the equivalent width EW of the Hα emission line.…”

Section: Beating Between Orbit (P 1 ) and Precession (P 2 )mentioning

confidence: 99%

Understanding the periodicities in radio and GeV emission from LS I +61°303

Jaron

Torricelli‐Ciamponi

Massi

2016

A&A

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Context. One possible scenario to explain the emission from the stellar binary system LS I +61• 303 is that the observed flux is emitted by precessing jets powered by accretion. Accretion models predict two ejections along the eccentric orbit of LS I +61• 303: one major ejection at periastron and a second, lower ejection towards apastron. Our GeV gamma-ray observations show two peaks along the orbit (orbital period P 1 ) but reveal that at apastron the emission is also affected by a second periodicity, P 2 . Strong radio outbursts also occur at apastron, which are affected by both periodicities (i.e. P 1 and P 2 ), and radio observations show that P 2 is the precession of the radio jet. Consistently, a long-term modulation, equal to the beating of P 1 and P 2 , affects both radio and gamma-ray emission at apastron but it does not affect gamma-ray emission at periastron. Aims. If there are two ejections, why does the one at periastron not produce a radio outburst there? Is the lack of a periastron radio outburst somehow related to the lack of P 2 from the periastron gamma-ray emission? Methods. We develop a physical model in which relativistic electrons are ejected twice along the orbit. The ejecta form a conical jet that is precessing with P 2 . The jet radiates in the radio band by the synchrotron process and the jet radiates in the GeV energy band by the external inverse Compton and synchrotron self-Compton processes. We compare the output fluxes of our physical model with two available large archives: Owens Valley Radio Observatory (OVRO) radio and Fermi Large Area Telescope (LAT) GeV observations, the two databases overlapping for five years. Results. The larger ejection around periastron passage results in a slower jet, and severe inverse Compton losses result in the jet also being short. While large gamma-ray emission is produced, there is only negligible radio emission. Our results are that the periastron jet has a length of 3.0 × 10 6 r s and a velocity β ∼ 0.006, whereas the jet at apastron has a length of 6.3 × 10 7 r s and β ∼ 0.5. Conclusions. In the accretion scenario the observed periodicities can be explained if the observed flux is the intrinsic flux, which is a function of P 1 , times the Doppler factor, a function of β cos( f (P 2 )). At periastron, the Doppler factor is scarcely influenced by P 2 because of the low β. At apastron the larger β gives rise to a significant Doppler factor with noticeable variations induced by jet precession.

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Evidence of coupling between the thermal and nonthermal emission in the gamma-ray binary LS I +61 303

Cited by 26 publications

References 24 publications

Study of orbital and superorbital variability of LSI +61° 303 with X-ray data

Study of orbital and superorbital variability of LSI +61° 303 with X-ray data

Origin of the long-term modulation of radio emission of LS I +61°303

Understanding the periodicities in radio and GeV emission from LS I +61°303

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