Multiband Studies of the Optical Periodic Modulation in the X-Ray Binary Sax J1808.4–3658 During Its Quiescence and 2008 Outburst

Wang, Zhongxiang; Breton, R. P.; Heinke, C. O.; Deloye, Christopher J.; Zhong, Jing

doi:10.1088/0004-637x/765/2/151

Cited by 44 publications

(52 citation statements)

References 57 publications

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“…The same might have occurred even some years later: our observations in 2014 were made only 327 days before the 2015 outburst took place, thus possibly explaining why a strong flaring activity was detected, together with the brightening of the source with respect to the level of normal quiescence (D'Avanzo et al 2007). A similar behaviour was also stated in Wang et al (2013) for the AMXP SAX J1808.4-3658, for which a brightening of the accretion disc emission 1.5 months before the onset of a bright outburst was observed.…”

Section: Discussionsupporting

confidence: 73%

The puzzling case of the accreting millisecond X-ray pulsar IGR J00291+5934: flaring optical emission during quiescence

Baglio

Campana

D’Avanzo

et al. 2017

A&A

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We present an optical (gri) study during quiescence of the accreting millisecond X-ray pulsar IGR J00291+5934 performed with the 10.4m Gran Telescopio Canarias (GTC) in August 2014. Although the source was in quiescence at the time of our observations, it showed a strong optical flaring activity, more pronounced at higher frequencies (i.e. the g band). After subtracting the flares, we tentatively recovered a sinusoidal modulation at the system orbital period in all bands, even when a significant phase shift with respect to an irradiated star, typical of accreting millisecond X-ray pulsars, was detected. We conclude that the observed flaring could be a manifestation of the presence of an accretion disc in the system. The observed light curve variability could be explained by the presence of a superhump, which might be another proof of the formation of an accretion disc. In particular, the disc at the time of our observations was probably preparing the new outburst of the source, which occurred a few months later, in 2015.

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Section: Discussionsupporting

confidence: 73%

The puzzling case of the accreting millisecond X-ray pulsar IGR J00291+5934: flaring optical emission during quiescence

Baglio

Campana

D’Avanzo

et al. 2017

A&A

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“…variability is also reminiscent of the quiescent optical light curves of other AMXPs (Homer et al 2001;Campana et al 2004;D'Avanzo et al 2007;Deloye et al 2008;Wang et al 2009Wang et al , 2013 and recycled millisecond pulsars with irradiated companions (see, e.g., Breton et al 2013).…”

Section: Optical Light Curvesmentioning

confidence: 89%

“…We have performed the light curve fitting using a Markov chain Monte Carlo (MCMC) procedure similar to that reported in Wang et al (2013). We use a Gaussian prior on the distance of 8.0(M ns /1.4 M ) with 20% uncertainty, which corresponds to the value derived from type I bursts by Strohmayer et al (2003).…”

Section: Fitting With Icarusmentioning

confidence: 99%

The long-term evolution of the X-ray pulsar XTE J1814-338: A receding jet contribution to the quiescent optical emission?

Baglio

D’Avanzo

Muñoz-Darias

et al. 2013

A&A

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Aims. We present a study of the quiescent optical counterpart of the accreting millisecond X-ray pulsar XTE J1814-338 that is aimed at unveiling the different components, which contribute to the quiescent optical emission of the system. Methods. We carried out multiband (BVR) orbital phase-resolved photometry of the system using the ESO Very Large Telescope (VLT) that is equipped with the FORS2 camera, covering about 70% of the 4.3 hour orbital period. Results. The optical light curves are consistent with a sinusoidal variability that are modulated with an orbital period with a semiamplitude of 0.5−0.7 mag. They show evidence of a strongly irradiated companion star, which agrees with previous findings for this system. However, the observed colours cannot be accounted for by the companion star alone, suggesting the presence of an accretion disc during quiescence. The system seems to be fainter in all analysed bands compared to previous observations. The R band light curve displays a possible phase offset with respect to the B and V band. Through a combined fit of the multi-band light curve performed with a Markov chain Monte Carlo technique, we derive constraints on the companion star, disc fluxes, system distance, and companion star mass. Conclusions. The irradiation luminosity required to account for the observed day-side temperature of the companion star is consistent with the spin-down luminosity of a millisecond radio pulsar. Compared to our data with previous observations, which were collected over 5 years, the flux decrease and spectral evolution of the observed quiescent optical emission cannot be satisfactorily explained with the combined contribution of an irradiated companion star and of an accretion disc alone. The observed progressive flux decrease as the system gets bluer could be due to a continuum component that evolves towards a lower, bluer spectrum. While most of the continuum component is likely due to the disc, we do not expect it to become bluer in quiescence. Hence, we hypothesize that an additional component, such as synchrotron emission from a jet was significantly contributing in the data obtained earlier during quiescence and then progressively fading or moving its break frequency towards longer wavelengths.

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“…The low temperature of SAX J1808.4−3658 suggests it has a higher mass than that of other quiescent NSs, with the latter presumably near the typical mass of 1.4M e . However, current evidence indicates that SAX J1808.4−3658 does not have a particularly high mass, with M NS <1.6 M e (at ∼2σ; see Wang et al 2013). In comparison, the relatively high and stable temperature of X7 Figure 6.…”

Section: X7mentioning

confidence: 92%

Neutron Star Mass–radius Constraints of the Quiescent Low-Mass X-Ray Binaries X7 and X5 in the Globular Cluster 47 Tuc

Bogdanov

Heinke

Özel

et al. 2016

ApJ

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We present Chandra/ACIS-S subarray observations of the quiescent neutron star (NS) low-mass X-ray binaries X7 and X5 in the globular cluster 47Tuc. The large reduction in photon pile-up compared to previous deep exposures enables a substantial improvement in the spectroscopic determination of the NS radius and mass of these NSs. Modeling the thermal emission from the NS surface with a non-magnetized hydrogen atmosphere and accounting for numerous sources of uncertainties, we obtain for the NS in X7 a radius of = -+ R 11.1 0.7 0.8 km for an assumed stellar mass of M=1.4 M e (68% confidence level). We argue, based on astrophysical grounds, that the presence of a He atmosphere is unlikely for this source. Due to the excision of data affected by eclipses and variable absorption, the quiescent low-mass X-ray binary X5 provides less stringent constraints, leading to a radius of = -+ R 9.6 1.1 0.9 km, assuming a hydrogen atmosphere and a mass of M=1.4 M e . When combined with all existing spectroscopic radius measurements from other quiescent low-mass X-ray binaries and Type I X-ray bursts, these measurements strongly favor radii in the 9.9-11.2 km range for a ∼1.5 M e NS and point to a dense matter equation of state that is somewhat softer than the nucleonic ones that are consistent with laboratory experiments at low densities.

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Multiband Studies of the Optical Periodic Modulation in the X-Ray Binary Sax J1808.4–3658 During Its Quiescence and 2008 Outburst

Cited by 44 publications

References 57 publications

The puzzling case of the accreting millisecond X-ray pulsar IGR J00291+5934: flaring optical emission during quiescence

The puzzling case of the accreting millisecond X-ray pulsar IGR J00291+5934: flaring optical emission during quiescence

The long-term evolution of the X-ray pulsar XTE J1814-338: A receding jet contribution to the quiescent optical emission?

Neutron Star Mass–radius Constraints of the Quiescent Low-Mass X-Ray Binaries X7 and X5 in the Globular Cluster 47 Tuc

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