On the timing properties of SAX J1808.4−3658 during its 2015 outburst

Sanna, A.; Salvo, T. Di; Burderi, L.; Riggio, A.; Pintore, Fabio; Gambino, A. F.; Iaria, R.; Tailo, M.; Scarano, F.; Papitto, A.

doi:10.1093/mnras/stx1588

Cited by 48 publications

(106 citation statements)

References 74 publications

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“…SAX J1808.4−3658 was detected in outburst with the SwiftBurst Alert Telescope (BAT) on 2015 April 9(MJD 57121; Sanna et al 2015). During the closest previous SwiftXRT observation, which occurred on April 3(MJD 57195), SAX J1808.4−3658 was still in quiescence (Campana et al 2015).…”

Section: X-ray Light Curvementioning

confidence: 98%

Radio Pulse Search and X-Ray Monitoring of SAX J1808.4−3658: What Causes Its Orbital Evolution?

Patruno

Jaodand

Kuiper

et al. 2017

ApJ

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The accreting millisecond X-ray pulsar SAX J1808.4−3658 shows a peculiar orbital evolution that proceeds at a very fast pace. It is important to identify the underlying mechanism responsible for this behavior because it can help to understand how this system evolves and which physical processes (such asmass loss or spin-orbit coupling) are occurring in the binary. It has also been suggested that, when in quiescence, SAX J1808.4−3658 turns on as a radio pulsar, a circumstance that might provide a link between accreting millisecond pulsars and black-widow (BW) radio pulsars. In this work, we report the results of a deep radio pulsation search at 2 GHz using the Green Bank Telescope in 2014 August and an X-ray study of the 2015 outburst with Chandra, SwiftXRT, and INTEGRAL. In quiescence, we detect no radio pulsationsand place the strongest limit to date on the pulsed radio flux density of any accreting millisecond pulsar. We also find that the orbit of SAX J1808.4−3658 continues evolving at a fast pace. We compare the orbital evolution of SAX J1808.4−3658 to that of several other accreting and nonaccreting binaries, including BWs, redbacks, cataclysmic variables, black holes, and neutron stars in lowmass X-ray binaries. We discuss two possible scenarios: either the neutron star has a large moment of inertia and is ablating the donor, generating massloss with an efficiency of 40%, or the donor star has a strong magnetic field of at least 1 kG and is undergoing quasi-cyclic variations due to spin-orbit coupling.

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Section: X-ray Light Curvementioning

confidence: 98%

Radio Pulse Search and X-Ray Monitoring of SAX J1808.4−3658: What Causes Its Orbital Evolution?

Patruno

Jaodand

Kuiper

et al. 2017

ApJ

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“…In each of the eight outbursts from SAX J1808 that occurred between 1996 and 2015, at least one X-ray burst has been detected (in't Zand et al 2001;Bult & van der Klis 2015;Patruno et al 2017;Sanna et al 2017). The majority of these bursts showed burst oscillations * Einstein Fellow (Bilous & Watts 2018) and were observed near peak luminosity of their respective outbursts, when the accretion rate was ≈ (3−5)×10 −10 M yr −1 (Bult & van der Klis 2015).…”

Section: Introductionmentioning

confidence: 99%

A NICER Thermonuclear Burst from the Millisecond X-Ray Pulsar SAX J1808.4–3658

Bult

Jaisawal

Güver

et al. 2019

ApJL

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The Neutron Star Interior Composition Explorer (NICER) has extensively monitored the August 2019 outburst of the 401 Hz millisecond X-ray pulsar SAX J1808.4-3658. In this Letter, we report on the detection of a bright helium-fueled Type I X-ray burst. With a bolometric peak flux of (2.3 ± 0.1) × 10 −7 erg s −1 cm −2 , this was the brightest X-ray burst among all bursting sources observed with NICER to date. The burst shows a remarkable two-stage evolution in flux, emission lines at 1.0 keV and 6.7 keV, and burst oscillations at the known pulsar spin frequency, with ≈ 4% fractional sinusoidal amplitude. We interpret the burst flux evolution as the detection of the local Eddington limits associated with the hydrogen and helium layers of the neutron star envelope. The emission lines are likely associated with Fe, due to reprocessing of the burst emission in the accretion disk.

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“…the chemical or thermal evolution of the companion star, as well as any calculation of the convective and radiative zones of it, therefore these results have to be considered with a reasonable dose of caution. These arguments might explain why S4 and S9 do not give evidence for a non-conservative mass-transfer although a non-conservative evolution has been hypothesized (di Sanna et al 2016Sanna et al , 2017b with an independent argument, in order to justify the large value of the orbital period derivative measured for both systems 6 .…”

Section: Discussionmentioning

confidence: 99%

“…The duration of the outbursts can also be quite long, as in the case of HETE J1900.1-2455 (in outburst for ∼ 10 years, Šimon 2018) and MAXI J0911-655 (which is in an ongoing outburst since 2016, Sanna et al 2017c). In order to explain the strong orbital expansion of the AMXPs SAX J1808.4-3658 (di Burderi et al 2009;Sanna et al 2017a) and SAX J1748.9-2021 it was proposed that only a fraction of the mass transferred from the secondary is effectively accreted onto the neutron star (see also Tailo et al 2018). Matter ejections have been also suggested to explain the low, average, masstransfer rate derived for XTE J1814-338 ( Van et al 2018).…”

Section: Introductionmentioning

confidence: 99%

“…A short-term variability induced by tidal dissipation and magnetic activity in the companion, which is required to be at least partially nondegenerate, convective, and magnetically active(Applegate & Shaham 1994;Hartman et al 2008), has been alternatively invoked to explain the observed orbital period expansion, although this possibility appears quite unlikely(Sanna et al 2017a) Article number, page 8 of 12Marino, A.: Indications of non-conservative mass-transfer in AMXPs…”

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confidence: 99%

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Indications of non-conservative mass transfer in AMXPs

Marino

Salvo

Burderi

et al. 2019

A&A

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Context. Since the discovery of the first Accreting Millisecond X-ray Pulsar SAX J1808.4-3658 in 1998, the family of these sources kept growing on. Currently, it counts 22 members. All AMXPs are transients with usually very long quiescence periods, implying that mass accretion rate in these systems is quite low and not constant. Moreover, for at least three sources, a non-conservative evolution was also proposed. Aims. Our purpose is to study the long term averaged mass-accretion rates in all the Accreting Millisecond X-ray Pulsars discovered so far, to investigate a non-conservative mass-transfer scenario. Methods. We calculated the expected mass-transfer rate under the hypothesis of a conservative evolution based on their orbital periods and on the (minimum) mass of the secondary (as derived from the mass function), driven by gravitational radiation and/or magnetic braking. Using this theoretical mass-transfer, we determined the expected accretion luminosity of the systems. Thus, we achieved the lower limit to the distance of the sources by comparing the computed theoretical luminosity and the observed flux averaged over a time period of 20 years. Then, the lower limit to the distance of the sources has been compared to the value of the distance reported in literature to evaluate how reasonable is the hypothesis of a conservative mass-transfer. Results. Based on a sample of 18 sources, we found strong evidences of a non-conservative mass-transfer for five sources, for which the estimated distance lower limits are higher than their known distances. We also report hints for mass outflows in other six sources. The discrepancy can be fixed under the hypothesis of a non-conservative mass-transfer in which a fraction of the mass transferred onto the compact object is swept away from the system, likely due to the (rotating magnetic dipole) radiation pressure of the pulsar.

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On the timing properties of SAX J1808.4−3658 during its 2015 outburst

Cited by 48 publications

References 74 publications

Radio Pulse Search and X-Ray Monitoring of SAX J1808.4−3658: What Causes Its Orbital Evolution?

Radio Pulse Search and X-Ray Monitoring of SAX J1808.4−3658: What Causes Its Orbital Evolution?

A NICER Thermonuclear Burst from the Millisecond X-Ray Pulsar SAX J1808.4–3658

Indications of non-conservative mass transfer in AMXPs

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