Discovery of Coherent Millisecond X-Ray Pulsations in Aquila X-1

Casella, P.; Altamirano, D.; Patruno, A.; Wijnands, Rudy; Klis, M.B.M. van der

doi:10.1086/528982

Cited by 163 publications

(197 citation statements)

References 35 publications

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“…Burgay et al 2003), but, despite the eleven additional systems discovered since (e.g. Galloway et al 2002;Casella et al 2008), we have not obtained a positive result yet.…”

Section: Introductioncontrasting

confidence: 64%

Search for pulsations at high radio frequencies from accreting millisecond X-ray pulsars in quiescence

Iacolina

Burgay

Burderi

et al. 2010

A&A

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Context. It is commonly believed that millisecond radio pulsars have been spun up by transfer of matter and angular momentum from a low-mass companion during an X-ray active mass transfer phase. A subclass of low-mass X-ray binaries is that of the accreting millisecond X-ray pulsars, transient systems that show periods of X-ray quiescence during which radio emission could switch on. Aims. The aim of this work is to search for millisecond pulsations from three accreting millisecond X-ray pulsars, XTE J1751−305, XTE J1814−338, and SAX J1808.4−3658, observed during their quiescent X-ray phases at high radio frequencies (5 ÷ 8 GHz) in order to overcome the problem of the free-free absorption due to the matter engulfing the system. A positive result would provide definite proof of the recycling model, providing the direct link between the progenitors and their evolutionary products. Methods. The data analysis methodology has been chosen on the basis of the precise knowledge of orbital and spin parameters from X-ray observations. It is subdivided in three steps: we corrected the time series for the effects of (I) the dispersion due to interstellar medium and (II) of the orbital motions, and finally (III) folded modulo the spin period to increase the signal-to-noise ratio. Results. No radio signal with spin and orbital characteristics matching those of the X-ray sources has been found in our search, down to very low flux density upper limits. Conclusions. We analysed several mechanisms that could have prevented the detection of the signal, concluding that the low luminosity of the sources and the geometric factor are the most likely reasons for this negative result.

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“…Burgay et al 2003), but, despite the eleven additional systems discovered since (e.g. Galloway et al 2002;Casella et al 2008), we have not obtained a positive result yet.…”

Section: Introductioncontrasting

confidence: 64%

Search for pulsations at high radio frequencies from accreting millisecond X-ray pulsars in quiescence

Iacolina

Burgay

Burderi

et al. 2010

A&A

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“…Aql X-1 is in outburst very often, the neutron star spin frequency is known (νs ≃ 550 Hz; Casella et al 2008), and a distance has been inferred from X-ray burst studies (D ≃5 kpc; Rutledge et al 2001). Therefore, the source may serve as a promising asset to advance our understanding of shallow heating in neutron star crusts, as it provides the opportunity to measure crust cooling curves after different outbursts.…”

Section: Future Prospects For Crust Cooling Studiesmentioning

confidence: 99%

Constraining the properties of neutron star crusts with the transient low-mass X-ray binary Aql X-1

Waterhouse

Degenaar

Wijnands

et al. 2016

Mon. Not. R. Astron. Soc.

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Aql X-1 is a prolific transient neutron star low-mass X-ray binary that exhibits an accretion outburst approximately once every year. Whether the thermal X-rays detected in intervening quiescent episodes are the result of cooling of the neutron star or due to continued low-level accretion remains unclear. In this work we use Swift data obtained after the long and bright 2011 and 2013 outbursts, as well as the short and faint 2015 outburst, to investigate the hypothesis that cooling of the accretion-heated neutron star crust dominates the quiescent thermal emission in Aql X-1. We demonstrate that the X-ray light curves and measured neutron star surface temperatures are consistent with the expectations of the crust cooling paradigm. By using a thermal evolution code, we find that ≃1.2 − 3.2 MeV nucleon −1 of shallow heat release describes the observational data well, depending on the assumed mass-accretion rate and temperature of the stellar core. We find no evidence for varying strengths of this shallow heating after different outbursts, but this could be due to limitations of the data. We argue that monitoring Aql X-1 for up to ≃1 year after future outbursts can be a powerful tool to break model degeneracies and solve open questions about the magnitude, depth and origin of shallow heating in neutron star crusts.

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“…Since 1998, fourteen such systems have been discovered, with orbital periods in the range of 40 min to 19 h and spin frequencies from 1.7 to 5.4 ms (Wijnands & van der Klis 1998;Chakrabarty & Morgan 1998;Markwardt et al 2002;Galloway et al 2002;Campana et al 2003;Strohmayer et al 2003;Galloway et al 2005;Kaaret et al 2006;Krimm et al 2007;Casella et al 2008;Altamirano et al 2008;Altamirano et al 2010;Papitto et al 2010;Markwardt & Strohmayer 2010;Altamirano et al 2011;Papitto et al 2011). Since they have been spun up by accretion (see, e.g., Falanga et al 2005), their initial mass should have increased by at least 0.1-0.2 M compared to the canonical neutron star mass (e.g., Thorsett & Chakrabarty 1999).…”

Section: Introductionmentioning

confidence: 99%

A search for the near-infrared counterpart of the eclipsing millisecond X-ray pulsar Swift J1749.4–2807

D’Avanzo

Campana

Muñoz-Darias

et al. 2011

A&A

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Context. Swift J1749.4-2807 is a transient accreting millisecond X-ray pulsars and the first to display X-ray eclipses. It therefore holds a strong potential for accurate mass measurements in a low-mass X-ray binary system. Aims. Determining the companion star's radial velocity would make it possible to fully resolve the system and to accurately measure the mass of the neutron star based on dynamical measurements. Unfortunately, no optical or near infrared (NIR) counterpart has been identified to date for this system, whether in outburst or in quiescence.Methods. We performed a photometric study of the field of Swift J1749.4-2807 during quiescence to search for a variable counterpart. The source direction lies on the Galactic plane, making any search for its optical/NIR counterpart challenging. To minimize the effects of field crowding and interstellar extinction, we carried out our observations using the adaptive optics NIR imager NACO mounted at the ESO Very Large Telescope (VLT).Results. From the analysis of public Swift X-ray data obtained during outburst, we derived the most precise (1.6 radius) position for this source. Due to the extreme stellar crowding of the field, 41 sources are detected in our VLT images within the X-ray error circle, with some of them possibly showing variability consistent with the expectations. Conclusions. We carried out the first deep imaging campaign devoted to the search for the quiescent NIR counterpart of Swift J1749.4-2807. Our results allow us to provide constraints on the nature of the companion star of this system. Furthermore, they suggest that future phase-resolved NIR observations (performed with large-aperture telescopes and adaptive optics) covering the full orbital period of the system are likely to identify the quiescent counterpart of Swift J1749.4-2807, through measuring its orbital variability, opening the possibility of dynamical studies of this unique source.

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Discovery of Coherent Millisecond X-Ray Pulsations in Aquila X-1

Cited by 163 publications

References 35 publications

Search for pulsations at high radio frequencies from accreting millisecond X-ray pulsars in quiescence

Search for pulsations at high radio frequencies from accreting millisecond X-ray pulsars in quiescence

Constraining the properties of neutron star crusts with the transient low-mass X-ray binary Aql X-1

A search for the near-infrared counterpart of the eclipsing millisecond X-ray pulsar Swift J1749.4–2807

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