Discovery of 442 Hz Pulsations from an X-Ray Source in the Globular Cluster NGC 6440

Gavriil, F. P.; Strohmayer, Tod E.; Swank, J. H.; Markwardt, C. B.

doi:10.1086/523758

Cited by 35 publications

(45 citation statements)

References 15 publications

(24 reference statements)

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“…We searched for, but did not detect, oscillations at 410 Hz in SAX J1748.9À2021 (as claimed by Kaaret et al 2003); this source has subsequently exhibited intermittent persistent pulsations at 442 Hz (Gavriil et al 2007;Altamirano et al 2008), strongly suggesting the earlier detection was spurious. We also made a targeted search around 1122 Hz for the bursts from XTE J1739À285, without success (cf.…”

Section: Thermonuclear X-ray Bursts Observed By Rxtementioning

confidence: 77%

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Thermonuclear (Type I) X‐Ray Bursts Observed by theRossi X‐Ray Timing Explorer

Galloway

Muno

Hartman

et al. 2008

Astrophysical Journal Supplement Series, The

674

1,183

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We have assembled a sample of 1187 thermonuclear (type I) X-ray bursts from observations of 48 accreting neutron stars by the Rossi X-ray Timing Explorer, spanning more than 10 years. The sample contains examples of two of the three theoretical ignition regimes (confirmed via comparisons with numerical models) and likely examples of the third. We present a detailed analysis of the variation of the burst profiles, energetics, recurrence times, presence of photospheric radius expansion, and presence of burst oscillations, as a function of accretion rate. We estimated the distance for 35 sources exhibiting radius-expansion bursts, and found that the peak flux of such bursts varies typically by 13%. We classified sources into two main groups based on the burst properties: (1) both long and short bursts (indicating mixed H/ He accretion), and (2) consistently short bursts (primarily He accretion), and we calculated the mean burst rate as a function of accretion rate for the two groups. The decrease in burst rate observed at >0:06Ṁ Edd (k2 ; 10 37 ergs s À1) is associated with a transition in the persistent spectral state and (as has been suggested previously) may be related to the increasing role of steady He burning. We found many examples of bursts with recurrence times <30 minutes, including burst triplets and even quadruplets. We describe the oscillation amplitudes for 13 of the 16 burst oscillation sources, as well as the stages and properties of the bursts in which the oscillations are detected. The burst properties are correlated with the burst oscillation frequency; sources spinning at <400 Hz generally have consistently short bursts, while the more rapidly spinning systems have both long and short bursts. This correlation suggests either that shear-mediated mixing dominates the burst properties, or alternatively that the nature of the mass donor (and hence the evolutionary history) has an influence on the long-term spin evolution.

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Section: Thermonuclear X-ray Bursts Observed By Rxtementioning

confidence: 77%

“…A subsequent outburst was detected in PCA scans of the Galactic bulge region on 2005 May 12Y16 ( Markwardt & Swank 2005a). Intermittent persistent pulsations at 442 Hz were detected during the 2001 and 2005 outbursts (Gavriil et al 2007;Altamirano et al 2008). The pulsations exhibited Doppler shifts from an 8.7 hr orbit.…”

Section: A29 1a 1744à361mentioning

confidence: 99%

Thermonuclear (Type I) X‐Ray Bursts Observed by theRossi X‐Ray Timing Explorer

Galloway

Muno

Hartman

et al. 2008

Astrophysical Journal Supplement Series, The

674

1,183

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“…It is instructive to note that a deviation from a quadratic function was not apparent in the first 24 yrof data, which suggests that a very long timescale periodicity (or quasi-periodicity) might still be present even in binaries where a constant P ḃ is observed over baselines of a few decades. The globular cluster source SAX J1748.9-2021 isan intermittent AMXP (Gavriil et al 2007;Altamirano et al 2008;Patruno et al 2009a;Sanna et al 2016), and it has been observed in outburst five times. Its companion star is likely to be an ∼0.8 M e star close to the turnoff mass of the globular cluster NGC 6440, although much smaller masses down to 0.1 M e cannot be excluded (Altamirano et al 2008).…”

Section: Other Lmxbsmentioning

confidence: 99%

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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“…For this sub-class of X-ray systems, generally the coherent NS pulsation is persistent during the source outbursts, with the exception of three AMXPs (Aql X-1, HETE 1900.1-2455 and SAX J1748.9-2021) that showed intermittent pulsations whose origin is still uncertain (Kaaret et al 2006, Messenger & Patruno 2015Galloway et al 2007Gavriil et al 2007. In this work, we focus on the AMXP SAX J1748.9-2021, discovered by Beppo-SAX during the 1998 outburst, located in the globular cluster NGC 6440 (in 't Zand et al 1999a) at a distance of ∼ 8.5 kpc and 0.6 kpc above the Galactic plane (Martins et al 1980;Ortolani et al 1994;Kuulkers et al 2003;Valenti et al 2007).…”

Section: Introductionmentioning

confidence: 99%

Broad-band spectral analysis of the accreting millisecond X-ray pulsar SAX J1748.9−2021

Pintore

Sanna

Salvo

et al. 2016

Mon. Not. R. Astron. Soc.

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We analyzed a 115 ks XMM-Newton observation and the stacking of 8 days of INTE-GRAL observations, taken during the raise of the 2015 outburst of the accreting millisecond X-ray pulsar SAX J1748.9-2021. The source showed numerous type-I burst episodes during the XMM-Newton observation, and for this reason we studied separately the persistent and burst epochs. We described the persistent emission with a combination of two soft thermal components, a cold thermal Comptonization component (∼2 keV) and an additional hard X-ray emission described by a power-law (Γ ∼ 2.3). The continuum components can be associated with an accretion disc, the neutron star (NS) surface and a thermal Comptonization emission coming out of an optically thick plasma region, while the origin of the high energy tail is still under debate. In addition, a number of broad (σ = 0.1-0.4 keV) emission features likely associated to reflection processes have been observed in the XMM-Newton data. The estimated 1.0-50 keV unabsorbed luminosity of the source is ∼5×10 37 erg s −1 , about 25% of the Eddington limit assuming a 1.4 M NS. We suggest that the spectral properties of SAX J1748.9-2021 are consistent with a soft state, differently from many other accreting X-ray millisecond pulsars which are usually found in the hard state. Moreover, none of the observed type-I burst reached the Eddington luminosity. Assuming that the burst ignition and emission are produced above the whole NS surface, we estimate a neutron star radius of ∼ 7 − 8 km, consistent with previous results.

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Discovery of 442 Hz Pulsations from an X-Ray Source in the Globular Cluster NGC 6440

Cited by 35 publications

References 15 publications

Thermonuclear (Type I) X‐Ray Bursts Observed by theRossi X‐Ray Timing Explorer

Thermonuclear (Type I) X‐Ray Bursts Observed by theRossi X‐Ray Timing Explorer

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

Broad-band spectral analysis of the accreting millisecond X-ray pulsar SAX J1748.9−2021

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