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

Bult, Peter; Jaisawal, Gaurava K.; Güver, T.; Strohmayer, Tod E.; Altamirano, D.; Arzoumanian, Zaven; Ballantyne, D. R.; Chakrabarty, Deepto; Chenevez, J.; Gendreau, Keith C.; Guillot, Sebastien; Ludlam, R. M.

doi:10.3847/2041-8213/ab4ae1

Cited by 61 publications

(72 citation statements)

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“…Similar excesses have been seen in Type I bursts in many other sources observed with NICER, e.g. Aql X-1 (Keek et al 2018a), 4U 1820-30 (Keek et al 2018b) and SAX J1808.4-3658 (Bult et al 2019). This could be due to other extra components such as re-emission from the disc (corresponding to the extra black body, Keek et al 2018a) or enhanced accretion through Poynting-Robertson drag (corresponding to the change in persistent emission normalisation, Worpel et al 2013).…”

Section: Time Resolved Spectroscopysupporting

confidence: 81%

“…Additionally, helium fuelled bursts are also more common during the soft accretion state and the dip in apparent radius below the final value is more typical of soft state bursts (Kajava et al 2014). Further, bursts can reach the Eddington limit for helium even where accreted material is hydrogen rich, either by the hydrogen being burnt between bursts or the hydrogen rich atmosphere being blown off by the burst (Bult et al 2019;Galloway et al 2006). This would imply that the further distance estimates (blue curves in Figure 7) are more likely (12.8 +0.7 −0.6 kpc for i = 80 • ).…”

Section: Distance Estimate and Implicationsmentioning

confidence: 99%

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Discovery of thermonuclear (Type I) X-ray bursts in the X-ray binary Swift J1858.6–0814 observed with NICER and NuSTAR

Buisson

Altamirano

Bult

et al. 2020

Monthly Notices of the Royal Astronomical Society

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Swift J1858.6–0814 is a recently discovered X-ray binary notable for extremely strong variability (by factors >100 in soft X-rays) in its discovery state. We present the detection of five thermonuclear (Type I) X-ray bursts from Swift J1858.6–0814, implying that the compact object in the system is a neutron star. Some of the bursts show photospheric radius expansion, so their peak flux can be used to estimate the distance to the system. The peak luminosity, and hence distance, can depend on several system parameters; for the most likely values, a high inclination and a helium atmosphere, $D=12.8_{-0.6}^{+0.8}$ kpc, although systematic effects allow a conservative range of 9-18 kpc. Before one burst, we detect a QPO at 9.6 ± 0.5 mHz with a fractional rms amplitude of 2.2 ± 0.2% (0.5 − 10 keV), likely due to marginally stable burning of helium; similar oscillations may be present before the other bursts but the light curves are not long enough to allow their detection. We also search for burst oscillations but do not detect any, with an upper limit in the best case of 15% fractional amplitude (over 1 − 8 keV). Finally, we discuss the implications of the neutron star accretor and this distance on other inferences which have been made about the system. In particular, we find that Swift J1858.6–0814 was observed at super-Eddington luminosities at least during bright flares during the variable stage of its outburst.

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Section: Time Resolved Spectroscopysupporting

confidence: 81%

Section: Distance Estimate and Implicationsmentioning

confidence: 99%

Discovery of thermonuclear (Type I) X-ray bursts in the X-ray binary Swift J1858.6–0814 observed with NICER and NuSTAR

Buisson

Altamirano

Bult

et al. 2020

Monthly Notices of the Royal Astronomical Society

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“…Moreover, significant soft excesses with respect to the hardstate persistent emission were measured in the burst spectra of EXO 0748-676 (Asai & Dotani 2006), SAX J1808. 4-3658 (in 't Zand et al 2013;Bult et al 2019), and Aql X-1 (Keek et al 2018). These excesses suggest a temporary enhancement of the accretion rate induced by the burst, probably via Poynting-Robsertson drag of the accretion flow (Ballantyne & Everett 2005).…”

Section: Introductionmentioning

confidence: 93%

Burst-induced coronal cooling in GS 1826–24

Sánchez–Fernández

Kajava

Poutanen

et al. 2020

A&A

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Type I X-ray bursts in GS 1826-24, and in several other systems, may induce cooling of the hot inner accretion flow that surrounds the bursting neutron star. Given that GS 1826-24 remained persistently in the hard state over the period 2003-2008 and presented regular bursting properties, we stacked the spectra of the X-ray bursts detected by INTEGRAL (JEM-X and ISGRI) and XMM-Newton (RGS) during that period to study the effect of the burst photons on the properties of the Comptonizing medium. The extended energy range provided by these instruments allows the simultaneous observation of the burst and persistent emission spectra. We detect an overall change in the shape of the persistent emission spectrum in response to the burst photon shower. For the first time, we observe simultaneously a drop in the hard X-ray emission, together with a soft X-ray excess with respect to the burst blackbody emission. The hard X-ray drop can be explained by burst-induced coronal cooling, while the bulk of the soft X-ray excess can be described by fitting the burst emission with an atmosphere model, instead of a simple blackbody model. Traditionally, the persistent emission was assumed to be invariant during X-ray bursts, and more recently to change only in normalization but not in spectral shape; the observed change in the persistent emission level during X-ray bursts may thus trigger the revision of existing neutron star massradius constraints, as the derived values rely on the assumption that the persistent emission does not change during X-ray bursts. The traditional burst fitting technique leads to up to a 10% overestimation of the bolometric burst flux in GS 1826-24, which significantly hampers the comparisons of the KEPLER and MESA model against this 'textbook burster'.

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“…Additionally, S1 showed burst oscillations. Bult et al (2019) found that the pause, the dip between the X-ray burst's double peaks, and the onset of burst oscillations all occur at similar count rates, suggesting that the similar count rates are related to the Eddington limit of a hydrogen envelope.…”

Section: Pauses and Comparisonmentioning

confidence: 86%

“…what we observe as a pause is in reality a very short, weak peak of a double-peaked X-ray burst), or the pause is unrelated to the physical process that produces multi-peak X-ray bursts. Bult et al (2019) recently reported on a bright, Hefueled PRE Type-I X-ray burst from the accreting millisecond X-ray pulsar SAX J1808.4-3658. The light curve profile of the X-ray burst (hereafter S1) was complex: it showed a pause in the rise and a double peak unrelated to the PRE event.…”

Section: Pauses and Comparisonmentioning

confidence: 99%

Discovery of thermonuclear Type-I X-ray bursts from the X-ray binary MAXI J1807+132

Albayati

Altamirano

Jaisawal

et al. 2020

Monthly Notices of the Royal Astronomical Society

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MAXI J1807+132 is a low-mass X-ray binary (LMXB) first detected in outburst in 2017. Observations during the 2017 outburst did not allow for an unambiguous identification of the nature of the compact object. MAXI J1807+132 was detected in outburst again in 2019 and was monitored regularly with NICER. In this paper we report on five days of observations during which we detected three thermonuclear (Type-I) X-ray bursts, identifying the system as a neutron star LMXB. Time-resolved spectroscopy of the three Type-I bursts revealed typical characteristics expected for these phenomena. All three Type-I bursts show slow rises and long decays, indicative of mixed H/He fuel. We find no strong evidence that any of the Type-I bursts reached the Eddington Luminosity; however, under the assumption that the brightest X-ray burst underwent photospheric radius expansion, we estimate a <12.4 kpc upper limit for the distance. We searched for burst oscillations during the Type-I bursts from MAXI J1807+132 and found none ($<10\%$ amplitude upper limit at 95% confidence level). Finally, we found that the brightest Type-I burst shows a ∼ 1.6 sec pause during the rise. This pause is similar to one recently found with NICER in a bright Type-I burst from the accreting millisecond X-ray pulsar SAX J1808.4–3658. The fact that Type-I bursts from both sources can show this type of pause suggests that the origin of the pauses is independent of the composition of the burning fuel, the peak luminosity of the Type-I bursts, or whether the NS is an X-ray pulsar.

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

Cited by 61 publications

References 50 publications

Discovery of thermonuclear (Type I) X-ray bursts in the X-ray binary Swift J1858.6–0814 observed with NICER and NuSTAR

Discovery of thermonuclear (Type I) X-ray bursts in the X-ray binary Swift J1858.6–0814 observed with NICER and NuSTAR

Burst-induced coronal cooling in GS 1826–24

Discovery of thermonuclear Type-I X-ray bursts from the X-ray binary MAXI J1807+132

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