The 2015 outburst of the accretion-powered pulsar IGR J00291+5934: INTEGRAL andSwiftobservations

Abstract

The pulsar IGR J00291+5934 is the fastest-known accretion-powered X-ray pulsar, discovered during a transient outburst in 2004. In this paper, we report on INTEGRAL and Swift observations during the 2015 outburst, which lasts for ∼ 25 d. The source has not been observed in outburst since 2008, suggesting that the long-term accretion rate has decreased by a factor of two since discovery. The averaged broad-band (0.1 -250 keV) persistent spectrum in 2015 is well described by a thermal Comptonization model with a column density of N H ≈ 4 × 10 21 cm −2 , a plasma temperature of kT e ≈ 50 keV, and a Thomson optical depth of τ T ≈ 1. Pulsations at the known spin period of the source are detected in the INTEGRAL data up to the ∼ 150 keV energy band. We also report on the discovery of the first thermonuclear burst observed from IGR J00291+5934, which lasts around 7 min and occurs at a persistent emission level corresponding to roughly 1.6% of the Eddington accretion rate. The properties of the burst suggest it is powered primarily by helium ignited at a depth of y ign ≈ 1.5 × 10 9 g cm −2 following the exhaustion by steady burning of the accreted hydrogen. The Swift/BAT data from the first ∼ 20 s of the burst provide indications of a photospheric radius expansion phase. Assuming this is the case, we infer a source distance of d = 4.2 ± 0.5 kpc.

XMM-Newton and NICER Measurement of the Rms Spectrum of the Millihertz Quasiperiodic Oscillations in the Neutron-star Low-mass X-Ray Binary 4U 1636–53

“…The possibility that this 8 mHz QPO is connected to marginally stable nuclear burning on the neutron star surface can neither be excluded nor more solidly confirmed. The reason is that there is only one type I X-ray burst ever detected in this source, which occurred about three days before this XMM-Newton observation (De Falco et al 2017). The rms amplitude vs. energy relation derived in this work, and the work of Strohmayer et al (2018) may help us decide whether this 8 mHz QPO originates from nuclear burning.…”

Modelling spin-up episodes in accreting millisecond X-ray pulsars

“…The luminosity for the 2015 outburst is inferred from data given in Tudor et al (2017), who did not include comptonization or bolometric corrections, by adopting the correction factor used by Falanga et al (2005) for the 2004 burst. Note however that the peak and mean values for both the 2004 and 2015 bursts differ between De Falco et al (2017) and Falanga et al (2005); Tudor et al (2017), respectively: the former authors suggest a higher (∼ 40%) flux (see Table 2 therein).…”

“…Some notes are as follows. Assuming the 2015 burst was of a pure helium nature, De Falco et al (2017) constrained the distance of J00291 to be 4.2 ± 0.5 kpc. Falanga et al (2005) report a peak luminosity of 6.3×10 36 erg s −1 , though assumed d = 5 kpc [see also Andersson, Jones & Ho (2014)].…”

“…1; though cf. De Falco et al (2017)]. As such, unless we seriously underestimate the accretion rate Ṁ (cf.…”

Search for gravitational waves from five low mass X-ray binaries in the second Advanced LIGO observing run with an improved hidden Markov model

“…It was discovered in a 14 d outburst in 2004 [51,63]. Searches in the RXTE All Sky Monitor data indicate marginal evidence for two prior outbursts during 1998 and 2001 [64,65]. A double outburst was observed in 2008, lasting 9 d in August and 15 d in September [66,67].…”