Broad-band X-ray spectra and timing of the accretion-powered millisecond pulsar Swift J1756.9$-$2508 during its 2018 and 2019 outbursts

Abstract

The accreting millisecond X-ray pulsar Swift J1756.9$-$2508 went into outburst in April 2018 and June 2019, 8.7 yr after the previous activity period. We investigated the temporal, timing and spectral properties of these two outbursts using data from NICER, XMM-Newton, NuSTAR, INTEGRAL, Swift and Insight-HXMT. The two outbursts exhibited similar broad-band spectra and X-ray pulse profiles. For the first time, we report the detection of the pulsed emission up to $\sim 100$ keV observed by Insight-HXMT during the 2018 outburst. We also found the pulsation up to $\sim 60$ keV observed by NICER and NuSTAR during the 2019 outburst. We performed a coherent timing analysis combining the data from two outbursts. The binary system is well described by a constant orbital period over a time span of $\sim 12$ years. The time-averaged broad-band spectra are well fitted by an absorbed thermal Comptonization model in a slab geometry with the electron temperature $k{T}_{\mathrm{e}}=40$-50 keV, Thomson optical depth $\tau \sim 1.3$, blackbody seed photon temperature $k{T}_{\mathrm{bb},\mathrm{seed}}\sim$0.7-0.8 keV and hydrogen column density of $N_{\mathrm{H}}\sim 4.2\times 10^{22}$ cm${}^{-2}$. We searched the available data for type-I (thermonuclear) X-ray bursts, but found none, which is unsurprising given the estimated low peak accretion rate ($\approx 0.05$ of the Eddington rate) and generally low expected burst rates for hydrogen-poor fuel. Based on the history of four outbursts to date, we estimate the long-term average accretion rate at roughly $5\times 10^{-12}{M}_{\odot }{\mathrm{yr}}^{-1}$ for an assumed distance of 8 kpc. The expected mass transfer rate driven by gravitational radiation in the binary implies the source can be no closer than 4 kpc.

arXiv commentAccepted for publication in A&A

References in corpus (55)

• The European Photon Imaging Camera on XMM-Newton: The MOS Cameras
• ISGRI: the INTEGRAL Soft Gamma-Ray Imager
• Thermonuclear (type-I) X-ray bursts observed by the Rossi X-ray Timing Explorer
• Swings between rotation and accretion power in a millisecond binary pulsar
• The Two-Phase Pair Corona Model for Active Galactic Nuclei and X-ray Binaries: How to Obtain Exact Solutions
• The INTEGRAL Science Data Centre (ISDC)
• The INTEGRAL/IBIS Scientific Data Analysis
• The long-term evolution of the spin, pulse shape, and orbit of the accretion-powered millisecond pulsar SAX J1808.4-3658
• Six new candidate ultracompact X-ray binaries
• Discovery of a High-Latitude Accreting Millisecond Pulsar in an Ultracompact Binary
• White Dwarf Donors in Ultracompact Binaries: The Stellar Structure of Finite Entropy Objects
• Discovery of the accretion-powered millisecond X-ray pulsar IGR J00291+5934
• The Multi-INstrument Burst ARchive (MINBAR)
• Helium-rich thermonuclear bursts and the distance to the accretion-powered millisecond pulsar SAX J1808.4-3658
• A Brown Dwarf Companion for the Accreting Millisecond Pulsar SAX J1808.4-3658
• INTEGRAL and RXTE observations of accreting millisecond pulsar IGR J00291+5934 in outburst
• Models of Type I X-Ray Bursts in 4U 1820-30
• Models of Type I X-ray Bursts from GS 1826-24: A Probe of rp-Process Hydrogen Burning
• Thermonuclear X-ray bursts
• Physics of accretion in the millisecond pulsar XTE J1751-305
• The INTEGRAL IBIS/ISGRI System Point Spread Function and Source Location Accuracy
• A decade of timing an accretion-powered millisecond pulsar: The continuing spin down and orbital evolution of SAX J1808.4-3658
• INTEGRAL spectroscopy of the accreting millisecond pulsar XTE J1807-294 in outburst
• Accreting Millisecond X-Ray Pulsars
• Discovery of the Millisecond X-Ray Pulsar HETE J1900.1-2455
• The X-ray spectrum of the newly discovered accreting millisecond pulsar IGR J17511-3057
• X-ray emission and absorption features during an energetic thermonuclear X-ray burst from IGR J17062-6143
• Intermediate long X-ray bursts from the ultra-compact binary source SLX 1737-282
• Discovery of a 205.89 Hz accreting-millisecond X-ray pulsar in the globular cluster NGC 6440
• A Double Outburst from IGR J00291+5934: Implications for Accretion Disk Instability Theory
• Discovery of 105 Hz coherent pulsations in the ultracompact binary IGR J16597-3704
• Accretion-powered millisecond pulsars
• The long-term evolution of the accreting millisecond X-ray pulsar Swift J1756.9-2508
• XMM-Newton observation of the 5.25 ms transient millisecond pulsar XTE J1807-294 in outburst
• Spectral and timing properties of the accreting X-ray millisecond pulsar IGR J17511-3057
• X-ray Reflection and An Exceptionally Long Thermonuclear Helium Burst from IGR J17062-6143
• SAX J1808.4-3658: high resolution spectroscopy and decrease of pulsed fraction at low energies
• Discovery of a new accreting millisecond X-ray pulsar in the globular cluster NGC 2808
• NICER Discovers the Ultracompact Orbit of the Accreting Millisecond Pulsar IGR J17062-6143
• Mass transfer during low mass X-ray transient decays
• NuSTAR and NICER reveal IGR J17591-2342 as a new accreting millisecond X-ray pulsar
• The 2015 outburst of the accretion-powered pulsar IGR J00291+5934: INTEGRAL and Swift observations
• Spectral and timing properties of the accreting X-ray millisecond pulsar IGR J17498-2921
• Timing Calibration of the NuSTAR X-ray Telescope
• NICER Discovery of Millisecond X-ray Pulsations and an Ultracompact Orbit in IGR J17494-3030
• INTEGRAL, Swift, and RXTE observations of the 518 Hz accreting transient pulsar Swift J1749.4-2807
• SWIFT J1756.9-2508: spectral and timing properties of its 2018 outburst
• The transitional millisecond pulsar IGR J18245-2452 during its 2013 outburst at X-rays and soft gamma-rays
• High-energy characteristics of the accretion-powered millisecond pulsar IGR J17591-2342 during its 2018 outburst
• Timing and spectral properties of the accreting millisecond pulsar SWIFT J1756.9-2508
• IGR J17451-3022: a dipping and eclipsing low mass X-ray binary
• Mixed H/He bursts in SAX J1748.9-2021 during the spectral change of its 2015 outburst
• The INTEGRAL view of the pulsating hard X-ray sky: from accreting and transitional millisecond pulsars to rotation-powered pulsars and magnetars
• On the 2018 outburst of the accreting millisecond X-ray pulsar Swift J1756.9-2508 as seen with NICER
• Evidence of a non-conservative mass transfer in the ultra-compact X-ray source XB 1916-053

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