Demonstrating the likely neutron star nature of five M31 globular cluster sources with<i>Swift</i>-NuSTAR spectroscopy

Nearby galaxy surveys have long classified X-ray binaries (XRBs) by the mass category of their donor stars (high-mass and low-mass). The NuSTAR observatory, which provides imaging data at E > 10 keV, has enabled the classification of extragalactic XRBs by their compact object type: neutron star (NS) or black hole (BH). We analyzed NuSTAR/Chandra/XMM-Newton observations from a NuSTAR-selected sample of 12 galaxies within 5 Mpc having stellar masses (M ⋆ ) 10 7−11 M ⊙ and star formation rates (SFR) ≈ 0.01 − 15 M ⊙ yr −1 . We detect 128 NuSTAR sources to a sensitivity of ≈ 10 38 erg s −1 . Using NuSTAR color-intensity and color-color diagrams we classify 43 of these sources as candidate NS and 47 as candidate BH. We further subdivide BH by accretion states (soft, intermediate, and hard) and NS by weak (Z/Atoll) and strong (accreting pulsar) magnetic field. Using 8 normal (Milky Way-type) galaxies in the sample, we confirm the relation between SFR and galaxy X-ray point source luminosity in the 4 − 25 and 12 − 25 keV energy bands. We also constrain galaxy X-ray point source luminosity using the relation L X = αM ⋆ + βSFR, finding agreement with previous work. The XLF of all sources in the 4 − 25 and 12 − 25 keV energy bands matches with the α = 1.6 slope for high-mass XRBs. We find that NS XLFs suggest a decline beginning at the Eddington limit for a 1.4 M ⊙ NS, whereas the BH fraction shows an approximate monotonic increase in the 4 − 25 and 12 − 25 keV energy bands. We calculate the overall ratio of BH to NS to be ≈ 1 for 4 − 25 keV and ≈ 2 for 12 − 25 keV.

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“…Maccarone et al (2016) demonstrated the likely NS nature of 5 M31 GCs, contrary to the previous BH candidate classification for 2 of these…”

contrasting

confidence: 75%

“…also ULXs), which turn over more quickly than BH (e.g. Maccarone et al 2016). There are ∼ 10 NuSTAR sources that overlap the isolated Z/Atoll sources (not identified as ULXs based on L X ) and are undetected in HR2; however, the upper limits constrain them to the NS region.…”

Section: Nustar Xrb Diagnostic Diagramsmentioning

confidence: 99%

Black Holes and Neutron Stars in Nearby Galaxies: Insights from NuSTAR

Vulic

Hornschemeier

Wik

et al. 2018

ApJ

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“…NuSTAR's harder energy bandpass constrains and classifies the nature of the resolved sources and accretion states for both BH and NS systems (Wik et al 2014b;Maccarone et al 2016). This is only the second deep NuSTAR survey of "resolved" compact object populations in a starforming galaxy outside of the MW following our first study of the nearby starburst NGC 253.…”

Section: Discussionmentioning

confidence: 97%

A HARD X-RAY STUDY OF THE NORMAL STAR-FORMING GALAXY M83 WITH NuSTAR

Yukita

Hornschemeier

Lehmer

et al. 2016

ApJ

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We present the results from sensitive, multi-epoch NuSTAR observations of the late-type star-forming galaxy M83 (d = 4.6 Mpc). This is the first investigation to spatially resolve the hard (E 10 > keV) X-ray emission of this galaxy. The nuclear region and ∼20 off-nuclear point sources, including a previously discovered ultraluminous X-ray source, are detected in our NuSTAR observations. The X-ray hardnesses and luminosities of the majority of the point sources are consistent with hard X-ray sources resolved in the starburst galaxy NGC 253. We infer that the hard X-ray emission is most likely dominated by intermediate accretion state black hole binaries and neutron star low-mass X-ray binaries (Z-sources). We construct the X-ray binary luminosity function (XLF) in the NuSTAR band for an extragalactic environment for the first time. The M83 XLF has a steeper XLF than the X-ray binary XLF in NGC 253, which is consistent with previous measurements by Chandra at softer X-ray energies. The NuSTAR integrated galaxy spectrum of M83 drops quickly above 10 keV, which is also seen in the starburst galaxies NGC 253, NGC 3310, and NGC 3256. The NuSTAR observations constrain any active galactic nucleus (AGN) to be either highly obscured or to have an extremely low luminosity of 10 38 erg s −1 (10-30 keV), implying that it is emitting at a very low Eddington ratio. An X-ray point source that is consistent with the location of the nuclear star cluster with an X-ray luminosity of a few times 10 38 erg s −1 may be a low-luminosity AGN but is more consistent with being an X-ray binary.

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“…Migliari et al 2004;Miller-Jones et al 2010;Migliari 2011;Fender & Muñoz-Darias 2016;Gusinskaia et al 2017). Winds, on the contrary, are typically not seen in the hard state (Ponti et al 2012;Neilsen 2013), although see Xu et al (2018) and Maccarone et al (2016) for possible counterexamples.…”

Section: Introductionmentioning

confidence: 99%

Chandra reveals a possible ultrafast outflow in the super-Eddington Be/X-ray binary Swift J0243.6+6124

Eijnden

Degenaar

Schulz

et al. 2019

Monthly Notices of the Royal Astronomical Society

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Accretion at super-Eddington rates is expected to be accompanied by strong outflows. Such outflows are observed in Galactic X-ray binaries and extragalactic Ultra-luminous X-ray sources (ULXs). However, due to their large source distances, ULX outflows are challenging to detect and study in detail. Galactic neutron stars accreting from a Be-star companion at super-Eddington rates show many similarities to ULX pulsars, and therefore offer an alternative approach to study outflows in this accretion regime. Here, we present Chandra high-resolution spectroscopy of such a super-Eddington accreting neutron star, Swift J0243.6+6124, to search for wind outflow signatures during the peak of its 2017/2018 giant outburst. We detect narrow emission features at rest from Ne, Mg, S, Si, and Fe. In addition, we detect a collection of absorption features which can be identified in two ways: either as all Fe transitions at rest (with a possible contribution from Mg), or a combination of three blue-shifted Ne and Mg lines at ∼ 0.22c, while the remaining lines are at rest. The second scenario would imply an outflow with a velocity similar to those seen in ULXs, including the ULX pulsar NGC 300 ULX-1. This result would also imply that Swift J0243.6+6124 launches both a jet, detected in radio and reported previously, and an ultra-fast wind outflow simultaneously at super-Eddington accretion rates.

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Demonstrating the likely neutron star nature of five M31 globular cluster sources withSwift-NuSTAR spectroscopy

Cited by 20 publications

References 128 publications

Black Holes and Neutron Stars in Nearby Galaxies: Insights from NuSTAR

Black Holes and Neutron Stars in Nearby Galaxies: Insights from NuSTAR

A HARD X-RAY STUDY OF THE NORMAL STAR-FORMING GALAXY M83 WITH NuSTAR

Chandra reveals a possible ultrafast outflow in the super-Eddington Be/X-ray binary Swift J0243.6+6124

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