Super-Eddington accretion on to the neutron star NGC 7793 P13: Broad-band X-ray spectroscopy and ultraluminous X-ray sources

Walton, D. J.; Fürst, Felix; Harrison, F.; Stern, Daniel; Bachetti, Matteo; Barret, D.; Brightman, Murray; Fabian, A. C.; Middleton, M.; Ptak, A.; Tao, Lian

doi:10.1093/mnras/stx2650

Cited by 69 publications

(84 citation statements)

References 81 publications

(154 reference statements)

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“…To place these spectra in context, we show in Figure 8 the spectrum of ULX7 which was obtained from a joint XMM-Newton and NuSTAR observing campaign in 2019 (M. Brightman et al 2020, in preparation). The spectrum of ULX7 is similar to that of other ULXs with good quality broadband spectra (e.g., Walton et al 2018), consisting of two disk-like components with different temperatures. ULX7 also has a similar flux and luminosity as M51 XT-1 at its peak, therefore serving as a good comparison.…”

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confidence: 56%

Swift Monitoring of M51: A 38 day Superorbital Period for the Pulsar ULX7 and a New Transient Ultraluminous X-Ray Source

Brightman

Earnshaw

Fürst

et al. 2020

ApJ

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We present the results from a monitoring campaign made with the Neil Gehrels Swift Observatory of the M51 galaxies, which contain several variable ultraluminous X-ray sources (ULXs). The ongoing campaign started in 2018 May, and we report here on ∼1.5 yr of observations. The campaign, which consists of 106 observations, has a typical cadence of 3-6 days, and has the goal of determining the long-term X-ray variability of the ULXs. Two of the most variable sources were ULX7 and ULX8, both of which are known to be powered by neutron stars that are exceeding their isotropic Eddington luminosities by factors of up to 100. This is further evidence that neutron-starpowered ULXs are the most variable. Our two main results are, first, that ULX7 exhibits a periodic flux modulation with a period of 38 days varying over a magnitude and a half in flux from peak to trough. Since the orbital period of the system is known to be 2 days, the modulation is superorbital, which is a near-ubiquitous property of ULX pulsars. Second, we identify a new transient ULX, M51 XT-1, the onset of which occurred during our campaign, reaching a peak luminosity of ∼10 40 erg s −1 , before gradually fading over the next ∼200 days until it slipped below the detection limit of our observations. Combined with the high-quality Swift/X-ray Telescope lightcurve of the transient, serendipitous observations made with Chandra and XMM-Newton provide insights into the onset and evolution of a likely super-Eddington event. Unified Astronomy Thesaurus concepts: X-ray point sources (1270); X-ray transient sources (1852); X-ray photometry (1820); X-ray bright point (1812); X-ray active galactic nuclei (2035); Transient sources (1851); Light curves (918); Galaxy nuclei (609); Active galactic nuclei (16)

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confidence: 56%

Swift Monitoring of M51: A 38 day Superorbital Period for the Pulsar ULX7 and a New Transient Ultraluminous X-Ray Source

Brightman

Earnshaw

Fürst

et al. 2020

ApJ

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“…The spectral properties of the four pulsar ULXs are similar to typical ULXs, although pulsar ULXs show a further excess at high energy whose origin may be associated to the accretion column above the NS surface. However, even though less robustly, indications of such an excess are observed also in other non-pulsating ULXs, suggesting that the ULX population can host a larger number of neutron stars than previously expected (Walton et al 2018a).…”

Section: Introductionmentioning

confidence: 63%

X-ray properties of two transient ULX candidates in galaxy NGC 7090

O’Brien

Osborne

et al. 2019

Monthly Notices of the Royal Astronomical Society

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We report the X-ray data analysis of two transient ultraluminous X-ray sources (ULXs, hereafter X1 and X2) located in the nearby galaxy NGC 7090. While they were not detected in the 2004 XMM-Newton and 2005 Chandra observations, their 0.3-10 keV X-ray luminosities reached > 3 × 10 39 erg s −1 in later XMM-Newton or Swift observations, showing increases in flux by a factor of > 80 and > 300 for X1 and X2, respectively. X1 showed indications of spectral variability: at the highest luminosity, its X-ray spectra can be fitted with a powerlaw (Γ = 1.55 ± 0.15), or a multicolour disc model with T in = 2.07 +0.30 −0.23 keV; the X-ray spectrum became softer (Γ = 2.67 +0.69 −0.64 ), or cooler (T in = 0.64 +0.28 −0.17 keV) at lower luminosity. No strong evidence for spectral variability was found for X2. Its X-ray spectra can be fitted with a simple powerlaw model (Γ = 1.61 +0.55 −0.50 ), or a multicolour disc model (1.69 +1.17 −0.48 keV). A possible optical counterpart for X1 is revealed in HST imaging. No optical variability is found, indicating that the optical radiation may be dominated by the companion star. Future X-ray and optical observations are necessary to determine the true nature of the compact object.

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“…We note that J2150−0551 is unlikely to be one of ultraluminous X-ray pulsars, whose luminosities have been detected 85 to be up to 10 41 erg s −1 . The ultrasoft X-ray spectra (photon index ≥4.8) of J2150−0551 are in contrast with the very hard spectra (photo index <2.0 below 5 keV) of four known ultraluminous X-ray pulsars 85,86 .…”

Section: The Off-center Imbh Explanationmentioning

confidence: 79%

A luminous X-ray outburst from an intermediate-mass black hole in an off-centre star cluster

Lin¹,

Strader²,

Carrasco³

et al. 2018

Nat Astron

134

100

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A unique signature for the presence of massive black holes in very dense stellar regions is occasional giant-amplitude outbursts of multiwavelength radiation from tidal disruption and subsequent accretion of stars that make a close approach to the black holes 1 . Previous strong tidal disruption event (TDE) candidates were all associated with the centers of largely isolated galaxies 2-6 . Here we report the discovery of a luminous X-ray outburst from a massive star cluster at a projected distance of 12.5 kpc from the center of a large lenticular galaxy. The luminosity peaked at ∼10 43 erg s −1 and decayed systematically over 10 years, approximately following a trend that supports the identification of the event as a TDE. The X-ray spectra were all very soft, with emission confined to be 3.0 keV, and could be described with a standard thermal disk. The disk cooled significantly as the luminosity decreased, a key thermal-state signature often observed in accreting stellar-mass black holes. This thermal-state signature, coupled with very high luminosities, ultrasoft X-ray spectra and the characteristic powerlaw evolution of the light curve, provides strong evidence that the source contains an intermediate-mass black hole (IMBH) with a mass of a few ten thousand solar mass. This event demonstrates that one of the most effective means to detect IMBHs is through X-ray flares from TDEs in star clusters.We discovered the X-ray source 3XMM J215022.4−055108 (referred to as J2150−0551 hereafter) in our project of searching for TDEs from the XMM-Newton X-ray source catalog. The source was serendipitously detected in 2006-2009 in two XMM-Newton observa-tions and one Chandra observation of a field in the second Canadian Network for Observational Cosmology Field Galaxy Redshift Survey 7 . It was still detected, but with much lower X-ray fluxes, in our followup Swift observation in 2014 and Chandra observation in 2016. Figure 1 shows the Hubble Space Telescope (HST) ACS F775W image around the field of J2150−0551 taken in 2003. The source lies at an angular offset of 11.6 arcsec from the center of the barred lenticular galaxy 6dFGS gJ215022.2-055059 (referred to as Gal1 hereafter) and is spatially coincident with a faint optical object. Gal1 is at a redshift of z = 0.055 or a luminosity distance of DL = 247 Mpc (for H0 = 70 km s −1 Mpc −1 , ΩM = 0.3, ΩΛ = 0.7). The chance probability for J2150−0551 to be within 11.6 arcsec from the center of a bright galaxy like Gal1 is very small (0.01%, see SI), strongly supporting the association of J2150−0551 with Gal1.The fits to the X-ray spectra with a standard thermal thin disk are shown in the lower panels in Figure 2 (see also Table 1), and the inferred long-term evolution of the bolometric disk luminosity is plotted in the upper panel. The dependence of the bolometric disk luminosity on the apparent maximum disk temperature is plotted in Figure 3. The most striking feature is that the disk luminosity approximately scales with the temperature as L ∝ T 4 (i.e., a constant inner disk radi...

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Super-Eddington accretion on to the neutron star NGC 7793 P13: Broad-band X-ray spectroscopy and ultraluminous X-ray sources

Cited by 69 publications

References 81 publications

Swift Monitoring of M51: A 38 day Superorbital Period for the Pulsar ULX7 and a New Transient Ultraluminous X-Ray Source

Swift Monitoring of M51: A 38 day Superorbital Period for the Pulsar ULX7 and a New Transient Ultraluminous X-Ray Source

X-ray properties of two transient ULX candidates in galaxy NGC 7090

A luminous X-ray outburst from an intermediate-mass black hole in an off-centre star cluster

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