A Model for Spectral States and Their Transition in Cyg X-1

ABSTRACT Using archival data from Suzaku, XMM–Newton, and NuSTAR, nine representative ultra-luminous X-ray sources (ULXs) in nearby galaxies were studied. Their X-ray spectra were all reproduced with a multicolour disc emission model plus its Comptonization. However, the spectral shapes of individual sources changed systematically depending on the luminosity, and defined three typical spectral states. These states differ either in the ratio between the Comptonizing electron temperature and the innermost disc temperature, or in the product of Compton y-parameter and fraction of the Comptonized disc photons. The luminosity range at which a particular state emerges was found to scatter by a factor of up to 16 among the eight ULXs. By further assuming that the spectral state is uniquely determined by the Eddington ratio, the sample ULXs are inferred to exhibit a similar scatter in their masses. This gives a model-independent support to the interpretation of ULXs in terms of relatively massive black holes. None of the spectra showed noticeable local structures. Especially, no Fe K-shell absorption/emission lines were detected, with upper limits of 30–40 eV in equivalent width from the brightest three among the sample: NGC 1313 X-1, Holmberg IX X-1, and IC 342 X-1. These properties disfavour ordinary mass accretion from a massive companion star, and suggest direct Bondi–Hoyle accretion from dense parts of the interstellar medium.

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The nature of the soft excess and spectral variability in the Seyfert 1 galaxy Zw 229.015

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz1988 ◽

2019 ◽

Vol 488 (4) ◽

pp. 4831-4842 ◽

Cited By ~ 3

Author(s):

S Tripathi ◽

S G H Waddell ◽

L C Gallo ◽

W F Welsh ◽

C-Y Chiang

Keyword(s):

Power Law ◽

Temporal Variability ◽

Accretion Disc ◽

Spectral Variability ◽

Systematic Analysis ◽

X Ray ◽

Soft State ◽

Hard State ◽

Partial Covering ◽

Spectral States

ABSTRACT We have carried out a systematic analysis of the nearby (z = 0.0279) active galaxy Zw 229.015 using multi-epoch, multi-instrument, and deep pointed observations with XMM–Newton, Suzaku, Swift,and NuSTAR. Spectral and temporal variability are examined in detail on both the long (weeks-to-years) and short (hours) time-scales. A deep Suzaku observation of the source shows two distinct spectral states; a bright-soft state and a dim-hard state in which changes in the power-law component account for the differences. Partial covering, blurred reflection, and soft Comptonization models describe the X-ray spectra comparably well, but the smooth, rather featureless, spectrum may be favouring the soft Comptonization scenario. Moreover, independent of the spectral model, the observed spectral variability is ascribed to the changes in the power-law continuum only and do not require changes in the properties of the absorber or blurred reflector incorporated in the other scenarios. The multi-epoch observations between 2009 and 2018 can be described in similar fashion. This could be understood if the primary emission is originating at a large distance from a standard accretion disc or if the disc is optically thin and geometrically thick as recently proposed for Zw 229.015. Our investigation shows that Zw 229.015 behaves similar to sources like Akn 120 and Mrk 530 that exhibit a strong soft excess, but weak Compton hump and Fe Kα emission.

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On the complex disc-corona interactions in the soft spectral states of soft X-ray transients

Monthly Notices of the Royal Astronomical Society ◽

10.1111/j.1365-2966.2001.04698.x ◽

2001 ◽

Vol 326 (4) ◽

pp. 1367-1380 ◽

Cited By ~ 20

Author(s):

Piotr T. Życki ◽

Chris Done ◽

David A. Smith

Keyword(s):

X Ray ◽

Spectral States

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Mixed H/He bursts in SAX J1748.9–2021 during the spectral change of its 2015 outburst

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833857 ◽

2018 ◽

Vol 620 ◽

pp. A114 ◽

Cited By ~ 2

Author(s):

Z. Li ◽

V. De Falco ◽

M. Falanga ◽

E. Bozzo ◽

L. Kuiper ◽

...

Keyword(s):

Plasma Temperature ◽

Compact Object ◽

Recurrence Time ◽

Type I ◽

Slab Geometry ◽

X Ray ◽

Soft State ◽

Hard State ◽

Best Fit ◽

Spectral States

SAX J1748.9–2021 is a transiently accreting X-ray millisecond pulsar. It is also known as an X-ray burster source discovered by Beppo-SAX. We analyzed the persistent emission and type-I X-ray burst properties during its 2015 outburst. The source changed from hard to soft state within half day. We modeled the broadband spectra of the persistent emission in the (1–250) keV energy band for both spectral states using the quasi-simultaneous INTEGRAL and Swift data. The broadband spectra are well fitted by an absorbed thermal Componization model, COMPPS, in a slab geometry. The best-fits for the two states indicate significantly different plasma temperature of 18 and 5 keV and the Thomson optical depths of three and four, respectively. In total, 56 type-I X-ray bursts were observed during the 2015 outburst, of which 26 detected by INTEGRAL in the hard state, 25 by XMM-Newton in the soft state, and five by Swift in both states. As the object transited from the hard to the soft state, the recurrence time for X-ray bursts decreased from ≈2 to ≈1 h. The relation between the recurrence time, Δtrec, and the local mass accretion rate per unit area onto the compact object, ṁ, is fitted by a power-law model, and yielded as best fit at Δtrec ∼ ⟨ṁ⟩−1.02±0.03 using all X-ray bursts. In both cases, the observed recurrence times are consistent with the mixed hydrogen and helium bursts. We also discuss the effects of type-I X-ray bursts prior to the hard to soft transition.

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