The broad-band spectrum of the narrow-line Seyfert 1 NGC 4748: from UV to hard X-ray

ABSTRACT We present the results of X-ray spectral and timing analyses of the closest gamma-ray emitting narrow-line Seyfert 1 (γ-NLS1) galaxy, 1H 0323+342. We use observations from a recent, simultaneous XMM–Newton/NuSTAR campaign. As in radio-quiet NLS1s, the spectrum reveals a soft excess at low energies (≲2 keV) and reflection features such as a broad iron K emission line. We also find evidence of a hard excess at energies above ∼35 keV that is likely a consequence of jet emission. Our analysis shows that relativistic reflection is statistically required, and using a combination of models that includes the reflection model relxill for the broad-band spectrum, we find an inclination of $i=63^{+7}_{-5}$ degrees, which is in tension with much lower values inferred by superluminal motion in radio observations. We also find a flat (q = 2.2 ± 0.3) emissivity profile, implying that there is more reflected flux than usual being emitted from the outer regions of the disc, which in turn suggests a deviation from the thin disc model assumption. We discuss possible reasons for this, such as reflection off of a thick accretion disc geometry.

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NuSTAR view of Be/X-ray binary pulsar 2S 1417−624 during 2018 giant outburst

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz2795 ◽

2019 ◽

Vol 490 (2) ◽

pp. 2458-2466 ◽

Cited By ~ 1

Author(s):

Shivangi Gupta ◽

Sachindra Naik ◽

Gaurava K Jaisawal

Keyword(s):

Broad Band ◽

Gaussian Function ◽

Physical Models ◽

Spectral Studies ◽

Band Spectrum ◽

X Ray ◽

Binary Pulsar ◽

Double Peak Structure ◽

Peak Structure ◽

Cyclotron Line

ABSTRACT We report the results obtained from a detailed timing and spectral studies of Be/X-ray binary pulsar 2S 1417−624 using data from Swift and NuSTAR observatories. The observations were carried out at the peak of a giant outburst of the pulsar in 2018. X-ray pulsations at ∼17.475 s were detected in the source light curves up to 79 keV. The evolution of the pulse profiles with energy was found to be complex. A four-peaked profile at lower energies gradually evolved into a double-peak structure at higher energies. The pulsed fraction of the pulsar, calculated from the NuSTAR observation was found to follow an anticorrelation trend with luminosity as observed during previous giant X-ray outburst studies in 2009. The broad-band spectrum of the pulsar is well described by a composite model consisting of a cut-off power-law model modified with the interstellar absorption, a thermal blackbody component with a temperature of ≈1 keV, and a Gaussian function for the 6.4 keV iron emission line. Though the pulsar was observed at the peak of the giant outburst, there was no signature of presence of any cyclotron line feature in the spectrum. The radius of the blackbody emitting region was estimated to be ≈2 km, suggesting that the most probable site of its origin is the stellar surface of the neutron star. Physical models were also explored to understand the emission geometry of the pulsar and are discussed in the paper.

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The December 2015 re-brightening of V404 Cygni

Astronomy and Astrophysics ◽

10.1051/0004-6361/201731768 ◽

2018 ◽

Vol 616 ◽

pp. A129 ◽

Cited By ~ 2

Author(s):

J. J. E. Kajava ◽

S. E. Motta ◽

C. Sánchez-Fernández ◽

E. Kuulkers

Keyword(s):

Broad Band ◽

High Energy ◽

Accretion Disc ◽

Band Spectrum ◽

Hard Photon ◽

Time Resolved ◽

X Ray ◽

Spectral Behaviour ◽

Black Hole Binary ◽

Spectral Cut

In December 2015 the black hole binary V404 Cyg underwent a secondary outburst after the main June 2015 event. We monitored this re-brightening with the INTEGRAL and Swift satellites, and in this paper we report the results of the time-resolved spectral analysis of these data. The December outburst shared several characteristics with the June event. The well-sampled INTEGRAL light curve shows up to ten Crab flares, which are separated by relatively weak non-flaring emission phases when compared to the June outburst. The spectra are nicely described by absorbed Comptonization models, with hard photon indices, Γ ≲ 2, and significant detections of a high-energy cut-off only during the bright flares. This is in contrast to the June outburst, where the Comptonization models gave electron temperatures mostly in the 30–50 keV range, while some spectra were soft (Γ ~ 2.5) without signs of any spectral cut-off. Similarly to the June outburst, we see clear signs of a variable local absorber in the soft energy band covered by Swift/XRT and INTEGRAL/JEM-X, which causes rapid spectral variations observed during the flares. During one flare, both Swift and INTEGRAL captured V404 Cyg in a state where the absorber was nearly Compton thick, N H ≈ 1024 cm−2, and the broad-band spectrum was similar to obscured AGN spectra, as seen during the X-ray plateaus in the June outburst. We conclude that the spectral behaviour of V404 Cyg during the December outburst was analogous with the first few days of the June outburst, both having hard X-ray flares that were intermittently influenced by obscuration due to nearly Compton-thick outflows launched from the accretion disc.

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Broad-band spectral analysis of LMXB XTE J1710−281 with Suzaku

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1516 ◽

2020 ◽

Vol 496 (1) ◽

pp. 197-205

Author(s):

Prince Sharma ◽

Rahul Sharma ◽

Chetana Jain ◽

Anjan Dutta

Keyword(s):

Spectral Analysis ◽

Broad Band ◽

Emission Spectra ◽

Band Spectrum ◽

Surface Boundary ◽

Hot Electron ◽

Spectral Parameters ◽

Surface Boundary Layer ◽

X Ray ◽

Single Temperature

ABSTRACT This work presents the broad-band time-averaged spectral analysis of neutron star (NS) low-mass X-ray binary, XTE J1710−281 by using the Suzaku archival data. The source was in a hard or an intermediate spectral state during this observation. This is the first time that a detailed spectral analysis of the persistent emission spectra of XTE J1710−281 has been done up to 30 keV with improved constraints on its spectral parameters. By simultaneously fitting the X-ray Imaging Spectrometer (0.6–9.0 keV) and the HXD-PIN (15.0–30.0 keV) data, we have modelled the persistent spectrum of the source with models comprising a soft component from accretion disc and/or NS surface/boundary layer and a hard Comptonizing component. The 0.6–30 keV continuum with neutral absorber can be described by a multicolour disc blackbody with an inner disc temperature of kTdisc = 0.28 keV, which is significantly Comptonized by the hot electron cloud with electron temperature of kTe ≈ 5 keV and described by photon index Γ = 1.86. A more complex three-component model comprising a multicolour disc blackbody ≈0.30 keV, single-temperature blackbody ≈0.65 keV, and Comptonization from the disc, partially absorbed (about 38 per cent) by an ionized absorber (log(ξ) ≈ 4) describes the broad-band spectrum equally well.

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The first broad-band X-ray view of the narrow-line Seyfert 1 Ton S180

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa2076 ◽

2020 ◽

Vol 497 (2) ◽

pp. 2352-2370 ◽

Cited By ~ 2

Author(s):

G A Matzeu ◽

E Nardini ◽

M L Parker ◽

J N Reeves ◽

V Braito ◽

...

Keyword(s):

Thermal Emission ◽

Spectral Energy Distribution ◽

Broad Band ◽

Outer Part ◽

Spectral Energy ◽

X Rays ◽

Narrow Line ◽

X Ray ◽

Extreme Uv ◽

Reflection Grating

ABSTRACT We present joint XMM–Newton and NuSTAR observations of the ‘bare’ narrow-line Seyfert 1 Ton S180 (z = 0.062), carried out in 2016 and providing the first hard X-ray view of this luminous galaxy. We find that the 0.4–30 keV band cannot be self-consistently reproduced by relativistic reflection models, which fail to account simultaneously for the soft and hard X-ray emission. The smooth soft excess prefers extreme blurring parameters, confirmed by the nearly featureless nature of the Reflection Grating Spectrometer (RGS) spectrum, while the moderately broad Fe K line and the modest hard excess above 10 keV appear to arise in a milder gravity regime. By allowing a different origin of the soft excess, the broad-band X-ray spectrum and overall spectral energy distribution (SED) are well explained by a combination of (a) direct thermal emission from the accretion disc, dominating from the optical to the far/extreme UV; (b) Comptonization of seed disc photons by a warm (kTe ∼ 0.3 keV) and optically thick (τ ∼ 10) corona, mostly contributing to the soft X-rays; (c) Comptonization by a standard hot ($kT_{\rm \mathrm{ e}}\gtrsim 100$ keV) and optically thin (τ < 0.5) corona, responsible for the primary X-ray continuum; and (d) reflection from the mid/outer part of the disc. The two coronae are suggested to be rather compact, with $R_{\rm hot}\lesssim R_{\rm warm}\lesssim 10\, r_{\rm g}$. Our SED analysis implies that Ton S180 accretes at super-Eddington rates. This is a key condition for the launch of a wind, marginal (i.e. 3.1σ significance) evidence of which is indeed found in the RGS spectrum.

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The long-term enhanced brightness of the magnetar 1E 1547.0–5408

Astronomy and Astrophysics ◽

10.1051/0004-6361/201936317 ◽

2020 ◽

Vol 633 ◽

pp. A31 ◽

Cited By ~ 1

Author(s):

Francesco Coti Zelati ◽

Alice Borghese ◽

Nanda Rea ◽

Daniele Viganò ◽

Teruaki Enoto ◽

...

Keyword(s):

Thermal Emission ◽

Broad Band ◽

Spectral Shape ◽

Band Spectrum ◽

Pulse Profile ◽

X Ray ◽

Time Period ◽

Order Of Magnitude ◽

Cooling Trend

We present the evolution of the X-ray emission properties of the magnetar 1E 1547.0–5408 since February 2004 over a time period covering three outbursts. We analyzed new and archival observations taken with the Swift, NuSTAR, Chandra, and XMM–Newton X-ray satellites. The source has been observed at a relatively steady soft X-ray flux of ≈10−11 erg cm−2 s−1 (0.3–10 keV) over the last 9 years, which is about an order of magnitude fainter than the flux at the peak of the last outburst in 2009, but a factor of ∼30 larger than the level in 2006. The broad-band spectrum extracted from two recent NuSTAR observations in April 2016 and February 2019 showed a faint hard X-ray emission up to ∼70 keV. Its spectrum is adequately described by a flat power law component, and its flux is ∼7 × 10−12 erg cm−2 s−1 (10–70 keV), that is a factor of ∼20 smaller than at the peak of the 2009 outburst. The hard X-ray spectral shape has flattened significantly in time, which is at variance with the overall cooling trend of the soft X-ray component. The pulse profile extracted from these NuSTAR pointings displays variability in shape and amplitude with energy (up to ≈25 keV). Our analysis shows that the flux of 1E 1547.0–5408 is not yet decaying to the 2006 level and that the source has been lingering in a stable, high-intensity state for several years. This might suggest that magnetars can hop among distinct persistent states that are probably connected to outburst episodes and that their persistent thermal emission can be almost entirely powered by the dissipation of currents in the corona.

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A disc reflection model for ultra-soft narrow-line Seyfert 1 galaxies

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa2625 ◽

2020 ◽

Vol 498 (3) ◽

pp. 3888-3901

Author(s):

Jiachen Jiang ◽

Luigi C Gallo ◽

Andrew C Fabian ◽

Michael L Parker ◽

Christopher S Reynolds

Keyword(s):

Thermal Emission ◽

Spectral Energy Distribution ◽

Broad Band ◽

Continuum Emission ◽

Spectral Energy ◽

Narrow Line ◽

Ionization State ◽

X Ray ◽

Reflection Model ◽

Photon Index

ABSTRACT We present a detailed analysis of the XMM–Newton observations of five narrow-line Seyfert 1 galaxies (NLS1s). They all show very soft continuum emission in the X-ray band with a photon index of Γ ≳ 2.5. Therefore, they are referred to as ‘ultra-soft’ NLS1s in this paper. By modelling their optical/UV–X-ray spectral energy distribution (SED) with a reflection-based model, we find indications that the disc surface in these ultra-soft NLS1s is in a higher ionization state than other typical Seyfert 1 AGN. Our best-fitting SED models suggest that these five ultra-soft NLS1s have an Eddington ratio of λEdd = 1–20 assuming available black hole mass measurements. In addition, our models infer that a significant fraction of the disc energy in these ultra-soft NLS1s is radiated away in the form of non-thermal emission instead of the thermal emission from the disc. Due to their extreme properties, X-ray observations of these sources in the iron band are particularly challenging. Future observations, e.g. from Athena, will enable us to have a clearer view of the spectral shape in the iron band and thus distinguish the reflection model from other interpretations of their broad-band spectra.

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Swift monitoring and Suzaku spectroscopy of the γ-ray detected narrow-line Seyfert 1 galaxy 1H 0323+342

Proceedings of the International Astronomical Union ◽

10.1017/s1743921315007504 ◽

2014 ◽

Vol 10 (S312) ◽

pp. 66-67

Author(s):

S. Yao ◽

W. Yuan ◽

S. Komossa ◽

D. Grupe ◽

L. Fuhrmann ◽

...

Keyword(s):

Active Galactic Nuclei ◽

Broad Band ◽

Galactic Nuclei ◽

Optical Monitoring ◽

Narrow Line ◽

Black Hole Mass ◽

X Ray ◽

Small Black Hole ◽

Special Subset ◽

Γ Ray

Abstract1H 0323+342 is one of the rare γ-ray detected narrow-line Seyfert 1 galaxies (NLS1s), a special subset of active galactic nuclei (AGN) owing to their hybrid behavior of both NLS1s and blazars. The rarity of such kind of sources makes their properties far from being understood. We analyze simultaneous X-ray and UV/optical monitoring observations of 1H 0323+342 performed by Swift over ~7 years. The UV/X-ray correlation and the broad band SED reveal that the X-ray band is dominated by the disk/corona emission during the observations. The large normalized excess variance of the X-ray variability detected with Suzaku suggests a relatively small black hole mass of the order of 107M⊙, consistent with the estimation based on the broad Hβ line in the optical band.

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A new transient ultraluminous X-ray source in NGC 7090

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3666 ◽

2020 ◽

Vol 501 (1) ◽

pp. 1002-1012

Author(s):

D J Walton ◽

M Heida ◽

M Bachetti ◽

F Fürst ◽

M Brightman ◽

...

Keyword(s):

Signal To Noise Ratio ◽

Broad Band ◽

Small Population ◽

Band Spectrum ◽

X Ray ◽

The Galaxy ◽

Long Time ◽

Complex Models ◽

Peak Luminosity

ABSTRACT We report on the discovery of a new, transient ultraluminous X-ray source (ULX) in the galaxy NGC 7090. This new ULX, which we refer to as NGC 7090 ULX3, was discovered via monitoring with Swift during 2019–2020, and to date has exhibited a peak luminosity of LX ∼ 6 × 1039 erg s−1. Archival searches show that, prior to its recent transition into the ULX regime, ULX3 appeared to exhibit a fairly stable luminosity of LX ∼ 1038 erg s−1. Such strong long-time-scale variability may be reminiscent of the small population of known ULX pulsars, although deep follow-up observations with XMM–Newton and NuSTAR do not reveal any robust X-ray pulsation signals. Pulsations similar to those seen from known ULX pulsars cannot be completely excluded, however, as the limit on the pulsed fraction of any signal that remains undetected in these data is ≲20 per cent. The broad-band spectrum from these observations is well modelled with a simple thin disc model, consistent with sub-Eddington accretion, which may instead imply a moderately large black hole accretor (MBH ∼ 40 M⊙). Similarly, though, more complex models consistent with the super-Eddington spectra seen in other ULXs (and the known ULX pulsars) cannot be excluded given the limited signal-to-noise ratio of the available broad-band data. The nature of the accretor powering this new ULX therefore remains uncertain.

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Unfolding the X-ray spectral curvature of Mkn 421 for further clues

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3022 ◽

2020 ◽

Vol 499 (2) ◽

pp. 2094-2103

Author(s):

Pranjupriya Goswami ◽

Sunder Sahayanathan ◽

Atreyee Sinha ◽

Rupjyoti Gogoi

Keyword(s):

Linear Regression Analysis ◽

Broad Band ◽

Turbulence Energy ◽

Band Spectrum ◽

Model Parameters ◽

Strongly Correlated ◽

X Ray ◽

Peak Energy ◽

Wide Range ◽

Energy Dependent

ABSTRACT The X-ray observations of Mkn 421 show significant spectral curvature that can be reproduced by a log-parabola function. The spectra can also be fitted by an analytical model considering synchrotron emission from an electron distribution that is accelerated at a shock front with an energy-dependent diffusion (EDD model). The spectral fit of NuSTAR and Swift-XRT observations using EDD model during different flux states reveals that the model parameters are strongly correlated. We perform a detailed investigation of this correlation to decipher the information hidden underneath. The model predicts the synchrotron peak energy to be correlated with the peak spectral curvature, which is consistent with the case of Mkn 421. Expressing the energy dependence of the diffusion in terms of the magnetohydrodynamic turbulence energy index, it appears that the turbulence shifts from Kolmogorov/Kraichnan type to Bohm limit during high flux states. Further, the correlation between the best-fitting parameters of EDD model lets us derive an expression for the product of source magnetic field(B) and jet Doppler factor(δ) in terms of synchrotron and Compton peak energies. The synchrotron peak energy is obtained using the simultaneous Swift-XRT–NuSTAR observations, whereas the Compton peak energy is estimated by performing a linear regression analysis of the archival spectral peaks. The deduced δB varies over a wide range; however, it satisfies reasonably well with the values estimated solely from the spectral peak energies independent of the EDD model. This highlights the plausible connection between the microscopic description of the electron diffusion with the macroscopic quantities deciding the broad-band spectrum of Mkn 421.

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