Single-temperature Blackbody Research Articles

Optically Quiet, But FUV Loud: Results from comparing the far-ultraviolet predictions of flare models with TESS and HST

Abstract The far-ultraviolet (FUV) flare activity of low-mass stars has become a focus in our understanding of the exoplanet atmospheres and how they evolve. However, direct detection of FUV flares and measurements of their energies and rates are limited by the need for space-based observations. The difficulty of obtaining such observations may push some works to use widely available optical data to calibrate multi-wavelength spectral models that describe UV and optical flare emission. These models either use single temperature blackbody curves to describe this emission, or combine a blackbody curve with archival spectra. These calibrated models would then be used to predict the FUV flare rates of low-mass stars of interest. To aid these works, we used TESS optical photometry and archival HST FUV spectroscopy to test the FUV predictions of literature flare models. We tested models for partially (M0-M2) and fully convective (M4-M5) stars, 40 Myr and field age stars, and optically quiet stars. We calculated FUV energy correction factors that can be used to bring the FUV predictions of tested models in line with observations. A flare model combining optical and NUV blackbody emission with FUV emission based on HST observations provided the best estimate of FUV flare activity, where others underestimated the emission at all ages, masses and activity levels, by up to a factor of 104 for combined FUV continuum and line emission and greater for individual emission lines. We also confirmed previous findings that showed optically quiet low-mass stars exhibit regular FUV flares.

Relativistic X-ray reflection and highly ionized absorption in the spectrum of NS LMXB 1A 1744−361

ABSTRACT We present the results from the spectral and timing analysis of the accreting neutron star (NS) 1A 1744−361 from the Nuclear Spectroscopic Telescope ARray observation performed in its 2022 outbursts. The unabsorbed bolometric X-ray luminosity during this observation in the energy band 0.1–100 keV is 3.9 × 1037 erg s−1, assuming a distance of 9 kpc. During this observation, the source was in the banana branch of the atoll track. The source spectrum exhibits relativistic disc reflection and clear absorption features when an absorbed blackbody and cut-off power-law model describes the continuum emission. The 3–50 keV source spectrum is well fitted using a model combination consisting of an absorbed single-temperature blackbody and a reflection model along with the addition of a warm absorber component. The inner-disc radius, Rin, obtained from the reflection fit is ∼(1.61–2.86)RISCO = (8.4–14.9)Rg (17.6–31.2 km for a 1.4 M⊙ NS). This measurement allowed us to further constrain the magnetic field strength to B ≲ 0.94 × 109 G. The strong absorption features ∼6.91 keV and ∼7.99 keV imply the presence of highly ionized absorbing material with a column density NH of ∼3 × 1022 cm−2, emanating from the accretion disc in the form of disc wind with an outflow velocity of vout ≃ 0.021c ≃ 6300 km s−1.

On the Blackbody Spectrum of Kilonovae

The early spectra of the kilonova AT2017gfo have a remarkably smooth blackbody continuum, which reveals information on the thermal properties and radioactive heating within the ejecta. However, the widespread use of a single-temperature blackbody to fit kilonova data is theoretically invalid, because (1) the significant travel-time delays for a rapidly cooling surface result in a broad distribution of temperatures and (2) the relativistic Doppler correction varies across different surface elements. Thus, the observed spectrum should be a modified blackbody with a range of temperatures over the surface. In this paper we quantify the impact of these effects and illustrate the typical wavelength-dependent spectral corrections. We apply the multitemperature blackbody framework to the first-epoch X-shooter AT2017gfo spectrum, to deconvolve the underlying physical temperature at the photosphere from the relativistic Doppler shift. We show that the cooling and Doppler effects individually result in a variation of temperatures over the photosphere of up to 30%, but in combination these effects nearly cancel and produce the single-temperature blackbody observed. Finally, we show that fitting the UV, optical, or near-infrared separately yields blackbody temperatures consistent at the percent level, which puts stringent limits on any proposed modification of the spectral continuum.

Evolution of a Relativistic Outflow and X-Ray Corona in the Extreme Changing-look AGN 1ES 1927+654

1ES 1927+654 is a paradigm-defying active galactic nucleus (AGN) and one of the most peculiar X-ray nuclear transients. In early 2018, this well-known AGN underwent a changing-look event, in which broad optical emission lines appeared and the optical flux increased. Yet, by 2018 July, the X-ray flux had dropped by over two orders of magnitude, indicating a dramatic change in the inner accretion flow. With three years of observations with NICER, XMM-Newton, and NuSTAR, we present the X-ray evolution of 1ES 1927+654, which can be broken down into three phases: (1) an early super-Eddington phase with rapid variability in X-ray luminosity and spectral parameters, (2) a stable super-Eddington phase at the peak X-ray luminosity, and (3) a steady decline back to the pre-outburst luminosity and spectral parameters. For the first time, we witnessed the formation of the X-ray corona, as the X-ray spectrum transitioned from thermally dominated to primarily Comptonized. We also track the evolution of the prominent, broad 1 keV feature in the early X-ray spectra and show that this feature can be modeled with blueshifted reflection (z = −0.33) from a single-temperature blackbody irradiating spectrum using xillverTDE, a new flavor of the xillver models. Thus, we propose that the 1 keV feature could arise from reflected emission off the base of an optically thick outflow from a geometrically thick, super-Eddington inner accretion flow, connecting the inner accretion flow with outflows launched during extreme accretion events (e.g., tidal disruption events). Lastly, we compare 1ES 1927+654 to other nuclear transients and discuss applications of xillverTDE to super-Eddington accretors.

Detection of an Extremely Large Impact Flash on Jupiter by High-cadence Multiwavelength Observations

We report the detection of an optical impact flash on Jupiter on 2021 October 15 by a dedicated telescope, Planetary ObservatioN Camera for Optical Transient Surveys, for the first time. Our temporally resolved three-band observations of the flash allowed investigations of its optical energy without the need for approximations on the impact brightness temperature. The kinetic energy of the impactor was equivalent to approximately two megatons of TNT, an order of magnitude greater than that of previously detected flashes on Jupiter and comparable with the Tunguska impact on Earth in 1908. This detection indicates that Tunguska-like impact events on Jupiter occur approximately once per year, two to three orders of magnitude more frequently than terrestrial impacts. The observed flash displayed a single-temperature blackbody spectrum with an effective temperature of approximately 8300 K without clear temporal variation, possibly representing common radiative features of terrestrial Tunguska-class superbolides.

Classifying IGR J18007−4146 as an intermediate polar using XMM and NuSTAR

ABSTRACT Many new and unidentified Galactic sources have recently been revealed by ongoing hard X-ray surveys. A significant fraction of these have been shown to be the type of accreting white dwarfs known as cataclysmic variables (CVs). Follow-up observations are often required to categorize and classify these sources, and may also identify potentially unique or interesting cases. One such case is IGR J18007−4146, which is likely a CV based on follow-up Chandra observations and constraints from optical/IR catalogues. Utilizing simultaneous XMM–Newton and NuSTAR observations, as well as the available optical/IR data, we confirm the nature of IGR J18007−4146 as an intermediate polar type CV. Timing analysis of the XMM data reveals a periodic signal at 424.4 ± 0.7 s that we interpret as the spin period of the white dwarf. Modelling the 0.3–78 keV spectrum, we use a thermal bremsstrahlung continuum but require intrinsic absorption as well as a soft component and strong Fe lines between 6 and 7 keV. We model the soft component using a single-temperature blackbody with $kT = 73^{+8}_{-6}$ eV. From the X-ray spectrum, we are able to measure the mass of the white dwarf to be $1.06^{+0.19}_{-0.10}$ $\mathrm{ M}_{\mathord \odot }$, which means IGR J18007−4146 is more massive than the average for magnetic CVs.

Relativistic X-Ray Reflection Models for Accreting Neutron Stars

Abstract We present new reflection models specifically tailored to model the X-ray radiation reprocessed in accretion disks around neutron stars, in which the primary continuum is characterized by a single-temperature blackbody spectrum, emitted either at the surface of the star or at the boundary layer. These models differ significantly from those with a standard power-law continuum, typically observed in most accreting black holes. We show comparisons with earlier reflection models and test their performance in the NuSTAR observation of the neutron star 4U 1705−44. Simulations of upcoming missions such as XRISM-Resolve and Athena X-IFU are shown to highlight the diagnostic potential of these models for high-resolution X-ray reflection spectroscopy. These new reflection models xillverNS, and their relativistic counterpart relxillNS, are made publicly available to the community as an additional flavor in the relxill suite of reflection models.

Tidal disruption event discs are larger than they seem: removing systematic biases in TDE X-ray spectral modelling

ABSTRACT The physical sizes of tidal disruption event (TDE) accretion discs are regularly inferred, from modelling of the TDEs X-ray spectrum as a single-temperature blackbody, to be smaller than the plausible event horizons of the black holes which they occur around – a clearly unphysical result. In this Lltter, we demonstrate that the use of single-temperature blackbody functions results in the systematic underestimation of TDE accretion disc sizes by as much as an order of magnitude. In fact, the radial ‘size’ inferred from fitting a single-temperature blackbody to an observed accretion disc X-ray spectrum does not even positively correlate with the physical size of that accretion disc. We further demonstrate that the disc-observer inclination angle and absorption of X-ray photons may both lead to additional underestimation of the radial sizes of TDE discs, but by smaller factors. To rectify these issues, we present a new fitting function which accurately reproduces the size of an accretion disc from its 0.3−10 keV X-ray spectrum. Unlike traditional approaches, this new fitting function does not assume that the accretion disc has reached a steady-state configuration, an assumption which is unlikely to be satisfied by most TDEs.

The Changing-look Blazar B2 1420+32

Abstract Blazars are active galactic nuclei with their relativistic jets pointing toward the observer, comprising two major subclasses, flat-spectrum radio quasars (FSRQs) and BL Lac objects. We present multiwavelength photometric and spectroscopic monitoring observations of the blazar B2 1420+32, focusing on its outbursts in 2018–2020. Multiepoch spectra show that the blazar exhibited large-scale spectral variability in both its continuum and line emission, accompanied by dramatic gamma-ray and optical variability by factors of up to 40 and 15, respectively, on week to month timescales. Over the last decade, the gamma-ray and optical fluxes increased by factors of 1500 and 100, respectively. B2 1420+32 was an FSRQ with broad emission lines in 1995. Following a series of flares starting in 2018, it transitioned between BL Lac and FSRQ states multiple times, with the emergence of a strong Fe pseudocontinuum. Two spectra also contain components that can be modeled as single-temperature blackbodies of 12,000 and 5200 K. Such a collection of “changing-look” features has never been observed previously in a blazar. We measure gamma-ray–optical and interband optical lags implying emission-region separations of less than 800 and 130 gravitational radii, respectively. Since most emission-line flux variations, except the Fe continuum, are within a factor of 2–3, the transitions between FSRQ and BL Lac classifications are mainly caused by the continuum variability. The large Fe continuum flux increase suggests the occurrence of dust sublimation releasing more Fe ions in the central engine and an energy transfer from the relativistic jet to subrelativistic emission components.

Origin of the UV to X-Ray Emission of Radio Galaxy NGC 1275 Explored by Analyzing Its Variability

Abstract We analyze the ultraviolet (UV) and X-ray data of NGC 1275 obtained with Swift/UV/Optical Telescope (UVOT), X-ray Telescope (XRT), Burst Alert Telescope (BAT) and Fermi Large Area Telescope over about 10 yr to investigate the origin of the nuclear emission from NGC 1275. We confirm that the UV and soft/hard X-ray fluxes gradually increased along with the GeV gamma rays. At times, short-term variations in the UV or soft X-ray spectral regions showed rapid variations correlated with the GeV gamma rays. However there was no significant correlation between the UV and soft X-rays. The UV spectrum had a narrow spectral shape that could be represented by single-temperature blackbody radiation. These results could possibly indicate that the long-term variability of UV and X-ray emissions is caused by the jet, while the emissions from the accretion disk contribute to the UV and X-ray bands to some extent.

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

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.

On the disc reflection spectroscopy of NS LMXB Serpens X-1: analysis of a recent NuSTAR observation

ABSTRACT We present NuSTAR observation of the atoll type neutron star (NS) low-mass X-ray binary (LMXB) Serpens X-1 (Ser X-1) performed on 2018 February 17. We observed Ser X-1 in a soft X-ray spectral state with 3–79 keV luminosity of LX ∼ 0.4 × 1038 erg s−1 (${\sim}23{{\ \rm per\ cent}}$ of the Eddington luminosity), assuming a distance of 7.7 kpc. A positive correlation between intensity and hardness ratio suggests that the source was in the banana branch during this observation. The broad-band 3–30 keV NuSTAR energy spectrum can be well described either by a three-component continuum model consisting of a disc blackbody, a single temperature blackbody, and a power law or by a two-component continuum model consisting of a disc blackbody and a Comptonization component. A broad iron line ∼5–8 keV and the Compton back-scattering hump peaking at ∼10–20 keV band are clearly detected in the X-ray spectrum. These features are best interpreted by a self-consistent relativistic reflection model. Fits with relativistically blurred disc reflection model suggests that the inner disc radius Rin is truncated prior to the ISCO at (1.9–2.5) RISCO (${\simeq}11.4\!-\!15\, R_{g}\: \text{or}\: 26\!-\!34$ km) and the accretion disc is viewed at a low inclination of i ≃ 16°−20°. The disc is likely to be truncated either by a boundary layer or by the magnetosphere. Based on the measured flux and the mass accretion rate, the maximum radial extension for the boundary layer is estimated to be ∼6.4 Rg from the NS surface. The truncated inner disc in association with pressure from a magnetic field sets an upper limit of B ≤ 1.9 × 109 G.

AstroSat/LAXPC view of GX 17+2: spectral evolution along the Z-track

In this paper, we present the first results obtained using $\sim 50$ ks observations of the bright low-mass X-ray binary (LMXB) GX 17+2 with Large Area X-ray Proportional Counter (LAXPC) onboard AstroSat. The source traced out a complete Z-track in the hardness intensity diagram (HID). The spectra at different sections of the Z-diagram are well described by either a combination of a thermal Comptonization component, a power-law and a relativistic iron line or a model consisting of a thermal disk component, a single temperature blackbody, a power-law and a relativistic iron line. Fitting the spectra with both phenomenological models suggests that the power-law component is strong in the horizontal branch (HB), becomes weaker as the source moves down the normal branch (NB) and then again becomes stronger as the sources moves up the flaring branch (FB). However, we find that the strength of the power-law component is model dependent, although the trend in the variation of the power-law strength along the Z-track is similar. A simple model composed by a Comptonized emission and power-law component, convolved with the ionized reflection, also describes the spectra very well. A normal branch oscillation (NBO) with a centroid frequency $7.42 \pm 0.23$ Hz, quality factor $\text{(Q)} \sim 4.88$, rms $1.41 \pm 0.29$% and significance 5.1$\sigma $ is detected at the middle of the NB. The parameters of the Comptonized emission show a systematic evolution along the Z-diagram. The optical depth of the corona increases as the source moves up along the FB, suggesting possible trigger of an outflow or dumping of the disc material in to the corona by radiation pressure.

A broad-band look of the accreting millisecond X-ray pulsar SAX J1748.9−2021 using AstroSat and XMM–Newton

ABSTRACT SAX J1748.9−2021 is a transient accretion powered millisecond X-ray pulsar located in the globular cluster NGC 6440. We report on the spectral and timing analysis of SAX J1748.9−2021 performed on AstroSat data taken during its faint and short outburst of 2017. We derived the best-fitting orbital solution for the 2017 outburst and obtained an average local spin frequency of 442.361098(3) Hz. The pulse profile obtained from 3 to 7 and 7 to 20 keV energy bands suggest constant fractional amplitude ∼0.5 per cent for fundamental component, contrary to previously observed energy pulse profile dependence. Our AstroSat observations revealed the source to be in a hard spectral state. The 1–50 keV spectrum from SXT (Soft X-ray Telescope) and LAXPC (Large Area X-ray Proportional Counter) on-board AstroSat can be well described with a single temperature blackbody and thermal Comptonization. Moreover, we found that the combined spectra from XMM–Newton (EPIC-PN) and AstroSat (SXT + LAXPC) indicated the presence of reflection features in the form of iron (Fe Kα) line that we modelled with the reflection model xillvercp. One of the two X-ray burst observed during the AstroSat/LAXPC observation showed hard X-ray emission (>30 keV) due to Compton up-scattering of thermal photons by the hot corona. Time-resolved analysis performed on the bursts revealed complex evolution in emission radius of blackbody for second burst suggestive of mild photospheric radius expansion.

Study of the reflection spectrum of the bright atoll source GX 3 + 1 with NuSTAR

ABSTRACT We report on the NuSTAR observation of the atoll type neutron star (NS) low-mass X-ray binary GX 3 + 1 performed on 2017 October 17. The source was found in a soft X-ray spectral state with 3–70 keV luminosity of LX ∼ 3 × 1037 erg s−1 (${\sim } 16{{\ \rm per\ cent}}$ of the Eddington luminosity), assuming a distance of 6 kpc. A positive correlation between intensity and hardness ratio suggests that the source was in the banana branch during this observation. The broad-band 3–70 keV NuSTAR spectral data can be described by a two-component continuum model consisting of a disc blackbody (kTdisc ∼ 1.8 keV) and a single temperature blackbody model (kTbb ∼ 2.7 keV). The spectrum shows a clear and robust indication of relativistic reflection from the inner disc which is modelled with a self-consistent relativistic reflection model. The accretion disc is viewed at an inclination of i ≃ 22°–26° and extended close to the NS, down to $R_\text{in}=(1.2\!-\!1.8) R_\text{ISCO}\:(\simeq 6.1\!-\!9.1\, R_{\mathrm{ g}}\: \text{or}\: 14\!-\!20.5$ km) which allows an upper limit on the NS radius (≤13.5 km). Based on the measured flux and the mass accretion rate, the maximum radial extension for the boundary layer is estimated to be ∼6.3 Rg from the NS surface. However, if the disc is not truncated by the boundary layer but by the magnetosphere, an estimated upper limit on the polar magnetic field would be of B ≤ 6 × 108 G.

Universal detection of high-temperature emission in X-ray isolated neutron stars

Abstract Strongly magnetized isolated neutron stars (NSs) are categorized into two families, according mainly to their magnetic field strength. Those with a higher magnetic field of 1014–1015 G are called magnetars, characterized by repeated short bursts, and the others are X-ray isolated neutron stars (XINSs) with 1013 G. Both magnetars and XINSs show thermal emission in X-rays, but it has been considered that the thermal spectrum of magnetars can be reproduced with a two-temperature blackbody (2BB), while that of XINSs shows only a single-temperature blackbody (1BB) and the temperature is lower than that of magnetars. On the basis of the magnetic field and temperature, it is often speculated that XINSs may be old and cooled magnetars. Here we report that all seven known XINSs show a high-energy component in addition to the 1BB model. Analyzing all the XMM-Newton data for the XINSs with the highest statistics ever achieved, we find that their X-ray spectra are all reproduced with a 2BB model, similar to magnetars. Their emission radii and temperature ratios are also similar to those of magnetars except for two XINSs, which show significantly smaller radii than the others. The remarkable similarity in the X-ray spectra between XINSs and magnetars suggests that the origins of their emissions are the same. The lower temperature in XINSs can be explained if XINSs are older than magnetars. Therefore, these results are an observational indication that supports the standard hypothesis on the classification of highly magnetized NSs.

On the Interpretation of Far-infrared Spectral Energy Distributions. I. The 850 μm Molecular Mass Estimator

Abstract We use a suite of cosmological zoom galaxy formation simulations and dust radiative transfer calculations to explore the use of the monochromatic 850 μm luminosity (L ν,850) as a molecular gas mass (M mol) estimator in galaxies between 0 < z < 9.5 for a broad range of masses. For our fiducial simulations, where we assume that the dust mass is linearly related to the metal mass, we find that empirical L ν,850–M mol calibrations accurately recover the molecular gas mass of our model galaxies and that the L ν,850-dependent calibration is preferred. We argue that the major driver of scatter in the L ν,850–M mol relation arises from variations in the molecular gas-to-dust mass ratio, rather than variations in the dust temperature, in agreement with the previous study of Liang et al. Emulating a realistic measurement strategy with ALMA observing bands that are dependent on the source redshift, we find that estimating S ν,850 from continuum emission at a different frequency contributes 10%–20% scatter to the L ν,850–M mol relation. This additional scatter arises from a combination of mismatches in assumed T dust and β values, as well as the fact that the SEDs are not single-temperature blackbodies. However, this observationally induced scatter is a subdominant source of uncertainty. Finally, we explore the impact of a dust prescription in which the dust-to-metals ratio varies with metallicity. Though the resulting mean dust temperatures are ∼50% higher, the dust mass is significantly decreased for low-metallicity halos. As a result, the observationally calibrated L ν,850–M mol relation holds for massive galaxies, independent of the dust model, but below L ν,850 ≲ 1028 erg s−1 (metallicities ) we expect that galaxies may deviate from literature observational calibrations by ≳0.5 dex.

Kilonova Emission from Black Hole–Neutron Star Mergers: Observational Signatures of Anisotropic Mass Ejection

The gravitational wave event GW170817 associated with the short gamma-ray burst (GRB) 170817A confirms that binary neutron star (BNS) mergers are one of the origins of short GRBs. The associated kilonova emission, radioactively powered by nucleosynthesized heavy elements, was also detected. Black hole-neutron star (BH-NS) mergers have been argued to be another promising origin candidate of short GRBs and kilonovae. Numerical simulations show that the ejecta in BH-NS mergers is geometrically much more anisotropic than the BNS merger case. In this paper, we investigate observational signatures of kilonova emission from the anisotropic ejecta in BH-NS mergers. We find that a bump appears on the bolometric luminosity light curve due to the inhomogeneous mass distribution in the latitudinal direction. The decay slope of the single-band light curve becomes flatter and the spectrum also deviates from a single-temperature blackbody radiation spectrum due to the gradient in the velocity distribution of the ejecta. Future detection or non-detection of such signatures would be useful to test the mass ejection geometry in BH-NS mergers.

Multicolor Blackbody Emission in GRB 081221

Abstract The radiation mechanism of the prompt emission of gamma-ray bursts (GRBs) remains an open question. Although their spectra are usually well fitted with the empirical Band function, which is widely believed to be fully nonthermal and interpreted as an optically thin synchrotron emission, accumulating evidence shows that a thermal component actually exists. In this paper, a multicolor blackbody (mBB) model is proposed for the time-integrated spectrum of GRB 081221 by assuming a power-law distribution of the thermal luminosities with temperature, which manifests photospheric emissions from a different radius and/or angle. The effects of the minimum temperature kT min, the maximum temperature kT max, and the power-law index m of the luminosity distribution of an mBB are discussed. The fitting to the time-integrated spectrum during the bright phase (from 20 to 30 s since the trigger) of GRB 081221 by the mBB model yields kT min = 4.4 ± 0.3 keV, , and . When the time bin is small enough, the time-resolved spectra of GRB 081221 are well fitted with a series of single-temperature blackbodies. Our results imply the prompt emission of GRB 081221 is dominated by the photosphere emission and its time-integrated spectrum is a superposition of pure blackbody components at different times, indicating that some empirical Band spectra may be interpreted as mBB if the temperature is widely distributed.

Spectral properties of MXB 1658–298 in the low/hard and high/soft state

We report results from a broadband spectral analysis of the low mass X-ray binary MXB 1658-298 with the Swift/XRT and NuSTAR observations made during its 2015-2017 outburst. The source showed different spectral states and accretion rates during this outburst. The source was in low/hard state during 2015; and it was in high/soft state during the 2016 NuSTAR observations. This is the first time that a comparison of the soft and hard spectral states during an outburst is being reported in MXB 1658-298. Compared with the observation of 2015, the X-ray luminosity was about four times higher during 2016. The hard state spectrum can be well described with models consisting of a single-temperature blackbody component along with Comptonized disc emission, or three component model comprising of multi-colour disc, single-temperature blackbody and thermal Comptonization components. The soft state spectrum can be described with blackbody or disc blackbody and Comptonization component, where the neutron star surface (or boundary layer) is the dominant source for the Comptonization seed photons. We have also found a link between the spectral state of the source and the Fe K absorber. The absorption features due to highly ionized Fe were observed only in the soft state. This suggests a probable connection between accretion disc wind (or atmosphere) and spectral state (or accretion state) of MXB 1658-298.