Broad-band X-ray Spectrum Research Articles

Revealing the burning and soft heart of the bright bare active galactic nucleus ESO 141-G55: X-ray broadband and SED analysis

Context. ESO 141-G55 is a nearby X-ray bright broad-line Seyfert 1 (BLS1) that has been classified as a bare active galactic nucleus (AGN) due to a lack of warm absorption along its line of sight, providing an unhampered view into its disc-corona system. Aims. We aim to probe its disc-corona system thanks to the first simultaneous XMM-Newton and NuSTAR observation obtained October 1–2, 2022. Methods. We carried out an X-ray broadband spectral analysis to determine the dominant process(es) at work as well as a spectral energy distribution (SED) analysis to determine the disc-corona properties. Results. The simultaneous broadband X-ray spectrum of ESO 141-G55 is characterised by the presence of a prominent smooth soft X-ray excess, a broad Fe Kα emission line, and a significant Compton hump. The high-resolution reflection grating spectrometer spectra confirmed the lack of intrinsic warm-absorbing gas along our line of sight in the AGN rest frame, verifying that it is still in a bare state. However, soft X-ray emission lines were observed, indicating substantial warm gas out of our line of sight. The intermediate inclination of the disc-corona system (∼43°) may offer us a favourable configuration to observe ultra-fast outflows from the disc, but none were found in this 2022 observation, contrary to a previous 2007 XMM-Newton one. We ruled out relativistic reflection alone on a standard disc based on the X-ray broadband analysis, while a combination of soft and hard Comptonisation by a warm and hot corona (RELAGN) plus relativistic reflection (REFLKERRD) reproduces the ESO 141-G55 SED quite well. The hot corona temperature is very hot, ∼140 keV, and much higher than about 80% of AGNs, whereas the warm corona temperature, ∼0.3 keV, is similar to the values found in other sub-Eddington AGNs. ESO 141-G55 is accreting at a moderate Eddington accretion rate (∼10–20%). Conclusions. Our analysis points to a significant contribution of an optically thick warm corona to both the soft X-ray and UV emission in ESO 141-G55, adding to the growing evidence that the accretion of AGNs (even at a moderate accretion rate) appears to deviate from standard disc theory.

Evidence for a Cyclotron Absorption Line and Spectral Transition in EXO 2030+375 during the 2021 Giant Outburst

Based on Insight-HXMT observations of EXO 2030+375 during its 2021 giant outburst, we report the analysis of pulse variations and the broadband X-ray spectrum, and find the presence of a potential cyclotron resonant scattering feature (CRSF) with the fundamental line at ∼47 keV from both average spectra and phase-resolved spectroscopy. During the outburst, the source reached an X-ray luminosity of ∼1038 erg s−1 from 2 to 105 keV at a distance of 7.1 kpc. The X-ray pulsar at the spin period of 41.27 ± 0.61 s exhibits complex timing and spectral variations with both energy and luminosity during the outburst. The shapes of the pulse profiles show the single main peak above ∼20 keV, while appearing to exhibit multipeak patterns in low-energy bands, and the transition of the 10–20 keV pulse profiles from multipeak to single peak is observed at ∼0.8 × 1038 erg s−1, which suggests the evolution from the subcritical luminosity (pencil-beam dominated) to the supercritical luminosity (fan-beam dominated) regime. A dip structure before the energy of the CRSFs is found in the pulse fraction–energy relation of EXO 2030+375 near the peak luminosity. A detailed analysis of spectral parameters showed that the power-law photon index exhibits three distinct trends as luminosity increases, and these spectral changes also signify a spectral transition from subcritical to supercritical regimes. The critical luminosity infers a magnetic field of ∼(4.8−6.0) × 1012 G, which supports the presence of the cyclotron line at ∼47 keV. A Comptonization model applied for the broad X-ray spectra during the outburst also suggests the surface magnetic field ranging from ∼(5−9) × 1012 G.

Detection of a cyclotron line in the Be X-ray pulsar IGR J06074+2205

Context. IGR J0607.4+2205 is a transient Be X-ray binary discovered two decades ago. IGR J0607.4+2205 underwent an outburst in 2023 during which it was observed twice with NuSTAR. Aims. The main goal of this work is to model the broadband X-ray spectrum of IGR J0607.4+2205 during the outburst and to study the variations of the spectral and timing features at different intensities. Methods. We extracted the light curve and spectrum of the source from the two NuSTAR observations carried out during the recent outburst in the energy range of 3−78 keV. We used the epoch folding technique to find pulsation from the source and to study the changes in emission characteristics from the source with energy across an order of magnitude variation in source luminosity. Results. IGR J0607.4+2205 shows pulsations with a period of ∼347.6 s during both the observations, with a pulse fraction of ≥50%. The broadband spectrum of the source was modelled using a power-law continuum with a high-energy cutoff. During the first observation, a cyclotron absorption line at ∼51 keV was also present in the source with an optical depth of ∼1.3. However, no cyclotron line feature was detected in the second observation when the source was an order of magnitude fainter. Additionally, soft excess was detected in the second observation, which was modelled with a black body component emerging from close to the neutron star (NS). Conclusions. We report the first ever detection of a cyclotron line in the broadband spectrum of IGR J0607.4+2205 centred at 51 ± 1 keV. The magnetic field strength of the NS is estimated to be ∼4 × 1012 G from the centroid energy of the absorption line. A significant change is observed in the pulse profile with luminosity during the decay of the outburst, indicating an associated change in the beaming pattern.

The high energy X-ray probe (HEX-P): the future of hard X-ray dual AGN science

A fundamental goal of modern-day astrophysics is to understand the connection between supermassive black hole (SMBH) growth and galaxy evolution. Merging galaxies offer one of the most dramatic channels for galaxy evolution known, capable of driving inflows of gas into galactic nuclei, potentially fueling both star formation and central SMBH activity. Dual active galactic nuclei (dual AGNs) in late-stage mergers with nuclear pair separations <10 kpc are thus ideal candidates to study SMBH growth along the merger sequence since they coincide with the most transformative period for galaxies. However, dual AGNs can be extremely difficult to confirm and study. Hard X-ray (>10 keV) studies offer a relatively contamination-free tool for probing the dense obscuring environments predicted to surround the majority of dual AGN in late-stage mergers. To date, only a handful of the brightest and closest systems have been studied at these energies due to the demanding instrumental requirements involved. We demonstrate the unique capabilities of HEX-P to spatially resolve the soft and - for the first time - hard X-ray counterparts of closely-separated (∼2″−5″) dual AGNs in the local Universe. By incorporating physically-motivated obscuration models, we reproduce realistic broadband X-ray spectra expected for deeply embedded accreting SMBHs. Hard X-ray spatially resolved observations of dual AGNs—accessible only to HEX-P—will hence transform our understanding of dual AGN in the nearby Universe.

The On-axis Jetted Tidal Disruption Event AT2022cmc: X-Ray Observations and Broadband Spectral Modeling

AT2022cmc was recently reported as the first on-axis jetted tidal disruption event (TDE) discovered in the last decade, and the fourth on-axis jetted TDE candidate known so far. In this work, we present NuSTAR hard X-ray (3–30 keV) observations of AT2022cmc, as well as soft X-ray (0.3–6 keV) observations obtained by NICER, Swift, and XMM-Newton. Our analysis reveals that the broadband X-ray spectra can be well described by a broken power law with f ν ∝ ν −0.5 (f ν ∝ ν −1) below (above) the rest-frame break energy of E bk ∼ 10 keV at the observer frame t obs = 7.8 and 17.6 days since discovery. At t obs = 36.2 days, the X-ray spectrum is consistent with either a single power law or a broken power law. By modeling the spectral energy distribution from radio to hard X-ray across the three NuSTAR observing epochs, we find that the submillimeter/radio emission originates from external shocks at large distances ≳1017 cm from the black hole, the UV/optical light comes from a thermal envelope with radius ∼1015 cm, and the X-ray emission is consistent with synchrotron radiation powered by energy dissipation at intermediate radii within the (likely magnetically dominated) jet. We constrain the bulk Lorentz factor of the jet to be of the order 10–100. Our interpretation differs from the model proposed by Pasham et al. where both the radio and X-rays come from the same emitting zone in a matter-dominated jet. Our model for the jet X-ray emission has broad implications on the nature of relativistic jets in other sources such as gamma-ray bursts.

Examining the nature of the ultraluminous X-ray source Holmberg II X-1

We present a comprehensive spectral analysis of the ultraluminous X-ray source Holmberg II X-1 using broadband and high-resolution X-ray spectra taken with the XMM-Newton satellite over a period of 19 yr, taking advantage of data from a recent campaign. We tested several models for the broadband spectra, including a double thermal component provided a reasonable description for the continuum between 0.3 and 10 keV and enabled us to constrain the properties of the accretion disc. The luminosity–temperature trends of the inner and outer disc components broadly agree with the expectations for a thin disc, although the exact values of the slopes are slightly sensitive to the adopted model. However, all tested models show L − T trends that deviate from a power law above a bolometric luminosity of about 5 × 1039 erg s−1, particularly for the hot thermal component associated with the inner accretion flow. Assuming that such deviations are due to the accretion rate exceeding its Eddington limit or, most likely, the super-critical rate, a compact object with a mass of 16–36 M⊙ was inferred, specifically, a stellar-mass black hole. The time-averaged (2021) high-resolution spectra present narrow emission lines at 1 keV primarily from Ne IX-X and a very strong at 0.5 keV from N VII, which indicate Ne–N-rich gas with non-solar abundances. This favours a nitrogen-rich donor star, such as a blue or red supergiant, which has escaped from its native stellar cluster characterised by a low-metallicity environment.

Dealing with broad-band X-ray spectra of faint AGN: a case study

ABSTRACT In this work, we analyse three average-luminosity hard X-ray selected AGN: ESO 506-G27, IGR J19039+3344, and NGC 7465. They have simultaneous Swift/XRT and NuSTAR data never published before and have been poorly studied at X-ray energies. These sources make for interesting targets both from a methodological and scientific point of view. Scientifically, they are of interest since they are possibly heavily absorbed objects, belong to a peculiar class and are variable both in flux and in spectral shape. Methodologically, because it is an interesting exercise to understand how existing spectral models can be applied to faint sources and how the use of NuSTAR data alone and then simultaneous and/or average data impacts on the spectral parameters determination. In this work, we demonstrate that simultaneous data are not sufficient if their statistical quality is poor. Moreover, we show that also the use of time-averaged data when dealing with faint AGN does not always provide confident results as for brighter AGN. Regardless of the poor data quality employed in our analysis, we are able to provide insights into the spectral characteristics of each source. We analyse in detail for the first time the iron line complex of ESO 506-G27, finding not only the presence of the iron K α and K β lines, but also of the iron K edge around 7 keV in the NuSTAR data. We also highlight changes in the absorption properties of IGR J19039+3344 and confirm NGC 7465 to be an unabsorbed type 1 LINER.

X-Ray and Near-Infrared Observations of the Middle-aged Pulsar B1055–52, Its Multiwavelength Spectrum, and Proper Motion* * Based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA. Based also on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by

Previous observations of the middle-aged γ-ray, X-ray, and radio pulsar B1055–52 indicated some peculiarities, such as a suspected changing of the X-ray flux and spectral parameters, a large excess of the alleged thermal component of the UV spectrum over the Rayleigh–Jeans extension of the X-ray thermal spectrum, and a possible double break in the nonthermal spectral component between the optical and X-ray bands. We observed PSR B1055–52 with the XMM-Newton observatory in X-rays and the Hubble Space Telescope in near-infrared (NIR). The analysis of the XMM-Newton observations does not support the notion of long-term changes in the X-ray flux and broadband X-ray spectrum of the pulsar. Using an observing mode less affected by background noise than the previous XMM-Newton observations, we constrain the power-law (PL) spectral index as (F ν ∝ ν α ) in the energy band 3–10 keV. From the NIR–optical data we obtain a PL slope α O = −0.24 ± 0.10 for the color index E(B − V) = 0.03 mag. The slopes and fluxes of the NIR–optical and X-ray nonthermal spectra suggest that the NIR through X-ray emission can be described by the same PL and is generated by the same mechanism, unlike the pulsar’s γ-ray emission. The excess of the UV thermal component over the extension of the X-ray thermal component became smaller but did not disappear, indicating a nonuniformity of the bulk surface temperature. The NIR data also enable us to measure the proper motion accurately, with values μ α = 47.5 ± 0.7 mas yr−1 and μ δ = −8.7 ± 0.7 mas yr−1.

Coronal properties of low-accreting AGNs using Swift, XMM–Newton, and NuSTAR observations

ABSTRACT We studied the broad-band X-ray spectra of Swift/Burst Alert Telescope selected low-accreting active galactic nuclei (AGNs) using the observations from XMM–Newton, Swift, and NuSTAR in the energy range of 0.5–150 keV. Our sample consists of 30 AGNs with Eddington ratio, λEdd < 10−3. We extracted several coronal parameters from the spectral modelling, such as the photon index, hot electron plasma temperature, cutoff energy, and optical depth. We tested whether there exist any correlation/anticorrelation among different spectral parameters. We observe that the relation of hot electron temperature with the cutoff energy in the low accretion domain is similar to what is observed in the high accretion domain. We did not observe any correlation between the Eddington ratio and the photon index. We studied the compactness–temperature diagram and found that the cooling process for extremely low-accreting AGNs is complex. The jet luminosity is calculated from the radio flux, and observed to be related to the bolometric luminosity as $L_{\rm jet} \propto L_{\rm bol}^{0.7}$, which is consistent with the standard radio-X-ray correlation.

X-ray radiative transfer in full 3D with SKIRT

Context. Models of active galactic nuclei (AGN) suggest that their circumnuclear media are complex with clumps and filaments, while recent observations hint towards polar extended structures of gas and dust, as opposed to the classical torus paradigm. The X-ray band could form an interesting observational window to study these circumnuclear media in great detail. Aims. We want to extend the radiative transfer code SKIRT with the X-ray processes that govern the broad-band X-ray spectra of obscured AGN, to study the structure of AGN circumnuclear media in full 3D, based on their reflected X-ray emission. Methods. We extended the SKIRT code with Compton scattering on free electrons, photo-absorption and fluorescence by cold atomic gas, scattering on bound electrons, and extinction by dust. This includes a novel treatment of extreme-forward scattering by dust, and a detailed description of anomalous Rayleigh scattering. To verify our X-ray implementation, we performed the first dedicated benchmark of X-ray torus models, comparing five X-ray radiative transfer codes. Results. The resulting radiative transfer code covers the X-ray to millimetre wavelength range self-consistently, has all the features of the established SKIRT framework, is publicly available, and is fully optimised to operate in arbitrary 3D geometries. In the X-ray regime, we find an excellent agreement with the simulation results of the MYTORUS and REFLEX codes, which validates our X-ray implementation. We find some discrepancies with other codes, which illustrates the complexity of X-ray radiative transfer and motivates the need for a robust framework that can handle non-linear 3D radiative transfer effects. We illustrate the 3D nature of the code by producing synthetic X-ray images and spectra of clumpy torus models. Conclusions. SKIRT forms a powerful new tool to model circumnuclear media in full 3D, and make predictions for the X-ray band in addition to the dust-dominated infrared-to-UV wavelength range. The new X-ray functionalities of the SKIRT code allow for uncomplicated access to a broad suite of 3D X-ray models for AGN that can easily be tested and modified. This will be particularly useful with the advent of X-ray microcalorimeter observations in the near future.

Investigating the Time Evolution of the Thermal Emission from the Putative Neutron Star in SN 1987A for 50+ Years

Observations collected with the Atacama Large Millimeter/submillimeter Array (ALMA) and analysis of broadband X-ray spectra have recently suggested the presence of a central compact object (CCO) in SN 1987A. However, no direct evidence of the CCO has been found yet. Here we analyze Chandra X-ray observations of SN 1987A collected in 2007 and 2018, and synthesize 2027 Chandra and 2037 Lynx spectra of the faint inner region of SN 1987A. We estimate the temporal evolution of the upper limits of the intrinsic luminosity of the putative CCO in three epochs (2018, 2027, and 2037). We find that these upper limits are higher for higher neutron star (NS) kick velocities due to increased absorption from the surrounding cold ejecta. We compare NS cooling models with both the intrinsic luminosity limits obtained from the X-ray spectra and the ALMA constraints with the assumption that the observed blob of SN 1987A is primarily heated by thermal emission. We find that the synthetic Lynx spectra are crucial to constrain the physical properties of the CCO, which will be confirmed by future observations in the 2040s. We draw our conclusions based on two scenarios, namely the nondetection and detection of the NS by Lynx. If the NS is not detected, its kick velocity should be ≃700 km s−1. Furthermore, nondetection of the NS would suggest rapid cooling processes at the age of 40 yr, implying strong crust superfluidity. Conversely, in the case of NS detection, the mass of the NS envelope must be high.

Capturing the lowest luminosity state of the supergiant fast X-ray transient XTE J1739−302

Here, we report the results of our analysis of recent Chandra, XMM-Newton, and NuSTAR observations of the supergiant fast X-ray transient XTE J1739−302. The source was caught in a low X-ray luminosity state, from a few 1031–1034 erg s−1 (0.5–10 keV). A very low X-ray luminosity was captured during an XMM-Newton observation performed in October 2022, at a few 1031 erg s−1 (0.5–10 keV), which had never been observed before in XTE J1739−302. The XMM-Newton spectrum could be well fitted either by an absorbed, steep power-law model (photon index of 3.5) or by a collisionally ionized diffuse gas with a temperature of 0.7 keV that would very likely have been produced by shocks in the supergiant donor wind. These observations covered different orbital phases, but they all appear compatible with the low luminosity level expected from the orbital INTEGRAL light curve. The absorbing column density is variable in the range between 1022 and 1023 cm−2. The broadband X-ray spectrum was feasibly investigated at 1034 erg s−1 (0.5–30 keV) for the first time in XTE J1739−302 with non-simultaneous (albeit at similar orbital phases) Chandra and NuSTAR data, showing a power-law spectral shape with a photon index of ∼2.2 and an absorbing column density of ∼1023 cm−2. Remarkably, owing to the XMM-Newton observation, the amplitude of the X-ray variability now exceeds five orders of magnitude, making XTE J1739−302 one of the most extreme SFXTs.

The Complex X-Ray Obscuration Environment in the Radio-loud Type 2 Quasar 3C 223

3C 223 is a radio-loud, Type 2 quasar at z = 0.1365 with an intriguing X-ray Multi-mirror Mission (XMM)-Newton spectrum that implicated it as a rare, Compton-thick (N H ≳ 1.25 × 1024 cm−2) active galactic nucleus (AGN). We obtained contemporaneous XMM-Newton and Nuclear Spectroscopic Telescope Array (NuSTAR) spectra to fit the broadband X-ray spectrum with the physically motivated MYTorus and borus02 models. We confirm earlier results that the obscuring gas is patchy with both high (though not Compton-thick) levels of obscuration (N H > 1023 cm−2) and gas clouds with column densities up to an order of magnitude lower. The spectral fitting results indicate additional physical processes beyond those modeled in the spectral grids of MYTorus and borus02 impact the emergent spectrum: the Compton-scattering region may be extended beyond the putative torus; a ring of heavy Compton-thick material blocks most X-ray emission along the line of sight; or the radio jet is beamed, boosting the production of Fe Kα line photons in the global medium compared with what is observed along the line of sight. We revisit a recent claim that no radio-loud Compton-thick AGN have yet been conclusively shown to exist, finding three reported cases of radio-loud AGN with global average (but not line-of-sight) column densities that are Compton thick. Now that it is possible to separately determine line-of-sight and global column densities, inhomogeneity in the obscuring medium has consequences for how we interpet the spectrum and classify an AGN as “Compton thick.”

Investigating the variability of Swift-BAT blazars with NICER

ABSTRACT We present results of X-ray spectral and time-domain variability analyses of four faint, ‘quiescent’ blazars from the Swift-BAT 105-month catalogue. We use observations from a recent, 5-month long NICER campaign, as well as archival BAT data. Variations in the 0.3–2 keV flux are detected on minute, ∼weekly, and monthly time-scales, but we find that the fractional variability Fvar on these time-scales is <25 per cent and decreases on longer time-scales, implying generally low-amplitude variability across all sources and showing very low variability on monthly time-scales ($F_{\rm var}\lesssim 13{{\ \rm per\ cent}}$), which is at odds with previous studies that show that blazars are highly variable in the X-rays on a wide range of time-scales. Moreover, we find that the flux variability on very short time-scales appears to be characterized by long periods of relative quiescence accompanied by occasional short bursts, against the relatively time-stationary nature of the variability of most other AGN light curves. Our analysis also shows that the broadband X-ray spectra (0.3–195 keV) of our sources can be described with different power-law models. As is the case with most blazars, we find that two sources (2MASS J09343014-1721215 and PKS 0312-770) are well-modelled with a simple power law, while the remaining two (1RXS J225146.9-320614 and PKS 2126-15) exhibit curvature in the form of a log-parabolic power law. We also find that, in addition to the continuum, PKS 2126-15 requires significant absorption at the soft X-rays (≲1 keV) to fully describe the observed curvature, possibly due to absorption from the intergalactic medium.

Discovery of two cyclotron resonance scattering features in X-ray pulsar cen X-3 by Insight-HXMT

ABSTRACT We present the results of the neutron star X-ray binary system Cen X-3 performed by Insight-HXMT with two observations during 2017 and 2018. During these two observations, the source reached a X-ray luminosity of ∼1038 erg s−1 from 2–105 keV. The analysis of the broadband X-ray spectrum reports the presence of two cyclotron resonance scattering features (CRSFs) with the fundamental line at ∼ 28 keV and the harmonic line at ∼47 keV. The multiple lines exist by fittings with different continuum models, like the absorbed negative and positive power-law with an exponential cutoff (NPEX) model and a power-law with high energy exponential cutoff model. This is the first time that both fundamental and harmonic lines are detected in Cen X-3. We also show evidence of two cyclotron lines in the phase-resolved spectrum of Cen X-3. The CRSF and continuum spectral parameters show evolution with the pulse profile, and the two line centroid energy ratio does not change significantly and locates in a narrow value range of 1.6−1.7 over the pulse phase. The implications of the discovering two cyclotron absorption features and phase-resolved spectral properties are discussed.

Multiwavelength Analysis of a Nearby Heavily Obscured AGN in NGC 449

We present the multiwavelength analysis of a heavily obscured active galactic nucleus (AGN) in NGC 449. We first constructed a broadband X-ray spectrum using the latest NuSTAR and XMM-Newton data. Its column density (≃1024 cm−2) and photon index (Γ ≃ 2.4) were reliably obtained by analyzing the broadband X-ray spectrum. However, the scattering fraction and the intrinsic X-ray luminosity could not be well constrained. Combined with the information obtained from the mid-infrared spectrum and spectral energy distribution fitting, we derived its intrinsic X-ray luminosity (≃8.54 × 1042 erg s−1) and scattering fraction (f scat ≃ 0.26%). In addition, we also derived the following results. (1) The mass accretion rate of the central AGN is about 2.54 × 10−2 M ⊙ yr−1, and the Eddington ratio is 8.39 × 10−2. (2) The torus of this AGN has a high gas-to-dust ratio (N H/A V = 8.40 × 1022 cm−2 mag−1). (3) The host galaxy and central AGN are both in the early stage of coevolution.

Seven Years of Coordinated Chandra–NuSTAR Observations of SN 2014C Unfold the Extreme Mass-loss History of Its Stellar Progenitor

We present the results from our 7 yr long broadband X-ray observing campaign of SN 2014C with Chandra and NuSTAR. These coordinated observations represent the first look at the evolution of a young extragalactic SN in the 0.3–80 keV energy range in the years after core collapse. We find that the spectroscopic metamorphosis of SN 2014C from an ordinary type Ib SN into an interacting SN with copious hydrogen emission is accompanied by luminous X-rays reaching L x ≈ 5.6 × 1040 erg s−1 (0.3–100 keV) at ∼1000 days post-explosion and declining as L x ∝ t −1 afterwards. The broadband X-ray spectrum is of thermal origin and shows clear evidence for cooling after peak, with . Soft X-rays of sub-keV energy suffer from large photoelectric absorption originating from the local SN environment with . We interpret these findings as the result of the interaction of the SN shock with a dense (n ≈ 105 − 106 cm−3), H-rich disk-like circumstellar medium (CSM) with inner radius ∼2 × 1016 cm and extending to ∼1017 cm. Based on the declining NHint(t) and X-ray luminosity evolution, we infer a CSM mass of ∼(1.2 f–2.0 , where f is the volume filling factor. We place SN 2014C in the context of 121 core-collapse SNe with evidence for strong shock interaction with a thick circumstellar medium. Finally, we highlight the challenges that the current mass-loss theories (including wave-driven mass loss, binary interaction, and line-driven winds) face when interpreting the wide dynamic ranges of CSM parameters inferred from observations.

Tell-tale Spectral Signatures of MHD-driven Ultrafast Outflows in AGNs

We aim to explore spectral signatures of the predicted multi-ion ultrafast outflows (UFOs) in the broadband X-ray spectra of active galactic nuclei by exploiting an accretion disk-wind model in the context of a simple magnetohydrodynamic (MHD) framework. We are focused primarily on examining the spectral dependences on a number of key properties: (1) ionizing luminosity ratio λ ion, (2) line-of-sight wind density slope p, (3) optical/UV-to-X-ray strength α OX, (4) inclination θ, (5) X-ray photon index Γ, and (6) wind density factor f D . With an emphasis on radio-quiet Seyferts in the sub-Eddington regime, multi-ion UFO spectra are systematically calculated as a function of these parameters to show that MHD-driven UFOs imprint a unique asymmetric absorption line profile with a pronounced blue tail structure on average. Such a characteristic line signature is generic to the simplified MHD disk-wind models presented in this work due to their specific kinematics and density structure. The properties of these absorption line profiles could be utilized as a diagnostics to distinguish between different wind-driving mechanisms or even the specific values of given MHD wind parameters. We also present high-fidelity microcalorimeter simulations in anticipation of the upcoming XRISM/Resolve and Athena/X-IFU instruments to demonstrate that such a “tell-tale” sign may be immune to a spectral contamination by the presence of additional warm absorbers and partially covering gas.

Broad-band spectral analysis of Mrk 926 using multi-epoch X-ray observations

ABSTRACT The X-ray spectra of some active galactic nuclei (AGNs) show a soft X-ray excess, emission in excess to the extrapolated primary X-ray continuum below 2 keV. Recent studies have shown that this soft excess can be described well as originating from either a relativistic ionized reflection, the extreme blurring of the reprocessed emission from the innermost region of the accretion disc, or Comptonization from an optically thick and warm region called the ‘warm corona’, in which electron scattering is the dominant source of opacity. To constrain the origin of the soft excess in the Seyfert 1 galaxy Mrk 926, we carry out a multi-epoch X-ray spectral study using observations from Suzaku (2009), XMM–Newton and NuSTAR (2016), and NuSTAR and Swift-XRT (2021). The broad-band X-ray spectra of Mrk 926 contains a thermally Comptonized primary continuum, a variable soft excess, and distant reflection. We find that in Mrk 926 as in so many sources, it is difficult to make a definite statement as to what is causing the observed soft excess. A warm coronal-like component is slightly preferred by the data but a reflection origin is also possible. Using archival radio data, we detect an optically thin radio component in our broad-band study of Mrk 926. While this component is consistent with an optically thin radio jet, future multiwavelength observations including high spatial resolution radio observations at multiple frequencies are required to probe the origin of the radio emission in more detail.

On the Formation of Over-ionized Plasma in Evolved Supernova Remnants

One of the outstanding mysteries surrounding the rich diversity found in supernova remnants (SNRs) is the recent discovery of over-ionized or recombining plasma from a number of dynamically evolved objects. To help decipher its formation mechanism, we have developed a new simulation framework capable of modeling the time evolution of the ionization state of the plasma in an SNR. The platform is based on a one-dimensional hydrodynamics code coupled to a fully time-dependent nonequilibrium ionization calculation, accompanied by a spectral synthesis code to generate space-resolved broadband X-ray spectra for SNRs at arbitrary ages. We perform a comprehensive parametric survey to investigate the effects of different circumstellar environments on the ionization state evolution in SNRs up to a few 104 yr. A two-dimensional parameter space, spanned by arrays of interstellar medium (ISM) densities and mass-loss rates of the progenitor, is used to create a grid of models for the surrounding environment, in which a core-collapse explosion is triggered. Our results show that a recombining plasma can be successfully reproduced in the case of a young SNR (a few 100 to 1000 yr old) expanding fast in a spatially extended low-density wind, an old SNR (>a few 1000 yr) expanding in a dense ISM, or an old SNR broken out from a confined dense wind region into a tenuous ISM. Finally, our models are confronted with observations of evolved SNRs, and an overall good agreement is found except for a couple of outliers.