Optical Spectral Features Research Articles

CHAOS. VIII. Far-ultraviolet Spectra of M101 and the Impact of Wolf–Rayet Stars* ∗Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the Data Archive at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

We investigate the stellar and nebular properties of nine H ii regions in the spiral galaxy M101 with far-ultraviolet (FUV; ∼900–2000 Å) and optical (∼3200–10,000 Å) spectra. We detect significant C iii] λλ1907,1909 nebular emission in seven regions, but O iii] λ1666 only in the lowest-metallicity region. We produce new analytic functions of the carbon ionization correction factors as a function of metallicity in order to perform a preliminary C/O abundance analysis. The FUV spectra also contain numerous stellar emission and P-Cygni features that we fit with luminosity-weighted combinations of single-burst Starburst99 and BPASS models. We find that the best-fit Starburst99 models closely match the observed very-high-ionization P-Cygni features, requiring very hot, young (≲3 Myr), metal-enriched massive stars. The youngest stellar populations are strongly correlated with broad He ii emission, nitrogen Wolf–Rayet (WR) FUV and optical spectral features, and enhanced N/O gas abundances. Thus, the short-lived WR phase may be driving excess emission in several N P-Cygni wind features (λ955, λ991, λ1720) that bias the stellar continuum fits to higher metallicities relative to the gas-phase metallicities. Accurate characterization of these H ii regions requires additional inclusion of WR stars in the stellar population synthesis models. Our FUV spectra demonstrate that the ∼900–1200 Å FUV can provide a strong test bed for future WR atmosphere and evolution models.

Dual-modal identification of jadeite based on optical coherence tomography images and Raman spectral features.

Low-quality jadeite is often subjected to bleaching, filling, and dyeing to improve its texture and consequently increase its value. In this study, natural jadeite, bleached and filled jadeite, and dyed jadeite were investigated by combining Raman spectroscopy and optical coherence tomography (OCT). The results show that jadeite composition can be identified from Raman peaks around 205, 377, 700, and 1040c m -1. The presence of epoxy filler can be detected from Raman peaks at 1113, 1187, and 1609c m -1, among which the features of 1113 and 1609c m -1 are particularly significant. Dyed jadeite exhibits a pronounced fluorescence background in its Raman spectrum due to the injected dye. After noise reduction, texture vectors representing the texture of bleached or dyed jadeite can be obtained from OCT images. These vectors differ from the corresponding texture vector of natural jadeite. Most processed jadeites have relatively low texture vector intensities due to particle reduction and texture damage during processing. However, the texture vector strengths of jadeites can be increased through internal silting.

New Insight into the FS CMa System MWC 645 from Near-Infrared and Optical Spectroscopy

The B[e] phenomenon is manifested by a heterogeneous group of stars surrounded by gaseous and dusty circumstellar envelopes with similar physical conditions. Among these stars, the FS CMa-type objects are suspected to be binary systems, which could be experiencing or have undergone a mass-transfer process that could explain the large amount of material surrounding them. We aim to contribute to the knowledge of a recently confirmed binary, MWC 645, which could be undergoing an active mass-transfer process. We present near-infrared and optical spectra, identify atomic and molecular spectral features, and derive different quantitative properties of line profiles. Based on publicly available photometric data, we search for periodicity in the light curve and model the spectral energy distribution. We have detected molecular bands of CO in absorption at 1.62 μm and 2.3 μm for the first time. We derive an upper limit for the effective temperature of the cool binary component. We found a correlation between the enhancement of the Hα emission and the decrease in optical brightness that could be associated with mass-ejection events or an increase in mass loss. We outline the global properties of the envelope, possibly responsible for brightness variations due to a variable extinction, and briefly speculate on different possible scenarios.

Al/Si dopants effect on the electronic and optical behaviors of graphene mono-layers useful for infrared detector devices

Two-dimensional (2D) graphene with different forms is a prosperous class of materials beneficial in nano-electronics, and infrared-detector devices. Herein, we analyze the electronic and optical behaviours of electron acceptor (Al)- and isovalent (Si) inserted into graphene sheets, which are computed by utilizing ab-initio simulations. We find that the individual doping impurities of Al or Si atoms onto monolayer graphene result in p-type and semiconducting behaviours, respectively, attributed to the contribution of the valence electrons number of these atoms to the host 2D honeycomb lattice of graphene. Even though the Al atom contributing one less electron to the host lattice, both individual impurities of the Al- or Si-doped materials are found to cause a splitting in the valence states and conduction states at the K-point, leading to the opening of the Dirac cone. In monolayer graphene, doping two Al atoms into the nearest neighbour sites creates a trivial metallic system, while doping two Si atoms into the nearest neighbour sites causes the Dirac cone to re-emerge. Owing to the stark difference in the electronic structure results of mono- and double-atom substitution of Al/Si in graphene single-layers, we find different optical behaviours in these doped systems. Additionally, X-ray absorption spectroscopy simulations are employed to inspect the core-level spectra of pure and substitutional doped graphene single layers. Accordingly, the optical spectral features of graphene single-layers substituted with foreign impurities, such as Al/Si have revealed the tailoring of optical absorption from the infrared to the visible windows. Due to the outstanding characteristics of this 2D dimensional gapless graphene, our simulated results could provide a guidance for future experimental investigations into the fabrication of doped graphene sheets suitable for infrared detectors, photonics, and modern optoelectronic devices integrated into advanced technologies.

The optical spectral features of 27 Fermi blazars

ABSTRACT Spectral variation accompanied by flux variability is a commonly observed phenomenon for blazars. In order to investigate the optical spectral feature of blazars further, we collected the long-term optical V- and R-band data of 27 blazars (14 BL Lacaerte objects, BL Lacs, and 13 flat-spectrum radio quasars, FSRQs) and calculated their optical spectral indices. The results show that the spectral indices vary with respect to brightness for all of these blazars. In general, the optical spectrum progressively becomes flatter (or steeper), when the brightness increases. However the spectrum changes more and more slowly, until it tends to stability. In other words, the source becomes bluer (or redder) and then gradually stabilizes when it brightens, behaviours that are referred to as bluer-stable-when-brighter (BSWB) and redder-stable-when-brighter (RSWB), respectively. A total of 13 of the 14 BL Lacs show the BSWB behaviour, the exception being AO 0235+164. In contrast, most of the FSRQs (10 out of 13) exhibit the RSWB trend. It is confirmed that blazars follow the two universal optical spectral behaviours, namely BSWB and RSWB. The model of two constant-spectral-index components can explain the optical spectral features well both qualitatively and quantitatively. The results illustrate that the optical emission is composed mainly of two stable-colour components, namely less variable thermal emission and highly variable synchrotron radiation. Furthermore, in most cases, the thermal component of BL Lacs is redder than that of synchrotron radiation, whereas the opposite is true for FSRQs.

AGN Selection and Demographics in GOODS-S/HUDF from X-Ray to Radio

We present a comprehensive census of the active galactic nuclei (AGNs) in the GOODS-S/HUDF region from the X-ray to the radio, covering both the obscured and unobscured populations. This work includes a robust analysis of the source optical to mid-IR spectral energy distributions (SEDs) featuring (semi)empirical AGN and galaxy dust emission models and Bayesian fitting techniques, ultra-deep Very Large Array 3 and 6 GHz observations, and an integrated analysis of various AGN selection techniques, including X-ray properties, UV to mid-IR SED analysis, optical spectral features, mid-IR colors, radio-loudness and spectral slope, and AGN variability. In total, we report ∼900 AGNs over the ∼170 arcmin2 3D-HST GOODS-S footprint, which has doubled the AGN number identified in the previous X-ray sample, with ∼26% of our sample undetected in the deepest Chandra image. With a summary of AGN demographics from different selection methods, we find that no one single band or technique comes close to selecting a complete AGN sample despite the great depth of the data in GOODS-S/HUDF. We estimate the yields of various approaches and explore the reasons for incompleteness. We characterize the statistical properties, such as source number density, obscuration fraction, and luminosity function of the AGN sample in this field, and discuss their immediate implications. We also provide some qualitative predictions of the AGN sample that might be discovered by the upcoming JWST surveys.

The relation between quasars’ optical spectra and variability

Abstract Brightness variation is an essential feature of quasars, but its mechanism and relationship to other physical quantities are not understood well. We aimed to find the relationship between the optical variability and spectral features to reveal the regularity behind the random variation. It is known that a quasar’s Fe ii/Hβ flux ratio and equivalent width of [O iii]5007 are negatively correlated; this is called Eigenvector 1. In this work, we visualized the relationship between the position on this Eigenvector 1 (EV1) plane and how the brightness of the quasars had changed after ∼10 yr. We conducted three analyses, using a different quasar sample in each. The first analysis showed the relation between the quasars’ distributions on the EV1 plane and how much they had changed brightness, using 13438 Sloan Digital Sky Survey quasars. This result shows how brightness changes later are clearly related to the position on the EV1 plane. In the second analysis, we plotted the sources reported as “changing-look quasars” (or “changing-state quasars”) on the EV1 plane. This result shows that the position on the EV1 plane corresponds to the activity level of each source, and the bright or dim states of them are distributed on the opposite sides divided by the typical quasar distribution. In the third analysis, we examined the transition vectors on the EV1 plane using sources with multiple-epoch spectra. This result shows that the brightening and dimming sources move on a similar path and they reach a position corresponding to the opposite activity level. We also found this trend is opposite to the empirical rule that $R_{\rm {Fe\, \small {II}}}$ positively correlated with the Eddington ratio, which has been proposed based on the trends of a large number of quasars. From all these analyses, it is indicated that quasars tend to oscillate between both sides of the distribution ridge on the EV1 plane; each of them corresponds to a dim state and a bright state. This trend in optical variation suggests that significant brightness changes, such as changing-look quasars, are expected to repeat.

Sub-megahertz spectral dip in a resonator-free twisted gain medium

Ultra-narrow optical spectral features resulting from highly dispersive light–matter interactions are essential for a broad range of applications such as spectroscopy, slow-light and high-precision sensing. Features approaching sub-megahertz or, equivalently, Q-factors up to one billion and beyond, are challenging to obtain in solid-state systems, ultimately limited by loss. We present a novel approach to achieve tunable sub-megahertz spectral features at room temperature without resonators. We exploit gain-enhanced polarization pulling in a twisted birefringent medium where polarization eigenmodes are frequency-dependent. Using Brillouin gain in a commercial spun fibre, we experimentally achieve a 0.72 MHz spectral dip, the narrowest backward Brillouin scattering feature ever reported. Further optimization can potentially reduce the linewidth to <0.1 MHz. Our approach is simple and broadly applicable, offering on-demand tunability and high sensitivity, with a wide range of applications such as microwave photonic filters, slow and fast light, and optical sensing. Tunable sub-megahertz spectral features are demonstrated without resonators. The approach, which exploits gain-enhanced polarization pulling in a twisted birefringent medium, may be useful in applications such as microwave photonic filters, slow and fast light, and optical sensing.

X-Ray Evidence Against the Hypothesis that the Hyperluminous z = 6.3 Quasar J0100+2802 is Lensed

Abstract The z = 6.327 quasar SDSS J010013.02+280225.8 (hereafter J0100+2802) is believed to be powered by a black hole more massive than 1010 M ⊙, making it the most massive black hole known in the first billion years of the universe. However, recent high-resolution ALMA imaging shows four structures at the location of this quasar, potentially implying that it is lensed with a magnification of μ ∼ 450 and thus its black hole is significantly less massive. Furthermore, for the underlying distribution of magnifications of z ≳ 6 quasars to produce such an extreme value, theoretical models predict that a larger number of quasars in this epoch should be lensed, implying further overestimates of early black hole masses. To provide an independent constraint on the possibility that J0100+2802 is lensed, we reanalyzed archival XMM-Newton observations of the quasar and compared the expected ratios of X-ray luminosity to rest-frame UV and IR luminosities. For both cases, J0100+2802's X-ray flux is consistent with the no-lensing scenario; while this could be explained by J0100+2802 being X-ray faint, we find it does not have the X-ray or optical spectral features expected for an X-ray faint quasar. Finally, we compare the overall distribution of X-ray fluxes for known, typical z ≳ 6 quasars. We find a 3σ tension between the observed and predicted X-ray-to-UV flux ratios when adopting the magnification probability distribution required to produce a μ = 450 quasar.

Eye‐Friendly Reflective Structural Colors with Shortwave Infrared Shielding

AbstractA large number of structural colors proposed concentrate on the optical spectral features in the visible region for improving their color gamut, purity, and brightness. However, there are few attentions on the shortwave infrared region of structural colors, detrimental to human eyes under the long‐term exposure. Here, an asymmetric Fabry–Pérot cavity‐based reflective structural color, composed of planar alternating multilayers of Ti and indium tin oxide (ITO), is proposed and demonstrated, which possesses distinguishing optical features in both visible and shortwave infrared regions. The resonant optical filter at the visible region exhibits a high‐contrast reflective peak due to the constructive interference, generating purer and brighter reflective colors. While displaying vivid colors, the designed structure can also achieve an average light absorption up to 89% across the whole shortwave infrared region to effectively prevent it entering human eyes, benefitting from destructive interference. By controlling the dielectric ITO spacer thickness, full‐color display covering the entire visible region can be realized, even including black color. Consequently, the color gamut exhibits around 135% of standard Red Green Blue (sRGB) and 100% of Adobe RGB. Meanwhile, the proposed structural colors also demonstrate an angle tolerance of 60°, a good thermal stability, and mechanical flexibility.

Estimating Teff, radius, and luminosity of M-dwarfs using high-resolution optical and NIR spectral features

ABSTRACT We estimate effective temperature (Teff), stellar radius, and luminosity for a sample of 271 M-dwarf stars (M0V-M7V) observed as a part of CARMENES (Calar Alto high-Resolution search for M dwarfs with Exo-earths with Near-infrared and optical Echelle Spectrographs) radial-velocity planet survey. For the first time, using the simultaneously observed high-resolution ($R\sim 90\, 000$) spectra in the optical (0.52–0.96 $\mu$m) and near-infrared (0.96–1.71 $\mu$m) bands, we derive empirical calibration relationships to estimate the fundamental parameters of these low-mass stars. We select a sample of nearby and bright M-dwarfs as our calibrators for which the physical parameters are acquired from high-precision interferometric measurements. To identify the most suitable indicators of Teff, radius, and luminosity (log L/L⊙), we inspect a range of spectral features and assess them for reliable correlations. We perform multivariate linear regression and find that the combination of pseudo-equivalent widths and equivalent width ratios of the Ca ii at 0.854 $\mu$m and Ca ii at 0.866 $\mu$m lines in the optical and the Mg i line at 1.57 $\mu$m in the near-infrared give the best fitting linear functional relations for the stellar parameters with root mean square errors of 99K, 0.06 R⊙, and 0.22 dex, respectively. We also explore and compare our results with literature values obtained using other different methods for the same sample of M dwarfs.

Prediction and observation of intermodulation sidebands from anharmonic phonons in NaBr

A quantum Langevin model, similar to models used recently for optomechanics, was used to predict intermodulation phonon sidebands (IPS). Ab initio calculations of anharmonic phonons in rocksalt NaBr showed these spectral features as "many-body effects". Modern inelastic neutron scattering measurements on a crystal of NaBr at 300K revealed diffuse intensity at high phonon energy from a predicted upper IPS. The transverse optical (TO) part of the new features originates from phonon intermodulation between the transverse acoustic (TA) and TO phonons. The longitudinal optical (LO) spectral features originate from three-phonon coupling between the TA modes and the TO lattice modes. The partner lower IPS proves to be an "intrinsic localized mode". Interactions with the thermal bath broaden and redistribute the spectral weight of the IPS pair. These sidebands are a probe of anharmonicity and quantum noise, which originate from interactions between the phonons in NaBr.

Modeling Type Ic Supernovae with tardis: Hidden Helium in SN 1994I?

Abstract Supernovae (SNe) with photospheric spectra devoid of hydrogen and helium features are generally classified as SNe Ic. However, there is ongoing debate as to whether helium can be hidden in the ejecta of SNe Ic (that is, helium is present in the ejecta, but produces no obvious features in the spectra). We present the first application of the fast, 1D radiative transfer code tardis to an SN Ic, and we investigate the question of how much helium can be hidden in the outer layers of the SN Ic ejecta. We generate tardis models for the nearby, well-observed, and extensively modeled SN Ic 1994I, and we perform a code comparison to a different, well-established Monte Carlo based radiation transfer code. The code comparison shows that tardis produces consistent synthetic spectra for identical ejecta models of SN 1994I. In addition, we perform a systematic experiment of adding outer He shells of varying masses to our SN 1994I models. We find that an outer He shell of only 0.05M ⊙ produces strong optical and near-infrared (NIR) He spectral features for SN 1994I which are not present in observations, thus indicating that the SN 1994I ejecta is almost fully He deficient compared to the He masses of typical He-rich SN progenitors. Finally we show that the He i λ20851 line pseudo-equivalent width of our modeled spectra for SN 1994I could be used to infer the outer He shell mass which suggests that NIR spectral follow-up of SNe Ic will be critical for addressing the hidden helium question for a statistical sample of SNe Ic.

Synthesis, TDDFT Calculations and Biological Evaluation of Dicationic Porphyrins as Groove Binders and Antimicrobial Agents

AbstractA2B2 porphyrin bearing 2/3‐thienyl and 2‐pyridyl moieties (P1a, P3a) and its dicationic derivatives (P2a, P4a) were synthesized in reasonably good yield. The corresponding Copper (II) (P1‐4 b) and Zinc (II) metallated (P1‐4 c) analogs were obtained by conventional methods. The synthesized compounds were characterized by various spectroscopic techniques, electrochemical studies and thermogravimetric analysis. The Copper (II) porphyrin, P1b is structurally characterized by single‐crystal X‐ray structure analysis. The ground state electronic structure and geometry optimizations are carried out by DFT calculations. The computed TD‐DFT results validate the observed optical bands and spectral features. DNA interaction studies of trans‐dicationic porphyrins were performed using spectroscopic titrations, docking studies, and gel electrophoresis experiments. All porphyrins interact with the calf thymus DNA by outside groove binding mode with self‐stacking, and the highest intrinsic binding constant of 1.29 ± 0.14×106 M‐1 is observed for P4a. Molecular docking studies reveal that the binding energy of porphyrins with DNA is around −10 kcal/mol. The antimicrobial properties of the dicationic derivatives (P2,4 a, b, c) were investigated against E. Coli and S. aureus under light and dark conditions, and the growth inhibitory effect is found to be negligible when unilluminated.

Raman Ink for Steganography

AbstractSteganography, also known as “invisible” communication, refers to the technique of hiding information into another medium such as video, audio, image, and text. Surface‐enhanced Raman scattering (SERS) nanotags are well suited to information encoding owing to their nanoscale dimensions, fingerprint optical spectral features, and remarkable multiplexing capability. Herein, Raman ink, fabricated by doping a new type of SERS nanotags (gap‐enhanced Raman tags, GERTs) into commercial ink, is demonstrated as security ink for multiplexing steganography. A stego‐text is written using two types of Raman ink containing different GERTs with diverse Raman signals, imaged via a confocal Raman system, and processed by the classical least squares method to extract the hidden message. The Raman ink generates distinct spectral profiles with low background from pure ink upon near‐infrared laser irradiation. A multiplexing combination of seven kinds of messages extracted from the written stego‐text is demonstrated, which adds enhanced safety and flexibility to information encoding. In addition, Raman ink exhibits good photostability and long‐term stability. Therefore, GERTs‐based Raman ink is promising for steganographic use in information security.

New Observations with Gemini and GTC of the VHE Blazar KUV 00311–1938: About Its Redshift and Environment

Extragalactic very-high-energy (VHE; E > 100 GeV) sources are unique objects to study the most powerful particle accelerators in nature, as active galactic nuclei are likely sources of ultra-high-energy cosmic rays. BL Lacertae blazars are the most frequent extragalactic objects found in the VHE gamma-ray catalogs. It is very difficult to estimate their redshifts, considering they have no strong enough optical spectral features, hence ∼20% of them have unknown or poorly constrained redshifts. KUV 00311–1938 is a VHE BL Lacertae blazar, with an uncertain redshift in the range of 0.5 < z < 0.98. We have obtained deep spectroscopy using Gemini and the GTC telescopes of KUV 00311–1938 and its surroundings with high signal-to-noise ratio in 2016–2017. The lack of features did not allow us to determine the spectroscopic redshift of KUV 00311–1938; nevertheless, we obtain a lower limit of z ≳ 0.475. We determined the redshifts of 41 galaxies observed in the field-of-view of the blazar and through a population study, identified three pairs and four groups consisting of 3 or 4 members with redshifts in the range z = 0.1468–0.4756. Due to the absence of a large group of galaxies, we could not associate KUV 00311–1938 with any of the groups detected.

On the Fraction of X-Ray-weak Quasars from the Sloan Digital Sky Survey

Abstract We investigate systematically the X-ray emission from type 1 quasars using a sample of 1825 Sloan Digital Sky Survey non-broad absorption line (non-BAL) quasars with Chandra archival observations. A significant correlation is found between the X-ray-to-optical power-law slope parameter (α OX) and the 2500 Å monochromatic luminosity (L 2500Å), and the X-ray weakness of a quasar is assessed via the deviation of its α OX value from that expected from this relation. We demonstrate the existence of a population of non-BAL X-ray-weak quasars, and the fractions of quasars that are X-ray weak by factors of ≥6 and ≥10 are 5.8% ± 0.7% and 2.7% ± 0.5%, respectively. We classify X-ray-weak quasars (X-ray weak by factors of ≥6) into three categories based on their optical spectral features: weak emission-line quasars (WLQs; C iv rest-frame equivalent width &lt; 16 Å), red quasars (Δ(g − i) &gt; 0.2), and unclassified X-ray-weak quasars. The X-ray-weak fraction of within the WLQ population is significantly higher than that within non-WLQs, confirming previous findings that WLQs represent one population of X-ray-weak quasars. The X-ray-weak fraction of within the red quasar population is also considerably higher than that within the normal quasar population. The unclassified X-ray-weak quasars do not have unusual optical spectral features, and their X-ray weakness may be mainly related to quasar X-ray variability.

The Curious Case of PHL 293B: A Long-lived Transient in a Metal-poor Blue Compact Dwarf Galaxy

Abstract We report on small-amplitude optical variability and recent dissipation of the unusually persistent broad emission lines in the blue compact dwarf galaxy PHL 293B. The galaxy’s unusual spectral features (P Cygni-like profiles with ∼800 km s−1 blueshifted absorption lines) have resulted in conflicting interpretations of the nature of this source in the literature. However, analysis of new Gemini spectroscopy reveals the broad emission has begun to fade after being persistent for over a decade prior. Precise difference imaging light curves constructed with the Sloan Digital Sky Survey and the Dark Energy Survey reveal small-amplitude optical variability of ∼0.1 mag in the g band offset by 100 ± 21 pc from the brightest pixel of the host. The light curve is well-described by an active galactic nuclei (AGN)-like damped random walk process. However, we conclude that the origin of the optical variability and spectral features of PHL 293B is due to a long-lived stellar transient, likely a Type IIn supernova or nonterminal outburst, mimicking long-term AGN-like variability. This work highlights the challenges of discriminating between scenarios in such extreme environments, relevant to searches for AGNs in dwarf galaxies. This is the second long-lived transient discovered in a blue compact dwarf, after SDSS1133. Our result implies such long-lived stellar transients may be more common in metal-deficient galaxies. Systematic searches for low-level variability in dwarf galaxies will be possible with the upcoming Legacy Survey of Space and Time at the Vera C. Rubin Observatory.

A compact X-ray emitting binary in likely association with 4FGL J0935.3+0901

ABSTRACT 4FGL J0935.3+0901 is a γ-ray source detected by the Large Area Telescope (LAT) onboard the Fermi Gamma-Ray Space Telescope. We have conducted detailed analysis of the LAT data for this source and multiwavelength studies of the source field. Its γ-ray emission can be described with a power law (Γ = 2.0 ± 0.2) with an exponential cut-off (Ec = 2.9 ± 1.6 GeV), while the flux shows significant long-term variations. From analysis of archival Neil Gehrels Swift Observatory X-Ray Telescope data, we find only one X-ray source in the LAT’s 2σ error region. Within a $3.7\,{\rm arcsec}$ radius error circle of the X-ray source, there is only one optical object down to r′ ∼ 23 mag. Time-resolved photometry of the optical object indicates a likely 2.5 h periodic modulation, while its spectrum shows double-peaked hydrogen and helium emission lines (similar to those seen in accretion discs in low-mass X-ray binaries). Combining these results, we conclude that we have discovered a compact X-ray emitting binary in likely association with 4FGL J0935.3+0901, i.e. a millisecond pulsar (MSP) binary. We discuss the implication of the optical spectral features: this binary could be a transitional MSP system at a subluminous disc state, although the other possibility, the binary in a rotation-powered state showing the optical emission lines due to intrabinary interaction processes, cannot be excluded. Further observational studies will help to determine detailed properties of this candidate MSP binary and thus clarify its current state.

Tidal disruption events as a site of an evolving relativistic spectral line

AbstractIn nuclei of galaxies, strong tidal forces can destroy stars passing within a critical distance from the central supermassive black hole (SMBH). Observational signatures of tidal disruption events (TDEs) depend on the environment around the SBMH horizon and the level of its accretion activity. Evidence for optical and ultraviolet spectral features has been reported in TDE flares; nevertheless, to test the effects of general relativity in the immediate vicinity of SMBH, the relativistically broadened and skewed X‐ray line would tell us significantly more useful information. This will require to proceed beyond inactive nuclei. To this end, we consider a system where the material from a disrupted star forms a gaseous ring that circularizes near the tidal radius around SMBH, it gradually spreads in radius by viscous processes and resides embedded within a hot corona. In our test calculation, the remnant trail is assumed to be fully circularized and embedded in a hot environment and illuminated by X‐rays from a surrounding corona or a jet base of (mild) active galactic nucleus activity. We show the expected effects on the observed profile and the centroid energy. In the future, the evolving spectral features can enhance the diagnostic capability and provide a novel way to reveal the parameters of TDEs in such sources; the distance of the remnant gas from the SMBH, the radial extent of the gaseous trail, and the spin of the SMBH could be measured.