Double-peaked Profiles Research Articles

XMM-Newton observations of PSR J0726−2612, a radio-loud XDINS

We present the results of an XMM-Newton observation of the slowly rotating (P = 3.4 s), highly magnetized (B ≈ 3 × 1013 G) radio pulsar PSR J0726–2612. A previous X-ray observation with the Chandra satellite showed that some of the properties of PSR J0726–2612 are similar to those of the X-ray-dim isolated neutron stars (XDINSs), a small class of nearby slow pulsars characterized by purely thermal X-ray spectra and undetected in the radio band. We confirm the thermal nature of the X-ray emission of PSR J0726–2612, which can be fitted by the sum of two blackbodies with temperatures kT1=0.074+0.006-0.011 keV and kT2=0.14+0.004-0.002 keV and emitting radii R1=10.4+10.8-2.8 km and R2=0.5+0.9-0.3 km, respectively (assuming a distance of 1 kpc). A broad absorption line modeled with a Gaussian profile centered at 0.39+0.02-0.03 keV is required in the fit. The pulse profile of PSR J0726–2612 is characterized by two peaks with similar intensity separated by two unequal minima, a shape and pulsed fraction that cannot be reproduced without invoking magnetic beaming of the X-ray emission. The presence of a single radio pulse suggests that in PSR J0726–2612 the angles that the dipole axis and the line of sight make with the rotation axis, ξ and χ, respectively, are similar. This geometry differs from that of the two radio-silent XDINSs with double-peaked pulse profiles similar to that of PSR J0726–2612, for which ξ ∼ 90° and χ ∼ 45° have recently been estimated. These results strengthen the similarity between PSR J0726–2612 and the XDINSs and support the possibility that the lack of radio emission from the latter might simply be due to an unfavorable viewing geometry.

Investigation of heat transfer and fluid flow in high current GTA welding by a unified model

This research is aimed to understand the heat transfer and fluid flow of the arc plasma and weld pool with a significant deformation of the weld pool surface during high current gas tungsten arc welding (GTAW). A unified model including the tungsten electrode, arc plasma and the weld pool of low carbon steel is developed by presetting a free surface deformation from the experimental observations. Buoyance, Lorentz force, plasma drag force and Marangoni force are taken into account to investigate the weld pool dynamics with a great depressed free surface. Heat flux, current density, Marangoni force and plasma drag force at the weld pool surface are presented to understand the heat and momentum transfer from the arc plasma to the weld pool. It is found that the distributions of the heat flux and current density as well as temperature at the depressed weld pool surface are double-peak profiles; the molten metal flow of the weld pool with severe surface depression are determined by the plasma drag force rather than the Marangoni force. The effect of the Lorentz force is more important than that of the buoyance, but weaker than the Marangoni force. The results are consistent with the existing results of both the experiment and the theory.

Understanding the escape of LyC and Lyα photons from turbulent clouds

Understanding the escape of Lyman continuum (LyC) and Lyman alpha (Lya) photons from molecular clouds is one of the keys to constraining the reionization history of the Universe and the evolution of galaxies at high redshift. Using a set of radiation-hydrodynamic simulations with adaptive mesh refinement, we investigate how photons propagate and escape from turbulent clouds with different masses, star formation efficiencies (SFEs), and metallicities, as well as with different models of stellar spectra and supernova feedback. We find that the escape fractions in both LyC and Lya are generally increasing with time if the cloud is efficiently dispersed by radiation and supernova feedback. When the total SFE is low (1% of the cloud mass), 0.1-5% of LyC photons leave the metal-poor cloud, whereas the fractions increase to 20-70% in clouds with a 10% SFE. LyC photons escape more efficiently if gas metallicity is lower, if the upper mass limit in the stellar initial mass function is higher, if binary interactions are allowed in the evolution of stars, or if additional strong radiation pressure, such as Lya pressure, is present. As a result, the number of escaping LyC photons can easily vary by a factor of $\sim4$ on cloud scales. The escape fractions of Lya photons are systemically higher (60-80%) than those of LyC photons despite large optical depths at line centre ($\tau_0\sim10^6-10^9$). Scattering of Lya photons is already significant on cloud scales, leading to double-peaked profiles with peak separations of $v_{\rm sep}\sim400\,{\rm km\,s^{-1}}$ during the initial stage of the cloud evolution, while it becomes narrower than $v_{\rm sep} \le 150 \, {\rm km\,s^{-1}}$ in the LyC bright phase. Comparisons with observations of low-redshift galaxies suggest that Lya photons require further interactions with neutral hydrogen to reproduce their velocity offset for a given LyC escape fraction.

Local chemical instabilities in 20Cr[sbnd]25Ni Nb-stabilised austenitic stainless steel induced by proton irradiation

We have assessed the local solute redistribution at defect sinks in 20Cr25Ni Nb-stabilised austenitic stainless steel after proton irradiation at three temperatures, i.e. 420, 460 and 500 °C, up to a maximum damage level of 0.8 dpa. This material is currently being used as cladding in Advanced Gas-cooled Reactors (AGR), and potential local Cr depletions would compromise its resistance to intergranular corrosion attack during wet storage of spent fuel elements. Irradiation induces the depletion of Cr, Fe and, to a lesser extent, Mn from grain boundaries, whereas Ni and Si become enriched at those locations. The elemental profiles are symmetric and primarily W-shaped at 420 °C, whereas at higher temperatures asymmetric and double-peaked profiles are also detected, most likely as a result of grain boundary migration. High-angle grain boundaries with a misorientation angle ≥40° become mobile at 460 °C and especially at 500 °C, and also experience a relatively large solute redistribution, with local Cr contents in a significant number of boundaries falling below 12 wt% and profile widths ≥100 nm. However, coincidence site lattice boundaries (CSL) Σ3 boundaries prove to be resistant to Cr depletion and to boundary mobility. Local elemental patterns at radiation-induced dislocations seem to mimic those at grain boundaries, but do not trigger the formation of Ni3Si precipitates. Additionally, Ni and Si form a shell-like structure around the pre-existing Nb(C,N) precipitates, potentially leading to the transition into G-phase at higher damage levels.

The Double-peaked Radio Light Curve of Supernova PTF11qcj

Abstract We present continued radio and X-ray follow-up observations of PTF11qcj, a highly energetic broad-lined Type Ic supernova (SN), with a radio peak luminosity comparable to that of the γ-ray burst (GRB) associated SN 1998bw. The latest radio observations, carried out with the Karl G. Jansky Very Large Array, extend up to ∼5 yr after the PTF11qcj optical discovery. The radio light curve shows a double-peak profile, possibly associated with density variations in the circumstellar medium (CSM), or with the presence of an off-axis GRB jet. Optical spectra of PTF11qcj taken during both peaks of the radio light curve do not show the broad Hα features typically expected from H-rich circumstellar interaction. Modeling of the second radio peak within the CSM-interaction scenario requires a flatter density profile and an enhanced progenitor mass-loss rate compared to those required to model the first peak. Our radio data alone cannot rule out the alternative scenario of an off-axis GRB powering the second radio peak, but the derived GRB parameters are somewhat unusual compared to typical values found for cosmological long GRBs. On the other hand, Chandra X-ray observations carried out during the second radio peak are compatible with the off-axis GRB hypothesis, within the large measurement errors. We conclude that VLBI measurements of the PTF11qcj radio ejecta are needed to unambiguously confirm or rule out the off-axis GRB jet scenario.

Observational Signatures of Planets in Protoplanetary Disks: Planet-induced Line Broadening in Gaps

Abstract Protoplanets can produce structures in protoplanetary disks via gravitational disk–planet interactions. Once detected, such structures serve as signposts of planet formation. Here we investigate the kinematic signatures in disks produced by multi-Jupiter mass (M J) planets using 3D hydrodynamics and radiative transfer simulations. Such a planet opens a deep gap, and drives transonic vertical motions inside. Such motions include both a bulk motion of the entire half-disk column, and turbulence on scales comparable to and smaller than the scale height. They significantly broaden molecular lines from the gap, producing double-peaked line profiles at certain locations, and a kinematic velocity dispersion comparable to thermal after azimuthal averaging. The same planet does not drive fast vertical motions outside the gap, except at the inner spiral arms and the disk surface. Searching for line broadening induced by multi-M J planets inside gaps requires an angular resolution comparable to the gap width, an assessment of the gap gas temperature to within a factor of 2, and a high sensitivity needed to detect line emission from the gap.

DoPS: A Double-Peaked Profiles Search Method Based on the RS and SVM

The double-peaked profiles in spectral data are very rare and valuable for the astronomers. Their recognitions are largely depended on visually inspect. The main reasons for auto-search of such spectra are the complex and distinct characteristics of astronomical data. In this paper, we address the problems by a double-peaked profiles search algorithm (called DoPS) based on relevant subspace (RS) and support vector machine (SVM). First, characteristics subspace is extracted by using the relevant subspace mining algorithm, in which the local density factor λ is particularly defined to measure the data sparsity. The characteristics of double-peaked profiles are represented by using the locations, the interval spaces, and strength ratio of double peaks. Second, the characteristics set is analyzed and grouped into three subsets according to the correlations among the characteristics based on the frequent patterns and rough set theory. Third, the double-peaked profiles search algorithm is proposed by using the support vectors trained from the labeled samples as thresholds. Finally, several spectral data sets from the LAMOST survey are employed to test the DoPS. The experimental results indicate that DoPS presents high performance than other similar algorithms in terms of time efficiency, noise immunity and recall, and reduced rates.

Study on Design Rainstorm Profile in Liuzhou City Based on Pilgrim & Cordery Method

Liuzhou City is located in Guangxi Zhuang Autonomous Region of China. It has a warm and rainy climate and belongs to the middle subtropical monsoon climate. It is a rainstorm and flood-prone area. The work of flood drainage and waterlogging prevention is very important. The “minute to minute” rainfall process data of Liuzhou National Meteorological Observation Station from 1975 to 2014 and the Pilgrim & Cordery method were used to estimate the short-time design rainstorm profile of Liuzhou City, and the profiles of the rainfall lasting for 30, 60, 90, 120, 150, and 180 min were obtained. The research shows that the same rain duration and different recurrence period conditions are consistent with the rainstorm profile. The rainfall duration of 30, 60, 90, 120, and 180 min generally shows single-peak rainstorm profile, and the rainfall duration of 150 min shows double-peak rainstorm profile. Most peaks of each short-time design rainstorm profile are at or ahead of the 1/3 part of the entire rainfall process. During the same recurrence period, the rainfall in peak period fluctuated with the increase of the duration, and the intensity of rainfall increased with the prolonging of the recurrence period.

Outflows in the inner kiloparsec of NGC 1566 as revealed by molecular (ALMA) and ionized gas (Gemini-GMOS/IFU) kinematics

Context. Tracing nuclear inflows and outflows in active galactic nuclei (AGNs), determining the mass of gas involved in them, and their impact on the host galaxy and nuclear black hole requires 3D imaging studies of both the ionized and molecular gas. Aims. We map the distribution and kinematics of molecular and ionized gas in a sample of active galaxies to quantify the nuclear inflows and outflows. Here, we analyze the nuclear kinematics of NGC 1566 via ALMA observations of the CO J:2-1 emission at 24 pc spatial and ∼2.6 km s−1 spectral resolution, and Gemini-GMOS/IFU observations of ionized gas emission lines and stellar absorption lines at similar spatial resolution, and 123 km s−1 of intrinsic spectral resolution. Methods. The morphology and kinematics of stellar, molecular (CO), and ionized ([N II]) emission lines are compared to the expectations from rotation, outflows, and streaming inflows. Results. While both ionized and molecular gas show rotation signatures, there are significant non-circular motions in the innermost 200 pc and along spiral arms in the central kpc (CO). The nucleus shows a double-peaked CO profile (full width at zero intensity of 200 km s−1), and prominent (∼80 km s−1) blue- and redshifted lobes are found along the minor axis in the inner arcseconds. Perturbations by the large-scale bar can qualitatively explain all features in the observed velocity field. We thus favor the presence of a molecular outflow in the disk with true velocities of ∼180 km s−1 in the nucleus and decelerating to 0 by ∼72 pc. The implied molecular outflow rate is 5.6 M⊙ yr−1, with this gas accumulating in the nuclear 2″ arms. The ionized gas kinematics support an interpretation of a similar but more spherical outflow in the inner 100 pc, with no signs of deceleration. There is some evidence of streaming inflows of ∼50 km s−1 along specific spiral arms, and the estimated molecular mass inflow rate, ∼0.1 M⊙ yr−1, is significantly higher than the SMBH accretion rate (ṁ = 4.8 × 10−5 M⊙ yr−1).

The Hα line-profile variations for B-emission stars

Spectroscopic variations of Hα line profiles from 9 B-emission (Be) stars in the southern sky, taken from the 5th revised of Bright Star Catalogue year 1991, are analyzed. These variations, emission and/or absorption lines, are due to the presence of the circumstellar envelopes surrounding the stars and also describe the phase changing/evolution phases of the stellar spectra if we Have data for some years. Therefore, we compare the spectra to data from BeSS database and references for the recent years. Five stars show double-peaked emission line profile of Hα. One star shows Be phase with a single peaked Hα emission line, and three stars show evolution phases of the Hα line profile. By studying this evolution of the line variations, we can fit the suitable envelope models for each star taken from references.

Frequency Analysis of a Potential SPB Star η Tau

In this study, five years of photometric data of η Tau obtained from the STEREO satellite between 2007 and 2011 are presented. The high-precision data are compared with the results derived from the spectroscopic findings to gain a better understanding of the Be phenomenon in the star. The spectroscopic data cover the same time interval as the photometric observations. η Tau displays a double peaked Hα emission profile in its spectra. In order to analyze this profile, the Hα emission lines are examined by measuring their equivalent widths and line intensities. As a result of the photometric and spectroscopic analyses, it is revealed that the frequency distribution and amplitude intensities of the star are different from those of a typical Be star. Based on its physical parameters such as temperature and luminosity values, it may be conclude that the star is a Slowly Pulsating B type emission star. On the other hand, the equivalent width values of the emission lines appear to be related to the oscillation frequencies and their amplitudes. This indicates that the photometric variations may be related to the environmental disc structure.Doğuş ÖZUYAR, dozuyar@ankara.edu.tr, ORCID: https://orcid.org/ 0000-0001-8544-0950

Effects of oblique shock waves on turbulent structures and statistics of supersonic mixing layers

A supersonic mixing layer at a convective Mach number of 0.8 was investigated by large eddy simulation. Turbulent structures and statistics of the mixing layer interacting with an oblique shock at different strengths in the self-preserving stage were investigated and compared with the shock-free mixing layer. An inflection point arises on the velocity profiles in the self-preserving region where the incident shock wave impinges, in addition to the three inflection points existing in the shock-free mixing layer. It is caused by the hairpin vortices induced through the baroclinic mechanism of the interaction of the incident shock wave. However, the induced hairpin vortices disappear quickly within a short distance. The vorticity thickness of the shocked-mixing layer experiences a sudden decrease in the vicinity of the shock impingement point, which is due to the induced hairpin vortices, followed by a more rapid growth than that of the shock-free mixing layer. So the incident shock has positive effects on the growth of the mixing layer. Both the hairpin vortices and the vortices originated from the hairpin vortices can result in a double-peak profile of the streamwise Reynolds stress in the transient stage of the mixing layer. In addition, the asymmetric profiles for the Reynolds stress are due to the hairpin vortices breakup earlier in the upper stream. The amplitudes of the Reynolds stress increase slightly and their peak positions move toward the center of the mixing layer even in the self-preserving stage. Moreover, the profiles of the transverse Reynolds stress and Reynolds shear stress have two peaks for the shocked-mixing layer which are caused by the reflected shock waves and the mixing layer. The incident shock increases energy transport and convection between the mixing layer and the mainstream. As a result, the mixing process of the shocked-mixing layer is enhanced.

ASASSN-18ey: The Rise of a New Black Hole X-Ray Binary

Abstract We present the discovery of ASASSN-18ey (MAXI J1820+070), a new black hole low-mass X-ray binary (LMXB) discovered by the All-Sky Automated Survey for SuperNovae (ASAS-SN). A week after ASAS-SN discovered ASASSN-18ey as an optical transient, it was detected as an X-ray transient by MAXI/GCS. Here, we analyze ASAS-SN and Asteroid Terrestrial-impact Last Alert System pre-outburst optical light curves, finding evidence of intrinsic variability for several years prior to the outburst. While there was no long-term rise leading to the outburst, as has been seen in several other systems, the start of the outburst in the optical preceded that in the X-rays by 7.20 ± 0.97 days. We analyze the spectroscopic evolution of ASASSN-18ey from pre-maximum to >100 days post-maximum. The spectra of ASASSN-18ey exhibit broad, asymmetric, double-peaked Hα emission. The Bowen blend (λ ≈ 4650 Å) in the post-maximum spectra shows highly variable double-peaked profiles, likely arising from irradiation of the companion by the accretion disk, typical of low-mass X-ray binaries. The optical and X-ray luminosities of ASASSN-18ey are consistent with black hole low-mass X-ray binaries, both in outburst and quiescence.

Double-peaked narrow emission-line galaxies in LAMOST survey

We outline a full-scale search for galaxies exhibiting double-peaked profiles of promi- nent narrow emission lines, motivated by the prospect of finding objects related to merging galaxies, and even dual active galactic nuclei candidates as by-product, from the Large Sky Area Multi-object Fiber Spectroscopic Telescope (LAMOST) Data Re- lease 4. We assemble a large sample of 325 candidates with double-peaked or strong asymmetric narrow emission lines, with 33 objects therein appearing optically resolved dual-cored structures, close companions or signs of recent interaction on the Sloan Dig- ital Sky Survey images. A candidate from LAMOST (J074810.95+281349.2) is also stressed here based on the kinematic and spatial decompositions of the double-peaked narrow emission line target, with analysis from the cross-referenced Mapping Nearby Galaxies at the Apache Point Observatory (MaNGA) survey datacube. MaNGA en- ables us to constrain the origin of double peaks for these sources, and with the IFU data we infer that the most promising origin of double-peaked profiles for LAMOST J074810.95+281349.2 is the `Rotation Dominated + Disturbance' structure.

The Remarkable Be+sdOB Binary HD 55606. I. Orbital and Stellar Parameters*

Abstract Prompted by peculiar spectroscopic variability observed in SDSS/APOGEE H-band spectra, we monitored the Be star HD 55606 using optical spectroscopy and found that it is an exotic double-lined spectroscopic binary (SB2) consisting of a Be star and a hot, compact companion that is probably an OB subdwarf (sdOB) star. The motion of the sdOB star is traced by its impact on the strong He i lines, observed as radial velocity (V r ) variable, double-peaked emission profiles with narrow central absorption cores. Weak He ii 4686 Å absorption associated with the companion star is detected in most spectra. Use of the emission peaks of low-ionization emission lines to trace the Be star V r and the He i lines to trace the companion star V r yields a circular orbital solution with a 93.8 day period and masses of M Be = 6.2 M ⊙ and M sdOB = 0.9 M ⊙ in the case of i = 80°. HD 55606 exhibits a variety of phase-locked variability, including the development of shell lines twice per orbit. The shell phases coincide with variation in the double emission peak separations, and both forms of variability are likely caused by a two-armed spiral density perturbation in the Be disk. The intensity ratios of the double emission peaks are also phase-locked, possibly indicating heating by the sdOB star of the side of the Be disk facing it. HD 55606 is a new member of the growing sample of Be+sdOB binaries, in which the Be star’s rapid rotation and ability to form a disk can be attributed to past mass-transfer.

Detection of a cyclotron line in SXP 15.3 during its 2017 outburst

ABSTRACT We report the results of AstroSat and NuSTAR observations of the Be/X-ray binary pulsar SXP 15.3 in the Small Magellanic Cloud during its outburst in late 2017, when the source reached a luminosity level of ∼1038 erg s−1, close to the Eddington limit. The unprecedented broad-band coverage of the source allowed us to perform timing and spectral analysis between 3 and 80 keV. The pulse profile exhibits a significant energy dependence, and morphs from a double-peaked profile to a single broad pulse at energies >15 keV. This can be explained by a spectral hardening during an intensity dip seen between the two peaks of the pulse profile. We detect a Cyclotron Resonance Scattering Feature at ∼5 keV in the X-ray spectrum, independent of the choice of the continuum model. This indicates a magnetic field strength of 6 × 1011 G for the neutron star.

Puzzling Lyman-alpha line profiles in green pea galaxies

Context. The Lyman-alpha (Lyα) line of hydrogen is of prime importance for detecting galaxies at high redshift. For a correct data interpretation, numerical radiative transfer models are necessary due to Lyα resonant scattering off neutral hydrogen atoms. Aims. Recent observations have discovered an escape of ionizing Lyman-continuum radiation from a population of compact, actively star-forming galaxies at redshift z ~ 0.2−0.3, also known as “green peas”. For the potential similarities with high-redshift galaxies and impact on the reionization of the universe, we study the green pea Lyα spectra, which are mostly double-peaked, unlike in any other galaxy sample. If the double peaks are a result of radiative transfer, they can be a useful source of information on the green pea interstellar medium and ionizing radiation escape. Methods. We select a sample of twelve archival green peas and we apply numerical radiative transfer models to reproduce the observed Lyα spectral profiles, using the geometry of expanding, homogeneous spherical shells. We use ancillary optical and ultraviolet data to constrain the model parameters, and we evaluate the match between the models and the observed Lyα spectra. As a second step, we allow all the fitting parameters to be free, and examine the agreement between the interstellar medium parameters derived from the models and those from ancillary data. Results. The peculiar green pea double-peaked Lyα line profiles are not correctly reproduced by the constrained shell models. Conversely, unconstrained models fit the spectra, but parameters derived from the best-fitting models are not in agreement with the ancillary data. In particular: 1) the best-fit systemic redshifts are larger by 10–250 km s−1 than those derived from optical emission lines; 2) the double-peaked Lyα profiles are best reproduced with low-velocity (≲150 km s−1) outflows that contradict the observed ultraviolet absorption lines of low-ionization-state elements with characteristic velocities as large as 300 km s−1; and 3) the models need to consider intrinsic Lyα profiles that are on average three times broader than the observed Balmer lines. Conclusions. Differences between the modelled and observed velocities are larger for targets with prominent Lyα blue peaks. The blue peak position and flux appear to be connected to low column densities of neutral hydrogen, leading to Lyα and Lyman-continuum escape. This is at odds with the kinematic origin of the blue peak in the homogeneous shell models. Additional modelling is needed to explore alternative geometries such as clumpy media and non-recombination Lyα sources to further constrain the role and significance of the Lyα double peaks.

Supersoft X-Ray Sources Identified with Be Binaries in the Magellanic Clouds*

Abstract We investigated four luminous supersoft X-ray sources (SSSs) in the Magellanic Clouds suspected to have optical counterparts of Be spectral type. If the origin of the X-rays is in a very hot atmosphere heated by hydrogen burning in accreted envelopes of white dwarfs (WDs), like in the majority of SSSs, these objects are close binaries with very massive WD primaries. Using the South African Large Telescope, we obtained the first optical spectra of the proposed optical counterparts of two candidate Be stars associated with SUZAKU J0105–72 and XMMU J010147.5–715550, respectively, a transient and a recurrent SSS, and confirmed the proposed Be classification and Small Magellanic Cloud membership. We also obtained new optical spectra of two other Be stars proposed as optical counterparts of the transient SSS XMMU J052016.0–692505 and MAXI J0158–744. The optical spectra with double-peaked emission-line profiles are typical of Be stars and present characteristics similar to many high-mass X-ray binaries with excretion disks truncated by the tidal interaction with a compact object. The presence of a massive WD that sporadically ignites nuclear burning, accreting only at certain orbital or evolutionary phases, explains the supersoft X-ray flares. We measured equivalent widths and distances between line peaks and investigated the variability of the prominent emission-line profiles. The excretion disks seem to be small in size and are likely to be differentially rotating. We discuss possible future observations and the relevance of these objects as a new class of SN Ia progenitors.

MIKE High Resolution Spectroscopy of Raman-scattered O VI and C II Lines in the Symbiotic Nova RR Telescopii

AbstractWe present a high-resolution optical spectrum of the symbiotic nova RR Tel obtained with MIKE at Magellan-Clay telescope. RR Tel is a wide binary system of a hot white dwarf and a Mira with an orbital period of a few decades, where the white dwarf is accreting through gravitational capture of some fraction of material shed by the Mira. We find broad emission features at 6825, 7082, 7023, and 7053 Å, which are formed through Raman scattering of far-UV O VI ⋋⋋ 1032 and 1038 Å, C II ⋋⋋ 1036 and 1037 Å with atomic hydrogen. Raman O VI features exhibit clear double-peak profiles indicative of an accretion flow with a characteristic speed ∼ 30 km s−1, whereas the Raman C II features have a single Gaussian profile. We perform a profile analysis of the Raman O VI by assuming that O VI emission traces the accretion flow around the white dwarf with a fiducial scale of 1 AU. A comparison of the restored fluxes of C II ⋋⋋ 1036 and 1037 from Raman C II features with the observed C II ⋋ 1335 multiplet is consistent with the distance of RR Tel ∼ 2.6 kpc based on interstellar extinction of C II.

Kinematic Signatures of Reverberation Mapping of Close Binaries of Supermassive Black Holes in Active Galactic Nuclei

Abstract Close binaries of supermassive black holes (CB-SMBHs) with separations of ≲0.1 pc as the final stage of galaxy mergers are sources of low-frequency gravitational waves; however, they are still elusive observationally because they are not spatially resolved. Fortunately, reverberation as echoes of broad emission lines to ionizing continuum conveys invaluable information on the dynamics of broad-line regions (BLRs) governed by SMBHs in the central regions of active galactic nuclei (AGNs). In this paper, we demonstrate how to compose the hybrid two-dimensional transfer functions (TFs) of binary BLRs around the CB-SMBHs in AGNs, providing an opportunity for identifying them from reverberation mapping (RM) data. It is found that there are variation-coupling effects in the TFs arising from the coupling of CB-SMBH light curves in the Fourier space. We provide semi-analytical formulations of the TFs for kinematic maps of the gas. For cases with the simplest variation-coupling effects, we make calculations for several BLR models and reveal significant distinctions from those of single active black holes. In principle, the difference is caused by the orbital motion of the CB-SMBH systems. In order to search for CB-SMBHs in time-domain space, selection of target candidates should focus on local AGNs with Hβ double-peaked profiles and weaker near-infrared emission. High-fidelity RM campaigns of monitoring the targets in future will provide opportunities to reveal these kinematic signatures of the CB-SMBHs and hence measurements of their orbital parameters.