Individual Pulses Research Articles

Tunable and switchable harmonic h-shaped pulse generation in a 303 km ultralong mode-locked thulium-doped fiber laser

We experimentally demonstrated a type of tunable and switchable harmonic h-shaped pulse generation in a thulium-doped fiber (TDF) laser passively mode locked by using an ultralong nonlinear optical loop mirror. The total cavity length was ∼3.03 km, the longest ever built for a TDF laser to our best knowledge, which resulted in an ultralarge anomalous dispersion over −200 ps2 around the emission wavelength. The produced h-shaped pulse can operate either in a fundamental or in a high-order harmonic mode-locking (HML) state depending on pump power and intra-cavity polarization state (PS). The pulse duration, no matter of the operation state, was tunable with pump power. However, pulse breaking and self-organizing occurred, resulting in high-order HML, when the pump power increased above a threshold. At a fixed pump power, the order of HML was switchable from one to another by manipulating the PS. Switching from the 8th up to the 48th order of HML was achieved with a fixed pump power of ∼4.15 W. Our results revealed the detailed evolution and switching characteristics of the HML and individual pulse envelope with respect to both the pump power and PS. We have also discussed in detail the mechanisms of both the h-shaped pulse generation and the switching of its HML. This contribution would be helpful for further in-depth study on the underlying dynamics of long-duration particular-envelope pulses with ultralarge anomalous dispersion and ultralong roundtrip time.

Flow‐mediated movement of freshwater catfish, Tandanus bostocki, in a regulated semi‐urban river, to inform environmental water releases

AbstractMovement and migration of fish are critical for sustaining riverine fish populations. Water resource development alters natural flow regimes and can disconnect habitats and interfere with hydrological cues for fish movement. Environmental flow releases can counter these impacts, but to be effective they must be based on quantitative flow–biota relationships. We used radio‐telemetry to investigate the association between flow and movement of Tandanus bostocki, a plotosid fish endemic to south‐western Australia. Movement was assessed for 15 adult fish at three temporal scales: weekly, daily and bihourly to reveal seasonal patterns in movement, movement around individual flow pulses, and to describe changes in home range respectively. We used a predictive modelling approach to assess the importance of discharge and other covariates on the directional distance travelled or linear home range size. Our seasonal and flow pulse study revealed that T. bostocki undertook larger downstream movements during higher flows and smaller upstream movements during lower flows. Daily movements tended to be downstream on the ascending limb of flow pulses and upstream on the descending limb. Flow‐dependent movements at weekly or daily time scales were relatively modest (typically hundreds of metres) and were moderated by time of year and gender; however, fish underwent a synchronised 1‐km movement upstream during the known reproductive period in October. The home range study revealed that T. bostocki had larger home ranges (night‐time foraging) when baseflow was elevated. These results can assist the design of customised environmental flows in the study river and other flow‐regulated rivers.

Mega-Hertz repetition rate broadband nano-second pulses from an actively mode-locked Yb-fiber laser

This work demonstrates an actively mode-locked all-normal dispersion Yb-fiber ring laser, delivering pulses of few nano-seconds (ns) to sub-ns duration at a 4 MHz repetition rate. Employing a filterless cavity architecture and different, long-length intra-cavity nonlinear fibers; a broadband output spectrum in the 1060–1140 nm wavelength region was obtained. With an increasing pump power, the pulse width reduced along with the appearence of new pulses, resulting into a muti-pulsing output. For a fixed pump power, the number of pulses and the amount of spectral broadening varied for different non-linear fibers. In the multi-pulsing state, the pulses were found to be located seperately in both time and wavelength, where Raman stokes corresponding to individual pulses could also be observed. The maximum output pulse energy achieved in a single pulse state was around 8.7 nJ, which increased to 14.5 nJ in a multi-pulse state. To the best of the authors’ knowledge, this is the first demonstration of a filterless active mode-locked fiber ring laser producing high-repetition rate broadband nano-second pulses in single and multi-pulse states at 1 µm.

Measurement of the absolute number of photons of the hard X-ray beamline at the Linac Coherent Light Source

X-ray free-electron lasers provide intense pulses of coherent X-rays with a short pulse duration. These sources are chaotic by nature and therefore, to be used at their full potential, require that every X-ray pulse is characterized in terms of various relevant properties such as intensity, photon energy, position and timing. Diagnostics are for example installed on an X-ray beamline to specifically monitor the intensity of individual X-ray pulses. To date, these can however only provide a single-shot value of the relative number of photons per shot. Here are reported measurements made in January 2015 of the absolute number of photons in the hard X-ray regime at LCLS which is typically 3.5 × 1011 photons shot-1 between 6 and 9.5 keV at the X-ray Pump-Probe instrument. Moreover, an average transmission of ≉62% of the hard X-ray beamline over this energy range is measured and the third-harmonic content of ≉0.47% below 9 keV is characterized.

10 kHz, 10 ns, 13.4 mJ Nd:YAG based frequency-tripled burst-mode MOPA source at 355 nm

We demonstrated a Nd:YAG based Q-switched burst-mode MOPA laser with frequency-tripled ultraviolet output by nonlinear harmonic generation. The individual pulse energy of 13.4 mJ with a repetition rate of 10 kHz at 355 nm was obtained. The short pulse width of ∼10 ns provides a high peak power up to 1.3 MW at 355 nm. This high-energy and high-repetition-rate ultraviolet source has the potential in applications such as pumping the dye laser systems for PLIF imaging.

BDNF Val66Met genotype moderates the impact of rumination on cortisol awakening response and subjective well-being

The cortisol awakening response (CAR) is a well-established biomarker for the integrity of the hypothalamic-pituitary-adrenal (HPA) axis in healthy as well as clinical samples. Cortisol rise during the first 60 min after awakening is often used as a proxy of HPA axis regulation in health and disease. Ultradian pulsatility of cortisol is known to superimpose its circadian rhythmicity with the CAR being the first rise after awakening. However, the exact length of the complete first pulse (rise and fall) after awakening, as well as the association between the CAR, the complete first pulse, and successive ultradian pulses, has not yet been studied systematically.Aim of this study was to investigate cortisol dynamics after awakening beyond the standard assessment duration of 60 min in order to assess the cortisol awakening pulse, in relation to ultradian rhythmicity of cortisol after awakening. In a sample of 51 healthy participants, salivary cortisol was collected for the first 270 min after awakening in intervals of 30 min, on two separate days. Different parameters describing individual cortisol pulses over time with respect to inter- and intraindividual variations such as duration, amplitude and area under the curve (AUC) were calculated. Special emphasis was put on the first rise and fall after awakening, called the cortisol awakening pulse (CAP).Mean duration of the CAP was 108 min with high interindividual differences. Duration of first and second pulse were associated with subject’s sex and menstrual cycle status, with a longer first pulse and an attenuated second pulse in male and female subjects in the luteal phase, compared to female subjects in the follicular phase, or women taking oral contraceptives.These results point to the potential usefulness of a longer sampling period for assessing ultradian pulsatility of cortisol in the morning, especially the CAP. To assess the complete pulse rather than the rise alone, measurement of cortisol levels after awakening for 120 min is recommended.

Ultrafast, > 50 Hz LA‐ICP‐MS Spot Analysis Applied to U–Pb Dating of Zircon and other U‐Bearing Minerals

LA‐ICP‐MS U–Pb detrital zircon studies typically analyse 50–200 grains per sample, with the consequent risk that minor but geologically important age components (e.g., the youngest detrital zircon population) are not detected, and higher abundance age components are misrepresented, rendering quantitative comparisons between samples impossible. This study undertook rapid U–Pb LA‐ICP‐MS analyses (8 s per 18–47 μm diameter spot including baseline and ablation) of zircon, apatite, rutile and titanite using an aerosol rapid introduction system (ARIS). As the ARIS resolves individual single pulses at fast sampling rates, spot analyses require a high repetition rate (> 50 Hz) so the signal does not return to baseline and mass sweep times (> 80 ms) that span several laser pulses (i.e., major undersampling of the signal). All rapid U–Pb spot analyses employed 250–300 pulses, repetition rates of 53–65 Hz (total ablation times of 4.1–5.7 s) and low fluence (1.75–2.5 J cm−2), resulting in pit depths of ca. 15 μm. Zircon, apatite, rutile and titanite reference material data yield an accuracy and precision (2s) of < 1% for pre‐Cenozoic reference materials and < 2% for younger reference materials. We present a detrital zircon data set from a Neoproterozoic tillite where > 1000 grains were analysed in < 3 h with a precision and accuracy comparable to conventional LA‐ICP‐MS analytical protocols, demonstrating the rapid acquisition of huge detrital data sets.

Exploring the contribution of unconventional parameters on spark gap formation and its minimization during WEDM of layered composite

Cladded materials are heterogenous in nature and considered as difficult-to-cut especially via conventional machining operations. Gas and/or plasma cutting are common in practice to cut clad materials. However, these processes induce deeper heat-affected zones and provide very rough surface integrity. Wire electric discharge machining (WEDM) is a capable alternate yielding better cut quality. Formation of a significant spark gap between the cut surfaces is the iconic problem of WEDM which is addressed in this study. WEDM has been performed on stainless-clad steel with a focus on identifying the significant parameters affecting the amount of spark gap and its minimization in the final cut. Eight input control factors, namely workpiece orientation, thickness of individual layer, servo voltage, pulse on-time, wire diameter, wire feed, and pressure ratio, have been employed to investigate their effects on spark gap development. Experimentation has been performed according to L18 orthogonal array followed by comprehensive statistical analyses. ANOVA shows that wire diameter and pressure ratio are the two main influential parameters for spark gap having percentage contribution of 71% and 16%, respectively. Optimal settings of control variables are also achieved through S/N ratio analysis. Improvement of 23.4% towards spark gap reduction is realized.

On the α–intensity correlation in gamma-ray bursts: subphotospheric heating with varying entropy

The emission mechanism during the prompt phase in gamma-ray bursts (GRBs) can be investigated through correlations between spectral properties. Here, we revisit the correlation relating the instantaneous flux, $F$, and the photon index below the spectral break, $\alpha$, in individual emission pulses, by studying the 38 most prominent pulses in the Fermi/GBM GRB catalogue. First, we search for signatures of the bias in the determination of $\alpha$ due to the limited spectral coverage (window effect) expected in the synchrotron case. The absence of such a characteristic signature argues against the simplest synchrotron models. We instead find that the observed correlation between $F$ and $\alpha$ can, in general, be described by the relation $F(t) \propto {\rm e}^{k\,\alpha(t)}$, for which the median $k = 3$. We suggest that this correlation is a manifestation of subphotospheric heating in a flow with a varying entropy. Around the peak of the light curve, a large entropy causes the photosphere to approach the saturation radius, leading to an intense emission with a narrow spectrum. As the entropy decreases the photosphere secedes from the saturation radius, and weaker emission with a broader spectrum is expected. This simple scenario naturally leads to a correlated variation of the intensity and spectral shape, covering the observed range.

From coloured stars to colour flow imaging – or when is ‘Doppler’ not Doppler?

In 1842 Christian Doppler wrote a paper entitled ‘On the Coloured Light of the Double Stars’ in which he sort to explain why some stars appear bluish and some reddish. His theory was that when a star is approaching an observer the wavelength of its light will be shorter and the star thus appears to be blue, whilst when a star is receding from an observer the wavelengths of its light will be longer and it would appear to be red. Doppler was actually wrong on a number of counts as to the explanation for the colour of stars (as will be explained during the talk) although his theory was correct. It is therefore perhaps slightly ironic that Doppler's theory is now widely used in astronomy to measure the speed with which stars are receding from the earth. Doppler's theory was challenged by the young Dutch scientist Christophorus Buys-Ballot, who believed that Doppler's theory could not explain the colours of double stars and set out to prove experimentally, using sound rather that light, that the Doppler effect did not exist. He carried out a number of experiments involving horn players travelling on the Amsterdam-Utrecht railway line, but instead of disproving the Doppler effect, showed that Doppler's theory was correct. The possibility of using the Doppler effect for measuring blood flow was introduced by Shigeo Satomura and colleagues in a number of papers published between 1955 and 1960, and a major advance took place around 1969 when Peter Wells, Pierre Peronneau, and Donald Baker independently described Pulsed ‘Doppler’ units which enabled blood flow signals from specific ranges to be acquired. Further important advances took place around 1982 when Kasai and Namekawa introduced real-time blood flow imaging. Curiously enough, however, whilst continuous wave Doppler units rely on the Doppler shift on the back-scattered ultrasound to measure blood flow velocity, instruments which use pulsed waves do not (and could not for reasons that will once again be explained during the talk) measure the Doppler shift on individual pulses, but rather measure the relative phase-shifts of returning signals with respect to a master oscillator in each inter-pulse interval. Fortunately for most practical purposes the resulting signal is equivalent to a Doppler shift signal. In summary, this talk will explain why the apparent colour of stars could not be due to the Doppler effect, and why pulsed ‘Doppler’ devices cannot detect Doppler frequency shifts.

Ground-Based Observations of Terrestrial Gamma Ray Flashes Associated with Downward-Directed Lightning Leaders

Terrestrial gamma-ray flashes (TGFs) are bursts of gamma-rays initiated in the Earth’s atmosphere. TGFs were serendipitously first observed over twenty years ago by the BATSE gamma ray satellite experiment. Since then, several satellite experiments have shown that TGFs are produced in the upward negative breakdown stage at the start of intracloud lightning discharges. In this proceeding, we present ground-based observation of TGFs produced by downward negative breakdown occurring at the beginning of negative cloud-to-ground flashes.The Terrestrial gamma-ray flashes discussed in this work were detected between 2014-2017 at ground level by the Telescope Array surface detector (TASD) together with Lightning Mapping Array (LMA) and the slow electric field antenna (SA). The TASD detector is a 700 km2ultra high energy cosmic ray detector in the southwestern desert of Utah. It is comprised of 507 (3 m2) plastic scintillator detectors on a 1.2 km square grid. The LMA detector, a three-dimensional total lightning location system, is comprised of nine stations located within and around the array. The slow electric field antenna records the electric field change in lightning discharges.The observed Gamma ray showers were detected in the first 1-2 ms of downward negative breakdown prior to cloud-to-ground lightning strikes. The shower sources were observed by the LMA detector at altitudes of a few kilometers above ground level. The detected energetic burst showers have a footprint on the ground typically ~ 3-5 km in diameter. The bursts comprise of several (2-5) individual pulses, each of which have a span of a few to tens of microseconds and an overall duration of several hundred microseconds. Using a forward-beamed cone of half-angle of 16 degrees, GEANT simulation studies indicate that the showers are consistent with gamma rays of 1012- 1014primary photons. We hypothesize that the observed terrestrial gamma-ray flashes are similar to those detected by satellites, but that the ground-based observations are closer to the source and therefore are able to observe weaker sources and report on the structure of the temporal distribution at the source. This result and future studies will enable us to better identify and constrain the mechanisms of downward TGF production.

Auto clustering of the variety of pulse signals based on their symbolic description

In a number of applied studies of geophysics, medicine, cosmophysics, atomic physics and other fields of knowledge, useful information is often hidden in the character of the behavior of a stream of frequency modulated pulses, which are represented by a large variety of forms, significantly different from each other up to several orders value of magnitude amplitude and durations. Noise is often present in the signal. Under these conditions, the problem arises of identifying both individual pulses and groups of pulses to assess the connection between their dynamic characteristics and the state of system. To solve the problem by a method is proposed that includes signal cleaning from interference, the operation of extracting and converting pulses into a code representing a sequence of invariant amplitude and time transformations of similar pulses combined by a single graphic pattern called “symbol”. All symbols extracted from the signal make up the alphabet. A procedure for narrowing the dimension of the alphabet is shown, which allows you to automatically divide it into clusters according to the degree of coincidence of the code. The results of the practical application of the developed method for the selection of base classes of the geoacoustic emission (GAS) signals related to the objective data of the state of the signal-generating medium are presented. The study used data from the archives of observations IKIR FEB RAS.

Impact of optical–electrical conversion responsivity in sub-sampled photonic analog-to-digital converter

This Letter investigates the impact of the photodiode (PD) saturation in a sub-sampled photonic analog-to-digital converter (PADC) with two individual pulse lasers. It is essentially proved that when the optical power to the saturated PD increases, the optical–electrical conversion (OEC) responsivity and digitized output power of the PADC decrease. If femtosecond pulses are employed for the PADC sampling clock, the time-stretching process in a dispersive medium is necessary to decrease the impact of the PD saturation. In contrast, when the sampling clock with picosecond pulses is utilized, the PD saturation is more tolerable, and thus, the OEC responsivity can be improved by an increase of the optical power to the PD no matter if the time-stretching process is employed.

The duration of the cortisol awakening pulse exceeds sixty minutes in a meaningful pattern

The cortisol awakening response (CAR) is a well-established biomarker for the integrity of the hypothalamic-pituitary-adrenal (HPA) axis in healthy as well as clinical samples. Cortisol rise during the first 60 min after awakening is often used as a proxy of HPA axis regulation in health and disease. Ultradian pulsatility of cortisol is known to superimpose its circadian rhythmicity with the CAR being the first rise after awakening. However, the exact length of the complete first pulse (rise and fall) after awakening, as well as the association between the CAR, the complete first pulse, and successive ultradian pulses, has not yet been studied systematically.Aim of this study was to investigate cortisol dynamics after awakening beyond the standard assessment duration of 60 min in order to assess the cortisol awakening pulse, in relation to ultradian rhythmicity of cortisol after awakening. In a sample of 51 healthy participants, salivary cortisol was collected for the first 270 min after awakening in intervals of 30 min, on two separate days. Different parameters describing individual cortisol pulses over time with respect to inter- and intraindividual variations such as duration, amplitude and area under the curve (AUC) were calculated. Special emphasis was put on the first rise and fall after awakening, called the cortisol awakening pulse (CAP).Mean duration of the CAP was 108 min with high interindividual differences. Duration of first and second pulse were associated with subject’s sex and menstrual cycle status, with a longer first pulse and an attenuated second pulse in male and female subjects in the luteal phase, compared to female subjects in the follicular phase, or women taking oral contraceptives.These results point to the potential usefulness of a longer sampling period for assessing ultradian pulsatility of cortisol in the morning, especially the CAP. To assess the complete pulse rather than the rise alone, measurement of cortisol levels after awakening for 120 min is recommended.

Moisture pulse-reserve in the soil-plant continuum observed across biomes.

The degree to which individual pulses of available water drive plant activity across diverse biomes and climates is not well understood. It has previously only been investigated in a few dryland locations. Here, plant water uptake following pulses of surface soil moisture, an indicator for the pulse-reserve hypothesis, is investigated across South America, Africa and Australia with satellite-based estimates of surface soil and canopy water content. Our findings show that this behaviour is widespread: occurring over half of the vegetated landscapes. We estimate spatially varying soil moisture thresholds at which plant water uptake ceases, noting dependence on soil texture and proximity to the wilting point. The soil type and biome-dependent soil moisture threshold and the plant soil water uptake patterns at the scale of Earth system models allow a unique opportunity to test and improve model parameterization of vegetation function under water limitation.

Nanoscale quantum calorimetry with electronic temperature fluctuations

Motivated by the recent development of fast and ultrasensitive thermometry in nanoscale systems, we investigate quantum calorimetric detection of individual heat pulses in the sub-meV energy range. We propose a hybrid superconducting injector-calorimeter setup, with the energy of injected pulses carried by tunneling electrons. It is shown that the superconductor constitutes a versatile injector, with tunable tunnel rates and energies. Treating all heat transfer events microscopically, we analyze the statistics of the calorimeter temperature fluctuations and derive conditions for an accurate measurement of the heat pulse energies. Our results pave the way for fundamental quantum thermodynamics experiments, including calorimetric detection of single microwave photons.

Soil moisture dynamics under two rainfall frequency treatments drive early spring CO2 gas exchange of lichen-dominated biocrusts in central Spain.

BackgroundBiocrusts, communities dominated by mosses, lichens, cyanobacteria, and other microorganisms, largely affect the carbon cycle of drylands. As poikilohydric organisms, their activity time is often limited to short hydration events. The photosynthetic and respiratory response of biocrusts to hydration events is not only determined by the overall amount of available water, but also by the frequency and size of individual rainfall pulses.MethodsWe experimentally assessed the carbon exchange of a biocrust community dominated by the lichen Diploschistes diacapsis in central Spain. We compared the effect of two simulated precipitation patterns providing the same overall amount of water, but with different pulse sizes and frequency (high frequency: five mm/day vs. low frequency: 15 mm/3 days), on net/gross photosynthesis and dark respiration.ResultsRadiation and soil temperature, together with the watering treatment, affected the rates of net and gross photosynthesis, as well as dark respiration. On average, the low frequency treatment showed a 46% ± 3% (mean ± 1 SE) lower rate of net photosynthesis, a 13% ± 7% lower rate of dark respiration, and a 24% ± 8% lower rate of gross photosynthesis. However, on the days when samples of both treatments were watered, no differences between their carbon fluxes were observed. The carbon flux response of D. diacapsis was modulated by the environmental conditions and was particularly dependent on the antecedent soil moisture.DiscussionIn line with other studies, we found a synergetic effect of individual pulse size, frequency, environmental conditions, and antecedent moisture on the carbon exchange fluxes of biocrusts. However, most studies on this subject were conducted in summer and they obtained results different from ours, so we conclude that there is a need for long-term experiments of manipulated precipitation impacts on the carbon exchange of biocrusts. This will enable a more complete assessment of the impacts of climate change-induced alterations in precipitation patterns on biocrust communities.

Sinus or not: a new beat detection algorithm based on a pulse morphology quality index to extract normal sinus rhythm beats from wrist-worn photoplethysmography recordings

Objective: Wrist-worn photoplethysmography (PPG) can enable free-living physiological monitoring of people during diverse activities, ranging from sleep to physical exercise. In many applications, it is important to remove the pulses not related to sinus rhythm beats from the PPG signal before using it as a cardiovascular descriptor. In this manuscript, we propose an algorithm to assess the morphology of the PPG signal in order to reject non-sinus rhythm pulses, such as artefacts or pulses related to arrhythmic beats. Approach: The algorithm segments the PPG signal into individual pulses and dynamically evaluates their morphological likelihood of being normal sinus rhythm pulses via a template-matching approach that accounts for the physiological variability of the signal. The normal sinus rhythm likelihood of each pulse is expressed as a quality index that can be employed to reject artefacts and pulses related to arrhythmic beats. Main results: Thresholding the pulse quality index enables near-perfect detection of normal sinus rhythm beats by rejecting most of the non-sinus rhythm pulses (positive predictive value 98%–99%), both in healthy subjects and arrhythmic patients. The rejection of arrhythmic beats is almost complete (sensitivity to arrhythmic beats 7%–3%), while the sensitivity to sinus rhythm beats is not compromised (96%–91%). Significance: The developed algorithm consistently detects normal sinus rhythm beats in a PPG signal by rejecting artefacts and, as a first of its kind, arrhythmic beats. This increases the reliability in the extraction of features which are adversely influenced by the presence of non-sinus pulses, whether related to inter-beat intervals or to pulse morphology, from wrist-worn PPG signals recorded in free-living conditions.

Impact of Cardiovascular Factors on Pulse Wave Velocity and T otal Vascular Resistance in Different Age Group Patients with Cardiovascular Disorders.

Background: Pulse Wave Velocity (PWV) is the propagation speed of the wave-induced along the aorta and arterial tree, each time the heart beats. PWV increases with increased arterial stiffness, thus establishing it as a reliable prognostic marker for cardiovascular morbidity and mortality. On the other hand, Total Vascular Resistance (TVR) is the overall resistance offered by systemic circulation and pulmonary circulation. This resistance needs to be overcome in order to create the flow of blood through the circulatory system. The goal of this study was to investigate the influence of different cardiovascular factors on arterial stiffness and vascular resistance in CVD patient from eastern India population.Methods: Total of 782 patients with Cardiovascular Disease (CVD) like hypertension, Ischemic heart disease, Congestive cardiac failure and peripheral arterial disease were included to evaluate the cardiovascular hemodynamic and non-hemodynamic parameter by oscillometric method and investigated those factors on PWV and TVR in subjects of both sexes aged between 15 to 87 years.Results: The old age (> 55 years) was found to have greatest impact on PWV as compared with younger age group. Systolic Blood Pressure (SBP), Heart Rate (HR), augmentation pressure and Body Surface Area (BSA) had a positive association with the PWV. Augmentation Index and Body Mass Index (BMI) had a negative impact on the PWV.Conclusion: Despite the limitations, like unequal number of male and female participants, wide variation of the age of the subjects and analyzing association of many factors at a time, our large and community-based study show individual blood pressure and pulse pressure depending on complex interaction between large arteries and arterioles. This study sheds light on the relationship between proximal and distal part (PWV and TVR) of the arterial tree as well as their association with different hemodynamic and non-hemodynamic parameters.

Explaining the asymmetric line profile in Cepheus X-4 with spectral variation across pulse phase

The high mass X-ray binary Cep X-4, during its 2014 outburst, showed evidence for an asymmetric cyclotron line in its hard X-ray spectrum. The 2014 spectrum provides one of the clearest cases of an asymmetric line profile among all studied sources with Cyclotron Resonance Scattering Features (CRSF). We present a phase-resolved analysis of NuSTAR and Suzaku data taken at the peak and during the decline phases of this outburst. We find that the pulse-phased resolved spectra are well-fit by a single, symmetric cyclotron feature. The fit parameters vary strongly with pulse phase: most notably the central energy and depth of the cyclotron feature, the slope of the power-law component, and the absorbing column density. We synthesise a phase averaged spectrum using the best-fit parameters for these individual pulse phases, and find that this combined model spectrum has a similar asymmetry in the cyclotron features as discovered in phase-averaged data. We conclude that the pulse phase resolved analysis with simple symmetric line profiles when combined can explain the asymmetry detected in the phase-averaged data.