Unidentified Sources Research Articles

An analysis of customer-based and supplier-based trade credit gaps

PurposeThis paper aims to examine the customer-based and supplier-based trade credit gaps for USA firms from 1970 to 2020.Design/methodology/approachThe authors' study examines USA companies from 1970 to 2020. The authors begin with an analysis of the trends in aggregate working capital, the capital's components and the trade credit gaps. Various regression models are used to estimate the impacts of identified firm characteristics and unidentified sources on customer-based and supplier-based trade credit gaps over time. The authors then decompose the impacts of firm characteristics to further understand whether changing firm characteristics and/or changing sensitivity to firm characteristics drive the variation in trade credit gaps.FindingsThere is a gradual reduction in the customer-based trade credit gap and a substantial expansion in the supplier-based trade credit gap. Though identified firm characteristics have dominant impacts on observed trade credit gaps, there is evidence of the effects of time and unobservable factors. The main source of changes in customer-based and supplier-based trade credit gaps lies in changes in sensitivity to firm characteristics. In addition, the authors find that firm age is the factor with the largest average effect on both trade credit gaps when examining the full sample period. However, different firm characteristics appear to be the key driver of variations in trade credit gaps over time and across the two types of trade credit gaps. The authors also find that financial distress has the least impact on both customer-based and supplier-based trade gaps. There are variations in the firm characteristics with the largest impacts when evaluating decade-long evaluation periods.Originality/valueTo the authors' knowledge, this is the first paper to examine the customer-based and supplier-based trade credit gaps. The connection between trade credit and the trade credit's corresponding inventory (INV) component extends prior literature on the joint management of trade credit and INV. The authors analyze both identified firm characteristics and unidentified sources in the search for explanations of the trade credit gaps. Furthermore, the authors' study explores the channels through which firm characteristics affect different types of trade credit gaps. The authors' findings help identify relevant and irrelevant risk factors of corporate working capital policy.

Multi-messenger high-energy signatures of decaying dark matter and the effect of background light

The IceCube Neutrino Observatory at the South Pole has measured astrophysical neutrinos using through-going and starting events in the TeV to PeV energy range. The origin of these astrophysical neutrinos is still largely unresolved, and among their potential sources could be dark matter decay. Measurements of the astrophysical flux using muon neutrinos are in slight tension with starting event measurements. This tension is driven by an excess observed in the energy range of 40–200 TeV with respect to the through-going expectation. Previous works have considered the possibility that this excess may be due to heavy dark matter decay and have placed constraints using gamma-ray and neutrino data. However, these constraints are not without caveats, since they rely on the modeling of the astrophysical neutrino flux and the sources of gamma-ray emission. In this work, we derive background-agnostic galactic and extragalactic constraints on decaying dark matter by considering Tibet-ASγ data, Fermi-LAT diffuse data, and the IceCube high-energy starting event sample. For the gamma-ray limits, we investigate the uncertainties on secondary emission from electromagnetic cascades during propagation arising from the unknown intensity of the extragalactic background light. We find that such uncertainties amount to a variation of up to ∼ 55% in the gamma-ray limits derived with extragalactic data. Our results imply that a significant fraction of the astrophysical neutrino flux could be due to dark matter and that ruling it out depends on the assumptions on the gamma-ray and neutrino background. The latter depends on the yet unidentified sources.

Characteristics of health care workers undiagnosed with SAR-COV-2 infection at Hanoi Medical University

Healthcare workers are among the most at-risk groups to get infected by SARS-CoV-2 due to the exposure to disease sources in specific working environment. However, after experiencing four waves of epidemics, there was a certain proportion of healthcare workers who have ever been diagnosed to be infected with SARS-CoV-2, regardless of whether they have a history of contact with or an unknown history of contact with an unidentified source of infection. This research aimed to identify the characteristics of healthcare workers who have not diagnosed with SARS-CoV-2 or have never been infected by SARS-CoV-2. 79 staffs of Hanoi Medical University were selected at the time of April 2022. 16 out of 79 individuals were infected with SARS-CoV-2 but had not been identified. 50% of this group were physicians working at primary care unit. Subjects who had been infected by SARS-CoV-2 showed greater levels of anti-receptor-binding domain (RBD) of SARS-CoV-2 antibodies than those who had never been infected (p=0.001). Anti-RBD antibody levels in 93.67% of research individuals were above the FDA-recommended threshold of 4.8 U/mL for the use of convalescent plasma. In the group that had never been infected by SARS-CoV-2, the antibody levels against RBD-SARS-CoV-2 were lower in those vaccinated above 90 days than those vaccinated below 90 days (p=0.02). 20.25% of research subjects who had never been diagnosed had infected by SARS-CoV-2, with greater levels of anti-RBD-SARS-CoV-2 antibodies than the uninfected group. In the uninfected group, antibody levels gradually decreased over time.

Ozone-Facilitated Formation of Uranyl Peroxide in Humid Conditions.

Metaschoepite, [(UO2)8O2(OH)12](H2O)10, maintained in a high relative humidity (RH) environment with air initially transformed into an intermediate phase that subsequently was replaced by the peroxide phase studtite, [(UO2)(O2)(H2O)2](H2O)2, over the course of 42 days, as observed using Raman and infrared spectroscopy and powder X-ray diffraction. Addition of atmospheric ozone vastly increased the rate and extent of the transformation to studtite but only in a high-RH atmosphere. Owing to its strong affinity for peroxide, uranyl reacted with hydrogen peroxide as it formed and precipitated stable studtite. In this work, we provide a previously unidentified source of hydrogen peroxide and make a case for the re-examination of storage systems where the consequences of atmospheric ozone are not considered.

Classifying Unidentified X-Ray Sources in the Chandra Source Catalog Using a Multiwavelength Machine-learning Approach

The rapid increase in serendipitous X-ray source detections requires the development of novel approaches to efficiently explore the nature of X-ray sources. If even a fraction of these sources could be reliably classified, it would enable population studies for various astrophysical source types on a much larger scale than currently possible. Classification of large numbers of sources from multiple classes characterized by multiple properties (features) must be done automatically and supervised machine learning (ML) seems to provide the only feasible approach. We perform classification of Chandra Source Catalog version 2.0 (CSCv2) sources to explore the potential of the ML approach and identify various biases, limitations, and bottlenecks that present themselves in these kinds of studies. We establish the framework and present a flexible and expandable Python pipeline, which can be used and improved by others. We also release the training data set of 2941 X-ray sources with confidently established classes. In addition to providing probabilistic classifications of 66,369 CSCv2 sources (21% of the entire CSCv2 catalog), we perform several narrower-focused case studies (high-mass X-ray binary candidates and X-ray sources within the extent of the H.E.S.S. TeV sources) to demonstrate some possible applications of our ML approach. We also discuss future possible modifications of the presented pipeline, which are expected to lead to substantial improvements in classification confidences.

Statistics for dark matter subhalo searches in gamma rays from a kinematically constrained population model: Fermi-LAT-like telescopes

Cold dark matter subhalos are expected to populate galaxies in numbers. If dark matter self-annihilates, these objects turn into prime targets for indirect searches, in particular with gamma-ray telescopes. Incidentally, the Fermi-LAT catalog already contains many unidentified sources that might be associated with subhalos. In this paper, we determine the probability for subhalos to be identified as gamma-ray pointlike sources from their predicted distribution properties. We use a semi-analytical model for the Galactic subhalo population, which, in contrast to cosmological simulations, can be made fully consistent with current kinematic constraints in the Milky Way and has no resolution limit. The model incorporates tidal stripping effects from a realistic distribution of baryons in the Milky Way. The same baryonic distribution contributes a diffuse gamma-ray foreground which adds up to that, often neglected in subhalo searches, generated by the smooth dark matter and the unresolved subhalos. This configuration implies a correlation between pointlike subhalo signals and diffuse background. Based on this semi-analytical modeling, we generate mock gamma-ray data assuming an idealized telescope resembling Fermi-LAT and perform a likelihood analysis to estimate the current and future sensitivity to subhalos in the relevant parameter space. We find a number of detectable subhalos of order ${\cal O}(<1)$ for optimistic model parameters and a WIMP mass of 100~GeV, maximized for a cored host halo. This barely provides support to the current interpretation of several Fermi unidentified sources as subhalos. We also find it more likely to detect the smooth Galactic halo itself before subhalos, should dark matter in the GeV-TeV mass range self-annihilate through $s$-wave processes.

Rigorous Assessment of Cl- -Based Anolytes on Electrochemical Ammonia Synthesis.

Many challenges in the electrochemical synthesis of ammonia have been recognized with most effort focused on delineating false positives resulting from unidentified sources of nitrogen. However, the influence of oxidizing anolytes on the crossover and oxidization of ammonium during the electrolysis reaction remains unexplored. Here it is reported that the use of analytes containing halide ions (Cl- and Br- ) can rapidly convert the ammonium into N2 , which further intensifies the crossover of ammonium. Moreover, the extent of migration and oxidation of ammonium is found to be closely associated with external factors, such as applied potentials and the concentration of Cl- . These findings demonstrate the profound impact of oxidizing anolytes on the electrochemical synthesis of ammonia. Based on these results, many prior reported ammonia yield rates are calibrated. This work emphasizes the significance of avoiding selection of anolytes that can oxidize ammonium, which is believed to promote further progress in electrochemical nitrogen fixation.

Cryptogenic stroke and extrasystolic arrythmia: is there any correlation?

Abstract Up to 45% of all ischemic strokes (IS) are cryptogenic. Purpose To reveal the possible reasons of cryptogenic IS. Methods We analyzed the cases of computer tomography verified IS in patients admitted the hospital during the period of 3 years. All these 268 patients had unidentified source of IS. We analyzed hemostasiograms, lipids levels, performed echocardiography, Doppler ultrasound of brachiocephalic arteries, 24-hours ECG monitoring and common carotid arteries sphygmography (SG). Results None of the patients had atrial fibrillation, hemodynamically significant stenoses of brachiocephalic arteries or hematological pathology associated with hypercoagulation. 234 (87.3%) patients had atherosclerotic plaques in carotid area bifurcation (in 36 (13.4%) – intima-media thickness was 1.1 mm, in 74 (27.6%)– stenosis &amp;lt;40%, in 124 (46.3%) had 40–69% stenosis in diameter). The internal carotid stenosis in diameter is calculated by ECST, NASCET and St. Mary's ratio criteria. To detect the type of the plaques we used Gray-Weale–Nicolaides ultrasound classification. In 39 (14.5%) was type I: uniformly echolucent plaque; in 88 (32.8%) type II: predominately echolucent plaque; in 71 (26.5%) type III: predominantly echogenic plaque, none had type IV: uniformly echogenic plaque or type V: heavy calcification. In 24-hours ECG monitoring and SG we revealed that most of the patients – 244 (91.0%) had extrasystolic arrhythmia which ventricular contraction of extrasystole appeared in the early phase of cardiocycle – before the transmitral blood flow peak. In 1st post-extrasystolic wave after such extrasystole we detected the growth of linear blood flow speed in carotid bifurcation (2.5 m/sec) and kinetic arteries parameters of SG (2.6 times). Conclusion The appearance of IS is higher in patients with extrasystolic arrhythmia appearing in the cardiocycle before the transmitral blood flow peak. In cryptogenic stroke, the reason of it can be the atherosclerotic plaque defragmentation with further embolism, caused by the additional mechanical trauma of increased hemodynamical and kinetic parameters of pulse wave of the 1st post-extrasystolic contraction. Funding Acknowledgement Type of funding sources: None.

Revisiting Michael Bonell's work on humid tropical rainforest catchments: Isotope tracers reveal seasonal shifts in catchment hydrology

It has been almost 50 years since the foundational work at the Babinda catchments in North Queensland kickstarted the field of tropical hydrology globally. To expand upon this work and build a more generalized hydrological understanding of steep rainforest catchments, we studied the seasonal evolution of hydrological response from two catchments with broadly similar characteristics to the Babinda catchments. Both hydrometric and water stable isotope data were collected at relatively high frequencies during one wet season (Thompson Creek) and a 3-year period (Atika Creek). The longer dataset spans a wide range of environmental conditions experienced in the humid tropics, including events that cover the wetting-up transitional period of the wet season and tropical cyclones (TC). Both catchments displayed a fast streamflow response to rainfall with the shallow upper soil profile responding quickly to rainfall at Atika Creek. New findings from this study include the importance of pre-event water (>50% using the two component hydrograph separation technique) for overall event flows, especially when the catchment was wet. Rainfall, surface runoff and groundwater isotope and specific electrical conductivity (SEC) compositions varied between rainfall events with the most complex bivariate mixing plots observed for multi-peak events that occurred at the start of the wet season and after a dry period within the wet season. Two-tracer, 3 component hydrograph separations did not provide satisfactory results in identifying source water contributions to streamflow. These results highlighted the time-variant and non-conservative behaviour of the rainfall, surface runoff and shallow groundwater source waters over the seasonal timescale, with soil water being an important unidentified source contributor. Our findings highlight the need for high frequency multi-source sampling to accurately interpret catchment behaviour and the importance of soil water contributions to streamflow. We propose a framework to describe the seasonal evolution of streamflow response in steep tropical rainforest catchments experiencing seasonal rainfall activity.

Population synthesis of pulsar wind nebulae and pulsar halos in the Milky Way

Context.The discovery of extended gamma-ray emission toward a number of middle-aged pulsars suggests the possibility of long-lived particle confinement beyond the classical pulsar wind nebula (PWN) stage. How this emerging source class can be extrapolated to a Galactic population remains unclear.Aims.We aim to evaluate how pulsar halos fit in existing TeV observations, under the assumption that all middle-aged pulsars develop halos similar to those observed toward the J0633+1746 or B0656+14 pulsars.Methods.We modeled the populations of supernova remnants, PWNe, and pulsar halos in the Milky Way. The PWN-halo evolutionary sequence is described in a simple yet coherent framework, and both kinds of objects are assumed to share the same particle injection properties. We then assessed the contribution of the different source classes to the very-high-energy emission from the Galaxy.Results.The synthetic population can be made consistent with the flux distribution of all known objects, including unidentified objects, for a reasonable set of parameters. The fraction of the populations predicted to be detectable in surveys of the Galactic plane with HESS and HAWC is then found to be in good agreement with their actual outcome, with a number of detectable halos ranging from 30 to 80% of the number of detectable PWNe. Prospects for CTA involve the detection of 250 − 300 sources in the Galactic Plane Survey, including 170 PWNe and up to 100 halos. The extent of diffusion suppression in halos has a limited impact on such prospects but its magnitude has a strong influence. The level of diffuse emission from unresolved populations in each survey is found to be dominated by halos and comparable to large-scale interstellar radiation powered by cosmic rays above 0.1–1 TeV.Conclusions.Pulsar halos are shown to be viable counterparts to a fraction of the currently unidentified sources if they develop around most middle-aged pulsars. Yet, if the phenomenon is rare, with an occurrence rate of 5 − 10% as suggested in a previous work from the local positron flux constraint, the total number of currently known TeV sources including unidentified ones cannot be accounted for in our model from young PWNe only. This calls for continued efforts to model pulsar-powered emission along the full evolutionary path, including the late stages past the young nebula phase.

Airborne estimation of SO2 emissions rates from a coal-fired power plant using two top-down methods: A mass balance model and Gaussian footprint approach

In this study, two top-down methods—mass balance and Gaussian footprint—were used to determine SO2 emissions rates via three airborne sampling studies over Korea's largest coal power plant in October 2019 and 2020. During the first two flights in October 2019, mass balance approaches significantly underestimated the SO2 emissions rates by 75 % and 28 %, respectively, as obtained from the real-time stack monitoring system. Notably, this large discrepancy accounted for the insufficient number of transects altitudes and high levels of background SO2 along the upwind side. Alternatively, the estimated SO2 emissions rates of the third flight (October 2020) displayed a difference of <10 % from rea-time monitoring data (630 vs. 690 kg·hr−1), owing to the enhanced vertical resolution with increased transects and lower background SO2 levels. In contrast to the mass balance method, Gaussian footprints offered significantly improved accuracy (relative error: 41 %, 32 %, and 2 % for Flights 1, 2, and 3, respectively). This relatively good performance was attributed to prior emissions knowledge via the Clean Air Policy Support System (CAPSS) emissions inventory and its unique ability to accurately estimate stack-level SO2 emissions rates. Theoretically, the Gaussian footprint was less prone to sparse transects and upwind background levels. However, it can be substantially influenced by atmospheric stability and consequently by effective stack heights and dispersion parameters; basically, all factors with minimal-to-no influence on the mass balance approach. Conversely, the mass balance method was the only plausible approach to estimate unidentified source emissions rates when well-defined prior emission information was unknown. Here, the footprint approach supplemented the mass balance method when the emission inventories were known, and employing both strategies approaches greatly enhanced the integrity of top-down emissions inventories from the power plant sources, thus, supporting their potential for ensuring operational compliance with SO2 emissions regulation.

Searching for Cataclysmic Variable Stars in Unidentified X-Ray Sources

We carry out a photometric search for new cataclysmic variable stars (CVs), with the goal of identification for candidates of AR Scorpii-type binary systems. We select GAIA sources that are likely associated with unidentified X-ray sources, and analyze the light curves taken by the Zwicky Transient Facility, Transiting Exoplanet Survey Satellite, and Lulin One-meter Telescope in Taiwan. We investigate eight sources as candidates for CVs, among which six sources are new identifications. Another two sources have been recognized as CVs in previous studies, but no detailed investigations have been done. We identify two eclipsing systems that are associated with an unidentified XMM-Newton or Swift source, and one promising candidate for polar associated with an unidentified ASKA source. Two polar candidates may locate in the so-called period gap of a CV, and the other six candidates have an orbital period shorter than that of the period gap. Although we do not identify a promising candidate for AR Scorpii-type binary systems, our study suggests that CV systems that have X-ray emission and do not show frequent outbursts may have been missed in previous surveys.

Particle cycling rates at Station P as estimated from the inversion of POC concentration data

Particle cycling rates in marine systems are difficult to measure directly, but of great interest in understanding how carbon and other elements are distributed throughout the ocean. Here, rates of particle production, aggregation, disaggregation, sinking, remineralization, and transport mediated by zooplankton diel vertical migration were estimated from size-fractionated measurements of particulate organic carbon (POC) concentration collected during the NASA EXport Processes in the Ocean from RemoTe Sensing (EXPORTS) cruise at Station P in summer 2018. POC data were combined with a particle cycling model using an inverse method. Our estimates of the total POC settling flux throughout the water column are consistent with those derived from thorium-234 disequilibrium and sediment traps. A budget for POC in two size fractions, small (1–51 µm) and large (&amp;gt; 51 µm), was produced for both the euphotic zone (0–100 m) and the upper mesopelagic zone (100–500 m). We estimated that POC export at the base of the euphotic zone was 2.2 ± 0.8 mmol m−2 d−1, and that both small and large particles contributed considerably to the total export flux along the water column. The model results indicated that throughout the upper 500 m, remineralization leads to a larger loss of small POC than does aggregation, whereas disaggregation results in a larger loss of large POC than does remineralization. Of the processes explicitly represented in the model, zooplankton diel vertical migration is a larger source of large POC to the upper mesopelagic zone than the convergence of large POC due to particle sinking. Positive model residuals reveal an even larger unidentified source of large POC in the upper mesopelagic zone. Overall, our posterior estimates of particle cycling rate constants do not deviate much from values reported in the literature, i.e., size-fractionated POC concentration data collected at Station P are largely consistent with prior estimates given their uncertainties. Our budget estimates should provide a useful framework for the interpretation of process-specific observations obtained by various research groups in EXPORTS. Applying our inverse method to other systems could provide insight into how different biogeochemical processes affect the cycling of POC in the upper water column.

Treatment of ACTH-ectopic syndrome with long-acting octreotide: effective control of disease activity

ACTH — ectopic syndrome (ACTH-ES) is a severe multisystem disease caused by paraneoplastic secretion of ACTH itself and/or much less often corticoliberin (CL) by tumor tissue. The frequency of ACTH-ES is 12–20% of cases of endogenous hypercortisolism, i.e. about 1–2 cases per million population, and covers a range of tumors, from benign neoplasms to malignant tumors with widespread metastases, while the most common causes of ACTH-ES are tumors of the lung, pancreas and thymus, and more rare localizations are neuroendocrine tumors (NET) of the intestine, medullary thyroid cancer, pheochromocytoma and mesothelioma. The optimal treatment for ACTH-ES is to remove the ACTH-secreting tumor. For patients with an unidentified source of ectopic hormone secretion, the choice is narrowed to bilateral adrenalectomy followed by hormone replacement therapy with glucocorticoids and mineralocorticoids. Medication options are generally a low-effective/palliative treatment option. In this article, we present a clinical case of the successful use of long-acting octreotide in a 36-year-old woman with severe ACTH-ES for long-term control of paraneoplastic ACTH secretion, against which a clinical and biochemical improvement comparable to complete remission of the disease was achieved.

X-ray investigation of the X-ray source 1RXS J121902.7–630910 with Suzaku

We present a study of the unidentified X-ray source 1RXS J121902.7–630910 based on Suzaku X-ray Imaging Spectrometer observation. We aim at clarifying the nature of the emission from 1RXS J121902.7–630910. We found that the spectrum is well represented by a thermal plasma model with an electron temperature of kTe∼ 3.7 keV, the upper limit of ionization time-scale of τ∼ 5.6 ×1010 cm−3 s, and the absorbing column density of NH∼ 0.5 ×1021 cm−2. We investigated the possible origin of 1RXS J121902.7–630910, and found optical counterpart candidates to this X-ray source. We conclude that it could be a point-like source compared to the analysis results of an extended source, and observations at other wavelengths are needed to confirm its nature.

The importance of evaluating standard monitoring methods: Observer bias and detection probabilities for moose pellet group surveys.

Counting is not always a simple exercise. Specimens can be misidentified or not detected when they are present, giving rise to unidentified sources of error. Deer pellet group counts are a common method to monitor abundance, density, and population trend. Yet, detection errors and observer bias could introduce error into sometimes very large (spatially, temporally) datasets. For example, in Scandinavia, moose (Alces alces) pellet group counts are conducted by volunteer hunters and students, but it is unknown how much uncertainty observer error introduces into these datasets. Our objectives were to 1) estimate the detection probability of moose pellet groups; 2) identify the primary variables leading to detection errors including prior observer experience; and 3) compare density estimates using single and double observer counts. We selected a subset of single observer plots from a long-term monitoring project to be conducted as dependent double observer surveys, where primary and secondary observers worked simultaneously in the field. We did this to quantify detection errors for moose pellet groups, which were previously unknown in Scandinavia, and to identify covariates which introduced variation into our estimates. Our study area was in the boreal forests of southern Norway where we had a nested grid of 100-m2 plots that we surveyed each spring. Our observers were primarily inexperienced. We found that when pellet groups were detected by the primary observer, the secondary observer saw additional pellet groups 42% of the time. We found search time was the primary covariate influencing detection. We also found density estimates from double observer counts were 1.4 times higher than single observer counts, for the same plots. This density underestimation from single observer surveys could have consequences to managers, who sometimes use pellet counts to set harvest quotas. We recommend specific steps to improve future moose pellet counts.

Pulsar Wind Nebulae and Unidentified Galactic Very High Energy Sources

The riddle of the origin of Cosmic Rays (CR) has been an open question for over a century. Gamma ray observations above 100 MeV reveal the sites of cosmic ray acceleration to energies where they are unaffected by solar modulation; recent evidence supports the existence of hadronic acceleration in Supernova Remnants (SNR), as expected in the standard model of cosmic ray acceleration. Nevertheless, the results raise new questions, and no final answer has been provided thus far. Among the suggested possible alternative accelerators in the Very High Energy (VHE) gamma ray sky, pulsar wind nebulae (PWNe, which together with dark matter are the main candidates to explain the local positron excess as well) are the dominant population among known Galactic sources. However, the most numerous population in absolute terms is represented by unidentified sources (~50% of VHE gamma ray sources). The relationship between PWNe and unidentified sources seems very close; in fact, in a PWN, the lifetime of inverse Compton (IC) emitting electrons not only exceeds the lifetime of its progenitor pulsar, but also exceeds the age of the electrons that emit via synchrotron radiation. Therefore, during its evolution, a PWN can remain bright in IC such that its GeV-TeV gamma ray flux remains high for timescales much larger than the lifetimes of the pulsar and the X-ray PWN. In addition, the shell-type remnant of the supernova explosion in which the pulsar was formed has a much shorter lifetime than the electrons responsible for IC emission. Hence, understanding PWNe and VHE unidentified sources is a crucial piece of the solution to the riddle of the origin of cosmic rays. Both theoretical aspects (with particular emphasis on the ancient pulsar wind nebulae scenario) and their observational proofs are discussed in this paper. Specifically, the scientific cases of HESS J1616-508 and HESS J1813-126 are examined in detail.

Classification of Fermi-LAT unidentified gamma-ray sources using catboost gradient boosting decision trees

ABSTRACT The latest Fermi-LAT gamma-ray catalogue, 4FGL-DR3, presents a large fraction of sources without clear association to known counterparts, i.e. unidentified sources (unIDs). In this paper, we aim to classify them using machine learning algorithms, which are trained with the spectral characteristics of associated sources to predict the class of the unID population. With the state-of-the-art catboost algorithm, based on gradient boosting decision trees, we are able to reach a 67 per cent accuracy on a 23-class data set. Removing a single of these classes – blazars of uncertain type – increases the accuracy to 81 per cent. If interested only in a binary AGN/pulsar distinction, the model accuracy is boosted up to 99 per cent. Additionally, we perform an unsupervised search among both known and unID population, and try to predict the number of clusters of similar sources, without prior knowledge of their classes. The full code used to perform all calculations is provided as an interactive python notebook.

Inferring Pulsar Periods from Synchro-curvature Spectra

The period and the period derivative of a pulsar are critical magnitudes for defining the properties of the magnetospheric size and plasma dynamics. The pulsar light cylinder, the magnetic field intensity nearby it, and the curvature radius all depend on these timing properties, and shape the observed high-energy synchro-curvature emission. Therefore, the radiative properties of pulsars are inextricably linked to them. This fact poses the question of how well does a given pulsar’s spectral energy distribution embed information of the timing parameters, and if so, whether we can deduce them if they have not been measured directly. This is relevant to possibly constrain the timing properties of potential pulsar candidates among unidentified γ-ray sources. We consider well-measured pulsar spectra blinding us from the knowledge of their timing properties, and address this question by using our radiative synchro-curvature model that was proven able to fit the observed spectra of the pulsar population. We find that in the majority of the cases studied (8 out of 13), the spin period is constrained within a range of about 1 order of magnitude, within which the real period lies. In the other cases, there is degeneracy and no period range can be constrained. This can be used to facilitate the blind search of pulsed signals.

Highly heterogeneous mantle caused by recycling of oceanic lithosphere from the mantle transition zone

Geochemical heterogeneities observed in the mantle are usually attributed to recycling of oceanic lithosphere through subduction. However, it remains hotly debated where recycled material stagnates, and how quickly it can be liberated back to surface. This knowledge gap hinders our understanding of mantle circulation and the chemical evolution of the Earth. Here we address these questions using a combination of geochronology and geochemistry from South China Sea (SCS) seamounts. The Shixingbei seamount lavas formed during active seafloor spreading at c. 19.1 Ma show limited geochemical variability, whereas the Zhenbei-Huangyan seamount chain formed during the post-spreading stage at c. 7.8 Ma and displays a wide range of compositions. However, melt inclusions in olivine and plagioclase from the Zhenbei-Huangyan basalts show considerably greater isotopic variability than seen in the whole rock compositions of both the SCS syn- and post-spreading lavas. A previously unidentified third mantle source component (FOZO) revealed by olivine-hosted melt inclusions along with both depleted (DMM) and enriched (EMII) mantle components is required in the source region to explain the observed isotopic and chemical variability. On the basis of our results, the age of the recycled ocean crust and sediments in this region are estimated to be c. 120 – 350 Ma. We infer that these enriched components in the SCS lavas come from the mantle transition zone. Variations in mantle source heterogeneity coupled with melting process control spatial–temporal (spreading vs. post-spreading stage) geochemical variations of lavas from the SCS and surrounding areas. Together with the results from published studies, we propose that marginal basins are one of the major locations on Earth where oceanic and/or continental lithosphere is transferred into the upper mantle and transition zone, representing an important source of upper mantle heterogeneity. We provide a simple conceptual model linking plate subduction and upper mantle heterogeneity and the volcanism in the SCS and surrounding areas.