Lower Limit Research Articles

Non-enzymatic cholesterol biosensor: Electrochemical sensing based on peptide-polylactic acid thin film

Cholesterol is a fundamental lipid prevalent in eukaryotic cell membranes and circulating in the bloodstream bound to lipoproteins. It serves as a precursor to steroid hormones and is regarded as a biomarker for cardiovascular disease and other metabolic disorders. Numerous cholesterol detection methods predominantly rely on enzymes, which suffer from instability, leading to non-cost-effective biosensors with low sensitivity and poor reusability. Therefore, monitoring cholesterol levels with a feasible, rapid, and stable biosensor is critical for diagnosing and treating various disorders. This study aimed to develop a non-enzymatic cholesterol biosensor based on a selected cholesterol recognition peptide as the detection element. Screen-printed carbon electrodes (SPEs) modified with biocompatible poly-L-lactic acid (PLLA) porous nanomembranes (NMs) were utilized as support for the covalent immobilization of the peptide. Data obtained from electrochemical impedance spectroscopy (EIS) demonstrated the peptide's effective binding affinity towards cholesterol, paving the way for its implementation. The determination of cholesterol with the proposed biosensor exhibited a low limit of detection of 6.31 μM with linear responses ranging from 2–15 μM and 20–40 μM. These findings present an alternative method for cholesterol sensing by integrating novel peptides as biorecognition motifs with biocompatible polymeric materials, potentially useful as biocompatible and future point-of-care sensors.

An In2O3/In2S3 photoanode-driven whole-cell biocathode sensor for sensitive detection of nitrate

Whole-cell biocathode sensor is a new form of self-regenerable biosensor and promising for environmental monitoring especially in the scenario with low organic substrate. However, external power supply such as electrochemical workstation is required to drive the biocathode reaction, which greatly limits its application. Herein, a new strategy based on the visible-light-driven whole-cell biocathode was proposed and validated for self-powered sensitive detections. To be specific, 1-OH phenazine was selected as the optimal electron shuttle for a Shewanella oneidensis MR-1 inoculated biocathode, which efficiently mediate the cathodic reaction at an electrode potential below -0.6V (vs. SCE). Meanwhile, an In2O3/In2S3 photoanode with nanoflower-like structure was fabricated to match the kinetic of the biocathode. The photo-driven biocathode reduction was convinced by comparing with the performance of biocathode in the conventional three-electrode system. With this basis, a self-powered whole-cell biocathode sensor was developed for nitrate detection. An extreme low limit of detection of 0.028 μM (S/N=3) and linear detection range of 0.1~20 μM was achieved. Moreover, this biocathode sensor also exhibited excellent selectivity, reusability, accuracy, stability and was reliable for the detection of complex environmental samples. Therefore, this work developed a new photo-driven whole-cell biocathode sensor with excellent detection capacity of nitrate, which opens up new prospects for the development of high-performance biosensors.

Liquid chromatography-tandem mass spectrometry analysis of nitrogen mustard degradation products after derivatization with benzoylimidazole

Nitrogen mustards are highly toxic compounds and strictly controlled by the Chemical Weapons Convention. When those agents are used, exposure must be confirmed by analyzing biological samples from victims to allow prompt medication and reduction of secondary damage. In this study, a derivatization-liquid chromatography (LC)-tandem mass spectrometry (MS/MS) method to analyze nitrogen mustard degradation products (ethanolamines; EAs) in human urine was developed. Benzoylimidazole (BzI) was used as a derivatization reagent, and two highly hydrophilic EAs (methyldiethanolamine and ethyldiethanolamine) were analyzed by using a reversed-phase column with sufficient retention. For urine samples, after solid-phase extraction with cation exchange cartridge and derivatization, EAs were analyzed at low limits of detection (5 ng/mL). The calibration curves had a wide linear range (50–1000 ng/mL), and the quantitation results were sufficient for screening. Compared with our previous derivatization-LC-MS/MS method using pentafluorobenzoyl chloride as a derivatization reagent and hydrophilic interaction liquid chromatography (HILIC)-MS/MS method, not only the limits of detection but also the operability and throughput were improved. The performance of the newly developed derivatization reagent was also evaluated using density functional theory (DFT) calculations.

Neutrophil elastase specific fluorescent probe for early diagnosis of thyroiditis via serum sample testing and fluorescence imaging

Autoimmune thyroid diseases (AITD) often interfere with early detection due to asymptomatic symptoms and normal thyroid function in routine tests. Developing early diagnostic tools is crucial for timely and accurate treatment, potentially reducing complications and improving patient outcomes. In this study, we developed Ox-NE, a novel fluorescent probe designed for the specific detection and quantification of neutrophil elastase (NE), a key biomarker of inflammation. Unlike the traditional probes, Ox-NE utilizes a unique mechanism that minimizes background fluorescence and enhances photostability, offering rapid, non-invasive, and apparent diagnostic capabilities. Ox-NE had a low limit of detection (LOD) of 1.54μg/mL and exhibited high sensitivity and specificity with strong anti-interference properties. Through in vitro experiments, Ox-NE could accurately detect elevated NE levels in the serum of thyroiditis patients. Additionally, it could differentiate between normal thyroid cells, inflamed thyroid cells, and thyroid cancer cells. It also effectively facilitated the screening of sivelestat, a therapeutic agent for thyroiditis. Successful fluorescence imaging in mouse models further confirmed the potential of Ox-NE in advancing thyroid disease diagnostics.

An Investigation of Pharmacokinetic Interaction of Vericiguat with Apigenin based on a Newly Developed Ultra-performance Liquid Chromatography-tandem Mass Spectrometry Assay.

Vericiguat, as a new stimulator of soluble guanylate cyclase (s- GC), was recently approved as a first-in-class treatment for reducing risks in patients with ejection fraction less than 45 percent and heart failure (HF) in the USA. The main aim of the present experiment was to establish an acceptable, sensitive assay based on ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) for quantitatively analyzing the plasma concentration levels of vericiguat in rats, and to further evaluate the effect of apigenin on the metabolism of vericiguat in vivo. In sample processes, acetonitrile was finally chosen for quickly precipitating protein. The levels of vericiguat in plasma were analyzed by a Xevo TQ-S triple quadrupole tandem mass spectrometry (Milford, MA, USA) in a positive ion mode. The scope of the calibration standard for vericiguat ranged from 0.5 to 1000 ng/mL, where a great linearity was acceptable. The lower limit of quantification (also called LLOQ) of vericiguat presented the sensitivity of this assay was evaluated as low as 0.5 ng/mL. Additionally, selectivity, accuracy and precision, extraction recovery, matrix effect, and stability were all verified. Subsequently, this approach also supported to assess the plasmatic concentrations of vericiguat from an interaction survey on herb-- drug, in which oral administration of apigenin (20 mg/kg) obviously increased the plasmatic levels of vericiguat and altered the pharmacokinetics of vericiguat in rats. These results would help us to further understand the pharmacokinetic properties of vericiguat when co-administration with apigenin, and to avoid unexpected clinical risks in the future.

The Pharmacokinetic Interaction of Tirabrutinib with Voriconazole, Itraconazole, and Fluconazole in SD Rats by UPLC-MS/MS.

Tirabrutinib is an orally effective, approved, and highly selective second-generation Bruton's tyrosine kinase (BTK) inhibitor for the treatment of recurrent or refractory primary central nervous system lymphoma (PCNSL). This study aimed to develop an ultra-high performance liquid chromatography- tandem mass spectrometry (UPLC-MS/MS) method for the determination of tirabrutinib concentration in rat plasma, where zanubrutinib was used as an internal standard (IS). This method was also applied to study whether tirabrutinib would interact with voriconazole, itraconazole, and fluconazole in rats, providing a reference value for clinical medication guidance. In the current study, the organic solvent protein precipitation method was used to treat plasma samples, which is simple and reproducible. Tirabrutinib (m/z 455.32 → 320.21) and zanubrutinib (m/z 472.13 → 455.04) were separated on a Waters Acquity BEH C18 column (2.1 × 50 mm, 1.7 μm) and detected by multiple reaction monitoring (MRM) in positive ionization mode. The method showed good linearity in the range of 5-3000 ng/mL for tirabrutinib with the lower limit of quantification (LLOQ) of 5 ng/mL. The recovery and matrix effects were 85.7-91.0% and 102.0-113.3%, respectively. The accuracy, precision, stability, and carry-over effect were also acceptable. The method could also be used for determining the pharmacokinetic interaction of tirabrutinib in rats. The results showed AUC0→∞ of tirabrutinib to be increased by 139.3% and 83.9% in the presence of voriconazole and fluconazole, respectively, while itraconazole had little effect. It is necessary to monitor the concentration of tirabrutinib in patients when it is combined with voriconazole and fluconazole to achieve a better therapeutic effect and reduce the risk of adverse reaction. Further research should be conducted in the future.

Rapid optical flare in the extreme teraelectronvolt blazar 1ES 0229+200 on intraday timescales with the Transiting Exoplanet Survey Satellite

Context. The extreme teraelectronvolt (TeV) blazar 1ES 0229+200 is a high-frequency-peaked BL Lacertae object. It has not shown intraday variability in extensive optical and X-ray observations, nor has it shown any significant variability on any measurable timescale in the 1–100 GeV energy range over a 14-year span; however, variations in the source flux around its average are present in the energy range above 200 GeV. Aims. We aim to search for intraday optical variability in 1ES 0229+200 as part of an ongoing project to search for variability and quasi-periodic oscillations in the high-cadence (2 min), nearly uniformly sampled optical light curves of blazars provided by the Transiting Exoplanet Survey Satellite (TESS). Methods. 1ES 0229+200 was monitored by TESS in its Sectors 42, 43, and 44. We analysed the data of all these three sectors both with the TESS-provided lightkurve software and the eleanor reduction pipeline. We detected a strong, essentially symmetric flare that lasted about 6 h in Sector 42. We fitted the flare’s rising and declining phases to exponential functions. We also analysed the light curve of Sector 42 using the Lomb-Scargle periodogram (LSP) and continuous auto-regressive moving average (CARMA) methods. Results. The optical light curve of Sector 42 of the TESS observations displayed in the present work provides the first evidence of a strong, rapid, short-lived optical flare on the intraday timescale in the TeV blazar 1ES 0229+200. The variability timescale of the flare provides the upper limit for the size of the emission region to be within (3.3 ± 0.2–8.3 ± 0.5)×1015 cm. Away from the flare, the slope of the periodogram’s power spectrum is fairly typical of many blazars (α < 2), but the nominal slopes for the flaring regions are very steep (α ∼ 4.3), which may indicate that the electron distribution undergoes a sudden change. We discuss possible emission mechanisms that could explain this substantial and rapid flare.

Efficacy Analysis of PTCD + TACE vs PTCD + Apatinib in the Treatment of HCC with Obstructive Jaundice: A Retrospective Study.

The aim was to evaluate the safety and effectiveness of PTCD combined with TACE in the treatment of hepatocellular carcinoma with obstructive jaundice and to compare the efficacy of TACE in patients with different levels of bilirubin after PTCD. The clinical data of 141 patients with HCC complicated with obstructive jaundice were analyzed retrospectively. The patients underwent PTCD first. When the total bilirubin decreased, the patients received TACE or Apatinib treatment. They were divided into two groups: (1) PTCD+TACE group, N=68; (2) PTCD+Apatinib group, N=73. The PTCD+TACE group had higher ORR and DCR than the PTCD+Apatinib group (57.4% vs 12.3%, p < 0.001;80.9% vs 60.3%, p = 0.010). The mPFS of the PTCD+TACE group was longer than that of the PTCD+Apatinib group (7.1 months vs 3.8 months, p < 0.001). The mOS of the PTCD+TACE group was longer than that of the PTCD+Apatinib group(11.5 months vs 7.7 months, p < 0.001). In the subgroup analysis of the PTCD+TACE group, the results showed that the survival benefits of the groups with total bilirubin <2 times and 2-3 times were greater. In patients with HCC and obstructive jaundice, superselective TACE(lipiodol+epirubicin emulsion) significantly prolonged OS and PFS compared with Apatinib after using PTCD to reduce total bilirubin to <100umol/L. Patients whose total bilirubin dropped to ≤3 times of the upper limit of normal value after PTCD had longer OS and PFS than patients >3 times.

High-energy Neutrinos from Late-time Jets of Gamma-Ray Bursts Seeded with Cocoon Photons

In gamma-ray bursts (GRBs), ∼100–1000 s after the prompt emission, afterglow observations have consistently shown X-ray excesses detected in the form of flares (in long GRBs) or extended emission (in short GRBs). These observations are interpreted as emissions from jets launched by late central engine activity. However, the characteristics of these late-time jets, particularly the dissipation radius (r diss), Lorentz factor (Γ), and cosmic-ray loading factor (ξ p ), remain unknown despite their importance. Here, in order to understand the properties of the late-time jets with future multimessenger observations, we estimate the detectability of neutrinos associated with late-time emissions for a wide range of r diss and Γ, assuming ξ p = 10. We take into account external seed photons from the cocoon around the jets, which can enhance the neutrino production through photohadronic interaction in the jet dissipation region. Our results are still consistent with the upper limit obtained by IceCube. Our calculations indicate a promising prospect for neutrino detection with IceCube-Gen2 through the stacking of ∼1000–2000 events, for a wide range of r diss and Γ. We found that setting an optimal energy threshold of 10 TeV can significantly reduce noise without negatively affecting neutrino detection. Furthermore, even in the case of nondetection, we show that meaningful constraints on the characteristics of the late-time jets can be obtained.

Liver Injury in People With HIV on Antituberculosis and/or Antiretroviral Therapy-Assessing Causality Using the Updated Roussel Uclaf Causality Assessment Method.

We compared performance of the Roussel Uclaf Causality Assessment Method (RUCAM) with multidisciplinary expert panel review in identifying a drug-induced liver injury (DILI) due to antituberculosis therapy (ATT) and/or antiretroviral therapy (ART). Cases were drawn from a prospective registry of hospitalised adults with suspected DILI due to ATT and/or ART in Cape Town, South Africa. Participants had to fulfil American Thoracic Society criteria for ATT interruption (alanine transaminase [ALT] ≥5 times upper limit of normal [ULN]/ALT ≥3 times [ULN] and symptomatic). Causality assessment by expert panel review served as reference standard. The panel ranked potentially implicated drugs as certain, probable, possible or unlikely causes guided by World Health Organization Uppsala Monitoring Centre criteria. The RUCAM was performed for each potentially implicated drug. We calculated sensitivity and specificity of the RUCAM in identifying a probable/certain drug cause for liver injury. We included 48 participants. All were people with HIV (PWH). Twenty-seven were on concomitant ART and ATT, with a median of six potentially hepatotoxic drugs per case. Sensitivity and specificity of the RUCAM in identifying a probable/certain drug cause of liver injury compared with expert panel review was 7% and 100% respectively. Implicated drugs (times ranked probable/certain by panel) were isoniazid (18/0), pyrazinamide (17/0), rifampicin (15/1), efavirenz (6/4) and lopinavir/ritonavir (1/0). PWH with liver injury received multiple potentially implicated drugs, which may increase liver injury risk and complicate causality assessment. Compared with expert panel review, the RUCAM had low sensitivity in detecting probable or certain drug causes of liver injury.

Tartaric acid anion intercalated layered double hydroxides constructed a CO2-favorable transport channel in PIM-1 mixed matrix membranes for CO2/N2 separation

As a unique polymer of intrinsic microporosity, PIM-1 has great potential in mixed matrix membranes (MMMs) for gas separation with ultra-high permeability. However, the separation performance, e.g. CO2/N2 separation, is still limited by its poor selectivity. In this work, PIM-1-based MMMs containing tartaric acid anion intercalated layered double hydroxides (TA-LDH) nanofillers are successfully prepared. The uniformly dispersed TA-LDH in the PIM-1 matrix contributes to optimizing the stacking of polymer chains for accessible pores, which is conducive to CO2 diffusion. In addition, the assistant experiment and theoretical calculation point out that the -COO-, –OH between the TA-LDH layers had an affinity for CO2, creating a two-dimensional fast transport channel between the enlarged interlayer space. Compared with the pristine PIM-1 membrane, the CO2 permeability and CO2/N2 selectivity of 0.7 % TA-LDH/PIM-1 membrane is increased by 43.19 % and 105.48 %. The excellent gas separation performance with CO2 permeability of 8343.18 Barrer and CO2/N2 selectivity of 39.02 exceeds the 2019 Robson upper limit. This paves a new way to improve the gas separation performance of PIM-1-based MMMs and suggests high perspectives for real applications.

Dexamethasone is non-inferior to antihistamine plus dexamethasone premedication in preventing ramucirumab plus nab-paclitaxel infusion-related reactions in gastric cancer: a multicenter retrospective study

PurposeRamucirumab (RAM) is recommended as premedication with H1-receptor antagonists (H1RA) to prevent infusion-related reactions (IRRs). However, RAM is a human antibody with a low incidence of IRRs. We evaluated the noninferiority of non-H1RA (dexamethasone [DEX] alone) premedication to H1RA (plus DEX) premedication in terms of IRRs in patients with gastric cancer receiving RAM plus nanoparticle albumin-bound paclitaxel (nab-PTX).MethodsThis was a noninferiority, multicenter, retrospective trial conducted in three Japanese centers to assess the incidence of IRRs in patients receiving RAM plus nab-PTX for gastric cancer between 2018 and 2023. Patients with gastric cancer receiving RAM plus nab-PTX were divided into groups with and without H1RA premedication. The incidence of IRRs was compared between the two groups.ResultsNinety patients were evaluated, with non-H1RA and H1RA premedications in 43 and 47 cases, respectively. After the first dose of RAM, IRRs were not observed in either group. IRRs during the overall doses were 0% for non-H1RA premedication and 2.1% for H1RA premedication (90% confidence interval (CI): –5.6%–1.3% for each comparison). The upper limit of the 90% CI (1.3%) did not exceed the noninferiority margin (Δ) of + 10% and therefore met the noninferiority criteria.ConclusionRAM plus nab-PTX for gastric cancer with DEX premedication may be possible without H1RA premedication.

Structured Jet Model for Multiwavelength Observations of the Jetted Tidal Disruption Event AT 2022cmc

AT 2022cmc is a recently documented tidal disruption event that exhibits a luminous jet, accompanied by fast-declining X-ray and long-lasting radio and millimeter emission. Motivated by the distinct spectral and temporal signatures between the X-ray and radio observations, we propose a multizone model involving relativistic jets with different Lorentz factors. We systematically study the evolution of faster and slower jets in an external density profile, considering the continuous energy injection rate associated with time-dependent accretion rates before and after the mass fallback time. We investigate time-dependent multiwavelength emission from both the forward shock (FS) and reverse shock (RS) regions of the fast and slow jets, in a self-consistent manner. Our analysis demonstrates that the energy injection rate can significantly impact the jet evolution and subsequently influence the lightcurves. We find that the X-ray spectra and lightcurves could be described by electron synchrotron emission from the RS of the faster jet, in which the late-time X-ray upper limits, extending to 400 days after the disruption, could be interpreted as a jet break. Meanwhile, the radio observations can be interpreted as a result of synchrotron emission from the FS region of the slower jet. We also discuss prospects for testing the model with current and future observations.

Energy storage configuration method for distribution networks based on moment difference analysis

The integration of a high proportion of distributed PV into distribution networks can cause power backfeeding and voltage limit violations. This paper introduces moment difference analysis theory for distribution networks, reframing PV consumption as the balancing moment difference equations. When maximum node voltage approaches the upper limit, the moment difference between PV and load stabilizes to an approximately constant, termed the standard moment difference. The standard moment difference represents the limit of the network's capacity to consume distributed PV. Essentially, the PV moment is the target for integration, while the load moment serves as the resource to consume the PV moment. Based on this theory, a method for energy storage configuration is proposed. Simplifying a complex multi-branch distribution network into single-branch lines and solving linear equations determines the optimal storage configuration. This method was tested on the Jibei Power Grid and the IEEE 33 and 69 bus systems, increasing computational efficiency by 1611.47–4973.82 times compared to the PSO algorithm, while maintaining an error margin of less than 2.6 %. Furthermore, the discharging strategy reduces the ESS capacity to between 12.39 % and 31.69 % of the original estimate, thereby enhancing both the economic and practical appeal of the approach.

Joint ALMA/X-ray monitoring of the radio-quiet type 1 active galactic nucleus IC 4329A

The origin of a compact millimeter (mm, 100–250 GHz) emission in radio-quiet active galactic nuclei (RQ AGN) remains debated. Recent studies propose a connection with self-absorbed synchrotron emission from the accretion disk X-ray corona. We present the first joint ALMA (∼100 GHz) and X-ray (NICER/XMM-Newton/Swift; 2–10 keV) observations of the unobscured RQ AGN, IC 4329A (z = 0.016). The time-averaged mm-to-X-ray flux ratio aligns with recently established trends for larger samples, but with a tighter scatter (∼0.1 dex) compared to previous studies. However, there is no significant correlation on timescales of less than 20 days. The compact mm emission exhibits a spectral index of −0.23 ± 0.18, remains unresolved with a 13 pc upper limit, and shows no jet signatures. Notably, the mm flux density varies significantly (by factor of 3) within four days, exceeding the contemporaneous X-ray variability and showing the largest mm variations ever detected in RQ AGN over daily timescales. The high amplitude variability rules out scenarios of heated dust and thermal free–free emission, pointing toward a synchrotron origin for the mm radiation in a source of ∼1 light day (∼120 gravitational radii) size. While the exact source is not yet certain, an X-ray corona scenario emerges as the most plausible compared to a scaled-down jet or outflow-driven shocks.

Stress-dilatancy behavior of marine coral sand incorporating non-plastic fines

The existed understanding of stress-dilatancy behavior is predominantly based on experiments conducted with clean quartz sand, with limited research focusing on coral sand. Particularly, impacts of fines and density state on stress-dilatancy response of marine coral sand is of significant concern. This work presents a systematic investigation into these issues through meticulously controlled geotechnical tests, coupled with corresponding discussion and interpretation. Results show that at a high stress level, both pure coral sand and its mixtures consistently undergo shear contraction regardless of fines proportion and density state. However, mixtures with minimal fines experience shear contraction initially, followed by dilatancy under a medium-low stress level. Friction angle at peak state (φps) and critical state (φcs), excess friction angle (φex), and maximum dilatancy angle (ψmax) decrease powerfully as increasing fines content. Besides, the lower and upper limits of variation for φps, φcs, φex concerning ψmax were presented. Correlation between φex and ψmax highlights that Bolton's stress-dilatancy equation, developed for pure sand, remains applicable provided that fines content remains below the threshold value. Additionally, gray correlation result suggests that fines post the dominant influence on above behaviors, followed by density state and stress level. Finally, potential mechanism behinds the influences of fines and density state was explored from the view of particle column buckling.

Early Planet Formation in Embedded Disks. XI. A High-resolution View Toward the BHR 71 Class 0 Protostellar Wide Binary

We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of the binary Class 0 protostellar system BHR 71 IRS1 and IRS2 as part of the Early Planet Formation in Embedded Disks (eDisk) ALMA Large Program. We describe the 12CO (J = 2–1), 13CO (J = 2–1), C18O (J = 2–1), H2CO (J = 32,1–22,0), and SiO (J = 5–4) molecular lines along with the 1.3 mm continuum at high spatial resolution (∼0.″08 or ∼5 au). Dust continuum emission is detected toward BHR 71 IRS1 and IRS2, with a central compact component and extended continuum emission. The compact components are smooth and show no sign of substructures such as spirals, rings, or gaps. However, there is a brightness asymmetry along the minor axis of the presumed disk in IRS1, possibly indicative of an inclined geometrically and optically thick disk-like component. Using a position–velocity diagram analysis of the C18O line, clear Keplerian motions were not detected toward either source. If Keplerian rotationally supported disks are present, they are likely deeply embedded in their envelope. However, we can set upper limits of the central protostellar mass of 0.46 M ⊙ and 0.26 M ⊙ for BHR 71 IRS1 and BHR 71 IRS2, respectively. Outflows traced by 12CO and SiO are detected in both sources. The outflows can be divided into two components, a wide-angle outflow and a jet. In IRS1, the jet exhibits a double helical structure, reflecting the removal of angular momentum from the system. In IRS2, the jet is very collimated and shows a chain of knots, suggesting episodic accretion events.

Search for dark matter annihilation to gamma-rays from SPT-SZ selected galaxy clusters

We search for dark matter annihilation from galaxy clusters in the energy range from 1–300 GeV using nearly 16 years of Fermi-LAT data. For this purpose, we use 350 galaxy clusters selected fromthe 2500 deg2 SPT-SZ survey. We model the dark matter distribution using the NFW profile for the main halo along with the Einasto profile for the substructure. The largest signal is seen for the cluster SPT-CL J2021-5257 with a significance of around 3σ. The best-fit dark matter mass and annihilation cross-section for this cluster are equal to (60.0 ± 11.8) GeV and ⟨σv⟩ = (6.0 ± 0.6) × 10-25 cm3 s-1 for the b̅ b annihilation channel. However, this central estimate is in conflict with the limits on annihilation cross-section from dwarf spheroidal galaxies, and hence cannot be attributed to dark matter annihilation. Three other clusters show significance between 2-2.5σ, whereas all the remaining clusters show null results. The most stringent 95% c.l. upper limit for the WIMP annihilation cross-section among all the clusters is from SPT-CL J0455-4159, viz. ⟨σv⟩ = 6.44 × 10-26 cm3 s-1 for m χ = 10 GeV and b b̅ annihilation channel.

Searching for the Highest-z Dual Active Galactic Nuclei in the Deepest Chandra Surveys

We present an analysis searching for dual active galactic nuclei (AGN) among 62 high-redshift (2.5 < z < 3.5) X-ray sources selected from the X-UDS, AEGIS-XD, CDF-S, and COSMOS-Legacy Chandra surveys. We aim to quantify the frequency of dual AGN in the high-redshift Universe, which holds implications for black hole merger timescales and low-frequency gravitational wave detection rates. We analyze each X-ray source using BAYMAX, an analysis tool that calculates the Bayes factor for whether a given archival Chandra AGN is more likely a single or dual point source. We find no strong evidence for dual AGN in any individual source in our sample. We increase our sensitivity to search for dual AGN across the sample by comparing our measured distribution of Bayes factors to that expected from a sample composed entirely of single point sources and find no evidence for dual AGN in the sample distribution. Although our analysis utilizes one of the largest Chandra catalogs of high-z X-ray point sources available to study, the findings remain limited by the modest number of sources observed at the highest spatial resolution with Chandra and the typical count rates of the detected sources. Our nondetection allows us to place an upper limit on the X-ray dual AGN fraction at 2.5 < z < 3.5 of 4.8% at the 95% confidence level. Expanding substantially on these results at X-ray wavelengths will require future surveys spanning larger sky areas and extending to fainter fluxes than has been possible with Chandra. We illustrate the potential of the AXIS mission concept in this regard.

A Luminous X-Ray Active Galactic Nucleus in the Dwarf–Dwarf Galaxy Merger RGG 66

We present the discovery of a luminous X-ray active galactic nucleus (AGN) in the dwarf galaxy merger RGG 66. The black hole is predicted to have a mass of M BH ∼ 105.4 M ⊙ and to be radiating close to its Eddington limit (L bol/L Edd ∼ 0.75). The AGN in RGG 66 is notable both for its presence in a late-stage dwarf–dwarf merger and for its luminosity of L 2–10 keV = 1042.2 erg s−1, which is among the most powerful AGNs known in nearby dwarf galaxies. The X-ray spectrum has a best-fit photon index of Γ = 2.4 and an intrinsic absorption of N H ∼ 1021 cm−2. These results come from a follow-up Chandra X-ray Observatory study of four irregular/disturbed dwarf galaxies with evidence for hosting AGNs based on optical spectroscopy. The remaining three dwarf galaxies do not have detectable X-ray sources with upper limits of L 2–10 keV ≲ 1040 erg s−1. Taken at face value, our results on RGG 66 suggest that mergers may trigger the most luminous of AGNs in the dwarf galaxy regime, just as they are suspected to do in more massive galaxy mergers.