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The Deep Operator Network (DeepONet) structure has shown great potential in approximating complex solution operators with low generalization errors. Recently, a sequential DeepONet (S-DeepONet) was proposed to use sequential learning models in the branch of DeepONet to predict final solutions given time-dependent inputs. In the current work, the S-DeepONet architecture is extended by modifying the information combination mechanism between the branch and trunk networks to simultaneously predict vector solutions with multiple components at multiple time steps of the evolution history, which is the first in the literature using DeepONets. Two example problems, one on transient fluid flow and the other on path-dependent plastic loading, were shown to demonstrate the capabilities of the model to handle different physics problems. The use of a trained S-DeepONet model in inverse parameter identification via the genetic algorithm is shown to demonstrate the application of the model. In almost all cases, the trained model achieved an $R^2$ value of above 0.99 and a relative $L_2$ error of less than 10\% with only 3200 training data points, indicating superior accuracy. The vector S-DeepONet model, having only 0.4\% more parameters than a scalar model, can predict two output components simultaneously at an accuracy similar to the two independently trained scalar models with a 20.8\% faster training time. The S-DeepONet inference is at least three orders of magnitude faster than direct numerical simulations, and inverse parameter identifications using the trained model is highly efficient and accurate.

There is growing evidence for high-frequency gravitational waves (HFGWs) ranging from MHz to GHz. Several HFGW detectors have been operating for over a decade, and two GHz events have been reported recently. However, a confirmed detection might take a decade. This essay argues that unexplained observed astrophysical phenomena, like Fast Radio Bursts (FRBs), might provide indirect evidence for HFGWs. In particular, using the Gertsenshtein-Zel$'$dovich effect, we show that our model can explain three key features of FRBs: generate peak-flux up to $1000~{\rm Jy}$, naturally explain the pulse width and the coherent nature of FRBs. In short, our model offers a novel perspective on the indirection detection of HFGWs beyond current detection capabilities. Thus, transient events like FRBs are a rich source for multi-messenger astronomy., Comment: Received Honourable mention in Gravity Research Foundation essay competition-2023. Matches the published version. arXiv admin note: text overlap with arXiv:2202.00032

We present an extensive recent multi-band optical photometric observations of the blazar S5 0716+714 carried out over 53 nights with two telescopes in India, two in Bulgaria, one in Serbia, and one in Egypt during 2019 November -- 2022 December. We collected 1401, 689, 14726, and 165 photometric image frames in B, V, R, and I bands, respectively. We montiored the blazar quasi-simultaneously during 3 nights in B, V, R, and I bands; 4 nights in B, V, and R; 2 nights in V, R, and I; 5 nights in B and R; and 2 nights in V and R bands. We also took 37 nights of data only in R band. Single band data are used to study intraday flux variability and two or more bands quasi-simultaneous observations allow us to search for colour variation in the source. We employ the power-enhanced F-test and the nested ANOVA test to search for genuine flux and color variations in the light curves of the blazar on intraday timescales. Out of 12, 11, 53, and 5 nights observations, intraday variations with amplitudes between ~3% and ~20% are detected in 9, 8, 31 and 3 nights in B, V, R, and I bands, respectively, corresponding to duty cycles of 75%, 73%, 58% and 60%. These duty cycles are lower than those typically measured at earlier times. On these timescales color variations with both bluer-when-brighter and redder-when-brighter are seen, though nights with no measurable colour variation are also present. We briefly discuss possible explanations for this observed intraday variability., Comment: 19 pages, 5 figures, 4 tables, Accepted for Publication in MNRAS

We study the optical flux and polarization variability of the binary black hole blazar OJ 287 using quasi-simultaneous observations from 2015 to 2023 carried out using telescopes in the USA, Japan, Russia, Crimea, and Bulgaria. This is one of the most extensive quasi-simultaneous optical flux and polarization variability studies of OJ 287. OJ 287 showed large amplitude, ~3.0 mag flux variability, large changes of ~37% in degree of polarization, and a large swing of ~215 degrees in the angle of the electric vector of polarization. During the period of observation, several flares in flux were detected. Those flares are correlated with a rapid increase in the degree of polarization and swings in electric vector of polarization angle. A peculiar behavior of anticorrelation between flux and polarization degree, accompanied by a nearly constant polarization angle, was detected from JD 2,458,156 to JD 2,458,292. We briefly discuss some explanations for the flux and polarization variations observed in OJ 287., Comment: 14 pages, 4 figures, 2 tables, Published in Astrophysical Journal Letters, 2023 November 1

Transition blazars exhibit a shift from one subclass to the next during different flux states. It is therefore crucial to study them to understand the underlying physics of blazars. We probe the origin of the multi-wavelength emission from the transition blazar B2 1308+326 using 14-year-long gamma-ray light curve from Fermi and the quasi-simultaneous data from Swift. We used the Bayesian block algorithm to identify epochs of flaring and quiescent flux states and modelled the broadband SEDs for these epochs. We employed the one-zone leptonic model in which the synchrotron emission causes the low-energy part of the SED and the high-energy part is produced by the IC emission of external seed photons. We also investigated its multi-band variability properties and gamma-ray flux distribution, and the correlation between optical and gamma-ray emissions. We observed a historically bright flare from B2 1308+326 across the optical to gamma-ray bands in June and July 2022. The highest daily averaged gamma-ray flux was (14.24$\pm$2.36) $\times$ 10$^{-7}$ ph cm$^{-2}$ s$^{-1}$ and was detected on 1 July 2022. The gamma-ray flux distribution was found to be log-normal. The optical and gamma-ray emissions are well correlated with zero time lag. The synchrotron peak frequency changes from $\sim 8 \times$ 10$^{12}$ Hz (in the quiescent state) to $\sim 6 \times$ 10$^{14}$ Hz (in the flaring state), together with a decrease in the Compton dominance providing a hint that the source transitions from a LSP to an ISP. The SEDs for these two states are well-fitted by one-zone leptonic models. The parameters in the model fits are essentially consistent between both SEDs, except for the Doppler-beaming factor, which changes from $\sim$15.6 to $\sim$27 during the transition. An increase in the Doppler factor might cause both the flare and the transition of B2 1308+326 from an LSP to an ISP blazar., Comment: 10 pages, 7 figures, 2 tables, accepted for publication in the Astronomy & Astrophysics journal

We present a comprehensive spectro-polarimetric study of persistent Black hole X-ray binary 4U $1957\!+\!115$ with {\it IXPE} and {\it NICER} observations. The source is observed in disk dominated thermal state with disk temperature, kT$_{in}\approx1.4$ keV. The emission during thermal state from the source is found to be moderately polarized and \textit{IXPE} measures a degree of polarization (PD) $= 1.95\pm0.37\%$ ($>4.79\sigma$) along with a polarization angle (PA) $= -42.78^{\circ}\pm5.41^{\circ}$ in the energy range of $2-8$ keV. PD is found to be an increasing function of energy, whereas PA indicates switching within the energy range which could be due to high inclination and the returning radiation within the system. Simultaneous energy spectra ($0.6-10$ keV) from {\it NICER} are modelled to study the spectral properties. Furthermore, the spin parameter of the black hole is estimated with spectro-polarimetric data as a$_{\ast}=0.988\pm0.001\,(1\sigma)$, which is corroborated by {\it NICER} observations. Finally, we discuss the implications of our findings., Comment: 5 pages, 4 figures, 3 tables, Submitted to MNRAS Letters on 30 September 2023. arXiv admin note: text overlap with arXiv:2303.05462

The compound Ba3HoRu2O9 magnetically orders at 50 K (TN1) followed by another complex magnetic ordering at 10.2 K (TN2). The 2nd magnetic phase transition was characterized by the co-existence of two competing magnetic ground states associated with two different magnetic wave vectors (K1=1/2 0 0 and K2=1/4 1/4 0). Here, we have discussed the origin of spin-driven ferroelectricity, which is not known yet. We demonstrate through time-of-flight Neutron diffraction and theoretical calculation that the non-collinear structure involving two different magnetic ions, Ru(4d) and Ho(4f), break the spatial inversion symmetry via inverse Dzyaloshinskii-Moriya (D-M) interaction through strong 4d-4f magnetic correlation, which shifts the oxygen atoms and results in non-zero polarization. Such an observation of inverse D-M interaction from two different magnetic ions which caused ferroelectricity is rarely observed. We have systematically studied the spin and dipolar dynamics, which exhibit intriguing behavior with shorter coherence lengths of 2nd magnetic phase associated with the k2-wave vector. The results manifest the development of finite-size magnetoelectric domains instead of true long-range ordering which justifies the experimentally obtained low value of ferroelectric polarization. The synchrotron XRD analysis predicts a non-centrosymmetric space group P-62c. Furthermore, we have investigated the effect of external pressure on this complex magnetism. The result reveals an enhancement of ordering temperature by the application of external pressure (1.6 K/GPa). The external pressure might favor stabilizing the magnetic ground state associated with 2nd magnetic phase. Our study shows an unconventional mechanism of spin-driven ferroelectricity., Comment: Accepted in PRB

Localizing a moving sound source in the real world involves determining its direction-of-arrival (DOA) and distance relative to a microphone. Advancements in DOA estimation have been facilitated by data-driven methods optimized with large open-source datasets with microphone array recordings in diverse environments. In contrast, estimating a sound source's distance remains understudied. Existing approaches assume recordings by non-coincident microphones to use methods that are susceptible to differences in room reverberation. We present a CRNN able to estimate the distance of moving sound sources across multiple datasets featuring diverse rooms, outperforming a recently-published approach. We also characterize our model's performance as a function of sound source distance and different training losses. This analysis reveals optimal training using a loss that weighs model errors as an inverse function of the sound source true distance. Our study is the first to demonstrate that sound source distance estimation can be performed across diverse acoustic conditions using deep learning., Comment: Accepted in WASPAA 2023

We report a comprehensive spectro-polarimetric study of the black hole binary LMC X$-3$ using simultaneous {\it IXPE}, {\it NICER} and {\it NuSTAR} observations in 0.5$-$20 keV energy band. The broad-band energy spectrum (0.5$-$20 keV) with {\it NICER} and {\it NuSTAR} is well described by the disc emission of temperature $\sim$1.1 keV and a weak Comptonizing tail beyond $\sim$10 keV. This evidently suggests a disc-dominated spectral state of the source with disc contribution of $\sim$96\%. The lack of variability ($rms$$\sim$0.5\%) in the power spectrum further corroborates the high/soft nature of the source. A significant polarization degree (PD) of 3.04$\pm$0.40\% (>7$\sigma$) at a polarization angle (PA) of $-$44.24$^{\circ}$$\pm$3.77$^{\circ}$ (>7$\sigma$) is found in 2$-$8 keV energy range of {\it IXPE}. In addition, PD is seen to increase with energy up to $\sim$4.35$\pm$0.98\% (>3$\sigma$) in 4$-$8 keV band. Further, we attempt to constrain the source spin ($a_{*}$) using broad-band spectral modelling that indicates a weakly rotating `hole' in LMC X$-3$ with $a_{*}=0.273_{-0.012}^{+0.011}-0.295_{-0.021}^{+0.008}$ ($90\%$ confidence). Based on the spectro-polarimetric results, we infer that the polarization in LMC X$-3$ is resulted possibly due to the combined effects of the direct and/or reflected emissions from a partially ionized disc atmosphere. Finally, we discuss the relevance of our findings., Comment: 6 pages, 4 figures, 3 tables, accepted for publication in MNRAS Letters

Ce$_{3}$Bi$_{4}$Au$_{3}$ crystallizes in the same non-centrosymmetric cubic structure as the prototypical Kondo insulator Ce$_{3}$Bi$_{4}$Pt$_{3}$. Here we report the physical properties of Ce$_{3}$Bi$_{4}$Au$_{3}$ single crystals using magnetization, thermodynamic, and electrical-transport measurements. Magnetic-susceptibility and heat-capacity data reveal antiferromagnetic (AFM) order below $T_N=3.2$ K. The magnetic entropy $S_{\rm mag}$ reaches $R$ln2 slightly above $T_N$, which suggests localized $4f$-moments in a doublet ground state. Multiple field-induced magnetic transitions are observed at temperatures below $T_N$, which indicate a complex spin structure with competing interactions. Ce$_{3}$Bi$_{4}$Au$_{3}$ shows semimetallic behavior in electrical resistivity measurements in contrast to the majority of reported Cerium-based 343 compounds. Electrical-resistivity measurements under hydrostatic pressure reveal a slight enhancement of $T_N$ under pressures up to 2.3 GPa, which supports a scenario wherein Ce$_{3}$Bi$_{4}$Au$_{3}$ belongs to the far left of the Doniach phase diagram dominated by Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions. Using realistic many-body simulations, we confirm the semi-metallic electronic structure of Ce$_{3}$Bi$_{4}$Au$_{3}$ and quantitatively reproduce its local moment behavior in the paramagnetic state., Comment: 10 pages, 10 figures

We present a novel approach to identify ransomware campaigns derived from attack timelines representations within victim networks. Malicious activity profiles developed from multiple alert sources support the construction of alert graphs. This approach enables an effective and scalable representation of the attack timelines where individual nodes represent malicious activity detections with connections describing the potential attack paths. This work demonstrates adaptability to different attack patterns through implementing a novel method for parsing and classifying alert graphs while maintaining efficacy despite potentially low-dimension node features., Comment: Preprint. Under Review

The microscopic properties of superconducting cubic skutterudite-like material Y$_3$Ru$_4$Ge$_{13}$ are investigated using muon spin relaxation and rotation ($\mu$SR) measurements. Zero-field $\mu$SR measurements reveal the presence of a spontaneous internal field with a magnitude of $\approx$ 0.18~mT below the superconducting transition temperature, indicating broken time-reversal symmetry in the ground state. In line with previous experiments, transverse-field $\mu$SR measurements are consistent with a fully developed superconductivity gap in Y$_3$Ru$_4$Ge$_{13}$. Our observations point towards the relevance of electronic correlations beyond electron-phonon coupling as origin and indicate that spin-orbit coupling is likely not the key driving force behind the spontaneous breaking of time-reversal symmetry in this system., Comment: 7 pages, 3 figures