arXiv subjects

Ankita Ghosh

Publications and source records attributed to Ankita Ghosh.

14 recordsLinked to original sources

arXiv2026

The GMRT High-Resolution Southern Sky Survey for pulsars and transients -- VIII: Orbital Variability and the Evolution of a 1-Day He-WD Millisecond Pulsar J2101-4802

We present timing and orbital phase-resolved polarimetry of the millisecond pulsar (MSP) J2101$-$4802, having a spin period of 9.48~ms and dispersion measure (DM) $25.05\ \mathrm{pc\ cm^{-3}}$ discovered with the Giant Meter Radio Telescope (GMRT). From the phase-connected timing of this MSP spanning 3.7 years, we identify that PSR J2101-4802 is in a $\sim$1-day binary orbit with a likely helium-white-dwarf (He-WD) companion having a median companion mass of $\simeq0.15\, M_\odot$, consistent with canonical recycling in the Galactic field. The timing solution further reveals an unusually large orbital period derivative, $\dot{P}_b$ ($\sim10^{-11}\,{\rm s\,s}^{-1}$), compared to typical Galactic-field MSP--HeWD binaries, which cannot be explained by the contributions from kinematic effects (Shklovskii and Galactic acceleration) or general-relativistic damping. Using wideband, full-Stokes observations, we also trace the linear and circular polarization variation across the orbital phase and fit a rotating-vector model (RVM) to its position-angle swing across the pulse phase, yielding constraints on the emission geometry (magnetic inclination and impact angle) of this system. The combination of a $\sim$1-day orbit, $\sim0.15\,M_\odot$ companion, modest spin-down power, unusually large $\dot{P}_b$, and phase-locked magnetized intrabinary plasma signatures suggests that PSR~J2101$-$4802 represents a transitional system linking redback-like spiders to detached He--WD MSP binaries.

astro-ph.HE↗

arXiv2026

Egosurg: Arbitrary view synthesis for egocentric replay of operating room workflows from ambient cameras

Observing surgical practice has historically relied on fixed vantage points or recollections, leaving the egocentric perspectives that shape clinical decisions undocumented. Ambient fixed cameras capture the operating room (OR) at room scale but cannot recover what any individual team member actually saw. We present EgoSurg, a framework that reconstructs dynamic OR scenes from sparse wall-mounted stereo video and renders arbitrary, role-specific egocentric views without instrumenting personnel or interfering with clinical workflow. EgoSurg initializes a per-timestamp 3D Gaussian Splatting representation from scale-aware stereo depth and refines it with an image-conditioned diffusion model that corrects auxiliary rendered views, mitigating artifacts caused by limited camera coverage, crowding, and occlusion. We evaluated the framework on four real robotic pulmonology procedures and two simulated full-workflow sessions across two hospital sites. Near-field reconstruction fidelity was consistent (PSNR 26.8~dB, SSIM .895) across five workflow phases and both sites, and synthesized egocentric views reached a PSNR of 17.8~dB and an SSIM of .766 against paired hand-held point-of-view recordings. We further demonstrate three case studies for intended use: adjudicating a simulated sterile field violation, replaying a procedure from role-specific viewpoints, and testing a counterfactual change in personnel position. These results indicate that existing ambient camera infrastructure can be turned into a navigable 3D record of surgical work, supporting retrospective review of safety events, training, and workflow analysis from every angle.

cs.CV↗

arXiv2026

First monitoring campaign of a Main-sequence Radio Pulse emitter: the case of CU Vir

CU Vir, a magnetic hot star, is the first discovered Main-sequence Radio Pulse emitter (MRP) characterized by its ability to produce periodic radio pulses via electron cyclotron maser emission. Although significant advancements have been made in understanding MRPs, their temporal properties remain mostly unexplored. To overcome this limitation, we conducted a pilot study with the Australia Telescope Compact Array, in which we observed pulses from CU Vir at 36 epochs over $1-3$ GHz. In this frequency range, CU Vir produces two $\approx 100\%$ circularly polarized pulses, called `leading' and `trailing' pulses per rotation period. We find significant differences in the variability indices exhibited by the two pulses as a function of frequencies, with the leading pulse showing higher variability throughout our observing band. This result could be explained in the scenario of centrifugal breakout events in the magnetosphere of an oblique rotator causing correlated fluctuations across frequencies, along with intrinsic instabilities associated with coherent emission. In addition, we discover jittering in the arrival phases of pulses that must be considered in future monitoring campaigns. The pulses also exhibit a systematic shift to later arrival times during the course of our observing campaign, allowing us to refine the rotation period to $0.5206882$ days. Finally, we estimate that $\sim 30$ pulses will be needed to extract global pulse properties for the leading or trailing pulses. This relatively small number strongly motivates more extensive monitoring campaigns of MRPs, both to validate our results, and also to pinpoint the origin of the observed temporal variations.

astro-ph.SR↗

arXiv2026

TwinOR: Photorealistic Digital Twins of Dynamic Operating Rooms for Embodied AI Research

Developing embodied AI for intelligent surgical systems requires safe, controllable environments for continual learning and evaluation. However, safety regulations and operational constraints in operating rooms (ORs) limit agents from freely perceiving and interacting in realistic settings. Digital twins provide high-fidelity, risk-free environments for exploration and training. How we may create dynamic digital representations of ORs that capture relevant spatial, visual, and behavioral complexity remains an open challenge. We introduce TwinOR, a real-to-sim infrastructure for constructing photorealistic and dynamic digital twins of ORs. The system reconstructs static geometry and continuously models human and equipment motion. The static and dynamic components are fused into an immersive 3D environment that supports controllable simulation and facilitates future embodied exploration. The proposed framework reconstructs complete OR geometry with centimeter-level accuracy while preserving dynamic interaction across surgical workflows. In our experiments, TwinOR synthesizes stereo and monocular RGB streams as well as depth observations for geometry understanding and visual localization tasks. Models such as FoundationStereo and ORB-SLAM3 evaluated on TwinOR-synthesized data achieve performance within their reported accuracy ranges on real-world indoor datasets, demonstrating that TwinOR provides sensor-level realism sufficient for emulating real-world perception and localization challenge. By establishing a perception-grounded real-to-sim pipeline, TwinOR enables the automatic construction of dynamic, photorealistic digital twins of ORs. As a safe and scalable environment for experimentation, TwinOR opens new opportunities for translating embodied intelligence from simulation to real-world clinical environments.

cs.CV↗

arXiv2026

Concentration Inequalities for Suprema of Empirical Processes with Dependent Data via Generic Chaining with Applications to Statistical Learning

This paper develops a general concentration inequality for the suprema of empirical processes with dependent data. The concentration inequality is obtained by combining generic chaining with a coupling-based strategy. Our framework accommodates high-dimensional and heavy-tailed (sub-Weibull) data. We demonstrate the usefulness of our result by deriving non-asymptotic predictive performance guarantees for empirical risk minimization in regression problems with dependent data. In particular, we establish an oracle inequality for a broad class of nonlinear regression models and, as a special case, a single-layer neural network model. Our results show that empirical risk minimzaton with dependent data attains a prediction accuracy comparable to that in the i.i.d. setting for a wide range of nonlinear regression models.

econ.EM↗

arXiv2025

Deciphering Profile Stability in Millisecond Pulsars: Timescales, Frequency Evolution, and Implications on Emission Mechanisms

Pulse profile stability in millisecond pulsars (MSPs) is a key factor in achieving high-precision timing essential for detecting nanohertz gravitational waves with Pulsar Timing Arrays (PTAs). In this work, we present a systematic analysis of profile stabilization timescales in MSPs using a direct method based on pulse stacking, applied to long-term multi-epoch observations. Our study utilizes data from the upgraded GMRT (uGMRT) between 300--750 MHz for nine MSPs over 3--5 years and Parkes Ultra-Wideband low-frequency receiver observations (Parkes UWL; covering 704--4032 MHz) for three of them. We find that stable profiles typically require averaging over $10^{5}$--$10^{6}$ pulses. This is the first time such a quantitative approach has been applied to MSPs across a wide frequency range, providing an indirect but practical estimate of jitter noise, a dominant noise source in PTA datasets. We observe that stabilization timescales depend on signal-to-noise ratio, pulse morphology, and surface magnetic field strength, with a moderate correlation indicating a possible role of the magnetic field in emission stability. A complementary single-epoch analysis of nine bright MSPs with uGMRT Band-3 (300--500 MHz) reinforces these results and demonstrates the method's applicability to broader MSP populations. We show that a strong correlation exists between profile-stability slope and the jitter parameter, implying that for faint MSPs, profile-stability analysis can act as an effective proxy for intrinsic pulse-shape variability. Our work provides a novel and scalable framework to assess intrinsic profile variability, helping to guide integration time choices and reduce timing noise in PTA experiments.

astro-ph.HE↗

arXiv2025

Exploring Unusual High-frequency Eclipses in MSP J1908+2105

This paper presents a comprehensive study of the eclipse properties of the spider millisecond pulsar (MSP) J1908$+$2105, using wide-band observations from the uGMRT and Parkes UWL. For the first time, we observed that this pulsar exhibits extended eclipses up to 4 GHz, the highest frequency band of the UWL, making it one of only three MSPs known to have such high-frequency eclipses. This study reveals synchrotron absorption as the primary eclipse mechanism for J1908$+$2105. We present modeling of synchrotron optical depth with various possible combinations of the parameters to explain the observed eclipsing in this as well as other spider MSPs. Observed eclipses at unusually high frequencies for J1908$+$2105 significantly aided in constraining the magnetic field and electron column density in the eclipse medium while modeling the synchrotron optical depth. Combining our findings with data from other MSPs in the literature, for the first time we note that a higher cutoff frequency of eclipsing, particularly above 1 GHz, is consistently associated with a higher electron column density ($>$ 10$^{17}$ cm$^{-2}$) in the eclipse medium. Additionally, we present the first evidence of lensing effects near eclipse boundaries in this MSP, leading to significant magnification of radio emissions. The orbital phase resolved polarization analysis presented in this paper further indicates variation in rotation measure and consequently stronger magnetic fields in the eclipse region.

astro-ph.HE↗

arXiv2024

Unveiling Low-Frequency Eclipses in Spider MSPs using wideband GMRT Observations

Eclipses of radio emission have been reported for ~ 58 spider millisecond pulsars (MSP), of which only around 19% have been extensively studied. Such studies at low frequencies are crucial for probing the properties of the eclipse medium, as eclipses are more prominent at such frequencies. This study investigates eclipses in 10 MSPs in compact orbit using wide-bandwidth observations with the upgraded Giant Metrewave Radio Telescope. We report the first evidence of eclipsing for PSR J2234+0944 and J2214+3000 in one epoch, while no evidence of eclipsing was observed in the subsequent two epochs, indicating temporal evolution of the eclipse cutoff frequency in these systems. Constraints on the eclipse cutoff frequency were obtained for PSR J1555-2908, J1810+1744, and J2051-0827. Moreover, for the first time, we detected an eclipse at a non-standard orbital phase (~ 0.5) for PSR J1810+1744, with a duration longer than the eclipse observed at superior conjunction. No eclipses were detected for PSR J0751+1807, J1738+0333, and J1807-2459A at 300-500 MHz and 550-750 MHz, for which we discuss the possible reasons. We calculated the mass loss rates of the companions for PSR J1555-2908 and PSR J1810+1744, and found that these rates are insufficient to ablate the companion stars. We cataloged the $\dot{E}/a^2$, mass function, roche lobe filling factor, and inclination angle for compact MSP binaries with low-mass companions and found that higher spin-down flux does not guarantee eclipses. Our analysis, supported by the Kolmogorov-Smirnov statistic, reveals that eclipsing black widow binaries generally exhibit a higher mass function compared to non-eclipsing black widow binaries, as reported by previous studies for a limited sample of black widow MSPs.

astro-ph.HE↗

arXiv2024

Flux Density Stability and Temporal Changes in the Spectra of Millisecond Pulsars using the GMRT

This paper presents an investigation of spectral properties of 10 millisecond pulsars (MSPs) discovered by the uGMRT, observed from 2017-2023 using band 3 (300-500 MHz) and 4 (550-750 MHz) of uGMRT. For these MSPs, we have reported a range of spectral indices from ~0 to -4.8, while averaging the full observing band and all the observing epochs. For every MSP, we calculated the mean flux densities across 7-8 sub-bands each with approximately 25 MHz bandwidth spanning band 3 and band 4. We computed their modulation indices as well as average and maximum-to-median flux densities within each subband. Using a temporal variation of flux density we calculated the refractive scintillation time scales and estimated structure function with time lag for 8 MSPs in the sample. We note a significant temporal evolution of the in-band spectra, classified into three categories based on the nature of the best-fit power-law spectra, having single positive spectral indices, multiple broken power law, and single negative spectral indices. Additionally, indications of low-frequency turnover and a temporal variation of the turnover frequency (to the extent that turnover was observed for some of the epochs while not seen for the rest) were noted for all the MSPs. To the best of our knowledge, this is the first systematic investigation probing temporal changes in the MSP spectra as well as in turnover frequency. Future exploration with dense monitoring combined with modeling of spectra can provide vital insight into the intrinsic emission properties of the MSPs and ISM properties.

astro-ph.HE↗

arXiv2024

Unveiling frequency-dependent eclipsing in spider millisecond pulsars using broadband polarization observations with the Parkes

This study presents an orbital phase-dependent analysis of three black widow spider millisecond pulsars (BW MSPs), aiming to investigate the magnetic field within the eclipse environment. The ultra-wide-bandwidth low-frequency receiver (UWL) of the Parkes 'Murriyang' radio telescope is utilised for full polarisation observations covering frequencies from 704-4032 MHz. Depolarisation of pulsed emission is observed during the eclipse phase of three BW MSPs namely, J0024-7204J, J1431-4715 and PSR J1959+2048, consistent with previous studies of other BW MSPs. We estimated orbital phase dependent RM values for these MSPs. The wide bandwidth observations also provided the constraints on eclipse cutoff frequency for these BW MSPs. For PSR J0024-7204J, we report temporal variation of the eclipse cutoff frequency coupled with changes in the electron column density within the eclipse medium across six observed eclipses. Moreover, the eclipse cutoff frequency for PSR J1431-4715 is determined to be 1251 $\pm$ 80 MHz, leading to the conclusion that synchrotron absorption is the primary mechanism responsible for the eclipsing. Additionally, for PSR J1959+2048, the estimated cutoff frequency exceeded 1400 MHz, consistent with previous studies. With this investigation, we have doubled the sample size of BW MSPs with orbital phase-resolved studies allowing a better probe to the eclipse environment.

astro-ph.HE↗

arXiv2024

The GMRT High-Resolution Southern Sky Survey for pulsars and transients -- VII: Timing of Spider MSP J1242-4712, A Bridge Between Redback and Black Widow Pulsars

We present the timing solution for the 5.31-ms spider millisecond pulsar (MSP) J1242-4712, discovered with the GMRT. PSR J1242-4712 orbits a companion of minimum mass 0.08 M$_{\odot}$ with an orbital period of 7.7 hrs and occupies a relatively unexplored region in the orbital period versus companion mass space. We did not detect gamma-ray pulsations for this MSP, and also could not identify the optical counterpart for PSR J1242-4712 in available optical/near-infrared data. The profile of J1242-4712 evolves with frequency showing a clear single component at lower frequencies and a three-component profile at 650 MHz. PSR J1242-4712 eclipses for a very short duration near superior conjunction (orbital phase ~ 0.23-0.25) below 360 MHz. Moreover, significant DM delays and errors in pulse times of arrivals are observed near inferior conjunction (orbital phase ~ 0.7), along with an observed eclipse in one epoch at 650 MHz. Observed eclipses and significant orbital period variability suggest that PSR J1242-4712 is possibly not a He-WD binary, but has a semi or non-degenerate companion, indicating that this is a ``spider" MSP lying in a region between typical black widows and redbacks. This system may represent a distinct category of spider MSPs, displaying characteristics that bridge the gap between known black widow and redback MSPs.

astro-ph.HE↗

arXiv2022

XCI-Sketch: Extraction of Color Information from Images for Generation of Colored Outlines and Sketches

Sketches are a medium to convey a visual scene from an individual's creative perspective. The addition of color substantially enhances the overall expressivity of a sketch. This paper proposes two methods to mimic human-drawn colored sketches by utilizing the Contour Drawing Dataset. Our first approach renders colored outline sketches by applying image processing techniques aided by k-means color clustering. The second method uses a generative adversarial network to develop a model that can generate colored sketches from previously unobserved images. We assess the results obtained through quantitative and qualitative evaluations.

cs.CV↗

arXiv2021

Semi-Supervised Classification and Segmentation on High Resolution Aerial Images

FloodNet is a high-resolution image dataset acquired by a small UAV platform, DJI Mavic Pro quadcopters, after Hurricane Harvey. The dataset presents a unique challenge of advancing the damage assessment process for post-disaster scenarios using unlabeled and limited labeled dataset. We propose a solution to address their classification and semantic segmentation challenge. We approach this problem by generating pseudo labels for both classification and segmentation during training and slowly incrementing the amount by which the pseudo label loss affects the final loss. Using this semi-supervised method of training helped us improve our baseline supervised loss by a huge margin for classification, allowing the model to generalize and perform better on the validation and test splits of the dataset. In this paper, we compare and contrast the various methods and models for image classification and semantic segmentation on the FloodNet dataset.

cs.CV↗

arXiv2020

IS-CAM: Integrated Score-CAM for axiomatic-based explanations

Convolutional Neural Networks have been known as black-box models as humans cannot interpret their inner functionalities. With an attempt to make CNNs more interpretable and trustworthy, we propose IS-CAM (Integrated Score-CAM), where we introduce the integration operation within the Score-CAM pipeline to achieve visually sharper attribution maps quantitatively. Our method is evaluated on 2000 randomly selected images from the ILSVRC 2012 Validation dataset, which proves the versatility of IS-CAM to account for different models and methods.

cs.CV↗