arXiv subjects

Rahul Jayaraman

Publications and source records attributed to Rahul Jayaraman.

At least 19 recordsLinked to original sources

arXiv2026

Constraints on Late-Time Flaring from Luminous Fast Blue Optical Transients using the Transiting Exoplanet Survey Satellite and the Zwicky Transient Facility

The Luminous Fast Blue Optical Transient (LFBOT) AT2022tsd exhibited minutes-timescale optical flares in the tens of days following the initial transient event, likely due to a central engine -- either an accreting black hole or a magnetar. In this paper, we use data from the Transiting Exoplanet Survey Satellite (TESS) and the Zwicky Transient Facility (ZTF) to constrain the occurrence of similar flares in the 12 (of 14) known LFBOTs that had observational coverage with TESS from tens of days to thousands of days after the transient's initial emission. We find seven flare-like signals at the locations of four unique LFBOTs; all seven can likely be attributed to a solar system object (SSO) moving through the TESS aperture. Assuming all seven flares arise from SSOs, for the LFBOT AT2024qfm we rule out flaring with a similar timescale (40--65 d) and luminosity ($\nu L_\nu\sim10^{43}$ erg s$^{-1}$) as in AT2022tsd, while for AT2022tsd itself we rule out flares between 380--430 d after the initial transient that were as luminous as the earlier flares. This observation suggests that the engine power in AT2022tsd declined or shut off on a timescale of hundreds of days. We also find that there is no late-time activity detectable in TESS thousands of days after the prototype LFBOT, AT2018cow. We discuss our constraints on the duty cycle of such flaring and then present estimates for the number of minutes-duration flares detectable with ongoing and upcoming high-cadence ($\ll1$ d) wide-field surveys.

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arXiv2026

Rapidly oscillating Ap stars observed with TESS. The LAMOST Ap sample and 49 Cam

The rapidly oscillating chemically peculiar A-type (roAp) stars offer valuable insights into the internal physical processes of all stars, but their study is challenged by their rarity. The large-scale TESS surveys have allowed for the collection of data for a sizeable dataset of roAp stars. Nevertheless, asteroseismic data obtained with TESS and Gaia has not been explored to its full potential. We develop an algorithm capable of analysing large quantities of data to search for new roAp stars and increase the current sample. We focus on data products that have not been previously explored for the search of roAp stars, namely the 200-s FFIs and 20-s cadence light curves. 20-s and 200-s cadence light curves of target stars are retrieved from the MAST server and cleaned. DFTs are computed for each light curve which are used to pre-whiten the data to remove any low frequency signals. A final DFT is calculated which is used to classify stars as non-pulsating (NP), delta Scuti or roAp based on the remaining signal. We apply our algorithm to two independent datasets: i) ~2700 Ap stars spectroscopically classified with LAMOST and observed by TESS in the 200-s FFIs and ii) all TESS 20-s cadence light curves available for known or candidate roAp stars. These two samples have no overlap, i.e. none of the LAMOST stars have been observed with 20-s cadence. We identify four new roAp stars: TIC 312111544, TIC 252881095, TIC 46054683, and 49 Cam (TIC 393276640). We find evidence in TESS data that TIC 252881095 may be part of a binary system. If the tentative ~30-d orbital signal is confirmed, TIC 252881095 could be one of the shortest-period roAp binary currently known. Furthermore, the detection of high-frequency pulsations in 49 Cam is particularly relevant, as this well-known roAp candidate star is here confirmed to be roAp based on TESS 20-s cadence data.

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arXiv2025

Broad-band Spectral Modeling of Prompt Emission from Gamma-Ray Bursts Observed by the Transiting Exoplanet Survey Satellite

Optical observations of gamma-ray bursts (GRBs) contemporaneous with their prompt high-energy emission are rare, but they can provide insights into the physical processes underlying these explosive events. The Transiting Exoplanet Survey Satellite's (TESS) large field of view and continuous observation capabilities make it uniquely positioned to detect and characterize prompt optical flashes from GRBs. In this work, we fit phenomenological models to the gamma-ray through optical spectral energy distributions (SEDs) of 24 bursts with arcsecond-level localizations that fell within the TESS field of view between 2018 July and 2024 December. In four cases, the extrapolation of the high-energy SED agrees with the observed optical flux to within 1-$\sigma$. In one case, there is a significant excess of optical flux relative to the extrapolation. In two cases, upper limits from TESS did not constrain the optical portion of the SED. In the remaining 17 cases, the optical flux is overpredicted by the extrapolation from high energies. This discrepancy could be explained by dust extinction in the host galaxy.

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arXiv2025

The Luminous, Slow-Rising Orphan Afterglow AT2019pim as a Candidate Moderately Relativistic Outflow

Classical gamma-ray bursts (GRBs) have two distinct emission episodes: prompt emission from ultrarelativistic ejecta and afterglow from shocked circumstellar material. While both components are extremely luminous in known GRBs, a variety of scenarios predict the existence of luminous afterglow emission with little or no associated high-energy prompt emission. We present AT2019pim, the first spectroscopically confirmed afterglow with no observed high-energy emission to be identified. Serendipitously discovered during follow-up observations of a gravitational-wave trigger and located in a contemporaneous TESS sector, it is hallmarked by a fast-rising (t ~ 2 hr), luminous (M_UV,peak ~ -24.4 mag) optical transient with accompanying luminous X-ray and radio emission. No gamma-ray emission consistent with the time and location of the transient was detected by Fermi-GBM or by Konus, placing constraining limits on an accompanying GRB. We investigate several independent observational aspects of the afterglow in the context of constraints on relativistic motion and find all of them are consistent with an initial Lorentz factor of Gamma_0 ~ 10-30 for the on-axis material, significantly lower than in any well-observed GRB and consistent with the theoretically predicted "dirty fireball" scenario in which the high-energy prompt emission is stifled by pair production. However, we cannot rule out a structured jet model in which only the line-of-sight material was ejected at low-Gamma, off-axis from a classical high-Gamma jet core, and an on-axis GRB with below-average gamma-ray efficiency also remains a possibility. This event represents a milestone in orphan afterglow searches, demonstrating that luminous optical afterglows lacking detected GRB counterparts can be identified and spectroscopically confirmed in real time.

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arXiv2024

Tidally distorted stars are triaxial pulsators

Stars in close binaries are tidally distorted, and this has a strong effect on their pulsation modes. We compute the mode frequencies and geometries of tidally distorted stars using perturbation theory, accounting for the effects of the Coriolis force and the coupling between different azimuthal orders $m$ of a multiplet induced by the tidal distortion. For tidally coupled dipole pressure modes, the tidal coupling dominates over the Coriolis force and the resulting pulsations are ``triaxial", with each of the three modes in a multiplet ``tidally tilted" to be aligned with the one of the three principal axes of the star. The observed amplitudes and phases of the dipole modes aligned orthogonal to the spin axis are modulated throughout the orbit, producing doublets in the power spectrum that are spaced by exactly twice the orbital frequency. Quadrupole modes have similar but slightly more complex behavior. This amplitude modulation allows for mode identification which can potentially enable detailed asteroseismic analyses of tidally tilted pulsators. Pressure modes should exhibit this behavior in stellar binaries close enough to be tidally synchronized, while gravity modes should remain aligned with the star's spin axis. We discuss applications to various types of pulsating stars, and the relationship between tidal tilting of pulsations and the ``single-sided" pulsations sometimes observed in very tidally distorted stars.

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arXiv2024

MAUVE: An Ultraviolet Astrophysics Probe Mission Concept

We present the mission concept "Mission to Analyze the UltraViolet universE" (MAUVE), a wide-field spectrometer and imager conceived during the inaugural NASA Astrophysics Mission Design School. MAUVE responds to the 2023 Announcement of Opportunity for Probe-class missions, with a budget cap of \$1 billion, and would hypothetically launch in 2031. However, the formulation of MAUVE was an educational exercise and the mission is not being developed further. The Principal Investigator-led science of MAUVE aligns with the priorities outlined in the 2020 Astrophysics Decadal Survey, enabling new characterizations of exoplanet atmospheres, the early-time light curves of some of the universe's most explosive transients, and the poorly-understood extragalactic background light. Because the Principal Investigator science occupies 30% of the observing time available during the mission's 5 yr lifespan, we provide an observing plan that would allow for 70% of the observing time to be used for General Observer programs, with community-solicited proposals. The onboard detector (THISTLE) claims significant heritage from the Space Telescope Imaging Spectrograph on Hubble, but extends its wavelength range down to the extreme UV. We note that MAUVE would be the first satellite in decades with the ability to access this regime of the electromagnetic spectrum. MAUVE has a field of view of 900" x 900" a photometric sensitivity extending to $m_{UV}\leq 24$, and a resolving power of $R\sim1000$. This paper provides full science and mission traceability matrices for this concept, and also outlines cost and scheduling timelines aimed at enabling a within-budget mission and an on-time launch.

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arXiv2024

TIC 435850195: The Second Tri-Axial, Tidally Tilted Pulsator

The Transiting Exoplanet Survey Satellite (TESS) has enabled the discovery of numerous tidally tilted pulsators (TTPs), which are pulsating stars in close binaries where the presence of a tidal bulge has the effect of tilting the primary star's pulsation axes into the orbital plane. Recently, the modeling framework developed to analyze TTPs has been applied to the emerging class of tri-axial pulsators, which exhibit nonradial pulsations about three perpendicular axes. In this work, we report on the identification of the second-ever discovered tri-axial pulsator, with sixteen robustly-detected pulsation multiplets, of which fourteen are dipole doublets separated by 2$\nu_{\rm orb}$. We jointly fit the spectral energy distribution (SED) and TESS light curve of the star, and find that the primary is slightly evolved off the zero-age main sequence, while the less massive secondary still lies on the zero-age main sequence. Of the fourteen doublets, we associate eight with $Y_{10x}$ modes and six with novel $Y_{10y}$ modes. We exclude the existence of $Y_{11x}$ modes in this star and show that the observed pulsation modes must be $Y_{10y}$. We also present a toy model for the tri-axial pulsation framework in the context of this star. The techniques presented here can be utilized to rapidly analyze and confirm future tri-axial pulsator candidates.

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arXiv2024

Gamma-Ray Bursts Observed by the Transiting Exoplanet Survey Satellite: Prompt Optical Counterparts and Afterglows of Swift-XRT Localized GRBs

Very few detections have been made of optical flashes contemporaneous with prompt high-energy emission from a gamma-ray burst (GRB). In this work, we present and analyze light curves of GRB-associated optical flashes and afterglows from the Transiting Exoplanet Survey Satellite (TESS). Our sample consists of eight GRBs with arcsecond-level localizations from the X-Ray Telescope on board the Neil Gehrels Swift Observatory. For each burst, we characterize the prompt optical emission and any observed afterglow, and constrain physical parameters for four of these bursts using their TESS light curves. This work also presents a straightforward method to correct for TESS's cosmic ray mitigation on 20-second timescales, which allows us to estimate the "true" brightness of optical flashes associated with prompt GRB emission. We also highlight TESS's continuous wide-field monitoring capability, which provides an efficient means of identifying optical emission from GRBs and characterizing early-time afterglow light curves. Based on empirical detection rates from Swift and the Fermi Gamma-Ray Space Telescope, up to 10 GRBs per year may fall within the contemporaneous TESS field of view.

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arXiv2023

Transient Corotating Clumps Around Adolescent Low-Mass Stars From Four Years of TESS

Complex periodic variables (CPVs) are stars that exhibit highly structured and periodic optical light curves. Previous studies have indicated that these stars are typically disk-free pre-main-sequence M dwarfs with rotation periods ranging from 0.2 to 2 days. To advance our understanding of these enigmatic objects, we conducted a blind search using TESS 2-minute data of 65,760 K and M dwarfs with $T$<16 mag and $d$<150 pc. We found 50 high-quality CPVs, and subsequently determined that most are members of stellar associations. Among the new discoveries are the brightest ($T$$\approx$9.5 mag), closest ($d$$\approx$20 pc), and oldest ($\approx$200 Myr) CPVs known. One exceptional object, LP 12-502, exhibited up to eight flux dips per cycle. Some of these dips coexisted with slightly different periods, and the shortest-duration dips precisely matched the expected timescale for transiting small bodies at the corotation radius. Broadly, our search confirms that CPVs are mostly young ($\lesssim$150 Myr) and low-mass ($\lesssim$0.4 $M_\odot$). The flux dips characteristic of the class have lifetimes of $\approx$100 cycles, although stellar flares seem to induce sudden dip collapse once every few months. The most plausible explanation for these phenomena remains corotating concentrations of gas or dust. The gas or dust is probably entrained by the star's magnetic field, and the sharp features could result from a multipolar field topology, a hypothesis supported by correspondences between the light curves of CPVs and of rapidly rotating B stars known to have multipolar magnetic fields.

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arXiv2023

TIC 184743498: The First Tri-Axial Stellar Pulsator

We have discovered a $δ$ Scuti pulsator in a tight binary (P = 1.053 d) with nine pulsation modes whose frequencies are between 38 and 56 d$^{-1}$. Each of these modes exhibits amplitude modulations and $π$-rad phase shifts twice per orbital cycle. Five of these modes exhibit amplitude and phase shifts that are readily explained by dipole pulsations along an axis that is aligned with the binary's tidal axis. The novelty of the system lies in the remaining four pulsation modes, which we show are dipole pulsations along an axis that is perpendicular to both the tidal axis and the binary's orbital angular momentum axis. There are additionally two pulsation modes whose amplitudes and phases do not change significantly with orbital phase; they are explained as dipole modes along an axis aligned with the orbital/rotation axis. Hence, we propose that TIC 184743498 is a tri-axial pulsator, the first of its kind.

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arXiv2023

Multi-messenger astrophysics in the gravitational-wave era

The observation of GW170817, the first binary neutron star merger observed in both gravitational waves (GW) and electromagnetic (EM) waves, kickstarted the age of multi-messenger GW astronomy. This new technique presents an observationally rich way to probe extreme astrophysical processes. With the onset of the LIGO-Virgo-KAGRA Collaboration's O4 observing run and wide-field EM instruments well-suited for transient searches, multi-messenger astrophysics has never been so promising. We review recent searches and results for multi-messenger counterparts to GW events, and describe existing and upcoming EM follow-up facilities, with a particular focus on WINTER, a new near-infrared survey telescope, and TESS, an exoplanet survey space telescope.

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arXiv2023

101 Eclipsing Quadruple Star Candidates Discovered in TESS Full Frame Images

We present our second catalog of quadruple star candidates, containing 101 systems discovered in TESS Full-Frame Image data. The targets were initially detected as eclipsing binary stars with the help of supervised machine learning methods applied to sectors Sectors 1 through 54. A dedicated team of citizen scientists subsequently identified through visual inspection two sets of eclipses following two different periods. All 101 systems presented here pass comprehensive photocenter motion tests confirming that both sets of eclipses originate from the target star. Some of the systems exhibit prominent eclipse time variations suggesting dynamical interactions between the two component binary stars. One target is an eclipsing quintuple candidate with a (2+1)+2 hierarchical configuration, such that the (2+1) subsystem produces eclipses on the triple orbit as well. Another has recently been confirmed as the second shortest period quadruple reported to date. This catalog provides ephemerides, eclipse depths and durations, sample statistics, and highlights potentially interesting targets for future studies.

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arXiv2023

Four years of Type Ia Supernovae Observed by TESS: Early Time Light Curve Shapes and Constraints on Companion Interaction Models

We present 307 Type Ia supernova (SN) light curves from the first four years of the TESS mission. We use this sample to characterize the shapes of the early time light curves, measure the rise times from first light to peak, and search for companion star interactions. Using simulations, we show that light curves must have noise $<$10% of the peak to avoid biases in the early time light curve shape, restricting our quantitative analysis to 74 light curves. We find that the mean power law index $t^{β_1}$ of the early time light curves is 1.93$\pm$ 0.57 and the mean rise time to peak is 15.7 $\pm$ 3.5 days. We also estimate the underlying population distribution and find a Gaussian component with mean $β_1 = 2.29$, width 0.34, and a tail extending to values less than 1.0. We use model comparison techniques to test for the presence of companion interactions. In contrast to recent results in the literature, we find that the data can rarely distinguish between models with and without companion interactions, and caution is needed when claiming detections of early time flux excesses. Nevertheless, we find three high-quality SN light curves that tentatively prefer the addition of a companion interaction model, but the statistical evidence is not robust. We also find two SNe that disfavor the addition of a companion interaction model to a curved power law model. Taking the 74 SNe together, we calculate 3$σ$ upper limits on the presence of companion signatures to control for orientation effects that can hide companions in individual light curves. Our results rule out common progenitor systems with companions having Roche lobe radii $>$ 31 R$_{\odot}$ (99.9% confidence level) and disfavor companions having Roche lobe radii $>$ 10 R$_{\odot}$ (95% confidence level). Lastly, we discuss the implications of our results for the intrinsic fraction of single degenerate progenitor systems.

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arXiv2023

BU Canis Minoris -- the Most Compact Known Flat Doubly Eclipsing Quadruple System

We have found that the 2+2 quadruple star system BU CMi is currently the most compact quadruple system known, with an extremely short outer period of only 121 days. The previous record holder was TIC 219006972 (Kostov et al. 2023), with a period of 168 days. The quadruple nature of BU CMi was established by Volkov et al. (2021), but they misidentified the outer period as 6.6 years. BU CMi contains two eclipsing binaries (EBs), each with a period near 3 days, and a substantial eccentricity of about 0.22. All four stars are within about 0.1 solar mass of 2.4 solar masses. Both binaries exhibit dynamically driven apsidal motion with fairly short apsidal periods of about 30 years, thanks to the short outer orbital period. The outer period of 121 days is found both from the dynamical perturbations, with this period imprinted on the eclipse timing variations (ETV) curve of each EB by the other binary, and by modeling the complex line profiles in a collection of spectra. We find that the three orbital planes are all mutually aligned to within 1 degree, but the overall system has an inclination angle near 83.5 degrees. We utilize a complex spectro-photodynamical analysis to compute and tabulate all the interesting stellar and orbital parameters of the system. Finally, we also find an unexpected dynamical perturbation on a timescale of several years whose origin we explore. This latter effect was misinterpreted by Volkov et al. (2021) and led them to conclude that the outer period was 6.6 years rather than the 121 days that we establish here.

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arXiv2023

Observations of GRB 230307A by TESS

We present the TESS light curve of GRB 230307A. We find two distinct components: a bright, prompt optical component at the time of the Fermi observation that peaked at TESS magnitude 14.49 (averaged over 200 seconds), followed by a gradual rise and fall over 0.5 days, likely associated with the afterglow, that peaked at 17.65 mag. The prompt component is observed in a single 200s Full Frame Image and was undetectable in the next TESS image ($T_{\rm mag} > 17.79$). Assuming that the onset of the optical transient was coincident with the gamma-ray emission, the prompt emission lasted less than 73.6 seconds, which implies the true peak was actually brighter than $T_{\rm mag} =$ 13.40. We also fit parametric models to the afterglow to characterize its shape. The TESS light curve can be retrieved at https://tess.mit.edu/public/tesstransients/light_curves/lc_grb230307A_cleaned.txt.

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arXiv2023

Searching for Gravitational-Wave Counterparts using the Transiting Exoplanet Survey Satellite

In 2017, the LIGO and Virgo gravitational wave (GW) detectors, in conjunction with electromagnetic (EM) astronomers, observed the first GW multi-messenger astrophysical event, the binary neutron star (BNS) merger GW170817. This marked the beginning of a new era in multi-messenger astrophysics. To discover further GW multi-messenger events, we explore the synergies between the Transiting Exoplanet Survey Satellite (TESS) and GW observations triggered by the LIGO-Virgo-KAGRA Collaboration (LVK) detector network. TESS's extremely wide field of view of ~2300 deg^2 means that it could overlap with large swaths of GW localizations, which can often span hundreds of deg^2 or more. In this work, we use a recently developed transient detection pipeline to search TESS data collected during the LVK's third observing run, O3, for any EM counterparts. We find no obvious counterparts brighter than about 17th magnitude in the TESS bandpass. Additionally, we present end-to-end simulations of BNS mergers, including their detection in GWs and simulations of light curves, to identify TESS's kilonova discovery potential for the LVK's next observing run (O4). In the most optimistic case, TESS will observe up to one GW-found BNS merger counterpart per year. However, TESS may also find up to five kilonovae which did not trigger the LVK network, emphasizing that EM-triggered GW searches may play a key role in future kilonova detections. We also discuss how TESS can help place limits on EM emission from binary black hole mergers, and rapidly exclude large sky areas for poorly localized GW events.

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arXiv2022

TIC 114936199: A Quadruple Star System with a 12-day Outer Orbit Eclipse

We report the discovery with TESS of a remarkable quadruple star system with a 2+1+1 configuration. The two unique characteristics of this system are that (i) the inner eclipsing binary (stars Aa and Ab) eclipses the star in the outermost orbit (star C), and (ii) these outer 4th body eclipses last for $\sim$12 days, the longest of any such system known. The three orbital periods are $\sim$3.3 days, $\sim$51 days, and $\sim$2100 days. The extremely long duration of the outer eclipses is due to the fact that star B slows binary A down on the sky relative to star C. We combine TESS photometric data, ground-based photometric observations, eclipse timing points, radial velocity measurements, the composite spectral energy distribution, and stellar isochones in a spectro-photodynamical analysis to deduce all of the basic properties of the four stars (mass, radius, $T_{\rm eff}$, and age), as well as the orbital parameters for all three orbits. The four masses are $M_{\rm Aa} =0.382$M$_\odot$, $M_{\rm Ab} =0.300$M$_\odot$, $M_{\rm B} =0.540$M$_\odot$ and $M_{\rm C} =0.615$M$_\odot$, with a typical uncertainty of 0.015 M$_\odot$.

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arXiv2022

TIC 5724661: A Long-Period Binary with a Pulsating sdB Star and $δ$ Scuti Variable

Using TESS 20-sec cadence data, we have discovered an unusual combination of pulsating stars in what we infer to be a binary system. The binary consists of a standard $δ$ Scuti star with pulsations over the range 32-41 d$^{-1}$; this is in a likely wide orbit with a hot subdwarf B (sdB) star, which itself has a large-amplitude p-mode pulsation at 524 d$^{-1}$. We establish constraints on the period of the putative binary by using radial velocity measurements of the $δ$~Scuti star and show that any sdB companion star must orbit with a period greater than a few tens of days. Our identification of this sdB binary serves as an important addition to the relatively small number of sdB binaries known to have orbital periods longer than a few days. We model such a binary using {\tt MESA} and find that this system could be formed through stable, nonconservative mass transfer from either a low- or intermediate-mass progenitor, without undergoing a common envelope phase.

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