arXiv subjects

Delina Levine

Publications and source records attributed to Delina Levine.

9 recordsLinked to original sources

arXiv2026

VLASS Discovery of a Luminous Galactic Radio Transient Evolving on Decade Timescales

We present a multiwavelength analysis of the radio transient VT J1906+0849, discovered as a 70 mJy source in Epoch 1 of the Very Large Array Sky Survey (VLASS), 21 yr after an NRAO VLA Sky Survey (NVSS) non-detection. Radio observations reveal the source was first detected in 2005, peaking at $\gtrsim200$ mJy in 2014, then declining until a late 2025 rebrightening. The transient sits at a Galactic latitude of $\approx0.74^\circ$ and the properties of its optical-infrared counterpart support a Galactic origin. At $d\gtrsim15$ kpc, the extreme radio luminosity is likely powered by sustained accretion onto a compact object. However, a Swift-XRT non-detection shows it is X-ray faint relative to the Galactic X-ray binary population, and the radio emission is distinct from X-ray binaries in its temporal and spectral behavior. Broadband radio spectra suggest synchrotron self-absorption, but size constraints from equipartition and very long baseline interferometry show little to no expansion in the radio-emitting region over 5+ yr, despite significant spectral evolution. Near-infrared spectroscopy reveals a single broad emission line with a stable centroid but variable width and luminosity. We attribute this feature to blueshifted Br$\gamma$ tracing a persistent asymmetric $\approx2000$ km s$^{-1}$ outflow. These properties are unlike any previously identified Galactic radio source. One possible interpretation is that VT J1906+0849 is a young analog of the microquasar SS 433, with a dense disk wind confining a continuously powered synchrotron outflow. This jet-wind interaction explains the compact, slowly expanding radio source and may contribute to the absence of bright X-ray emission.

astro-ph.HE↗

arXiv2026

A spectacular multi-wavelength transient associated with an off-axis relativistic jet

Many of the most luminous extragalactic transients originate from the accretion of material onto a black hole (BH) via core-collapse, stellar mergers, or the tidal disruption of a star. Some produce energetic multi-wavelength emission, displaying short, blue optical flares and bright, long-lived radio afterglows. In rare cases, these have also launched powerful relativistic jets almost exclusively detected on-axis via high-energy emission. Here we report AT 2019ijn, a radio transient discovered in the Very Large Array Sky Survey, associated with a powerful relativistic jet viewed off-axis and accompanied by a luminous ($\nu L_{\nu, opt} \sim 10^{44}$ erg/s) optical transient. Originating from a star-forming dwarf galaxy at z = 0.273, AT 2019ijn's optical flare exhibited a fast rise ($t_{rise, rest} \sim 7$ d) and shallow decline ($t_{dec, rest} > 38$ d), followed a year later by an energetic ($E \sim 2\times10^{52}$ erg) radio counterpart persisting for $>6$ years. These combined properties are unprecedented and preclude known classes of stellar explosion powered by core-collapse. Instead, the implied accretion onto a BH and associated off-axis jet invokes an exotic BH-stellar merger or a jetted tidal disruption event (TDE) by a $10^4 - 10^6 M_\odot$ black hole. Favoring a TDE, this work determines the jet-launching occurrence, with the low redshift allowing constraints on the late-time evolution in contrast to prior events. Upcoming radio sky surveys will offer an unprecedented new window for further discovery of AT 2019ijn-like off-axis relativistic transients.

astro-ph.HE↗

arXiv2025

Fast Luminous Extragalactic Transients in the VLA Sky Survey: Implications for the rates of Accretion-Induced Collapse Events, Fast Blue Optical Transients and Gamma Ray Burst Afterglows

Radio wavelengths offer a unique window into high-energy astrophysical phenomena that may be obscured or too rapidly evolving to be captured at other wavelengths. Leveraging data from the Very Large Array Sky Survey, we perform a systematic search for fast, luminous transients with characteristic timescales $\lesssim 3$ years in the nearby universe ($z \leq 0.3$). We report the discovery of five such transients, and classify them based on their synchrotron emission energetics and host galaxy properties. From this sample, we derive observational constraints on the volumetric rates of certain corresponding transient classes. We limit the rates of accretion-induced collapse of white dwarfs with dense circumstellar medium interaction (and those producing pulsar wind nebulae) at $\lesssim 1.10_{-0.90}^{+2.60}$% ($\lesssim 0.20_{-0.10}^{+5.80}$%) of the local Type Ia supernova rate, respectively, broadly consistent with theoretical predictions. For AT2018cow-like radio-bright luminous fast blue optical transients, we estimate a rare occurrence rate of $\lesssim 0.02_{-0.01}^{+0.32}$% of the local core-collapse supernova rate. We constrain the local volumetric rates of long- and short-duration gamma-ray bursts (GRBs) to be $\lesssim 11.46_{-9.48}^{+26.28}$~Gpc$^{-3}$~yr$^{-1}$ and $\lesssim 80.88_{-66.90}^{+185.87}$~Gpc$^{-3}$~yr$^{-1}$, respectively. These estimates incorporate beaming corrections, with median detectable viewing angles derived from afterglow simulations of $\sim 0.4$ and $\sim 0.3$ radians for long- and short-duration GRBs. Our findings highlight the potential of radio surveys to uncover rare, energetic transients. We emphasize the critical role of coordinated multi-wavelength follow-up in fully characterizing these enigmatic events.

astro-ph.HE↗

arXiv2023

A Stochastic Approach To Reconstruct Gamma Ray Burst Lightcurves

Gamma-Ray Bursts (GRBs), being observed at high redshift (z = 9.4), vital to cosmological studies and investigating Population III stars. To tackle these studies, we need correlations among relevant GRB variables with the requirement of small uncertainties on their variables. Thus, we must have good coverage of GRB light curves (LCs). However, gaps in the LC hinder the precise determination of GRB properties and are often unavoidable. Therefore, extensive categorization of GRB LCs remains a hurdle. We address LC gaps using a 'stochastic reconstruction,' wherein we fit two pre-existing models (Willingale 2007; W07 and Broken Power Law; BPL) to the observed LC, then use the distribution of flux residuals from the original data to generate data to fill in the temporal gaps. We also demonstrate a model-independent LC reconstruction via Gaussian Processes. At 10% noise, the uncertainty of the end time of the plateau, its correspondent flux, and the temporal decay index after the plateau decreases, on average, by 33.3% 35.03%, and 43.32%, respectively for the W07, and by 33.3%, 30.78%, 43.9% for the BPL. The slope of the plateau decreases by 14.76% in the BPL. After using the Gaussian Process technique, we see similar trends of a decrease in uncertainty for all model parameters for both the W07 and BPL models. These improvements are essential for the application of GRBs as standard candles in cosmology, for the investigation of theoretical models and for inferring the redshift of GRBs with future machine learning analysis.

astro-ph.HE↗

arXiv2022

Interpretation of Radio Afterglows in the framework of the Standard Fireball and Energy Injection models

Gamma-Ray Bursts (GRBs) are panchromatic, highly energetic transients whose energy emission mechanism is still debated. One of the possible explanations is the standard fireball model, which can be tested with the closure relations (CRs), or relations between the temporal and spectral indices of a GRB. To test these, we compile an extensive sample of radio afterglow light curves (LCs) that span from 1997 to 2020, the most comprehensive analysis of GRBs with radio observations to date. We fit 202 LCs from 82 distinct GRBs with a broken power law, obtaining a sample of 26 that display a clear break and a subsample of 14 GRBs that present a radio plateau. We test these samples against CRs corresponding to a constant-density interstellar medium (ISM) or a stellar wind medium in both fast- and slow-cooling regimes, as well as three additional density profiles, $k = 1, 1.5, 2.5,$ following $n \propto r^{-k}$ , and consider sets of CRs both with and without energy injection. We find that 12 of the 26 GRBs (46%), of which 7/12 present a radio plateau, fulfill at least one CR in the sets tested, suggesting our data is largely incompatible with the standard fireball model. Of the fulfilled CRs, the most preferred environment is the ISM, SC, $ν_m < ν< ν_c$ without energy injection. Our results are consistent with previous studies that test the standard fireball model via the CRs in radio.

astro-ph.HE↗

arXiv2022

The Optical Two and Three-Dimensional Fundamental Plane Correlations for Nearly 180 Gamma-Ray Burst Afterglows with Swift/UVOT, RATIR, and the SUBARU Telescope

Gamma-ray bursts (GRBs) are fascinating events due to their panchromatic nature. We study optical plateaus in GRB afterglows via an extended search into archival data. We comprehensively analyze all published GRBs with known redshifts and optical plateaus observed by many ground-based telescopes (e.g., Subaru Telescope, RATIR) around the world and several space-based observatories such as the Neil Gehrels Swift Observatory. We fit 500 optical light curves (LCs), showing the existence of the plateau in 179 cases. This sample is 75% larger than the previous one (arXiv:2105.10717), and it is the largest compilation so far of optical plateaus. We discover the 3D fundamental plane relation at optical wavelengths using this sample. This correlation is between the rest-frame time at the end of the plateau emission, $T^{*}_{\rm opt}$, its optical luminosity, $L_{\rm opt}$, and the peak in the optical prompt emission, $L_{\rm peak, opt}$, thus resembling the three-dimensional (3D) X-ray fundamental plane relation (arXiv:1604.06840). We correct our sample for redshift evolution and selection effects, discovering that this correlation is indeed intrinsic to GRB physics. We investigate the rest-frame end time distributions in X-rays and optical ($T^{*}_{\rm opt}$, $T^{*}_{\rm X}$), and conclude that the plateau is achromatic only when selection biases are not considered. We also investigate if the 3D optical correlation may be a new discriminant between optical GRB classes and find that there is no significant separation between the classes compared to the Gold sample plane after correcting for evolution.

astro-ph.HE↗

arXiv2022

A Note On Exemplary Off-Shell Constructions Of 4D, ${\mathbf {\cal N}}$ = 2 Supersymmetry Representations

We continue the search for rules that govern when off-shell 4D, $\cal N$ = 1 supermultiplets can be combined to form off-shell 4D, $\cal N$ = 2 supermultiplets. We study the ${\mathbb S}_8$ permutations and Height Yielding Matrix Numbers (HYMN) embedded within the adinkras that correspond to these putative 4D, $\cal N$ = 2 supermultiplets off-shell supermultiplets. Even though the HYMN definition was designed to distinguish between the raising and lowering of nodes in one dimensional valises supermultiplets, they are shown to accurately select out which combinations of off-shell 4D, $\cal N$ = 1 supermultiplets correspond to off-shell 4D, $\cal N$ = 2 supermultiplets. Only the combinations of the chiral + vector and chiral + tensor are found to have valises in the same class. This is consistent with the well known structure of 4D, $\cal N$ = 2 supermultiplets.

hep-th↗

arXiv2021

Accounting for Selection Bias and Redshift Evolution in GRB Radio Afterglow Data

Gamma-ray Bursts (GRBs) are highly energetic events that can be observed at extremely high redshift. However, inherent bias in GRB data due to selection effects and redshift evolution can significantly skew any subsequent analysis. We correct for important variables related to the GRB emission, such as the burst duration, $T_{90}^*$, the prompt isotropic energy, $E_{\rm iso}$, the rest-frame end time of the plateau emission, $T_{\rm a, radio}^*$, and its correspondent luminosity $L_{\rm a, radio}$, for radio afterglow. In particular, we use the Efron-Petrosian method presented in 1992 for the correction of our variables of interest. Specifically, we correct $E_{\rm iso}$ and $T_{90}^*$ for 80 GRBs, and $L_{\rm a, radio}$ and $T_{\rm a, radio}^*$ for a subsample of 18 GRBs that present a plateau-like flattening in their light curve. Upon application of this method, we find strong evolution with redshift in most variables, particularly in $L_{\rm a, radio}$, with values similar to those found in past and current literature in radio, X-ray and optical wavelengths, indicating that these variables are susceptible to observational bias. This analysis emphasizes the necessity of correcting observational data for evolutionary effects to obtain the intrinsic behavior of correlations to use them as discriminators among the most plausible theoretical models and as reliable cosmological tools.

astro-ph.HE↗

arXiv2021

Examining Two-Dimensional Luminosity-time Correlations for Gamma Ray Burst Radio Afterglows with VLA and ALMA

Gamma-ray burst (GRB) afterglow emission can be observed from sub-TeV to radio wavelengths, though only 6.6\% of observed GRBs present radio afterglows. We examine GRB radio light curves (LCs) to look for the presence of radio plateaus, resembling the plateaus observed in X-ray and optical. We analyze 404 GRBs from the literature with observed radio afterglow and fit 82 GRBs with at least 5 data points with a broken power law (BPL) model, requiring 4 parameters. From these, we find 18 GRBs that present a break feature resembling a plateau. We conduct the first multi-wavelength study of the Dainotti correlation between the luminosity $L_a$ and the rest-frame time of break $T_a^*$ for those 18 GRBs, concluding that the correlation exists and resembles the corresponding correlation in X-ray and optical wavelengths after correction for evolutionary effects. We compare the $T_a^*$ for the radio sample with $T_a^*$ values in X-ray and optical data (Dainotti et al. 2013, 2020b), finding significantly later break times in radio. We propose that this late break time and compatibility in slope suggests either a long-lasting plateau or the passage of a spectral break in the radio band. We also correct the distribution of the isotropic energy $E_{\rm iso}$ vs. the rest-frame burst duration $T^*_{90}$ for evolutionary effects and conclude that there is no significant difference between the $T^*_{90}$ distribution for the radio LCs with a break and those without.

astro-ph.HE↗