skip to main content

Search for: All records

Creators/Authors contains: "Villar, V. A."

Note: When clicking on a Digital Object Identifier (DOI) number, you will be taken to an external site maintained by the publisher. Some full text articles may not yet be available without a charge during the embargo (administrative interval).
What is a DOI Number?

Some links on this page may take you to non-federal websites. Their policies may differ from this site.

  1. Abstract GW190814 was a compact object binary coalescence detected in gravitational waves by Advanced LIGO and Advanced Virgo that garnered exceptional community interest due to its excellent localization and the uncertain nature of the binary’s lighter-mass component (either the heaviest known neutron star, or the lightest known black hole). Despite extensive follow-up observations, no electromagnetic counterpart has been identified. Here, we present new radio observations of 75 galaxies within the localization volume at Δ t ≈ 35–266 days post-merger. Our observations cover ∼32% of the total stellar luminosity in the final localization volume and extend to later timescales than previouslymore »reported searches, allowing us to place the deepest constraints to date on the existence of a radio afterglow from a highly off-axis relativistic jet launched during the merger (assuming that the merger occurred within the observed area). For a viewing angle of ∼46° (the best-fit binary inclination derived from the gravitational wave signal) and assumed electron and magnetic field energy fractions of ϵ e = 0.1 and ϵ B = 0.01, we can rule out a typical short gamma-ray burst-like Gaussian jet with an opening angle of 15° and isotropic-equivalent kinetic energy 2 × 10 51 erg propagating into a constant-density medium n ≳ 0.1 cm −3 . These are the first limits resulting from a galaxy-targeted search for a radio counterpart to a gravitational wave event, and we discuss the challenges—and possible advantages—of applying similar search strategies to future events using current and upcoming radio facilities.« less
    Free, publicly-accessible full text available December 1, 2022
  2. Abstract We present panchromatic observations and modeling of calcium-strong supernovae (SNe) 2021gno in the star-forming host-galaxy NGC 4165 and 2021inl in the outskirts of elliptical galaxy NGC 4923, both monitored through the Young Supernova Experiment transient survey. The light curves of both, SNe show two peaks, the former peak being derived from shock cooling emission (SCE) and/or shock interaction with circumstellar material (CSM). The primary peak in SN 2021gno is coincident with luminous, rapidly decaying X-ray emission ( L x = 5 × 10 41 erg s −1 ) detected by Swift-XRT at δ t = 1 day after explosion,more »this observation being the second-ever detection of X-rays from a calcium-strong transient. We interpret the X-ray emission in the context of shock interaction with CSM that extends to r < 3 × 10 14 cm. Based on X-ray modeling, we calculate a CSM mass M CSM = (0.3−1.6) × 10 −3 M ⊙ and density n = (1−4) × 10 10 cm −3 . Radio nondetections indicate a low-density environment at larger radii ( r > 10 16 cm) and mass-loss rate of M ̇ < 10 − 4 M ⊙ yr −1 . SCE modeling of both primary light-curve peaks indicates an extended-progenitor envelope mass M e = 0.02−0.05 M ⊙ and radius R e = 30−230 R ⊙ . The explosion properties suggest progenitor systems containing either a low-mass massive star or a white dwarf (WD), the former being unlikely given the lack of local star formation. Furthermore, the environments of both SNe are consistent with low-mass hybrid He/C/O WD + C/O WD mergers.« less
    Free, publicly-accessible full text available June 1, 2023
  3. Abstract For the first ∼3 yrs after the binary neutron star merger event GW 170817, the radio and X-ray radiation has been dominated by emission from a structured relativistic off-axis jet propagating into a low-density medium with n < 0.01 cm −3 . We report on observational evidence for an excess of X-ray emission at δt > 900 days after the merger. With L x ≈ 5 × 10 38 erg s −1 at 1234 days, the recently detected X-ray emission represents a ≥3.2 σ (Gaussian equivalent) deviation from the universal post-jet-break model that best fits the multiwavelength afterglow atmore »earlier times. In the context of JetFit afterglow models, current data represent a departure with statistical significance ≥3.1 σ , depending on the fireball collimation, with the most realistic models showing excesses at the level of ≥3.7 σ . A lack of detectable 3 GHz radio emission suggests a harder broadband spectrum than the jet afterglow. These properties are consistent with the emergence of a new emission component such as synchrotron radiation from a mildly relativistic shock generated by the expanding merger ejecta, i.e., a kilonova afterglow. In this context, we present a set of ab initio numerical relativity binary neutron star (BNS) merger simulations that show that an X-ray excess supports the presence of a high-velocity tail in the merger ejecta, and argues against the prompt collapse of the merger remnant into a black hole. Radiation from accretion processes on the compact-object remnant represents a viable alternative. Neither a kilonova afterglow nor accretion-powered emission have been observed before, as detections of BNS mergers at this phase of evolution are unprecedented.« less
    Free, publicly-accessible full text available March 1, 2023