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1. Improved Upper Limits on Gravitational-wave Emission from NS 1987A in SNR 1987A

   https://doi.org/10.3847/2041-8213/ad2263  

   Owen, Benjamin J. ; Lindblom, Lee ; Soares Pinheiro, Luciano ; Rajbhandari, Binod ( February 2024 , The Astrophysical Journal Letters)

   We report on a new search for continuous gravitational waves from NS 1987A, the neutron star born in SN 1987A, using open data from Advanced LIGO and Virgo’s third observing run (O3). The search covered frequencies from 35–1050 Hz, more than 5 times the band of the only previous gravitational-wave search to constrain NS 1987A. Our search used an improved code and coherently integrated from 5.10 to 14.85 days depending on frequency. No astrophysical signals were detected. By expanding the frequency range and using O3 data, this search improved on strain upper limits from the previous search and was sensitive at the highest frequencies to ellipticities of 1.6 × 10⁻⁵andr-mode amplitudes of 4.4 × 10⁻⁴, both an order of magnitude improvement over the previous search and both well within the range of theoretical predictions.

    

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2. First Constraining Upper Limits on Gravitational-wave Emission from NS 1987A in SNR 1987A

   https://doi.org/10.3847/2041-8213/ac84dc  

   Owen, Benjamin J. ; Lindblom, Lee ; Pinheiro, Luciano Soares ( August 2022 , The Astrophysical Journal Letters)

   We report on a search for continuous gravitational waves (GWs) from NS 1987A, the neutron star born in SN 1987A. The search covered a frequency band of 75–275 Hz, included a wide range of spin-down parameters for the first time, and coherently integrated 12.8 days of LIGO data below 125 Hz and 8.7 days of LIGO data above 125 Hz from the second Advanced LIGO–Virgo observing run. We found no astrophysical signal. We set upper limits on GW emission as tight as an intrinsic strain of 2 × 10⁻²⁵at 90% confidence. The large spin-down parameter space makes this search the first astrophysically consistent one for continuous GWs from NS 1987A. Our upper limits are the first consistent ones to beat an analog of the spin-down limit based on the age of the neutron star and hence are the first GW observations to put new constraints on NS 1987A.

    

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3. Radiative Transfer Modeling of an SN 1987A Light Echo—AT 2019xis

   https://doi.org/10.3847/1538-4357/ac1069  

   Ding, Jiachen ; Wang, Lifan ; Brown, Peter ; Yang, Ping ( September 2021 , The Astrophysical Journal)
4. An Independent Determination of the Distance to Supernova SN 1987A by Means of the Light Echo AT 2019xis

   https://doi.org/10.3847/2041-8213/acd37c  

   Cikota, Aleksandar ; Ding, Jiachen ; Wang, Lifan ; Baade, Dietrich ; Cikota, Stefan ; Höflich, Peter ; Maund, Justyn ; Yang, Ping ( May 2023 , The Astrophysical Journal Letters)

   Accurate distance determination to astrophysical objects is essential for the understanding of their intrinsic brightness and size. The distance to SN 1987A has been previously measured by the expanding photosphere method and by using the angular size of the circumstellar rings with absolute sizes derived from light curves of narrow UV emission lines, with reported distances ranging from 46.77 to 55 kpc. In this study, we independently determined the distance to SN 1987A using photometry and imaging polarimetry observations of AT 2019xis, a light echo of SN 1987A, by adopting a radiative transfer model of the light echo developed in Ding et al. We obtained distances to SN 1987A in the range from 49.09 ± 2.16 kpc to 59.39 ± 3.27 kpc, depending on the interstellar polarization and extinction corrections, which are consistent with the literature values. This study demonstrates the potential of using light echoes as a tool for distance determination to astrophysical objects in the Milky Way, up to kiloparsec level scales.

    

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5. The Matter Beyond the Ring: The Recent Evolution of SN 1987A Observed by the Hubble Space Telescope

   https://doi.org/10.3847/1538-4357/ab4ff2  

   Larsson, J. ; Fransson, C. ; Alp, D. ; Challis, P. ; Chevalier, R. A. ; France, K. ; Kirshner, R. P. ; Lawrence, S. ; Leibundgut, B. ; Lundqvist, P. ; et al ( December 2019 , The Astrophysical Journal)