Spitzer Space Telescope Infrared Observations of the Binary Neutron Star Merger GW170817

V.~A. Villar, P.~S. Cowperthwaite, E. Berger, P.~K. Blanchard, S. Gomez, K.~D. Alexander, R. Margutti, R. Chornock, T. Eftekhari, G.~G. Fazio, J. Guillochon, J.~L. Hora, M. Nicholl, P.~K.~G. Williams

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We present Spitzer Space Telescope 3.6 and 4.5 μm observations of the binary neutron star merger GW170817 at 43, 74, and 264 days post-merger. Using the final observation as a template, we uncover a source at the position of GW170817 at 4.5 μm with a brightness of 22.9 ± 0.3 AB mag at 43 days and 23.8 ± 0.3 AB mag at 74 days (the uncertainty is dominated by systematics from the image subtraction); no obvious source is detected at 3.6 μm to a 3σ limit of >23.3 AB mag in both epochs. The measured brightness is dimmer by a factor of about 2–3 times compared to our previously published kilonova model, which is based on UV, optical, and near-infrared data at ≲30 days. However, the observed fading rate and color (m3.6–m4.5 ≳ 0 AB mag) are consistent with our model. We suggest that the discrepancy is likely due to a transition to the nebular phase, or a reduced thermalization efficiency at such late time. Using the Spitzer data as a guide, we briefly discuss the prospects of observing future binary neutron star mergers with Spitzer (in the Laser Interferometer Gravitational-Wave Observatory (LIGO)/Virgo Observing Run 3) and the James Webb Space Telescope (in LIGO/Virgo Observing Run 4 and beyond).
Original languageEnglish
Pages (from-to)L11
JournalThe Astrophysical Journal Letters
Issue number1
Publication statusPublished - 1 Jul 2018


  • gravitational waves
  • infrared: general
  • stars: neutron
  • Astrophysics - High Energy Astrophysical Phenomena


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