Abstract
We present the complete set of Hubble Space Telescope imaging of the binary neutron star merger GW170817 and its optical counterpart AT 2017gfo. Including deep template imaging in F814W, F110W, F140W, and F160W at 3.4 yr post-merger, we reanalyze the full light curve of AT 2017gfo across 12 bands from 5 to 1273 rest-frame days after merger. We obtain four new detections of the short γ-ray burst 170817A afterglow from 109 to 170 rest-frame days post-merger. These detections are consistent with the previously observed β = -0.6 spectral index in the afterglow light curve with no evidence for spectral evolution. We also analyze our limits in the context of kilonova afterglow or IR dust echo emission but find that our limits are not constraining for these models. We use the new data to construct deep optical and IR stacks, reaching limits of M = -6.3 to -4.6 mag, to analyze the local environment around AT 2017gfo and low surface brightness features in its host galaxy NGC 4993. We rule out the presence of any globular cluster at the position of AT 2017gfo to 2.3 × 104 L ⊙, including those with the reddest V - H colors. Finally, we analyze the substructure of NGC 4993 in deep residual imaging and find shell features that extend up to 71.″8 (14.2 kpc) from NGC 4993. The shells have a cumulative stellar mass of 6.3 × 108 M ⊙, roughly 2% of NGC 4993, and mass-weighted ages of >3 Gyr. We conclude that it was unlikely that the GW170817 progenitor system formed in the galaxy merger.
| Original language | English (US) |
|---|---|
| Article number | 49 |
| Journal | Astrophysical Journal |
| Volume | 926 |
| Issue number | 1 |
| DOIs | |
| State | Published - Feb 1 2022 |
Funding
We thank W. Lu for providing the IR dust echo models presented in this paper and Jay Strader for helpful discussions. Support for program No. 15886 was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. The Fong Group at Northwestern acknowledges support by the National Science Foundation under grant Nos. AST-1814782, AST-1909358, and CAREER grant No. AST-2047919. A.H. is partially supported by a Future Investigators in NASA Earth and Space Science and Technology (FINESST) award No. 80NSSC19K1422. Some of the data used in this paper were obtained from the Mikulski Archive for Space Telescopes (MAST), which is operated by NASA. These data come from programs GO-14270 (PI Levan), GO-14607 (PI Troja), GO-14771 (PI Tanvir), GO-14804 (PI Levan), SNAP-14840 (PI Bellini), GO-14850 (PI Troja), GO-15329 (PI Berger), GO-15346 (PI Kasliwal), GO-15482 (PI Lyman), and GO-15606 (Co-PIs Margutti and Fong). K.D.A. acknowledges support provided by NASA through the NASA Hubble Fellowship grant HST-HF2-51403.001 awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555.
ASJC Scopus subject areas
- Astronomy and Astrophysics
- Space and Planetary Science