A deep chandra X-Ray study of neutron star coalescence GW170817

Daryl Haggard, Melania Nynka, John J. Ruan, Vicky Kalogera, S. Bradley Cenko, Phil Evans, Jamie A. Kennea

Research output: Contribution to journalArticlepeer-review


We report Chandra observations of GW170817, the first neutron star–neutron star merger discovered by the joint LIGO-Virgo Collaboration, and the first direct detection of gravitational radiation associated with an electromagnetic counterpart, Fermi short γ-ray burst GRB 170817A. The event occurred on 2017 August 17 and subsequent observations identified an optical counterpart, SSS17a, coincident with NGC 4993 (∼1000 separation). Early Chandra (∆t ∼ 2 days) and Swift (∆t ∼ 1 − 3 days) observations yielded non-detections at the optical position, but ∼9 days post-trigger Chandra monitoring revealed an X-ray point source coincident with SSS17a. We present two deep Chandra observations totaling ∼95 ks, collected on 2017 September 01–02 (∆t ∼ 15 − 16 days). We detect X-ray emission from SSS17a with L0.3−10keV = 2.6+00..54 ×1038 erg s−1, and a power law spectrum of Γ = 2.4 ±0.8. We find that the X-ray light curve from a binary NS coalescence associated with this source is consistent with the afterglow from an off-axis short γ-ray burst, with a jet angled &23 from the line of sight. This event marks both the first electromagnetic counterpart to a LIGO-Virgo gravitational-wave source and the first identification of an off-axis short GRB. We also confirm extended X-ray emission from NGC 4993 (L0.3−10keV ∼ 9 × 1038 erg s−1) consistent with its E/S0 galaxy classification, and report two new Chandra point sources in this field, CXOU J130948 and CXOU J130946. Keywords: gravitational waves: individual (GW170817); gamma-ray burst: individual (GRB 170817A); stars: neutron; galaxies: individual (NGC 4993); X-rays: binaries

Original languageEnglish (US)
JournalUnknown Journal
StatePublished - Oct 16 2017

ASJC Scopus subject areas

  • General

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