A Deep Chandra X-Ray Study of Neutron Star Coalescence GW170817

By D. Haggard, M. Nynka, J. Ruan, Vicky Kalogera, S. Cenko, P. Evans, J. Kennea. 2017

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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 (∼10″ separation). Early Chandra ( days) and Swift ( 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 ( days). We detect X-ray emission from SSS17a with erg s−1, and a power law spectrum of . 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 ( 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.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/af496148b63c8b9999490e225d0e4a428624670a

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Citations in the corpus

• The evolution of the X-ray afterglow emission of GW 170817 / GRB 170817A in XMM-Newton observations (2018, background): “…in the X-ray and radio bands only at relatively late times (starting from ∼9 and 16 d after the GW/GRB trigger, respectively; Alexander et al. 2017; Haggard et al. 2017; Hallinan et al. 2017; Margutti et al. 2017; Troja et al. 2017a), while earlier Article published by EDP Sciences L1, page 1 of…”
• Long-term GRMHD simulations of neutron star merger accretion discs: implications for electromagnetic counterparts (2018, background): “The non-thermal emission from GW170817 can also be produced by a jet viewed off-axis, which has an angle-dependent Lorentz factor (a ‘structured jet’, e.g. Haggard et al. 2017; Lazzati et al. 2018; Margutti et al. 2018).”
• A Decline in the X-Ray through Radio Emission from GW170817 Continues to Support an Off-axis Structured Jet (2018, methodology): “G = - - +1 0.51x 0.27 0.26 is consistent with previously reported values (e.g., βx= −0.61± 0.17 at ∼160 days; Haggard et al. 2017; Margutti et al. 2017, 2018; Troja et al. 2017, 2018; Ruan et al. 2018).”
• Binary Neutron Star Mergers: Mass Ejection, Electromagnetic Counterparts, and Nucleosynthesis (2018, background): “Eleven hours after the detection of GW170817, a kilonova transient consistent with a binary NS merger was detected and intensively followed up for a few weeks (AT2017gfo; Abbott et al. 2017e; Arcavi et al. 2017; Coulter et al. 2017; Drout et al. 2017; Evans et al. 2017; Kasliwal et al. 2017; Nicholl”
• Constraints on the neutron star equation of state from AT2017gfo using radiative transfer simulations (2018, background): “…emitting from the X-ray to radio (Alexander et al. 2017; Chornock et al. 2017; Cowperthwaite et al. 2017; Drout et al. 2017; Evans et al. 2017; Haggard et al. 2017; Hallinan et al. 2017; Kasliwal et al. 2017; Kilpatrick et al. 2017; Margutti et al. 2017; McCully et al. 2017; Nicholl et al.…”
• Constraining the Maximum Mass of Neutron Stars from Multi-messenger Observations of GW170817 (2017, background): “The delayed rise of synchrotron X-ray and radio emission is consistent with the afterglow from a much more powerful relativistic jet pointed away from our line of sight (Troja et al. 2017; Hallinan et al. 2017; Margutti et al. 2017; Alexander et al. 2017; Evans et al. 2017; Haggard et al. 2017).”
• The Binary Neutron Star Event LIGO/Virgo GW170817 160 Days after Merger: Synchrotron Emission across the Electromagnetic Spectrum (2018, background): “Further CXO observations obtained at δt ≈ 9d (Troja et al. 2017b, observation ID 19294; PI: Troja; Program 18500489) and δt ≈ 15d (Haggard et al. 2017; Margutti et al. 2017a; Troja et al. 2017b, observation IDs 18988, 20728; PIs: Haggard, Troja; Programs 18400410,18508587) since merger revealed…”