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The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/Virgo GW170817. V. Rising X-Ray Emission from an Off-axis Jet

The Astrophysical Journal Letters · 2017 · Vol. 848(2) · pp. L20–L20

R. Margutti✉(Northwestern University)E. Berger(Center for Astrophysics Harvard & Smithsonian)W. Fong(Northwestern University)C. Guidorzi(University of Ferrara)K. D. Alexander(Center for Astrophysics Harvard & Smithsonian)B. D. Metzger(Columbia University)P. K. Blanchard(Center for Astrophysics Harvard & Smithsonian)P. S. Cowperthwaite(Center for Astrophysics Harvard & Smithsonian)R. Chornock(Ohio University)T. Eftekhari(Center for Astrophysics Harvard & Smithsonian)M. Nicholl(Center for Astrophysics Harvard & Smithsonian)V. A. Villar(Center for Astrophysics Harvard & Smithsonian)P. K. G. Williams(Center for Astrophysics Harvard & Smithsonian)J. Annis(Fermi National Accelerator Laboratory)D. A. Brown(Syracuse University)H. Chen(University of Chicago)Z. Doctor(University of Chicago)J. A. Frieman(Fermi National Accelerator Laboratory)D. E. Holz(University of Chicago)M. Sako(University of Pennsylvania)M. Soares-Santos(Fermi National Accelerator Laboratory)

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Abstract

Abstract We report the discovery of rising X-ray emission from the binary neutron star merger event GW170817. This is the first detection of X-ray emission from a gravitational-wave (GW) source. Observations acquired with the Chandra X-ray Observatory ( CXO ) at <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>t</mml:mi> <mml:mo>≈</mml:mo> <mml:mn>2.3</mml:mn> </mml:math> days post-merger reveal no significant emission, with <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>L</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>x</mml:mi> </mml:mrow> </mml:msub> <mml:mo>≲</mml:mo> <mml:mn>3.2</mml:mn> <mml:mo>×</mml:mo> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>38</mml:mn> </mml:mrow> </mml:msup> <mml:mspace width="0.25em"/> <mml:mi>erg</mml:mi> <mml:mspace width="0.25em"/> <mml:msup> <mml:mrow> <mml:mi mathvariant="normal">s</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:math> (isotropic-equivalent). Continued monitoring revealed the presence of an X-ray source that brightened with time, reaching <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>L</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>x</mml:mi> </mml:mrow> </mml:msub> <mml:mo>≈</mml:mo> <mml:mn>9</mml:mn> <mml:mo>×</mml:mo> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>38</mml:mn> </mml:mrow> </mml:msup> <mml:mspace width="0.25em"/> <mml:mi>erg</mml:mi> <mml:mspace width="0.25em"/> <mml:msup> <mml:mrow> <mml:mi mathvariant="normal">s</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:math> at <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo>≈</mml:mo> <mml:mn>15.1</mml:mn> </mml:math> days post-merger. We interpret these findings in the context of isotropic and collimated relativistic outflows (both on- and off-axis). We find that the broadband X-ray to radio observations are consistent with emission from a relativistic jet with kinetic energy <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>E</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>k</mml:mi> </mml:mrow> </mml:msub> <mml:mo>∼</mml:mo> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>49</mml:mn> <mml:mo>−</mml:mo> <mml:mn>50</mml:mn> </mml:mrow> </mml:msup> <mml:mspace width="0.25em"/> <mml:mi>erg</mml:mi> </mml:math> , viewed off-axis with <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>θ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>obs</mml:mi> </mml:mrow> </mml:msub> <mml:mo>∼</mml:mo> <mml:mn>20</mml:mn> <mml:mo>°</mml:mo> <mml:mo>–</mml:mo> <mml:mn>40</mml:mn> <mml:mo>°</mml:mo> </mml:math> . Our models favor a circumbinary density <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>n</mml:mi> <mml:mo>∼</mml:mo> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>4</mml:mn> </mml:mrow> </mml:msup> <mml:mo>–</mml:mo> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> <mml:mspace width="0.25em"/> <mml:msup> <mml:mrow> <mml:mi>cm</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>3</mml:mn> </mml:mrow> </mml:msup> </mml:math> , depending on the value of the microphysical parameter <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>ϵ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>B</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow>

Gamma-ray bursts and supernovae Pulsars and Gravitational Waves Research Astrophysical Phenomena and ObservationsNeutron starJet (fluid)Context (archaeology)Collimated lightAstrophysical jetBinary numberEvent (particle physics)Neutron emissionKinetic energy