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

Here, 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 $$t\approx 2.3$$ days post-merger reveal no significant emission, with $${L}_{x}\lesssim 3.2\times {10}^{38}\,\mathrm{erg}\,{{\rm{s}}}^{-1}$$ (isotropic-equivalent). Continued monitoring revealed the presence of an X-ray source that brightened with time, reaching $${L}_{x}\approx 9\times {10}^{38}\,\mathrm{erg}\,{{\rm{s}}}^{-1}$$ at $$\approx 15.1$$ 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 $${E}_{k}\sim {10}^{49-50}\,\mathrm{erg}$$, viewed off-axis with $${\theta }_{\mathrm{obs}}\sim 20^\circ \mbox{--}40^\circ $$. Our models favor a circumbinary density $$n\sim {10}^{-4}\mbox{--}{10}^{-2}\,{\mathrm{cm}}^{-3}$$, depending on the value of the microphysical parameter $${\epsilon }_{B}={10}^{-4}\mbox{--}{10}^{-2}$$. A central-engine origin of the X-ray emission is unlikely. Future X-ray observations at $$t\gtrsim 100$$ days, when the target will be observable again with the CXO, will provide additional constraints to solve the model degeneracies and test our predictions. Our inferences on $${\theta }_{\mathrm{obs}}$$ are testable with GW information on GW170817 from advanced LIGO/Virgo on the binary inclination.
Authors:
ORCiD logo [1] ;  [2] ;  [1] ;  [3] ;  [2] ;  [4] ;  [2] ;  [2] ;  [5] ;  [2] ;  [2] ;  [2] ;  [2] ;  [6] ;  [7] ;  [8] ;  [8] ;  [9] ;  [8] ;  [10] more »;  [11] « less
  1. Northwestern Univ., Evanston, IL (United States)
  2. Harvard-Smithsonian Center for Astrophysics, Cambridge, MA (United States)
  3. Univ. of Ferrara, Ferrara (Italy)
  4. Columbia Univ., New York, NY (United States)
  5. Ohio Univ., Athens, OH (United States)
  6. Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
  7. Syracuse Univ., Syracuse, NY (United States)
  8. Univ. of Chicago, Chicago, IL (United States)
  9. Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Univ. of Chicago, Chicago, IL (United States)
  10. Univ. of Pennsylvania, Philadelphia, PA (United States)
  11. Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Brandeis Univ., Waltham, MA (United States)
Publication Date:
Report Number(s):
arXiv:1710.05431; FERMILAB-PUB-17-499-A-AE-CD
Journal ID: ISSN 2041-8213; 1630774; TRN: US1702935
Grant/Contract Number:
AC02-07CH11359
Type:
Accepted Manuscript
Journal Name:
The Astrophysical Journal. Letters
Additional Journal Information:
Journal Volume: 848; Journal Issue: 2; Journal ID: ISSN 2041-8213
Publisher:
Institute of Physics (IOP)
Research Org:
Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
Sponsoring Org:
USDOE Office of Science (SC), High Energy Physics (HEP) (SC-25)
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; stars: neutron; gravitational waves; relativistic processes
OSTI Identifier:
1408215

Margutti, Raffaella, Berger, E., Fong, W., Guidorzi, C., Alexander, K. D., Metzger, B. D., Blanchard, P. K., Cowperthwaite, P. S., Chornock, R., Eftekhari, T., Nicholl, M., Villar, V. A., Williams, P. K. G., Annis, J., Brown, D. A., Chen, H., Doctor, Z., Frieman, J. A., Holz, D. E., Sako, M., and Soares-Santos, M.. The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/Virgo GW170817. V. Rising X-Ray Emission from an Off-axis Jet. United States: N. p., Web. doi:10.3847/2041-8213/aa9057.
Margutti, Raffaella, Berger, E., Fong, W., Guidorzi, C., Alexander, K. D., Metzger, B. D., Blanchard, P. K., Cowperthwaite, P. S., Chornock, R., Eftekhari, T., Nicholl, M., Villar, V. A., Williams, P. K. G., Annis, J., Brown, D. A., Chen, H., Doctor, Z., Frieman, J. A., Holz, D. E., Sako, M., & Soares-Santos, M.. The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/Virgo GW170817. V. Rising X-Ray Emission from an Off-axis Jet. United States. doi:10.3847/2041-8213/aa9057.
Margutti, Raffaella, Berger, E., Fong, W., Guidorzi, C., Alexander, K. D., Metzger, B. D., Blanchard, P. K., Cowperthwaite, P. S., Chornock, R., Eftekhari, T., Nicholl, M., Villar, V. A., Williams, P. K. G., Annis, J., Brown, D. A., Chen, H., Doctor, Z., Frieman, J. A., Holz, D. E., Sako, M., and Soares-Santos, M.. 2017. "The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/Virgo GW170817. V. Rising X-Ray Emission from an Off-axis Jet". United States. doi:10.3847/2041-8213/aa9057. https://www.osti.gov/servlets/purl/1408215.
@article{osti_1408215,
title = {The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/Virgo GW170817. V. Rising X-Ray Emission from an Off-axis Jet},
author = {Margutti, Raffaella and Berger, E. and Fong, W. and Guidorzi, C. and Alexander, K. D. and Metzger, B. D. and Blanchard, P. K. and Cowperthwaite, P. S. and Chornock, R. and Eftekhari, T. and Nicholl, M. and Villar, V. A. and Williams, P. K. G. and Annis, J. and Brown, D. A. and Chen, H. and Doctor, Z. and Frieman, J. A. and Holz, D. E. and Sako, M. and Soares-Santos, M.},
abstractNote = {Here, 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 $t\approx 2.3$ days post-merger reveal no significant emission, with ${L}_{x}\lesssim 3.2\times {10}^{38}\,\mathrm{erg}\,{{\rm{s}}}^{-1}$ (isotropic-equivalent). Continued monitoring revealed the presence of an X-ray source that brightened with time, reaching ${L}_{x}\approx 9\times {10}^{38}\,\mathrm{erg}\,{{\rm{s}}}^{-1}$ at $\approx 15.1$ 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 ${E}_{k}\sim {10}^{49-50}\,\mathrm{erg}$, viewed off-axis with ${\theta }_{\mathrm{obs}}\sim 20^\circ \mbox{--}40^\circ $. Our models favor a circumbinary density $n\sim {10}^{-4}\mbox{--}{10}^{-2}\,{\mathrm{cm}}^{-3}$, depending on the value of the microphysical parameter ${\epsilon }_{B}={10}^{-4}\mbox{--}{10}^{-2}$. A central-engine origin of the X-ray emission is unlikely. Future X-ray observations at $t\gtrsim 100$ days, when the target will be observable again with the CXO, will provide additional constraints to solve the model degeneracies and test our predictions. Our inferences on ${\theta }_{\mathrm{obs}}$ are testable with GW information on GW170817 from advanced LIGO/Virgo on the binary inclination.},
doi = {10.3847/2041-8213/aa9057},
journal = {The Astrophysical Journal. Letters},
number = 2,
volume = 848,
place = {United States},
year = {2017},
month = {10}
}