Host of neutron star merger detected as gravitational wave GW170817 and gamma-ray burst GRB 170817A
Other designations
NGC 4994, ESO 508-18, AM 1307-230, MCG -4-31-39, PGC 45657, WH III 766[4]
NGC 4993 starmap near ψ Hydrae, near galaxies of NGC 4968, NGC 4970, NGC 5042, IC 4180, IC 4197
NGC 4993 is the site of GW170817, the first astronomical event detected in both electromagnetic and gravitational radiation, the collision of two neutron stars, a discovery given the Breakthrough of the Year award for 2017 by the journal Science.[8][9] Detecting a gravitational wave event associated with the gamma-ray burst provided direct confirmation that binary neutron star collisions produce short gamma-ray bursts.[10]
Physical characteristics
NGC 4993 has several concentric shells of stars and large dust lane with diameter of approximately a few kiloparsecs which surrounds the nucleus and is stretched out into an "s" shape. The dust lane appears to be connected to a small dust ring with a diameter of ~330ly (0.1kpc).[11] These features in NGC 4993 may be the result[12] of a recent merger with a gaseous late-type galaxy that occurred about 400 million years ago.[13] However, Palmese et al. suggested that the galaxy involved in the merger was a gas-poor galaxy.[14]
Dark matter content
NGC 4993 has a dark matter halo with an estimated mass of 193.9×1010M☉.[13]
The luminosity of NGC 4993 indicates that the globular cluster system surrounding the galaxy may be dominated by metal-poor globular clusters.[15]
Supermassive black hole
NGC 4993 has a supermassive black hole with an estimated mass of roughly 80 to 100 million solar masses (8×107M☉).[16]
Galactic nucleus activity
The presence of weak O III, NII and SII emission lines in the nucleus of NGC 4993 and the relatively high ratio of [NII]λ6583/Hα suggest that NGC 4993 is a low-luminosity AGN (LLAGN).[16] The activity may have been triggered by gas from the late-type galaxy as it merged with NGC 4993.[13]
Neutron star merger observations
Main article: GW170817
In August 2017, rumors circulated[17] regarding a short gamma-ray burst designated GRB 170817A, of the type conjectured to be emitted in the collision of two neutron stars.[18] On 16October 2017, the LIGO and Virgo collaborations announced that they had detected a gravitational wave event, designated GW170817. The gravitational wave signal matched prediction for the merger of two neutron stars, two seconds before the gamma-ray burst. The gravitational wave signal, which had a duration of about 100seconds, was the first gravitational wave detection of the merger of two neutron stars.[1][19][20][21][22]
An optical transient, AT 2017gfo (also known as SSS17a), was detected in NGC4993 11hours after the gravitational wave and gamma-ray signals, allowing the location of the merger to be determined. The optical emission is thought to be due to a kilonova. The discovery of AT2017gfo was the first observation (and first localisation) of an electromagnetic counterpart to a gravitational wave source.[19][21][22][23][24]
GRB 170817A was a gamma-ray burst (GRB) detected by NASA's Fermi and ESA's INTEGRAL on 17August 2017.[17][25][26][27] Although only localized to a large area of the sky, it is believed to correspond to the other two observations,[23] in part due to its arrival time 1.7seconds after the GW event.
Hjorth, Jens; Levan, Andrew J.; Tanvir, Nial R.; Lyman, Joe D.; Wojtak, Radosław; Schrøder, Sophie L.; Mandel, Ilya; Gall, Christa; Bruun, Sofie H. (16 October 2017). "The Distance to NGC 4993: The Host Galaxy of the Gravitational-wave Event GW170817". The Astrophysical Journal. 848 (2): L31. arXiv:1710.05856. Bibcode:2017ApJ...848L..31H. doi:10.3847/2041-8213/aa9110. hdl:2381/41880. S2CID51812508.
Blanchard, P. K.; Berger, E.; Fong, W.; Nicholl, M.; Leja, J.; Conroy, C.; Alexander, K. D.; Margutti, R.; Williams, P. K. G. (16 October 2017). "The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/Virgo GW170817. VII. Properties of the Host Galaxy and Constraints on the Merger Timescale". The Astrophysical Journal. 848 (2): L22. arXiv:1710.05458. Bibcode:2017ApJ...848L..22B. doi:10.3847/2041-8213/aa9055. S2CID119336499.
Im, Myungshin; Yoon, Yongmin; Lee, Seong-Kook J.; Lee, Hyung Mok; Kim, Joonho; Lee, Chung-Uk; Kim, Seung-Lee; Troja, Eleonora; Choi, Changsu (26 October 2017). "Distance and Properties of NGC 4993 as the Host Galaxy of the Gravitational-wave Source GW170817". The Astrophysical Journal. 849 (1): L16. arXiv:1710.05861. Bibcode:2017ApJ...849L..16I. doi:10.3847/2041-8213/aa9367. S2CID55716501.
Ebrová, Ivana; Bílek, Michal (2020). "NGC 4993 the shell galaxy host of GW170817: constraints on the recent galactic merger". Astronomy & Astrophysics. 634: A73. arXiv:1801.01493. Bibcode:2020A&A...634A..73E. doi:10.1051/0004-6361/201935219. S2CID56354361.
Palmese, A.; Hartley, W.; Tarsitano, F.; Conselice, C.; Lahav, O.; Allam, S.; Annis, J.; Lin, H.; Soares-Santos, M. (9 November 2017). "Evidence for Dynamically Driven Formation of the GW170817 Neutron Star Binary in NGC 4993". The Astrophysical Journal. 849 (2): L34. arXiv:1710.06748. Bibcode:2017ApJ...849L..34P. doi:10.3847/2041-8213/aa9660. S2CID55049352.
Lee, Myung Gyoon; Kang, Jisu; Im, Myungshin (20 May 2018). "A Globular Cluster Luminosity Function Distance to NGC 4993 Hosting a Binary Neutron Star Merger GW170817/GRB 170817A". The Astrophysical Journal Letters. 859 (1): L6. arXiv:1805.01127. Bibcode:2018ApJ...859L...6L. doi:10.3847/2041-8213/aac2e9. S2CID73713875.
Wu, Qingwen; Feng, Jianchao; Fan, Xuliang (6 March 2018). "The Possible Submillimeter Bump and Accretion-jet in the Central Supermassive Black Hole of NGC 4993". The Astrophysical Journal. 855 (1): 46. arXiv:1710.09590. Bibcode:2018ApJ...855...46W. doi:10.3847/1538-4357/aaac28. S2CID89606053.
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