Late Engine Activity in Neutron Star Mergers and Its Cocoon: An Alternative Scenario for the Blue Kilonova
Follow-up observations of short gamma-ray bursts (sGRBs) have continuously unveiled late extended/plateau emissions, attributed to jet launch due to late engine activity, the nature of which remains enigmatic. Observations of GW170817 have confirmed that sGRBs are linked to neutron star (NS) mergers...
| Main Authors: | , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
IOP Publishing
2024-01-01
|
| Series: | The Astrophysical Journal |
| Subjects: | |
| Online Access: | https://doi.org/10.3847/1538-4357/ad20d0 |
| _version_ | 1797271089586372608 |
|---|---|
| author | Hamid Hamidani Shigeo S. Kimura Masaomi Tanaka Kunihito Ioka |
| author_facet | Hamid Hamidani Shigeo S. Kimura Masaomi Tanaka Kunihito Ioka |
| author_sort | Hamid Hamidani |
| collection | DOAJ |
| description | Follow-up observations of short gamma-ray bursts (sGRBs) have continuously unveiled late extended/plateau emissions, attributed to jet launch due to late engine activity, the nature of which remains enigmatic. Observations of GW170817 have confirmed that sGRBs are linked to neutron star (NS) mergers, and discovered a kilonova (KN) transient. Nevertheless, the origin of the early blue KN in GW170817 remains unclear. Here, we investigate the propagation of late jets in the merger ejecta. By analytically modeling jet dynamics, we determine the properties of the jet-heated cocoon, and estimate its cooling emission. Our results reveal that late jets generate significantly brighter cocoons compared to prompt jets, primarily due to reduced energy loss by adiabatic cooling. Notably, with typical late jets, emission from the cocoon trapped inside the ejecta can reproduce the blue KN emission. We estimate that the forthcoming Einstein Probe mission will detect the early cocoon emission at a rate of $\sim {2.1}_{-1.6}^{+3.2}$ yr ^−1 , and that optical/UV follow-ups in the LIGO-Virgo-KAGRA O5 run will be able to detect $\sim {1.0}_{-0.7}^{+1.5}$ cocoon emission events. As an electromagnetic counterpart, this emission provides an independent tool to probe NS mergers in the Universe, complementing insights from sGRBs and gravitational waves. |
| first_indexed | 2024-04-25T02:14:37Z |
| format | Article |
| id | doaj.art-18d2a224288d4202989066e81da5ca99 |
| institution | Directory Open Access Journal |
| issn | 1538-4357 |
| language | English |
| last_indexed | 2024-04-25T02:14:37Z |
| publishDate | 2024-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | The Astrophysical Journal |
| spelling | doaj.art-18d2a224288d4202989066e81da5ca992024-03-07T10:03:09ZengIOP PublishingThe Astrophysical Journal1538-43572024-01-01963213710.3847/1538-4357/ad20d0Late Engine Activity in Neutron Star Mergers and Its Cocoon: An Alternative Scenario for the Blue KilonovaHamid Hamidani0https://orcid.org/0000-0003-2866-4522Shigeo S. Kimura1https://orcid.org/0000-0003-2579-7266Masaomi Tanaka2https://orcid.org/0000-0001-8253-6850Kunihito Ioka3https://orcid.org/0000-0002-3517-1956Astronomical Institute, Graduate School of Science, Tohoku University , Sendai 980-8578, Japan ; hhamidani@astr.tohoku.ac.jpAstronomical Institute, Graduate School of Science, Tohoku University , Sendai 980-8578, Japan ; hhamidani@astr.tohoku.ac.jp; Frontier Research Institute for Interdisciplinary Sciences, Tohoku University , Sendai 980-8578, JapanAstronomical Institute, Graduate School of Science, Tohoku University , Sendai 980-8578, Japan ; hhamidani@astr.tohoku.ac.jpYukawa Institute for Theoretical Physics, Kyoto University , Kyoto 606-8502, JapanFollow-up observations of short gamma-ray bursts (sGRBs) have continuously unveiled late extended/plateau emissions, attributed to jet launch due to late engine activity, the nature of which remains enigmatic. Observations of GW170817 have confirmed that sGRBs are linked to neutron star (NS) mergers, and discovered a kilonova (KN) transient. Nevertheless, the origin of the early blue KN in GW170817 remains unclear. Here, we investigate the propagation of late jets in the merger ejecta. By analytically modeling jet dynamics, we determine the properties of the jet-heated cocoon, and estimate its cooling emission. Our results reveal that late jets generate significantly brighter cocoons compared to prompt jets, primarily due to reduced energy loss by adiabatic cooling. Notably, with typical late jets, emission from the cocoon trapped inside the ejecta can reproduce the blue KN emission. We estimate that the forthcoming Einstein Probe mission will detect the early cocoon emission at a rate of $\sim {2.1}_{-1.6}^{+3.2}$ yr ^−1 , and that optical/UV follow-ups in the LIGO-Virgo-KAGRA O5 run will be able to detect $\sim {1.0}_{-0.7}^{+1.5}$ cocoon emission events. As an electromagnetic counterpart, this emission provides an independent tool to probe NS mergers in the Universe, complementing insights from sGRBs and gravitational waves.https://doi.org/10.3847/1538-4357/ad20d0Gamma-ray burstsNeutron starsHydrodynamicsRelativistic fluid dynamicsRelativistic jetsGravitational waves |
| spellingShingle | Hamid Hamidani Shigeo S. Kimura Masaomi Tanaka Kunihito Ioka Late Engine Activity in Neutron Star Mergers and Its Cocoon: An Alternative Scenario for the Blue Kilonova The Astrophysical Journal Gamma-ray bursts Neutron stars Hydrodynamics Relativistic fluid dynamics Relativistic jets Gravitational waves |
| title | Late Engine Activity in Neutron Star Mergers and Its Cocoon: An Alternative Scenario for the Blue Kilonova |
| title_full | Late Engine Activity in Neutron Star Mergers and Its Cocoon: An Alternative Scenario for the Blue Kilonova |
| title_fullStr | Late Engine Activity in Neutron Star Mergers and Its Cocoon: An Alternative Scenario for the Blue Kilonova |
| title_full_unstemmed | Late Engine Activity in Neutron Star Mergers and Its Cocoon: An Alternative Scenario for the Blue Kilonova |
| title_short | Late Engine Activity in Neutron Star Mergers and Its Cocoon: An Alternative Scenario for the Blue Kilonova |
| title_sort | late engine activity in neutron star mergers and its cocoon an alternative scenario for the blue kilonova |
| topic | Gamma-ray bursts Neutron stars Hydrodynamics Relativistic fluid dynamics Relativistic jets Gravitational waves |
| url | https://doi.org/10.3847/1538-4357/ad20d0 |
| work_keys_str_mv | AT hamidhamidani lateengineactivityinneutronstarmergersanditscocoonanalternativescenarioforthebluekilonova AT shigeoskimura lateengineactivityinneutronstarmergersanditscocoonanalternativescenarioforthebluekilonova AT masaomitanaka lateengineactivityinneutronstarmergersanditscocoonanalternativescenarioforthebluekilonova AT kunihitoioka lateengineactivityinneutronstarmergersanditscocoonanalternativescenarioforthebluekilonova |