| 11. |
- Akiyama, Kazunori, et al.
(author)
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First M87 Event Horizon Telescope Results. VI. The Shadow and Mass of the Central Black Hole
- 2019
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In: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8213 .- 2041-8205. ; 875:1
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Journal article (peer-reviewed)abstract
- We present measurements of the properties of the central radio source in M87 using Event Horizon Telescope data obtained during the 2017 campaign. We develop and fit geometric crescent models (asymmetric rings with interior brightness depressions) using two independent sampling algorithms that consider distinct representations of the visibility data. We show that the crescent family of models is statistically preferred over other comparably complex geometric models that we explore. We calibrate the geometric model parameters using general relativistic magnetohydrodynamic (GRMHD) models of the emission region and estimate physical properties of the source. We further fit images generated from GRMHD models directly to the data. We compare the derived emission region and black hole parameters from these analyses with those recovered from reconstructed images. There is a remarkable consistency among all methods and data sets. We find that >50% of the total flux at arcsecond scales comes from near the horizon, and that the emission is dramatically suppressed interior to this region by a factor >10, providing direct evidence of the predicted shadow of a black hole. Across all methods, we measure a crescent diameter of 42 +/- 3 mu as and constrain its fractional width to be
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| 12. |
- Ciroletti, M., et al.
(author)
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FRB 150418: clues to its nature from European VLBI Network and e-MERLIN observations
- 2016
-
In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 593, s. L16-L19
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Journal article (peer-reviewed)abstract
- Aims: We investigate the nature of the compact and possibly variable nuclear radio source in the centre of WISE J0716-19, the proposed host galaxy of the fast radio burst FRB 150418. Methods: We observed WISE J0716-19 at 5.0 GHz with the European VLBI Network (EVN) four times between 2016 March 16 and June 2. At three epochs, we simultaneously observed the source with e-MERLIN at the same frequency. Results: We detected a compact source in the EVN data in each epoch with a significance of up to ~8σ. The four epochs yielded consistent results within their uncertainties for the peak surface intensity and positions. The mean values for these quantities are Ipeak = (115 ± 9)μJy beam-1 and RA = 07h16m34.55496(7)s, Dec = -19°00'39.4754(8)''. The e-MERLIN data provided ~3-5σ detections at a position consistent with those of the EVN data. The emission on angular scales intermediate between the EVN and e-MERLIN is consistent with being null. The brightness temperature of the EVN core is Tb ≳ 108.5 K, close to the value previously required to explain the short-term radio variability properties of WISE J0716-19 in terms of interstellar scintillation. Conclusions: Our observations provide direct and independent evidence of a nuclear compact source in WISE J0716-19, a physical scenario without evident connection with FRB 150418. However, the EVN data do not indicate the variability observed with the VLA.
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| 13. |
- Marcote, B., et al.
(author)
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The origin of Fast Radio Bursts, still an open question
- 2016
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In: Proceedings of the 12th Scientific Meeting of the Spanish Astronomical Society - Highlights of Spanish Astrophysics IX, SEA 2016.
-
Conference paper (peer-reviewed)abstract
- FRB 150418 is the first Fast Radio Burst (FRB) with a proposed counterpart. Keane et al. (2016) claimed that the galaxy WISE J0716-19 is the host of this event. Such association would provide extremely important clues about the possible extragalactic origin of the FRBs. It is still a mystery what kind of events produces the FRBs. We observed the proposed host galaxy with the European VLBI Network (EVN) during four epochs at 5 GHz, revealing a compact and persistent radio source located in the center of the galaxy. These data, together with contemporaneous observations, strongly support the presence of an active galactic nuclei (AGN) in the galaxy with variability on short timescales due to refractive scintillation. Therefore, WISE J0716-19 would not be related with FRB 150418.
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| 14. |
- Porth, Oliver, et al.
(author)
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The Event Horizon General Relativistic Magnetohydrodynamic Code Comparison Project
- 2019
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In: Astrophysical Journal, Supplement Series. - : American Astronomical Society. - 1538-4365 .- 0067-0049. ; 243:2
-
Journal article (peer-reviewed)abstract
- Recent developments in compact object astrophysics, especially the discovery of merging neutron stars by LIGO, the imaging of the black hole in M87 by the Event Horizon Telescope, and high- precision astrometry of the Galactic Center at close to the event horizon scale by the GRAVITY experiment motivate the development of numerical source models that solve the equations of general relativistic magnetohydrodynamics (GRMHD). Here we compare GRMHD solutions for the evolution of a magnetized accretion flow where turbulence is promoted by the magnetorotational instability from a set of nine GRMHD codes: Athena++, BHAC, Cosmos++, ECHO, H-AMR, iharm3D, HARM-Noble, IllinoisGRMHD, and KORAL. Agreement among the codes improves as resolution increases, as measured by a consistently applied, specially developed set of code performance metrics. We conclude that the community of GRMHD codes is mature, capable, and consistent on these test problems.
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