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加速・収束

磁場トポロジー磁化率

γ線フレア・粒子加速(衝撃波・磁気再結合) 多層構造

組成ローブHotspot

母銀河へのエネルギー輸送フィードバック

ジェットパワー/統一モデル- R-loud vs R-quiet?

- FR-I vs FR-II?

• The Transient Universe

• Donnarumma+ “SKA as a powerful hunter of jetted tidal disruption events”

• Yu+ “Early Phase Detection and Coverage of Extragalactic and Galactic Black Hole X-ray Transientswith SKA”

• The Continuum Universe• Smolcic+ “Exploring AGN Activity over Cosmic Time with the SKA”

• Alfonso+ “Identifying the first generation of radio powerful AGN in the Universe with the SKA”

• Gitti+ “The SKA view of cool-core clusters: evolution of radio mini-halos and AGN feedback”

• McAlpine+ “The SKA view of the Interplay between SF and AGN Activity and its role in Galaxy Evolution”

• Orienti+ “The physics of the radio emission in the quiet side of the AGN population with the SKA”

• Magnetism• Agudo+ “Studies of Relativistic Jets in Active Galactic Nuclei with SKA”

• Laing+ “Kinematics and Dynamics of kiloparsec-scale Jets in Radio Galaxies with SKA”

• Taylor+ “SKA Deep Polarization and Cosmic Magnetism”

• Synergies and Other Science• Paragi+ “Very Long Baseline Interferometry with the SKA”

• Giroletti+ “The connection between radio and high energy emission in black hole powered systems in the SKA era”

• Deane+ “Multiple supermassive black hole systems: SKA’s future leading role”

SKA-VLBI

) ) ( (

© 2018 Macmillan Publishers Limited, part of Springer Nature. All rights reserved. © 2018 Macmillan Publishers Limited, part of Springer Nature. All rights reserved.

PERSPECTIVE NATURE ASTRONOMY

from the nuclear source24,25. Imaging of AGN structures is also a key science subject of the EAVN and its precursor KaVA. The KaVA AGN Large Program is intensively monitoring two key sources, M87 and Sgr A*. The jet stream launched from and collimated close to the SMBH in the centre of M87, a supergiant elliptical galaxy in the constellation Virgo26, is observed on a biweekly basis at 22 and 43 GHz simultaneously. With the unprecedented high cadence and high-fidelity polarimetric VLBI images, the astronomers expect to get precise velocity field and spectral index evolution along and across the jet to constrain the magnetic field structure close to the jet launching site and related processes. At the border of the scat-ter-broadening regime of Sgr A* hosting a 4× 106 Mʘ SMBH in the centre of the Milky Way, KaVA provides the most sensitive images. These allow the radiation mechanism of the closest SMBH to be studied. The KVN by itself provides the unique astrometry of the frequency-dependent location of Sgr A*, and the KaVA AGN Large Program is producing the most sensitive milliarcsecond-resolution images of Sgr A* at 43 GHz. Other AGN studies obtained with the EAVN subarrays are related to imaging of compact nuclear structures and studies of jet physics27,28. Even higher sensitiv-ity with wider and agile frequency coverage of the EAVN enables

astronomers to probe a broader power range of AGNs, up to the highest redshifts in the early Universe29.

Star formation and stellar evolution in the nearby Universe. The discovery of astronomical masers in the microwave bands has encouraged VLBI studies, owing to their compact size and high brightness. Masers are often used as excellent probes to determine trigonometric distances to massive star-forming regions and evolved stars, to study the kinematics and magnetic fields of the interstel-lar and circumstellar environments around these regions30. High-accuracy radio astrometry of up to 100 water (H2O) maser sources with VERA, VLBA and EVN has made it possible to determine the dynamical structure of the Milky Way31,32. VERA with the JVN and Nobeyama Radio Observatory (NRO) have made progress on meth-anol (CH3OH) and silicon-monoxide (SiO) maser observations33,34. By linking the JVN to the Sheshan 25 m telescope, a large programme was conducted for measurement of internal proper motions of more than 30 methanol maser sources around young massive stars35. The KVN has operated a Key Science Program for simultaneous monitoring observations of circumstellar H2O and SiO masers at 22, 43, 86, and 129 GHz (http://radio.kasi.re.kr/kvn/ksp.php).

Nobeyama 45 m

KASI/KJCC

Kashima 34 m

Ogasawara 20 m

Iriki 20 m

Ishigakijima 20 m

Yamaguchi 32 m

Nanshan 26 m

Sejong 22 m

Hitachi 32 m

Mizusawa 20 m

Usuda 64 m

Gifu 11 m

Ulsan 21 m

Yonsei 21 m

6.7 GHz 8.4 GHz 22 GHz 43 GHz

FAST 500 m

SHAO/DIFX

Takahagi 32 m

Sheshan 25 m

Tianma 65 m

Miyun 50 m

Chinese

Korean

Japanese

Tamna 21 m

Kunming 40 m

The East Asia VLBI network

Fig. 1 | Geographic distribution of the EAVN telescopes and correlators. The EAVN can be flexibly operated using subarrays to support diverse science projects. The coloured circles show telescopes affiliated with each subarray. The small coloured dots above each telescope name indicate their available frequency bands. Note that only four common frequency bands (6.7, 8.4, 22 and 43 GHz) of the EAVN are marked here, but some individual telescopes have broader frequency coverage (see details in Table 2). Credit: Tamna 21 m and Yonsei 21 m, KASI; Sejong 22 m, NGII; KASI/KJCC and Ulsan 21 m, KASI; Mizusawa 20 m, VERA; Takahagi 32 m and Hitachi 32 m, Ibaraki University; Kashima 34 m, NICT; Ogasawara 20 m, VERA; Nobeyama 45 m, Nobeyama Radio Observatory; Usuda 64 m, JAXA; Gifu 11 m, Gifu University; Ishigakijima 20 m and Iriki 20 m, VERA; Yamaguchi 32 m, Yamaguchi University; FAST 500 m, NAOC; Kunming 40 m, SHAO/DIFX, Sheshan 25 m, Tianma 65 m, Miyun 50 m and Nanshan 26 m, CVN; background map, NASA.

NATURE ASTRONOMY | VOL 2 | FEBRUARY 2018 | 118–125 | www.nature.com/natureastronomy120

An, Sohn, Imai 2018

• B BTI N V A ( E L A

/ FG -F 5.3 6 GH EA /- 6

© 2018 Macmillan Publishers Limited, part of Springer Nature. All rights reserved. © 2018 Macmillan Publishers Limited, part of Springer Nature. All rights reserved.

PERSPECTIVE NATURE ASTRONOMY

from the nuclear source24,25. Imaging of AGN structures is also a key science subject of the EAVN and its precursor KaVA. The KaVA AGN Large Program is intensively monitoring two key sources, M87 and Sgr A*. The jet stream launched from and collimated close to the SMBH in the centre of M87, a supergiant elliptical galaxy in the constellation Virgo26, is observed on a biweekly basis at 22 and 43 GHz simultaneously. With the unprecedented high cadence and high-fidelity polarimetric VLBI images, the astronomers expect to get precise velocity field and spectral index evolution along and across the jet to constrain the magnetic field structure close to the jet launching site and related processes. At the border of the scat-ter-broadening regime of Sgr A* hosting a 4× 106 Mʘ SMBH in the centre of the Milky Way, KaVA provides the most sensitive images. These allow the radiation mechanism of the closest SMBH to be studied. The KVN by itself provides the unique astrometry of the frequency-dependent location of Sgr A*, and the KaVA AGN Large Program is producing the most sensitive milliarcsecond-resolution images of Sgr A* at 43 GHz. Other AGN studies obtained with the EAVN subarrays are related to imaging of compact nuclear structures and studies of jet physics27,28. Even higher sensitiv-ity with wider and agile frequency coverage of the EAVN enables

astronomers to probe a broader power range of AGNs, up to the highest redshifts in the early Universe29.

Star formation and stellar evolution in the nearby Universe. The discovery of astronomical masers in the microwave bands has encouraged VLBI studies, owing to their compact size and high brightness. Masers are often used as excellent probes to determine trigonometric distances to massive star-forming regions and evolved stars, to study the kinematics and magnetic fields of the interstel-lar and circumstellar environments around these regions30. High-accuracy radio astrometry of up to 100 water (H2O) maser sources with VERA, VLBA and EVN has made it possible to determine the dynamical structure of the Milky Way31,32. VERA with the JVN and Nobeyama Radio Observatory (NRO) have made progress on meth-anol (CH3OH) and silicon-monoxide (SiO) maser observations33,34. By linking the JVN to the Sheshan 25 m telescope, a large programme was conducted for measurement of internal proper motions of more than 30 methanol maser sources around young massive stars35. The KVN has operated a Key Science Program for simultaneous monitoring observations of circumstellar H2O and SiO masers at 22, 43, 86, and 129 GHz (http://radio.kasi.re.kr/kvn/ksp.php).

Nobeyama 45 m

KASI/KJCC

Kashima 34 m

Ogasawara 20 m

Iriki 20 m

Ishigakijima 20 m

Yamaguchi 32 m

Nanshan 26 m

Sejong 22 m

Hitachi 32 m

Mizusawa 20 m

Usuda 64 m

Gifu 11 m

Ulsan 21 m

Yonsei 21 m

6.7 GHz 8.4 GHz 22 GHz 43 GHz

FAST 500 m

SHAO/DIFX

Takahagi 32 m

Sheshan 25 m

Tianma 65 m

Miyun 50 m

Chinese

Korean

Japanese

Tamna 21 m

Kunming 40 m

The East Asia VLBI network

Fig. 1 | Geographic distribution of the EAVN telescopes and correlators. The EAVN can be flexibly operated using subarrays to support diverse science projects. The coloured circles show telescopes affiliated with each subarray. The small coloured dots above each telescope name indicate their available frequency bands. Note that only four common frequency bands (6.7, 8.4, 22 and 43 GHz) of the EAVN are marked here, but some individual telescopes have broader frequency coverage (see details in Table 2). Credit: Tamna 21 m and Yonsei 21 m, KASI; Sejong 22 m, NGII; KASI/KJCC and Ulsan 21 m, KASI; Mizusawa 20 m, VERA; Takahagi 32 m and Hitachi 32 m, Ibaraki University; Kashima 34 m, NICT; Ogasawara 20 m, VERA; Nobeyama 45 m, Nobeyama Radio Observatory; Usuda 64 m, JAXA; Gifu 11 m, Gifu University; Ishigakijima 20 m and Iriki 20 m, VERA; Yamaguchi 32 m, Yamaguchi University; FAST 500 m, NAOC; Kunming 40 m, SHAO/DIFX, Sheshan 25 m, Tianma 65 m, Miyun 50 m and Nanshan 26 m, CVN; background map, NASA.

NATURE ASTRONOMY | VOL 2 | FEBRUARY 2018 | 118–125 | www.nature.com/natureastronomy120

An, Sohn, Imai 2018

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2.4. Observational consequences

From the radio/X-ray correlation we can al-ready deduce which compact sources we can ex-pect to observe with the SKA at radio frequencies.

! XRBs: Compared with AGN all XRB are X-rayloud (up to a factor 108 more X-ray flux for agiven jet power), but relatively weak in the radioregime hence X-ray telescopes are better suitedfor low-mass black holes. However, as the radioflux can be relativistically beamed in somesources the SKA will allow us to observe thesesources not only in our Galaxy, but also innearby galaxies.

! AGN: With their large total jet power and highblack hole masses these sources can be radio-loud. Additional relativistic beaming allowsthe detection of AGN up to very high-redshifts.The SKA will boost AGN research, as it willallow to observe AGN of lower luminositiesand at larger distances.

! Intermediate mass black holes (IMBHs): If thisintriguing class of objects should exist it wouldlie in between AGN and XRBs on the radio/X-ray correlation. With new generation radio tele-scopes these objects should be visible in nearbygalaxies. As Maccarone (2004) points out,IMBHs in the center of globular clusters areeasier detected in the radio regime. Their X-ray luminosity would be further reduced as

low accretion rate systems might not start accel-erating relativistic particles (e.g. Sgr A* in itsquiescent state).

In Fig. 4 we show predicted radio core fluxesas a function of redshift for a range of radio coremodels at 5 GHz and for different masses andaccretion rates relative to the Eddington rate.The fluxes are predicted on the basis of Eq. (4)for an inclination angle of i = 50! and takingthe mass scaling into account as discussed in Fal-cke et al. (2004). The left figure corresponds to ablack hole similar to Sgr A* in the Milky Way(see, e.g., Melia and Falcke, 2001) and the rightone to a black hole in a massive elliptical galaxy.The bottom line on the left corresponds to theactivity level in Sgr Ajast, while the top one onthe right corresponds to a bright radio-loud qua-sar. Assuming that the SKA, after long integra-tion, can reach levels as low as 10 nJy, we seethat Sgr A*-like objects, i.e., essentially everysupermassive black hole in the local universe,can be detected out to 40 Mpc.

Quasar radio cores, on the other hand, canessentially be seen all the way out to redshifts ofz > 30. For a survey with detection limits around0.1 lJy we can even see black holes in normal gal-axies shining at the Eddington rate out to z . 8.Assuming that the formation of galaxies proceedsrapidly in the early phases of the universe at z > 10and black holes accrete at the Eddington limit, we

.M .M

Fig. 4. Predicted fluxes of radio cores in AGN observed at 5 GHz as a function of redshift for a range of Eddington accretion rates(solid lines from top to bottom) and two black hole masses: 3 · 106Mx (left) and 109Mx (right). An inclination angle of 50! isassumed, i.e. negligible beaming.

H. Falcke et al. / New Astronomy Reviews 48 (2004) 1157–1171 1163

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L40 S. Frey et al.: High-resolution double morphology of the most distant known radio quasar at z = 6.12

observations presented here was to reveal the radio structure ofJ1427+3312 on the linear scales of ∼10−100 pc. Assuming aflat cosmological model with H0 = 70 km s−1 Mpc−1, Ωm = 0.3,and ΩΛ = 0.7, the redshift z = 6.12 corresponds to 0.9 Gyr afterthe Big Bang (<7% of the present age of the Universe). In thismodel, 1 mas angular separation is equivalent to a linear separa-tion of 5.65 pc.

2. VLBI observations and data reduction

We observed J1427+3312 with the European VLBI Network(EVN) at 1.6 GHz on 11 March 2007 and at 5 GHz on3 March 2007. The observed frequencies correspond to∼11 GHzand ∼36 GHz in the rest frame of the quasar. The a-priori coor-dinates with nominal uncertainties of 520 mas and 390 mas inright ascension and declination, respectively, were taken fromCiliegi et al. (1999). At a recording rate of 1024 Mbit s−1,ten antennas of the EVN participated in the 7-h observations:Effelsberg (Germany), Hartebeesthoek (South Africa), JodrellBank Mk2 (UK), Medicina, Noto (Italy), Torun (Poland), Onsala(Sweden), Sheshan, Nanshan (PR China), and the phased arrayof the 14-element WSRT (The Netherlands). The data from thelatter array were analysed as well, providing us with simultane-ous measurements of the total flux density of the source at bothfrequencies. Eight intermediate frequency channels (IFs) wereused in both left and right circular polarisation. The total band-width was 128 MHz in both polarisations. The correlation of therecorded VLBI data took place later at the EVN Data Processorat the Joint Institute for VLBI in Europe (JIVE), Dwingeloo, TheNetherlands.

A mJy-level weak radio source, J1427+3312 was observedin phase-reference mode. This allowed us to increase the co-herent integration time spent on the target source and thus toimprove the sensitivity of the observations. Phase-referencinginvolves regularly interleaving observations between the targetsource and a nearby, bright, and compact reference source (e.g.Beasley & Conway 1995). The delay, delay rate, and phase so-lutions derived for the phase-reference calibrator were interpo-lated and applied to J1427+3312 within the target-reference cy-cle time of 7 min. The target source was observed for ∼4.5-minintervals in each cycle. The total observing time on J1427+3312was 3.2 h at both frequencies.

The phase-reference calibrator source we used wasJ1422+3223, a compact extragalactic radio source with 1.36 an-gular separation from J1427+3312. The J2000 right as-cension (α = 14h22m30.s378956) and declination (δ =+3223′10.′′44012) of the reference source in the InternationalCelestial Reference Frame (ICRF) are available from the VeryLong Baseline Array (VLBA) Calibrator Survey1. The posi-tional uncertainty is 0.49 mas.

The US National Radio Astronomy Observatory (NRAO)Astronomical Image Processing System (AIPS, e.g. Diamond1995) was used for the data calibration and imaging. The vis-ibility amplitudes were calibrated using system temperaturesregularly measured at the antennas. Fringe-fitting was per-formed for the calibrator and fringe-finder sources (J1422+3223,J1407+2827, and J1331+3030) using 3-min solution inter-vals. The data were exported to the Caltech Difmap package(Shepherd et al. 1994) for imaging. The conventional hybridmapping procedure, involving several iterations of CLEANingand phase (then amplitude) self-calibration, resulted in the im-ages and brightness distribution models for the calibrators.

1 http://www.vlba.nrao.edu/astro/calib/index.shtml

Dec

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Right Ascension (mas)20 10 0 -10 -20 -30

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20

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Fig. 1. The naturally weighted 1.6-GHz VLBI image of J1427+3312.The positive contour levels increase by a factor of

√2. The first con-

tours are drawn at −50 and 50 µJy/beam. The peak brightness is460 µJy/beam. The Gaussian restoring beam is 6.2 mas × 5.0 mas ata major axis position angle PA = 29. The coordinates are related to thebrightness peak of which the absolute position is given in the text.

Overall antenna gain correction factors (∼15% or less) were de-termined and applied to the visibility amplitudes in AIPS. Thenfringe-fitting was repeated in AIPS, now taking the clean com-ponent models of J1422+3223 into account. The residual phasecorrections that resulted from the non-pointlike structure of thephase-reference calibrator were considered this way. The solu-tions obtained were interpolated and applied to the target sourcedata. The visibility data of J1427+3312, unaveraged in time andfrequency, were also exported to Difmap for imaging. The nat-urally weighted images at 1.6 GHz (Fig. 1) and 5 GHz (Fig. 2)were made after several cycles of CLEANing in Difmap. Thelowest contours are drawn at ∼3σ image noise levels. The the-oretical thermal noise values were 10 and 12 µJy/beam (1σ) at1.6 GHz and 5 GHz, respectively.

3. Results and discussion

The source was clearly detected with the EVN at 1.6 GHz, show-ing a prominent double structure (Fig. 1). The two componentsare separated by 28.3 mas, corresponding to a projected lineardistance of ∼160 pc. Circular Gaussian brightness distributionmodel fitting in Difmap indicates that both components are re-solved (Table 1). The brightest one has 0.92 mJy flux densityand 5.8 mas angular size (full width at half maximum, FWHM),and the weaker and more extended one has 0.62 mJy flux den-sity and 18.6 mas angular size. In the position of the brightestcomponent at 1.6 GHz, we detected mas-scale radio emission at5 GHz as well (Fig. 2), fitted by a circular Gaussian model with0.46 mJy flux density and 3.2 mas angular size. The equatorialcoordinates of the brightness peak are αJ2000 = 14h27m38.s58563and δJ2000 = +3312′41.′′9252. The positional uncertainty is de-termined by the phase-reference calibrator source position accu-racy, the target-calibrator angular separation, the angular resolu-tion of the interferometer array, and the signal-to-noise ratio. In

予想されるSMBH電波コアフラックス(Falcke+2004)

• H F 2H ( ) M SaNGH V sM w

0 ? >

• 74- n + /-9 0-7 =A??AE B• S w ~w K

現在VLBIで検出された最遠方クエーサー

J1427+3312 (z=6.21)

160pc

[μJy]

0.1110

103102

104105

SKA1EAVNFASTEAVN

Frey+2008(EVN@1.6GHz)

• EAVNO .%1 ,SKA* +2"

• 6.7-43GHz: KC3X5=• ~1GHz: FAST9VLBIV>• PolarizationAD %/ETJ

• <7N!2#S8FHWAGN2 M54R$'?B+()$high-zP• ;ULI &,02, QK@G -

• SKA-JP 6SWG Y:• ?B, high-z, transients, ISM

© 2018 Macmillan Publishers Limited, part of Springer Nature. All rights reserved. © 2018 Macmillan Publishers Limited, part of Springer Nature. All rights reserved.

PERSPECTIVE NATURE ASTRONOMY

from the nuclear source24,25. Imaging of AGN structures is also a key science subject of the EAVN and its precursor KaVA. The KaVA AGN Large Program is intensively monitoring two key sources, M87 and Sgr A*. The jet stream launched from and collimated close to the SMBH in the centre of M87, a supergiant elliptical galaxy in the constellation Virgo26, is observed on a biweekly basis at 22 and 43 GHz simultaneously. With the unprecedented high cadence and high-fidelity polarimetric VLBI images, the astronomers expect to get precise velocity field and spectral index evolution along and across the jet to constrain the magnetic field structure close to the jet launching site and related processes. At the border of the scat-ter-broadening regime of Sgr A* hosting a 4× 106 Mʘ SMBH in the centre of the Milky Way, KaVA provides the most sensitive images. These allow the radiation mechanism of the closest SMBH to be studied. The KVN by itself provides the unique astrometry of the frequency-dependent location of Sgr A*, and the KaVA AGN Large Program is producing the most sensitive milliarcsecond-resolution images of Sgr A* at 43 GHz. Other AGN studies obtained with the EAVN subarrays are related to imaging of compact nuclear structures and studies of jet physics27,28. Even higher sensitiv-ity with wider and agile frequency coverage of the EAVN enables

astronomers to probe a broader power range of AGNs, up to the highest redshifts in the early Universe29.

Star formation and stellar evolution in the nearby Universe. The discovery of astronomical masers in the microwave bands has encouraged VLBI studies, owing to their compact size and high brightness. Masers are often used as excellent probes to determine trigonometric distances to massive star-forming regions and evolved stars, to study the kinematics and magnetic fields of the interstel-lar and circumstellar environments around these regions30. High-accuracy radio astrometry of up to 100 water (H2O) maser sources with VERA, VLBA and EVN has made it possible to determine the dynamical structure of the Milky Way31,32. VERA with the JVN and Nobeyama Radio Observatory (NRO) have made progress on meth-anol (CH3OH) and silicon-monoxide (SiO) maser observations33,34. By linking the JVN to the Sheshan 25 m telescope, a large programme was conducted for measurement of internal proper motions of more than 30 methanol maser sources around young massive stars35. The KVN has operated a Key Science Program for simultaneous monitoring observations of circumstellar H2O and SiO masers at 22, 43, 86, and 129 GHz (http://radio.kasi.re.kr/kvn/ksp.php).

Nobeyama 45 m

KASI/KJCC

Kashima 34 m

Ogasawara 20 m

Iriki 20 m

Ishigakijima 20 m

Yamaguchi 32 m

Nanshan 26 m

Sejong 22 m

Hitachi 32 m

Mizusawa 20 m

Usuda 64 m

Gifu 11 m

Ulsan 21 m

Yonsei 21 m

6.7 GHz 8.4 GHz 22 GHz 43 GHz

FAST 500 m

SHAO/DIFX

Takahagi 32 m

Sheshan 25 m

Tianma 65 m

Miyun 50 m

Chinese

Korean

Japanese

Tamna 21 m

Kunming 40 m

The East Asia VLBI network

Fig. 1 | Geographic distribution of the EAVN telescopes and correlators. The EAVN can be flexibly operated using subarrays to support diverse science projects. The coloured circles show telescopes affiliated with each subarray. The small coloured dots above each telescope name indicate their available frequency bands. Note that only four common frequency bands (6.7, 8.4, 22 and 43 GHz) of the EAVN are marked here, but some individual telescopes have broader frequency coverage (see details in Table 2). Credit: Tamna 21 m and Yonsei 21 m, KASI; Sejong 22 m, NGII; KASI/KJCC and Ulsan 21 m, KASI; Mizusawa 20 m, VERA; Takahagi 32 m and Hitachi 32 m, Ibaraki University; Kashima 34 m, NICT; Ogasawara 20 m, VERA; Nobeyama 45 m, Nobeyama Radio Observatory; Usuda 64 m, JAXA; Gifu 11 m, Gifu University; Ishigakijima 20 m and Iriki 20 m, VERA; Yamaguchi 32 m, Yamaguchi University; FAST 500 m, NAOC; Kunming 40 m, SHAO/DIFX, Sheshan 25 m, Tianma 65 m, Miyun 50 m and Nanshan 26 m, CVN; background map, NASA.

NATURE ASTRONOMY | VOL 2 | FEBRUARY 2018 | 118–125 | www.nature.com/natureastronomy120