Testing the expansion of the universe beyond z=2 with AGN: Presenting the record measurements of luminosity distance
Jeffrey Hodgson (Korea Astronomy and Space science Institute)
Until now, the only truly independent method of measuring distances at extra-galactic distances has been with Type 1a supernova. Baryonic Acouustic Oscillations (BAOs) have potential to extend to higher redshifts, but are currently limited by observations. In this talk I will present the preliminary results of standardizing AGN for use as a 'standard candle'. Currently, both BAOs and Type 1a supernova cannot extend much farther than z~1.5. In this talk, I will present the first model independent measure of the luminosity distance beyond redshift 2 and as high as redshift 3.2 and demonstrate the method. I will make the case for starting an observing program to extend the distance measures to z>6.
VLBI studies of radio-loud high redshift quasar
Tao An (Shanghai Astronomical Observatory) et al.
Radio-loud high-redshift quasars (RLHRQs), although only a few of them are known to date, are crucial for the studies of the growth of supermassive black holes (SMBHs) and the evolution of active galactic nuclei (AGN) at early cosmological epochs. Radio jets directly indicate the activity of SMBHs, and their radio structures can be studied with highest-resolution VLBI observations. Here we report our latest progress on RLHRQs and prospect the potential capability of EAVN in this study.
Young radio sources and the duty-cycle of the radio emission
Monica Orienti (INAF - IRA), D. Dallacasa, F. D'Ammando
It is currently accepted that intrinsically compact and bright radio sources characterized by a convex spectrum peaking at frequencies ranging from 100 MHz to a few GHz are young objects. Following the evolutionary models, these objects would evolve into the population of classical radio galaxies. However, the fraction of young radio sources in flux density-limited samples is much larger than expected from the number counts of large radio sources. This may suggest that additional ingredients, like the recurrence of the radio emission, or the interplay between the source and its environment, must be taken into account. The discovery of the young radio sources characterized by an uncommonly steep spectrum confirms that the radio emission may switch off shortly after its onset. In this talk I will present results on multi-frequency high-resolution radio observations of young radio sources and I will discuss implications on the evolutionary models of radio sources.
VLBI survey of the most compact AGNs: Core properties
Xiaopeng Cheng (Shanghai Astronomical Observatory), Tao An
We observed 134 AGNs at 43 GHz and 20 bright and compact AGNs at 86 GHz for the first time with the VLBA to enlarge and complete the database. Combining with the previous low frequency observations, we study the brightness temperatures of AGN cores in a statistical manner and explore the acceleration mechanism. We further study the compactness of the core and select suitable sources for future space mm-VLBI mission. The analysis results of the correlation between radio and γ-ray emissions is also present in our work.
Revealing the nature of blazar radio cores through multi-frequency polarization observations with KVN
Jongho Park (Seoul National University Korea), Sascha Trippe, Minchul Kam, Daewon Kim
We study linear polarization of the radio cores of 10 blazars at 22, 43, 86, and 129 GHz with 3 epochs observations of the Korean VLBI Network (KVN) from late 2016 to early 2017. We investigate Faraday rotation measure (RM) of the cores which is expected to increase with observing frequency if core positions are dependent on frequency due to synchrotron self-absorption. We find that many of our sources show systematic increase of RMs at higher observing frequencies indeed which can be described as power-laws with indices distributed around 2, indicating conically expanding outflows serving as Faraday rotating media. Comparing our KVN data with contemporaneous optical polarization data from the Steward Observatory for a few sources, we show an indication of the power-law increase of RM being saturated at a certain frequency. We claim that blazars core become fully transparent and no more core-shift effect is expected above that frequency, implying that we look at a standing recollimation shock as a radio core. We suggest that the Faraday screen for two sources, 3C 345 and CTA 102, might be external and a sub-relativistic sheath surrounding the relativistic jets is a promising candidate for the location of the observed RM but it is still unclear whether it is internal or external to the jets for other sources. We detect a sign change in the observed RMs of CTA 102 over 1 month, which might be related to a new superluminal component emerging from the core undergoing acceleration/deceleration and/or bending. We show that quasars tend to have higher core RM than BL Lac objects, which could be due to more matters in inflows/outflows in quasars. We relate the breaks in electric vector position angle (EVPA) rotations as a function of wavelength squared with polarized emission from one of the recollimation shocks in the core region being dominant in a short frequency range, with inner ones closer to the jet base becoming more dominant at higher frequencies.
Investigating the jet structure and its link with the location of the high-energy emitting region in radio-loud AGN
Filippo D'Ammando (INAF-IRA / Bologna University), M. Orienti, M. Giroletti
The location and mechanisms responsible for the high-energy emission and their connection to the jet structure are among the greatest challenges in the study of AGN. There is observational evidence supporting either a location of the gamma-ray emitting region close to the SMBH, or a site downstream along the jet, at parsec scale distance from the central engine. The emission in radio-loud AGN is explained either by single-zone models where radio and gamma-ray emission is produced by the same mechanism, like a shock, or by two-zone models, where radio and gamma-rays originate in different regions, like in a stratified jet. By analyzing high-resolution VLBI observations of gamma-ray emitting AGN, it is possible to discriminate between the models, either detecting superluminal components which are the manifestation of a propagating shock, or observing changes along the jet surface brightness, like the transition from edge-brightening to limb-brightening. In this talk, I will present recent results on multiwavelength campaigns of different kind of radio-loud AGN detected by Fermi-LAT.
The peculiar nuclear structure of 3C84
Gabriele Giovannini (INAF-IRA & Bologna University) et al.
I will present Space VLBI observations of 3C84 at 5 and 22 GHz. I will discuss nuclear properties of this source in comparison with previous high resolution VLBI images to discuss the jet properties and evolution.
Long-Term KVN and KaVA monitoring of 3C 84 at millimeter wavelengths
Kiyoaki Wajima (Korea Astronomy and Space Science Institute)
We conducted long-term VLBI monitoring of a nearby radio galaxy 3C 84 in 2015 and 2016, which is in an active phase at gamma-ray, to study properties of sub-pc-scale structure and the circumnuclear environment. We carried out multi-epoch KVN observations at 86 and 129 GHz, and monthly monitoring with KaVA at 43 GHz. Quasi-simultaneous 43 and 86 GHz observations revealed that the emission from the pc-scale northern lobe (N1) showed inverted spectral feature, which can be interpreted as the existence of sub-pc-scale plasma torus responsible for free-free absorption. On the other hand, we detected an abrupt flux increase of 3.7 times in eight months at 43 GHz in the peak intensity of the pc-scale southern lobe (C3). We also found that the beginning of the flux increase coincided with change in direction of motion of C3 from transversal to outward with respect to the core (C1) in 2015 October. We consider that those phenomena are possibly due to interaction of C3 with the sub-pc-scale plasma torus and the ambient medium.
Multi-frequency VLBI observations of Mrk 501 with KVN and VLBA
Guang-Yao Zhao (KASI)
TBD
On the time-variable rotation measure in the core region of Markarian 421
Rocco Lico (UniBO & IRA/INAF), Jose Luis Gomez, Keiichi Asada, Antonio Fuentes
In this talk we will discuss and interpret the time variable rotation measure (RM) observed in the core region of the TeV blazar Markarian 421 (Mrk 421). These results are based on a one-year, multi-frequency (15, 24, and 43 GHz) Very Long Baseline Array monitoring campaign. We explore the possible connection between the RM and the accretion rate and we investigate the Faraday screen properties and its location with respect to the jet emitting region. Among the various scenarios, the jet sheath is the most promising candidate for being the main source of Faraday rotation. We interpret the two RM sign reversals observed during the one-year monitoring within the context of the magnetic tower models. We invoke the presence of two nested helical magnetic fields in the relativistic jet with opposite helicities, whose relative contribution produce the observed RM values. Additional scenarios are considered to explain the observed RM time evolution.
Imaging and variability studies of CTA 102 during the 2016 January γ-ray flare
Xiaofeng Li (Shanghai Astronomical Observatory), Tao An, et al.
The blazar CTA~102 was imaged with the Very Long Baseline Array (VLBA) at 15 and 43 GHz during the 2016 January γ-ray flare. The current 15 GHz observations was conducted on 2016 January 25 and the 43 GHz data is from the monitoring program of bright γ-ray blazars of Boston University. The archival Fermi daily binned γ-ray light curve and Steward and Lick observatories based optical (R-band photometry, polarization degree and electric vector position angle, EVPA) light curves between 2015 June 1 and 2016 October 1 are present. The pc-scale jet indicates expansion with oscillatory features upto 17 mas. Component proper motions are in the range 0.03 - 0.48 mas yr^-1 with acceleration upto 1.2 mas then with a slowing down beyond 1.5 mas. The jet bulk Lorentz factor ≥ 25.4, position angle of 157.3°, inclination angle ≤ 4.5° and intrinsic half opening angle ≤ 1.5° are derived from the VLBA data. A core distance of 21.6 pc, and a magnetic field strength at 1 pc and the core location of 1.57 G and 0.07 G respectively are inferred using the core shift method. Application of a helical jet model to simulate optical flux density, polarization degree and EVPA variability and projected component trajectory suggest that helical signatures at the pc scales contribute to the observed variability.
Study of the TeV blazar Mrk 501 with mm-VLBI
Shoko Koyama (ASIAA)
To probe the innermost region of blazars, Mrk 501 is one of the best sources thanks to its proximity and brightness. We have performed 6-epoch astrometric observations to study the precise location of the radio core with the VLBA at 43 GHz during 2012-2013. Our results suggest a stable position of the core within 15 +/- 21 micro-arcseconds along the south-east jet direction, refining our earlier findings by VERA in 2011, which pinpointed the position within 200 micro-arcseconds. By using the different calibrator, we also found a stable position of the core within 24 +/- 28 micro-arcseconds toward the NE component, northeast of the core. From the stational positions of the radio core, we will further discuss the location of the jet origin. We also would like to talk about our observations performed with global VLBI at 43 GHz this year, and will be performed with EHT+ALMA in 2018.
KJCC and recent system development status
Se-Jin Oh (KASI), Jae-Hwan Yeom, Duk-Gyoo Roh, Dong-Kyu Jung, Hyo-Ryoung Kim, Chungsik Oh, Ju-Yeon Hwang, Jae-Sik Shin
KJCC (Korea-Japan Correlation Center) is now operating the DiFX SW correlator and Daejeon hardware correlator together. In VLBI, the correlator is very import equipment and should be focused on expand its functions to be served for users requests. In case of KaVA (KVN and VERA Array) and EAVN (East-Asian VLBI Network) observations, normal 1 Gbps and wideband such as over 2 Gbps observations are conducted and its correlations are conducted by Daejeon hardware correlator. And to support various data format, KJCC developed data format converter SWs. And recently new recorder over 8 Gbps was also developed. For wideband observation over 32 Gbps in KVN, RF-direct sampler named OCTAD was introduced and its commissioning work is performing to be used next 2018. In this talk, recent system development and KJCC status will be briefly discussed.
On the origin of the multi-band variability in the flat spectrum radio source 1633+382
Juan Carlos Algaba (SNU) and the iMOGABA collaboration
The flat spectrum radio quasar 1633+382 (4C 38.41) showed a significant increase of its radio flux density during the period 2012 March - 2015 August which correlates with γ-ray flaring activity. Multi-frequency simultaneous VLBI observations were conducted as part of the interferometric monitoring of gamma-ray bright active galactic nuclei (iMOGABA) program and supplemented with additional monitoring observations at various bands across the electromagnetic spectrum. The epochs of the maxima for the two largest gamma-ray flares coincide with the ejection of two respective new VLBI components and the evolution of the physical properties seem to be in agreement with the shock-in-jet model. Derived synchrotron self absorption magnetic fields, of the order of 0.1 mG, do not seem to dramatically change during the flares, and are much smaller, by a factor 10^4, than the estimated equipartition magnetic fields, indicating that the source of the flare may be associated with a particle dominated emitting region.
VLBI observation on M87
Keiichi Asada (ASIAA)
TBD
EATING VLBI observations in 2016/2017
Kazuhiro Hada (NAOJ)
I will talk about the two early but memorial EATING VLBI experiments: one we did with VERA+Italy in April 2016, and the other one performed in spring 2017 with a more complete form of EATING array. I wish to obtain some initial results before the meeting!
Investigation of LLAGN M81* up to 87 GHz
Wu Jiang (SHAO), Zhiqiang Shen, Mati-Vidal Ivan, Noriyuki Kawaguchi, Dongrong Jiang
TBD
Measuring the core shift of Sgr A*
Ilje Cho (KASI/UST), Bongwon Sohn, Taehyun Jung, Guang-Yao Zhao, Motoki Kino, Ivan Agudo, Maria Rioja, Richard Dodson
Sagittarius A* (Sgr A*), the supermassive black hole (SMBH) in our Galactic Center, is one of the best laboratories to study the origin of mm/sub-mm emission from SMBHs because it is only ~8 kpc away, resulting in a projected angular size of ∼10 uas corresponding to the Schwarzschild radius (r_Sch) of ~0.1 AU (Genzel et al. 2010). At present, a variety of observation and theoretical models converge on the fact that the mm/sub-mm radiation is emitted from a region within several r_Sch of the black hole. This region is thought to be the jet base of Sgr A* or a radiatively inefficient accretion flow (RIAF) (Falcke & Markoff 2000; Yuan et al. 2003) or a combination of both (Yuan et al. 2002).
In general, matter accretion onto a SMBH results in the launching of relativistic jets extending from sub-pc to Mpc scales in the most powerful cases. Sgr A* also shows some evidence of the outflow at pc scale (Yusef-Zadeh et al. 2012; Li et al. 2013), but it has never been detected at sub-pc scale, where the jet launching region is thought to lie.
In very long baseline interferometry (VLBI) observations, an optically thick surface (the photo-sphere) is shown as a radio core at a given observing frequency and moves toward the central SMBH with increasing frequency when the structure is elongated (e.g., conical jet), which is known as core shift effect (Blandford & Konigl 1979; Lobanov 1998). Therefore this is an important tool to constrain the emission models. In general, however, astrometric studies are difficult at high frequencies because the non-dispersive effect on the phase by the Earth’s atmosphere gets larger at higher frequencies.
The Korean VLBI Network (KVN) is one of the best VLBI arrays to study the core shift, thanks to its quasi-optics system at four frequencies (i.e., 22 ,43, 86 and 129 GHz) so that it enables to correct the phase of target frequency using a lower frequency phase solution, so called the frequency phase transfer (FPT). By applying the phase referencing with a combination of FPT, the so called source frequency phase referencing (SFPR), the relative astrometric measurements can be recovered (Rioja & Dodson, 2011). We conducted several observations for Sgr A* using KVN and found the positional shift of its center at different frequencies. We present our recent results of the Sgr A* core shift measurements and discussions to remove the residual positional uncertainties.
Searching for jets from M31* with VLBA and TianMa
Sijia Peng (Nanjing University), Zhiyuan Li, Zhiqiang Shen, Wu Jiang
The Andromeda galaxy (M31) hosts the second nearest super-massive black hole, known as M31*, which holds promise for providing physical insights beyond what has been learned from Sgr A*. We have conducted joint VLBA and TianMa 65-m 6 GHz observations in four epochs in 2016, aiming at detecting the putative radio jet from M31*. Signals were not detected on an RMS flux density level of ~ 5μJy/beam. This may suggest that either the jet is extended and thus resolved out, or the radio flux has experienced a substantial decrease during our observations, compared to the average flux level measured in out previous VLA observation.
Italy-Japan collaboration of high-mass star-formation studies
Tomoya Hirota (NAOJ), Luca Moscadelli, Riccardo Cesaroni, et al.
Since the last EATING VLBI workshop in 2014, we have started observational studies on H2O maser sources associated with high-mass young stellar objects using VERA common-use observations under collaboration between NAOJ and the Arcetri Observatory (Beltran et al. 2016). This year, we plan to organize colloquium and discussion session for high-mass star-formation studies at the Arcetri Observatory after the IAUS 336 on astrophysical masers. I will report current activities of collaboration between Italy and Japan for high-mass star-formation studies.
VLBI observations of microquasars: The case of Cyg X-3
Elise Egron (INAF-OAC), M. Giroletti, A. Pellizzoni, S. Righini, C. Migoni, A. Melis
Microquasars mimic quasars on much smaller scales. They spend most of their time in a dormant state and suddenly enter into periods of outburst activity. They represent ideal laboratories to study accretion-ejection processes, in particular thanks to VLBI observations. The KaVA and EAVN could represent key VLBI networks to better understand ejection processes in such sources. After more than 5 years of quiescence, the microquasar Cygnus X-3 underwent two giant radio flares in September 2016 and April 2017, reaching 13 and 17 Jy at 8.5 GHz, respectively. These very bright and spectacular radio events are clearly associated with the ultra-soft X-ray state and gamma-ray emission. We performed the first VLBI observations based on the Italian network (SRT, Medicina, Noto) and extended to European antennas during the 2016 mini-flare and the decay phases of the giant flare. The mini and short-lived flare was produced close to the core, with the indication of a slight increase of the source size. An observation performed 4 days after the peak of the 2016 giant flare allows us to infer constraints on the size and velocity of the jet. The jet emission was most likely extended over 30 mas with a jet knot velocity > 0.3c assuming a blob formation at the peak emission as suggested by the change in the spectral index we observed. We then triggered two EVN observations during the second giant flare of Cyg X-3 in April 2017. The data analysis is on-going. An extended structure is clearly observed at 5 GHz.
Sardinia Radio Telescope: Status, ongoing and future development
Andrea Melis (INAF-Osservatorio Astronomico di Cagliari), Carlo Migoni
TBD
A Compact Triple Band Receiver System for Millimeter Wave VLBI
Seog-Tae Han (Korea Astronomy and Space Science Institute)
A novel receiver optical system designed for KVN (Korean VLBI Network) has been used for conducting simultaneous millimeter-wave VLBI observations at frequencies of 22 GHz, 43 GHz, 86 GHz and 129 GHz. This multi-frequency band receiver system has been effective in compensation of atmospheric phase fluctuation by unique phase referencing technique in mm-VLBI observations. However, because the original optics system incorporated individual cryogenic receivers in separate cryostats, a rather bulky optical bench of size about 2600 mm x 2300 mm x 60 mm was required. To circumvent difficulties in installation and beam alignment, an integrated quasi-optical circuit incorporating a more compact triple-band receiver in single cryostat is proposed in this presentation. The recommended frequency bands of the improved triple-band receiver are K(18~26 GHz)-band, Q(35~50 GHz)-band, and W(85~115 GHz)-band. A frequency independent quasi-optical circuit for triple band is adopted to obtain constant aperture efficiency as a function of the observed frequencies. The simulation results show that total aperture efficiency of each recommended frequency band is maintained almost constant within 1 %. We present the design details of the compact wideband quasi-optical circuit and the triple-band receiver optimized for simultaneous observations.
mm-VLBI observation using a simultaneous multi-frequency VLBI receiving system and its prospects
Taehyun Jung (Korea Astronomy and Space Science Institute)
The Korean VLBI Network (KVN) has a unique receiver system that can perform simultaneous multi-frequency (i.e. 22, 43, 86 and 130 GHz) VLBI observations, which enables to calibrate tropospheric fluctuations effectively. For that, many observational demonstrations have been made by the KVN and now this system is extending to other VLBI telescopes. In 2015, two quasi optical systems for the simultaneous 22/43 GHz observations were installed at the Mizusawa and Iriki and carried out the first observation successfully. Other two radio telescopes of VERA (i.e., Ogasawara and Ishigaki-jima) will install this system and we will conduct full KaVA 22/43 GHz observation this year. In this talk, we present the results of the first simultaneous 22/43 GHz observing campaign of KaVA and discuss its prospects including EATING VLBI stations.
Italian status report
Marcello Giroletti (INAF Istituto di Radioastronomia)
TBD
KVN Status report (with recent EATING VLBI news) & KaVA observations of HFP candidates from the Deep X-ray Radio Blazar Survey
Bong Won Sohn (KASI), Franco Mantovani, Yongjin Jeong
X-ray observations provide a near complete selection of AGN with low contamination from non-AGN systems (Padovani et al. 2017). Among them, the Deep X-ray Radio Blazar Survey (DXRBS; Landt et al. 2001) sample is currently the faintest, down to ~ 50mJy at 5GHz and power ~ 10^24WHz-1 (Mantovani et al. 2011). From the follow up radio survey of Mantovani et al. (2011), sources with convex spectra have been found. We observed sub-sample of these sources with KaVA at 22 and 43GHz. We will present the preliminary results of the observations.