The KVN now enters into the full fledged stage for its scientific use as a millimeter-wave VLBI array. The KVN Key Science Program (KSP) has been designed to look for unique science demonstrating the characteristics and advantages of the KVN system. The KVN KSP proposals can be submitted through the same procedure as other normal proposals, but will be selected in the special selection committee based on the following criteria: The KSP should aim at a clear scientific goal, which may manifest the strength and power of KVN. The KSP is recommended to request less than 300 hours of observing time a year (for up to about 3 years), and it should not be a combination of small programs. The proposers of the KSP may be requested to present the proposal in the committee. The KSP is open to all researchers working in Korea, and the KVN team will assist fully for the success of the accepted KSP proposals. As of 2015 March, there are two KVN KPSs selected through KSP selection committee as follows:
Simultaneous Monitoring of KVN 4 Bands toward Evolved Stars
PI: Cho, Se-Hyung
Origins of Gamma-ray Flares in Active Galactic Nuclei
PI: Lee, Sang-Sung
The Plasma-physics of Active Galactic Nuclei (PAGaN)
PI: Trippe, Sascha
Using the characteristics of the KVN 4 band receiving system, we set up following scientific goals.
(1) We aim at investigating spatial structures and dynamical effects from SiO to 22 GHz H2O maser regions (i. e., atmosphere to circumstellar envelope) according to stellar pulsation through simultaneous monitoring observations of KVN 4 bands using both KVN single dish and VLBI network. The SiO maser lines, due to their high excitation temperature and density, are suitable for investigating nearby regions of central star which are under accelerating and decelerating by the influence of a stellar pulsation. On the other hand, 22 GHz H2O maser traces the region above dust forming layer in which outflow velocities approach to a terminal velocity of mass-loss. Therefore, both masers are good probes for investigating the development of outflow motion and asymmetry from the atmosphere to the circumstellar envelope. Furthermore, we can investigate the shock propagation effect from SiO to H2O maser regions because both masers are affected by shock waves. These works will lead us to understand how the mass-loss process is connected to stellar pulsation.
(2) Mutual association and difference between SiO and H2O maser properties are also investigated based on combined studies of SiO and H2O masers for a basis. In the last analysis, SiO and H2O maser models coupled to hydrodynamical model of circumstellar envelope should be established.
(3) We trace correlation and difference of SiO maser properties including spatio-kinematic properties among SiO J = 1-0, J = 2-1, and J = 3-2 transition masers according to different type of stars (for example, H2O strong, weak and non-detected sources, SiO v = 2, J = 2-1 rare maser detected sources). Our goal is to constrain SiO maser pumping models which are still under debate between collisional and radiative pumping models including the effects of line overlap between the ro-vibrational transitions of SiO and H2O.
(4) Through the development of outflow motion and asymmetry from SiO to H2O maser regions in individual stars at different evolutionary stages, we want to find a clue to the dynamical evolution from AGB to post-AGB stars connected to the development process of asymmetric mass-loss, for example, bipolar outflow and water fountain jet motions. In parallel, we make an effort to examine the cause of large detection rates of SiO v= 2, J = 1-0 only maser emission at late AGB evolutionary stage and different detection rates between SiO and H2O masers in post-AGB RI and LI regions which are obtained from the KVN single dish results.
Using both KVN single dish and VLBI network, we perform regular monitoring of H2O 22 GHz / SiO 43/86/129 GHz bands toward 15 objects of KSP (every one-two months according to their periods). Three years as the first term of KSP are required for covering at least 2 pulsation periods of 15 sources. Single dish monitoring observations at 4 bands go on being performed toward 15 objects for grasping the global features of SiO and H2O masers and for reciprocally complemented researches with VLBI. Total integration time for each target source is required for about 5 hours in order to obtain a sufficient (u, v) coverage for a good quality imaging. Therefore, we need ~350 hrs per year for VLBI monitoring and ~100 hrs for single dish monitoring. Source Frequency Phase Referencing (SFPR) technique will be adopted for registering both H2O and SiO masers using the KVN 4-bands receiving system for simultaneous observations at different bands.
Note: These sources were selected from KVN single dish and VLBI feasibility test observations. R Cas is a spare candidate source. S.A. is the angular separations from maser sources.
|Se-Hyung Cho (P.I)||firstname.lastname@example.org||Korea Astronomy & Space Science Institute (KASI)|
|Yoon Kyung Choiemail@example.com||KASI|
|Dong-Hwan Yoonfirstname.lastname@example.org||SNU/KASI (Doctor course)|
|Dong-Jin Kimemail@example.com||Yonsei Univ/KASI (Master course)|
|Richard Dodsonfirstname.lastname@example.org||ICRAR (Australia)|
|Maria Riojaemail@example.com||OAN (Spain)|
|Hiroshi Imaifirstname.lastname@example.org||Kagoshima Univ.(Japan)|
Welcome to join KVN Evolved Star KSP. The fields are observations, pipeline post-correlation data processing (~AIPS/ParselTongue scripts), database for calibration visibilities and image cubes, scientific analyses, theoretical model fit for KVN H2O and SiO maser data etc. Please contact P. I. Se-Hyung Cho (email@example.com).
KVN Single Dish Surveys and Monitoring Observations
At the first stage of KVN single dish operation, we have carried out simultaneous surveys of SiO and H2O masers toward 166 evolved stars which are known as both SiO and H2O maser sources. We detected both SiO and H2O masers from 112 stars at one epoch (Kim et al. 2010, Paper I). As the second and third surveys, we have carried out those observations toward previous 83 SiO-only detected sources and 152 H2O-only detected sources, respectively (Cho & Kim 2012: Paper II, Kim, Cho, & Kim 2013: Paper III). We insured a large number of new both SiO and H2O maser sources. We also performed statistical studies based on these homogeneous data (Kim, Cho, & Kim 2014: Paper IV). Simultaneous observations of SiO and H2O masers toward 252 OH/IR stars (Cho et al. 2013), 164 post-AGB and 132 AGB stars (Yoon et al. 2014), and 47 symbiotic stars (Cho et al. 2010) were added. Based on these surveys, we have also performed monitoring observations toward about 60 relatively strong SiO and H2O maser sources for single dish researches and future KVN and KaVA (KVN+VERA) VLBI observations. They are composed of semi-regular variables, Mira variables, OH/IR stars, and several post-AGB stars including water fountain sources at different evolutionary stages. From 2014A observing season, we selected 16 KVN KSP candidate sources and performed regular intensive monitoring of 22 GHz H2O and 43/86/129 GHz SiO maser lines.
VLBI Feasibility Test Observations for Key Science Program
A simultaneous fringe survey at 22/43/86/129 GHz bands was performed toward 41 sources in 2013 April (Yun et al. 2015 in prep.). The objects were selected from KVN single dish monitoring sources including 7 water fountain sources and post-AGB stars. Five frequencies of H2O: 22.235 GHz, SiO v = 1, J = 1-0: 43.122 GHz, SiO v = 2, J = 1-0: 42.821 GHz, SiO v = 1, J = 2-1: 86.243 GHz, and SiO v = 1, J = 3-2: 129.363 GHz were observed simultaneously. On source integration time was from 30 to 70 minutes depending on sources. The correlation was done with the DiFX correlator. As a result, both SiO and H2O maser fringes were detected from 15 sources among 30 both H2O and SiO maser sources (50%) at one epoch. The fringe of 129 GHz SiO maser was detected from 6 sources (17%) and fringes at all 4 bands were detected from 4 sources. The fringe detection rates of 22, 43, 86 GHz bands were 62, 83, 54 %, respectively. We also performed 4 band snapshot imaging observations toward 14 sources in 2013 May. On source integration time of snapshot was from 40 to 160 minutes. The sample snapshot images of VY CMa simultaneously obtained at 4 bands are shown in Figure 4. These results of the fringe survey and the snapshot imaging inform a promising future of simultaneous observations at four bands of KVN. We also carried out full track imaging at 4 bands toward several stars via Open Use and pilot project of KSP. All four-band images including 129 GHz were obtained from VY CMa, IK Tau (Cho et al. 2015 in prep.). For registering these different maser lines, Multi-Frequency Phase Referencing (MFPR) was highly required together with astrometry. Therefore, SFPR technique for KSP with the astrometric alignment of the SiO masers with respect to H2O maser emission are under testing like R LMi by Dodson et al. (2014).
Figure: Snapshot image of maser spots observed from supergiant VY CMa. All maser lines were observed simultaneously at 4 bands for 1 hour. From the very left panel, each image corresponds to 22 GHz H2O, 43 GHz SiO, 42 GHz SiO, 86 GHz SiO, and 129 GHz SiO, respectively. The color bar of 22 GHz H2O maser map represents the velocity along the line of sight, and the color bar of SiO maser maps represents the integrated intensity. The contour of 129 GHz SiO maser map also represents the integrated intensity.
A KVN Key Science Program with the title of Origins of Gamma-ray flares in AGNs (PI: Sang-Sung Lee, firstname.lastname@example.org) is a three-year project consisting of VLBI monitoring observations (or iMOGABA) and single dish (SD) rapid response observations (RRO, or MOGABA). The VLBI monitoring observations are comprised of ten 24-hr observations per year (every month) of about 30 gamma-ray brigt active galactic nuclei (AGNs)(see http://radio.kasi.re.kr/sslee/) with Korea VLBI Network (KVN) at 22, 43, 86, and 129 GHz. The SD RROs may consist of twelve 7-hr observations per source (every week for 3 months after triggering) of gamma-ray flaring sources with two KVN SD telescopes at 22, 43, and 86 GHz (and/or 129 GHz)in dual polarization. We expect one or two sources per year for the SD RROs. Gamma-ray flares of AGNs are known to occur in innermost regions of relativistic jets which radiate in whole ranges of electromagnetic spectra due to synchrotron radiation, syschrotron self absorption, inverse-compton scttering, doppler boosting etc. Here we may eraise two questions on the natures of the gamma-ray flares of AGN such as: a) What is the basic casue of the gamma-ray flares from AGNs? b) What is the physical process of the causes? For the first question, there are several suggestions like 1) a relativistic jet of high energy plasma (Marscher et al. 2008), 2) Doppler boosting of synchrotron radiation of the jet (Dermer 1995), 3) inverse Compton scattering by relativistic electrons, etc. For the second question, we may find some candidates and detail mechanism for the gamma-ray flares such as 1) compression and heating of the plasma in the relativistic jets, 2) generation of the relativistic particles, 3) rapid variability in flux and magnetic field. In order to answer to the questions, we may conduct either 1) studies of large samples of flaring AGNs for investigating statistics and correlation of observed properties (Lister et al. 2011), 2) multi-wavelength observations of individual objects for testing time profiles of flares (Jorstad et al. 2010), for studying physical properties of emission features (jet knots) (Agudo et al. 2011), and studying evolution of SEDs (Wehrle et al. 2013), or 3) polarization observations for looking at magnetic field environments (Jorstad et al. 2013). Possible explanations of the gamma-ray flares in AGNs are a) shocks-in-jets propagating within jet flow and b) bending of the whole jets. For both cases, we should expect changes in polarization, luminosity, particle distribution, and structures of jets at mas-scale. The multifrequency simultaneous VLBI/SD observations with KVN are the best tool for detecting such changes correlated with gamma-ray flares. This KSP aims to answer the fundamental questions about the basic nature of the flares of AGN.
The observations consist of ten 24-hr VLBI observations per year from 2015 January to 2018 January of about 30 gamma-ray brigt active galactic nuclei (AGNs) with Korea VLBI Network (KVN) at 22, 43, 86, and 129 GHz. Ten observations will be conducted every month. Our first priority is to measure changes of jet structures at mas-scale of about 30 γ-ray bright AGNs when they are flaring in the gamma-ray. Our targets are chosen to have flares in gamma-ray detected with Fermi-LAT gamma-ray space telescope (see http://radio.kasi.re.kr/sslee/). Since most of them are very bright at KVN’s operating frequencies, they are able to be detected at KVN baselines within coherence times (20-100 sec) at correponding frequencies. However, we have confirmed that it was possible to improve fringe detection sensitivity with longer integration time than canonical coherence times. Therefore, we observe each source with several 5-min-long scans distributed over its LST time range in order to have uniform uv-coverages. With this snap-shot mode observations, we are able to detect sizes and flux densities of compact jets. However, some target sources with complicated jet structures at KVN’s resolution should be carefully imaged. This issue may be resolved with full-track observations for each sources. Our second priority is to measure flux density changes of AGN jets at mas-scale. Since atmospheric fluctuation are very high at millimeter wavelengths, careful amplitude calibration should be conducted for individual observations. For usual VLBI imaging observations, one can self-calibrate the amplitude with closure-amplitudes. However, unfortunately, with only three antennas of the KVN, the amplitude self-calibration is not possible. Therefore, we conduct very frequent measurements for atmospheric opacity (every hour) and antenna system noise temperature (every scan). More importantly, constant monitor and adjustment for antenna pointing (and/or focus) are performed.
Please see http://radio.kasi.re.kr/sslee/ for the list of target sources in addition to calibrators in this project.
The KVN KSP is a joint project based on the contributions from the following members:KASI (Korea)
Please see a list of papers that have been published using the data from MOGABA and iMOGABA projects.
A fraction of all active galactic nuclei (AGN) shows extended, highly collimated outflows of gas – jets – from their centers. This phenomenon is probably caused by an interplay of black hole rotation, accreted matter, and magnetic fields (the Blandford–Znajek mechanism). For a rapidly spinning Kerr black hole, the innermost stable circular orbit, and thus the inner edge of the accretion disk, can be located within the ergosphere. This permits the transfer of rotational energy from the black hole to the accreted matter. In addition, accretion disks are likely to be permeated by magnetic fields. Within the ergosphere, magnetic field lines will be twisted by frame-dragging, thus forming “tunnels” or “chimneys” made of magnetic field lines. A part of the material in the innermost parts of the accretion disk will be ejected along those magnetic “tunnels”; the magnetic field keeps the material collimated even over large distances, leading to jets ranging over a few megaparsecs in the most extreme cases. However, despite their importance, none of the key features of AGN jets – their launching, collimation, propagation, and interaction with interstellar gas – is understood. AGN jets are objects of ongoing research and their physical properties are hotly debated.
The PAGaN project analyzes the physical – especially plasma-physical – properties of selected AGN via multi-frequency polarization monitoring with KVN. It observes polarization both as function of time and frequency, thus constraining the evolution and propagation of shocks, particle densities, and magnetic field geometries.
PAGaN exploits the unique capability of KVN to observe the full polarization state of a source at four cm-to-mm frequencies spanning a factor six in frequency. PAGaN observes seven radio-bright AGN twice per year and uses dual-frequency phase referencing to improve the quality of the 86 and 129-GHz data. For each source, linear polarization maps are constructed and rotation measures as function of frequency are calculated.
Throughout 2016, a limited number of observations has been obtained in order to test the feasibility of the project. After a successful proof-of-concept, regular observations will begin in 2017. The KVN data will be complemented by archival VLBA, SMA, optical, and gamma-ray data to provide a multiwavelength view on the selected targets.
BL Lac, 3C 111, 3C 120, 3C 273, 3C 345, 4C +11.69, 4C +21.35