Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Chengyu Shao
Xiaopeng Cheng
Tam Pak-Hin Thomas
Lili Yang
Yudong Cui
Partha Sarathi Pal
Zhongli Zhang
Bong Won Sohn
Koichiro Sugiyama
Wen Chen
Longfei Hao
Abstract： Fermi J1544-0649 is a transient GeV source first detected during its GeV flares in 2017. Multi-wavelength observations during the flaring time demonstrate variability and spectral energy distribution(SED) that are typical of a blazar. Other than the flare time, Fermi J1544-0649 is quiet in the GeV band and looks rather like a quiet galaxy (2MASX J15441967-0649156) for a decade. Together with the broad absorption lines feature we further explore the "misaligned blazar scenario". We analyzed the Very Long Baseline Array (VLBA) and East Asian VLBI Network (EAVN) data from 2018 to 2020 and discovered the four jet components from Fermi J1544-0649. We found a viewing angle around 3.7{\deg} to 7.4{\deg}. The lower limit of the viewing angle indicates a blazar with an extremely low duty cycle of the gamma-ray emission, the upper limit of it supports the "misaligned blazar scenario". Follow-up multi-wavelength observations after 2018 show Fermi J1544-0649 remains quiet in GeV, X-ray, and optical bands. Multi-messenger search of neutrinos is also performed, and an excess of 3.1 {\sigma} significance is found for this source.
Peer Review Status:
Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Phrudth Jaroenjittichai
Koichiro Sugiyama
Busaba H. Kramer
Boonrucksar Soonthornthum
Takuya Akahori
Kitiyanee Asanok
Willem Baan
Sherin Hassan Bran
Shari L. Breen
Se-Hyung Cho
Thanapol Chanapote
Richard Dodson
Simon P. Ellingsen
Sandra Etoka
Malcolm D. Gray
James A. Green
Kazuhiro Hada
Marcus Halson
Tomoya Hirota
Mareki Honma
Abstract： This White Paper summarises potential key science topics to be achieved with Thai National Radio Telescope (TNRT). The commissioning phase has started in mid 2022. The key science topics consist of "Pulsars and Fast Radio Bursts (FRBs)", "Star Forming Regions (SFRs)", "Galaxy and Active Galactic Nuclei (AGNs)", "Evolved Stars", "Radio Emission of Chemically Peculiar (CP) Stars", and "Geodesy", covering a wide range of observing frequencies in L/C/X/Ku/K/Q/W-bands (1-115 GHz). As a single-dish instrument, TNRT is a perfect tool to explore time domain astronomy with its agile observing systems and flexible operation. Due to its ideal geographical location, TNRT will significantly enhance Very Long Baseline Interferometry (VLBI) arrays, such as East Asian VLBI Network (EAVN), Australia Long Baseline Array (LBA), European VLBI Network (EVN), in particular via providing a unique coverage of the sky resulting in a better complete "uv" coverage, improving synthesized-beam and imaging quality with reducing side-lobes. This document highlights key science topics achievable with TNRT in single-dish mode and in collaboration with VLBI arrays.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Hyunwook Ro
Motoki Kino
Bong Won Sohn
Kazuhiro Hada
Jongho Park
Masanori Nakamura
Yuzhu Cui
Kunwoo Yi
Aeree Chung
Jeffrey Hodgson
Tomohisa Kawashima
Tao An
Sascha Trippe
Juan-Carlos Algaba
Jae-Young Kim
Satoko Sawada-Satoh
Kiyoaki Wajima
Zhiqiang Shen
Xiaopeng Cheng
Ilje Cho
Abstract： Because of its proximity and the large size of its black hole, M87 is one of the best targets for studying the launching mechanism of active galactic nucleus jets. Currently, magnetic fields are considered to be an essential factor in the launching and accelerating of the jet. However, current observational estimates of the magnetic field strength of the M87 jet are limited to the innermost part of the jet or to HST-1. No attempt has yet been made to measure the magnetic field strength in between. We aim to infer the magnetic field strength of the M87 jet out to a distance of several thousand $r_s$ by tracking the distance-dependent changes in the synchrotron spectrum of the jet from high-resolution very long baseline interferometry observations. In order to obtain high-quality spectral index maps, quasi-simultaneous observations at 22 and 43 GHz were conducted using the KVN and VERA Array (KaVA) and the VLBA. We compared the spectral index distributions obtained from the observations with a model and placed limits on the magnetic field strengths as a function of distance. The overall spectral morphology is broadly consistent over the course of these observations. The observed synchrotron spectrum rapidly steepens from $\alpha_{22-43 GHz}$ ~ -0.7 at ~ 2 mas to $\alpha_{22-43 GHz}$ ~ -2.5 at ~ 6 mas. A spectral index model in which nonthermal electron injections inside the jet decrease with distance can adequately reproduce the observed trend. This suggests the magnetic field strength of the jet at a distance of 2 - 10 mas (~ 900 $r_s$ - ~ 4500 $r_s$ in the deprojected distance) has a range of $B=(0.3 - 1.0 G)(z/2 mas)^{-0.73}$. Extrapolating to the EHT scale yields consistent results, suggesting that the majority of the magnetic flux of the jet near the black hole is preserved out to ~ 4500 $r_s$ without significant dissipation.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Kazunori Akiyama
Juan-Carlos Algaba
Tao An
Keiichi Asada
Kitiyanee Asanok
Do-Young Byun
Thanapol Chanapote
Wen Chen
Zhong Chen
Xiaopeng Cheng
James O. Chibueze
Ilje Cho
Se-Hyung Cho
Hyun-Soo Chung
Lang Cui
Yuzhu Cui
Akihiro Doi
Jian Dong
Kenta Fujisawa
Wei Gou
Abstract： The East Asian VLBI Network (EAVN) is an international VLBI facility in East Asia and is operated under mutual collaboration between East Asian countries, as well as part of Southeast Asian and European countries. EAVN currently consists of 16 radio telescopes and three correlators located in China, Japan, and Korea, and is operated mainly at three frequency bands, 6.7, 22, and 43 GHz with the longest baseline length of 5078 km, resulting in the highest angular resolution of 0.28 milliarcseconds at 43 GHz. One of distinct capabilities of EAVN is multi-frequency simultaneous data reception at nine telescopes, which enable us to employ the frequency phase transfer technique to obtain better sensitivity at higher observing frequencies. EAVN started its open-use program in the second half of 2018, providing a total observing time of more than 1100 hours in a year. EAVN fills geographical gap in global VLBI array, resulting in enabling us to conduct contiguous high-resolution VLBI observations. EAVN has produced various scientific accomplishments especially in observations toward active galactic nuclei, evolved stars, and star-forming regions. These activities motivate us to initiate launch of the 'Global VLBI Alliance' to provide an opportunity of VLBI observation with the longest baselines on the earth.
Peer Review Status:Awaiting Review
Hits
Hits
Downloads
Comment