East ASIA VLBI Network Observationsat 230 GHz
Kenta Fujisawa (Yamaguchi univ.)
on behalf of Asada-san and EAVN -hi- collaboration

Introduction

Event Horizon Telescope (230 GHz)

Credit: D. Marrone

One sessions / yr: End of March
Each session: ~ 5 day within 10 days slots
Open sky policy
Host institute: EHTC
Due for the proposal: ~ April 20th (propose to ALMA)Further Possible expansion of EHT

1.
2.
3.
4.

KVN at 230 GHz with FPT?
Balloon - Borne VLBI led by ISAS/JAXA
Re-activate ASTE for VLBI ?
Seek the process to use ACA ?

Two important direction for mm/submm VLBI
community in EAa.

Participate/contribute to global efforts (e.g., EHT and GMVA)– KVN participate GMVA
– JCMT is one of the initial stations of EHT– GLT started to participate EHT and GMVA from this year
– Approved ALMA CY7 EHT projects: Koyama+ Mrk501

b.

Do unique things as (regional) efforts– KVN is unique VLBI array observable at 86 and 129 GHz with FPT– NRO45m at 86 GHz led by Imai-san and Niinuma-san– We (will) have JCMT and GLT at (86) and 230 GHzEAVN at 86 GHz, 230 GHz and even higher?

EA mm/submm White Paper

Experiences 230 GHz VLBI with EA stations
1.

JCMT became stand alone station.

2.

GLT started to participate EHT observations since 2018, and got fringes

3.

SPART experiments have already demonstrated mm-VLBI feasibility ofSPART telescope in 2015

⇒ We are ready to start regional coherent efforts to form 230/(86 GHz) array

Observations

The first EAVN -hi- test observations••••••

Date: 2019 March 18, 19
Duration: UT11-18, 7 h each day
Frequency range: 230200 – 232248 MHz*
Stations: GLT-12m, SPART-10m, SNRAO-6m
Sources: M87, 3C345, 1633+382, 3C371,
1928+738, N6251, Mrk501, CO2-1 sources forverification purpose
Weather: Cloudy (SPART), Fine (GLT)System Setup
GLT 12 m

SRAO 6 m

SPART 10 m

SEFD

4 900 Jy

78 000 Jy

18 000 Jy

Start Freq.

230.200 GHz

230.200 GHz

230.200 GHz

Bandwidth

2 048 MHz

1 024 MHz

512 MHz

Polarization

Dual circular

Single circular

Single linear

RecorderR2DBE
Mark6R2DBE
Mark6ADS3000+OCTAVE

Preparation for each site

GLT- ALMA-NA prototype 12 m- 3 receivers (86, 230 and 345 GHz)
- 64 Gbps system with
4 x Mark6 + 4 x R2DBE- Phase stability test for receiver with tone injection
before and after the observations
ASD ~ 10-14 @ 1 sec- Monitoring reference signal with respect to OCXO
ASD ~ 10-13 @ 1 - 10 sec

Observations ~ -30 degree
Wen-Ping Lo, Kevin Koay, and Keiichi Asada at the site

- Detection of Fringe for GMVA campaign 2019(just after the EAVN -hi-)
Stability should be fine for GLTR2DBEs at receiver cabin

Mark6sJCMTDiameter: 15m
Location: Maunakea summit, Hawaii(3 receiver cartridge (86. 230, 345 GHz))
Editting by Izumi

RxA:
Retired June 23, 2018

Namakanui (GLT spare):Commissioning
The JCMT. Image Credit: William Montgomerie

JCMT

SPART 10 m
Solar Planetary Atmosphere Research Telescope● Operated by Osaka Prefecture
University, Japan● One of the antennas of the former
Nobeyama Millimeter Array● Normally observing solar planets andothers at 230 GHz as a single dish
● VLBI system temporarily installed:○ The system of Yamaguchi 32-m
was disassembled andtransported to SPARTSPART 10 m
● VLBI system installedin Shed 1○ GPS antenna tied
on a laundry pole
● Two coaxial cables
connecting SPART
and Shed 1,transporting the IF and10 MHz signals

SPART VLBI System

SPART Bandcharacteristics

SPART Preparation

SPART Preparation

SPART Preparation

SPART Preparation

SPART Preparation

Correlations

Correlator
Post processing

DiFX-2.6.1
HOPS-3.20

SHAO DiFX correlator

Status of correlation
 Data transfer:
Diskpacks (GLT, SPART, arrived), Internet (SRAO, arriving) Pre-correlation:
Raw data format of each station (GLT, SPART) was confirmed withdetections of CO-line spectrum data.
 Correlation:
Using ZOOM band to extract the same frequency bands from eachstation, GLT-SPART (512MHz), GLT-SRAO (1024MHz), SPARTSRAO (512MHZ)
Split the band into multiple 32MHz BW for larger delay search window
and incoherent averaging.

Status of correlation
Coherent fringe search

Limited SNR!
Incoherent fringe fittingThe first VLBI experiments at 230 GHz

That was a great first step for us,
while no fringe were detected so far.

Contents for Discussion Session

Set up 1. Simple BH shadow case
Input image: Simple BH shadow modelfrom Bubu
Noise:
Thermal Noise: Yes
Systematic Noise: No
BW: 2 GHz
Duration: Full Track(12° (EL) to 12° (EL))
Data: Generated with UVCON (AIPS)CLEAN: Difmap
All process done manuallyGLT+JCMT+SPART+SRAO+PICO+NOEMA +ALMA+APEX+SMA+SMTO+LMT

GLT+JCMT+SPART+SRAO

GLT+JCMT+SPART+SRAO+ALMA

GLT+JCMT+SPART+SRAO+ALMA +SMTO

GLT+JCMT+SPART+SRAO+ALMA +LMT

GLT+JCMT+SPART+SRAO+APEX +SMTO

Peak[Jy/beam]

Rms[Jy/beam]DRchi2

GLT+JCMT+SPART+SRAO

0.118

0.00069

171

1.13GLT+JCMT+SPART+S
RAO+ALMA

0.118

0.00027442

1.17

GLT+JCMT+SPART+S
RAO+ALMA+SMTO

0.119

0.00045264

1.14

GLT-JCMT-SPARTSRAO-APEX-SMTO

0.118

0.00049

243

1.13

GLT-JCMT-SPARTSRAO-APEX-LMT

0.118

0.00063

187

1.29

FULL

0.111

0.00027407

1.25

1. Simple BH shadow caseTentative summary for BH shadow imaging(1). We need EAVN (GLT-JCMT-SPART-SRAO) + Chile + LMT or SMA(2). ALMA may not be crucial for imaging
EAVN hi + ASTE (or ACA) +SMTO may be sufficient and flexible+ALL+ALMA+SMTO+ALMA+LMT+APEX+SMTO

Where are we?

The first VLBI experiments at 230 GHz

That was a great first step for us,
while no fringe were detected so far.

No Fringes between GLT - SPART so far?
CO2-1 was detected with GLT and SPART -> sky signal is there

Two possibilities?:
1. Low sensitivity ?
2. Stability of system was not sufficient ?

1. Low sensitivity?
SEFDs: GLT 5300, SPART 18000Jy
Effective BW: 512 MHz
Integration time: 10 sec
Fringe sensitivity: 965 mJy for 7 sigma (551 mJy for 4 sigma)
Could be challenging? Marginal even for strong QSOs.

2. Phase stability?
Let's check stabilities
1. Let's make sure the purity of reference signals with 1 Hz resolution
2. Let's try to conduct tone injection test
3. Let's make sure the stability of frequency standard

Points for discussions

How we can detect the first fringes- Participation of JCMT
- Increase the BW from 512 to 2048 GHz- Spend more time for QSOs, not for RGs- Phase stability tests- More challenges

How we can extend- Participate to EHT with keeping regional efforts- ACA/APEX? KVN?
- other stations? SMTO, KP, LMT?