Band 4 & 8 Imaging Verification Test Report: 30 May 2014
ALMA Technical Note Number: 3
Status: FINAL
Prepared by:

Organization:

Date:

Takahashi Satoko

JAO/NAOJ

30 May 2014

Band 4 Imaging Verification Report (Xf8c)
Reporter: Satoko Takahashi
ver.1: 2014-04-08
ver.2: 2014-04-15
ver.3: 2014-05-30
Abstract:
Band 4 verification data was obtained toward quasars (J1908-2941 and J1923-210) andblank sky using 22 usable antennas. Images from all the four BBs were successfully
obtained and their fluxes and position are consistent within the expected measurements
errors. The measured rms noise levels on the blank sky were consistent within factor of1.6 compared to those expected from the ALMA sensitivity calculator. This can beexplained by considering Tsys variations (both by time as well as by antennas) during
the observations.

Observations & Data Reduction:
The observation was made on 2014-03-15 using fifteen 12m antennas and seven 7m
antennas with the BL correlator (described below). The PWV during the observations
was around 0.37mm. Elevation of the observed sources was between 59 and75°(Figure 1). The detailed scheduling block information is as follows, and the observed
field and spectral settings are listed in Table 1 and Table 2, respectively.

12m antennas used:
DA43, DA55, DA59, DA60, DA61, DA64, DV01, DV10, DV14, DV16, DV17, DV18,DV20, DV22, and PM04
7m antennas used:
CM01, CM02, CM03, CM06, CM09, CM11, and CM12
* Note that antennas include “operational”, “science”, and “engineering” status.

Scheduling block information:
Project name: Performance Regression V2.4 (Version 2.4)
Project Code: 0000.0.00133.CSV
SchedBlock BL-B4-RA 19h Correct1

PI: dgunawan;

ExecBlock: uid://A002/X7cbdcd/X8fc

Table 1: Observed fields

Table 2: Spectral settings

Figure 1: Elevation plots. Each color shows the different field: black (J1924-2914), pink(Ceres), orange (J1921-293), green (Blank sky), brown (J1908-294), and blue(J1923-219-offset).

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CASA version 4.2.0 (r28322) + the standard Cycle I data reduction procedure (i.e.,Eric’s script) was used for the data reduction. Baseline correction was applied based on
the baseline measurements carried out on March 16. Due to ICT-1770 (Scans start 1-3
seconds before antenna arrives on source), the first scan of each sequence wasflagged using “quack” option in a task flagdata. The used reduction script(uid___A002_X7cbdcd_X8fc.ms.scriptForCalibration.py)

andCLEAN

commands(Imaging-X8fc.txt) are attached in this JIRA ticket.

Results:
The positions and peak flux of sources were estimated by elliptical Gaussian fitting
using imfit and rms noises were measured using imstat. The images and summary of
the image properties are posted as Figure 2 and Table 3.

*BB1:

3

*BB2:*BB3:

4*BB4Figure 2: The images obtained from the experiments. J1921-293 (phase calibrator),
blank sky, J1923-219, which offsets from the phase center, J1908-2942 (fainter QSO).
Image toward J1921-293 was zoomed in.

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Table 3: Image properties

Flux scaling: Derived absolute flux value of J1921-293 using the primary flux
calibrator, Ceres, is ~4.4 Jy. The value is consistent with an expected flux of 4.2 Jy,
which was derived from an independent measurement at Band 3, which is 5.63 Jy,
performed on 2014-04-03, assuming with the spectral index of -0.71 (The spectral
index was estimated from the grid survey results in Band 7 (performed on2014-03-24) and Band 3).

Positions: The positional offsets between the apriori positions and measured
positions of observing targets (J908-2942 and J1923-210) listed in Table 3. The
positional differences in the right ascension are several times larger than those
expected from the positional offsets such as originated to (i) the fitting error (~10-3
arcsec),(ii)

thepositional

accuracies

determinedbysource

S/N(σ~(1/2π)*(θ/S/N)~ several x 10-3 arcsec), and (iii) the positional error caused by
the baseline error (Δθ=(Δλ/λ)xθx d/360~ a few times 10-3 arcsec). Here, we
adopted that the baseline error of 0.2mm, which is retrieved from a systemverification report #154 by Sugimoto-san. Nonetheless, the target position are still
consistent within ~0.1”. The offset corresponds to 4.5 % of the synthesized beam
size. This could be explained by the systematic phase offset could be caused by
the baseline error (which can be slightly different from the one we assumed from6the Sugminoto-san’s report) as well as the phase offset originate to thetroposphere structure (which is not easy to quantitatively estimate). This much of
the positional offset is within our expectation (normally the positional offset of
5-10% of the beam size be seen in the ALMA experiments). Interestingly, theoffsets measured in the declination direction (order of 10-6 arcsec) were smaller
than those expected from the accuracies of positional determination (orders of 10-3arcsec, meaning that there is positional offset is zero..). One possibility could be
explain this is that, again, unknown baseline error or atmospheric effect could
cancel out the positional error.
Noise estimations: Adopting the mean measured Tsys during observations of ~50 K
and the integration on-source time of 1288 sec, the theoretical noise level is estimatedto be ~0.054 mJy/beam from the ALMA sensitivity calculator with 2GHz bandwidth(scaling with antenna surface area as well as the system temperature). The measured
rms noise levels for BB1, BB2, BB3 (for the ~2GHz bandwidth), and BB4 (for the ~1GHzbandwidth) are 0.086, 0.089, 0.085, and 0.132 mJy/beam, respectively. These values
are consistent within factors of ~1.6 compared to those expected from the theoreticalvalues. This can be explained by considering Tsys variations (both by time as well as byantennas) during the observations.

Conclusions:
A performance evaluation data set in Band 4 was analyzed. The calibrated data showedthat the positional accuracies coincide within ~0.1” compared to the apriori positions,which is within expectation. The rms noise levels in a blank sky field measured in all thefour BBs are factor of ~1.6 higher than those expected from the ALMA sensitivity
calculator. This slightly higher value may be explained by the Tsys value variations
during the experiment.

7Band 8 Imaging Verification Report (X5ab)
Reporter: Satoko Takahashi
Ver2. (2014-04-08)* Modified part are written in the orange color
Abstract:
Band 8 verification data was obtained toward quasars (J1239-103 and 3c273) andblank sky with 20 usable antennas. Images from all the four BBs were successfully
obtained and their fluxes and position are consistent within the expected measurements
errors. The rms noise level on the blank sky images were measured to be 0.34
mJy/beam, which is more or less agreed (within 30%) with those estimated from theALMA sensitivity calculator adopting with the similar observing conditions (and without
considering Tsys variation during the observations).

Observations & Data Reduction:
The observation was made on 2014-03-15 using fourteen 12m antennas and seven 7m
antennas as described below with the BL correlator. The PWV during the observations
was around 0.35mm. Elevation of the observed sources was between 35 and 60°(Table1). The detailed scheduling block information is as follows, and the observed field andspectral settings are listed in Table 1 and Table 2, respectively.

12m antennas used:
DA43, DA55, DA59, DA61, DA64, DV01, DV10, (DV14), DV16, DV17, DV18, DV20,DV22, and PM04
7m antennas used:
CM01, CM02, CM03, CM06, CM09, CM11, and CM12
* Note that antennas include “operational”, “science”, and “engineering” status.

Scheduling block information:
Project name: Performance Regression V2.4 (Version 2.4)
Project Code: 0000.0.00133.CSV
SchedBlock BL-B8-RA 12h Correct
PI: dgunawan,

ExecBlock: uid://A002/X7cbdcd/X5ab8Table 1: Observed fields

Table 2: Spectral settings (revised)

Figure 1: Elevation plots. Each color shows the different field: black (J1256-0547/3c279),
pink (Ceres), orange (3c279), green (Blank sky), brown (J1239-103), and blue (3c273).

CASA version 4.2.0 (r28322) + the standard Cycle I data reduction procedure (i.e.,
Eric’s script) was used for the data reduction. Baseline correction was applied based on
the baseline measurements carried out on March 16. WVR data were not properly
obtained on DV14 (PRTSPR-3847), so the data associated with DV14 was flagged out.

9Moreover, due to ICT-1770 (Scans start 1-3 seconds before antenna arrives on source),
the first scan of each sequence was flagged using “quack” option in a task flagdata.
The used reduction script (uid___A002_X7cbdcd_X5ab.ms.scriptForCalibration.py) andCLEAN commands (Imaging-X5ab.txt) are attached in this JIRA ticket.

Results:
The positions and peak flux of sources were estimated by elliptical Gaussian fitting
using imfit and rms noises were measured using imstat. The images and summary of
the image properties are posted as Figure 2 and Table 3.

*BB1:

10

*BB2:

*BB3:

11

BB4:

12

Figure 2: The images obtained from the experiment. 3c279 (phase calibrator), blank sky,
3c273, which offsets from the phase center, J1239-103 (fainter QSO). Image toward
3c279 was zoomed in.

Table 3: Image properties

Flux scaling: Derived absolute flux value of 3C279 using the primary flux
calibrator, Ceres, is ~6.6 Jy. The value is consistent with an expected flux of 6.7 Jy,
which was derived from an independent measurement at Band 7, which is 7.48 Jy,
performed on 2014-03-20, adopting the spectral index of -0.65 (The spectral index
was derived from the grid survey results in Band 3 (performed on 2014-04-03) andBand 7).

Positions: The positional offsets between the actual position and measured
position for observing targets (J1239-103 and 3c273) listed in Table 3 areconsistent within the same orders of the positional uncertainties originated to thefitting errors and positional accuracies determined by source S/N, which is(σ~(1/2π)*(θ/S/N)).

Noise estimations: Adopting the mean measured Tsys during observations of~200 K, and the integration on-source time of 1288 sec, the theoretical noise levelis estimated to be 0.26 mJy/beam from the sensitivity calculator. The measured

13rms noise levels from the observed data on the blank sky are ~0.34 mJy/beam for
BB1, 2, 3 (with the ~2GHz bandwidth), and 0.55 mJy/beam for BB4 (with the~1GHz bandwidth), respectively. The measured values show factor of ~1.3 higher
values than those expected from the sensitivity calculator. However, the estimation
does not consider the Tsys variation during the observations.

Conclusions:
A performance regression data set in Band 8 was analyzed. The calibrated data showedthat the positional accuracies are within expected uncertainties. The rms noise levels ina blank sky field are more or less consistent with the theoretically expected values.

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