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\rhead{Monitoring southern hemisphere \Fermi-detected AGNs}
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\title{\hm\vspace{-8ex} \LARGE\bf Monitoring southern hemisphere \Fermi-detected AGNs with
the Radio Interferometer in New Zealand}

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% abstract:
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%   We propose to run a program of monitoring all southern hemisphere Fermi associated  active galactic nuclei brighter 50 mJy at 8 GHz with the Radio Interferometer in New Zealand. We propose to observe 773 program sources with a cadence of ~15 days and determine their flux densities with accuracy 5%. This program is complementary to the OVRO blazar monitoring program and targets 1/3 sky not covered by the OVRO program with 1/6 sky overlapping between the two programs for consistency control. In addition, we reserve a room for 50 sources that will be added to the observing list upon a request. The light curves will be made publicly available immediately, typically within 15 days of observations.


\maketitle

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\section{Introduction}
  
   Analysis of \Fermi\ LAT data revealed that more than one half of detected 
points sources are active galactic nuclei (AGNs). The intrinsic property of 
AGNs is variability at scales from days to decades at all wavelengths from 
radio to hard $\gamma$-rays. One of the major outcomes of \Fermi\ mission is 
monitoring of $\gamma$-ray loud AGNs. High energy light curves together with 
the spectrum in MeV--GeV range and position localisation is the legacy data 
product of the mission. In order to enhance the outcome of the \Fermi\ 
mission, matching monitoring programs at other wavelengths are needed. The 
most comprehensive matching program is the The OVRO 40-Meter Telescope 
Monitoring Program \citep{r:ovro} that observes for 10 year a list of 
1835~AGNs at declinations $>-20^\circ$, including 930~$\gamma$-rays associated 
sources from FL8Y catalogue of point sources with a cadence of 2 times a month.
The SED of AGNs has two distinctive broad peaks: one spanning from radio 
through optical to soft X-ray and another spanning from KeV to TeV. Emission 
mechanism of two peaks is different. Therefore, monitoring in radio does not 
duplicate monitoring in $\gamma$-ray range, but provides additional 
complementary information.

   Radio/$\gamma$-ray monitoring data are used for a statistical study of 
the  AGN population and for case studies of selected sources. The focus of 
the statistical studies is on deriving the radio and radio/$\gamma$-ray 
observational properties of the AGN population, including a) the radio 
variability properties of the AGN population, their dependence on redshift, 
spectral classification, luminosity, etc; b) any differences between the 
radio properties of \Fermi\ detected AGNs and AGNs with similar radio 
luminosity which have not been detected by \Fermi; c) the properties of 
cross-correlations between radio and $\gamma$-ray flares. The focus of case 
studies is to derive time delay between $\gamma$-ray and radio flares and 
detect periodicities and peculiarities in light curves.

   The OVRO blazar monitoring program is highly successful: by 2018 over
one hundred peer-reviewed and proceedings papers used the light curves
from that program. But geography sets the limit of the program: sources
with declinations below $-20^\circ$, i.e. 1/3 of the sky are excluded.

\section{New observing capabilities in the southern hemisphere}

  The majority of radio telescopes is located in the northern hemisphere.
Few existing telescopes are over-subscribed. To make things worse, 
budgeting restriction for last 2--5 years reduced the amount of time
existing radiotelecopes at the south are available to work for 
sciences, f.e. Parkes and Mopra. In this situation a large dedicated
program on existing radioastronomical facilities is highly problematic.
Our group spend XXX years for converting a former telecommunication 
32-m dish in Warkworth (latitude: $-36.4^\circ$, 
longitude: $174.7^\circ$), New Zealand, to a working radiotelescope. 
In 2014 the first successful results at 6.7 GHz receiver were obtained 
\citep{r:wa15} and in August 2017 first successful observations using 
a 8~GHz receiver were made. There is a smaller 12m radio-telescope 
designed for geodesy also equipped with a 8~GHz receiver at a distance 
of 185.226 meter from the 32m telescope. Since August 2017 both 
telescopes are participating in VLBI observations at X-band (8 GHz). 
Analysis of VLBI results at 185m long baseline showed excellent 
performance: residual phase delays over 24 hour period has a scatter 
of 5~ps, i.e. phase is stable with rms of $15^\circ$ and fringe 
amplitude is also stable.

  This prompts us to propose a program of using a former 
telecommunication dish and the geodetic radio telescope as a radio 
interferometer suitable for source flux density monitoring. We measured
the sensitivity of the interferometer and found that we can determine 
flux density of a 50~mJy source with the thermal noise of 5~mJy using 
8~minute integration time.

\section{Proposed work}

  We propose to run a program of monitoring \underline{\bf{all}}
\Fermi\ associated AGNs with declinations $< 0^\circ$ with flux densities
brighter 50~mJy at 8 GHz with the Radio Interferometer at New Zealand (RINZ) 
that consists of two radio telescopes 185 meter apart. We have identified
773 such sources in the FL8Y catalogue. Each source will be observed from
1 to 8 minutes, depending on flux density, at the interferometer. We plan
to observe two twenty four hour sessions per week, 2500 hours per year.
It will require four days to observe the entire list. Thus, our radio
monitoring program will provide light curves with a cadence $\sim\! 15$ days,
close to thgrpe ``at provided by the  OVRO monitoring program. We reserve
a room for $\sim\! 50$ more sources that will be added to the program upon
a request, for instance, newly detected sources or flaring \Fermi\ sources.
We intentionally set the overlap with the OVRO program in the declination
range of -$20^\circ$ to $0^\circ$. The purpose of this overlap is to check 
consistency of our results with respect to the OVRO monitoring results.

\section{Significance of the proposed work}

  The current OVRO monitoring program covers 2/3 of the sky. Our proposed 
program will cover 1/3 remaining sky with an overlap of 1/6 with OVRO
prorgram. Thus, the all sky $\gamma$-ray AGN monitoring mission will 
have a matching all sky OVRO+RINZ mission with no bright AGN left alone. 
The merit of the hemisphere bias elimination is the following:

\par\vspace{-1ex}\par
\begin{itemize}\setlength{\itemsep}{-0.25ex}
   \item the risk of losing an important variable source just because 
         there existing montitorin program covers only a part of the 
         sky is eliminated.

   \item the number of sources for which time delay in radio/$\gamma$ 
         light curves is known will be increaed by 50\%. Such sources
         are very valuable for case studies. \citet{r:ovro_delay}
         report 41 such sources. A number of papers were 
         devoted to analysis of light curves of such single 
         sources, for instance \citep{r:bha17}

   \item southern radio sky in time domain is mainly an unexplored 
         territory. We experct insteresting discoveries. 

   \item we expect our radio southern monitorinig program will help
         to launch monitoring at optical wavevelengths in the
         southern hemisphere creating a multiplication effect.
\end{itemize}

  One can argue that since 59\% the Moon area is visible from the Earth, 
the opposite, invisible side is expected to look the same. Luna--3 
mission has demonstrated that this is not the case. Notably, a number of 
extraordinary \Fermi\ detections has happened in the southern hemisphere 
at declination $< -20^\circ$ and therefore they were not observable by 
OVRO. A few examples of remarkable events include:

\par\vspace{-1ex}\par
\begin{itemize}\setlength{\itemsep}{-0.25ex}
   \item the gamma-ray burst GRB 080916C ($\delta= -56^\circ38'$) in September 
         2008. This burst had ``the largest apparent energy release yet measured'';

   \item detection and localization a gamma-ray burst in the southern sky designated 
         as GRB 170817A ($\delta=  -23^\circ23'$) within 1.7~s of the gravitational
         wave signal; 

   \item  detection a weak gamma-ray burst starting 0.4 seconds after the LIGO event 
          GW150914 ($\delta= -22^\circ$) on September 2015. The odds of such an event 
          being the result of a coincidence or noise is evaluated at a level of 0.2\%.
\end{itemize}

  The event GRB 170817A was followed-up by the southern hemisphere telescopes,
however, no monitoring in radio spectrum was conducted for these southern sources 
before or during the corresponding remarkable events, except for the one which was 
identified with the IceCube neutrino detection. Luckily, concurrently with the most 
powerful (2~PeV energy) neutrino event HESE-35, dubbed `BigBird' registered on 
4 December 2012 with the IceCube neutrino detector in Antarctica, both \Fermi\ and 
the Long Baseline Array (consisting of radio telescopes in Australia, NZ and SA) 
monitored the corresponding area of the southern sky. Careful analysis of both 
\Fermi\ and radio observations allowed a high probability cross-identification 
of the source of the ultra-energetic neutrino with the blazar PKS B1424--418 
($\delta = -41.8^\circ)$ --- the first ever identification of the source of 
ultra-energetic neutrinos.

  The paper about the northern hemisphere program, \citep{r:ovro}, has 
collected 197 citations for seven years after publication, and 91 papers
peer-reviewed are baeed on usin the light curves. This provides a strong
evidence that such a data product is indeed needed to the scientific community. 
Providing information about radio light curves of 1/3 \Fermi-detected blazars
not monitored by radio hitherto, their variability indices, epochs of flaring 
events, and their delay with respect to $\gamma$-ray flux will enhance the 
value of the \Fermi\ mission, especially its part related to a study of AGNs.

\section{Logistics of the proposed program}

  Observations will be performed in a sequence that minimizes slewing.
Integration time will be selected according to expected flux density
to have SNR $>$ 20 for weack sourecs and more than 30 for sources brighter
100~mJy. The data will be recorded at 2 Gbps rate in dual-polarizations and 
transferred via ftp to the computer center of Auckland University 
for correlation. Then the  data will be correlated, fringe-fitted, and 
calibrated. The estimates of flux density, including all four Stokes 
parameters, will be made publicly available at the project web site 
immediately after completion of analysis, i.e. within 5--15 days after 
observations.

  Calibration will be performed by firing the noise diode of the antenna 
calibration unit before observation of every program source, which is 
a standard procedure in radio interferometry, by observing amplitude 
calibrator radio sources, and by observing common sources with the OVRO 
program. Our goal is to reach 5\% accuracy in calibration and 5~mJy error 
floor. At the moment, only the 30m radiotelescope is equipped with the 
antenna calibration unit. The second 12m radiotelescope designed for geodesy
does not have it. The lack of the antenna calibration unit at the 2nd
antenna adversely affects accuracy of calibration, since antenna gain 
fluctuations at the 12m antenna remain unchecked. Our analysis of VLBI
observations with the 12m antenna provided us the estimate of accuracy of 
the antenna calibration without the noise diode at a level of 20\%. 

  Therefore, we request funds on amount of \$30,000 to purchase the antenna 
calibration unit by the performing organization from the Haystack observatory, 
MIT that manufactures them. The performing organization will loan the unit to 
the Auckland university for the duration of this observing program. Using 
antenna calibration units at both antennas will reduce calibration errors 
from 20\% to 5\%, which is typical for radio interferometers. Calibration 
accuracy 5\% is required for scientific analysis of light curves. For 
comparison, the OVRO program has calibration errors at a level of 2--3\%.

Roles of the team members:

\par\vspace{-1ex}\par
\begin{itemize}\setlength{\itemsep}{-0.25ex}
   \item  L.~Petrov --- development of the pipeline of data analysis 
          and calibration; overall management of the project;
   \item  S.~Gulyaesv --- data analys, management of the Auckland University team;
   \item  S.~Weston, T.~Natusch --- tuning hardware, running the observations;
   \item  two Ackland Universtiy mater level students --- running the 
          observations, maintaining the project web site.
\end{itemize}

  We request funds at 0.1 FTE level for the PI, Leonid Petrov, for development
of the pipeline of data analysis. No funds are requested for foreign 
co-investigators. Their labor cost as well as the operational cost of running the 
interferometer is covered by Auckland University. The total amount of requested
funds is \$55,000.

  This monitoring program will be the most valuable if preformed concurrently 
with \Fermi\ observations. Since the ten year old \Fermi\ mission will not last 
forever, we are hurring up to start the observing program as soon as possible
while it is operating. We intentionally set aside from the framework of this
proposal scientific interpretation of the monitoring results which we and other 
users of the RINZ AGN monitoring program will engage. This important work can
be done later, but delaying the launch of the southern hemisphere monitoring 
program we face a risk to lose the opportunity of concurrent \Fermi\ observations.

\section{Bibliography}

\begin{thebibliography}{8}\setlength{\itemsep}{0.05ex}

   \bibitem[Bhatta(2017)]{r:bha17}
      Bhatta~G., 2017. ApJ, 847: 7, 2017.

   \bibitem[Max-Moerbeck et al.(2014)]{r:ovro_delay}
      Max-Moerbeck, W. et al., MNRAS, 445, 42,  2014. 

   \bibitem[Richards et al.(2011)]{r:ovro}
      Richards, J.~L.,  et al., ApJS, 194, 29, 2011.

   \bibitem[Richards et al.(2014)]{r:ovro+fermi}
      Richards, J.~L.,  et al., MNRAS, 438, 3058, 2014.

   \bibitem[Petrov et al.(2015)]{r:wa15}
      Petrov, L. at al.  PASP, 127, 516--522, 2015.

\end{thebibliography}

\end{document}
