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\IBVShead{5559}{24 August 2004}

\IBVStitletl{Discovery of CVs ROTSE3~J151453.6+020934.2 and}{ ROTSE3~J221519.8-003257.2}

\IBVSauth{Rykoff, E. S.$^1$; Akerlof, C. W.$^1$; Ashley, M. C. B.$^2$;  G\"{o}\v{g}\"{u}\c{s}, E.$^3$; G\"{u}ver, T.$^4$; Kizilo\v{g}lu, \"{U}.$^5$;  McKay, T. A.$^1$; \"{O}zel, M.$^6$; Phillips, A.$^2$; Quimby, R.$^3$; Smith,  D. A.$^1$; Thorstensen, J. R.$^8$; Vestrand, W. T.$^9$; Wheeler, J. C.$^7$; Wren,  J.$^9$}

\IBVSinst{2477 Randall Laboratory, University of Michigan, 500 E. University
  Ave., Ann Arbor, MI, 48109, USA}
\IBVSinst{School of Physics, University of New South Wales, Sydney 2052,
  Australia}
\IBVSinst{Sabanci University, Turkey}
\IBVSinst{Istanbul University, Istanbul, Turkey}
\IBVSinst{Middle East Technical Institute, Ankara, Turkey}
\IBVSinst{\c{C}anakkale Onzekiz Mart University, Turkey}
\IBVSinst{University of Texas, Austin, TX, 78712, USA}
\IBVSinst{Dartmouth College, 6127 Wilder Laboratory, Hanover, NH, 03755, USA}
\IBVSinst{Los Alamos National Laboratories, Los Alamos, NM, 87545, USA}

\SIMBADobj{ROTSE3 J151453.6+020934.2}
\SIMBADobj{ROTSE3 J221519.8-003257.2}

\IBVStyp{ cataclysmic variable }
\IBVSkey{photometry}


\IBVSabs{We report on the discovery of outbursts from previously unknown high}
\IBVSabs{galactic latitude CVs ROTSE3 J151453.6+020934.2 and}
\IBVSabs{ROTSE3 J221519.8-003257.2.  These objects were detected by the}
\IBVSabs{ROTSE-IIIa telescope at Siding Spring Observatory, Australia,}
\IBVSabs{ROTSE-IIIb at McDonald Observatory, Texas, and ROTSE-IIId at}
\IBVSabs{Bakirlitepe, Turkey.  We also report on four-color images of}
\IBVSabs{J1514 from the MDM telescope, and five-color images of}
\IBVSabs{J2215 from the SDSS public archives.}


\begintext

The ROTSE-III telescope array is a worldwide network of 0.45~m robotic,
automated telescopes, built for fast ($\sim 6$ s) responses to Gamma-Ray Burst
(GRB) triggers from satellites such as Swift.  They have a wide 1.85 degree
field of view imaged onto a Marconi $2048\times2048$ back-illuminated thinned
CCD, and operate without filters, and we have a wide passband that peaks around
550 nm.  The ROTSE-III systems are described in detail in (Akerlof et
al. 2003).  While not observing GRB triggers, the ROTSE-III systems engage in a
search for short duration transients.  High galactic latitude equatorial fields
are scanned every night, with two pairs of images taken with a 30 minute
cadence.  Our search is optimized for finding transients lasting $\sim $1 hr
above our limiting magnitude of 19, although we also detect longer transients
including cataclysmic variables (CVs).  In this bulletin we report on the
discovery of two such CVs in 2004.

On 29 March, 2004, the ROTSE-IIIb telescope located at McDonald Observatory,
Texas, detected a bright 16$^{\rm th}$ magnitude object, which we designate
\\ROTSE3~J151453.6+020934.2 (hereafter J1514).  Only 20 hours earlier, on 28 March, 2004, the
ROTSE-IIIa telescope located at Siding Spring Observatory had imaged the same
field, and had not detected an object to a limiting magnitude of 18.2.  The
ROTSE-III observations were processed by our standard pipeline.  We measure
aperture magnitudes using SExtractor (Bertin \& Arnouts 1996), and then compare
all the field stars to the USNO A2.0 R-band catalog to obtain an astrometric
solution and to perform basic photometry to calculate at $m_{ROTSE}$.

The complete ROTSE-III light curve for J1514 is shown in
Figure~\ref{fig:5559-f1.eps}.  After outburst, the transient remained bright around
$m_{ROTSE} = 17$ for two weeks before fading below our threshold, rebrightened for
two days, and faded back to quiescence.

On 18 June, 2004, J1514 was observed in UBVI at the MDM Hiltner 2.4m telescope,
on Kitt Peak, Arizona.  Two sets of images were taken, with the colors listed
in Table 1.  Figure~\ref{fig:5559-f3.eps} shows the I-band image from the 18
June dataset.  These colors are consistent with a dwarf nova around minimum
light.  Furthermore, the variation in the $V$ magnitude between the two
observations is statistically significant and not seen in a check star; such
flickering is also consistent with a dwarf nova.

On 9 July, 2004, a second CV was detected by the ROTSE-IIId telescope located
at Bakirlitepe, Turkey at $m_{ROTSE} = 17.5$, which we designate
ROTSE3~J221519.8-003257.2.  On 8 July, the previous night, ROTSE-IIId had
imaged the same field, and did not detect any object at the transient location
to a limiting magnitude of 17.5. The nova faded over the next two days, as can
be seen in Figure~\ref{fig:5559-f2.eps}.

Reanalysis of archival ROTSE-IIIb data, which was not previously searched for
transients, reveals an earlier outburst on 22 July, 2003 to $m_{ROTSE} = 16.8$.
We do not know how long the outburst lasted, since we do not have good images
of the field in the following weeks.  In addition, the SDSS DR2 (Abazajian, et
al. 2004) includes a likely faint counterpart with colors consistent with a
dwarf nova at minimum light (Szkody et al. 2002).  The SDSS magnitudes are
listed in Table 2.

Each of these objects is at a high galactic latitude (48\deg\ and
$-$44\deg\ respectively), and they each have very dim quiescent
counterparts, which is unusual for galactic CVs.  However, there have been
other such CVs observed (Howell et al. 1997, Szkody et al. 2002), including
one discovered by ROTSE-III (Smith et al. 2002). It seems more such CVs have
not been found due to selection effects.  Although we do not have spectroscopic
confirmation, the light curves and quiescent colors of these objects lead us to
conclude that these are both galactic cataclysmic variables.


\vspace*{2cm}

\begin{table}[!hb]
\centerline{{\bf Table 1.}  The MDM Four-color Intensity Measurements for}
\centerline{ROTSE3~J151453.6+020934.2 during quiescence.}
\vskip 3mm
\begin{center}
\begin{tabular}{ccccc}
\hline
UTD       &    $U-B$    &    $B-V$    &    $V$    &   $V-I$   \\
\hline
040618.33 & $-1.217\pm0.046$ & $0.077\pm0.027$ & $20.055\pm0.021$ &
$0.537\pm0.038$ \\
040618.34 & $-1.206\pm0.043$ & $0.124\pm0.030$ & $20.285\pm0.022$ &
$0.561\pm0.041$ \\
\hline
\end{tabular}
\end{center}

\bigskip

\centerline{{\bf Table 2.}  The SDSS Five-color Intensity Measurements for}
\centerline{ROTSE3~J221519.8-003257.2 during quiescence.}
\vskip 3mm
\begin{center}
\begin{tabular}{cccccc}
\hline
UTD      &    $u'$    &    $g'$    &   $r'$    &    $i'$     &    $z'$   \\
\hline
011015.2   & $21.44\pm0.14$ & $21.69\pm0.06$ & $21.38\pm0.06$ & $21.25\pm0.07$ &
$20.74\pm0.18$ \\
\hline
\end{tabular}
\end{center}
\end{table}


\IBVSfig{9cm}{5559-f1.eps}{Light curve for ROTSE3~J151453.6+020934.2. 
  The triangles represent data from ROTSE-IIIa and
  the squares from ROTSE-IIIb.  The ROTSE-III unfiltered magnitudes of the 
  object have been calibrated relative to the USNO A2.0 $R$-band colors of 
  the field stars. Arrows indicate the mean limiting
  magnitudes of pairs of images in which the source was not detected.}
\IBVSfigKey{5559-f1.eps}{ROTSE3 J151453.6+020934.2}{light curve}

\IBVSfig{9cm}{5559-f2.eps}{Light curve for
  ROTSE3~J221519.8-003257.2.  The diamonds represent data from ROTSE-IIId. The 
  ROTSE-III unfiltered magnitudes of the object have been calibrated 
  relative to the USNO A2.0 $R$-band colors of the field stars.
  Arrows indicate the mean limiting magnitudes of pairs of images in which the
  source was not detected.}
\IBVSfigKey{5559-f2.eps}{ROTSE3 J221519.8-003257.2}{light curve}

\newpage

\IBVS2fig{7.5cm}{5559-f3.eps}{MDM I-band image   of ROTSE3~J151453.6+020934.2 during quiescence.}{5559-f4.eps}{SDSS $r'$-band image of ROTSE3~J221519.8-003257.2 during quiescence.}
\IBVSfigKey{5559-f3.eps}{ROTSE3 J151453.6+020934.2}{}
\IBVSfigKey{5559-f4.eps}{ROTSE3 J221519.8-003257.2}{}


\references

Abazajian, K., {\it et al.} 2004, {\it AJ}, {\bf 128}, 502. %\BIBCODE{2004AJ....128..502A}

Akerlof, C. W., {\it et al.} 2003, {\it PASP}, {\bf 115}, 132. %\BIBCODE{2003PASP..115..132A}

Bertin, E. \& Arnouts, S. 1996, {\it A\&AS}, {\bf 117}, 393. %\BIBCODE{1996A\&AS..117..393B}

Howell, S., {\it et al.} 1997, {\it MNRAS}, {\bf 287}, 929. %\BIBCODE{1997MNRAS.287..929H}

Smith, D. A. {\it et al.} 2002, {\it IBVS}, {\bf 5226}, 1. %\BIBCODE{2002IBVS.5226....1S}

Szkody, P., {\it et al.} 2002, {\it AJ}, {\bf 123}, 430. %\BIBCODE{2002AJ....123..430S}

\endreferences


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