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\input ibvs2.sty 
 
\begin{document} 
\IBVShead{6024}{15 May 2012} 
 
\IBVStitletl{Photometric sequences and astrometric positions}{ of SN 2011\lowercase{fe} in M101 and SN 2012\lowercase{aw} in M95}
  
\IBVSauth{Henden, Arne;$^1$ Krajci, Tom;$^1$ Munari, Ulisse$^2$}

\IBVSinst{AAVSO, American Association of Variable Star Observers, 49 Bay State Road, Cambridge, MA 02138, USA} 
\IBVSinst{INAF Osservatorio Astronomico di Padova, Sede di Asiago, I-36032 Asiago (VI), Italy} 
 
\SIMBADobj{SN 2011fe}
\SIMBADobj{SN 2012aw} 
\IBVStyp{ supernova } 
\IBVSkey{photometry, astrometry} 
\IBVSabs{Accurate BVRcIc photometric sequences to assist the monitoring of}
\IBVSabs{their light- and color-evolution are provided for SN 2011fe in M101}
\IBVSabs{and SN 2012aw in M95, together with accurate astrometric position of}
\IBVSabs{both SN liked to UCAC2 reference catalog.}

\begintext 

SN 2011fe was discovered in M101 by the Palomar Transient Factory (Nugent et
al. 2011a) on Aug. 24 with the Palomar 1.2m Schmidt telescope when the
object was at $g$ = 17.2 magnitude, and within a few hours from discovery it
was classified as a type Ia with the Liverpool Telescope (La Palma, Canary
Islands). Comparison with explosion models suggests that SN 2011fe was
discovered only about 11 hours after its actual explosion (Nugent et al. 
2011b). The supernova peaked at $V$$\approx$9.9 mag, making it the
fifth-brightest supernova in the past century. A flurry of papers have been
already published, mainly triggered by the absence of early radio emission,
the lack of an optical counterpart for the progenitor in archival HST
images, and negative detection in early X-ray observations. Analysis of
archival HST images of the location of SN 2011fe by Li et al. (2011) shows
that the luminosity of the progenitor system (especially the companion star)
is 10$-$100 times fainter than previous limits on other type Ia supernova
progenitor systems, which rules out luminous red giants and almost
all helium stars as the mass-donating companion to the exploding white
dwarf, and the Bloom et al. (2012) analysis also rules out main sequence stars. 
The absence of early radio and X-ray emission, induced by the SN ejecta
slamming onto or expanding through pre-existing, slowly moving circumstellar
material was used by Horesh et al. (2012) and Chomiuk et al. (2012), to
put stringent limits on the density of any circumstellar material, the mass loss
rate and therefore on the nature of the SN progenitor.

SN 2012aw was discovered by Paolo Fagotti (Bastia Umbra, Italy) in M95 on
CCD images taken on Mar.  16.86 UT with a 0.5-m reflector (cf.  CBET 3054).
It was classified by Itoh et al.  (2012) as a type-IIP supernova from spectra
obtained on March 19.5 UT, and confirmed by Siviero et al.  (2012) on Asiago
spectra obtained on Mar.  17.77 and 19.85 UT as a very young type-II
supernova, resembling the type-IIP supernova 1999gi about 4--5 days after the
core-collapse.

For both SNe, the amount of published multi-band photometry is minimal with
respect to the vast amount being continuously collected world-wide. One possible
reason is the absence of accurate local photometric sequences.  This
IBVS aims to remedy the situation.

In this note we present a $B$$V$$R_{\rm C}$$I_{\rm C}$ photometric sequence
around both SNe, optimized for CCD observations and their color corrections. 
To calibrate the sequences, we obtained CCD photometry with a 0.35-m
telescope located at Astrokolkhoz Observatory in Cloudcroft (New Mexico,
USA), during a large number of photometric nights, using $B$$V$$R_{\rm
C}$$I_{\rm C}$ filters and an SBIG STL-1001E CCD camera.  Pixel size is
1\farcs25/pix and the field of view is 20$\times$20\arcm. 
Observations on each photometric night included $B$$V$$R_{\rm C}$$I_{\rm C}$
exposures of Landolt standard fields (Landolt 1983, 1992) taken at
high and low airmasses.  The photometric sequences
are presented in Figures~1 and 2.  Astrometry was performed using SLALIB
(Wallace 1994) linear plate transformation routines in conjunction with the
UCAC2 reference catalog.  Errors in coordinates were less than 0.1 arcsec in
both coordinates, referred to the mean coordinate zero point of the
reference stars in each field.

The position we derived for SN 2011fe in M101 is: 
$\alpha_{\rm J2000}$ = 14\hr03\mm05\fsec711 ($\pm$0\farcs27),
$\delta_{\rm J2000}$ = +54\deg16\arcm25\farcs22 ($\pm$0\farcs23).
The end figures of the supernova position derived by Li et al. (2012) are
05\fsec733 and 25\farcs18 (J2000.0), who observed with the Near-Infrared Camera 2
(NIRC2) mounted behind the adaptive optics (AO) system on the Keck II
telescope. Other positions as appeared on CBET 2792 are:
05\fsec81 and 25\farcs4 (Palomar 1.2m Schmidt), 05\fsec75 and 25\farcs2 (R.A. Koff,
0.25m), 05\farcs74 and 25\farcs3 (J. Brimacombe, 0.5m), 05\fsec74 and
25\farcs7 (G. Masi, 0.43m). 

Our position for SN 2012aw in M95 is: $\alpha_{\rm J2000}$ = 10\hr43\mm53\fsec735
($\pm$0\farcs091), $\delta_{\rm J2000}$ = $+$11\deg40\arcm17\farcs63
($\pm$0\farcs084).  It is within 0.11 arcsec of the unweighted
mean of the other determinations of the supernova position so far published. 
Ending figure given at the time of discovery and summarized in CBET 3054
are: 53\fsec76 and 17\farcs9 (P.  Fagotti, 0.5m), 53\fsec78 and 17\farcs0 (A.  Dimai,
0.28m), 53\fsec72 and 17\farcs7 (J.  Skvarc, 0.6m), 53\fsec73 and 17\farcs8 (G.  Masi,
0.43m); a radio observation by Yadav et al.  (2012) provides 53\fsec72 and
17\farcs5.  Positive searches for the progenitor on archival HST images of M95
are mentioned by Elias-Rosa et al.  (2012) and Fraser et al.  (2012a,b), but
no explicit astrometric position is given for the SN.

\references 

Bloom, J.S. et al. 2012, {\it ApJ}, {\bf 744}, L17

Chomiuk, L. et al. 2012, {\it ApJ}, {\bf 750}, 164

Elias-Rosa, N. et al. 2012, {\it ATel}, {\bf 3991}

Fraser, M. et al. 2012a, {\it ATel}, {\bf 3994}

Fraser, M. et al. 2012b, arXiv:1204.1523 [astro-ph.CO]

Horesh, A. et al. 2012, {\it ApJ}, {\bf 746}, 21

Itoh, R. et al. 2012, {\it CBET}, {\bf 3054}

Landolt, A.U.  1983, {\it AJ}, {\bf 88}, 439

Landolt, A.U. 1992, {\it AJ}, {\bf 104}, 340

Li, W. et al. 2011, {\it Nature}, {\bf 480}, 348 

Nugent, P.E. et al. 2011a, {\it CBET}, {\bf 2792}

Nugent, P.E. et al. 2011b, {\it Nature}, {\bf 480}, 344

Siviero, A. et al. 2012, {\it CBET}, {\bf 3054}

Wallace, P. 1994, {\it ASPC}, {\bf 61}, 481

Yadav, N. et al. 2012, {\it ATel}, {\bf 4010}

\endreferences 

\IBVSfig{19cm}{6024-f1.ps}{$BVR_{\rm C}I_{\rm C}$ photometric
comparison sequence around SN 2011fe in M101.  The cross indicates the SN. 
$N$ is the number of nights in which the given star has been measured, the
photometric uncertainties are errors of the mean.  The errors in $\alpha$ and
$\delta$ are expressed in arcsec.  The panel covers a
20$^\prime$$\times$6$^\prime$ area.}

\IBVSedata{6024-t1.txt}
\IBVSfigKey{6024-t1.txt}{SN 2011fe}{sequence}
\AladinChart{6024-t1}
\IBVSecomment{photometric sequence}


\IBVSfig{19cm}{6024-f2.ps}{$BVR_{\rm C}I_{\rm C}$ photometric
comparison sequence around SN 2012aw in M95. The cross indicates the SN. 
$N$ is the number of nights in which the given star has been measured,
the photometric uncertainties are errors of the mean. 
The errors in $\alpha$ and $\delta$ are expressed in arcsec.  The
panel covers a 20$^\prime$$\times$20$^\prime$ area.}

\IBVSedata{6024-t2.txt}
\IBVSfigKey{6024-t2.txt}{SN 2012aw}{sequence}
\AladinChart{6024-t2}
\IBVSecomment{photometric sequence}

\end{document}

