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|%| arXiv:0812.3762
\documentclass[longauth,oldversion,letter]{aa}

\usepackage{graphicx}
\usepackage{natbib}
\bibpunct{(}{)}{;}{a}{}{,} % to follow AA style

\begin{document}

\newcommand{\Cerenkov}{Cherenkov\ }
\newcommand{\astar}{Sgr~A$^{\star}$}
\newcommand{\HMS}[3]{$#1^{\mathrm{h}}#2^{\mathrm{m}}#3^{\mathrm{s}}$}
\newcommand{\DMS}[3]{$#1^\circ #2' #3''$}
\newcommand{\TODO}[1]{\textbf{TODO: \emph{#1}}}
\renewcommand{\cite}{\citep} % default to parenthetical citations

\title{Simultaneous H.E.S.S. and Chandra observations of Sgr~A$^{\star}$ 
\\ during an X-ray flare}

\titlerunning{$\gamma$-ray/X-ray observations of Sgr~A$^{\star}$ during 
a flare}
 
\authorrunning{The H.E.S.S. Collaboration}


\author{
  F. Aharonian\inst{1,13}
 \and A.G.~Akhperjanian \inst{2}
 \and U.~Barres de Almeida \inst{8} \thanks{supported by CAPES 
Foundation, Ministry of Education of Brazil}
 \and A.R.~Bazer-Bachi \inst{3}
 \and Y.~Becherini  \inst{12}
 \and B.~Behera \inst{14}
 %\and M.~Beilicke \inst{4}
 \and W.~Benbow \inst{1}
 %\and D.~Berge \inst{1} \thanks{now at CERN, Geneva, Switzerland}
 \and K.~Bernl\"ohr \inst{1,5}
 \and C.~Boisson \inst{6}
 %\and O.~Bolz \inst{1}
 \and A.~Bochow \inst{1}
 \and V.~Borrel \inst{3}
 \and I.~Braun \inst{1}
 \and E.~Brion \inst{7}
 \and J.~Brucker \inst{16}
 \and P. Brun \inst{7}
 \and R.~B\"uhler \inst{1}
 \and T.~Bulik \inst{24}
 \and I.~B\"usching \inst{9}
 \and T.~Boutelier \inst{17}
 \and S.~Carrigan \inst{1}
 \and P.M.~Chadwick \inst{8}
 \and A.~Charbonnier \inst{19}
 \and R.C.G.~Chaves \inst{1}
 \and A.~Cheesebrough \inst{8}
 \and L.-M.~Chounet \inst{10}
 \and A.C. Clapson \inst{1}
 \and G.~Coignet \inst{11}
 %\and R.~Cornils \inst{4}
 %\and L.~Costamante \inst{1,29}
 \and M. Dalton \inst{5}
 \and B.~Degrange \inst{10}
 \and C.~Deil \inst{1}
 \and H.J.~Dickinson \inst{8}
 \and A.~Djannati-Ata\"i \inst{12}
 \and W.~Domainko \inst{1}
 \and L.O'C.~Drury \inst{13}
 \and F.~Dubois \inst{11}
 \and G.~Dubus \inst{17}
 \and J.~Dyks \inst{24}
 \and M.~Dyrda \inst{28}
 \and K.~Egberts \inst{1}
 \and D.~Emmanoulopoulos \inst{14}
 \and P.~Espigat \inst{12}
 \and C.~Farnier \inst{15}
 \and F.~Feinstein \inst{15}
 \and A.~Fiasson \inst{15}
 \and A.~F\"orster \inst{1}
 \and G.~Fontaine \inst{10}
 %\and Seb.~Funk \inst{5}
 \and M.~F\"u{\ss}ling \inst{5}
 \and S.~Gabici \inst{13}
 \and Y.A.~Gallant \inst{15}
 \and L.~G\'erard \inst{12}
 \and B.~Giebels \inst{10}
 \and J.F.~Glicenstein \inst{7}
 \and B.~Gl\"uck \inst{16}
 \and P.~Goret \inst{7}
 \and C.~Hadjichristidis \inst{8}
 \and D.~Hauser \inst{14}
 \and M.~Hauser \inst{14}
 \and S.~Heinz \inst{16}
 \and G.~Heinzelmann \inst{4}
 \and G.~Henri \inst{17}
 \and G.~Hermann \inst{1}
 \and J.A.~Hinton \inst{25}
 \and A.~Hoffmann \inst{18}
 \and W.~Hofmann \inst{1}
 \and M.~Holleran \inst{9}
 \and S.~Hoppe \inst{1}
 \and D.~Horns \inst{4}
 \and A.~Jacholkowska \inst{19}
 \and O.C.~de~Jager \inst{9}
 \and I.~Jung \inst{16}
 \and K.~Katarzy{\'n}ski \inst{27}
 \and S.~Kaufmann \inst{14}
 \and E.~Kendziorra \inst{18}
 \and M.~Kerschhaggl\inst{5}
 \and D.~Khangulyan \inst{1}
 \and B.~Kh\'elifi \inst{10}
 \and D. Keogh \inst{8}
 \and Nu.~Komin \inst{7}
 \and K.~Kosack \inst{1}
 \and G.~Lamanna \inst{11}
 %\and I.J.~Latham \inst{8}
 %\and A.~Lemi\`ere \inst{12}
 %\and M.~Lemoine-Goumard \inst{10}
 \and J.-P.~Lenain \inst{6}
 \and T.~Lohse \inst{5}
 \and V.~Marandon \inst{12}
 \and J.M.~Martin \inst{6}
 \and O.~Martineau-Huynh \inst{19}
 \and A.~Marcowith \inst{15}
 %\and C.~Masterson \inst{13}
 \and D.~Maurin \inst{19}
 %\and G.~Maurin \inst{12}
 \and T.J.L.~McComb \inst{8}
 \and M.C.~Medina \inst{6}
 \and R.~Moderski \inst{24}
 \and E.~Moulin \inst{7}
 \and M.~Naumann-Godo \inst{10}
 \and M.~de~Naurois \inst{19}
 \and D.~Nedbal \inst{20}
 \and D.~Nekrassov \inst{1}
 \and J.~Niemiec \inst{28}
 \and S.J.~Nolan \inst{8}
 \and S.~Ohm \inst{1}
 \and J-F.~Olive \inst{3}
 \and E.~de O\~{n}a Wilhelmi\inst{12,29}
 \and K.J.~Orford \inst{8}
 \and J.L.~Osborne \inst{8}
 \and M.~Ostrowski \inst{23}
 \and M.~Panter \inst{1}
 \and G.~Pedaletti \inst{14}
 \and G.~Pelletier \inst{17}
 \and P.-O.~Petrucci \inst{17}
 \and S.~Pita \inst{12}
 \and G.~P\"uhlhofer \inst{14}
 \and M.~Punch \inst{12}
 \and A.~Quirrenbach \inst{14}
 %\and S.~Ranchon \inst{11}
 \and B.C.~Raubenheimer \inst{9}
 \and M.~Raue \inst{1,29}
 \and S.M.~Rayner \inst{8}
 \and M.~Renaud \inst{1}
 \and F.~Rieger \inst{1,29}
 \and J.~Ripken \inst{4}
 \and L.~Rob \inst{20}
 %\and L.~Rolland \inst{7}
 \and S.~Rosier-Lees \inst{11}
 \and G.~Rowell \inst{26}
 \and B.~Rudak \inst{24}
 \and C.B.~Rulten \inst{8}
 \and J.~Ruppel \inst{21}
 \and V.~Sahakian \inst{2}
 \and A.~Santangelo \inst{18}
 %\and L.~Saug\'e \inst{17}
 \and R.~Schlickeiser \inst{21}
 \and F.M.~Sch\"ock \inst{16}
 \and R.~Schr\"oder \inst{21}
 \and U.~Schwanke \inst{5}
 \and S.~Schwarzburg  \inst{18}
 \and S.~Schwemmer \inst{14}
 \and A.~Shalchi \inst{21}
 \and J.L.~Skilton \inst{25}
 \and H.~Sol \inst{6}
 \and D.~Spangler \inst{8}
 \and {\L}. Stawarz \inst{23}
 \and R.~Steenkamp \inst{22}
 \and C.~Stegmann \inst{16}
 \and G.~Superina \inst{10}
 \and P.H.~Tam \inst{14}
 \and J.-P.~Tavernet \inst{19}
 \and R.~Terrier \inst{12}
 \and O.~Tibolla \inst{14}
 \and C.~van~Eldik \inst{1}
 \and G.~Vasileiadis \inst{15}
 \and C.~Venter \inst{9}
 \and J.P.~Vialle \inst{11}
 \and P.~Vincent \inst{19}
 \and M.~Vivier \inst{7}
 \and H.J.~V\"olk \inst{1}
 \and F.~Volpe\inst{10,29}
 \and S.J.~Wagner \inst{14}
 \and M.~Ward \inst{8}
 \and A.A.~Zdziarski \inst{24}
 \and A.~Zech \inst{6}
}

\institute{
Max-Planck-Institut f\"ur Kernphysik, P.O. Box 103980, D 69029
Heidelberg, Germany
\and
 Yerevan Physics Institute, 2 Alikhanian Brothers St., 375036 Yerevan,
Armenia
\and
Centre d'Etude Spatiale des Rayonnements, CNRS/UPS, 9 av. du Colonel 
Roche, BP
4346, F-31029 Toulouse Cedex 4, France
\and
Universit\"at Hamburg, Institut f\"ur Experimentalphysik, Luruper Chaussee
149, D 22761 Hamburg, Germany
\and
Institut f\"ur Physik, Humboldt-Universit\"at zu Berlin, Newtonstr. 15,
D 12489 Berlin, Germany
\and
LUTH, Observatoire de Paris, CNRS, Universit\'e Paris Diderot, 5 Place 
Jules Janssen, 92190 Meudon,
France
Obserwatorium Astronomiczne, Uniwersytet Ja
\and
IRFU/DSM/CEA, CE Saclay, F-91191
Gif-sur-Yvette, Cedex, France
\and
University of Durham, Department of Physics, South Road, Durham DH1 3LE,
U.K.
\and
Unit for Space Physics, North-West University, Potchefstroom 2520,
    South Africa
\and
Laboratoire Leprince-Ringuet, Ecole Polytechnique, CNRS/IN2P3,
 F-91128 Palaiseau, France
\and
Laboratoire d'Annecy-le-Vieux de Physique des Particules, CNRS/IN2P3,
9 Chemin de Bellevue - BP 110 F-74941 Annecy-le-Vieux Cedex, France
\and
Astroparticule et Cosmologie (APC), CNRS, Universite Paris 7 Denis Diderot,
10, rue Alice Domon et Leonie Duquet, F-75205 Paris Cedex 13, France
\thanks{UMR 7164 (CNRS, Universit\'e Paris VII, CEA, Observatoire de Paris)}
\and
Dublin Institute for Advanced Studies, 5 Merrion Square, Dublin 2,
Ireland
\and
Landessternwarte, Universit\"at Heidelberg, K\"onigstuhl, D 69117 
Heidelberg, Germany
\and
Laboratoire de Physique Th\'eorique et Astroparticules, CNRS/IN2P3,
Universit\'e Montpellier II, CC 70, Place Eug\`ene Bataillon, F-34095
Montpellier Cedex 5, France
\and
Universit\"at Erlangen-N\"urnberg, Physikalisches Institut, 
Erwin-Rommel-Str. 1,
D 91058 Erlangen, Germany
\and
Laboratoire d'Astrophysique de Grenoble, INSU/CNRS, Universit\'e Joseph 
Fourier, BP
53, F-38041 Grenoble Cedex 9, France
\and
Institut f\"ur Astronomie und Astrophysik, Universit\"at T\"ubingen,
Sand 1, D 72076 T\"ubingen, Germany
\and
LPNHE, Universit\'e Pierre et Marie Curie Paris 6, Universit\'e Denis 
Diderot
Paris 7, CNRS/IN2P3, 4 Place Jussieu, F-75252, Paris Cedex 5, France
\and
Institute of Particle and Nuclear Physics, Charles University,
    V Holesovickach 2, 180 00 Prague 8, Czech Republic
\and
Institut f\"ur Theoretische Physik, Lehrstuhl IV: Weltraum und
Astrophysik,
    Ruhr-Universit\"at Bochum, D 44780 Bochum, Germany
\and
University of Namibia, Private Bag 13301, Windhoek, Namibia
\and
Obserwatorium Astronomiczne, Uniwersytet Jagiello{\'n}ski, ul. Orla 171,
30-244 Krak{\'o}w, Poland
\and
Nicolaus Copernicus Astronomical Center, ul. Bartycka 18, 00-716 Warsaw,
Poland
 \and
School of Physics \& Astronomy, University of Leeds, Leeds LS2 9JT, UK
 \and
School of Chemistry \& Physics,
 University of Adelaide, Adelaide 5005, Australia
 \and
Toru{\'n} Centre for Astronomy, Nicolaus Copernicus University, ul.
Gagarina 11, 87-100 Toru{\'n}, Poland
\and
Instytut Fizyki J\c{a}drowej PAN, ul. Radzikowskiego 152, 31-342 Krak{\'o}w,
Poland
\and
European Associated Laboratory for Gamma-Ray Astronomy, jointly
supported by CNRS and MPG
}

\offprints{j.a.hinton@leeds.ac.uk}

\abstract{

The rapidly varying ($\sim$10 minute timescale) non-thermal X-ray
emission observed from Sgr A$^{\star}$ implies that particle acceleration
is occuring close to the event horizon of the supermassive black
hole. The TeV $\gamma$-ray source HESS\,J1745$-$290 is coincident with
Sgr A$^{\star}$ and may be closely related to its X-ray
emission. Simultaneous X-ray and TeV observations are required to
elucidate the relationship between these objects. We report on
joint H.E.S.S./Chandra observations performed in July 2005, during which an
X-ray flare was detected.  Despite a factor of $\approx$9 increase in the
X-ray flux of Sgr~A$^{\star}$, no evidence is found for an increase in
the TeV $\gamma$-ray flux from this region. We find that an increase
in the $\gamma$-ray flux of a factor of 2 or greater can be excluded at a
confidence level of 99\%. This finding disfavours scenarios in which
the keV and TeV emission are associated with the same population of
accelerated particles and in which the bulk of the $\gamma$-ray
emission is produced within $\sim$$10^{14}$ cm ($\sim$100$\,R_{S}$) of
the supermassive black hole.  }

\keywords{X-rays:individual sources:Sgr A*, gamma-rays:observations}

\maketitle