------------------------------------------------------------------------ gc_vhe.tex MNRAS, Feb.2010, 2010MNRAS.402.1342A From: Attila Abramowski To: gcnews@aoc.nrao.edu Content-Type: multipart/alternative; boundary=00148531b76719e6fe047fa53431 X-MailScanner-Information: Please contact the postmaster@aoc.nrao.edu for more information X-MailScanner: Found to be clean X-MailScanner-SpamCheck: not spam, SpamAssassin (not cached, score=0.001, required 5, autolearn=disabled, HTML_MESSAGE 0.00) X-MailScanner-From: attila.abramowski@googlemail.com X-Spam-Status: No --00148531b76719e6fe047fa53431 Content-Type: text/plain; charset=ISO-8859-1 %arXiv:1002.2364 \documentclass[useAMS, usenatbib,usegraphicx]{mn2e} \begin{document} \title{Locating the VHE source in the Galactic Centre with milli-arcsecond accuracy} \author[Abramowski et al.]{A.~Abramowski$^1$, S.~Gillessen$^2$, D.~Horns$^1$, H.-S.~Zechlin$^1$\\ $^1$Department of Physics, University of Hamburg, Luruper Chaussee 149, D-22761 Hamburg, Germany \\ $^2$MPI for Extraterrestrial Physics, Giessenbachstrasse, D-85748 Garching, Germany } \maketitle \begin{abstract} Very high-energy $\gamma$-rays (VHE; E$>$100 GeV) have been detected from the direction of the Galactic Centre up to energies E$>$10 TeV. Up to now, the origin of this emission is unknown due to the limited positional accuracy of the observing instruments. One of the counterpart candidates is the super-massive black hole (SMBH) \mbox{Sgr A$^{*}$}. If the VHE emission is produced within $\approx10^{15}$ cm $\approx1000 \ r_G$ ($r_G=G M/c^2$ is the Schwarzschild radius) of the SMBH, a decrease of the VHE photon flux in the energy range 100--300 GeV is expected whenever an early type or giant star approaches the line of sight within $\approx$ milli-arcseconds (mas). The dimming of the flux is due to absorption by pair-production of the VHE photons in the soft photon field of the star, an effect we refer to as pair-production eclipse (PPE). Based upon the currently known orbits of stars in the inner arcsecond of the Galaxy we find that PPEs lead to a systematic dimming in the 100--300 GeV band at the level of a few per cent and lasts for several weeks. Since the PPE affects only a narrow energy band and is well correlated with the passage of the star, it can be clearly discriminated against other systematic or even source-intrinsic effects. While the effect is too small to be observable with the current generation of VHE detectors, upcoming high count-rate experiments like the Cherenkov telescope array (CTA) will be sufficiently sensitive. Measuring the temporal signature of the PPE bears the potential to locate the position and size of the VHE emitting region within the inner 1000 $r_G$ or in the case of a non-detection exclude the immediate environment of the SMBH as the site of $\gamma$-ray production altogether. \end{abstract} \end{document} --00148531b76719e6fe047fa53431 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable %arXiv:1002.2364

\documentclass[useAMS,
usenatbib,usegraphicx]{m= n2e}
\begin{document}
=A0\title{Locating the VHE source in the Galact= ic Centre
=A0=A0=A0=A0=A0=A0=A0 with milli-arcsecond accuracy}
=A0\author[Abramowski et al.]{A.~Abramowski$^1$, S.~Gillessen$^2$, D.~Horns= $^1$, H.-S.~Zechlin$^1$\\
$^1$Department of Physics, University of Hambu= rg, Luruper Chaussee 149, D-22761 Hamburg, Germany \\
$^2$MPI for Extrat= errestrial Physics, Giessenbachstrasse, D-85748 Garching, Germany }
=A0\maketitle
=A0\begin{abstract}
Very high-energy $\gamma$-rays (VHE= ; E$>$100 GeV) have been detected from the
direction of the Galactic = Centre up to energies E$>$10 TeV. Up to now, the
origin of this emiss= ion is unknown due to the limited positional
accuracy of the observing instruments. One of the counterpart candidates is= the
super-massive black hole (SMBH) \mbox{Sgr A$^{*}$}.=A0=A0
If th= e VHE emission is produced within $\approx10^{15}$ cm $\approx1000 \ r_G$ <= br> ($r_G=3DG M/c^2$ is the Schwarzschild radius) of the SMBH, a decrease of th= e
VHE photon flux in the energy range 100--300 GeV is expected whenever<= br>an early type or giant star approaches the line of sight within $\approx= $ milli-arcseconds (mas).
The dimming of the flux is due to absorption by pair-production of the VHE = photons
in the soft photon field of the star, an effect we refer to as = pair-production eclipse (PPE).
Based upon the currently known orbits of = stars in the inner arcsecond of the Galaxy we find that PPEs
lead to a systematic dimming in the 100--300 GeV band at the level of a
= few per cent and lasts for several weeks.=A0 Since the PPE affects only a n= arrow energy band
and is well correlated with the passage of the star, i= t can be clearly discriminated against other
systematic or even source-intrinsic effects.
While the effect is too sm= all to be observable with the current generation of VHE detectors, upcoming= high
count-rate experiments like the Cherenkov telescope array (CTA) wi= ll be
sufficiently sensitive. Measuring the temporal signature of the PPE bears t= he
potential to locate the position and size of the VHE emitting region = within the
inner 1000 $r_G$ or in the case of a non-detection exclude th= e immediate environment of the SMBH
as the site of $\gamma$-ray production altogether.=A0
\end{abstract}\end{document}

--00148531b76719e6fe047fa53431--