------------------------------------------------------------------------ sgrapaper.tex ApJ, in press Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit 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, required 5, autolearn=disabled) X-MailScanner-From: reid@cfa.harvard.edu X-Spam-Status: No %astroph/0801.4505 \documentclass[12pt,preprint]{aastex} %\documentclass{emulateapj} \usepackage{amsmath} \usepackage{amssymb} \usepackage{graphicx} \voffset 0.5truecm \newcommand\bmath[1] {\mbox{\boldmath$\rm #1$}} %\bibliographystyle{mn2e} \usepackage{natbib} \bibliographystyle{aa} % Standard abbreviations \newcommand\cf{{cf.}} %.......confer \newcommand\eg{{e.g.}} %......exempli gratia \newcommand\ie{{i.e.}} %......id est \newcommand\etal{{et al.}} %..and others \newcommand\etc{{etc}} %......et cetera % Unit abbreviations %%% Temperature \newcommand\K{{\rm K}} %...........Kelvin %%% Time \newcommand\s{{\rm s}} %...........seconds \newcommand\ns{{\rm n}\s} %........nanoseconds \newcommand\mus{\mu\s} %...........microseconds \newcommand\ms{{\rm m}\s} %........milliseconds \newcommand\ks{{\rm k}\s} %........kiloseconds \newcommand\yr{{\rm yr}} %.........years \newcommand\Myr{{\rm M}\yr} %......megayears \newcommand\Gyr{{\rm G}\yr} %......gigayears \newcommand\hr{{\rm hr}} %%% Frequency \newcommand\Hz{{\rm Hz}} %.........Hertz \newcommand\muHz{\mu\Hz} %.........microhertz \newcommand\mHz{{\rm mHz}} %.......millihertz \newcommand\MHz{{\rm MHz}} %.......Megahertz \newcommand\GHz{{\rm GHz}} %.......Gigahertz \newcommand\THz{{\rm THz}} %.......Terahertz %%% Length \newcommand\m{{\rm m}} %...........meters %\newcommand\fm{{\rm f}\m} %........femtometers \newcommand\nm{{\rm n}\m} %........nanometers \newcommand\mum{\mu\m} %...........micrometers \newcommand\mm{{\rm m}\m} %........millimeters mjr> cat reid.tex %astroph/0801.4505 \documentclass[12pt,preprint]{aastex} %\documentclass{emulateapj} \usepackage{amsmath} \usepackage{amssymb} \usepackage{graphicx} \voffset 0.5truecm \newcommand\bmath[1] {\mbox{\boldmath$\rm #1$}} %\bibliographystyle{mn2e} \usepackage{natbib} \bibliographystyle{aa} % Standard abbreviations \newcommand\cf{{cf.}} %.......confer \newcommand\eg{{e.g.}} %......exempli gratia \newcommand\ie{{i.e.}} %......id est \newcommand\etal{{et al.}} %..and others \newcommand\etc{{etc}} %......et cetera % Unit abbreviations %%% Temperature \newcommand\K{{\rm K}} %...........Kelvin %%% Time \newcommand\s{{\rm s}} %...........seconds \newcommand\ns{{\rm n}\s} %........nanoseconds \newcommand\mus{\mu\s} %...........microseconds \newcommand\ms{{\rm m}\s} %........milliseconds \newcommand\ks{{\rm k}\s} %........kiloseconds \newcommand\yr{{\rm yr}} %.........years \newcommand\Myr{{\rm M}\yr} %......megayears \newcommand\Gyr{{\rm G}\yr} %......gigayears \newcommand\hr{{\rm hr}} %%% Frequency \newcommand\Hz{{\rm Hz}} %.........Hertz \newcommand\muHz{\mu\Hz} %.........microhertz \newcommand\mHz{{\rm mHz}} %.......millihertz \newcommand\MHz{{\rm MHz}} %.......Megahertz \newcommand\GHz{{\rm GHz}} %.......Gigahertz \newcommand\THz{{\rm THz}} %.......Terahertz %%% Length \newcommand\m{{\rm m}} %...........meters %\newcommand\fm{{\rm f}\m} %........femtometers \newcommand\nm{{\rm n}\m} %........nanometers \newcommand\mum{\mu\m} %...........micrometers \newcommand\mm{{\rm m}\m} %........millimeters \newcommand\cm{{\rm c}\m} %........centimeters \newcommand\km{{\rm k}\m} %........kilometers % Angnstroms are already \AA \newcommand\pc{{\rm pc}} %.........parsecs \newcommand\kpc{{\rm k}\pc} %......kiloparsecs \newcommand\Gpc{{\rm G}\pc} %......gigaparsecs \newcommand\au{{\rm au}} %.........astronomical units %%% Mass \newcommand\g{{\rm g}} %...........grams \newcommand\mug{\mu\g} %...........micrograms \newcommand\mg{{\rm m}\g} %........milligrams \newcommand\kg{{\rm k}\g} %........kilograms %\newcommand\Ms{M_\odot} %...........solar masses %%% Energy \newcommand\eV{{\rm eV}} %.........electron volts \newcommand\keV{{\rm k}\eV} %......kiloelectron volts \newcommand\MeV{{\rm M}\eV} %......megaelectron volts \newcommand\GeV{{\rm G}\eV} %......gigaelectron volts \newcommand\TeV{{\rm T}\eV} %......teraelectron volts \newcommand\PeV{{\rm P}\eV} %......petaelectron volts \newcommand\XeV{{\rm X}\eV} %......exaelectron volts \newcommand\ZeV{{\rm Z}\eV} %......zetaelectron volts \newcommand\erg{{\rm erg}} %.......ergs \newcommand\J{{\rm J}} %...........joules %%% Magnetic Fields \newcommand\G{{\rm G}} %...........gauss \newcommand\nG{{\rm n}\G} %........nanogauss \newcommand\muG{\mu\G} %...........microgauss \newcommand\mG{{\rm m}\G} %........milligauss \newcommand\kG{{\rm k}\G} %........kilogauss \newcommand\T{{\rm T}} %...........tesla \newcommand\muT{\mu\T} %...........microtesla \newcommand\mT{{\rm m}\T} %........millitesla %%% Angular Resolution % ^\circ is already degrees % ' is alrady minutes % `` is already seconds \newcommand\mas{{\rm mas}} %.......milli-arcseconds \newcommand\muas{\mu{\rm as}} %....micro-arcseconds \newcommand\nas{{\rm nas}} %.......nano-arcseconds %%% Spot & Disk Flux densities %\newcommand\Fspot{{\rm F}_{spot}} %\newcommand\Fdisk{{\rm F}_{disk}} \renewcommand\d{{\rm d}} \newcommand\e{{\rm e}} \newcommand\sinc{{\rm sinc}} \newcommand\SgrA{Sgr~A*} \newcommand\EGS{J1745$-$2820} \newcommand\kms{km~s$^{-1}$} \newcommand\uvplane{$(u,v)$-plane} \newcommand\Msun{M$_\odot$} \newcommand\Ro{R_0} \newcommand\hho{H$_2$O} %This is how to have an approximate sign under < or > : \newbox\grsign \setbox\grsign=\hbox{$>$} \newdimen\grdimen \grdimen=\ht\grsign \newbox\laxbox \newbox\gaxbox \setbox\gaxbox=\hbox{\raise.5ex\hbox{$>$}\llap {\lower.5ex\hbox{$\sim$}}}\ht1=\grdimen\dp1=0pt \setbox\laxbox=\hbox{\raise.5ex\hbox{$<$}\llap {\lower.5ex\hbox{$\sim$}}}\ht2=\grdimen\dp2=0pt \newcommand{\gax}{\mathrel{\copy\gaxbox}} \newcommand{\lax}{\mathrel{\copy\laxbox}} % \begin{document} \title{Limits on the Position Wander of Sgr A*} \author{Mark J. Reid$^1$, Avery E. Broderick$^{1,2}$, Abraham Loeb$^1$, Mareki Honma$^3$, Andreas Brunthaler$^4$} \affil{1. Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA\\ 2. Canadian Institute for Theoretical Astrophysics, 60 St. George Street, Toronto, ON Canada\\ 3. Mizusawa VERA Observatory, NAOJ, Mitaka, Tokyo 181-8588, Japan\\ 4. Max-Planck-Institute f\"ur Radioastronomie, 69 Auf dem H\"ugel, Bonn-53121, Germany} \shorttitle{} \shortauthors{Reid et al.} \begin{abstract} We present measurements with the VLBA of the variability in the centroid position of \SgrA\ relative to a background quasar at $7\,\mm$ wavelength. We find an average centroid wander of $71\pm 45\,\muas$ for time scales between 50 and $100\,\min$ and $113\pm50\,\muas$ for timescales between 100 and $200\,\min$, with no secular trend. These are sufficient to begin constraining the viability of the accretion hot-spot model for the radio variability of \SgrA. It is possible to rule out hot spots with orbital radii above $15\,G M_{\rm Sgr A*}/c^2$ that contribute more than 30\% of the total $7\,\mm$ flux. However, closer or less luminous hot spots remain unconstrained. Since the fractional variability of \SgrA\ during our observations was $\sim20$\% on time scales of hours, the hot-spot model for \SgrA's radio variability remains consistent with these limits. Improved monitoring of \SgrA's centroid position has the potential to place significant constraints upon the existence and morphology of inhomogeneities in a supermassive black hole accretion flow. \end{abstract} \end{document}