------------------------------------------------------------------------ heinke_c.tex Proceedings of "A Population Explosion", R. Bandyopadhyay et al. eds. Content-Type: multipart/mixed; boundary="------------020205090407070006040700" X-UVA-Virus-Scanned: by amavisd-new at fork3.mail.virginia.edu 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=0.751, required 5, autolearn=disabled, SARE_OBFU_ALL 0.75) X-MailScanner-From: coh5z@virginia.edu X-Spam-Status: No This is a multi-part message in MIME format. --------------020205090407070006040700 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit %astro-ph/0801.1279 --------------020205090407070006040700 Content-Type: text/x-tex; name="heinkec_PopExp.tex" Content-Transfer-Encoding: quoted-printable Content-Disposition: inline; filename="heinkec_PopExp.tex" \documentclass[12pt,twoside]{article} %\documentclass[onecolumn]{emulateapj} \usepackage{xrb2007} \pagestyle{myheadings} %\usepackage{graphics} %\usepackage{lscape} \usepackage{psfig} %% Use ps2pdf (preferably version 1.4) to convert a postscript file to PD= F: %%=20 %% latex file.tex %% dvips -Ppdf -G0 -o file.ps file.dvi %% ps2pdf14 file.ps file.pdf=20 %\def\Chandra{${\it Chandra}$\ } %\def\HST{${\it HST}$\ } %\newcommand{\Msun}{\ifmmode {M_{\odot}}\else${M_{\odot}}$\fi} \begin{document} % select your session by uncommenting the appropriate line %\session{Jets} %\session{Jet and Black Hole Binaries} \session{Faint Galactic XRB Populations} %\session{Faint XRBs and Galactic LMXBs} %\session{Obscured XRBs and INTEGRAL Sources} %\session{ULXs} %\session{Extragalactic Populations} %\session{Future Missions and Surveys} %\session{Population Synthesis} \shortauthor{Heinke et al.} \shorttitle{CVs in Globulars and the Galaxy} \title{Cataclysmic Variables in Globular Clusters, the Galactic Center, a= nd Local Space} \author{Craig O. Heinke} \affil{University of Virginia, Astronomy Dept., PO Box 400325, Charlottes= ville VA 22903; cheinke@virginia.edu} \author{Ashley J. Ruiter} \affil{Dept. of Astronomy, New Mexico State University, 1320 Frenger Mall= , Las Cruces, NM 88003} \author{Michael P. Muno} \affil{Space Radiation Laboratory, California Institute of Technology, Pa= sadena, CA 91125} \author{Krzysztof Belczynski} \affil{Dept. of Astronomy, New Mexico State University, 1320 Frenger Mall= , Las Cruces, NM 88003; Tombaugh Fellow} \begin{abstract} We compare the X-ray spectra and luminosities, in the 2-8 keV band, of kn= own and suspected cataclysmic variables (CVs) in different environments, = assessing the nature of these source populations. These objects include = nearby CVs observed with ASCA; the Galactic Center X-ray source populatio= n identified by Muno et al.; and likely CVs identified in globular cluste= rs. Both of the latter have been suggested to be dominated by magnetic C= Vs. We find that the brighter objects in both categories are likely to b= e magnetic CVs, but that the fainter objects are likely to include a subs= tantial contribution from normal CVs. The strangely hard spectra observe= d from the Galactic Center sources reflect the high and variable extincti= on, which is significantly greater than the canonical $6\times10^{22}$ cm= $^{-2}$ over much of the region, and the magnetic nature of many of the b= rightest CVs. The total numbers of faint Galactic Center sources are com= patible with expectations of the numbers of CVs in this field.=20 \end{abstract} \section{Introduction} The unprecedented spatial resolution of the {\it Chandra X-ray=20 Observatory} allows us to study populations of faint X-ray sources=20 at distances of kiloparsecs. Large numbers of X-ray sources of moderate luminosities=20 ($10^{31}$90 counts above 2 keV. We compare the fitted power-law photo= n indices and estimated X-ray luminosities of the globular cluster CVs wi= th the observed CV populations in Figure 1a. The locations of globular c= luster X-ray sources in this plot suggest that some (the brightest and ha= rdest) are likely magnetic systems, while many others are likely nonmagne= tic systems. =20 \begin{figure} \psfig{figure=3Dip_f1.eps,width=3D6.4in} % \includegraphics[scale=3D0.8]{ip_f1.eps} % \includegraphics[height=3D30mm]{Colors.eps} \caption{{\it Left:} X-ray luminosities vs. photon index measurements for= =20 various classes of nearby CVs vs. those measured for globular cluster X-r= ay=20 sources optically identified as CVs. =20 {\it Right:} Histograms of the photon indices of magnetic, nonmagnetic, a= nd globular cluster CVs. The bottom panel also shows the best-fit distri= bution of photon index produced by scaling the histograms of magnetic and= nonmagnetic CV photon indices to match the globular cluster CVs. } \end{figure} We selected an X-ray luminosity range ($10^{31}$ to $2\times10^{33}$ ergs= /s) that includes all globular cluster CVs in our list. In this range we= find 25 magnetic systems and 12 nonmagnetic systems with ASCA spectra. = We show histograms of the photon indices of magnetic, nonmagnetic, and cl= uster CVs in Fig. 1b. =20 We scaled the histograms of magnetic and nonmagnetic CV indices to match = the histogram of globular cluster CV indices. We find a best fit of 39$^{= +12}_{-15}$($1\sigma$)\% magnetic systems, i.e. 5 to 12 of the 23 confirm= ed globular cluster CVs, with the rest being nonmagnetic systems. Since = these systems have been identified in a nonuniform way, with strong X-ray= selection, it is likely that the fraction of magnetic CVs in globular cl= usters is lower than this value. We do not find evidence that the fracti= on of magnetic CVs (polars and intermediate polars) in globular clusters = is higher than the $\sim10$\% estimated for the field \citep{Liebert03}. \section{Galactic Center Sources} \citet{Muno04a} characterize the Galactic Center sources, finding typical= X-ray=20 luminosities of $3\times10^{31}$--$10^{33}$ ergs/s, and very hard X-ray s= pectra, with equivalent photon indices generally between 1 and -1. This = is rather harder than the typical globular cluster CV or field CV, or eve= n the magnetic CVs in either location \citep{Heinke06b}. \citet{Muno04a}= pointed out that selection effects (the high extinction and diffuse back= ground) probably had a role in the hardness of these sources. To test wh= ether the Galactic Center sources were consistent with a combination of m= agnetic and nonmagnetic CVs, or even with just magnetic CVs, we undertook= MARX simulations in which we added sources of known properties to 414 ks= (2/3 of the total used by \citet{Muno03}; the 3 longest observations, to= reduce computing time) of the real {\it Chandra} observations of the Gal= actic Center, ran detection algorithms and measured the colors of the det= ected fake sources. =20 For our simulated source population, we choose a population synthesis mod= el using the StarTrack code \citep{Belc08} as implemented in \citet{Ruite= r06}, with updates to compute the X-ray luminosities of magnetic and nonm= agnetic CVs using the prescription of \citet{Patterson85}. We show the l= uminosity functions for magnetic and nonmagnetic systems in Figure 2. We= assume that 10\% of the total CV population are magnetic systems. =20 \begin{figure} \psfig{figure=3Dip_f2.eps,width=3D6.4in} %\includegraphics{M7_rev.ps} %\includegraphics[scale=3D0.85]{ip_f2.eps} \caption{{\it Left:} Histograms of $L_X$ (2-8 keV) from StarTrack popula= tion synthesis for magnetic CVs. Blue: white dwarf--white dwarf systems, green: white d= warf--main sequence systems, red: white dwarf--evolved star systems. Bla= ck vertical line: rough lower limit of Muno observations.=20 {\it Right:} Same as left, but for nonmagnetic CVs. =20 } \end{figure} For the spectra of the simulated CVs, we choose absorbed power-law spectr= a with single gaussians to represent the Fe K line complex, with average = energies and equivalent widths based on the ASCA fits. Our absorption in= cludes both photoelectric absorption (using the XSPEC model {\it phabs}) = and scattering by dust (using P. Predehl's XSPEC model {\it scatter}, \ci= tet{Predehl03}). For nonmagnetic systems, we use an average photon index= of 1.97. For magnetic systems, we produce simulated systems with photon= indices of 0.72, 1.22, and 1.72, with a distribution set by the results = from the ASCA magnetic CV spectra. The only parameter we adjust to match= the observations is the extinction. We compare the simulated systems to= the real sources, extracted in the same way from the same Galactic Cente= r data. We compare the medium and hard colors \citep[defined by ][as (h-= s)/(h+s), where the medium color uses the 2.0-3.3 and 3.3-4.7 keV bands, = and 3.3-4.7 and 4.7-8 for the hard color]{Muno03} and measured photon flu= xes (see Figure 3). \begin{figure} \psfig{figure=3Dip_f3.eps,width=3D7in} %\includegraphics{phflux_just1e23.eps} %\includegraphics{colcol_just1e23.eps} %\includegraphics[scale=3D0.85]{ip_f3.eps} \caption{ Photon flux vs. hard color for Galactic Center sources=20 (black), and for our simulations with $N_H=3D6\times10^{22}$ (left, magen= ta) or $10^{23}$ cm$^{-2}$ (right, red).=20 Definitions of photon flux and hard color are the same as in \citet{Muno0= 4a}.=20 Triangles indicate simulations of magnetic systems, open pentagons nonmag= netic systems.=20 } \end{figure} \begin{figure} \psfig{figure=3Dip_f4.eps,width=3D6.4in} \caption{ Medium color vs. hard color for Galactic Center sources (black)= =20 and for our simulations with $N_H=3D6\times10^{22}$ (left, magenta) or $1= 0^{23}$ cm$^{-2}$ (right, red). =20 Definitions of colors as in \citet{Muno03}; triangles indicate simulation= s of magnetic systems and open pentagons nonmagnetic systems. } \end{figure} We find that the real data can be reasonably described with our model on= ly if a higher $N_H$ of $10^{23}$ cm$^{-2}$ (plus dust scattering) absorb= s the majority of the sources, rather than the canonical $N_H=3D6\times10= ^{22}$. =20 Figures 3 (color-flux) and 4 (color-color) show samples of our results, u= sing only $N_H=3D6\times10^{22}$ (left panels) or $10^{23}$ cm$^{-2}$ (r= ight panels). It can be seen that the right panels exhibit much better q= ualitative matches to the data. =20 Similar agreement can be reached using broader ranges of $N_H$ with an av= erage extinction of $10^{23}$ cm$^{-2}$. =20 %With this change, the color-color and color-flux diagrams are qualitativ= ely very well modeled, considering the large uncertainties in many aspect= s of the simulations. =20 \begin{figure} \psfig{figure=3Dip_f5_alt.eps,width=3D6.4in} %\includegraphics{plot_nh.eps} %\includegraphics[angle=3D90,height=3D3cm]{Glass87_trim.eps} %\includegraphics{ip_f4.eps} \caption{{\it Left:} Locations of Chandra X-ray sources from \citet{Muno0= 4a},=20 coded by the $N_H$ value in fits to thermal plasma spectra. Green: $N_H<= 6\times10^{22}$, red: $6-10\times10^{22}$, magenta: $10-20\times10^{22}$, blue: $>20\times= 10^{22}$.=20 {\it Right:} K-band image of Galactic Center, from the 2MASS survey. =20 } \end{figure} The interstellar absorption towards the Galactic Center is known to be in= homogeneous and filamentary. The variations in this absorption have a st= rong effect on the numbers and hardness of the galactic center X-ray sour= ces seen at different positions. This can be qualitatively seen in Figur= e 5, which compares a K-band image of the Galactic Center from the 2MASS = survey with the positions and fitted $N_H$ values of Galactic Center X-ra= y sources. =20 Current near-IR observations of the Galactic Center field \citep[e.g. ][]= {Gosling06} will improve our understanding of the effects of extinction u= pon X-rays from the Galactic Center. The total number of CVs in the Galactic Center may be inferred from our r= esults (with caveats, particularly the variability of extinction in the r= egion). The total number of simulated CVs required to match the numbers = of observed sources, using a single extinction of $N_H=3D10^{23}$ cm$^{-2= }$, is about 7000. Following \citet{Muno03}, and using an estimate of $1= \times10^{-5}$ CVs pc$^{-3}$ \citep{Grindlay05} in local space, we estima= te a total CV number in the Galactic Center of 5000. This numerical agre= ement indicates that CVs are indeed the major contributor to the Galactic= Center X-ray sources, and suggests that these CVs are not significiantly= different in their X-ray properties or formation mechanisms from CVs in = our galactic neighborhood. \section{Conclusions} Studies of faint ($10^{31}$ %%%\item Referenced in this volume, $<$author name$>$, p. $<$xxx$>$ %%%\item By the kind permission of $<$publisher, volume number, author and page number$>$ %%%\item Copyright held by $<$name and place$>$ %%%\end{itemize} %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% TITLE PAGE %%%%%%%%%%%%%%%%%%%%%%%%%%%% %%%%%%%%%%%%%%%%%%% (COMMENT OUT THE UNNEEDED COMMANDS) %%%%%%%%%%%%%%%% \newcommand{\maintitle}[1]{A POPULATION EXPLOSION: THE NATURE AND EVOLUTION OF X-RAY BINARIES IN DIVERSE ENVIRONMENTS} % In ALL CAPS \newcommand{\venue}[1]{**Where meeting was held**} % Spell out fully with the country also listed. \newcommand{\when}[1]{**When meeting was held**} % In 7--11 May 2001 format with no commas \newcommand{\firsteditor}[1]{**First Editor's Name**} \newcommand{\firstaffil}[1]{**First Editor's Affiliation**} \newcommand{\secondeditor}[1]{**Second Editor's Name**} \newcommand{\secondaffil}[1]{**Second Editor's Affiliation**} \newcommand{\thirdeditor}[1]{**Third Editor's Name**} \newcommand{\thirdaffil}[1]{**Third Editor's Affiliation**} \newcommand{\fourtheditor}[1]{**Fourth Editor's Name**} \newcommand{\fourthaffil}[1]{**Fourth Editor's Affiliation**} \newcommand{\fiftheditor}[1]{**Fifth Editor's Name**} \newcommand{\fifthaffil}[1]{**Fifth Editor's Affiliation**} \newcommand{\sixtheditor}[1]{**Sixth Editor's Name**} \newcommand{\sixthaffil}[1]{**Sixth Editor's Affiliation**} %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %%%%%%%%%%%%%%%%%%%%%%%%%%%%% COPYRIGHT PAGE %%%%%%%%%%%%%%%%%%%%%%%%%%% \def\@LCCN{**LCCN number**} \def\@ISBN{**ISBN**} %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %%%%%% %%%%%% %%%%%% IMPORTANT NOTE! 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\def\@citex[#1]#2{\if@filesw\immediate\write\@auxout{\string\citation{#2}}\fi \def\@citea{}\@cite{\@for\@citeb:=#2\do {\@citea\def\@citea{,\penalty\@m\ }\@ifundefined {b@\@citeb}{\@warning {Citation `\@citeb' on page \thepage \space undefined}}% {\csname b@\@citeb\endcsname}}}{#1}} \let\jnl@style=\rm \def\ref@jnl#1{{\jnl@style#1\/}} \def\aj{\ref@jnl{AJ}} \def\araa{\ref@jnl{ARA\&A}} \def\apj{\ref@jnl{ApJ}} \def\apjl{\ref@jnl{ApJ}} \def\apjs{\ref@jnl{ApJS}} \def\ao{\ref@jnl{Appl.Optics}} \def\apss{\ref@jnl{Ap\&SS}} \def\aap{\ref@jnl{A\&A}} \def\aapr{\ref@jnl{A\&A~Rev.}} \def\aaps{\ref@jnl{A\&AS}} \def\azh{\ref@jnl{AZh}} \def\baas{\ref@jnl{BAAS}} \def\ion#1#2{{\rm #1}~{\sc #2}} \def\jrasc{\ref@jnl{JRASC}} \def\memras{\ref@jnl{MmRAS}} \def\mnras{\ref@jnl{MNRAS}} \def\nat{\ref@jnl{Nat}} \def\pra{\ref@jnl{Phys.Rev.A}} \def\prb{\ref@jnl{Phys.Rev.B}} \def\prc{\ref@jnl{Phys.Rev.C}} \def\prd{\ref@jnl{Phys.Rev.D}} \def\prl{\ref@jnl{Phys.Rev.Lett}} \def\pasp{\ref@jnl{PASP}} 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\def\onethird{\hbox{$\,^1\!/_3$}} \def\twothirds{\hbox{$\,^2\!/_3$}} \def\onequarter{\hbox{$\,^1\!/_4$}} \def\threequarters{\hbox{$\,^3\!/_4$}} \def\ubv{\hbox{$U\!BV$}} \def\ubvr{\hbox{$U\!BV\!R$}} \def\ubvri{\hbox{$U\!BV\!RI$}} \def\ubvrij{\hbox{$U\!BV\!RI\!J$}} \def\ubvrijh{\hbox{$U\!BV\!RI\!J\!H$}} \def\ubvrijhk{\hbox{$U\!BV\!RI\!J\!H\!K$}} \def\ub{\hbox{$U\!-\!B$}} \def\bv{\hbox{$B\!-\!V$}} \def\vr{\hbox{$V\!-\!R$}} \def\ur{\hbox{$U\!-\!R$}} \newcount\lecurrentfam \def\LaTeX{\lecurrentfam=\the\fam \leavevmode L\raise.42ex \hbox{$\fam\lecurrentfam\scriptstyle\kern-.3em A$}\kern-.15em\TeX} \def\plotone#1{\centering \leavevmode \epsfxsize=.95\textwidth \epsfbox{#1}} \def\plottwo#1#2{\centering \leavevmode \epsfxsize=.45\textwidth \epsfbox{#1} \hfil \epsfxsize=.45\textwidth \epsfbox{#2}} \def\plotfiddle#1#2#3#4#5#6#7{\centering \leavevmode \vbox to#2{\rule{0pt}{#2}} \special{psfile=#1 voffset=#7 hoffset=#6 vscale=#5 hscale=#4 angle=#3}} \newif\if@finalstyle \@finalstyletrue \if@finalstyle \ps@myheadings \let\ps@title=\ps@paspcstitle \else \ps@plain \let\ps@title=\ps@plain \fi \ds@twoside % Added 7/11/06 by Jared \renewcommand\part{% \if@openright \cleardoublepage \else \clearpage \fi \thispagestyle{empty} \if@twocolumn \onecolumn \@tempswatrue \else \@tempswafalse \fi \null\vfil \secdef\@asppart\@spart} \def\@asppart[#1]#2{% \ifnum \c@secnumdepth >-2\relax \refstepcounter{part}% \addtocontents{toc}{\protect\partline{#2}}% \else \addtocontents{toc}{\protect\unpartline{#2}}% \fi \markboth{}{}% {\centering \interlinepenalty \@M \normalfont \ifnum \c@secnumdepth >-2\relax \huge\bfseries \partname\nobreakspace\thepart \par \vskip 20\p@ \fi \Huge \bfseries #2\par}% \@endpart} \newcommand\tocentry[2]{ \addtocontents{toc}{\protect\tocline{#1}{#2}{\thepage}} } \renewcommand\tableofcontents{% \pagestyle{myheadings}% \title{} \thispagestyle{plain}% \parindent 0pt% \markboth{Contents}{Contents}% \Large{\bf Contents}\normalsize\bigskip\linebreak% \@starttoc{toc}% } \def\tocline#1#2#3{\medskip\vbox{ \@dottedtocline{1}{\z@}{.4in}{#1}{#3} \smallskip \protect\@authortocline{1}{.4in}{#2} } } \def\@authortocline#1#2#3{\vskip \z@ plus .2pt {\leftskip #2\relax \rightskip \@tocrmarg \parindent\z@\relax\@afterindenttrue \interlinepenalty\@M \leavevmode \@tempdimb\textwidth \advance\@tempdimb by-#2 \advance\@tempdimb by-\@tocrmarg \parbox{\@tempdimb}{\pretolerance=10000\raggedright\small\sl#3}\par}} \newcounter{tocpart} \newcounter{tocsect}[tocpart] \def\sectline#1{\stepcounter{tocsect}\vskip 3.5ex {{\bf Section \Alph{tocsect}. #1}}\par\smallskip} %\def\unpartline#1{\stepcounter{tocpart}\vskip 5.5ex \def\unpartline#1{\vskip 5.5ex {\bf #1}\par\bigskip} \def\sectline#1{\stepcounter{tocsect}\vskip 3.5ex {{\bf Section \Alph{tocsect}. #1}}\par\smallskip} \def\partline#1{\stepcounter{tocpart}\vskip 5.5ex {\bf Part \arabic{tocpart}. #1}\par\bigskip} \def\@sect#1#2#3#4#5#6[#7]#8{% \ifnum #2>\c@secnumdepth \let\@svsec\@empty \else \refstepcounter{#1}% \protected@edef\@svsec{\@seccntformat{#1}\relax}% \fi \@tempskipa #5\relax \ifdim \@tempskipa>\z@ \begingroup #6{% \@hangfrom{\hskip #3\relax\@svsec}% \interlinepenalty \@M #8\@@par}% \endgroup \csname #1mark\endcsname{#7}% \else \def\@svsechd{% #6{\hskip #3\relax \@svsec #8}% \csname #1mark\endcsname{#7}% }% \fi \@xsect{#5}} --------------020205090407070006040700--