The Duty-cycle of Gamma-ray Blazars: a New Approach, New Results
S. Vercellone
We study several properties of blazars detected in the gamma-ray energy range by comparing the \egret sources with a sample of radio blazars which can be considered possible gamma-ray candidates. We define three classes: non-gamma-ray blazars, blazars with quasi-steady gamma-ray emission, and gamma-ray blazars with substantial activity level. By combining the information of detected and candidate AGNs, we characterise the blazar activity, including the discovery of a region of consistency between the gamma-ray flaring duty-cycle and the recurrence time between flares. We also find a possible relation between the activity index of FSRQs and their black hole mass.
Vercellone.tex
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%%%%% AUTHORS - PLACE YOUR OWN MACROS HERE %%%%%
\def \agile {{\it AGILE} }
\def \egret {{\it EGRET} }
\def \glast {{\it GLAST} }
\def \degmark{^\circ}
\def \ergsec{\hbox{erg s$^{-1}$}}
\def \ferg {erg cm$^{-2}$ s$^{-1}$}
\def \arcmin {\hbox{$^\prime$}}
\def \arcsec {\hbox{$^{\prime\prime}$}}
\def \chisq {$\chi ^{2}$}
\def \rchisq {$\chi_{\nu} ^{2}$}
\def \gray {$\gamma$-ray }
\def \jvas {JVAS$++$ }
\def \pqj {PQJ }


\def \apj {ApJ}
\def \apjs {ApJS}
\def \aap {A\&A}
\def \mnras {MNRAS}
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\begin{document}

\title{The Duty-cycle of Gamma-ray Blazars: a New Approach, New Results}


\author{S. Vercellone}{
  address={IASF-CNR Sezione di Milano, Via Bassini 15, 20133 Milano - Italy}
}

\author{S. Soldi}{
  address={ISDC,
  Chemin d'{\`E}cogia 16, 1290 Versoix - Switzerland}
}

\author{A.W. Chen}{
  address={IASF-CNR Sezione di Milano, Via Bassini 15, 20133 Milano - Italy}
  ,altaddress={CIFS, Viale Settimio Severo 63, Torino - Italy}
}

\author{M. Tavani}{
  address={IASF-CNR Sede di Roma, Via del Fosso del Cavaliere 101, Roma - Italy}
  ,altaddress={CIFS, Viale Settimio Severo 63, Torino - Italy}
}


\begin{abstract}
We study several properties of blazars detected in the gamma-ray energy range
by comparing the \egret sources with a sample of radio blazars
which can be considered possible gamma-ray candidates. We define three
classes: non-gamma-ray blazars, blazars with quasi-steady gamma-ray emission,
and gamma-ray blazars with substantial activity level. 
By combining the information of detected and candidate AGNs, we characterise
the blazar activity, including the discovery of a region of consistency between 
the gamma-ray flaring duty-cycle and the recurrence time between flares.
We also find a possible relation between the activity index of FSRQs and their
black hole mass. 

\end{abstract}

\maketitle

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%=============================================================
\section{Introduction}
%=============================================================
Among Active Galactic Nuclei (AGN), {\it blazars}
show strong flux variability at almost all frequencies of the
spectral energy distribution (SED). The \egret instrument  on-board of
CGRO detected, above 30~MeV, blazars as a {\em class} of \gray 
sources \cite{Hartman99}, identifying 67 objects, and detecting 27 candidates.
Gamma-ray blazars are characterised by high variability on different 
time--scales, from one day (e.g. PKS~1622-297) to one month 
(e.g. PKS~0208-512).
This large spread in time variability and the sparse coverage obtained by
\egret make it difficult to quantify parameters such as the {\it duty--cycle}
(i.e. the fraction of time spent in a flaring state)
and/or the characteristic time--scale  of \gray activity for this class
of sources. 

A preliminary result was obtained by \cite{Stecker96},
based on the Second \egret Catalogue assuming that the link between
the radio and the \gray emission can be used to derive the \gray luminosity 
function. Under these assumptions, they found that a duty--cycle
$\zeta = 0.03$ is consistent with the data. One weakness
of this analysis is that the radio-gamma relationship is highly
uncertain.

The aim of this Paper is to summarize a recent result
on the estimate of the blazar duty--cycle and \gray variability 
\cite{Vercellone04}.

%============================================================
\section{The Blazar \gray variability}
%=============================================================
In order to investigate the blazar \gray duty--cycle, we analysed 
the Third \egret Catalogue (3EG) AGN sample, looking for recurrent activity.
For each source we considered the number of viewing
periods (VPs) during which it was close enough to the pointing direction
($<40^{\circ}$, the FOV radius) that its exposure for that
VP was greater than zero.
%
For each source we calculated the {\it Exposure} ($EXP$), defined as
the sum of the exposures during each single viewing period.
%
%___________________>>>>>>> multi-fom - ME488rv_fig2.eps <<<<<<<______________
\begin{figure}[!ht]
  \includegraphics[height=.4\textheight]{Vercellone_fig1}
  \caption{Four different examples of blazar \gray activity as a function
      of exposure. {\it Top-left panel:} 3EG~J0845$+$7049 with $HSN=1$
      despite its high exposure; {\it Top-right panel:}
      3EG~J1733$-$1313 which, for a similar exposure, has $HSN=5$;
      {\it Bottom-left panel:} 3EG~J0530$+$1323 which showed a possible periodicity 
      in its high-state status, and {\it Bottom-right panel: } 3EG~J0340$-$0201 which 
      has a very low exposure ($\sim 64 \times 10^{7}$ cm$^{2}$s), but showed
      2 high-states in a few observations.
      Crosses show the value of the discrete $\psi$ for each VP containing the source.}
%      The inset displays the discrete $\psi$ curve on a smaller scale to show the
%      finer details.}
    \label{multi-fom}
\end{figure}
%_______________________________________________________________________________
%

In order to estimate the \gray activity level, we computed the number of times
that a source was in a {\it high-state} ($HSN$) i.e. when the flux of the
$i$-th VP was greater than a given threshold.
%Following \cite{Jorstad01b}, we establish that
We establish that
a source is in a high-state when 1) the flux of the $i$-th VP is in excess of
1.5 times the mean flux of the source, and 2) the 1-$\sigma$ uncertainty of the 
measurement at the high state is less than the deviation of the measurement 
from the mean.
%\footnote{The $HSN$ statistic is asymmetric, since we consider only those
%flux values {\it above} a given threshold, i.e. we consider only flares but not
%dips. This is acceptable because \egret detected most of the AGNs
%flaring off-axis, where it is more difficult to establish a significant upper 
%limit. For this reason, we do not expect a significant number of dips.}.
The mean flux is defined as the 
weighted mean of all the detections and upper limits, assuming the 
weight $w(\sigma)=1/\sigma$, where $\sigma$ is the uncertainty of the
measurement for detections, while $\sigma = UL$ for the upper limits.
%
%This definition can be represented by the following equation:
%
%\begin{equation}
%  \begin{array}{rll}
%  HSN_{\rm src} = \sum_{i=1}^{n} [F_{i} : F_{i} \ge 1.5 \times F_{\rm mean} =1]\,
%  HSN_{\rm src} & = & \sum_{i=1}^{n} C_{i}\,,\\
%  C_{i} & = & 1\,\,\,{\rm if}\,\,\,F_{i} \ge 1.5 \times F_{\rm mean}\,\\
%  C_{i} & = & 0\,\,\,{\rm otherwise}
%  \end{array}
%\label{def_HSN}
%\end{equation}
%
%where $F_{i}$ is the \gray flux (positive detection only) of the $i$-th VP,
%$F_{\rm mean}$ is the weighted mean flux for that particular source,
%and $n$ is the total number of VPs for which the source had a detection.
If two high-states were less than 2 weeks apart (the typical duration
of an \egret pointing), we gathered them into a single high-state
coincident with the first one.
%
%This definition of the \gray mean flux gives results comparable to those
%obtained by means of the {\tt ASURV Rev 1.2}  software package
%\citep{Isobe90,Lavalley92}, which implements the methods presented in
%\citet{Feigelson85} for univariate statistical problems dealing with detections
%and upper limits. 

%
Given $EXP$ and $HSN$, we computed an {\it activity index} ($\psi$) of 
each AGN as follows:
\begin{equation}
  \psi_{\rm src} = HSN_{\rm src} \times [EXP_{\rm src}]^{-1}\,\,\,
  [{\rm cm}^{-2}{\rm s}^{-1}]\,.
\end{equation}
This index provides an estimate of blazar \gray activity, weighted by the
exposure. Sources with high $\psi$ have a \gray
activity which is highly variable. Sources with $\psi = 0$
%are sources that do not show significant flux variability.
do not show significant flux variability.

We analysed the behaviour of each single source having $\psi \neq 0$
during its time history. Fig.~\ref{multi-fom} shows the discrete $\psi$ 
for some \egret sources as a function of $EXP$.
%
%\begin{equation}
%  \begin{array}{rll}
%    EXP_{\rm src}^{k} & = & \sum_{i=1}^{k} EXP_{i}(l_{\rm src},b_{\rm src}) 
%    \times [\Omega _{i}(l_{\rm src},b_{\rm src})]^{-1}\,, \\
%    & & \\
%    HSN_{\rm src}^{k} & = &\sum_{i=1}^{k} C_{i} \,, \\
%    & & \\
%    \psi_{\rm src}^{k} & = & HSN_{\rm src}^{k} \times [EXP_{\rm src}^{k}]^{-1}\,, \\
%    & & \\
%    k & = & 1,\cdots,n\,,
%  \end{array}
%\end{equation}
%where the $C_{i}$ definition is similar to that of Eqn.~\ref{def_HSN}.
We show four different examples of activity behaviour: 1) 3EG~J0845$+$7049,
with a single $HSN=1$ despite its large exposure; 2) 3EG~J1733$-$1313,
which, for a similar exposure, has $HSN=5$; 3) 3EG~J0530$+$1323,
showing a possible periodicity in its high-state status, and 4)
3EG~J0340$-$0201, which has a very low exposure ($\sim 64 \times 10^{7}$ cm$^{2}$s),
but showed 2 high-states in a few observations.

Sources that have $HSN=1$ (e.g., 3EG~J0845$+$7049) show a rise 
of $\psi_{src}^{k}$ followed by a decay after reaching a single high state,
while sources that have high $HSN$ (e.g. 3EG~J0530$+$1323) show a saw-tooth
pattern, corresponding to alternately increasing/decreasing of $\psi_{\rm src}^{k}$.

%
We distinguish sources for which the activity level 
$\psi = 0$ (population {\it A}, $36$ per cent), and the ones having
$\psi \neq 0$ (population {\it B}, $64$ per cent).
%
A remarkable difference appears in the two populations when we compare the
ratio between flat-spectrum radio quasars (FSRQs) and BL-Lac objects
(BLs). Population A is almost equally divided between FSRQs and BLs 
($\sim$60 and $\sim$40 per cent, respectively), while
Population B is dominated by FSRQs ($\sim 80$ per cent).
FSRQs are generally more variable and more luminous in the \gray
energy band than BLs, which could explain the higher fraction of these
sources in Population B.
%
A possible correlation is found between the activity level and the black hole
mass, with a probability $P_{\rm rand}$ of a randomly distributed 
%%%C sample of objects on the order of $\sim 10^{-3}$.
sample of objects on the order of $\sim 10^{-2}$.
We suggest that the
use of the $\psi$ statistic is more robust than the use of the $HSN$,
since the latter is not weighted by the \egret coverage.
%


%---------------------------------------------
\section{The blazar gamma-ray duty--cycle} \label{act_frac}
%--------------------------------------------
We develop a simplified
model of \egret blazar activity that yields rough, but quantifiable, estimate
of physical parameters of interest.
In this simplified model, we make several assumptions:
\begin{enumerate}
\item that all of the \egret blazars exhibit the same basic behaviour.  While
observationally unjustified, this assumption is necessary to model
the average behaviour. 
%In principle, two-tier or higher models can be 
%developed based on the simple model.
\item that only those blazars detected by \egret are part of the population of
interest. 
%At the end of this subsection we address the consequences when
%this assumption is relaxed.
\item that the behaviour of all \egret blazars can be characterised by a
simple model with only two free parameters, the duty--cycle, $\chi$, and the 
characteristic time--scale, $T$.  Each blazar will spend a period of time whose
average length is $T$ at a low flux level ({\it off}) before emitting a 
\gray flare of duration $\tau$ at a high flux level ({\it on}), then 
returning to a low level.  The duty--cycle is then defined as the 
fraction of time spent in the {\it on} state:
%
\begin{equation}
  \chi = \frac{\tau}{\tau + T}\;.
\end{equation}
%
Note that all blazars have the same characteristic time--scale $T$, but
the duration of each individual quiescent periods is drawn from a Poisson
distribution with mean $T$.
\end{enumerate}
%In the next subsubsection we describe the procedure used to estimate the
%range of values of $\chi$ and $T$ that are consistent with the \egret data.
%
%\subsubsection{Procedure}
We explored the parameter space of $(\chi,T)$.  For each pair of $\chi$ and
$T$ under consideration, we generated 100 sets of 67 simulated light curves
covering the entire time interval of \egret Cycle 1 to 4 (1620 days),
one for each blazar. The time sequence of {\it on-off} states was determined
by drawing the durations of the {\it off} states from a Poisson distribution 
with mean $T$. The durations of the {\it on} states were fixed at $\tau$.  
To obtain the observed fluxes, we used a bootstrap procedure.  Each light
curve was compared with the observation history of the corresponding AGN.
If a given viewing period (VP) coincided with an {\it on} state, the observed
flux was randomly drawn from the distribution of all fluxes {\it detected} from
all \egret blazars during a single VP. Otherwise, the observed flux was 
randomly drawn from the distribution of all {\it upper limits} 
(i.e. non-detections) at \egret blazar positions during a single VP. 
For each AGN the flux values assigned to each VP were used to calculate its 
$HSN$ (and therefore its categorisation as Population A or B) in the same 
manner as the actual \egret blazar $HSN$. 
The result is 100 sets of simulated blazar light curves, each 
with a ratio $R_{\rm AB}={\rm \# Pop.A/(\# Pop.A+\# Pop.B)}$.  Thus
for each pair of values of $(\chi,T)$, we have obtained a distribution of
100 simulated values of $R_{\rm AB}$, each with a mean and variance. Therefore,
we are able to define a confidence region of $(\chi,T)$ pairs whose mean
values of $R_{\rm AB}$ are within one standard deviation of the observed
value $R_{\rm AB} = 24/67 = 0.36$. For values of $R_{\rm AB}$ close to
the observed value, the simulations give a standard deviation of $0.05$.
We ran 100 simulations each for 390 $(\chi,T)$ pairs, ranging 
from $0<T<450$~days and from $0<\chi<1$.  Fig.~\ref{popab_005} 
shows the results.
%
%___________________>>>>>>> popab_005  - ME488rv_fig13.eps <<<<<<<______________
\begin{figure}[!ht]
  \includegraphics[height=.4\textheight]{Vercellone_fig2}
  \caption{Mean ratio $R_{\rm AB}={\rm \# Pop.A/(\# Pop.A+\# Pop.B)}$ from
    simulations of \egret-detected blazars only.}
%      Each point represents the mean value from 100 simulations of \egret
%      blazar light curves given the values of the mean interval between emission
%      states, $T$, and the duty--cycle,$\chi$, at that point. 
%      Filled triangles, small filled circles, and crosses represent ratio values
%      between $0.31 \le R_{\rm AB} \le 0.41$, $0.0 \le R_{\rm AB} < 0.31$, and
%      $0.41 < R_{\rm AB} \le 1.0$, respectively.  The filled triangles are
%      consistent with the observed \egret data assuming that all \egret-detected
%      blazars, and no other sources, have the same $T$ and $\chi$.}
  \label{popab_005}
\end{figure}
%________________________________________________________ 
%
%
%\subsubsection{Results}
%
Points in  Fig.~\ref{popab_005} represent the mean value of $R_{\rm AB}$ for 
each value of $T$ and $\chi$. The filled triangles represent
those ratio values between $0.31 \le R_{\rm AB} \le 0.41$, small filled
circles represent $0.0 \le R_{\rm AB} < 0.31$, while crosses represent 
$0.41 < R_{\rm AB} \le 1.0$.  Taking into account our simplifying assumptions,
including the restriction that the observed \egret blazars form the entire
population of \gray emitting blazars, the only region consistent with the
observations is the region where $0.31 \le R_{\rm AB} \le 0.41$.  The
region with high $R_{\rm AB}$ produces too few flaring sources, while
the region with low $R_{\rm AB}$ produces too many.  This implies that the
true characteristic time--scale $T$ lies between 50 and 400 days, the
duty--cycle $\chi$ becoming more extreme for lower values of $T$.
Note that for the Stecker \& Salamon duty--cycle of 0.03 the characteristic
time--scale $T$ would be on the order of 50 days.

If we should take into account a wider sample of \gray blazar, by including
radio blazars emitting at a level of 250~mJy, we would obtain that the 
low $R_{\rm AB}$ region to remain excluded, because adding more sources is 
unlikely to reduce the absolute number of Population B sources predicted, 
which is higher than the number observed. 
On the other hand, the $(\chi,T)$ pairs in the high $R_{\rm AB}$ region
may now be consistent with the \egret data.
Therefore, the region in $(\chi,T)$ space where formerly the $R_{\rm AB}$ was 
consistent with the observed value now forms a lower
bound to the possible values of $T$ for a given value of $\chi$.

%---------------------------------------------
\section{The Black Hole Mass -- Activity Relationship} \label{act_mbh}
%--------------------------------------------
%The possible relation between the black hole mass and the
%\gray luminosity deserves a deeper analysis. 
Recently, \cite{Fan04} 
estimated the black hole mass for 36 \egret AGNs from their optical continuum 
luminosity; they claim a positive correlation (significance level 96.6 per cent) between
the maximum \gray source luminosity and the black hole mass.

We look for a possible correlation between the \gray maximum
luminosity, $L_{\gamma}^{\rm max}$, and the black hole mass, $M_{\rm BH}$, 
obtained by adopting the black hole masses reported in \cite{Woo02} for
all the \egret blazars except for 3C~273, whose $M_{\rm BH}$ was taken from
\cite{Kaspi00}. 
%Horizontal bars represent the typical black hole mass estimate uncertainty
%as reported by \citet{Vestergaard04}. 
The correlation is absent when considering
%%%C the whole sample (Spearman statistics: $\rho = 0.48$, and $P = 0.11$),
the whole sample (Spearman statistic: $\rho = 0.44$, and $P = 0.15$),
and becomes marginal if we take into account the FSRQs only 
%%%C ($\rho = 0.79$, and $P=0.012$).
($\rho = 0.60$, and $P=0.08$).
The relation between luminosity and black hole mass is, approximately,
%%%C $L_{\gamma} \propto M_{\rm BH}^{1.01}$ for FSRQs, in agreement with the predicted 
$L_{\gamma} \propto M_{\rm BH}^{0.9}$ for FSRQs, consistent with the predicted 
relation by \cite{Dermer95}, although their assumptions
(\gray emission is isotropic radiation produced by the steady and Eddington--limited
accretion without considering the beaming effect) do not agree with
recent results on \gray blazars \cite{Jorstad01a}.
%
%___________________>>>>>>> act_vs_mbh.eps - ME488rv_fig9.eps<<<<<<<______________
\begin{figure}[!ht]
  \includegraphics[height=.4\textheight]{Vercellone_fig3}
  \caption{\gray activity ($\psi$) vs. black hole mass ($M_{\rm BH}$) for
    \egret Pop. B blazars. A marginal correlation is present
%%%C      ($\rho=0.87$ and $P=0.0012$, Spearman statistic). The solid line represent
%%%C      the best fit line, $\log (\psi)=0.096\times \log ({\rm M_{\rm BH}})-0.065$.
    ($\rho=0.76$ and $P=0.01$, Spearman statistic). The solid line represents
    the best fit line, $\log (\psi)=0.013\times \log ({\rm M_{\rm BH}})-0.099$.
    Horizontal bars represent the typical black hole 
    mass estimate uncertainty as reported by \cite{Vestergaard04}.}
  \label{act_vs_mbh}
\end{figure}
%________________________________________________________ 
%
%
%We should consider a possible bias induced by the black hole mass estimation
%method. For most of the \gray sources in the \cite{Woo02} sample,
%black hole masses have been estimated
%by means of their optical luminosity. This justifies the use of a partial
%correlation analysis when estimating the correlation parameters between 
%$L_{\gamma}^{\rm max}$ and  $M_{\rm BH}$. In this case, the marginal correlation
%%%C vanishes, since $\rho= 0.58$, and $P = 0.1$.
%vanishes, since $\rho= 0.38$, and $P = 0.3$.
%
%
When analysing the possible correlation between the activity level, $\psi$, 
and the maximum \gray luminosity, we find no correlation ($\rho= 0.14$, 
and $P = 0.39)$.
We found a possible correlation between the activity index
$\psi$ and $M_{\rm BH}$.
Fig.~\ref{act_vs_mbh} shows our results based on ten blazars with
non-zero $\psi$ and the black hole mass estimation.
The Spearman correlation parameters turn out to be 
%%%C $\rho=0.87$ and $P = 0.001$. 
$\rho=0.76$ and $P = 0.011$. 
This possible correlation seems to indicate that more massive 
BHs can induce
higher \gray activity, although our sample is too small to draw a firm
conclusion. More reliable BH mass estimates of a larger blazar sample
will be crucial in verifying the existence of this correlation.
%
%The absence of a correlation between the \gray luminosity and the activity, 
%and the possible existence of a correlation between the activity 
%and the BH mass, lead us to conclude that the correlation
%between the \gray luminosity and the BH mass is most likely spurious. 



% An alternative hypothesis presents itself based on the discussion in Section~3,
% however.  Let us assume instead that at least some of the Population 0 
% sources are in fact also \gray emitting blazars with the same 
% characteristic $\chi$ and $T$ as the detected blazars, but were below the 
% flux detection threshold in every VP during which they were within the 
% \egret field of view.  Although we have not performed detailed simulations of
% this second case, we can draw some general conclusions.
% First, we can expect that the $(\chi,T)$ pairs in the low $R_{\rm AB}$  
% region to remain excluded, because adding more sources is unlikely to reduce
% the absolute number of Population B sources predicted, which is higher than 
% the number observed.  On the other hand, the $(\chi,T)$ pairs in the 
% high $R_{\rm AB}$ region
% may now be consistent with the \egret data.  Assume that given the larger
% population of sources that the overall distribution of active to inactive
% sources remains the same.  We would expect more of the inactive sources to
% remain undetected than the active sources.  Therefore,
% the ratio $R_{\rm AB}$ calculated using only the 
% subset of detected blazars would be lower than the value calculated including
% the entire population, because, according to our definitions,
% all of the blazars with only upper limits would be classified as Population A,
% if they were detected. Thus the observed
% value of $R_{\rm AB}$ would be an underestimate of the ``true'' value.
% Therefore, the region in $(\chi,T)$ space where formerly the $R_{\rm AB}$ was 
% consistent with the observed value now forms a lower
% bound to the possible values of $T$ for a given value of $\chi$.  Note that in
% principle one could find an upper bound for $T(\chi)$ by running the 
% simulation with all possible \gray blazar candidates included.  However, 
% this upper bound would be far more uncertain, both because of the difficulty
% of defining the blazar candidate population, and because the simplification
% of a single parameter $\chi$ characterising both the duration and 
% fraction of time spent in an {\it on} state would begin to break down for
% very large values of $T$.

\section{Conclusions}
The results presented here summarize a more detailed analysis presented in
\cite{Vercellone04} where we discuss the implications on the duty--cycle
estimate of a sample of candidate \gray AGNs extracted from recently published
radio catalogues. A firm estimate of the duty--cycle will be a scientific goal 
of future \gray missions such as \agile and \glast. Their wide FOV ($\sim60^{\circ}$)
will allow monitoring of a large number of AGNs for each pointing on long time--scales.
For the time being, an extensive black hole
mass estimation by means of optical spectroscopy on FSRQs and BL~Lac objects will
allow us to better understand the relation between the  central engine 
and the \gray activity.



%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% BACKMATTER
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

%\begin{theacknowledgments}
%We acknowledge partial support by the Italian Space Agency (ASI).
%\end{theacknowledgments}

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\bibitem{Hartman99} 
  Hartman R.~C.~et al., 1999, ApJS, 123, 79 
%\bibitem{Isobe90} Isobe T., Figelson E.~D., 1990, 
%  BAAS, 22, 917
%\bibitem{Jackson02} Jackson C.~A., Wall J.~V., Shaver P.~A., 
%  Kellermann K.~I., Hook I.~M., Hawkins M.~R.~S., 2002, A\&A, 386, 97 
\bibitem{Jorstad01a} Jorstad S.~G.~et al., 
%  Marscher A.~P., Mattox J.~R., Wehrle A.~E., Bloom S.~D., Yurchenko A.~V., 
  2001a, \apjs, 134, 181 
%\bibitem{Jorstad01b} Jorstad S. et al., 2001, ApJ, 556, 738 
%  ~G., Marscher A.~P., Mattox J.~R., Aller M.~F., Aller H.~D., Wehrle A.~E., 
%  Bloom S.~D., 2001b, ApJ, 556, 738 
%\bibitem{Kanbach88} Kanbach G. et al., 1988,
%  Space Sci. Rew., 49,69
\bibitem{Kaspi00} 
  Kaspi S., Smith P.~S., Netzer H., Maoz D., Jannuzi B.~T., Giveon U., 2000, 
  ApJ, 533, 631 
%\bibitem{Kellermann04} Kellermann K.~I., et al., 2004, preprint, 
%  (astro-ph/0403320)
%\bibitem{Lahteenmaki03} L{\" a}hteenm{\" a}ki A., Valtaoja E., 2003, \apj, 590, 95 
%\bibitem{Lavalley92} Lavalley M., Isobe T., Feigelson E., 1992,
%  in Worrall D.M., Biemesderfer C., Barnes J., eds,
%   ASP Conf. Ser. Vol. 25, Astronomical Data Analysis Software and Systems I,
%  Astron. Soc. Pac., San Francisco, p. 245
%\bibitem{Mattox96} Mattox J.R. et al., 1996,
%  \apj, 461, 396
%\bibitem{Mattox97} Mattox J.~R., 
%  Schachter J., Molnar L., Hartman R.~C., Patnaik A.~R., 1997, \apj, 
%  481, 95 
%\bibitem{Mattox01} Mattox 
%  J.~R., Hartman R.~C., Reimer O., 2001, \apjs, 135, 155 
%\bibitem{McLaughlin96} McLaughlin M.~A., Mattox J.~R., 
%  Cordes J.~M., Thompson D.~J., 1996, \apj, 473, 763 
%\bibitem{Merloni03} Merloni 
%  A., Heinz S., Di Matteo T., 2003, \mnras, 345, 1057 
%\bibitem{Mucke97} Muecke A.~et al., 1997, 
%  \aap, 320, 33 
%\bibitem{Mukherjee97} Mukherjee R.~et al.,
%  1997, \apj, 490, 116 
%\bibitem{Nolan03} 
%  Nolan P.~L., Tompkins W.~F., Grenier I.~A., Michelson P.~F., 2003, ApJ, 
%  597, 615 
%\bibitem{Padovani93} Padovani P., Ghisellini G., Fabian 
%  A.~C., Celotti A., 1993, \mnras, 260, L21 
%\bibitem{Snellen02} Snellen I.~A.~G., McMahon R.~G., Hook 
%  I.~M., Browne I.~W.~A., 2002, MNRAS, 329, 700 
%\bibitem{Soldi03} Soldi S., 2003, Laurea Thesis, Univ. Milano
\bibitem{Stecker96} Stecker F.~W.,
  Salamon M.~H., 1996, \apj, 464, 600 
%\bibitem{Tavani00} 
%  Tavani M.~et al., 2000, in McConnelly M.L., Ryan J.M., eds,
%  AIP Conf. Proc. Vol. 510, The Fifth Compton Symposium, American Inst. of Phys.,
%  Melville NY, p. 746
%\bibitem{Tavani03} 
%  Tavani M.~et al., 2003, in Truemper J.E., Tananbaum H.D., eds,
%  Proc. of the SPIE Vol. 4851, X-Ray and Gamma-Ray Telescopes and Instruments for Astronomy,
%  p. 1151
%\bibitem{Thompson93} Thompson D.J.. et al., 1993,
%  \apjs, 86, 629
%\bibitem{Vercellone03} Vercellone S. et al., 2003,
%  in Takalo L.O., Valtaoja E., eds, 
%  ASP Conf. Ser. Vol. 299, High energy blazar astronomy,
%  Astron. Soc. Pac., San Francisco, p.19
\bibitem{Vestergaard04} 
  Vestergaard M., 2004, ASP Conf. Series, Vol. 311, p. 69
%\bibitem{Montigny95} von Montigny C. et al., 1995,
%  \apj, 440, 525
\bibitem{Woo02} Woo J.,
  Urry M.C., 2002, \apj, 579, 530 
%\bibitem{Zhang02} Zhang S. et al., 2002,
%  \aap, 386, 843
\bibitem{Vercellone04} Vercellone S., Soldi S., Chen A.W., Tavani M., 2004
  \mnras, 353, 890

\end{thebibliography}


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% You may have to change the BibTeX style below, depending on your
%% setup or preferences.
%%
%% If the bibliography is produced without BibTeX comment out the
%% following lines and see the aipguide.pdf for further information.
%%
%% For The AIP proceedings layouts use either
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

%%%CCCCCC \bibliographystyle{aipproc}   % if natbib is available
%\bibliographystyle{aipprocl} % if natbib is missing

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% You probably want to use your own bibtex database here
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%CCCCCC \bibliography{sample}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% Just a reminder that you may have to run bibtex
%% All of it up to \end{document} can be removed
%% if you don't like the warning.
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%CCCCCC \IfFileExists{\jobname.bbl}{}
%%%CCCCCC  {\typeout{}
%%%CCCCCC   \typeout{******************************************}
%%%CCCCCC   \typeout{** Please run "bibtex \jobname" to optain}
%%%CCCCCC   \typeout{** the bibliography and then re-run LaTeX}
%%%CCCCCC   \typeout{** twice to fix the references!}
%%%CCCCCC   \typeout{******************************************}
%%%CCCCCC   \typeout{}
%%%CCCCCC  }

\end{document}

\endinput
%%
%% End of file `template-6s.tex'.

aipcheck.tex
%
% $Id: aipcheck.tex,v 1.7 2002/01/11 19:50:46 frank Exp $
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Testing for potential problems with this class
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\newif\ifproblem
\newif\iftimesok

\makeatletter
\def\IfStandaloneCheck{\def\next{aipcheck}
  \edef\currjob{\jobname}
  \edef\next{\meaning\next}
  \edef\currjob{\meaning\currjob}
  \ifx\currjob\next
    \expandafter\@firstoftwo
  \else
    \expandafter\@secondoftwo
  \fi
}
\makeatother

\typeout{***********************************************}
\typeout{*}
\typeout{* Testing if all files required for the aipproc}
\typeout{* class are available ...}
\typeout{*}
\typeout{***********************************************}

\typeout{*}
\typeout{* Looking for LaTeX2e ... }
\ifx\documentclass\undefined
 \typeout{*}
 \typeout{* Sorry this is a fatal error:}
 \typeout{*}
 \typeout{* The aipproc class can only be used with LaTeX2e which is}
 \typeout{* the standard LaTeX since 1994!}
 \typeout{*}
 \typeout{* Please make sure that your version of LaTeX is up-to-date}
 \typeout{* before attempting to use this class.}
 \typeout{*}
 \expandafter\stop
\else
 \typeout{* ... ok }
\fi


\def\next#1/#2/#3\next{#1#2}
\typeout{*}
\typeout{* Testing that LaTeX2e is not too old ... }
\ifnum\expandafter\next\fmtversion\next<199612 \relax
 \typeout{* ... what a vintage! }
 \typeout{*}
 \typeout{* Sorry this is a fatal error:}
 \typeout{*}
 \typeout{* The aipproc class can only be used with a recent version}
 \typeout{* of LaTeX2e. Your version is dated \fmtversion\space --- but}
 \typeout{* at least the 1996/12/01 version is required!}
 \typeout{*}
 \typeout{* Please make sure that your version of LaTeX is up-to-date}
 \typeout{* before attempting to use this class.}
 \typeout{*}
 \expandafter\stop
\else
 \ifnum\expandafter\next\fmtversion\next<199806 \relax
   \typeout{* ... probably ok }
   \typeout{*}
   \typeout{* Your version of LaTeX2e is quite old --- the aipproc class}
   \typeout{* hasn't been tested with your release.}
   \typeout{*}
   \typeout{* We believe that it will probably work, but if you encounter}
   \typeout{* problems you will need upgrade your installation.}
   \typeout{*}
   \typein{* Type <return> to continue ...}
   \problemtrue
 \else
   \typeout{* ... ok }
 \fi
\fi


\typeout{*}
\typeout{* Looking for aipproc.cls ... }
\IfFileExists{aipproc.cls}
    {
     \typeout{* ... ok }
    }
    {
     \typeout{* ... not found! }
     \typeout{*}
     \typeout{* Sorry this is a fatal error:}
     \typeout{*}
     \typeout{* Before you can use the aipproc class you have to unpack}
     \typeout{* it from the documented source.}
     \typeout{*}
     \typeout{* Run LaTeX on the file 'aipproc.ins', e.g.,}
     \typeout{*}
     \typeout{* \space\space latex aipproc.ins}
     \typeout{*}
     \typeout{* or whatever is necessary on your installation to process}
     \typeout{* a file with LaTeX. This should unpack a number of files for you:}
     \typeout{*}
     \typeout{* aipproc.cls \space and \space aip-*.clo}
     \typeout{*}
     \typeout{* After that retry processing this guide.}
     \typeout{*}
     \stop
}

\typeout{*}
\typeout{* Looking for aipxfm.sty ... }
\IfFileExists{aipxfm.sty}
    {
     \typeout{* ... ok }
    }
    {
     \typeout{* ... not found! }
     \typeout{*}
     \typeout{* Sorry this is a fatal error:}
     \typeout{*}
     \typeout{* The aipxfm.sty file which is part of the aipproc distribution}
     \typeout{* must be installed in a directory which is searched by LaTeX.}
     \typeout{*}
     \typeout{* Please install this file and retry.}
     \typeout{*}
     \stop
}

\typeout{*}
\typeout{* Looking for aip-8s.clo ... }
\IfFileExists{aip-8s.clo}
    {
     \typeout{* ... ok }
    }
    {
     \typeout{* ... not found! }
     \typeout{*}
     \typeout{* Sorry this is a fatal error:}
     \typeout{*}
     \typeout{* The aip-8s.clo file which is part of the aipproc distribution}
     \typeout{* must be installed in a directory which is searched by LaTeX.}
     \typeout{*}
     \typeout{* Please install this file and retry.}
     \typeout{*}
     \stop
}

\typeout{*}
\typeout{* Looking for aip-8d.clo ... }
\IfFileExists{aip-8d.clo}
    {
     \typeout{* ... ok }
    }
    {
     \typeout{* ... not found! }
     \typeout{*}
     \typeout{* Sorry this is a fatal error:}
     \typeout{*}
     \typeout{* The aip-8d.clo file which is part of the aipproc distribution}
     \typeout{* must be installed in a directory which is searched by LaTeX.}
     \typeout{*}
     \typeout{* Please install this file and retry.}
     \typeout{*}
     \stop
}


\typeout{*}
\typeout{* Looking for aip-6s.clo ... }
\IfFileExists{aip-6s.clo}
    {
     \typeout{* ... ok }
    }
    {
     \typeout{* ... not found! }
     \typeout{*}
     \typeout{* Sorry this is a fatal error:}
     \typeout{*}
     \typeout{* The aip-6s.clo file which is part of the aipproc distribution}
     \typeout{* must be installed in a directory which is searched by LaTeX.}
     \typeout{*}
     \typeout{* Please install this file and retry.}
     \typeout{*}
     \stop
}


\typeout{*}
\typeout{* Looking for aip-arlo.clo ... }
\IfFileExists{aip-arlo.clo}
    {
     \typeout{* ... ok }
    }
    {
     \typeout{* ... not found! }
     \typeout{*}
     \typeout{* Sorry this is a fatal error:}
     \typeout{*}
     \typeout{* The aip-arlo.clo file which is part of the aipproc distribution}
     \typeout{* must be installed in a directory which is searched by LaTeX.}
     \typeout{*}
     \typeout{* Please install this file and retry.}
     \typeout{*}
     \stop
}

\typeout{*}
\typeout{* Looking for fixltx2e.sty ... }
\IfFileExists{fixltx2e.sty}
    {
     \typeout{* ... ok }
    }
    {
     \typeout{* ... not found, trying fix2col.sty instead ... }
     \typeout{*}
     \IfFileExists{fix2col.sty}
	 {
	  \typeout{* ... ok }
	 }
	 {
	  \typeout{* ... not found! }
	  \typeout{*}
	  \typeout{* Sorry this is a fatal error:}
	  \typeout{*}
	  \typeout{* Your LaTeX distribution contains neither fixltx2e.sty}
	  \typeout{* nor fix2col.sty.}
	  \typeout{*}
	  \typeout{* This means that it is either too old or incompletely}
	  \typeout{* installed.}
	  \typeout{*}
	  \typeout{* fixltx2e.sty is part of the standard LaTeX distribution}
	  \typeout{* since 1999; fix2col.sty is an earlier version of this}
	  \typeout{* package.}
	  \typeout{*}
	  \typeout{* Best solution is to get the latest LaTeX distribution.}
	  \typeout{* If this is impossible for you, download fix2col.sty.}
	  \typeout{* You can get this software from a CTAN host.}
          \typeout{* Refer to http://www.ctan.org and search for "fix2col".}
	  \typeout{*}
	  \typeout{* After you have updated your LaTeX distribution}
	  \typeout{* retry processing this guide.}
	  \stop
     }
}

\typeout{*}
\typeout{* Looking for fontenc.sty ... }
\IfFileExists{fontenc.sty}
    {
     \typeout{* ... ok }
    }
    {
     \typeout{* ... not found! }
     \typeout{*}
     \typeout{* Sorry this is a fatal error:}
     \typeout{*}
     \typeout{* The fontenc package, which is part of standard LaTeX}
     \typeout{* (base distribution) has to be installed at the site to}
     \typeout{* run the aipproc class.}
     \typeout{*}
     \typeout{* The fact that it cannot be found either means that}
     \typeout{* this LaTeX release is too old or that it was installed}
     \typeout{* improperly.}
     \typeout{*}
     \typeout{* Please make sure that your version of LaTeX is okay}
     \typeout{* before attempting to use this class. The LaTeX distribution}
     \typeout{* contains the file "ltxcheck.tex" which can be used to}
     \typeout{* test the basic functionality and integrity of your installation.}
     \typeout{*}
     \stop
    }

\typeout{*}
\typeout{* Looking for calc.sty ... }
\IfFileExists{calc.sty}
    {
     \typeout{* ... ok }
    }
    {
     \typeout{* ... not found! }
     \typeout{*}
     \typeout{* Sorry this is a fatal error:}
     \typeout{*}
     \typeout{* The calc package, which is part of standard LaTeX}
     \typeout{* (tool distribution) has to be installed at the site}
     \typeout{* to run the aipproc class.}
     \typeout{*}
     \typeout{* The fact that it cannot be found either means that}
     \typeout{* this LaTeX release is too old or that it was installed}
     \typeout{* only in parts.}
     \typeout{*}
     \typeout{* Please make sure that the tools distribution of LaTeX}
     \typeout{* is installed before attempting to use this class.}
     \typeout{*}
     \typeout{* (You might be able to get calc.sty separately for your}
     \typeout{* installation if you are unable to upgrade to a recent}
     \typeout{* distribution for some reason.)}
     \typeout{*}
     \stop
    }

\typeout{*}
\typeout{* Looking for varioref.sty ... }
\IfFileExists{varioref.sty}
    {
     \typeout{* ... ok }
     \gdef\variorefoptionifavailable{varioref,}
    }
    {
     \typeout{* ... not found! }
     \typeout{*}
     \typeout{* Problem detected:}
     \typeout{*}
     \typeout{* The varioref package, which is part of standard LaTeX}
     \typeout{* (tool distribution) is not installed at this site.}
     \typeout{*}
     \typeout{* The fact that it cannot be found either means that}
     \typeout{* this LaTeX release is too old or that it was installed}
     \typeout{* only in parts.}
     \typeout{*}
     \typeout{* You can use the aipproc class without this package but }
     \typeout{* you cannot make use of the options "varioref" or "nonvarioref".}
     \typeout{*}
     \typeout{* Please also note that the aipguide.tex documentation}
     \typeout{* normally uses the "varioref" option to show its}
     \typeout{* effects (which  will now fail).}
     \typeout{*}
     \typein{* Type <return> to continue ...}
     \problemtrue
     \gdef\variorefoptionifavailable{}
     \let\vpageref\pageref
     \let\vref\ref
    }

\typeout{*}
\typeout{* Looking for times.sty ... }
\IfFileExists{times.sty}
    {
     \begingroup
% load times and forget it immediately again
       \RequirePackage{times}
       \global\expandafter\let\csname ver@times.sty\endcsname\relax    
       \long\def\next{ptm}
       \ifx\rmdefault\next
         \typeout{* ... ok }
         \gdef\psnfssproblemoption{}
         \endgroup
         \timesoktrue
       \else
         \endgroup
     \typeout{* ... obsolete! }
     \typeout{*}
     \typeout{* Serious problem detected:}
     \typeout{*}
     \typeout{* The times package, which is part of standard LaTeX}
     \typeout{* (psnfss distribution) is obsolete at this site.}
     \typeout{*}
     \typeout{* The fact that it contains incorrect code either means that}
     \typeout{* this LaTeX release is too old or that it was installed}
     \typeout{* only in parts with old files remaining!}
     \typeout{*}
     \typeout{* You can use the aipproc class without this package but}
     \typeout{* you have to specify the option "cmfonts" which result in}
     \typeout{* documents which are not conforming to the AIP layout specification!}
     \typeout{*}
     \typeout{* You can also try using the class in the following way:}
     \typeout{*}
     \typeout{* \space\space \string\documentclass[cmfonts]{aipproc}}
     \typeout{* \space\space \string\usepackage{times}}
     \typeout{* \space\space ...}
     \typeout{*}
     \typeout{* With luck this will result in Times Roman output but chances}
     \typeout{* are that you will get a larger number of error messages in}
     \typeout{* which case you have to remove the \string\usepackage declaration.}
     \typeout{*}
     \typein{* Type <return> to continue ...}
          \problemtrue
          \gdef\psnfssproblemoption{cmfonts}
          \def\textdegree{$^\circ$}            % used below but now
                                               % not setup
       \fi
    }
    {
     \typeout{* ... not found! }
     \typeout{*}
     \typeout{* Serious problem detected:}
     \typeout{*}
     \typeout{* The times package, which is part of standard LaTeX}
     \typeout{* (psnfss distribution) can not be found.}
     \typeout{*}
     \typeout{* The fact that this package cannot be found either means that}
     \typeout{* this LaTeX release is too old or that it was installed}
     \typeout{* only in parts!}
     \typeout{*}
     \typeout{* You can use the aipproc class without this package but }
     \typeout{* you have to specify the option "cmfonts" which result in}
     \typeout{* documents which are not conforming to the AIP layout specification!}
     \typeout{*}
     \typein{* Type <return> to continue ...}
     \problemtrue
     \gdef\psnfssproblemoption{cmfonts,}
    }

\iftimesok % don't bother testing other font options if times already
           % bad

\typeout{*}
\typeout{* Looking for t1ptm.fd or T1ptm.fd ... }
\IfFileExists{t1ptm.fd}
    {
     \typeout{* ... ok }
    }
    {
     \typeout{* ... not found, trying T1ptm.fd ... }
     \IfFileExists{T1ptm.fd}
          {
           \typeout{* ... ok }
          }
          {
           \typeout{* ... not found}
           \typeout{* Serious problem detected:}
           \typeout{*}
           \typeout{* The times package, which is part of standard LaTeX}
           \typeout{* (psnfss distribution) is available but the corresponding}
           \typeout{* .fd file (defining how to load Times Roman) is missing.}
           \typeout{*}
           \typeout{* The fact that this package is only partially installed}
           \typeout{* means that you LaTeX installation is unable to use Times}
           \typeout{* Roman fonts!}
           \typeout{*}
           \typeout{* You can use the aipproc class without this package but }
           \typeout{* you have to specify the option "cmfonts" which result in}
           \typeout{* documents which are not conforming to the AIP layout}
           \typeout{* specification!}
           \typeout{*}
           \typein{* Type <return> to continue ...}
           \problemtrue
           \timesokfalse
           \gdef\psnfssproblemoption{cmfonts,}
          }
    }

\fi


\newcommand\CheckFDFile[3]{%
  \typeout{*}
  \typeout{* Looking for #1#3.fd or #2#3.fd ... }
  \IfFileExists{#1#3.fd}
    {
     \typeout{* ... ok }
    }
    {
     \IfFileExists{#2#3.fd}
      {
       \typeout{* ... ok }
      }
      {\problemtrue
       \typeout{* ... not found! }
      }
    }
}

\iftimesok % don't bother testing other font options if Times already bad

%\CheckFDFile{ot1}{OT1}{ot1ztmcm}
%\CheckFDFile{oml}{OML}{omlztmcm}
%\CheckFDFile{oms}{OMS}{omsztmcm}
%\CheckFDFile{omx}{OMX}{omxztmcm}

\typeout{*}
\typeout{* Looking for mathptm.sty ... }
\IfFileExists{mathptm.sty}
    {
     \typeout{* ... ok }
     \CheckFDFile{ot1}{OT1}{ptmcm}
     \CheckFDFile{oml}{OML}{ptmcm}
     \CheckFDFile{oms}{OMS}{pzccm}
     \CheckFDFile{omx}{OMX}{psycm}
     \ifproblem
      \typeout{*}
      \typeout{* Problem detected:}
      \typeout{*}
      \typeout{* The mathptm package, which is part of standard LaTeX}
      \typeout{* (psnfss distribution) was found but some or all of its}
      \typeout{* support files describing which fonts to load are missing!}
      \typeout{*}
      \typeout{*}
      \typeout{* The fact that this package is only partially installed}
      \typeout{* means that the mathptm package cannot be used!}
      \typeout{*}
      \typeout{* You can use the aipproc class without this package but }
      \typeout{* you have to specify the option "nomathfonts" so that}
      \typeout{* math formulas will be typeset using Computer Modern.}
      \typeout{*}
      \typein{* Type <return> to continue ...}
      \problemtrue
      \gdef\psnfssproblemoption{nomathfonts,}
     \else
      \typeout{*}
      \typeout{* Looking for mathptmx.sty ... }
      \IfFileExists{mathptmx.sty}
       {
        \typeout{* ... ok }
        \CheckFDFile{ot1}{OT1}{ztmcm}
        \CheckFDFile{oml}{OML}{ztmcm}
        \CheckFDFile{oms}{OMS}{ztmcm}
        \CheckFDFile{omx}{OMX}{ztmcm}
        \ifproblem
	  \typeout{*}
	  \typeout{* Problem detected:}
	  \typeout{*}
	  \typeout{* The mathptmx package, which is part of standard LaTeX}
	  \typeout{* (psnfss distribution) was found but some or all of its}
	  \typeout{* support files describing which fonts to load are missing!}
	  \typeout{*}
	  \typeout{*}
	  \typeout{* The fact that this package is only partially installed}
	  \typeout{* means that the mathptmx package cannot be used!}
	  \typeout{*}
	  \typeout{* You can use the aipproc class without this package but }
	  \typeout{* you have to specify the option "mathptm" (no x) so that}
	  \typeout{* math formulas use the older version with upright greek letters.}
	  \typeout{*}
	  \typein{* Type <return> to continue ...}
	  \problemtrue
	  \gdef\psnfssproblemoption{mathptm,}
        \fi
       }
       {
	\typeout{* ... not found! }
	\typeout{*}
	\typeout{* Problem detected:}
	\typeout{*}
	\typeout{* The mathptmx package, which is part of standard LaTeX}
	\typeout{* (psnfss distribution) can not be found.}
	\typeout{*}
	\typeout{* This is unfortunate but not a disaster as the older}
	\typeout{* version of the package "mathptm" (no x) seems to exist.}
	\typeout{*}
	\typeout{* You can use the aipproc class without this package but }
	\typeout{* you have to specify the option "mathptm" so that}
	\typeout{* math formulas use the older version with upright greek letters.}
	\typeout{*}
	\typein{* Type <return> to continue ...}
	\problemtrue
	\gdef\psnfssproblemoption{mathptm,}
       }
      \fi
    }
    {
     \typeout{* ... not found! }
     \typeout{*}
     \typeout{* Problem detected:}
     \typeout{*}
     \typeout{* The mathptm package, which is part of standard LaTeX}
     \typeout{* (psnfss distribution) can not be found.}
     \typeout{*}
     \typeout{* The fact that this package cannot be found either means that}
     \typeout{* this LaTeX release is too old or that it was installed}
     \typeout{* only in parts!}
     \typeout{*}
     \typeout{* You can use the aipproc class without this package but }
     \typeout{* you have to specify the option "nomathfonts" so that}
     \typeout{* math formulas will be typeset using Computer Modern.}
     \typeout{*}
     \typein{* Type <return> to continue ...}
     \problemtrue
     \gdef\psnfssproblemoption{nomathfonts,}
    }

\typeout{*}
\typeout{* Looking for mathtime.sty ... }
\IfFileExists{mathtime.sty}
    {
     \typeout{* ... ok }
    }
    {
     \typeout{* ... not found! }
     \typeout{*}
     \typeout{* The mathime package can not be found.}
     \typeout{*}
     \typeout{* This is not a serious problem because this package is}
     \typeout{* only of interest if you own the commerical MathTime fonts.}
     \typeout{*}
     \typeout{* You can use the aipproc class without this package but }
     \typeout{* you cannot use the "mathtime" option of the class.}
     \typeout{*}
     \typein{* Type <return> to continue ...}
     \problemtrue
    }
\else
\fi % iftimesok

\typeout{*}
\typeout{* Looking for graphicx.sty ... }
\IfFileExists{graphicx.sty}
    {
     \typeout{* ... ok }
    }
    {
     \typeout{* ... not found! }
     \typeout{*}
     \typeout{* Problem detected:}
     \typeout{*}
     \typeout{* The graphics package, which is part of standard LaTeX}
     \typeout{* (graphics distribution) can not be found.}
     \typeout{*}
     \typeout{* The fact that this package cannot be found either means that}
     \typeout{* this LaTeX release is too old or that it was installed}
     \typeout{* only in parts!}
     \typeout{*}
     \typeout{* You can use the aipproc class without this package but }
     \typeout{* you cannot use commands like \protect\includegraphics
                or \protect\resizebox}
     \typeout{* in this case.}
     \typeout{*}
     \typeout{* Please note that you will get a further error message below}
     \typeout{* about: "graphicx.sty not found" because the class will try}
     \typeout{* to load this package! Type return in response to that error.}
     \typeout{*}
     \typeout{* As a result the illustrations in aipguide will look strange.}
     \typeout{*}
     \typein{* Type <return> to continue ...}

     \gdef\resizebox##1##2{}
     \gdef\includegraphics{\textbf{graphics package missing:}}
     \problemtrue
    }

\typeout{*}
\typeout{* Looking for textcomp.sty ... }
\IfFileExists{textcomp.sty}
    {
     \typeout{* ... ok }
    }
    {
     \typeout{* ... not found! }
     \typeout{*}
     \typeout{* Problem detected:}
     \typeout{*}
     \typeout{* The textcomp package, which is part of standard LaTeX}
     \typeout{* (base distribution) can not be found.}
     \typeout{*}
     \typeout{* The fact that this package cannot be found either means that}
     \typeout{* this LaTeX release is too old or that it was installed}
     \typeout{* only in parts!}
     \typeout{*}
     \typeout{* You can use the aipproc class without this package but }
     \typeout{* you will always get the error: "textcomp.sty not found"}
     \typeout{* because the class will try to load this package!}
     \typeout{* Type return in response to that error.}
     \typeout{*}
     \typein{* Type <return> to continue ...}

     \def\textdegree{$^\circ$}         % used below but now
                                       % not set up
     \problemtrue
    }


\typeout{*}
\typeout{* Looking for url.sty ... }
\IfFileExists{url.sty}
    {
     \typeout{* ... ok }
    }
    {
     \typeout{* ... not found! }
     \typeout{*}
     \typeout{* Problem detected:}
     \typeout{*}
     \typeout{* The url package, which should be part of a good LaTeX}
     \typeout{* distribution, can not be found.}
     \typeout{*}
     \typeout{* Without this package you will not be able to use the \string\url}
     \typeout{* command. Try to download this package from a CTAN  host.}
     \typeout{* Refer to http://www.ctan.org and search for "url".}
     \typeout{*}
     \typein{* Type <return> to continue ...}

     \problemtrue
    }


\makeatletter

\typeout{*}
\typeout{* Looking for natbib.sty ... }
\IfFileExists{natbib.sty}
    {
     \IfStandaloneCheck
       {\begingroup
        \let\@listi\relax
        \let\thebibliography\@empty
        \let\bibstyle\@empty
        \RequirePackage{natbib}
        \@ifpackagelater{natbib}{1999/05/29}
	  {
           \typeout{* ... ok }
	  }{
           \typeout{* ... might be too old! }
           \typeout{*}
           \typeout{* Your version of the natbib package might be too}
           \typeout{* old to be usable. This class was designed to}
           \typeout{* work with the version 7.0 dated 1999/05/28}
           \typeout{*}
           \typeout{* If problems occur download a}
           \typeout{* recent version from a CTAN host.}
           \typeout{*}
           \typeout{* Refer to http://www.ctan.org and search for "natbib".}
           \typeout{*}
           \typein{* Type <return> to continue ...}

           \global\problemtrue
	  }
        \endgroup
        }{}
    }
    {
     \typeout{* ... not found! }
     \typeout{*}
     \typeout{* Serious problem detected:}
     \typeout{*}
     \typeout{* The natbib package, which should be part of a good LaTeX}
     \typeout{* distribution, can not be found.}
     \typeout{*}
     \typeout{* Without this package you will not be able to use certain}
     \typeout{* citation styles. See the aipguide documentation!}
     \typeout{*}
     \typeout{* Especially the layout for ARLO requires this package!}
     \typeout{*}
     \typeout{* Try to download this package from a CTAN  host.}
     \typeout{* Refer to http://www.ctan.org and search for "natbib".}
     \typeout{*}
     \typein{* Type <return> to continue ...}

     \problemtrue
    }

\makeatother


\typeout{*}
\typeout{* ... finished testing}
\typeout{*}
\ifproblem
\typeout{* The tests have revealed some problems in your TeX installation.}
\typeout{*}
\typeout{* Please review the above comments carefully and read the file}
\typeout{* README for further information.}
\typeout{*}
\typeout{*****************************************************************}
\typein{* Type <return> to continue ...}
\else
\typeout{****************************************************************}
\typeout{*}
\typeout{* The tests have reveiled no problems in your TeX installation.}
\typeout{*}
\typeout{****************************************************************}
\fi


% if this file is run standalone stop otherwise continue

\makeatletter
\IfStandaloneCheck
 {
\typeout{*}
\typeout{* This document only produces terminal output.}
\typeout{*}
\stop
 }
 {
\AtBeginDocument{\relax\ifx\xfm@address@loop\@undefined
  \typeout{***************************}
  \typeout{* Oooops ... you seem to have picked up an obsolete}
  \typeout{* aipproc.cls file from a previous installation!}
  \typeout{*}
  \typeout{* Please check that LaTeX finds the right one.}
  \typeout{*}
  \typeout{* Sorry have to give up ....}
  \typeout{***************************}
  \stop
 \fi}
 }
\makeatother

\endinput

astro-ph0411389.extracted_bib
\begin{thebibliography}{99}

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