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ms_c.tex ApJ, August 2009, in press
Date: Fri, 26 Jun 2009 14:49:42 -0600
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=EF=BF=BC
Craig Heinke
Asst. Prof. of Physics
University of Alberta
cheinke@phys.ualberta.ca
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%\documentclass[preprint]{aastex}=0A=0A%=20Discovery=20of=20two=20very=20=
fast=20X-ray=20transients=0A=0A%%=20This=20emulates=20the=20ApJ=0A=
\documentclass{emulateapj}=0A\usepackage{graphicx}=0A=
\usepackage[usenames,dvips]{color}=0A%\usepackage{apjfonts}=0A=
%\usepackage{landscape}=0A%\usepackage{psfig}=0A=
\def\arcsec{$\,^{\prime\prime}$}=0A\def\arcmin{$\,^\prime$~}=0A=
\def\deg{$^{\circ}$~}=0A\def\mdot{$\dot{m}$~}=20=20=0A\def\Lx{L$_x$~}=0A=
%some=20useful=20definitions=20for=20equations=0A=0A=0A%=20abbreviations=20=
for=20journals=20for=20Science=20refs.=20follows=20here:=0A\def\apj{=20=
ApJ}=0A\def\aap{=20A\&A}=0A\def\mn{MNRAS}=0A\def\pasp{PASP}=0A=
\def\araa{ARAA}=0A\def\aj{AJ}=0A\def\apjs{ApJ=20Supp}=0A=0A=
\def\Chandra{${\it=20Chandra}$}=0A\def\Suzaku{${\it=20Suzaku}$}=0A=
\def\HST{${\it=20HST}$\=20}=0A\newcommand{\Msun}{\ifmmode=20=
{M_{\odot}}\else${M_{\odot}}$\fi}=0A\def\XMMU{XMMU=20J174445.5-295044}=0A=
\def\IGR{IGR=20J17407-2808}=0A\def\CXOU{CXOU=20J174042.0-280724}=0A=0A=
\shorttitle{Two=20Fast=20X-ray=20Transients}=0A\shortauthors{Heinke=20et=20=
al.}=0A=0A\begin{document}=0A\title{Two=20Rapidly=20Variable=20Galactic=20=
X-ray=20Transients=20Observed=20with=20\Chandra,=20XMM=20and=20\Suzaku}=0A=
=0A\author{C.~O.=20Heinke\altaffilmark{1},=20J.~A.=20=
Grindlay\altaffilmark{4}}=0A=0A\altaffiltext{1}{University=20of=20=
Alberta,=20Dept.=20of=20Physics,=20Room=20\#238=20CEB,=2011322-89=20=
Avenue,=20Edmonton=20AB,=20T6G=202G7,=20Canada;=20=
cheinke@phys.ualberta.ca}=0A=0A\altaffiltext{2}{Space=20Sciences=20=
Laboratory,=207=20Gauss=20Way,=20University=20of=20California,=20=
Berkeley,=20CA=2094720-7450,=20USA}=0A=0A\altaffiltext{3}{Northwestern=20=
University,=20Dept.=20of=20Physics=20\&=0A=20=20Astronomy,=202145=20=
Sheridan=20Rd.,=20Evanston,=20IL=2060208,=20USA}=0A=0A=
\altaffiltext{4}{Harvard=20University,=20Dept.=20of=20Astronomy,=2060=20=
Garden=20Street,=20Cambridge,=20MA=2002138,=20USA}=0A=0A\begin{abstract}=0A=
=0AWe=20have=20identified=20two=20moderately=20bright,=20rapidly=20=
variable=20transients=20in=20new=20and=20archival=20X-ray=20data=20near=20=
the=20Galactic=20center.=20=20=20=0ABoth=20objects=20show=20strong,=20=
flaring=20variability=20on=20timescales=20of=20tens=20to=20thousands=20=
of=20seconds,=20evidence=20of=20$N_H$=20variability,=20and=20hard=20=
spectra.=20=0A=20\XMMU\=20is=20seen=20at=202-10=20keV=20fluxes=20of=20=
$3\times10^{-11}$=20to=20$<10^{-12}$=20ergs=20cm$^{-2}$=20s$^{-1}$,=20=
with=20$N_H$=20at=20or=20above=20$5\times10^{22}$=20cm$^{-2}$,=20by=20=
XMM,=20\Chandra,=20and=20\Suzaku.=20=20A=20likely=202MASS=20counterpart=20=
with=20$K_S=3D10.2$=20shows=20colors=20indicative=20of=20a=20late-type=20=
star.=20=0A\CXOU\=20is=20a=20likely=20counterpart=20to=20the=20fast=20=
hard=20transient=20\IGR.=20=20\Chandra\=20observations=20find=20=
$F_X$(2-10=20keV)$\sim10^{-12}$=20ergs=20cm$^{-2}$=20s$^{-1}$,=20with=20=
large=20$N_H$=20variations=20(from=20$2\times10^{22}$=20to=20=
$>2\times10^{23}$=20cm$^{-2}$).=20=20No=202MASS=20counterpart=20is=20=
visible,=20to=20$K_S>13$.=20=20\XMMU\=20seems=20likely=20to=20be=20a=20=
new=20symbiotic=20star=20or=20symbiotic=20X-ray=20binary,=20while=20=
\CXOU\=20is=20more=20mysterious,=20likely=20an=20unusual=20low-mass=20=
X-ray=20binary.=0A=0A\end{abstract}=0A=0A\keywords{binaries=20:=20X-rays=20=
---=20stars:=20neutron}=0A=0A\maketitle=0A=
%----------------------------------=0A=0A=0A=
\section{Introduction}\label{s:intro}=0A=0AThe=20wide=20field=20of=20=
view,=20sensitivity=20to=20hard=20X-rays,=20and=20program=20focused=20on=20=
the=20Galactic=20Plane=20of=20the=20INTEGRAL=20IBIS=20telescope=20has=20=
unveiled=20new=20kinds=20of=20hard=20X-ray=20transient=20behavior=20=
\citep{Sguera05}.=20=20Many=20of=20these=20systems=20are=20high-mass=20=
X-ray=20binaries=20containing=20neutron=20stars=20(NSs),=20either=20=
eccentric=20Be=20systems=20where=20the=20NS=20feeds=20from=20an=20=
excretion=20disk,=20or=20supergiant=20fast=20X-ray=20transient=20systems=20=
\citep{Negueruela06}=20where=20the=20NS=20feeds=20from=20a=20(clumpy)=20=
stellar=20wind=20\citep{Walter07}.=20=20A=20number=20of=20new=20INTEGRAL=20=
sources=20have=20now=20been=20identified=20with=20supergiant=20fast=20=
X-ray=20transients,=20showing=20rapid=20flaring=20behavior=20and=20=
variable=20$N_H$,=20and=20in=20some=20cases=20(slow)=20pulsations=20=
\citep{Patel04,Walter06,Chaty08}.=0A=0AHowever,=20some=20rapidly=20=
variable=20X-ray=20transient=20behavior=20may=20be=20produced=20by=20=
other=20systems,=20such=20as=20symbiotic=20stars=20\citep[with=20white=20=
dwarf=20accretors,=20e.g.][]{Smith08},=20symbiotic=20X-ray=20binaries=20=
\citep[with=20neutron=20star=20accretors,=20e.g.][]{Masetti07},=20some=20=
unusual=20black=20hole=20X-ray=20binaries=20\citep{iZ_fxt00},=20or=20=
magnetars=20\citep{CastroTirado08,Stefanescu08}.=20=20Identifying=20the=20=
optical/infrared=20counterparts=20of=20rapidly=20variable=20X-ray=20=
transients=20is=20important=20for=20understanding=20these=20systems,=20=
and=20requires=20accurate=20positions=20from=20focusing=20X-ray=20=
instruments.=20=20=0A=0AThe=20INTEGRAL=20hard=20X-ray=20source=20\IGR\=20=
was=20first=20identified=20by=20\citet{Kretschmar04}=20as=20a=20hard=20=
X-ray=20flaring=20source,=20positionally=20consistent=20with=20the=20=
faint=20ROSAT=20source=202RXP=20J174040.9-280852.=20=20\citet{Sguera06}=20=
described=20the=20X-ray=20activity=20as=20three=20fast=20(few=20minute=20=
timescale)=20bright=20(up=20to=200.8=20Crab)=20flares,=20and=20refined=20=
the=20position=20to=20a=201.7'=20radius.=20=20A=2023=20keV=20=
bremsstrahlung=20model=20was=20an=20acceptable=20fit=20to=20the=2020-60=20=
keV=20spectrum.=20=20\citet{Sguera06}=20noted=20that=20\IGR's=20outburst=20=
was=20unusually=20strong=20and=20brief=20compared=20to=20known=20=
supergiant=20fast=20X-ray=20transients,=20and=20refrained=20from=20=
ruling=20out=20alternative=20interpretations.=20=20=0A=0AWe=20have=20=
identified=20two=20spectrally=20hard,=20rapidly=20variable,=20X-ray=20=
transients=20in=20archival=20\Chandra,=20XMM-Newton,=20and=20\Suzaku\=20=
data=20near=20the=20Galactic=20Center.=20=20Our=20likely=20counterpart=20=
to=20the=20INTEGRAL=20IBIS=20fast=20transient=20\IGR\=20detected=20in=20=
2004,=20\CXOU,=20showed=20strong=20flaring=20activity=20in=20early=20=
2007.=20=20X-ray=20transient=20behavior=20has=20not=20been=20previously=20=
identified=20from=20the=20other,=20\XMMU,=20for=20which=20we=20identify=20=
hard=20X-ray=20flaring=20in=20late=202006=20and=20early=202007.=20=20=0A=0A=
\section{XMMU=20J174445.5-295044}\label{s:xmm}=0A=0A\subsection{Data}=0A=
We=20observed=20the=20supernova=20remnant=20G359.1-0.5=20on=20Sept.=20=
24,=202006=20(ObsId=200400340101)=20for=2042=20ksec=20with=20XMM's=20=
EPIC=20camera,=20using=20two=20MOS=20CCD=20detectors=20\citep{Turner01}=20=
with=20medium=20filters=20and=20one=20pn=20CCD=20detector=0A=
\citep{Struder01}=20with=20a=20thin=20filter.=20=20(The=20time=20=
resolution=20was=202.6=20s=20for=20the=20MOS=20cameras=20and=2073.4=20ms=20=
for=20the=20pn=20camera.)=20=20All=20data=20were=20reduced=20using=20=
HEASOFT=20=
6.5\footnote{http://heasarc.gsfc.nasa.gov/docs/software/lheasoft}=20and=20=
SAS=20version=208.0.0\footnote{http://xmm2.esac.esa.int/sas/}.=20=20The=20=
data=20were=20moderately=20affected=20by=20soft=20proton=20flares.=20=20=
For=20spectral=20analysis,=20we=20chose=20a=20compromise=20between=20=
retaining=20photon=20statistics=20and=20excluding=20background,=20using=20=
limiting=200.2-10=20keV=20rates=20of=205,=206,=20and=2040=20counts/s=20=
for=20MOS1,=20MOS2,=20and=20pn=20cameras=20(respectively).=20This=20left=20=
25.0,=2026.2=20and=2023.4=20kiloseconds=20of=20time=20for=20the=20MOS1,=20=
MOS2,=20and=20pn=20cameras.=20=20We=20excluded=20event=20grades=20higher=20=
than=2012=20for=20MOS,=20and=20higher=20than=204=20for=20the=20pn.=20=20=
The=20brightest=20point=20source=20was=20so=20much=20brighter=20than=20=
the=20background=20that=20all=20data=20could=20be=20used=20to=20produce=20=
lightcurves=20(see=20below).=0A=0AWe=20used=20\Chandra\=20archival=20=
ObsIDs=20658,=202278,=202289=20(all=20with=20the=20ACIS-I=20imaging=20=
CCD=20array),=20and=202714=20(using=20the=20HRC-I=20high=20resolution=20=
camera).=20=20The=20data=20were=20reduced=20with=20CIAO=204.1=20and=20=
CALDB=204.1,=20following=20standard=20data=20analysis=20=
threads\footnote{http://cxc.harvard.edu/ciao/threads}.=20=20=20=20=0AWe=20=
used=20archival=20XIS=20data=20from=20Suzaku=20ObsID=20501056010,=20=
reduced=20following=20the=20Suzaku=20Data=20Reduction=20Guide=20=
\footnote{http://heasarc.gsfc.nasa.gov/docs/suzaku/analysis/abc/}.=20=20=
We=20used=20the=20cleaned=20event=20files=20in=20the=20HEASARC=20=
archive,=20extracted=20spectra=20and=20backgrounds=20with=20XSELECT=20=
\footnote{http://heasarc.gsfc.nasa.gov/docs/software/ftools},=20and=20=
produced=20response=20files=20with=20the=20{\it=20xisresp}=20task.=20=20=0A=
Finally,=20we=20included=20archival=20XMM=20data=20from=20three=20=
previous=20observations=20of=201E=201740.7-2942,=20in=202001,=202003,=20=
and=202005.=20=20These=20observations=20were=20conducted=20with=20the=20=
pn=20camera=20in=20timing=20mode,=20so=20only=20the=20MOS=20detectors=20=
were=20useful=20for=20our=20imaging.=20=20We=20performed=20standard=20=
filtering,=20as=20discussed=20above.=20=20All=20of=20these=20data=20are=20=
described=20in=20Table=201.=0A=0A=0A\subsection{Discovery=20of=20\XMMU}=0A=
=0AXMMU=20J174445.5-295044=20is=20the=20brightest=20point=20source=20in=20=
the=202006=20XMM=20data.=20=20We=20extracted=20its=20spectrum=20(from=20=
the=20data=20with=20high=20background=20excluded)=20and=20lightcurve=20=
(from=20the=20full=20dataset)=20from=2020\arcsec\=20circles,=20with=20=
background=20regions=20nearby=20on=20the=20same=20chip.=20=20=0A=0A=
\XMMU\=20shows=20a=20very=20hard=20absorbed=20spectrum=20(Fig.=20=
\ref{fig:ew1_spec},=20Table=202),=20indicating=20it=20is=20not=20a=20=
nearby=20coronal=20source.=20A=20power-law=20fit=20to=20the=20pn=20and=20=
combined=20MOS=20data=20is=20acceptable,=20and=20finds=20an=20=
intrinsically=20hard=20spectrum=20($\Gamma=3D1.18^{+0.08}_{-0.07}$)=20=
with=20substantial=20extinction=20($N_H=3D8.6\pm0.4\times10^{22}$=20=
cm$^{-2}$).=20=20The=20spectrum=20is=20apparently=20featureless,=20with=20=
limits=20on=20the=20equivalent=20width=20of=20Fe=20lines=20at=206.4=20=
and=206.7=20keV=20at=2026=20and=209=20eV=20respectively.=20=20Its=20=
average=20unabsorbed=202-10=20keV=20X-ray=20luminosity=20would=20be=20=
$1.7\times10^{35}$=20ergs=20s$^{-1}$=20if=20it=20were=20located=20at=20=
an=208=20kpc=20distance.=20=20=0A=0A\begin{figure}=0A\figurenum{1}=0A=
%\epsscale{0.6}=0A\includegraphics[scale=3D.37]{f1c.eps}=0A=
\caption[ew1_powspec.eps]{=20\label{fig:ew1_spec}=0AUpper=20panel:=20=
Spectra=20of=20\XMMU\=20from=202006,=20with=20XMM=20EPIC=20pn=20(top)=20=
and=20MOS=20(below;=20red=20online),=20fit=20with=20an=20absorbed=20=
powerlaw=20(Table=202).=20Lower=20panel:=20residuals=20to=20the=20fit.=0A=
}=20=0A\end{figure}=0A=0AWe=20produced=20barycentered=20lightcurves=20=
for=20\XMMU,=20and=20found=20strong=20flaring=20on=20timescales=20of=20=
hundreds=20of=20seconds=20(Fig.=20\ref{fig:ew1_xmm_lc}).=20=20The=20=
hardness=20of=20the=20spectrum=20does=20not=20vary=20strongly,=20=
indicating=20that=20the=20flaring=20is=20intrinsic=20and=20not=20due=20=
to=20varying=20$N_H$.=20=0APower=20spectra,=20with=20a=20binning=20=
timescale=20of=200.4=20seconds,=20did=20not=20produce=20clear=20evidence=20=
of=20any=20periodicity,=20only=20red=20noise=20(rms=20variability=20of=20=
24\%,=20from=20$2\times10^{-4}$=20to=200.1=20Hz).=20=0A=0A\begin{figure}=0A=
\figurenum{2}=0A%\epsscale{0.6}=0A=
\includegraphics[angle=3D0,scale=3D.45]{f2c.eps}=0A=
\caption[ew1_100s_untfilt2_8bary.ps]{=20\label{fig:ew1_xmm_lc}=0A2006=20=
XMM=20pn=20background-subtracted=201.5-9=20keV=20lightcurve=20of=20=
\XMMU,=20binned=20at=20100s=20resolution.=20=20Below=20it=20(in=20red=20=
online),=20we=20plot=20the=20background=20(appropriately=20scaled)=20=
extracted=20from=20a=20nearby=20region=20on=20the=20same=20chip.=20=20=0A=
}=20=0A\end{figure}=0A=0A=0A=0A\begin{figure}=0A\figurenum{3}=0A=
\includegraphics[angle=3D0,scale=3D0.45]{f3.eps}=0A=
\caption[K_GLM_XMMU.ps]{=0AImages=20in=202MASS=20K=20band=20(left)=20and=20=
GLIMPSE=204.5=20micron=20band=20(right)=20of=20the=20\XMMU\=20field.=20=20=
Generous=204''=20error=20circles=20are=20plotted=20around=20the=20XMM=20=
position,=20containing=20only=20one=20possible=20counterpart.=20=20=0A=
\label{fig:K_XMM}=0A}=0A\end{figure}=0A=0AWe=20use=20an=20error=20radius=20=
of=202''\footnote{XMM-SOC-CAL-TN-0018,=20from=20http://xmm.esac.esa.int}=20=
for=20comparing=20the=20XMM=20position=20with=20accurate=20optical/IR=20=
catalogs=20(though=20we=20note=20that=20others,=20e.g.=20=
\citet{Walter06},=20tend=20to=20use=204'').=20=20=0AA=20potential=20=
2MASS\footnote{see=20http://irsa.ipac.caltech.edu/}=20counterpart=20=
(2MASS=20J17444541-2950446)=20is=20only=201.78\arcsec\=20from=20the=20=
XMM=20position,=20with=20$K_S$=3D10.2=20and=20$J-K_S$=3D4.7=20(Fig.=20=
\ref{fig:K_XMM},=20Tables=203,=204).=20=20=0AOnly=2012=202MASS=20stars=20=
with=20magnitude=20$K_S<10.2$=20lie=20within=2050\arcsec\=20of=20\XMMU,=20=
indicating=20that=20the=20probability=20of=20finding=20a=20star=20of=20=
this=20brightness=20within=202\arcsec=20(our=20search=20radius)=20is=20=
only=202\%.=20Thus,=20the=202MASS=20star=20is=20the=20likely=20=
counterpart=20of=20\XMMU.=0A=0ASince=20intrinsic=20$J-K$=20colors=20=
range=20from=20-0.2=20for=20O=20stars=20to=201.2=20for=20M=20giants,=20=
E(J-K)=20must=20be=20within=203.5=20to=204.9.=20=20For=20standard=20=
interstellar=20reddening=20laws,=20$A_V=3D$20=20to=2028,=20and=20=
$N_H=3D3.6\times10^{22}$=20to=20$5\times10^{22}$=20cm$^{-2}$.=0A=20=20=
These=20values=20suggest=20that=20if=20this=20star=20is=20the=20true=20=
counterpart,=20the=20X-rays=20probably=20suffer=20additional=20local=20=
absorption.=20=20=0A=0AWe=20use=20the=20system=20of=20\citet{Neg07}=20to=20=
compare=20the=20near-IR=20colors=20of=20the=202MASS=20counterpart=20with=20=
those=20expected=20for=20high-mass=20X-ray=20binaries.=20=20Following=20=
\citet{Comeron05},=20we=20define=20the=20reddening-free=20parameter=20=
$Q=3D(J-H)-1.70(H-K_S)$.=20=20Supergiants=20should=20have=20$K_S<11$=20=
and=20$Q<0.2$,=20Be=20stars=20should=20have=20$K_S<12$=20and=20$Q<0$,=20=
and=20typical=20late-type=20stars=20have=20$Q\sim0.5$.=20=20We=20find=20=
$Q=3D0.81$=20for=20the=202MASS=20counterpart,=20which=20is=20redder=20=
than=20expected=20even=20for=20late-type=20stars.=20=20=0A=0A%=20=
Late-type=20stars=20seem=20not=20to=20get=20redder=20than=20Q~0.5.=0A%=0A=
%If=20the=202MASS=20star=20is=20a=20typical=20Be=20B0V=20star=20with=20=
reddening=20$A_V$=3D28,=20then=20its=20distance=20should=20be=20only=20=
0.9=20kpc=20\citep{Cox00}.=20A=20supergiant=20B0I=20star=20would=20be=20=
4.4=20kpc=20away.=20=20If=20the=202MASS=20star=20is=20the=20counterpart,=20=
then=20this=20source=20is=20closer=20than=20the=20Galactic=20Center.=0A=0A=
\subsection{\XMMU\=20at=20lower=20fluxes}=0A=0A\begin{figure}=0A=
\figurenum{4}=0A%\epsscale{0.5}=0A=
\includegraphics[angle=3D0,scale=3D.5]{f4c.eps}=0A=
\caption[six_XMMU_img.ps]{=20\label{fig:ew1_imgs}=0A1.5-6=20keV=20images=20=
of=20all=206=20observations=20with=20detections=20or=20marginal=20=
detections=20of=20\XMMU.=20=20All=20images=20are=20on=20the=20same=20=
scale=20(dimensions=206.3'=20by=208.7'),=20though=20the=20binning=20and=20=
stretch=20vary.=20=20Two=20observations=20(July=202001=20and=20Sept.=20=
2003)=20have=20been=20smoothed=20to=20more=20clearly=20identify=20\XMMU.=20=
=20The=20Sept.=202003=20MOS=20observation=20is=20only=20at=20best=20a=20=
marginal=20detection.=20=20Note=20that=20four=20of=20the=20observations=20=
place=20\XMMU\=20near=20or=20at=20the=20edge=20of=20the=20detector.=20=20=
=0A}=20=0A\end{figure}=0A=0AThe=20location=20of=20\XMMU\=20($l$=3D359.13,=20=
$b$=3D-0.31),=20at=20the=20edge=20of=20the=20\Chandra\=20wide=20Galactic=20=
Center=20survey=20field=20\citep{Wang02},=20and=20within=2015'=20of=20=
the=20LMXB=201E=201740.7-2942,=20has=20been=20observed=20numerous=20=
times=20by=20X-ray=20satellites.=20=20We=20have=20searched=20the=20=
HEASARC=20=
archive\footnote{http://heasarc.gsfc.nasa.gov/db-perl/W3Browse/w3browse.pl=
}=20for=20detections=20or=20constraining=20upper=20limits.=20=20We=20=
report=20here=20archival=20detections=20of=20\XMMU\=20at=20lower=20=
fluxes=20by=20Suzaku,=20XMM,=20and=20\Chandra,=20and=20upper=20limits=20=
from=20\Chandra\=20and=20XMM=20(Table=202,=20Fig.=20\ref{fig:ew1_imgs}).=20=
=20Observations=20by=20ROSAT,=20ASCA,=20EXOSAT,=20and=20Einstein=20do=20=
not=20detect=20it,=20but=20the=20upper=20limits=20are=20not=20=
particularly=20constraining,=20so=20we=20do=20not=20discuss=20those=20=
observations=20further.=0A=0A\XMMU\=20is=20consistent=20with=20the=20=
position=20of=20CXOGC=20J174445.5-295042=20\citep{Muno06},=20seen=20in=20=
\Chandra\=20ObsID=202278.=20(The=20Chandra=20position=20is=20at=20the=20=
edge=20of=20a=20chip,=20so=20its=20positional=20uncertainty=20of=20=
2.8'',=20while=20consistent=20with=20\XMMU,=20may=20not=20be=20fully=20=
trustworthy.)=20=20We=20have=20attempted=20spectral=20fitting=20to=20an=20=
absorbed=20power-law=20and=20absorbed=20bremsstrahlung=20spectrum,=20=
using=20the=20unbinned=20data=20and=20the=20C=20statistic=20(Table=202).=20=
=20Testing=20the=20acceptability=20of=20a=20C-statistic=20fit=20is=20=
done=20through=20Monte=20Carlo=20simulations=20(we=20use=201000)=20of=20=
the=20model.=20=20The=20percentage=20of=20those=20simulations=20having=20=
a=20larger=20C-statistic=20than=20the=20data=20is=20reported=20as=20the=20=
'goodness';=20a=20high=20value=20(e.g.=2095\%)=20indicates=20a=20poor=20=
fit.=20=20Its=2010-count=20detection=20at=20the=20very=20edge=20of=20the=20=
chip=20makes=20conclusions=20tentative.=20=20=0A=0A=20=20=20=20A=20=
second=20\Chandra\=20ACIS-I=20observation=20(ObsID=20658)=20identifies=20=
\XMMU\=20on=20the=20off-axis=20S2=20chip,=20with=20over=20100=20counts.=20=
=20We=20extracted=20a=20spectrum=20(binning=20the=20data=20with=2010=20=
counts/bin)=20and=20a=20lightcurve=20with=20200s=20bins.=20=20Chi-square=20=
and=20KS=20tests=20found=20no=20evidence=20of=20variability=20in=20the=20=
lightcurve.=20=20We=20fit=20the=20spectrum=20(Fig.=20\ref{fig:658_spec})=20=
with=20absorbed=20power-law=20and=20bremsstrahlung=20models=20(Table=20=
2).=20Fitting=20the=20unbinned=20data=20with=20the=20C-statistic=20gave=20=
similar=20results=20(within=20the=20errors).=20=0A=0A\begin{figure}=0A=
\figurenum{5}=0A%\epsscale{0.6}=0A\includegraphics[scale=3D.35]{f5.eps}=0A=
\caption[ew1_658_spec.eps]{=20\label{fig:658_spec}=0A\Chandra\=20=
spectrum=20of=20\XMMU,=20from=202000=20data=20(ObsID=20658),=20fitted=20=
with=20an=20absorbed=20powerlaw=20model=20(Table=202).=0A}=20=0A=
\end{figure}=0A=0A=0AA=20third=20\Chandra\=20ACIS-I=20observation=20=
(ObsID=202289)=20did=20not=20detect=20\XMMU,=20at=20the=20extreme=20=
corner=20of=20the=20off-axis=20S2=20chip.=20=20Neither=20did=20a=20=
\Chandra\=20HRC-I=20observation=20where=20\XMMU\=20was=20far=20off-axis=20=
(ObsID=202714).=20=20To=20determine=20upper=20limits=20for=20=
nondetections=20of=20\XMMU\=20=20in=20this=20paper,=20we=20assume=20a=20=
spectrum=20similar=20to=20its=20faintest=20detections;=20an=20absorbed=20=
power-law=20with=20photon=20index=202=20and=20$N_H=3D10^{23}$=20=
cm$^{-2}$.=20=20We=20extract=20the=20number=20of=20photons=20in=20a=20=
circle=20corresponding=20to=20the=2050\%=20encircled=20energy=20radius=20=
for=20photons=20of=204.5=20keV=20at=20\XMMU's=20off-axis=20angle,=20=
using=20an=20energy=20range=20of=201.5-6=20keV.=20=20Using=20a=20larger=20=
nearby=20background=20region=20free=20of=20sources,=20we=20compute=20the=20=
expected=20number=20of=20background=20photons=20in=20this=20circle,=20=
scale=20it=20to=20the=20source=20region,=20and=20compute=20the=2090\%=20=
confidence=20lower=20limit=20\citep{Gehrels86}=20on=20the=20number=20of=20=
expected=20background=20photons=20in=20the=20source=20region.=20=20The=20=
upper=20limit=20on=20the=20source=20countrate=20is=20derived=20by=20=
subtracting=20this=20lower=20limit=20from=20the=20observed=20photons,=20=
accounting=20for=20the=20encircled=20energy=20fraction=20and=20the=20=
vignetting=20of=20the=20telescope.=20=20Finally,=20we=20calculate=20flux=20=
upper=20limits=20using=20=
PIMMS\footnote{http://asc.harvard.edu/toolkit/pimms.jsp}.=20=20=0A=0A=
\begin{figure}=0A\figurenum{6}=0A%\epsscale{0.6}=0A=
\includegraphics[scale=3D.34]{f6c.eps}=0A\caption[ew1_suzxis_spec.ps]{=20=
\label{fig:ew1_suz_spec}=0A\Suzaku\=20spectrum=20of=20\XMMU,=20fitted=20=
with=20an=20absorbed=20powerlaw=20model=20(fit=20only=20above=202=20=
keV).=20=20XIS1=20data=20(diagonal=20crosses,=20red=20online)=20are=20=
lower=20above=20$4$=20keV=20than=20the=20combined=20XIS0=20and=20XIS3=20=
data=20(boxes,=20black=20online).=0A}=20=0A\end{figure}=0A=0A=0A=
\begin{figure}=0A\figurenum{7}=0A%\epsscale{0.6}=0A=
\includegraphics[angle=3D0,scale=3D.45]{f7.eps}=0A=
\caption[xis_500s_sub.eps]{=20\label{fig:ew1_suz_lc}=0A\Suzaku\=20=
combined=20XIS=201.5-6=20keV=20lightcurve=20of=20\XMMU,=20using=20500s=20=
bins.=0A}=20=0A\end{figure}=0A=0A%\clearpage=0A=0AA=20recently=20=
archived=20\Suzaku\=20observation=20(ObsID=20501056010,=202007)=20=
clearly=20detects=20\XMMU\=20in=20all=20three=20operational=20XIS=20=
\citep{Koyama_XIS07}=20cameras=20(due=20to=20source=20confusion=20in=20=
the=20Galactic=20Center,=20we=20do=20not=20consider=20the=20PIN=20data=20=
here).=20=20We=20extract=20spectra=20from=20a=20100\arcsec\=20region=20=
of=20the=20cleaned=20data,=20combining=20the=20spectra=20from=20XIS=20=
CCDs=200=20and=203,=20and=20binning=20the=20data=20at=2040=20photons/bin=20=
(Fig.=20\ref{fig:ew1_suz_spec}).=20=20The=20variations=20in=20thermal=20=
emission=20from=20the=20Galactic=20Center=20and=20large=20PSF=20of=20=
\Suzaku\=20make=20background=20subtraction=20difficult=20below=202=20=
keV.=20=20Since=20\XMMU\=20shows=20little=20emission=20below=202=20keV,=20=
we=20choose=20to=20ignore=20data=20below=202=20keV=20for=20spectral=20=
fitting.=20=20The=20flux=20is=20a=20factor=20of=205=20lower=20than=20=
observed=20by=20XMM,=20with=20a=20softer=20spectrum,=20and=20slightly=20=
higher=20$N_H$.=20=20We=20created=20a=20lightcurve=20from=20all=20=
detectors,=20in=20the=20energy=20range=201.5-6=20keV,=20at=2016=20s=20=
binning.=20=20Variability,=20suggesting=20continued=20flaring,=20is=20=
best=20seen=20at=20500=20s=20binning=20(Fig.=20\ref{fig:ew1_suz_lc}).=0A=0A=
We=20retrieved=20three=20prior=20XMM=20observations=20of=201E1740.7-2942=20=
from=20the=20archive=20(Table=201),=20taken=20in=202001,=202003,=20and=20=
2005.=20=20In=20each=20case,=20the=20pn=20camera=20was=20in=20timing=20=
or=20small=20window=20mode,=20so=20we=20used=20only=20MOS=20data.=20=20=
The=202001=20and=202003=20data=20were=20heavily=20affected=20by=20=
background=20flaring,=20forcing=20us=20to=20use=20partly=20contaminated=20=
data.=20=20A=20combined=20MOS=20image=20of=20the=202001=20data=20=
produced=20only=20an=20upper=20limit=20on=20the=20existence=20of=20=
\XMMU.=20=20The=202005=20data=20produced=20a=20clear=20detection=20of=20=
\XMMU\=20(Fig.=20\ref{fig:ew1_imgs},=20lower=20left),=20with=20a=20flux=20=
comparable=20to=20the=20\Chandra\=20detections=20(Table=202).=20=20=20In=20=
the=202003=20data,=20the=20position=20of=20\XMMU\=20falls=20off=20the=20=
MOS2=20chips,=20but=20lies=20on=20a=20MOS1=20chip.=20=20Although=20the=20=
source=20is=20not=20detected=20with=20a=20blind=20detection=20algorithm,=20=
our=20upper=20limit=20method=20described=20above=20calculates=20=
$11^{+2.2}_{-4.8}$=20counts=20(at=2090\%=20confidence).=20=20Thus=20we=20=
consider=20this=20as=20a=20marginal=20detection=20(see=20Fig.=20=
\ref{fig:ew1_imgs},=20upper=20right).=20=20=0A=0A\section{\CXOU:=20An=20=
INTEGRAL=20Source?}\label{s:igr}=0A=0A%\subsection{\Chandra\=20Data=20=
Analysis}=0A\citet{Sguera06}=20give=20the=20revised=20INTEGRAL=20error=20=
circle=20as=20R.A.=3D$17^h40^m40^s.08$,=20decl.=3D$-28^d=2008'=2024''$=20=
(J2000),=20with=20error=20radius=20of=201.7'.=20=20\citet{Bird07}=20=
gives=20the=20error=20circle=20as=20$17^h40^m42^s$,=20$-28^d12.1'$=20,=20=
with=20a=204.2'=20error=20radius.=20=20=0AThe=20Galactic=20Bulge=20=
Latitude=20Survey=20(Grindlay=20et=20al.,=20in=20prep.)=20covers=20both=20=
error=20circles=20thoroughly,=20between=204=20overlapping=2015=20ks=20=
ACIS-I=20observations.=20=20We=20downloaded=20these=20four=20=
observations,=20plus=20the=20ACIS-S=20observation=20of=20=
\citet{Tomsick08}.=20=20We=20searched=20for=20periods=20of=20enhanced=20=
background,=20but=20found=20none.=20=20We=20created=20a=20mosaic=20image=20=
in=20the=200.5-7=20keV=20energy=20band=20(Fig.=20\ref{fig:igr_mosaic}).=20=
=0A=0A\begin{figure}=0A\figurenum{8}=0A%\epsscale{0.6}=0A=
\includegraphics[angle=3D0,scale=3D.47]{f8c.eps}=0A\caption[mosaic.ps]{=20=
\label{fig:igr_mosaic}=0AMosaic=20of=20five=20\Chandra\=20observations=20=
in=20the=200.5-7=20keV=20range,=20showing=20the=20large=20(green=20=
online)=20error=20circles=20for=20\IGR=20from=20\citet{Bird07}=20and=20=
\citet{Sguera06},=20and=20(red=20online)=20ellipses=20around=20detected=20=
sources.=20=20The=20candidate=20counterpart=20\CXOU\=20is=20indicated=20=
by=20two=20black=20ticks.=20=20The=20small=20thick=20(green=20online)=20=
error=20circle=20indicates=20the=20location=20of=202RXP=20=
J174040.9-280852;=20note=20that=20no=20\Chandra\=20sources=20lie=20near=20=
it.=20=20SLX=201737-282=20is=20the=20bright=20source=20producing=20a=20=
readout=20streak,=20near=20the=20bottom=20of=20the=20image.=0A}=20=
\end{figure}=0A=0AThe=20mosaic=20image=20shows=20eighteen=20sources=20in=20=
one=20or=20the=20other=20of=20the=20two=20overlapping=20error=20circles.=20=
=20(Note=20that=20no=20\Chandra\=20source=20is=20visible=20in=20the=20=
error=20circle=20for=20the=20ROSAT=20source=202RXP=20J174040.9-280852.)=20=
=20The=20brightest=20of=20these=20sources,=20CXOU=20J174042.0-280724=20=
(indicated),=20shows=20marked=20flaring=20variability=20and=20a=20hard=20=
spectrum=20showing=20strong=20variations=20in=20absorption,=20which=20=
suggest=20that=20this=20source=20is=20the=20soft=20X-ray=20counterpart=20=
to=20\IGR.=20=20None=20of=20the=20other=20sources=20within=20the=20\IGR\=20=
error=20circles=20show=20these=20behaviors,=20so=20we=20focus=20on=20=
CXOU=20J174042.0-280724.=20(Tomsick=20et=20al.=20(2008)=20identify=20the=20=
brightest=20source=20visible=20in=20Fig.=20\ref{fig:igr_mosaic}=20as=20=
the=20low-mass=20X-ray=20binary=20SLX=201737-282,=20which=20is=20not=20a=20=
likely=20counterpart=20for=20\IGR.)=0A=0A=0ACXOU=20J174042.0-280724=20is=20=
in=20the=20field=20of=20view=20of=20ObsIDs=208199,=208200=20(on=20the=20=
edge=20of=20the=20chip),=208202,=20and=207526,=20all=20of=20which=20were=20=
observed=20between=20July=2030=20and=20August=201,=202007=20(Table=201).=20=
=20The=20count=20rate=20is=20much=20higher=20in=20ObsID=208202=20than=20=
the=20others,=20by=20almost=20a=20factor=20of=2010.=20=20None=20of=20=
these=20datasets=20showed=20background=20flaring,=20so=20we=20used=20all=20=
the=20data,=20and=20extracted=20spectra=20and=20lightcurves=20using=20=
CIAO=20tools.=20=0A%=208202:=20370/14553=3D0.025=0A%=208199:=2058/14682=3D=
=200.0039=0A%=208200:=2024/14556=3D=200.0016=20=20(but=20partly=20off=20=
chip)=0A%=207526:=2015/5108=3D=20=200.0029=0A=0AA=20power-law=20spectral=20=
fit=20of=20CXOU=20J174042.0-280724=20in=20ObsID=208202=20finds=20a=20=
hard,=20absorbed=20spectrum,=20with=20photon=20index=20=
$\Gamma=3D0.9^{+0.4}_{-0.6}$=20and=20=
$N_H=3D1.7^{+0.7}_{-0.9}\times10^{22}$=20cm$^{-2}$=20(Table=205;=20Fig.=20=
\ref{fig:8202_spec}).=20=20A=20lightcurve=20(binned=20at=20100=20s)=20=
shows=20irregular=20sharp,=20short=20flares=20(Fig.=20=
\ref{fig:8202_lc}a),=20reaching=20at=20least=20100=20times=20the=20=
lowest=20flux.=20=20=20No=20periodicities=20are=20detected=20in=20the=20=
overall=20power=20spectrum.=20=20Although=20the=20count=20rates=20=
between=20flares=20are=20low,=20there=20is=20some=20indication=20that=20=
part=20of=20the=20variability=20is=20due=20to=20variable=20absorption,=20=
as=20the=20emission=20is=20systematically=20softer=20during=20the=20=
brightest=20periods=20(Fig.=20\ref{fig:8202_lc}).=20=20=0A=0A=0A=
\begin{figure}=0A\figurenum{9}=0A%\epsscale{0.5}=0A=
\includegraphics[scale=3D.38]{f9.eps}=0A\caption[8202a_spec.ps]{=20=
\label{fig:8202_spec}=0ASpectrum=20of=20\CXOU\=20in=20\Chandra\=20ObsID=20=
8202,=20fit=20with=20an=20absorbed=20bremsstrahlung=20spectrum.=0A}=20=0A=
\end{figure}=0A=0A=0A\begin{figure}=0A\figurenum{10}=0A%\epsscale{0.6}=0A=
\includegraphics[angle=3D0,scale=3D.43]{f10.eps}=0A=
\caption[8202a_100s.eps]{=20\label{fig:8202_lc}=0ATop:=20Lightcurve=20of=20=
\CXOU\=20in=20\Chandra\=20ObsID=208202,=200.5-7=20keV,=20binned=20at=20=
100=20s=20resolution.=20=20Bottom:=20Hardness=20ratio=20of=20\CXOU\=20in=20=
ObsID=208202,=204-8=20keV=20counts=20over=201-4=20keV=20counts,=20in=20=
500=20s=20bins.=20=20=0A}=20=0A\end{figure}=0A=0AWe=20test=20this=20by=20=
extracting=20spectra=20from=20bright=20and=20faint=20parts=20of=20ObsID=20=
8202,=20and=20fitting=20the=20(ungrouped)=20spectra=20with=20an=20=
absorbed=20power-law=20model,=20with=20photon=20index=20constrained=20=
between=200=20and=203.=20=0AOur=20spectral=20fit=20to=20the=20brightest=20=
220=20seconds=20of=20the=20first=20flare=20finds=20=
$N_H=3D0.8^{+1.5}_{-0.7}\times10^{22}$=20cm$^{-2}$,=20and=20a=202-10=20=
keV=20flux=20of=20$F_X=3D8^{+4}_{-2}\times10^{-12}$=20ergs=20cm$^{-2}$=20=
=20s$^{-1}$.=20=20(We=20note=20that=20there=20is=20no=20evidence=20for=20=
pileup=20in=20the=20spectrum=20or=20image=20of=20this=20flare,=20due=20=
to=20the=20source's=20off-axis=20location).=20This=20is=20still=20three=20=
orders=20of=20magnitude=20fainter=20than=20the=20peak=20INTEGRAL=20flux=20=
from=20\IGR.=20=20A=20similar=20fit=20to=20the=20data=20below=200.04=20=
counts/s=20(excluding=20the=20last=205=20ksec)=20gives=20=
$N_H=3D2.0^{+2.4}_{-1.6}\times10^{22}$=20cm$^{-2}$,=20and=20a=20flux=20=
of=20$F_X=3D3.6^{+2.2}_{-1.3}\times10^{-13}$=20ergs=20cm$^{-2}$=20=
s$^{-1}$.=20=20This=20exercise=20strongly=20supports=20intrinsic=20=
source=20variation,=20and=20does=20not=20prove=20$N_H$=20variations=20=
during=20ObsID=208202.=0A=20=0A=0A=0A\CXOU's=20substantially=20smaller=20=
count=20rate=20in=20the=20other=20three=20observations=20is=20explained=20=
by=20comparison=20of=20the=20spectra=20from=20ObsIDs=208199=20and=20=
8202.=20=20The=20spectrum=20observed=20in=208199=20is=20substantially=20=
harder=20than=20that=20in=208202,=20showing=20a=20low-energy=20cutoff=20=
near=204=20keV=20vs.=201.5=20keV=20(compare=20Fig.=20\ref{fig:8202_spec}=20=
vs.=20\ref{fig:8199_spec}).=20=20Fitting=20bremsstrahlung=20models=20to=20=
both=20spectra=20confirms=20that=20the=20$N_H$=20value=20changed=20=
dramatically=20between=20the=20two=20observations,=20from=20=
$N_H=3D29^{+36}_{-7}\times10^{22}$=20cm$^{-2}$=20to=20=
$N_H=3D2.2^{+0.5}_{-0.3}\times10^{22}$=20cm$^{-2}$,=20while=20the=20=
unabsorbed=202-8=20keV=20fluxes=20are=20consistent=20(Table=205).=20=20=
Thus=20the=20inter-observation=20variability=20may=20be=20ascribed=20=
entirely=20to=20varying=20$N_H$,=20although=20the=20flaring=20(present=20=
in=20ObsID=208199=20also;=20Fig.=20\ref{fig:8199_lc})=20cannot.=20=20=20=
The=20remaining=20two=20observations=20(ObsIDs=208200=20and=207526)=20=
offer=20less=20information=20(in=208200=20the=20source=20lies=20on=20a=20=
chip=20edge,=20while=207526=20was=20a=20shorter=20observation),=20=
producing=20spectra=20which=20are=20poorly=20constrained.=20=20However,=20=
the=20spectrum=20from=20ObsID=208200=20is=20as=20hard=20as=20that=20from=20=
8199=20(only=203=20of=2027=20photons=20are=20below=204=20keV=20in=20=
ObsID=208200,=20compared=20to=207=20of=2063=20in=20ObsID=208199),=20=
giving=20support=20to=20our=20explanation=20of=20the=20variability.=20=20=
The=20spectrum=20from=20ObsID=207526=20is=20rather=20softer=20(7=20of=20=
19=20counts=20below=204=20keV),=20which=20might=20be=20due=20to=20=
intrinsic=20spectral=20evolution,=20or=20to=20$N_H$=20variations.=20=20=
Future=20observations=20could=20probe=20\CXOU's=20spectral=20evolution.=20=
=20=0A=0A%(Identify=20how=20many=20counts???)=20PI=20between=200,=20274;=20=
274,685.=0A%=208200:=203=20cts=20below=204=20keV,=2024=20in=204-10=20=
keV.=0A%=208199:=207=20below,=2056=20above.=0A%=208202:=20233=20below,=20=
173=20above.=0A%=207526:=208=20below,=2014=20above.=20->=206.9=20=
below,12.5=20above.=0A%=207526_bg:=20120,162:1.1,1.5.=0A=0A=
\begin{figure}=0A\figurenum{11}=0A%\epsscale{0.6}=0A=
\includegraphics[scale=3D.35]{f12.eps}=0A\caption[8199a_spec.ps]{=20=
\label{fig:8199_spec}=0ASpectrum=20of=20\CXOU\=20in=20\Chandra\=20ObsID=20=
8199,=20fit=20with=20an=20absorbed=20bremsstrahlung=20spectrum.=20=20=
Note=20the=20higher=20low-energy=20cutoff=20in=20comparison=20with=20=
Fig.=20\ref{fig:8202_spec}.=20=0A}=20=0A\end{figure}=0A=0A\begin{figure}=0A=
\figurenum{12}=0A%\epsscale{0.6}=0A=
\includegraphics[angle=3D0,scale=3D.45]{f11.eps}=0A=
\caption[8199a_100s.eps]{=20\label{fig:8199_lc}=0ALightcurve=20of=20=
\CXOU\=20in=20\Chandra\=20ObsID=208199,=200.5-7=20keV,=20binned=20at=20=
500s=20resolution.=0A}=20=0A\end{figure}=0A=0A=0A%\begin{figure}=0A=
%\figurenum{13}=0A%\includegraphics[angle=3D0,scale=3D0.42]{K_GLM_images.p=
s}=0A%\caption[K_GLM_images.ps]{=0A%Images=20of=20the=20field=20of=20=
\CXOU\=20from=20the=202MASS=20K=20band=20(left)=20and=20GLIMPSE=203.6=20=
micron=20band=20(right).=20=20A=20generous=201''=20\Chandra\=20error=20=
circle=20is=20plotted,=20enclosing=20no=20sources.=0A%\label{fig:K_CXOU}=0A=
%}=0A%\end{figure}=0A=0AThe=20best=20Chandra=20position=20for=20\CXOU\=20=
is=20RA=3D17:40:42.05$\pm0.01$,=20=20Dec=3D-28:07:24.6$\pm0.1$.=20=20=
Without=20astrometric=20matching=20of=20nearby=20X-ray=20sources=20to=20=
other=20wavelengths,=20we=20must=20add=20a=20systematic=20uncertainty=20=
of=200.6''=20(90\%=20conf.).=20=20We=20have=20searched=20for=20possible=20=
counterparts=20in=20the=202MASS=20catalog,=20but=20the=20nearest=20star=20=
is=201.9''=20away,=20at=20a=20magnitude=20of=2011.8.=0A%(Fig.=20=
\ref{fig:K_CXOU})=0A=20=20Based=20on=20the=20faintest=202MASS=20sources=20=
detected=20within=201',=20rough=20limits=20of=20$J>14$=20and=20$K_S>13$=20=
can=20be=20set=20for=20the=20error=20circle.=20=20No=20counterparts=20=
exist=20in=20SIMBAD=20or=20the=20USNO=20catalog.=20=20=0A=0A=0A=0A=
\section{Discussion}=0A=0AWe=20show=20the=20fluxes,=20photon=20indices,=20=
and=20$N_H$=20measurements=20for=20\XMMU\=20in=20Fig.=20=
\ref{fig:longterm}.=20=20Clearly=20\XMMU\=20spends=20most=20of=20its=20=
time=20at=20lower=20fluxes,=20below=20$F_X=3D3\times=2010^{-12}$=20ergs=20=
cm$^{2}$=20s$^{-1}$.=20=20The=202006=20XMM=20and=202007=20\Suzaku\=20=
observations=20clearly=20show=20differences=20in=20photon=20index=20and=20=
$N_H$.=20=20The=20\Chandra\=20results=20also=20suggest=20a=20softening=20=
of=20the=20intrinsic=20spectrum,=20and=20increased=20$N_H$,=20at=20lower=20=
fluxes.=20=20=20The=20variable=20absorption=20and=20hard=20spectrum=20=
seem=20to=20rule=20out=20a=20coronal=20nature=20for=20the=20X-ray=20=
emission,=20suggesting=20an=20accreting=20compact=20object.=20=0A=0A=
\begin{figure}=0A\figurenum{13}=0A=
\includegraphics[angle=3D0,scale=3D.43]{f13.eps}=0A=
\caption{\label{fig:longterm}=0AFluxes,=20photon=20indices,=20and=20=
$N_H$=20measurements=20for=20\XMMU\=20from=20constrained=20($0.5=20<=20=
\Gamma=20<=203.0$)=20absorbed=20power-law=20spectral=20fits=20to=20XMM,=20=
\Chandra\=20and=20\Suzaku\=20data=20over=208=20years=20(see=20Table=20=
2).=20=20}=0A\end{figure}=0A=0AThe=20evidence=20of=20rapid=20variability=20=
on=20timescales=20of=20minutes,=20the=20hard=20spectrum,=20=20and=20the=20=
intrinsic=20and=20variable=20absorption=20suggest=20a=20high-mass=20=
X-ray=20binary=20nature=20for=20\XMMU\=20\citep{White95}.=20=0AHowever,=20=
the=20red=20colors=20of=20the=20infrared=20counterpart=20for=20\XMMU\=20=
are=20inconsistent=20with=20a=20high-mass=20X-ray=20binary=20nature,=20=
suggesting=20a=20red=20giant=20companion.=20=20=0AThe=20spectrum=20and=20=
variability=20are=20similar=20to=20those=20of,=20e.g.,=204U=201954+31=20=
\citep{Masetti07},=20suggesting=20a=20symbiotic=20X-ray=20binary=20=
nature.=20=20However,=20some=20symbiotic=20stars=20also=20show=20hard=20=
spectra=20and=20rapid=20variability=20\citep{Luna07},=20so=20a=20white=20=
dwarf=20accretor=20is=20also=20a=20viable=20explanation.=20=0AWe=20note=20=
that=20there=20are=20strong=20similarities=20between=20accretion=20from=20=
the=20clumpy=20stellar=20wind=20of=20high-mass=20stars=20vs.=20that=20=
from=20giant=20stars=20onto=20a=20compact=20object.=20=20=0AIndeed,=20=
several=20INTEGRAL=20sources=20with=20X-ray=20properties=20similar=20to=20=
high-mass=20X-ray=20binaries=20have=20recently=20been=20identified=20as=20=
symbiotic=20X-ray=20binaries=20\citep{Masetti07,Nespoli08,Tomsick08}.=20=20=
=0A=0A=0AThe=20substantial=20extinction=20to=20\XMMU's=20infrared=20=
counterpart=20suggests=20a=20distance=20of=20at=20least=20a=20kpc,=20and=20=
thus=20X-ray=20luminosities=20of=20$>10^{32}$=20ergs=20s$^{-1}$=20in=20=
quiescence,=20and=20$>10^{33}$=20ergs=20s$^{-1}$=20at=20maximum.=20=20=0A=
The=20flux=20range=20and=20strong=20variability=20of=20\XMMU\=20suggest=20=
it=20may=20fit=20into=20the=20category=20of=20very=20faint=20X-ray=20=
transients=20\citep{Wijnands06,Degenaar08},=20although=20it=20may=20=
reach=20higher=20fluxes=20at=20other=20times.=20=20Inspection=20of=20the=20=
ASM=20and=20RXTE=20bulge=20scan=20data=20finds=20no=20evidence=20of=20=
outbursts=20from=20this=20source,=20with=20the=20bulge=20scan=20=
providing=20typical=20upper=20limits=20of=202-10=20mCrab=20(C.\=20=
Markwardt,=20priv.\=20comm,=202008;=20R.\=20Remillard,=20priv.\=20comm,=20=
2008).=20=20Some=20of=20the=20other=20known=20very=20faint=20X-ray=20=
transients=20may=20be=20symbiotic=20systems;=20this=20possibility=20=
might=20be=20ruled=20out=20with=20deep=20infrared=20observations.=20=20=0A=
%For=208=20kpc,=20this=20gives=20=
$L_X$(2-10)$\lesssim$0.8-$2\times10^{36}$=20ergs/s=20.=20=20=0A=0A\CXOU\=20=
has=20a=20more=20mysterious=20nature=20than=20\XMMU,=20due=20to=20its=20=
lack=20of=20an=20optical=20counterpart.=20=20Even=20if=20it=20were=20not=20=
associated=20with=20\IGR\=20(which=20we=20think=20it=20is),=20its=20=
varying=20$N_H$=20and=20rapid=20variability=20suggest=20accretion=20onto=20=
a=20compact=20object.=20=20=0AThe=20high=20flux=20attained=20by=20\IGR\=20=
indicates=20a=20neutron=20star=20or=20black=20hole=20nature.=20=20=0A=20=20=
The=20distance=20to=20this=20source=20is=20unknown,=20as=20we=20do=20not=20=
have=20a=20measurement=20of=20the=20interstellar=20reddening,=20and=20at=20=
least=20some=20of=20the=20observed=20(variable)=20absorption=20must=20be=20=
intrinsic.=20=20=0A%%=20A_Ks=3D0.683,=20A_V=3D7.67,=20N_H=3D1.4e22=0A=
This=20direction=20($l$=3D0.12,=20$b$=3D1.35)=20is=20sufficiently=20=
reddened=20($N_H$=20up=20to=20$1.4\times10^{22}$=20cm$^{-2}$,=20=
\citet{Marshall06})=20that=20interstellar=20reddening=20could=20explain=20=
the=20observed=20$N_H$=20in=20ObsID=208202,=20which=20has=20the=20lowest=20=
observed=20$N_H$=20value.=20=20=0AThe=20$K_S$=20limit=20implies=20$M_K=20=
>=20-2.2$=20for=20a=20distance=20of=2010=20kpc,=20excluding=20main=20=
sequence=20stars=20with=20spectral=20types=20earlier=20than=20B1=20and=20=
giant=20stars=20with=20spectral=20types=20later=20than=20K2.=20=20At=20a=20=
distance=20of=2015=20kpc,=20these=20limits=20shift=20to=20excluding=20=
main=20sequence=20stars=20earlier=20than=20O9=20and=20giants=20later=20=
than=20K4,=20while=20supergiants=20are=20ruled=20out=20for=20either=20=
distance.=20=20=0A=0ASome=20low-=20or=20intermediate-mass=20X-ray=20=
binaries,=20such=20as=20V4641=20Sgr=20=
\citep{iZ_fxt00,Revnivtsev02,Chaty03}=20or=20XTE=20J1901+014=20=
\citep{Smith07,Karasev07},=20show=20rapid=20flaring=20similar=20to=20=
that=20seen=20from=20\IGR.=20=20Alternatively,=20this=20object=20could=20=
be=20a=20Be-type=20binary=20at=20a=20distance=20over=2010=20kpc.=20=20We=20=
note=20that=20for=20a=20distance=20of=2010=20kpc,=20the=20peak=20=
INTEGRAL=20flux=20corresponds=20to=20$L_X$(20-60=20=
keV)=3D$1.1\times10^{38}$=20ergs=20s$^{-1}$,=20suggesting=20a=20=
bolometric=20flux=20above=20the=20Eddington=20limit=20for=20a=20neutron=20=
star.=20=0A=0A=0AFurther=20studies=20of=20these=20mysterious=20sources=20=
are=20strongly=20encouraged=20to=20improve=20our=20understanding=20of=20=
their=20nature=20and=20of=20fast=20X-ray=20transient=20behavior.=20=20=
The=20most=20critical=20need=20is=20for=20deep=20optical=20and=20=
infrared=20imaging=20to=20search=20for=20\CXOU's=20expected=20donor=20=
star.=20=20Spectroscopy=20of=20such=20an=20object=20(if=20possible)=20=
would=20be=20very=20valuable.=20=20Optical=20and/or=20infrared=20=
spectroscopy=20of=20\XMMU's=20optical=20counterpart=20is=20also=20=
needed,=20to=20identify=20its=20spectral=20type=20and=20surface=20=
gravity=20and=20search=20for=20evidence=20of=20accretion.=20=20This=20=
will=20test=20the=20hypothesis=20presented=20here=20that=20\XMMU\=20is=20=
a=20symbiotic=20system.=20=20If=20the=20distance=20can=20be=20=
constrained,=20the=20nature=20of=20the=20accreting=20object=20(white=20=
dwarf=20or=20neutron=20star?)=20may=20be=20determined.=20=20=20=
Additional=20X-ray=20observations=20of=20both=20objects=20will=20also=20=
be=20useful=20to=20monitor=20their=20long-term=20activity,=20especially=20=
if=20\CXOU\=20produces=20additional=20outbursts=20detectable=20by=20=
INTEGRAL.=20=0A=0A=0A\acknowledgements=0A=0ACOH=20thanks=20Craig=20=
Markwardt=20and=20Ron=20Remillard=20for=20their=20rapid=20efforts=20to=20=
search=20the=20RXTE=20bulge=20scans=20and=20RXTE/ASM=20records,=20=
respectively.=20=20=0ACOH=20acknowledges=20support=20by=20NSERC=20and=20=
NASA=20XMM=20GOF=20funding.=20=20=0AJAT=20acknowledges=20partial=20=
support=20from=20{\em=20Chandra}=20award=20number=20GO8-9055X=20issued=20=
by=20the=20{\em=20Chandra=20X-Ray=20Observatory=20Center},=20which=20is=20=
operated=20by=20the=20Smithsonian=20Astrophysical=20Observatory=20for=20=
and=20on=20behalf=20of=20the=20National=20Aeronautics=20=0Aand=20Space=20=
Administration=20(NASA),=20under=20contract=20NAS8-03060.=20=20=0AThis=20=
publication=20makes=20use=20of=20data=20products=20from=20the=20Two=20=
Micron=20All=20Sky=20Survey,=20which=20is=20a=20joint=20project=20of=20=
the=20University=20of=20Massachusetts=20and=20IPAC/Caltech,=20funded=20=
by=20NASA=20and=20the=20NSF.=20=20This=20research=20has=20made=20use=20=
of=20the=20NASA/IPAC=20Infrared=20Science=20Archive,=20and=20the=20=
Spitzer=20Space=20Telescope,=20which=20are=20operated=20by=20the=20Jet=20=
Propulsion=20Laboratory,=20Caltech,=20under=20contract=20with=20NASA.=20=20=
This=20research=20has=20made=20use=20of=20data=20obtained=20from=20the=20=
High=20Energy=20Astrophysics=20Science=20Archive=20Research=20Center=20=
(HEASARC),=20provided=20by=20NASA's=20Goddard=20Space=20Flight=20Center.=20=
=20It=20is=20based=20in=20part=20on=20observations=20obtained=20with=20=
XMM-Newton,=20an=20ESA=20science=20mission=20with=20instruments=20and=20=
contributions=20directly=20funded=20by=20ESA=20member=20states=20and=20=
NASA.=20=20=0A=0A=0A\bibliography{fast_trans}=0A\bibliographystyle{apj}=0A=
=0A\begin{deluxetable}{lcccr}=0A\tabletypesize{\footnotesize}=0A=
\tablewidth{7truein}=0A\tablecaption{\textbf{X-ray=20observations=20of=20=
\XMMU\=20and=20\CXOU}}=0A\tablehead{=0A\colhead{Mission/Instrument}=20&=20=
\colhead{ObsID}=20&=20\colhead{Date}=20&=20=20\colhead{Exposure}=20&=20=
\colhead{Notes}=20=0A}=0A\startdata=0A\multicolumn{5}{c}{\XMMU}=20\\=0A=
\hline=0A\Chandra/ACIS-I=20&=20=20658=20&=202000-08-30=20&=209235=20=20&=20=
=20\\=0AXMM/MOS=20=20=20&=200112971701=20&=202001-03-31=20&=207003=20=20=
&=20Nondetection=20\\=0A\Chandra/ACIS-I=20&=202278=20&=202001-07-20=20&=20=
11611=20&=20At=20chip=20edge=20=20\\=0A\Chandra/ACIS-I=20&=202289=20&=20=
2001-07-21=20&=2011611=20&=20Nondetection=20\\=0A\Chandra/HRC-I=20=20&=20=
2714=20&=202002-03-02=20&=2029709=20&=20Nondetection=20\\=0AXMM/MOS=20=20=
=20&=200144630101=20&=202003-09-11=20&=204477=20=20&=20Marginal=20=
detection=20\\=0AXMM/MOS=20=20=20&=200303210201=20&=202005-10-02=20&=20=
21823=20=20&=20=20=20\\=0AXMM/MOS=20&=200400340101=20&=202006-09-24=20&=20=
41028(25026)=20=20&=20Source=20flaring=20=20\\=0AXMM/pn=20=20&=20=
0400340101=20&=202006-09-24=20&=2035337(23378)=20=20&=20Source=20flaring=20=
=20\\=0ASuzaku/XIS=20&=20501056010=20&=202007-03-13=20&=2026545=20&=20=
Variable=20=20\\=0A\hline=0A\multicolumn{5}{c}{\CXOU}=20\\=0A\hline=0A=
\Chandra/ACIS-I=20&=208199=20&=202007-07-30,=2001:31=20&=2014682=20&=20=
Source=20flaring=20\\=0A\Chandra/ACIS-I=20&=208200=20&=202007-07-30,=20=
05:57=20&=2014566=20&=20At=20chip=20edge=20\\=0A\Chandra/ACIS-I=20&=20=
8202=20&=202007-07-30,=2014:41=20&=2014300=20&=20Source=20flaring=20=20=
\\=0A\Chandra/ACIS-S=20&=207526=20&=202007-08-01,=20=2013:04=20&=205108=20=
=20&=20=20\\=0A\enddata=0A\tablecomments{For=20ObsID=200400340101,=20we=20=
give=20the=20exposure=20with=20background=20flares=20removed=20in=20=
parentheses=20(these=20data=20are=20used=20for=20spectral=20analysis).=20=
=20=0A\label{tab:obs}}=0A\end{deluxetable}=0A=0A=
\begin{deluxetable}{lcccccccr}=0A\tabletypesize{\footnotesize}=0A=
\tablewidth{7.4truein}=0A\tablecaption{\textbf{Spectral=20fits=20to=20=
\XMMU}}=0A\tablehead{=0A\colhead{Mission/Instrument}=20&=20=20=
\colhead{ObsID}=20&=20\colhead{Flux}=20&=20\colhead{$\Gamma$}=20&=20=
\colhead{$N_H$}=20&=20\colhead{$\chi^2$/dof}=20&=20\colhead{kT}=20&=20=
\colhead{$N_H$}=20&=20\colhead{$\chi^2$/dof}=20\\=0A=20=20&=20=20=20&=20=
ergs=20cm$^{-2}$=20s$^{-1}$=20&=20=20&=20$10^{22}$=20cm$^{-2}$=20&=20=20=
&=20keV=20&=20$10^{22}$=20cm$^{-2}$=20&=20=20=0A}=0A\startdata=0A=20&=20=20=
&=20\multicolumn{4}{c}{---------------------------Power-law=20=
fit------------------------------}=20&=20=
\multicolumn{3}{c}{----------Bremsstrahlung=20fit-----------}=20\\=0A=
\hline=0A\Chandra/ACIS-I=20=20&=20658=20&=20=
$1.6^{+0.6}_{-0.7}\times10^{-12}$=20&=20$3.0^{+0=20a}_{-1.1}$=20&=20=
$15^{+3}_{-6}$=20&=200.68/10=20&=20$1.8^{+5.0}_{-1.0}$=20&=20=
$19^{+14}_{-9}$=20&=200.57/10=20=20\\=20%ReDone=0AXMM/MOS=20=20=20&=20=
0112971701=20&=20$<3\times10^{-13}$=20=20\\=0A\Chandra/ACIS-I=20=20&=20=
2278=20&=20$2.8^{+1.5}_{-1.1}\times10^{-13}$=20&=20$0.5^{+2.5=20a}_{-0=20=
a}$=20&=20$5.1^{+21}_{-2.7}$=20&=20146/15$^b$=20&=20$>2.3$=20&=20=
$11^{+8}_{-7}$=20&=20146/85$^b$=20\\=20%redone=0A\Chandra/ACIS-I=20&=20=
2289=20&=20$<5\times10^{-13}$=20&=20=20\\=0A\Chandra/HRC-I=20=20&=202714=20=
&=20$<1.6\times10^{-12}$=20&=20=20\\=0AXMM/MOS=20=20=20&=200144630101=20=
&=20$1.3^{+0.3}_{-0.5}\times10^{-12}$=20&=20\\=20%done=0AXMM/MOS=20=20=20=
&=200303210201=20&=20$6^{+6}_{-2}\times10^{-13}$=20&=20$1.8^{+1.2=20=
a}_{-1.3=20a}$=20&=20$8^{+9}_{-5}$=20&=200.54/11=20&=20$>1.8$=20&=20=
$7.8^{+9.5}_{-3.3}$=20&=200.54/11=20=20\\=20%done=0AXMM/EPIC=20=20&=20=
0400340101=20&=20$2.29\pm0.05\times10^{-11}$=20&=20=
$1.18^{+0.08}_{-0.07}$=20&=20$8.6^{+0.4}_{-0.4}$=20&=200.91/368=20&=20=
$>126$=20&=20$8.8^{+0.2}_{-0.2}$=20&=200.92/368=20=20=20\\=20%Done=20=0A=
Suzaku/XIS=20&=20501056010=20&=20$5.2^{+2.8}_{-1.2}\times10^{-12}$=20&=20=
$2.4^{+0.6=20a}_{-0.6}$=20&=20$16^{+5}_{-4}$=20&=200.65/111=20&=20=
$6.6^{+11}_{-2.9}$=20=20&=20$13.9^{+3.9}_{-3.2}$=20&=200.66/111=20\\=20=
%done=0A\enddata=0A\tablecomments{Photon=20indices=20are=20restricted=20=
to=20the=20physically=20reasonable=20range=20of=200.5=20to=203.=20=20=
Fluxes=20are=20unabsorbed,=20for=202-10=20keV,=20using=20best-fit=20=
absorbed=20power-law=20model,=20or=20a=20power-law=20spectrum=20with=20=
$\Gamma=3D2$=20and=20$N_H=3D1\times10^{23}$=20cm$^{-2}$=20for=20upper=20=
limits.=20=20\\=0A$^a$:=20Error=20calculation=20reached=20hard=20=
limit.\\=0A$^b$:=20Used=20C-statistic,=20reporting=20C-statistic=20and=20=
``goodness''=20(see=20text)=20instead=20of=20$\chi^2$=20and=20degrees=20=
of=20freedom.=0A\label{tab:xmmu}}=0A\end{deluxetable}=0A=0A=0A=
\begin{deluxetable}{lcccr}=0A\tabletypesize{\footnotesize}=0A=
\tablewidth{4.5truein}=0A\tablecaption{\textbf{Positions=20of=20\XMMU,=20=
\CXOU,=20and=20possible=20counterparts}}=0A\tablehead{=0A\colhead{Name}=20=
&=20\colhead{RA}=20&=20\colhead{Dec}=20&=20\colhead{$\Delta$}=20=20&=20=
\colhead{Notes}=20=0A}=0A\startdata=0A\XMMU\=20&=2017:44:45.55=20&=20=
-29:50:44.3=20&=20$\pm2.0^a$=20=20&=20XMM=20pos.=20\\=0A\XMMU\=20&=20=
17:44:45.54=20&=20-29:50:42.1=20&=20$\pm2.8^b$=20=20=20=20&=20=20=20=
Muno+06=20\\=0A2MASS=20J17444541-2950446=20&=2017:44:45.41=20&=20=
29:50:44.6=20&=20$\pm0.07^a$=20&=20=20=20\\=0A\hline=20\\=0A\CXOU\=20&=20=
17:40:42.05=20&=20-28:07:24.6=20&=20$\pm0.6^b$=20&=20CXO=20pos.=20\\=0A=
\enddata=0A\tablecomments{Positions=20of=20detected=20(X-ray=20or=20=
optical/IR)=20source=20and=20error.=20=20$^a$:=201$\sigma$=20error.=20=20=
$^b$:=2090\%=20confidence=20error.=0A\label{tab:pos}}=0A=
\end{deluxetable}=0A=0A\begin{deluxetable}{lcr}=0A=
\tabletypesize{\footnotesize}=0A\tablewidth{3.5truein}=0A=
\tablecaption{\textbf{Magnitudes=20and=20Fluxes=20of=202MASS=20=
J17444541-2950446}}=0A\tablehead{=0A\colhead{Band}=20&=20=
\colhead{Magnitude}=20&=20\colhead{Flux}=20=20=0A}=0A\startdata=0A$J$=20=20=
=20&=2014.89(5)=20&=201.77=20=20=20\\=0A$H$=20=20=20&=2011.62(4)=20&=20=
23.1=20=20=20\\=0A$K_S$=20&=2010.17(3)=20&=2057.2=20=20=20\\=0A3.6$\mu$m=20=
&=209.06(5)=20&=2066(3)=20=20\\=0A4.5$\mu$m=20&=208.87(5)=20&=2051(2)=20=20=
\\=0A5.8$\mu$m=20&=208.67(4)=20&=2040(2)=20=20\\=0A8.0$\mu$m=20&=20=
8.67(5)=20&=2022(1)=20=20\\=0A\enddata=0A\tablecomments{Fluxes=20in=20=
mJy.=20=20Magnitudes=20from=202MASS=20and=20GLIMPSE.=0A\label{tab:ir}}=0A=
\end{deluxetable}=0A%=20=2017444541-2950446=20266.189228=20-29.845734=20=20=
=20=2017h44m45.41s=20=20=2029d50m44.64s=20=20=20=200.07=20=20=20=200.06=20=
=20=20=20=20=20=200=2014.889=20=20=200.045=20=20=20=20=200.047=20=20=20=20=
=20=20=20=206.9=2011.617=20=20=200.034=20=20=20=20=200.035=20=20=20=20=20=
=20=2039.5=2010.166=20=20=200.029=20=20=20=20=200.030=20=20=20=20=20=20=
128.8=20=20=20=20222=20=20=20=20000=20=20=20=20=20CAA=20=20=20=20=20=20=20=
=20=20=20=20=201.787321=20=20=20=20=20=20=20=20=20=20=20=20259.085=20=20=20=
=203.2720=20=20=20=201.4510=20=20=20=204.7230=20=0A=0A=0A=
\begin{deluxetable}{lcccccccc}=0A\tabletypesize{\footnotesize}=0A=
\tablewidth{7.2truein}=0A\tablecaption{\textbf{X-ray=20Spectra=20of=20=
\CXOU}}=0A\tablehead{=0A\colhead{Mission/Instrument}=20&=20=
\colhead{ObsID}=20&=20\colhead{Flux}=20&=20\colhead{$\Gamma$}=20&=20=
\colhead{$N_H$}=20&=20\colhead{$\chi^2$/dof}=20&=20\colhead{$kT$}=20&=20=
\colhead{$N_H$}=20&=20\colhead{$\chi^2$/dof}=20=20\\=0A=20=20&=20=20=20&=20=
ergs=20cm$^{-2}$=20s$^{-1}$=20&=20=20&=20$10^{22}$=20cm$^{-2}$=20&=20=20=
&=20keV=20&=20$10^{22}$=20cm$^{-2}$=20&=0A}=0A\startdata=0A=20&=20=20&=20=
\multicolumn{4}{c}{---------------------------Power-law=20=
fit------------------------------}=20&=20=
\multicolumn{3}{c}{----------Bremsstrahlung=20fit-----------}=20\\=0A=
\hline=20\\=0A\Chandra/ACIS-I=20&=208199=20&=20=
$7^{+24}_{-3}\times10^{-13}$=20&=20$0.5^{+2.5=20a}_{-0=20a}$=20&=20=
$24^{+37}_{-7}$=20&=201.5/3=20&=20$>2.4$=20&=20$29^{+36}_{-7}$=20&=20=20=
1.7/3=20\\=20%done=0A\Chandra/ACIS-I=20&=208200=20&=20=20=
$2.1^{+2.2}_{-1.6}\times10^{-12}$=20&=20$3^{+0=20a}_{-2.5=20a}$=20&=20=
$48^{+24}_{-27}$=20&=20147/30$^b$=20=20&=20$>0.5$=20&=20$58^{+69}_{-20}$=20=
=20&=20146/99$^b$=20\\=20%=20redone=0A\Chandra/ACIS-I=20&=208202=20&=20=20=
$1.3^{+0.2}_{-0.2}\times10^{-12}$=20&=20$0.8^{+0.5}_{-0.3=20a}$=20&=20=
$1.5^{+0.8}_{-0.6}$=20&=201.23/16=20&=20$>25$=20&=20$2.2^{+0.5}_{-0.3}$=20=
&=201.39/16=20\\=20%done=0A\Chandra/ACIS-S=20&=207526=20&=20=20=
$1.7^{+1.0}_{-0.8}\times10^{-13}$=20&=20$0.5^{+0.6}_{-0=20a}$=20&=20=
$2.8^{+4.7}_{-1.7}$=20&=20148/62$^b$=20&=20$>10$=20&=20$3.6^{+6}_{-1.8}$=20=
&=20152/85$^b$=20\\=20%redone=0A\enddata=0A\tablecomments{Fluxes=20are=20=
unabsorbed,=202-10=20keV,=20using=20best-fit=20absorbed=20powerlaw=20=
model=20(constraining=20photon=20index=20to=20range=200.5=20to=203).=20=20=
=20\\=0A$^a$:=20Error=20calculation=20reached=20hard=20limit.\\=0A$^b$:=20=
Used=20C-statistic,=20reporting=20C-statistic=20value=20and=20=
``goodness''=20(see=20text)=20instead=20of=20$\chi^2$=20and=20degrees=20=
of=20freedom.=0A\label{tab:cxou}}=0A\end{deluxetable}=0A=0A=
\end{document}=0A=0A=0AObsID=20658:=0AWe=20extracted=20the=20spectrum,=20=
and=20fit=20it=20with=20several=20standard=20models,=20including=20a=20=
power-law=20with=20$N_H=3D23^{+20}_{-12}\times10^{22}$=20and=20=
$\Gamma=3D4.4^{+3.7}_{-2.6}$,=20a=20bremsstrahlung=20spectrum=20with=20=
$N_H=3D19^{+15}_{-9}\times10^{22}$=20and=20$kT=3D1.9^{+8.7}_{-1.0}$=20=
keV,=20and=20a=20MEKAL=20spectrum=20with=20=
$N_H=3D24^{+13}_{-10}\times10^{22}$=20and=20$kT=3D1.2^{+1.4}_{-0.4}$=20=
keV.=20=20=0A=0A=0A=0A=0A=
--Apple-Mail-26--693273654
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Craig Heinke
Asst. Prof. of Physics
University of Alberta