------------------------------------------------------------------------ gcnews_tao.tex to appear in Proc. 3rd INTEGRAL Workshop, Taormina 98 Message-Id: Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII content-length: 13100 % % tao_tmp.tex % This is the latex format for camera ready papers to be published in the % proceeding volume of Astrophysical Letters and Communications. % % Please make sure that the following two files are on your area % % tao_tmp.tex % epsfig.sty % tao_example.tex % tao_example.ps % % If you don't have them, then get a copy % via the WWW pages for the Workshop: % http://www.ias.fra.cnr.it/ias-home/imager/tao98.htm % % If there are problems with epsfig insertions of figures please print % figures with Fig. number and caption in full page and leave the empty % space in the text. Figures will be reduced and inserted by the % publisher. % % Color images are accepted and should be provided separately. 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Bazzano, Via del Fosso del Cavaliere - 00133 Rome - Italy) % % The date of this delivery will be communicated in Taormina. % % PLEASE ADHERE TO THE PAGE LIMITS % Invited papers must not exceed 8 pages, contributed oral and poster % papers must not exceed 4 pages. % % %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %------------------begin definitions-------------------------------- \def \ni {\noindent} \def \cl {\centerline} \def \vs {\vskip} \def \hs {\hskip} \def \ssk {\vskip 5truept} \def \sk {\vskip 10truept} \def \bsk {\vskip 15truept} \def \newpage {\vfill\eject} \def \newline {\hfil\break} \def \u {\underbar} %------------end definitions----------------------------------------- \documentstyle[epsfig]{article} \begin{document} % \hsize 5truein \vsize 8truein \font\abstract=cmr8 \font\keywords=cmr8 \font\caption=cmr8 \font\references=cmr8 \font\text=cmr10 \font\affiliation=cmssi10 \font\author=cmss10 \font\mc=cmss8 \font\title=cmssbx10 scaled\magstep2 \font\alcit=cmti7 scaled\magstephalf \font\alcin=cmr6 \font\ita=cmti8 \font\mma=cmr8 \def\ref{\par\noindent\hangindent 15pt} \null \pagestyle{empty} %\vskip 3.0truecm %\baselineskip = 12pt % ------ beginning of font "title" ------ \title{\ni OBSERVATIONS OF THE GALACTIC CENTER \\ REGION WITH BEPPO-SAX} % beginning of font "author and affiliation" \bsk \bsk \author{\ni L.~Sidoli $^{1,2}$, S.~Mereghetti$^{2}$, L.~Chiappetti$^{2}$, J.~Heise$^{3}$, G.L.~Israel $^{4}$, E.~Kuulkers$^{3}$, M.~Orlandini$^{5}$, P.~Predehl$^{6}$, A.~Tiengo$^{1,2}$ \& A.~Treves$^{7}$ } \bsk \affiliation{1) Dipartimento di Fisica, Universit\`a di Milano, Milano, Italy \\ \indent {2) Istituto di Fisica Cosmica ``G. Occhialini" , Milano, Italy} \\ \indent {3) SRON-Utrecht, Utrecht, The Netherlands} \\ \indent {4) Osservatorio Astronomico di Roma, Monteporzio Catone, Roma, Italy} \\ \indent {5) TeSRE, Bologna, Italy} \\ \indent {6) MPE, Garching, Germany} \\ \indent {7) Dipartimento di Fisica, Universit\`a di Milano, sede di Como, Italy} \\ } \bsk \baselineskip = 12pt % beginning of font "abstract and keywords" \abstract{ABSTRACT \ni We are performing a survey of the Galactic Center region (Sidoli et al., 1998a) with the BeppoSAX satellite. Several known point sources are visible (including one at the position of SgrA*), as well as newly discovered sources and diffuse emission. Here we report the preliminary results of the on--going analysis of both the point sources and the diffuse X--ray emission. } \bsk \baselineskip = 12pt \keywords{\ni KEYWORDS: X--ray; BeppoSAX; Galactic Center; compact sources; diffuse emission. } \bsk \baselineskip = 12pt % beginning of font "text" \text{\ni 1. INTRODUCTION \ssk \ni The region ($ |l| < 2^\circ $})$\times$($|b| < 2^\circ $) around the Galactic Center was observed with the BeppoSAX satellite (Boella et al., 1997) during April 1997--1998 and August--September 1997 for a total of $\sim$120 hours of effective time exposure. An observation of the black hole candidate GRS1758--258 has also been obtained on April 10, 1997. Figure 1 shows a mosaic of the MECS images obtained during this project. In Table 1 we report the preliminary results of the spectral analysis of the point sources observed by the MECS instruments in the energy band 2--10 keV. Details on the analysis performed will be reported elsewhere (Sidoli et al., in preparation). \baselineskip = 12pt \bsk \ni 2. INDIVIDUAL SOURCES \ssk \ni X--ray emission from the core of the radio supernova remnant G0.9+0.1 was discovered in April 1997 (Mereghetti et al., 1998), confirming the composite morphology derived from the radio observations. A young, energetic pulsar in G0.9+0.1 could contribute to the unresolved gamma--ray excess observed by EGRET in the Galactic Center (Mayer-Hasselwander et al., 1998). %-------------------------- figure 1 %this section shows how to insert a figure in the text \begin{figure} \vskip .5truecm %\centerline{\psfig{file=/gaia/sidoli/galcen/sax/imamosaic/taormina/mosaico2_midas_la_ed.ps, width=7cm}} %\vskip -3.truecm %\centerline{\psfig{file=/gaia/sidoli/galcen/sax/imamosaic/taormina/mos2_color.ps, width=7cm}} %\vskip 0.truecm \centerline{\psfig{file=/gaia/sidoli/galcen/sax/imamosaic/taormina/tao_fig.ps, width=7cm}} \vskip 0.truecm \caption{FIGURE 1. Image of the Galactic Center region ($ |l| < 2^\circ $}) in the 2--10 keV energy range, not corrected for the exposure. North is to the top and East to the left. } \end{figure} %--------------------------------- %-----------------------------------TABLE 1 ------------------------------ \begin{center} \vskip 2.truecm \small{ \centerline{ TABLE 1. INDIVIDUAL SOURCES: MECS Results of the Spectral Analysis (errors are 90\% c.l.).}} \begin{tabular}[c]{cccccc} \hline % \\ Source & Class$^{a}$ & Obs. date & $N_{H}$ & Parameter$^{b}$ & Flux$^{c}$ \\ & & & ($10^{22}$ cm$^{-2}$) & of best fit & \\ %\\ \hline %\\ G0.9+0.1 & SNR & Apr/Sep 97 & $34^{+16}_{-9}$ & $\Gamma=3.7^{+1.3}_{-1.0}$ & $1.36^{+3.74}_{-0.72}$ \\ Galactic Center$^{d}$ & UN& Aug 1997 & $7.0\pm{0.3}$ & $kT_{M}= 4.1\pm{0.3} $ & $3.5\pm{0.2}$ \\ 1E1743.1--2843 & UN & Apr 1998 & $13\pm{0.5}$ & $kT_{bb}= 1.78\pm{0.03} $ & $16.5\pm0.3$ \\ SAX~J1747.0--2853 & NS & Apr 1998 & $8.3\pm{0.6}$ & $kT_{br}=6.1\pm{0.9} $ & $4.0\pm{0.3}$ \\ KS1741--293 & NS & Mar 1998 & $20\pm{0.2} $ & $kT_{br}=11\pm{3}$ & $13\pm{1}$ \\ 1E1740.7--2942 & BHC & Sep 1997 & $14.7\pm{0.4}$ & $\Gamma=1.52\pm{0.04}$ & $47.4\pm{0.04}$ \\ SLX1744--299 & NS & Sep 1997 &$5.1\pm{0.2}$ & $\Gamma=2.1\pm{0.1}$ & $20\pm{0.4}$ \\ SLX1744--300 & NS & Sep 1997 &$5.3\pm{0.2}$ & $\Gamma=2.2\pm{0.1}$ & $12\pm{0.3}$ \\ GRS1758--258 & BHC & Apr 1997 &$1.44\pm{0.1}$ & $\Gamma=1.55\pm{0.03}$ & $30\pm{0.2}$ \\ \end{tabular} \end{center} \begin{small} $^{a}${Class: BHC=black hole candidate; NS=neutron star; SNR=supernova remnant; UN=unknown}; $^{b}${ Power law photon index ($\Gamma$) or temperatures in keV for a black body (T$_{bb}$), bremsstrahlung (T$_{br}$) and emission from hot gas (T$_{M}$, MEKAL in XSPEC).} \\ $^{c}${Unabsorbed fluxes are in the energy band 2--10 keV in units of $10^{-11}$ ergs~cm$^{-2}$~s$^{-1}$}.\\ $^{d}${The total contribution of the sources within $\sim2'$ from the Galactic Center (see text).}\\ \end{small} \end{table} } %-----------------------------------TABLE 1 end--------------------------- \vskip 2.truecm \indent A type I X--ray burst from SAX~J1747.0--2853, an X--ray transient recently rediscovered with the WFC on-board BeppoSAX (in't Zand et al. 1998b, Bazzano et al. 1998) and positionally coincident with the X--ray transient GX~0.2--0.2, has been detected with both MECS (Sidoli et al., 1998b) and PDS on April 15, 1998. The burst light curve is shown in Fig. 2 as well as the luminosity, temperature and neutron star radius variations during the burst. %-------------------------- figure 2 %this section shows how to insert a figure in the text \begin{figure}[h] \vspace{2.9truecm} \psfig{figure=../2fig.ps,height=120mm,bbllx=15mm,bblly=60mm,bburx=140mm,bbury=220mm} \vskip -5.6truecm \caption{\small FIGURE 2. {\underline{Left panel}}: Light curve of the burst detected with the MECS and PDS from SAX~J1747.0--2853. The dotted and dashed lines indicate the level of the persistent emission in the contiguous interval respectively before and after the burst. {\underline{Right panel}}: Results obtained by fitting the burst emission in different time intervals with a blackbody spectrum. } \end{figure} %--------------------------------- \vskip -0.3truecm \indent The transient activity of a source positionally coincident with the burster KS1741--293 (in't Zand et al., 1998a) has been detected during the observation pointed on the molecular cloud SgrC. In March 1998 it had an X-ray luminosity (2--10 keV) L$_{X}\sim10^{36}$ erg~s$^{-1}$, while in September 1997 it was under the threshold of detectability (L$_{X}$ $<$ 10$^{35}$ erg~s$^{-1}$).The 0.1--200 keV spectra of the two black hole candidates 1E1740.7--2942 and GRS1758--258 have been fitted using LECS, MECS and PDS data. 1E1740.7--2942, observed in September 1996 and exactly one year later, did not show strong flux variability. For both sources a Sunyaev and Titarchuk comptonization model fitted the data better than a simple power law. For 1E1740.7--2942 the parameters are: N$_{H}=1.46\pm{0.02}\times10^{23}$ cm$^{-2}$, $T = 24\pm1$ keV, $\tau=5.5\pm0.1$ and unabsorbed flux F$_{2-10}\sim5\times10^{-10}$ ergs~cm$^{-2}$~s$^{-1}$ ($\chi^{2}=1.3$, 282 d.o.f.). The corresponding values for GRS1758--2588 are: N$_{H}=0.18\pm{0.01}\times10^{23}$ cm$^{-2}$, $T =32\pm{4}$ keV, $\tau=4\pm{0.3}$ and F$_{2-10}\sim3.5\times10^{-10}$ ergs~cm$^{-2}$~s$^{-1}$ ($\chi^{2}=1.05$, 748 d.o.f.). \baselineskip = 12pt \bsk \ni 3. SgrA. \ssk \ni The possible existence of an X--ray counterpart of the radio source SgrA*, the dynamical center of the Galaxy, is still an open issue. The Einstein Observatory source 1E~1742.5--2859 (Watson et al., 1981) was later resolved into three sources by ROSAT PSPC (Predehl \& Trumper, 1994). One of these sources, highly absorbed and located within $10''$ from Sgr A*, is very likely associated with it. About $1.5'$ SW of SgrA* ASCA revealed a harder source, possibly the quiescent state of the bright soft X-ray transient A1742-289 (Maeda et al. 1996, but see also Kennea \& Skinner 1996). The flux reported in Table 1 refers to the total contribution of the sources within $\sim2'$ from the Galactic Center. Indeed the BeppoSAX spatial resolution hampers a detailed analysis of the single sources present in this region. \bsk \ni 4. DIFFUSE X--RAY EMISSION. \ssk \ni The MECS spectrum of the diffuse emission in a circular corona from $2'$ to $8'$ around the Galactic Center is thermal (kT$\sim$7~keV, N$_{H}\sim4\times10^{22}$ cm$^{-2}$) and contains several emission lines, with the K-lines from iron and sulfur particularly bright. The corresponding luminosity is $\sim$$10^{36}$ ergs s$^{-1}$, while the luminosity of the other three molecular clouds (SgrB2, SgrC and SgrD) within $8'$ from the center of their emission ranges from 0.1 to 0.3$\times$$10^{36}$ ergs s$^{-1}$. The X--ray diffuse emission detected from the direction of these molecular clouds is harder and the intensity of the emission lines weaker with respect to SgrA. A 6.4 keV fluorescent iron line is detected and is found to be particularly strong in the direction of the molecular cloud SgrB2. \bsk \baselineskip = 12pt {\references \ni REFERENCES \ssk \ref A. Bazzano et al. 1998, IAU Circ. n.6873 \ref G. Boella, R.C. Butler, G.C. Perola et al., 1997, A\&AS 122, 299 \ref J.A. Kennea \& G.K. Skinner, 1996, PASJ 48, 117 \ref Y. Maeda et al., 1996, PASJ 48, 417 \ref H.A. Mayer-Hasselwander et al., 1998, A\&A 335, 161 \ref S. Mereghetti , L. Sidoli \& G.L. Israel, 1998, A\&A, 331, L77 \ref P. Predehl \& J. Trumper 1994, A\&A 290, L29 \ref L. Sidoli et al., 1998a, proc. XTE/SAX Symp. ``The Active X-ray Sky", Rome , 88 \ref L. Sidoli et al., 1998b, A\&A, 336, L81 \ref M.G. Watson et al., 1981, ApJ 250,142 \ref J.J. in't Zand et al., 1998a, IAU circ. n.6840 \ref J.J. in't Zand et al. 1998b, IAU circ. n.6846 } \end{document}