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Asa final test. we have tried to fit jointly tve ASCA data and the non simultaneous RNTE/HENTE |ard X-ray spectrum. | As a final test, we have tried to fit jointly the ASCA data and the non simultaneous RXTE/HEXTE hard X-ray spectrum. |
was observed by RATE about one year after. ASCA (from vovemuber lih to Sth for a tota ol 100 ksec. see Barre οἱ al. | was observed by RXTE about one year after ASCA (from November 4th to 8th for a total of $\sim 100$ ksec, see Barret et al. |
1905 for details about the observation. | 1998 for details about the observation). |
The HENTE spectrum is a time-averaged spec(run over the entire observation. and is mace of the cluster A and B spectra. | The HEXTE spectrum is a time-averaged spectrum over the entire observation, and is made of the cluster A and B spectra. |
We clo not include the PCA data. as the PCA has no sensitivity below 3 keV (i.e. aud will be better Cyustrained with ASC'À alone). aud the power law pa1 of the ASCA spectrum is sullicient to cletermine relianly the parameter 7 of he model (see below). | We do not include the PCA data, as the PCA has no sensitivity below 3 keV (i.e. and will be better constrained with ASCA alone), and the power law part of the ASCA spectrum is sufficient to determine reliably the parameter $\tau$ of the model (see below). |
For the fit. we have et the relative LOL]ualizatiols of the ASCA anc two HENTE cluser spectra be a free parameter of tle it. O account for the fact that 1je. observatio are not slmultaueo sas well as relative calibration certainties between the instrumelts. | For the fit, we have let the relative normalizations of the ASCA and two HEXTE cluster spectra be a free parameter of the fit, to account for the fact that the observations are not simultaneous as well as relative calibration uncertainties between the instruments. |
In order uot ive too 1jiuch weight to he ASCA data in t it. we used ον tre GUIS3 spectrum. | In order not to give too much weight to the ASCA data in the fit, we used only the GIS3 spectrum. |
We used t model assLune assherical geometry. | We used the model assuming a spherical geometry. |
T "eslts of the fit are listed in Table 2. | The results of the fit are listed in Table 2. |
As can seen. au excellen [i is obtained. | As can be seen, an excellent fit is obtained. |
Unfortunately. once agal1 we are unable o distinguish between the BB all DBB unodel to fit the soft component. | Unfortunately, once again we are unable to distinguish between the BB and DBB model to fit the soft component. |
In Fig. 1.. | In Fig. \ref{gis3_hexte}, |
we show the uufoked broad-baud ASCA/CUIS3 aud RXTE/HEXTE spectrum of the source associated wil Üidhe +BB best fit. | we show the unfolded broad-band ASCA/GIS3 and RXTE/HEXTE spectrum of the source associated with the +BB best fit. |
In Figure 2.. we show the allowed οric of variatious for the aud the blackbody tempe‘ature for that inodel. | In Figure \ref{contours}, we show the allowed grid of variations for the and the blackbody temperature for that model. |
No visible eimissiot1 lines are present in the source spectrum. | No visible emission lines are present in the source spectrum. |
We have set an upper limit on the presence of an [rou liue by adding a gaussian liue centered at 6.1 keV to the mocel described above. | We have set an upper limit on the presence of an Iron line by adding a gaussian line centered at 6.4 keV to the model described above. |
between the two sets. | between the two sets. |
We also tested the repeatability of our PSF photometry by comparing magnitudes of objects that appeared twice in our data set. due to some overlap between different fields in MBSI and MIOLI. | We also tested the repeatability of our PSF photometry by comparing magnitudes of objects that appeared twice in our data set, due to some overlap between different fields in M81 and M101. |
We found that the maguitude differences were cousisteut with the reported uncertainties. | We found that the magnitude differences were consistent with the reported uncertainties. |
We also performed au external photometry check bv comparing UST aud. ground-based plotometiry of bright. isolated stars in our 116123 fields. | We also performed an external photometry check by comparing HST and ground-based photometry of bright, isolated stars in our 1613 fields. |
The erouud-based photometry was obtained a the Las Caupanas 25-11 du Pout telescope using its iufrared. camera (Perssonctal.1992) over fourteen nights between November 1993 and November 1996. | The ground-based photometry was obtained at the Las Campanas 2.5-m du Pont telescope using its infrared camera \citep{per92} over fourteen nights between November 1993 and November 1996. |
Photometry was conducted using andDAOGROW (as described πι 893.1) ou 19 stars commun to our ο and IST nuages. | Photometry was conducted using and (as described in 3.1) on 19 stars common to our ground-based and HST images. |
Table | lists f1011 magnitudes and Figure 3 shows a comparison of the two svstenis the mean offset is 0011+0.061 mae. in the sense that the IIST magnitudes are marginally brighter. | Table 4 lists their magnitudes and Figure 3 shows a comparison of the two systems; the mean offset is $0.011\pm0.061$ mag, in the sense that the HST magnitudes are marginally brighter. |
Uufortunatelv. there was no published J- or A-baud photometry available for stars in any of our fiekls. so we were unable to check our transformation of NICMOS FLIOW aud F205W magnitudes. | Unfortunately, there was no published $J$ - or $K$ -band photometry available for stars in any of our fields, so we were unable to check our transformation of NICMOS F110W and F205W magnitudes. |
As described in 822.1. we targeted specific fields within cach galaxy in order to maximize the uuuber of variables and our coverage of the Period-Linuinosity plane. | As described in 2.1, we targeted specific fields within each galaxy in order to maximize the number of variables and our coverage of the Period-Luminosity plane. |
We selected the variables iu cach galaxy. based om published catalogs. applying the following selection criteria: 1) existence of both V. aud 7 photometry: ii) ranee iu color of0.5«V.fF1.25: i) periods between LO davs aud the width of the observing window (applicable to Cepheids discovered with UST). | We selected the variables in each galaxy based on published catalogs, applying the following selection criteria: i) existence of both $V$ and $I$ photometry; ii) range in color of $0.5 < \vi < 1.75$; iii) periods between 10 days and the width of the observing window (applicable to Cepheids discovered with HST). |
Our fields coutained 93 variables that met these criteria. | Our fields contained 93 variables that met these criteria. |
Cepheids in M21 aud IC16123 were identified by visual Inspection. wing fudine charts created from erouud-based nuaees. | Cepheids in M31 and IC1613 were identified by visual inspection, using finding charts created from ground-based images. |
These fields are sparse enough that ideutificatious did not present a problem. auc twelve variables were located. | These fields are sparse enough that identifications did not present a problem, and twelve variables were located. |
Iu the case of the other galaxies. ideutificatious followed a more rigorous process. | In the case of the other galaxies, identifications followed a more rigorous process. |
First. the FITS header coordinates for the center of tle mosaic were used to obtain a rough aliguiment and rotation relative to an optical image (from WFPC? in most cases). | First, the FITS header coordinates for the center of the mosaic were used to obtain a rough alignment and rotation relative to an optical image (from WFPC2 in most cases). |
Next. bright stars prescut in both the optical aud the near-IR inages were identifies and used as input to the IRAF task to determine he geometric traustormations between the images. | Next, bright stars present in both the optical and the near-IR images were identified and used as input to the IRAF task to determine the geometric transformations between the images. |
Lastly. he task was used to predict the coordinates of SI variables. | Lastly, the task was used to predict the coordinates of 81 variables. |
The DAOPIIOT star lists generated in 833.1 were usec o locate the object nearest to the predicted position of he variables. | The DAOPHOT star lists generated in 3.1 were used to locate the object nearest to the predicted position of the variables. |
In geucral. counterparts were found within oue pixel of their predicted location. | In general, counterparts were found within one pixel of their predicted location. |
Figure 1 shows he distribution of differences between the predicted auc actual positions. | Figure 4 shows the distribution of differences between the predicted and actual positions. |
Based on this figure. we decided to reject any candidate located more than 1.5 pixels (111) away roni its predicted position. | Based on this figure, we decided to reject any candidate located more than 1.5 pixels 11) away from its predicted position. |
This process resulted iu the rejection of 11 possible counterparts. | This process resulted in the rejection of 11 possible counterparts. |
Tn order το further discriminate between real counterparts and field contaminants. we plotted V.JT ve. V.f colors for all remaining candidates (Figure 5a). | In order to further discriminate between real counterparts and field contaminants, we plotted $\vh$ vs. $\vi$ colors for all remaining candidates (Figure 5a). |
The Cepheids follow a vector that is a combination of two closely degenerate «quantities: the reddening trajectory and the color-color relation for these bands. | The Cepheids follow a vector that is a combination of two closely degenerate quantities: the reddening trajectory and the color-color relation for these bands. |
Several objects deviate significantly from the rest of the sample: we suspect these are variables which are blended with uuresolved red or blue conxudons. | Several objects deviate significantly from the rest of the sample; we suspect these are variables which are blended with unresolved red or blue companions. |
We performed a least-squares fit to the sample. using a fixed slope of V.IH/VfF=1.71 (the average of the reddening aud color-color slopes). | We performed a least-squares fit to the sample, using a fixed slope of $\vh/\vi = 1.71$ (the average of the reddening and color-color slopes). |
The fit is shown in Fig. | The fit is shown in Fig. |
Sa as a solid line. while the dashed lues correspond to twice the deviation. or 0.16 1aο, | 5a as a solid line, while the dashed lines correspond to twice the deviation, or 0.46 mag. |
We rejeced twelve possible counterparts that fell outsice of the dashed bouudaries. | We rejected twelve possible counterparts that fell outside of the dashed boundaries. |
Figure 5b shows a histoex‘aun of the «eviations from the best-fit line. | Figure 5b shows a histogram of the deviations from the best-fit line. |
The asviumetric distribution of the outliers is to be expected. since we are more likely to detect a Cepheid that is bleuded with a red (i.c.. IR-bright) field star than with a blue (i.e.. IR-faint) one. | The asymmetric distribution of the outliers is to be expected, since we are more likely to detect a Cepheid that is blended with a red (i.e., IR-bright) field star than with a blue (i.e., IR-faint) one. |
Note that this color-color rejection process is msensitive to bleuds of Cepheids with stars of similar colors. a point to which we will return later. | Note that this color-color rejection process is insensitive to blends of Cepheids with stars of similar colors, a point to which we will return later. |
Iu conclusion. our final sample consists of 70 variables (93 original candidates — 11 astrometric rejections — 12 color-color rejections). | In conclusion, our final sample consists of 70 variables (93 original candidates – 11 astrometric rejections – 12 color-color rejections). |
Finding charts for ficlds containing at least one variable are shown in Figures Ga-f. while Figures 72-b contain close-up views of cach object. | Finding charts for fields containing at least one variable are shown in Figures 6a-f, while Figures 7a-b contain close-up views of each object. |
Table 5 presents periods aud iaguitudes for the final Cepheid sample. | Table 5 presents periods and magnitudes for the final Cepheid sample. |
We include in this Table the previously-published optical maguitudes of the variables. | We include in this Table the previously-published optical magnitudes of the variables. |
There are iiunor variations iu the V. and £ zeropoiuts used in the cdiffercut sources of optical photometry. reflecting the evolution iu our knowledge of the MST calibration from 1991 to the present (see Mouldetal.2000— for details). | There are minor variations in the $V$ and $I$ zeropoints used in the different sources of optical photometry, reflecting the evolution in our knowledge of the HST calibration from 1994 to the present (see \citealt{mou00} for details). |
For our target galaxies. the mean difference between the various calibrations used in the published papers aud the current calibration (Stetson1998) amounts to 0.03£0.03 mae mV. 0.05£0.01 12ag in P and. |0.02+0.02 mag in Vf. | For our target galaxies, the mean difference between the various calibrations used in the published papers and the current calibration \citep{st98} amounts to $-0.03\pm0.03$ mag in V, $-0.05\pm0.04$ mag in I and $+0.02\pm0.02$ mag in $\vi$. |
The iiethod used to derive observed distance moduli is the same as that used by the IST Ixev Project ou the Extragalactic Distance Scale (sceFreedimanetal.2001a.for details).. | The method used to derive observed distance moduli is the same as that used by the HST Key Project on the Extragalactic Distance Scale \citep[see][for
details]{fr01a}. |
It is based ou the Period-Liuuunosity relations of individually de-veddened EMC Cepheids from Udalskietal.(1999). CV and J) aud Perssonetal.(2001) (7. fF aud A). scaled to an assumed true distance modulus of pyprc = [8.50-EO.10 mae (total uncertainty). | It is based on the Period-Luminosity relations of individually de-reddened LMC Cepheids from \citet{ud99} $V$ and $I$ ) and \citet{per01} $J$, $H$ and $K$ ), scaled to an assumed true distance modulus of $\mu_{0,{\rm LMC}}$ = $\pm$ 0.10 mag (total uncertainty). |
The relations are: -Opt Iu fittine the data from each field and filter. we fix the slope to the one eiven iu the correspondius equation aud obtain a magnitude shift by munimizine the uuweightedàs dispersion. | The relations are: -6pt In fitting the data from each field and filter, we fix the slope to the one given in the corresponding equation and obtain a magnitude shift by minimizing the unweighted dispersion. |
The resulting magnitude shifts are converted to observed distance moduli by subtracting the relevant magnitude zeropoiut. | The resulting magnitude shifts are converted to observed distance moduli by subtracting the relevant magnitude zeropoint. |
Peviod-Liuuinosity relations were constructed for cach field and filter usine the data listed in Table 5 aud fitted | Period-Luminosity relations were constructed for each field and filter using the data listed in Table 5 and fitted |
in order to identify a possible sample of ACNs in the hieh huninosity N-rav binary candidate sample. | in order to identify a possible sample of AGNs in the high luminosity X-ray binary candidate sample. |
We find 20 sources to fulfill these criteria. | We find 20 sources to fulfill these criteria. |
Source LLS correlates with a SNR and has to be removed from this class. | Source 148 correlates with a SNR and has to be removed from this class. |
Three sources correlate within a radius of <60” with aSimbad star (cither forceround or SAIC). | Three sources correlate within a radius of $<60''$ with a star (either foreground or SMC). |
We refine and exteud the classification of candidate ACNs by comparing the measured harduess ratios with he predictions from simulated power-law spectra of slope 2.0 aud 2.6. | We refine and extend the classification of candidate AGNs by comparing the measured hardness ratios with the predictions from simulated power-law spectra of slope –2.0 and –2.6. |
We fiud 53 canclidates for classA aud 62 cancicdates if we also consider class=AB in Table 1. | We find 53 candidates for class=A and 62 candidates if we also consider class=AB in Table 1. |
Class=AB means a hard X-rav binary nature is also possible due to the harducss ratio criteria. | Class=AB means a hard X-ray binary nature is also possible due to the hardness ratio criteria. |
Tinney et al. ( | Tinney et al. ( |
1997) present 10 quasars behind the SAIC. | 1997) present 10 quasars behind the SMC. |
Seven of them are covered by the fields Nl aud C (cf. | Seven of them are covered by the fields X1 and C (cf. |
22) aud are listed in Tab. | 2) and are listed in Tab. |
7. | 7. |
Noue of these quasars was detected in the radio survey of Filipovic ct al. ( | None of these quasars was detected in the radio survey of Filipović et al. ( |
1998). | 1998). |
QJ0102-7516. one of the three quasars uot covered by our survev was detected in the RASS field (IXahabka Pietsch 1993). | QJ0102-7546, one of the three quasars not covered by our survey was detected in the RASS field (Kahabka Pietsch 1993). |
We independently calculate the number of background sources in the analyzed field bv taking the distribution of the neutral hydrogen iuto account. | We independently calculate the number of background sources in the analyzed field by taking the distribution of the neutral hydrogen into account. |
By making use of the standard loe(N}log(S) of the soft extragalactic X-rav background (Ilasiuser et al. | By making use of the standard log(N)–log(S) of the soft extragalactic X-ray background (Hasinger et al. |
1993) aud by taking iuto account the absorption due to the SAIC (from the lumaee of Stanimuirovic et al. | 1993) and by taking into account the absorption due to the SMC (from the image of Stanimirovic et al. |
1998) the expected number of background sources with absorbed fiuxes in excess of 10135 ⋅ ↙∣⋮∙↙∕↸⊳⋯−↴∖↴⊥∐⋜↧↴∖↴↴⋝↸∖↸∖∐≺∐∖↑↸∖↥⋅⋯∐∐∖≼↧∙↖↖↸∖≼ | 1998) the expected number of background sources with absorbed fluxes in excess of $10^{-13}\
erg\ {\rm cm}^{-2}\ {\rm s}^{-1}$ has been determined. |
∐∖∐↖↽↸∖⋜↧⇁ ⋅ uunmber of LO background sources for our covered field. | We derive a number of 10 background sources for our covered field. |
As we expect to be complete for this fux limit we consider LO backeround sources as the lower limit. | As we expect to be complete for this flux limit we consider 10 background sources as the lower limit. |
The lower ciel of the flux distribution extends to 10.tterecu2s1. | The lower end of the flux distribution extends to $10^{-14}\ {\rm erg}\
{\rm cm}^{-2}\ {\rm s}^{-1}$. |
Iu case of completeness we expect to detect 519 backerouud ↴∖↴≺∏∐∎↸ | In case of completeness we expect to detect 519 background sources. |
↾↸∖↴∖∎⋜↕↴∖↴ The fact that we classify 53-62 backeround sources is consistent with these nuuboers. | The fact that we classify 53-62 sources as background sources is consistent with these numbers. |
We- performed. an X-ray- survey of. a 8.95 dee? 206field iu. the direction of the Small Magellanic Cloud. | We performed an X-ray survey of a 8.95 $^2$ field in the direction of the Small Magellanic Cloud. |
We detect 218 point-like and moderately exteuded: sources. | We detect 248 point-like and moderately extended sources. |
Using criteria established here. six sources were classified as supersoft sources; 51 as hard N-rav binary candidates. 19 as supernova remnants. 19 as candidate foreground stars and 53 as candidate backeround ACNs. | Using criteria established here, six sources were classified as supersoft sources, 51 as hard X-ray binary candidates, 19 as supernova remnants, 19 as candidate foreground stars and 53 as candidate background AGNs. |
These iare of all catalog cutries. | These are of all catalog entries. |
The nunber of hard X-rav biuaries agrees with the nmubers predieted frou »opulation svuthesis caleulatious for Iuuinosities in excess of 10°!ergs+. | The number of hard X-ray binaries agrees with the numbers predicted from population synthesis calculations for luminosities in excess of $10^{34}\
{\rm erg}\ {\rm s}^{-1}$. |
Assuning the standard log(N)-log(S) of he soft extragalactic N-vav background we estimate that iu our field are 10 backerouud ACNs with fluxes in excess of 10Perecur7st and 519E background ACNs- with+ Huxes in excess of 10Movee>2s1. | Assuming the standard log(N)-log(S) of the soft extragalactic X-ray background we estimate that in our field are 10 background AGNs with fluxes in excess of $10^{-13}\ {\rm erg}\ {\rm cm}^{-2}\
{\rm s}^{-1}$ and 519 background AGNs with fluxes in excess of $10^{-14}\
{\rm erg}\ {\rm cm}^{-2}\ {\rm s}^{-1}$. |
We- propose three jw SNR caudidates. | We propose three new SNR candidates. |
"hisTL research| was supportedlted in part. |by he Netherlands Organization for Scientific Rescarch (NWO) hroughwough SpinozaS Grant.Grant 08-0OS-O to ELI.LP. van denlen Heuvel. | This research was supported in part by the Netherlands Organization for Scientific Research (NWO) through Spinoza Grant 08-0 to E.P.J. van den Heuvel. |
Lleuvel. 11P.I. hanks I5... van den Leuvel for stimulating discussions ancl X. Li for reading the manuscript. | P.K. thanks E.P.J. van den Heuvel for stimulating discussions and X. Li for reading the manuscript. |
S. Stanimirovic is thanked or providing the image of the SMC. | S. Stanimirovic is thanked for providing the image of the SMC. |
Part. of the work has been performed during the stay of Puy. at. the. Max-Planck-Institut [ürr extraterrestrische Physik in Garching. | Part of the work has been performed during the stay of P.K. at the Max-Planck-Institut fürr extraterrestrische Physik in Garching. |
Phe pproject is supported by the Alax-Planck-Cesellschaft and the )jundesministerium fürr Forschung und Technologie (DBMET). | The project is supported by the Max-Planck-Gesellschaft and the Bundesministerium fürr Forschung und Technologie (BMFT). |
This research made use of the Simbact data base operated at CDS. Strasbourg. France. | This research made use of the Simbad data base operated at CDS, Strasbourg, France. |
We thank the referee for useful comments and suggestions to improve this work. | We thank the referee for useful comments and suggestions to improve this work. |
population and a very metal-rich. vouneer population with an estimated age consistent wilh that of the merger (Ixuntschner&Davies1998).. masquerade as a single peak in optical colors. | population and a very metal-rich, younger population with an estimated age consistent with that of the merger \citep{kd98}, masquerade as a single peak in optical colors. |
It is possible that other svstems with an apparently. unimodal GC color distribution might in a similar wav be composed of several populations with large age differences. | It is possible that other systems with an apparently unimodal GC color distribution might in a similar way be composed of several populations with large age differences. |
The giant elliplical egalaxv NGC 4365 at the outskirts of the Virgo cluster is another example of a galaxy. will only a single broad peak in the GC color distribution (Forbesetal.1996:Gebhardt&INissler-Patig1999:Larsenοἱ 2001). | The giant elliptical galaxy NGC 4365 at the outskirts of the Virgo cluster is another example of a galaxy with only a single broad peak in the GC color distribution \citep{for96,gk99,lar01}. |
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