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44 Chapter 2. Multiwavelength approach to LS 5039 and 51176, when the flux density of LS 5039 seemed to have varied by more than a factor of ∼ 2 on less than one day. However, inspection of the GBI operational notes reveals that technical problems such as cryogenics warming, or weather problems such as snow on the dishes, were responsible of this behavior. The apparent bump between MJD 51180 and MJD 51200 is also a result of cryogenics warming. Hence, it seems that most of the features in the lightcurve are due to technical problems, because of the relatively low flux density of the source. Nevertheless, since Pooley et al. (1999) could detect the 5.6 d orbital period of Cygnus X-1 in similar radio lightcurves, we have performed a timing analysis of the LS 5039 lightcurves at both frequencies. Given the span of the observations, the search was restricted between 2 and 100 d. The methods employed were the Phase Dispersion Minimization (PDM) (Stellingwerf 1978) and the CLEAN algo- rithm (Roberts et al. 1987). Unfortunately, no convincing period was detected in this process. In particular, we do not detect the 4.117 d orbital period recently found by McSwain et al. (2001) from radial velocity measurements. Folding of the data with such a period does not reveal any significant difference on radio emission along the orbit. Since the orbit is quite eccentric (e=0.41), and this is a wind fed system (where the primary does not fill its Roche lobe), we expect the accretion rate onto the compact object to change significantly between periastron and apastron. Hence, the non detection of the orbital period in the GBI data can be attributed to its relatively high noise due to several facts (intrinsic measurement noise, technical problems, weather conditions, etc.). Although the 8.3 GHz data is dominated by noise, we can extract some infor- mation about the spectral index. The weighted mean of individual spectral indices is found to be α = −0.4 ± 0.3. On the other hand, if we use the mean flux densities at both frequencies we obtain a spectral index of α = −0.6 ± 0.4. These value are in good agreement with the results presented in Sect. 2.4.2 (Martí et al. 1998) obtained a few months before, thus suggesting that the non-thermal radio spectrum is a persistent property of the source. Set2 data This data set is not useful for timing analysis or other purposes due to its limited time span and total number of points. However, we have explicitly included the
2.4. The radio counterpart: NVSS J182614−145054 45 Flux density [mJy] Spectral index 100 80 60 40 20 0 0 −1 −2 GBI−NASA Monitoring Program (Set2 data) 2.25 GHz 8.3 GHz −3 51795 51800 51805 51810 51815 51820 51825 Modified Julian Date [JD−2400000.5] Figure 2.5: Same as Fig. 2.4 for the Set2 data. The flare is probably false (see text). light curve in Fig. 2.5 to comment on the intriguing flare seen at 8.3 GHz around MJD 51803. Although there could be an increase in flux density at 2.25 GHz, thus supporting a possible outburst, the GBI operational notes reveal that spikes were occasionally occurring at that time, and it is stated that single high scans should be ignored. Hence, we conclude that the flare shown in Fig. 2.5 is probably false. Conclusions LS 5039 is a persistent radio source. In the GBI monitoring it is clearly detected at 2.25 GHz, with a mean flux density of ∼ 31 mJy, and marginally detected at 8.3 GHz, with a mean flux density of ∼ 14 mJy. The spectral index of the source is α ∼ −0.5, confirming earlier results. In addition to the negative spectral index, the brightness temperature estimates for LS 5039 clearly yield to non-thermal values,
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UNIVERSITAT DE BARCELONA Departamen
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Per a la meva neboda Blanca, que va
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feina no presentada en aquesta tesi
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desfogar-nos conjuntament, per la s
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From the scientifical point of view
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Gràcies a la meva germana Nàdia,
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ii CONTENTS I Discovery and study o
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iv CONTENTS II A search for new mic
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vi CONTENTS
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viii Resum de la tesi d’Eddington
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x Resum de la tesi imprescindible p
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xii Resum de la tesi dels sistemes
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xiv Resum de la tesi un comportamen
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xvi Resum de la tesi MilliARC SEC 4
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xviii Resum de la tesi per poder de
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xx Resum de la tesi valors força s
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xxii Resum de la tesi 2. D’entre
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xxiv Resum de la tesi pano Alemán
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Page 74 and 75: 28 BIBLIOGRAPHY Lewin, W. H. G., va
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Page 79 and 80: Chapter 2 Multiwavelength approach
Page 81 and 82: 2.3. An interesting target in the s
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Page 135 and 136: Bibliography Blandford, R. D., & K
Page 137 and 138: BIBLIOGRAPHY 91 Merck, M., Bertsch,
Page 139 and 140: Chapter 3 LS 5039 as a runaway micr
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3.1. Positions and proper motions 9
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3.1. Positions and proper motions 9
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3.3. The past trajectory of LS 5039
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3.4. SNR G016.8−01.1 101 DECLINAT
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3.4. SNR G016.8−01.1 103 Normaliz
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3.4. SNR G016.8−01.1 105 Galactic
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3.5. The H i surroundings of LS 503
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3.6. Discussion 109 experienced a h
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3.6. Discussion 111 At this point w
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3.7. Conclusions 113 6. Finally, th
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Bibliography Ankay, A., Kaper, L.,
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BIBLIOGRAPHY 117 Schaerer, D., de K
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Part II A search for new microquasa
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122 Chapter 4. The cross-identifica
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130 BIBLIOGRAPHY
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132 Chapter 5. Radio and optical ob
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DECLINATION (J2000) DECLINATION (J2
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148 BIBLIOGRAPHY
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150 Chapter 6. EVN and MERLIN obser
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166 BIBLIOGRAPHY
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General conclusions 171 Since each
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