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158 Chapter 6. EVN and MERLIN observations Figure 6.2: Images of 1RXS J013106.4+612035 using the different arrays and with the parameters given in Table 6.4. The axes units are in mas. A (u, v)-tapering with a FWHM at 15 Mλ has been used to perform the combined EVN+MERLIN image. value, preventing to state that a proper motion has been detected. Summarizing, our results indicate that this source exhibits relativistic radio jets with β > 0.20 and, therefore, together with the results reported in Chapt. 5, we consider 1RXS J001442.2+580201 as a very promising microquasar candidate. 6.3.2 1RXS J013106.4+612035 and its one-sided jet We show in Fig. 6.2 the images obtained after our observations. Although the source appears compact at MERLIN and EVN+MERLIN scales, there is a weak one-sided radio jet towards the northwest in the EVN image. Model fitting with circular Gaussian components can reproduce the observed visibilities as follows: a central 15.4 mJy component with 0.64 mas FWHM, and a northwest 2.1 mJy component with a FWHM of 0.74 mas, located at 1.8 mas in P.A. −73 ◦ . As can be seen, this last component is located at a distance of ∼ 2 times the beam size from the core. Using the fact that we do not detect a counter-jet, we can use Eq. 6.2 replacing Sr with the 3σ level value. This, of course, will only provide a lower limit to β cos θ, expressed as follows: β cos θ > (Sa/3σ) 1/(k−α) − 1 (Sa/3σ) 1/(k−α) + 1 . (6.3) Using Sa = 2.1 mJy, 3σ = 0.30 mJy (the 1σ value has been taken as the root mean square noise in the image), α = −0.05 ± 0.05 (see Table 5.1), and k = 3 to be consistent with the lowest limit, we obtain β cos θ > 0.31 ± 0.05 (β > 0.31 ± 0.05
6.3. Results and discussion 159 and θ < 72 ± 3). Hence, a lower limit of β ≥ 0.3 is obtained, pointing towards relativistic radio jets as the origin of the elongated radio emission present in the EVN image. Although the one-sided jet morphology at mas scales is found mostly in extragalactic sources, it is also present in some galactic REXBs, like Cyg X-3 (Mioduszewski et al. 2001) or LS I +61 303 (Massi et al. 2001). Hence, we cannot rule out a possible galactic nature on the basis of the detected morphology. As done for the previous source, we can compare the VLA position with the MERLIN one, and find that they differ in ∆α cos δ = 39 ± 10 mas and ∆δ = −0.8 ± 10 mas. If the offsets are real, this would imply µα cos δ = 64 ± 16 mas yr −1 and µδ = −1 ± 16 mas yr −1 . Hence, it seems possible that we have detected a proper motion in right ascension at a 4σ level. However, we must be cautious since, as in the previous case, the phase-reference sources and observing frequencies were different in each observation. Overall, these results are indicative of relativistic radio jets, and hence, together with the results reported in Chapt. 5, allow us to classify this source as a promising microquasar candidate. 6.3.3 1RXS J042201.0+485610, a non-detected source This radio source was marginally seen in the cross-scans carried out in Effelsberg. In fact, this is compatible with the low flux density of 2.3±0.4 mJy at 1.4 GHz listed in the NVSS. The source was not detected with MERLIN or with the EVN, mainly due to problems with the phase-reference sources, as pointed out in Sect. 6.2.2. In fact, as discussed in Chapt. 5, VLA A configuration observations showed a flux density of 0.4 mJy at 5 GHz and an inverted spectrum with a spectral index up to α = +1.6, suggesting thermal radio-emission resolved at higher angular resolutions. However, we cannot exclude the possibility of having a highly variable source. 6.3.4 1RXS J062148.1+174736, a compact source As can be seen in our images, shown in Fig. 6.3, the radio source is compact on all scales. In fact, model fitting of the EVN visibilities converges to a point-like radio source (the FWHM of a circular Gaussian tends to zero). We must note that when
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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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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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xxvi Resum de la tesi 3.3 Observaci
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xxxii BIBLIOGRAFIA
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2 Chapter 1. Introduction and backg
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10 Chapter 1. Introduction and back
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28 BIBLIOGRAPHY Lewin, W. H. G., va
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30 BIBLIOGRAPHY
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Chapter 2 Multiwavelength approach
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2.3. An interesting target in the s
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2.4. The radio counterpart: NVSS J1
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2.5. The optical/IR star: LS 5039 5
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2.6. The X-ray counterpart: RX J182
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2.7. The γ-ray counterpart: 3EG J1
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2.7. The γ-ray counterpart: 3EG J1
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2.8. A proposed scenario to explain
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Figure 2.23: Scenario where the mul
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2.9. Conclusions 87 8. We have carr
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Bibliography Blandford, R. D., & K
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BIBLIOGRAPHY 91 Merck, M., Bertsch,
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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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