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138 Chapter 5. Radio and optical observations DECLINATION (J2000) -07 31 28 30 32 34 36 38 40 42 44 1RXS J072259.5-073131 VLA 20cm 07 23 00.2 00.0 22 59.8 59.6 59.4 59.2 RIGHT ASCENSION (J2000) Figure 5.3: Natural weighted map of the self-calibrated 20 cm data of 1RXS J072259.5−073131 obtained on the July 30 snapshot observation. Contours correspond to −3, 3, 4, 5, 7, 10, 15, 25, 40, 60, 85, 110 and 130 times 0.4 mJy beam −1 , the rms noise. 5.3.1 Results Promising optical counterparts for all observed sources, i.e., the first six ones in Ta- ble 4.1, were found in both observing runs. Thanks to the CAHA 2.2 m observations we were able to obtain accurate positions. For this purpose, we performed a detailed astrometric reduction of each image using field stars present in the USNO-A2.0 catalog (Monet et al. 1999). First of all we selected point-like objects in the image, not elliptical or binary objects due to crowded fields, and determined their positions (X, Y ). We also rejected very faint objects to allow a significant signal-to-noise ratio. On the other hand, very bright objects were also rejected, because the positions given in the USNO-A2.0 catalog are from plates obtained around 1950, and nearby (bright) stars could have experienced a shift in position since then due to relatively high proper motions. Then we fitted an astrometric solution to our image using the USNO-A2.0 (α, δ) and image (X, Y ) positions for the common stars in both
5.4. Discussion 139 the catalog and the image, and rejected spurious points above 3σ. We proceeded iteratively until convergence was achieved. This process allowed us to obtain plate solutions with an rms of ∼ 0.2 ′′ in each coordinate. This relatively high error prob- ably arises from the non-zero proper motions of the field stars finally used in the fit, between 36 and 155 depending on each image. We have to quadratically add to this error the 1σ empirical uncertainty estimate of the USNO-A2.0 catalog relative to the ICRF, which is also ∼ 0.2 ′′ in each coordinate (see Table 1 of Deutsch 1999). Therefore, the final 1σ error of our obtained coordinates is estimated to be 0.3 ′′ . We show the central 2 ′ × 2 ′ of the CAHA 2.2 m images in Fig. 5.1, with the optical counterparts marked with a circle (which is not any X-ray or radio error box). All sources appeared basically as point-like objects, except the quasar 1RXS J072418.3−071508, which had a complex structure with two separate optical components, hereafter NW (northwest) and SE (southeast). The NW position falls well within the NVSS error box and close to our obtained radio position. On the contrary, the SE position is clearly out the NVSS error box, and cannot be considered as a reliable counterpart to the radio source. Photometry was obtained thanks to the OAN 1.5 m observations. The absolute photometry is believed to be accurate only to ±0.1 magnitude in the best cases, because we could only determine the approximate photometric zero point by observing a few standard stars from Landolt (1992). The obtained results are presented in Table 5.2, where Col. 1 gives the RBSC object name, Cols. 2 and 3 give the J2000.0 ICRS coordinates of the optical position with the 1σ error of 0.3 ′′ below each coordinate, Col. 4 gives the observing dates and Cols. 5 to 7 give the Johnson V , R and I magnitudes. Magnitudes for 1RXS J072418.3−071508 correspond to the sum of both the NW and SE components. 5.4 Discussion The observations reported here provide accurate positions in the optical (0.3 ′′ ) and specially in the radio (0.01 ′′ ) domains. The astrometric agreement for each source can be seen in the radio maps of Fig. 5.1, and is numerically expressed in Table 5.3, where we list the offsets in right ascension, in declination and the total offset between
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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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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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Page 163 and 164: BIBLIOGRAPHY 117 Schaerer, D., de K
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