Universitat de - Departament d'Astronomia i Meteorologia ...

More documents

Recommendations

Info

142 Chapter 5. Radio and optical observations The optical emission seen in microquasars arises from the non-degenerated star of the system, i.e., the companion of the compact object. Hence, in microquasars containing a high mass companion spectral types O or B are found, while in those containing a low mass companion the spectral type is later than A (White et al. 1995). Therefore, as optical counterpart of a given candidate, we expect to find a non-degenerated star with any spectral type, and with a luminosity class ranging from the main sequence to supergiant. In fact, once photometric magnitudes of an object through different filters and its distance are known, one can easily deduce its spectral type assuming it is a star. However, we have no information about the distance to our sources, and no correction for extinction can be applied to our data. This is particularly important in our case, since our search has been carried out at low galactic latitudes, where a high degree of extinction is expected, preventing any spectral type classification from the photometric data alone. 5.4.1 Discussion on individual sources 1RXS J001442.2+580201. The radio counterpart, see Table 5.1, shows a mod- erate degree of variability but always displaying a negative spectral index of ∼ −0.2, suggesting an optically thin or partially self-absorbed synchrotron emitter. As can be seen in Fig. 5.2, the non-simultaneous NVSS flux density measurement at 20 cm wavelength is compatible with this behavior or even with a flattening of the spectrum at longer wavelengths, although this could be due to intrinsic variability. Non- thermal synchrotron radiation remains therefore as the most plausible interpretation for the radio emission of this source. The optical counterpart to the radio source (Fig. 5.1) appears as a point-like source with I ∼ 20, which makes it the weakest optical object of our sample. No R or V magnitudes could be obtained, although a typical behavior for low latitude highly absorbed sources is an increase of ∼ 1 magnitude when changing from I to R and from R to V , as can be seen in the other sources of Table 5.2. All the available information points towards a good REXB candidate. 1RXS J013106.4+612035. In the radio domain it shows a slightly negative or close to zero spectral index, reminiscent of optically thin or partially self-absorbed jets in REXBs, in which the non-simultaneous NVSS flux measurement fits well, and it displays a very low degree of variability of 2% at 3.6 cm and 4% at 6 cm. This
5.4. Discussion 143 object has also been observed within the Green Bank 5 GHz radio survey (Gregory & Condon 1991; Gregory et al. 1996) with a measured flux density of 24 mJy. This value is a little bit higher than the ones reported here, although this discrepancy could be due to intrinsic variability and/or to the different angular scales sampled by the interferometric VLA observations. In fact, VLA A configuration observations carried out by Laurent-Muehleisen et al. (1997) on October 19, 1992, indicate a flux density of 16 mJy at 5 GHz, in good agreement with our data. In the optical domain, the counterpart to the radio source appears as a point-like object with a nearby field object at ∼ 3 ′′ to the northeast, visible in Fig. 5.1, which is ∼ 1 magnitude fainter in the I band. The optical magnitudes in Table 5.2 correspond to the sum of both objects (unresolved in the OAN 1.5 m images), and are typical of low latitude highly absorbed sources. Overall it seems a good REXB candidate. 1RXS J042201.0+485610. In the RBSC this source appears catalogued with an X-ray extension of 17 ′′ , which could suggest an extragalactic origin of the source. However, X-ray halos produced by the scattering of the original X-ray photons by interstellar dust grains are seen in some galactic microquasars, like for example in a Chandra observation of Cyg X-3 (Predehl et al. 2000). In fact, Cyg X-3 has an X-ray extension of 63 ′′ within the RBSC, while SS 433 has one of 25 ′′ . Hence, the presence of an X-ray extension does not rule out a REXB nature for this source. The radio counterpart shows the lowest radio emission level of all sources in our sample, and displays an inverted spectrum up to α ∼ +1.6 (see Table 5.1), difficult to account for self-absorbed synchrotron radiation at such high frequencies. Nevertheless, as it happens in some AGN, a highly inverted spectrum would be expected if the jet is stopped in a dense medium on a compact scale. On the other hand, the non- simultaneous NVSS flux density measurement seems to be incompatible with self- absorbed synchrotron radiation. Although this could be due to intrinsic variability of the source, this would require variations of an order of magnitude in flux. This discrepancy can be explained if we assume a thermal origin for the radio emission and if we attribute the drop in flux density in our VLA A configuration observations due to over resolution when compared to the NVSS VLA D configuration observations. The optical counterpart to the radio source has a nearby field object at ∼ 3 ′′ to the west, marginally visible in Fig. 5.1, which is ∼ 2 magnitudes fainter in the I band. The optical magnitudes in Table 5.2 correspond to the sum of both objects (unresolved in the OAN 1.5 m images), although the nearby one is not expected to contaminate appreciably, and are again typical of low latitude highly absorbed
Page 1:
UNIVERSITAT DE BARCELONA Departamen
Page 5:
Per a la meva neboda Blanca, que va
Page 8 and 9:
feina no presentada en aquesta tesi
Page 10 and 11:
desfogar-nos conjuntament, per la s
Page 12 and 13:
From the scientifical point of view
Page 14 and 15:
Gràcies a la meva germana Nàdia,
Page 16 and 17:
ii CONTENTS I Discovery and study o
Page 18 and 19:
iv CONTENTS II A search for new mic
Page 20 and 21:
vi CONTENTS
Page 22 and 23:
viii Resum de la tesi d’Eddington
Page 24 and 25:
x Resum de la tesi imprescindible p
Page 26 and 27:
xii Resum de la tesi dels sistemes
Page 28 and 29:
xiv Resum de la tesi un comportamen
Page 30 and 31:
xvi Resum de la tesi MilliARC SEC 4
Page 32 and 33:
xviii Resum de la tesi per poder de
Page 34 and 35:
xx Resum de la tesi valors força s
Page 36 and 37:
xxii Resum de la tesi 2. D’entre
Page 38 and 39:
xxiv Resum de la tesi pano Alemán
Page 40 and 41:
xxvi Resum de la tesi 3.3 Observaci
Page 42 and 43:
xxviii Resum de la tesi habitual en
Page 44 and 45:
xxx Resum de la tesi Per tant, si l
Page 46 and 47:
xxxii BIBLIOGRAFIA
Page 48 and 49:
2 Chapter 1. Introduction and backg
Page 50 and 51:
Page 52 and 53:
Page 54 and 55:
Page 56 and 57:
10 Chapter 1. Introduction and back
Page 58 and 59:
Page 60 and 61:
Page 62 and 63:
Page 64 and 65:
Page 66 and 67:
Page 68 and 69:
Page 70 and 71:
Page 72 and 73:
Page 74 and 75:
28 BIBLIOGRAPHY Lewin, W. H. G., va
Page 76 and 77:
30 BIBLIOGRAPHY
Page 79 and 80:
Chapter 2 Multiwavelength approach
Page 81 and 82:
2.3. An interesting target in the s
Page 83 and 84:
2.4. The radio counterpart: NVSS J1
Page 85 and 86:
Page 87 and 88:
Page 89 and 90:
Page 91 and 92:
Page 93 and 94:
Page 95 and 96:
Page 97 and 98:
Page 99 and 100:
Page 101 and 102:
2.5. The optical/IR star: LS 5039 5
Page 103 and 104:
Page 105 and 106:
Page 107 and 108:
Page 109 and 110:
Page 111 and 112:
2.6. The X-ray counterpart: RX J182
Page 113 and 114:
Page 115 and 116:
Page 117 and 118:
Page 119 and 120:
Page 121 and 122:
2.7. The γ-ray counterpart: 3EG J1
Page 123 and 124:
2.7. The γ-ray counterpart: 3EG J1
Page 125 and 126:
2.8. A proposed scenario to explain
Page 127 and 128:
Figure 2.23: Scenario where the mul
Page 129 and 130:
Page 131 and 132:
Page 133 and 134:
2.9. Conclusions 87 8. We have carr
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
Page 141 and 142: 3.1. Positions and proper motions 9
Page 143 and 144: 3.1. Positions and proper motions 9
Page 145 and 146: 3.3. The past trajectory of LS 5039
Page 147 and 148: 3.4. SNR G016.8−01.1 101 DECLINAT
Page 149 and 150: 3.4. SNR G016.8−01.1 103 Normaliz
Page 151 and 152: 3.4. SNR G016.8−01.1 105 Galactic
Page 153 and 154: 3.5. The H i surroundings of LS 503
Page 155 and 156: 3.6. Discussion 109 experienced a h
Page 157 and 158: 3.6. Discussion 111 At this point w
Page 159 and 160: 3.7. Conclusions 113 6. Finally, th
Page 161 and 162: Bibliography Ankay, A., Kaper, L.,
Page 163 and 164: BIBLIOGRAPHY 117 Schaerer, D., de K
Page 165: Part II A search for new microquasa
Page 168 and 169: 122 Chapter 4. The cross-identifica
Page 176 and 177: 130 BIBLIOGRAPHY
Page 178 and 179: 132 Chapter 5. Radio and optical ob
Page 180 and 181: DECLINATION (J2000) DECLINATION (J2
Page 196 and 197: 150 Chapter 6. EVN and MERLIN obser
Page 214 and 215: ¡¢ ¢ ¢ ¡¢ £¤ ¡¢ ¤ ¢
Page 217 and 218: General conclusions 171 Since each
show all

Universitat de - Departament d'Astronomia i Meteorologia ...

Create successful ePaper yourself

Delete template?

Save as template?