Radio Observations of Supernova Remnants at 31 Ghz with the Cosmic

RADIO OBSERVATIONS OF SUPERNOVA REMNANTS AT 31GHZ WITH THE COSMIC BACKGROUND IMAGER A thesis submitted to the University of Manchester for the degree of Master of Science in the Faculty of Engineering and Physical Sciences 2015 By Shweta Agarwal School of Physics and Astronomy Contents Abstract 10 Declaration 12 Copyright 13 Acknowledgements 14 1 Introduction 15 1.1 Radio Observations ........................ 15 1.2 Diffuse Radiation ......................... 16 1.2.1 Synchrotron ........................ 17 1.2.2 Free-Free .......................... 20 1.2.3 Thermal Dust ....................... 22 1.2.4 Anomalous Microwave Emission (AME) ........ 24 1.3 Supernova Remnants ....................... 24 1.3.1 Galactic Supernova Remnants .............. 25 1.3.2 Radio Properties of Supernova Remnants ........ 29 1.3.3 Distances to Supernova Remnants ............ 30 1.4 Interferometry and Synthesis Imaging .............. 31 1.4.1 Imaging .......................... 33 1.5 Thesis Outline ........................... 34 2 Cosmic Background Imager and Data Analysis 36 2.1 The Cosmic Background Imager ................. 36 2.2 Observations ............................ 40 2 2.3 Data reduction .......................... 43 2.3.1 Flagging .......................... 46 2.3.2 Calibration ........................ 48 2.4 Imaging .............................. 53 3 Radio Observation of SNRs 56 3.1 Description ............................ 56 3.1.1 G20.0 0.2 ......................... 57 − 3.1.2 G312.5 3.0 ........................ 59 − 3.2 Data and Observations ...................... 60 3.3 Subtracting the UCHii region from G20.0 0.2 ......... 64 − 3.4 Multi-frequency Maps ...................... 68 3.4.1 Data description ..................... 68 3.4.2 The visual analysis .................... 69 4 Analysis 73 4.1 Photometry ............................ 73 4.1.1 Aperture Photometry ................... 73 4.1.2 Map Unit Conversion ................... 74 4.2 Uncertainties in the Measurements ............... 77 4.2.1 Total Uncertainty ..................... 79 4.2.2 Modelling the Ancillary Data with the CBI (u,v) Cov- erage ........................... 80 4.3 Flux Density and Spectral Index ................. 81 4.3.1 SED of G20.0 0.2 .................... 82 − 4.3.2 SED of G312.5 3.0 .................... 84 − 4.3.3 Discussion ......................... 86 5 Conclusions 88 5.1 Summary and Conclusions .................... 88 5.2 Future Prospects ......................... 90 Appendices 90 3 A Some definitions 91 B Scripts 94 Bibliography 108 Word count: 29309 4 List of Tables 1.1 Optical properties of supernovae ................. 26 1.2 Comparison between a single dish, and an interferometer. .. 31 2.1 Specifications for CBI1 and CBI2. ................ 40 2.2 The supernova remnants observed by CBI ........... 42 3.1 Observational details of G20.0 0.2. .............. 61 − 3.2 Observational details of G312.5 3.0. .............. 61 − 3.3 Flux density of sub-components of the UCHii region at 15GHz and 5GHz, as given by Wood & Churchwell (1989). ...... 67 4.1 Various methods applied on G20.0 0.2 to estimate the con- − tribution from ground and background contamination. .... 78 4.2 Photometry results for G20.0 0.2. The value is parentheses − is after subtracting UCHii regions. ............... 80 4.3 Results for G312.5 0.3. The values below 31GHz are taken − from Kane & Vaughan (2003). .................. 80 4.4 Final corrected flux densities for G20.0 0.2 (top) and G312.5 − − 0.3 (bottom). For G20.0 0.2 the flux was calculated using − the Effelsberg data at 2.7GHz, and for G312.5 0.3 using the − Parkes 5GHz data. ....................... 81 5 List of Figures 1.1 Atmospheric absorption by O2 and H2O molecules. ...... 16 1.2 Diffuse emission spectra at 1◦ resolution over the high latitude sky (not including the Galactic plane) as as a function of frequency. Synchrotron dominates below 10GHz, dust above ∼ 100GHz, free-free between 50GHz to 70GHz and spinning ∼ dust dominates at frequencies 30GHz. Figure reproduced ∼ from Planck Collaboration et al. (2015). ............ 17 1.3 The synchrotron spectrum of a single electron, pointed as flux density (F(x)) against frequency (x) on a linear scale. The details are given in (Pacholczyk, 1973). The critical frequency ν , is equal to 2πω , as shown in the figure at x 1. ω is c c ≈ c defined in Eq. 1.2. Image taken from http://www.cv.nrao.edu/. 19 1.4 Full-sky radio map at 408MHz (Haslam et al., 1982) in Moll- weide projection. Bright point-like sources have been removed. The emission in this map is dominated by diffuse Galactic synchrotron radiation. Note that the colour-scale has been his- togram equalized to highlight both bright and faint features Remazeilles et al. (2015). Synchrotron radiation dominates at low frequencies and is not a major contributor at frequencies 10GHz for most lines-of-sight. ................ 20 ≥ 1.5 Full sky composite Hα map at the 1◦ scale. It can be used to infer limits on free-free emission from ionized gas (Finkbeiner, 2003). The Hα intensity is in units of Rayleighs and there has been no correction made for extinction effects. ......... 22 6 1.6 857GHz all-sky map of thermal dust emission from the Planck (Planck Collaboration et al., 2014a) ............... 23 1.7 At the end of its life, the central core of a massive star collapses to form a neutron star. This collapse releases a tremendous amount of energy, powering a supernova explosion. Fig. taken from http://chandra.harvard.edu/ ................ 26 1.8 A forward and a reverse shock are created when a supernova shock wave interacts with the ISM. The forward shock con- tinues to expand into the ISM, the reverse shock travels back into the freely expanding supernova ejecta. Image taken from http://chandra.harvard.edu/. .................. 27 1.9 Geometry convention for a two-element interferometer. Figure taken from (Burke & Graham-Smith, 2014). .......... 33 2.1 CBI and CBI2 ........................... 37 2.2 The primary beam pattern of CBI. (a) 26 GHz, (b) 31 GHz, (c) 36 GHz. The main beam can be well approximated by a Gaussian with FWHM (44 31 ). ................ 39 × ν 2.3 Flowchart showing the procedure used to obtain calibrated data, and CLEANed image. The calibrated data are written to .uvf (uv-FITS) files. ...................... 43 2.4 This figure is of a total-power plot for channel 4 (all receivers) within the CBICAL program. Receiver 11 shows amplitude that deviates from the mean by more than 10%, so we flagged it out. The receiver should have a power reading of 1, but ∼− sometimes was lower than 0.3 ................. 44 − 2.5 CBICAL visibility plot ...................... 45 2.6 Primary calibrator ........................ 49 7 2.7 Plot of the visibility statistics of the calibration source (Jupiter). The observations were made on the 25 September 2007. Each colour represents a channel and each individual point is a dif- ferent baseline. In this plot Jupiter is calibrated from another observation of Jupiter and thus the phase is not exactly equal to zero. ............................... 51 3.1 VLA map of G20.0 0.2 with a maximum at 0.92Jy/beam − and a minimum at 0.00433Jy/beam. Image produced from − MAGPI survey (Helfand et al., 2006). ............. 58 3.2 The Parkes 4850MHz survey map of G312.5 3.0. The map − shows the morphology of the object at a resolution of 4.3arcmin. Image produced by (Griffith & Wright, 1993) data. ...... 60 3.3 CLEANED CBI map of G20.0 0.2 before subtracting the − flux for UCHII region. ...................... 62 3.4 CBI image of G312.5 3.0 having a maximum brightness of − 0.07 Jy/beam. ........................... 63 3.5 The CBI map of the G20.0 0.2 after subtracting the UCHii − region. The extended component in the south is G19.61 0.23, − which is a complex Hii region with RA = 18h 27m 38s and Dec = -11h 56m 40s (Wood & Churchwell, 1989). ....... 65 3.6 Image of the UCHii region at (left) 2cm and (right) 6cm. Sub-components of the region are marked as A,B and C. The three regions are studied separately. A is the brightest region, followed by B and then C. Taken from Wood & Churchwell (1989). ............................... 66 3.7 The free-free model for the three sources within the UCHii region. The data has been taken from Wood & Churchwell (1989). ............................... 67 8 3.8 Multi-frequency maps of G20.0 0.2 with the contours from − the CBI map at (0.1, 0.2, 0.5, 0.7, 0.9)*0.99Jy/beam. (a) is the Parkes 5GHz map, (b) is the IRAS 12 µ m map, (c) is the Planck map at 545GHz map, (d) is the Effelsberg 100m map. ................................ 70 3.9 Multi-frequency maps of G312.5 3.0 with CBI contours from − the CBI map at (0.1, 0.2, 0.5, 0.7, 0.9)*0.07Jy/beam. (a) is the Planck map at 545GHz, (b) is the IRAS map at 12 µm and the (c) is the Parkes map at 5 GHz. ............ 71 4.1 Spectral energy distribution of G20.0 0.2. The fit was ob- − tained using the data points as discussed in Table 4.2. (a) shows the power-law fit. (b) is the fit for the spectral break at 5 GHz. ............................ 83 ∼ 4.2 Spectral energy distribution of G312.5 3.0. The power law − was calculated using the methodology discussed in Table 4.3. 85 4.3 Distribution of spectral indices of Galactic SNRs compiled by Green (2009). Figure taken from Reynoso & Walsh (2015). .. 86 9 Abstract The explosion of a supernova releases almost instantaneously about 1051 ergs of mechanical energy, an event that irreversibly changes the physical and chemical properties of large regions of their host galaxy. A supernova remnant (SNR) consists of three components: the stellar ejecta, the nebula resulting from the powerful shock waves, and sometimes a compact stellar remnant. They can radiate their energy across the whole electromagnetic spectrum, but the great majority are strongest in the radio regime.

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