ASTRON/JIVE Summer Student Programme 2016

Summer student programme 2016

Group

Yuping Huang

With all the people, mentors and friends I met, my time at ASTRON/JIVE has been one of the most wonderful summer experiences I have ever had. I worked at JIVE with Dr. Aard Keimpema, Dr. Benito Marcote and Dr. Zsolt Paragi on localisation of fast radio transients with Very Long Baseline Interferometry. In this summer project, we developed techniques to search for and localize single pulses with the European VLBI Network (EVN) data and applied them to repeating sources (a pulsar and a RRAT) to understand the limitations and uncertainties of these techniques. It was an exciting project because most of these sources have only been discovered by large single dish telescopes, which cannot provide precise localizations due to their limited angular resolutions. The European VLBI Network (EVN), combining large collecting elements and superior angular resolution, is well-suited for searches and localizations of these pulses. In particular, searching for and localizing Fast Radio Bursts will enable us to identify their locations within their hosts and thereby unveiling their currently unknown origin.

I am grateful for the guidance and patience I received from my supervisors and other astronomers at ASTRON/JIVE that allowed me to jump-start from knowing next to nothing about radio interferometry. I miss the board game nights and all the fun trips we made to the telescopes as well as to the rest of the Netherlands. And finally, I appreciate the effort everyone has put in to make this programme such an inclusive place.

Xiaoxi Song

My name is Xiaoxi Song. I am from China and I am an undergraduate student studying astrophysics at University College London (UCL). I worked with Vlad Kondratiev and Anna Bilous on single-pulse analysis of pulsars. We focused on the phenomenon of Anomalously Intensive Pulses (AIPs), These single pulses exhibit bright and strong emissions at low frequencies, but it is not clear whether these emissions are linked with Giant Pulses (GPs), observed in young or millisecond pulsars at high frequencies.

We worked on PSR B0809+74, a bright nearly pulsar exhibiting AIPs. The data was taken by LOFAR Low Band Antenna (LBA). We found a distinct 50-pulse sequence of emission patches at the bottom end of the spectrum, which we named it as a "super-sequence". The emission patch starts at frequency of about 15 MHz, drifting in phase and growing in spectral width towards high frequencies. We conducted several statistical methods in Python, correcting the variations in both frequencies and time, to eliminate these patches. Unfortunately, the patches, potentially affect the analysis of AIPs, could not be resolved. We also plotted and examined these patchy emissions in various ways, leading to the conclusion that these emissions are unlikely to be pulsar intrinsic. The patches might be caused by the scintillation effect of the ionosphere. As these emissions are not "real", we need to be aware of this non-pulsar-originated modulation when carrying out low-frequency single-pulse analysis.

During my project, I learnt various pulsar tools such as PSRCHIVE and dspsr, and further developed my Python skills. I would like to specially thank my supervisors, who gave me immersion support both theoretically and technically, always sharing their great passion in pulsar studies. In addition, the special lecture series in radio astronomy broaden my knowledge in this field. I had an amazing 11-week at ASTRON, collaborating well with people, also enjoying a lot of activities such as playing contract bridge and board games!

Anjali Piette

My name is Anjali Piette and I'm an undergraduate at Cambridge University. This summer, I had the amazing opportunity to work with Jess Broderick and Antonia Rowlinson on a particularly exciting dataset - LOFAR's follow-up observations to the first two gravitational wave (GW) detections. The aim of my summer project was to look for electromagnetic (EM) counterparts to these black hole binary merger events; although EM radiation is not expected from such mergers, various theories propose that, under certain conditions, a synchrotron afterglow could be observed (e.g. Loeb 2016). Moreover, using the very wide total field of view of the LOFAR observations (~200 deg^2), we also conducted a more general search for low-frequency transients, in particular by comparing our data with the TGSS survey (Intema et al. 2016) to look for transients on a longer average time-scale of about 4.5 years. Although no LIGO EM counterparts or other transients were detected down to a median 6 sigma level of ~30 mJy, we were able to place valuable constraints on radio transient surface densities.

This summer programme has been an absolutely fantastic experience, and I would strongly recommend it to anyone considering a career in Astrophysics. Everyone I have met here has been immensely welcoming and friendly, which creates a fun, positive and constructive environment for learning. On top of that, I could not have imagined better supervisors than Jess and Antonia, who have been so supportive and helpful, as well as very fun to work with! The wide range of organised activities has also been brilliant, from the pancake party on my first day to weekly games nights, visits to ESTEC/WRST/LOFAR, and the very therapeutic wadlopen. This is a truly outstanding summer student programme, and I'd like to thank everyone who has been involved in organising it, as well as my fellow summer students, for making it such an incredible experience.

Anoj Khadka

My name is Anoj Khadka and finished my masters degree in physics from Tribhuvan University, Nepal. This was my first research experience and this summer I worked with Betsey Adams and Kelley Hess on galaxy formation/evolution project. I spent my time doing HI data reduction and imaging of one particular galaxy - HIZOA J0836-43. Detailed study of one particular galaxy is important for understanding the physical kinematics of the galaxy. Studying this galaxy was important for the reason that it has high SFR (star formation rate), very uncommon in the local universe (z<0.1) and huge HI gas reservoir. Understanding the interrelationship between the SFR and the gas reservoir it has helps us to know how galaxy formation and evolution takes place. Using CASA (common astronomical software application) software I did filtering of the data and made images from the data cube. Double horned spectral profile map i made for this galaxy matched quiet well with the previous study (Donley et al). Besides, i also made moment maps with contours overlaid. Moment maps of different orders tell us about the different physical characteristics of the galaxy. I also used infrared images provided by Michelle Cluver (University of Western Cape) to compare with the HI moment map I made. Preliminary image analysis showed that the old star formation in this galaxy is highly concentrated at the central region whereas the HI gas is distributed much beyond. Currently popular hierarchical model of galaxy formation/evolution suggests that galaxy formation occurs by clumping of smaller lumps of dwarf galaxies and gas clouds through merger interactions. However, contour maps I made showed no obvious merger interactions in this galaxy. All three of us also briefly tried for the first time to use ‘DiskFit' to do some modeling of the galaxy. Though we could constrain some properties like eccentricity, position angle etc. due to time constrain we could not dig much deeper to produce something interesting. I loved the work I did and wish to carry on with the galaxy formation/evolution study in future too.

I enjoyed every bits and pieces of this summer school. Having helpful and caring supervisors was a blessing. The friendly working environment ASRON/JIVE has, always ready to help people around and interesting combination of other summer student friends collectively contributed to make this summer school a remarkable experience of my life. Though it is not possible to list all the events I enjoyed this summer, events like bridge night, BBQ, lectures, astro-coffee, astro-lunch, biking around Dwingeloo, educational tour to Westerbork telescope, LOFAR etc were all sweet memories I carried. I also really treasure the weekend trips I regularly made with other friends and people from ASTRON/JIVE. It's hard to say what will happen ten years from now but I wish to do some cool science and remain in astrophysics/cosmology field in some way for which this summer school was an inspiration. Finally, I thank everyone involved in one or another way to make this summer school a memorable experience.

Floor Broekgaarden

I'm Floor Broekgaarden, and I'm just about to finish my double Bachelor's degree in Mathematics and Physics and Astronomy at the University of Amsterdam, and now also starting a double master program in Applied mathematics and Astrophysics. During the ASTRON/JIVE summer programme 2016, I worked together with Ilse van Bemmel and Zsolt Paragi (JIVE) on the analysis of e-EVN data of a Gamma-ray burst (GRB). I applied for the ASTRON/JIVE summer programme to get more experience in data analysis and radio astrophysics, and this project helped me with that perfectly. The main goal of the project was to constrain the image size of GRB130702A, a relatively nearby GRB (redshift z = 0.145). The diffraction limit of our observations was 3 milliarcseconds (mas), but we could constrain the size of our jet to have an upper limit of 0.35 mas one tenth of the diffraction limit. This was done by assuming a source intensity profile, and (model)fitting different source sizes to the visibility data. In addition, during this project, we also investigated the influence of the degree of phase errors on the robustness of this modelfitting.

Outside of this project, the summer programme was really an amazing experience. I liked how the programme really gives you the opportunity to learn about radio astronomy and research beyond a standard university course. Not only do you conduct research under the supervision of experienced radio astronomers, during the programme you're surrounded by so many enthusiastic and inspiring astronomers that are all more than willing to help you out with any problem. In addition, the scheduled lectures and excursions really motivate you and give you a great overview of nowadays problems in radio astronomy. Also it was incredible to get to know the fellow summer students so well during our stay, travel around in the Netherlands (and Germany) and join all the social activities that were organised for us that gave a great opportunity to meet all the special people from ASTRON/JIVE. All in all, I really enjoyed getting this unique opportunity to learn so much about astronomy, and making really good friends that I will definitely stay in touch with!