Boutiques & Experiments 2016 Radio Astronomy Caltech Campus, July 21{23, 2016 Brassica olaracea var. botrytis The stunning example of a brassica olaracea var. botrytis, or Romanesco broccoli, depicted on the cover exhibits numerous parallels with radio astronomy. The overall spiral arrangement of the florets immediately brings to mind the proposed configuration of SKA stations, and the increase in their sizes with radial distance is reminiscent of the log-periodic antenna. However, the fractal nature of the broccoli reminds us that objects of great beauty and complexity may exist even on bite-sized scales, and as pieces of larger objects, that are self-similar to the whole. i Preface Boutiques & Experiments (B&E) is an invitational workshop. The purpose of this (hopefully durable) series is to examine carefully near-term opportunities in astronomy, especially for those areas which are expected to get or are getting vibrant. Last year we focused on optical synoptic surveys.1 This year the workshop is focused on opportunities in meter-wave and cm-wave radio astronomy. In these bands astronomy is now both fecund and full of opportunities. As before, the workshop has an underlying contrarian flavor (in that the goal is to identify and harvest low-hanging fruits, especially ahead of future large projects). To start with, Fast Radio Bursts (FRBs) continue to be puzzling but their diagnostic power to probe the IGM and intense sites of star-formation in other galaxies is unques- tioned and supreme. A veritable industry (boutiques, experiments and large industrial machines), ranging from big facilities such as CHIME and Molonglo to small experiments such as DSA-10 at OVRO, centered around FRBs is now in full swing. New centimeter- and meter-wave facilities are either producing or are on the verge of producing large amounts of data: LOFAR, ASKAP, MeerKAT, MWA and LWA (the list is not complete!). VLA is about to start a major sky survey (VLASS). In the US there is a low awareness of Spektr-RG (expected to launch next year). However this mission carrying eROSITA is like ROSAT on steroids. With its cadenced and synoptic all-sky coverage this mission is expected to revolutionize X-ray astronomy. The combination of of VLASS and SRG survey will be a bonanza for TDE science (at the very least). We are pleased that R. Sunyaev kindly agreed to attend the workshop and talk on Spektr-RG. Next, we are officially in the era of GW astronomy. This is truly an exciting devel- opment. Stellar mass black holes exist in abundance, both singly and in binaries. In a curious way the LIGO discoveries offer hope that radio astronomers will soon discover a psr+bh system. Next, with regard to bh-ns and ns-ns coalescences, one could make a compelling case that radio observations will have as good a chance (and perhaps better than relative to other bands) of detecting long lived remnants. Techniques have played an important and arguably critical role in the development of radio astronomy. For instance, the first generation of interferometers were designed to evenly sample the u-v space, whence their fully redundant East-West configuration (e.g. WSRT). The invention of the CLEAN technique opened up a dizzying number of array configurations (e.g. the VLA). A single algorithm had a profound effect on civil engineering requirements of radio interferometers! We have an entire session to discuss new algorithms, developments in signal processing (spurred by requirements of SETI and searches for FRBs) and community based common development (CASPER). On the more traditional analog hardware side the demonstration of cooled phased arrays (AO-19) is now opening up a new era in single dish astronomy (e.g. AO-40). In the past, with considerable effort, joint surveys were undertaken (e.g. iPTF and VLA Stripe 82 survey). Thanks to the proliferation of optical synoptic surveys such initia- tives can be expected to become routine (MeerLICHT calls for joint observations between MeerKAT and an optical wide field imager). In that spirit, discussions have started for a joint program between ZTF and SDSS (once both programs have finished their prime surveys). We are following the same format as B&E 2015: have the proceedings available ahead of the workshop and expect the participants to read the extended abstracts (and the 1 http://www.astro.caltech.edu/~srk/BnE2015Notes.pdf ii diligent student to read the suggested references) ahead of the workshop. The speakers are expected to entirely skip introduction and proceed directly to the heart of their talk. Chairs of all sessions have been instructed to ensure that there is 5 minutes of discussion for each talk. An added attraction of B&E 2016 is that several radio astronomers who were heavily involved in the formulation and development of the VLA, VLBI & VLBA (B. Clark, M. Cohen, A. Readhead, & S. Weinreb) will be attending the meeting. It is a great pleasure to use this occasion to celebrate the ninetieth year of one of these astronomers (MC; page 67 of these proceedings). As with B&E 2015, we have included \historical" pictures but this time of radio astronomy facilities and personalities { in honor of the pioneering radio astronomers gracing this modest workshop. G. Hallinan took charge of this initiative and obtained vintage photographs from M. Cohen, A. Readhead and M. Goss, amongst others. We also have a fair number of young, novice and neophyte radio astronomers attending the workshop. In fact, all students who inquired or showed the slightest inclination were invited to attend the workshop. The workshop offers to be an intellectual treat and hopefully memorable to fans of radio astronomy. I would like to thank D. Frail and G. Hallinan for helping me formulate the slate of speakers and invitees. Vikram Ravi was the editor for \B&E 2016 Notebook". As with B&E 2015, we are publishing the proceedings ahead of the workshop. This unusual2 ap- proach worked very well for B&E 2015. In addition, extended abstracts contributed by various attendees not giving presentations are also included in each section of the proceed- ings. The Caltech Optical Observatories provided the logistical and secretarial support for this workshop. Specifically, I would like to thank Bronagh Glaser who took care of much of the administrative burden and logistical chores for the workshop. I am grateful to Tony Readhead, Director of the Owens Valley Radio Observatory (OVRO), for partial support of this workshop. S. R. Kulkarni Pasadena July 13, 2016 2In astronomy, proceedings are routinely published after the workshop and with delays of six months to a year. In computer science, the proceedings are published well ahead of the workshop. The latter is superior in that not only do the speakers come well prepared but so does the audience. The speakers can then directly proceed to their talk instead of starting off from Newton's Principia etc. iii Karl Jansky of Bell Labs was assigned the task of investigating the sources of static that might interfere with shortwave radio voice transmissions. In 1933, he serendipitously achieved the first detection of astrophysical radio emission at a frequency of 20.5 MHz (14.5 m) with the confirmation of a source with sidereal motion in the apparent direction of the Galactic center. The result was published by Jansky as "Electrical disturbances apparently of extraterrestrial origin" in Proc. IRE (now IEEE) in 1933 and was widely publicized, appearing in the New York Times on May 5th, 1933. However, despite it becoming apparent that the radio emission could not be explained by astrophysical phe- nomena that were well understood at the time (e.g. Whipple & Greenstein 1937), it was not until the 1950s, and the development of the theory of synchrotron emission, that its true importance was realized. iv In 1936, Gennady W. Potapenko, Professor of Physics at Caltech, together with graduate student Donald Folland, built an antenna in the Mojave desert that confirmed Janskys result. They campaigned for the construction of a much larger 90 180 ft. rotating rhom- × bic antenna (sketch above by R.W. Porter), but the request for $1000 was rejected ∼ by Robert Millikan, ending any involvement in radio astronomy at Caltech for 20 years. Adapted from Cohen, M.H., 1994. The Owens Valley Radio Observatory: The early years. Engineering and Science (Caltech), 57(3), 8{23. v Contents 1. Session A: Fast Radio Bursts 1 2. Session B: Propagation 20 3. Session C: GW, High Energy and UV 29 4. Session D: Relativistic Systems and Explosions 40 5. Sessions E and F: Transients 52 6. Session G: Methodology 73 7. Session H: Radio Boutiques and Experiments 86 8. Lunch discussions 97 vi In 1937, motivated by Jansky's discovery, amateur astronomer Grote Reber built a parabolic dish of diam- eter 31.5 ft. in his back yard in Wheaton, Illinois. In the following years, Reber produced the first radio map of the sky based on a series of systematic observations at 160 MHz (left; resolution of 12◦) and ∼ 480 MHz. Reber tried to interest astronomers at Yerkes Observatory, but all showed little interest, except for a young Jesse Greenstein, who was faculty at the University of Chicago. Although Reber and Greenstein would go on to write the first review of radio astronomy in 1947, US involvement in radio astronomy was hampered by both skepticism and lack of interest from the wider community. With the growing importance after WWII of the radio astronomy contributions being made in Britain and Australia, Reber's pioneering studies ultimately became widely recognized. After WWII, radar engineers in the UK and Australia migrated into radio astronomy and begin developing the techniques that underpin modern radio interferometry.