In August 2009, British amateur astronomer, Tom Boles broke Professor Fritz Zwicky’s 36-year-old record for the number of supernovae discovered by an individual when he bagged his 124th supernova. The fact Tom has been so prolific, observing from the cloudy, rainy United Kingdom makes this record even more remarkable.
Mike: What brought you to astronomy in the first place, and how did that evolve into a passion for discovering supernovae?
Tom: Hi Mike it’s good to talk to you.
Like so many amateur astronomers it happened at school. A boy in my class brought in a small telescope and let me look through it at Saturn and the Pleiades. (I lived in Scotland then and it is dark at 5 pm in winter) I was hooked immediately.
Searching for supernovae seemed a logical progression. I have always been interested in cosmology so there is a strong tie as supernovae are essential tools for studying the large scale Universe.
As you rightly say, the skies in the UK are less than ideal. It is difficult to find many good nights suitable for photometry but there is rarely a clear night when I don’t attempt to look for SNe. Even on very poor nights the brighter galaxies can be imaged. They are often not pretty pictures that I record but suitable for purpose, only the limiting magnitude drops.
Mike: Tell us about the observatory. Where is it located, how was it financed and built and what instruments do you currently employ in your search program.
Tom: The observatory is based on the periphery of a little quiet town called Coddenham in the heart of rural Suffolk in the UK. I moved here from central England because the light pollution there had deteriorated. Suffolk also offered me the chance to get a few extra clear nights each year. As a rule, the weather system in the UK improves slightly as you move farther east and south.
There are only two street lights in the village and they are in a dwell which keeps their glow hidden on all but the mistiest nights.
The observatory was privately financed by me. It was part of my ‘master plan’ when I took early retirement to get more involved with astronomy and supernovae in particular. I use three C14 SCTs on Paramounts. Two of my Paramounts are the original design and were the early form of the new ME. The third is the slightly later black version the 1100 which was the immediate precursor to the ME. I use three Apogee AP7, thinned and back illuminated CCD cameras which help me to get use from every photon the C14s provide. I think this is near the ideal set up for supernova hunting other than moving to much larger telescopes.
I did have a scare a couple of years ago when the observatory was struck by lightning. I lost three PCs, my network and one of the Paramount’s electronics. I was down for several months. Thankfully I had excellent support from Software Bisque who patiently talked me through replacing several controller boards that they supplied. I was glad on the excellent support that I received.
I built the observatory myself, not that I wanted to but when I described what I wanted to professional shed builders they just laughed and shook their heads. On reflection, I am glad that I did. Many challenges arose during the construction. I could work them out in bed at night. Had I had a tradesman it would have overrun and cost me a fortune.
Mike: How much of the process is automated? Do the telescopes work unattended, controlled by software, or do you control them to some degree from a control room nearby?
Tom: The telescopes are controlled over a local area network. The control room is in my house only about 100 feet from the observatory. I produce scripts, which consist of lists of target galaxies for the cameras to image. They point, settle for a few seconds, image, name and store each image automatically. A typical script is 200 galaxies long and will run unattended for up to 4 hours. I rarely leave them unsupervised in case the weather changes. On good nights I use 30 second integrations and on poorer nights 60 seconds. This can mean I collect up to 135 images an hour between the 3 systems. The image collection is the easy bit. Checking the images is where the hard work is. In mid winter, darkness can last 13 or 14 hours; that’s a lot of images. I use one PC to control each telescope and another indoors to monitor the images coming down and to ensure all is well. An additional one with an extra large screen is used to check the images against my master/library images.
Mike: You currently monitor around 12,000 galaxies. How has your search program evolved over time? Do you monitor a specific type of galaxy to maximize your efforts?
Tom: I started off very modestly just checking a few galaxies. That meant nice open face on spirals that maximized the chances of seeing the supernovae free from obscuring dust in the galaxy. I then added edge on spirals and moved on to others like SO galaxies and even irregulars and ellipticals. I use a galaxy’s size and recession velocity to give me an indication whether the SN will be too faint to see or not. To get to 12,000 galaxies I had to drop some of my criteria and add many other morphological types. Eventually the recession velocity (galaxy distance) where it was known, was the only criterion. I patrol 12,000 frames, that is, master fields. In practice there is often more than one galaxy in the same field so the full image needs to be checked.
As I added more and more galaxies I started to look for ways of making the search more effective. I soon split my galaxies into 3 categories depending on their brightness and distance. I do the easier ones on the poorer nights and vice versa. I also run a patrol worksheet which schedules how often I try to observe any given galaxy. This is to make sure that every part of every script gets sufficient attention. I also changed the order that I patrol galaxies so that the telescope has the minimum of movement between images. This speeds things up and maximizes the number of images I can capture. More images of course mean more supernovae.
I also never leave anything to memory. In the small hours your brain is not at maximum efficiency. I use a check list that I mechanically go through to eliminate anything that might not be a real supernova.
Mike: How many images have you taken to discover 127 supernovae, as of November 2009? Do you examine each one by eye, or do you have some part of the ‘blinking’ process automated as well?
Tom: I often get asked this question and fortunately it is easy to answer. I keep a very detailed log book of all my patrols. I also store every image that I have ever taken. These are used to eliminate unknown variables that appear in the fields. I check every image of a galaxy before I report a suspect. This sounds tedious but it isn’t. The log book and filing system make it easy.
I have recently celebrated breaking through the 500,000 count for images. It doesn’t take too much arithmetic to estimate the average discovery rate by patrol number and the number of hours spent patrolling.
I use two blinking methods. This is a recent development and has helped my productivity immensely. I use a small program called ‘GrepNova.’ This is a free program developed for me by Dr Dominic Ford from Cambridge University. A search on Google will show this up. The other program I use is Visual PinPoint. Each of these is best suited for different types of field, that is, whether the field has many reference stars or not.
Mike: Do you do follow up observations, and build light curves of your discoveries, or do you just keep the telescopes churning, looking for new ones?
Tom: The only time I do follow ups is when requested by a professional team who is also working on the supernova. I have no filters mounted on any of my systems so that I can get the maximum limiting magnitude on any given night. I usually achieve a limiting magnitude of around 20.5. I usually only admit to 19.5 to keep my reporting easier. That does mean that most of my discoveries are in the range 17.5 to 18.5. My skies are very challenging to do photometry on SNe this faint.
Mike: Can you explain the difference between the two types of supernovae, and why they are astrophysically interesting or important?
Tom: This used to be easier to answer than it is today. Once upon a time it used to be type Ia SNe and all the others. Type Ia are the sexy ones at the moment. Lots of progress has been made recently with these. They are not standard candles as once thought but they are ‘standardizable’ candles. This means that they can be used to measure cosmological distances and so discover the size and age of the Universe. They were used to discover the acceleration of the Universe at the end of the last century. All the others are core collapse supernovae. These occur when massive stars reach the end of their lives. These include all the type II SNe and the Ib and Ic types. The latter are often associated with Gamma Ray Bursters (GRBs) and are particularly interesting. Core collapse SNe shed their inner elements into space. By measuring the elements present and their quantities, it is possible to model what is happening in stars’ hidden interiors.
Mike: Have any of your discoveries been unusual or special, resulting in a research paper or further investigation with larger telescopes or satellites?
Tom: These change constantly. I was very proud of 2003L. This was the second most powerful supernova in history. That record didn’t last too long as new specimens keep getting discovered. Only last week a new paper was published describing one discovered behind the Magellanic Cloud that pushes it into somewhere like 5th or 6th place.
Strangely, I was also a co-author in a paper published in Nature on 2006jc. This was a SN that ‘appeared’ twice, once in a pre-explosion years earlier and then finally in 2006. It was a very useful tool for astrophysicists. I didn’t even discover that one. All I did was use my 12 years of archived data to prove that it hadn’t flared at any other times. There’s a good lesson here about keeping conscientious notes and logs.
My latest is still current and is the optical transient UGC2773-OT that I discovered in August 2009. Five teams are currently working on this very sub-luminous candidate. It is probably not a SN at all but an unusual outburst by a Luminous Blue Variable (LBV) star. It is only visible because the galaxy is so close. The precursor has been imaged by the HST.
All the major telescopes in the world, and in space, have followed up one or more of my supernovae. The VLA in New Mexico follows up all the radio noisy ones like 2003L. Very often a barrage of telescopes gets involved with the interesting ones, including the HST and space telescopes such as Chandra. My biggest thrill was when the 200 inch Hale was used. This was the biggest telescope in the world for so long when I was a boy and I remember marveling at its pictures at school. It is a thrill to know that these telescopes are looking at something because of something that I did. Patrolling is a lot of hard work and seeing large telescopes following up on your work keeps the motivation alive.
Mike: Is it still as fun and exciting after 127 discoveries as it was when you first started some 13 years ago?
Tom: I think it is more fun. When I made my first discovery I was terrified. I didn’t know what to do or whom to tell and I was afraid that I could make a false report. I was stressed for several days until it was confirmed spectrographically. With more experience that fear goes away (not entirely, which is good, so the buzz is still there) as a result I can enjoy my discoveries more as they happen.
Mike: Do you ever do any other kind of observing, like enjoying the night sky with a pair of binoculars or a small telescope while the C-14s are busy patrolling the universe?
Tom: I have a whole range of telescopes and binoculars. It will be a sad day when I stop using eyepieces. I have a ten inch that I use for visual use. I also take it to local schools and groups for Outreach sessions. In a few weeks I am accompanying a group of tourists over the Atlas Mountain in North Africa as their ‘teaching’ astronomer. They want to learn something about the skies and discuss cosmology over several bottles of wine by the camp fire in the evening. Astronomy is fun no matter how you do it. If it ever stops being fun I will stop doing it.
Mike: Do you have any advice for anyone considering supernova searching?
Tom: First of all expect some hard work before making your first discovery. AND IMPORTANTLY, you DON’T need expensive telescopes to do it. The Messier galaxies are being neglected by most patrollers. They are just too big for our tiny CCD chips. It would take me all night to check M31 properly. Visually it can be done in seconds. So the advice is, check the messier galaxies and the Caldwell and the brighter NGC galaxies. Do it as part of your normal observing run. The key is not just to look but to check. Some discoveries have been photographed by other people first but they didn’t check their images. Looking is not the same as checking. A SN discovered in one of these bright galaxies is often more valuable scientifically than a dozen fainter ones.
Finally, speak to someone already doing it and get encouragement and advice. They will save you a lot of effort. Most patrollers are happy to help. I am happy to help anyone wanting to give it a try.
Mike: Is there anything else on your supernovae wish list, like finding one in our own galaxy?
Tom: I need to be realistic. The first person to discover a SN in our galaxy won’t be me with my narrow fields of view. It will be someone walking along a lane and looking up, enjoying the sky, and spotting a constellation that no longer looks familiar. It will happen. Our next galactic supernova is well overdue. I bet when it comes it will be like busses, two or three will come together.
From a personal point of view I would like to discover another type Ic SN similar to 2003L probably associated with a GRB. SN2003L didn’t fit any of the theories for how central engines power SNe. Alicia Soderberg at the VLA in New Mexico proposed that it might be a new type of SNe. It was a very powerful SN with a very weak central engine. I won’t hold my breath. Even if it is, less than 1% of SNe are bright enough to qualify, so it could take longer than the next SN in our galaxy to prove it.
Mike: Thank you, Tom. It’s been great learning all about you and your discovery process.
Tom: Thanks Mike. It’s been a pleasure and privilege to take part.
You can see Tom's observatory and the full list of his supernovae discoveries at his observatory website.