On the hunt for X-ray signals from the extragalactic universe

Hunting X-ray signals from the distant universe requires years of strenuous work, a lot of dedicated scientists and an experienced leader to head the scientific efforts. Astrophysicist Niel Brandt of the Pennsylvania State University is just that type of academic guru, successfully leading his team to create the most sensitive cosmological X-ray surveys of the universe. For this enormous effort, he was recently honored with the 2016 Bruno Rossi Prize – a prestigious award given each year by the High Energy Astrophysics Division of the American Astronomical Society. In an interview with Astrowatch.net, Brandt talks about his outstanding career.

Astrowatch.net: What is it like to win the prestigious Bruno Rossi Prize?

Niel Brandt: I am thankful and happy to win the Rossi Prize. I consider this also an honor to my research group as well as my many collaborators. I have had great graduate students and postdoctoral researchers at Penn State working with me on the Chandra Deep Fields over the years. Many of them, after developing their skills via their Chandra Deep Fields research, have gone on to win professorial and permanent staff positions as well as distinguished fellowships and scholarships, becoming new leaders around the world in high-energy astrophysics.

Astrowatch.net: You've won many awards for scientific achievements like the National Science Foundation CAREER award or the Newton Lacy Pierce Prize in Astronomy. Is the Bruno Rossi Prize an another trophy on the shelf or does it mean something special for you?

Brandt: Well, I am grateful for all these awards and do not consider any of them just "another trophy on the shelf"—they each have their own unique aspects, and all of them have been most helpful in developing my research group and career.

The Rossi Prize, in particular, is given by true experts in my exact subject area of high-energy astrophysics. They understand thoroughly what is happening in the field and can assess the important results deeply and critically. This is borne out by the track records of the many amazing winners of the Rossi Prize in the past, and I just hope that I can keep up with them. For this reason, in particular, the Rossi Prize is special for me. It also recognizes, in my case, many years of effort and results—while some other prizes have a significant component of future potential, yet unrealized, being considered.

Astrowatch.net: You've been awarded for the creation of the most sensitive X-ray surveys of the extragalactic universe. How much challenging was this research?

Brandt: This research is very challenging, and it has required hard work over about 16 years to come as far as we have. Not only must one design and execute compelling X-ray observational programs, but then one must be able to use a wide range of multi-wavelength data to understand the nature of the detected X-ray sources. Then, with that understanding, there is another broader level where one must deduce what new the population of detected sources is telling us about supermassive black holes and galaxies in the distant universe.

To get further understanding of what we have learned from all this effort, please see (my) recent review article. While this is somewhat technical in places, a light reading of this should still clarify the main findings.

Astrowatch.net: Could you introduce your research team that was involved in the making of these surveys?

Brandt: Well, as mentioned earlier, I have had many great collaborators in my group. I believe my training of these people is even more important than the specific scientific findings.

Being able to work with Chandra's ACIS (Advanced CCD Imaging Spectrometer) team, especially in the early days after Chandra launched, was critical for letting all this stuff eventually happen.

Astrowatch.net: Is NASA's Chandra X-ray Observatory an indispensable tool for astrophysicists?

Brandt: Absolutely - Chandra has several unique capabilities that are indispensable! Relevant to the X-ray surveys work, Chandra has sub-arcsec angular resolution which, for long exposures, can give it truly amazing sensitivity. The faintest X-ray sources we are detecting in the Chandra Deep Fields have count rates of about one count per ten days! (For some more details on the capabilities of Chandra relevant to surveys, please see the fifth page of this article).

Astrowatch.net: Do you think NASA should invest more funds in developing next-generation X-ray space observatories to advance our knowledge in astrophysics?

Brandt: Absolutely! From a broad perspective of the overall federal budget, NASA has done a superb job of using its limited funds to deliver many fantastic results. Considering the amount of my family's annual taxes that go to funding NASA, and NASA's X-ray missions in particular, I see that we have more than gotten our "money's worth" in terms of enriching my young children's lives and sparking their curiosity.

There are some highly compelling and credible X-ray mission concepts that should be executed to give fantastic new results. One is Athena, where ESA is leading but NASA has significant participation (e.g., arxiv.org/abs/1207.2745). Another, further off, is the X-ray Surveyor (e.g., arxiv.org/abs/1505.00814). These missions should each provide a major step beyond the Chandra Deep Fields, clarifying further how supermassive black holes grow and affect galaxies. Like Chandra, they will also be broadly capable observatories delivering great results on many other topics as well.

Astrowatch.net: Did you always know you wanted to be an astrophysicist?

Brandt: I've always loved science, though I had broad interests when I was younger. I decided firmly that I wanted to become a scientist in high school. In college I studied physics, and I originally had the idea of wanting to do particle physics. However, after some good early astronomy classes and doing astronomy research over my summer vacations, I was hooked! I've always approached astronomy from a physics perspective, and that's one reason why I like X-ray astronomy—it "feels" more like physics, in terms of the methods and overall approaches, than some other areas of astronomy. No magnitudes or other silly astronomy jargon for me!

More information:
Beyond Chandra - the X-ray Surveyor. arxiv.org/abs/1505.00814

Athena (Advanced Telescope for High ENergy Astrophysics) Assessment Study Report for ESA Cosmic Vision 2015-2025. arxiv.org/abs/1207.2745

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