Posted on April 9, 2014 | by Serena | No CommentsMichael Burgess joined the Oskar Klein Centre in mid-January as OKC fellow, after finishing his PhD in the US. His specialty is GRBs and that is why he joined with Felix Ryde in the KTH group.
Why did you choose the Oskar Klein Centre for doing a postdoc?
When I was working on my PhD I studied a lot from the research that was occurring within the gamma-ray burst team of the OKC. When the possibility opened that I could come work with them I jumped to take it. It was really my first choice after graduate school. In addition, I think Sweden has a generally forward looking view when it comes to science compared with the US. It is appreciated here and I wanted to work in that kind of environment. There are so many projects going on both within and outside my field here that I’m sure I will be able to expand upon my current skill set and perhaps become involved in other fields.
How would you describe the experience of working in the OKC so far?
It has been a great experience so far. The variety of research that is going on both within the OKC and the institute in general has provided me with lots of resources to learn new subjects and improve my skills within my own field. The wealth of knowledge here is fresh and exciting.
What is your field of research and the project you are involved with?
I study the gamma-ray spectra of gamma-ray bursts (GRBs). My main project has been taking the theoretically predicted spectral models that have been around for some time and directly comparing them to the data instead of using the standard empirical models. The project has been quite fruitful and really builds upon work that has been occurring at the OKC for years. From this approach of physical modeling, we are extending the work done in the past with mainly empirical models and digging deeper into the structure of GRB jets and beginning to piece together the relatively unknown processes occurring in these star-shattereing events.
What do you find unique for your field of research about the OKC?
The experience with spectral analysis and physical modeling is uniquely high at OKC. In addition, the researchers such as Felix Ryde and the rest of the group, here have a very keen way of connecting the complicated nature of spectral analysis in GRBs to the bigger picture of the jet. It’s very close to storytelling and makes the science they do very accessible. The competence level of the team is also quite attractive. It’s nice to see that even graduate students here are involved in the decision making for new projects and have a high level of expertise.
Tell us something about you.
I grew up in Atlanta, Georgia back in the states. When I was in school, there was a very good science program in that city and I wanted to study black holes from a very early age.
I went graduate school at the University of A with the Fermi Gamma-Ray Bursts Monitor (GBM) team. While doing research on GRBs, I also had lots of access to the instrument team and gained a lot from their nearly 3 decades of experience working on GRB detection. The GBM team is great with a vibrant history and I made lots of great friends within the team. However, I always wanted to move to Scandinavia for the warm weather and sandy beaches.
And that was indeed a good reason for moving to Sweden
Thank you Michael!
Posted on March 21, 2014 | by Serena | 1 Comment
Supernova 2014J in the nearby galaxy M82 -less than 12 million light-years away- exploded on January 14, 2014 and was the closest ”standard candle” supernova since (at least) 42 years. An impressive coordinated observational effort orchestrated by the intermediate Palomar Transient Factory (iPTF) team and led by Ariel Goobar from the Oskar Klein Centre at Stockholm University (Goobar et al. 2014, The Astrophysical Journal Letters, 784, L12) provides important new clues into the nature of these explosions, as well as the environments where they take place. The proximity of SN2014J allowed the iPTF team to study this important class of stellar explosions, known as Type Ia supernovae, over a very wide wavelength range, starting just hours after the deduced explosion time.
Furthermore, Goobar and collaborators used pre-explosion images of the region of M82 where the supernova went off, both from the Hubble Space Telescope and from the Palomar Oschin Telescope, to search for a star in the location of the explosion, or possible earlier nova eruptions. The lack of pre-explosion detections suggests that the supernova may have originated in the merging of compact faint objects, e.g., two white dwarf stars, i.e., the kind of Earth size stars that our sun will evolve to once it runs out of nuclear fuel.
“Until very recently, the leading model for standard candle supernovae was thought to include a companion star from which material was stripped by the white dwarf until the accumulated mass could no longer be sustained by the outwards pressure, leading to a runaway thermonuclear explosion. The observations of SN2014J are challenging for this theoretical picture”, says Goobar.
Type Ia supernovae are among the best tools to measure cosmological distances. Thanks to their consistent peak brightness, these ”standard candles” are used to map the expansion history of the Universe. In 1998 distance measurements using supernovae lead to the a paradigm shift in cosmology and fundamental physics: the expansion of the Universe is speeding up, contrary to the expectations from the attractive nature of gravitational forces: a mysterious new cosmic component, ”dark energy”, has been invoked to explain this unexpected phenomenon. This discovery was awarded the 2011 Nobel Prize in physics.
“Since Type Ia supernovae are very rare, occurring only once every several hundred years in a galaxy like ours, there have been very few opportunities to study these explosions in great detail. SN2014J in the nearby galaxy M82 is a very welcome exception”, says Rahman Amanullah a researcher at OKC.
A better understanding of the physics behind Type Ia supernovae and the material surrounding the explosion and dimming some of the light is crucial to further refine the measurements of the expansion history of the Universe. Joel Johansson, a PhD student at OKC that played an essential role in the analysis fills in “many supernovae explode in clean environments, free of dust in the line of sight. This is not the case for SN2014J, which gives us a unique opportunity to study both the properties of the supernova explosion but also of the intervening dust”.
The lessons learned by the studies of SN2014J may be very useful for the analysis of the large Type Ia SN sample that scientists have collected over decades, especially the astrophysical corrections needed to make accurate distance estimates. Only then may we be able to tell what is causing the accelerated expansion of the cosmos.
The iPTF project is a scientific collaboration between Caltech; Los Alamos National Laboratory; the University of Wisconsin, Milwaukee; the Oskar Klein Centre in Sweden; the Weizmann Institute of Science in Israel; the TANGO Program of the University System of Taiwan; and the Kavli Institute for the Physics and Mathematics of the Universe in Japan.
The observations were carried out using multiple astronomical facilities. Besides the Palomar telescopes, data of SN2014J and M82 were obtained at the Nordic Optical Telescope, the Keck Telescope, the Faulkes Telescope North, the Mount Abu 1.2m Infrared telescope in India, the1.93m telescope of Haute-Provence Observatory, CNRS, France, the Spitzer Space Telescope and the Hubble Space Telescope.
Contact: Prof. Ariel Goobar (firstname.lastname@example.org)
Prof. Ariel Goobar, Dept of Physics, Stockholms universitet, tfn +46 8-55 37 86 59, e-mail email@example.com
Rahman Amanullah, researcher, Dept of Physics,, Stockholms universitet, tfn +46 8-55 37 88 48 e-mail: firstname.lastname@example.org
Joel Johansson, PhD student, Dept of Physics, Stockholms universitet, tfn +46 8-55 37 86 61, e-mail email@example.com
Link to APJ article: http://iopscience.iop.org/2041-8205/784/1/L12/
Read also: Hubble Space telescope images of a supernova in nearby galaxy M82
Posted on February 27, 2014 | by Serena | 2 Comments
A new bright supernova exploded in the nearby galaxy M82 on January 14 this year, at a distance of approximately 11.5 million light–years from Earth, that makes it to the nearest “normal” Type Ia supernova discovered in the past 42 years. Its small distance together with the fact that the first observations were carried out only a few hours after the explosion, makes it in itself a very important astronomical object, since it allows to study the details of many aspects of these kind of objects that are so important for cosmology.
Type Ia supernovae, used as distance indicators, lead to the the discovery of the accelerated expansion of the universe in 1998, an unexpected result awarded the Nobel Prize in physics in 2011.
The nature of the accelerated expansion is attributed to a repulsive force, called dark energy.
- You might want to see our video about Dark Energy Problem -
However, though they are readily used in cosmology, the explosion mechanism behind Type Ia supernovae is still unclear, mainly due to the difficulty of catching the explosion at early stages and the ability to study these explosions over a wide range of wavelengths.
Ariel Goobar and Rahman Amanullah from the Oskar Klein Centre realized the importance of this object and applied for the Hubble Space Telescope (HST) director’s discretionary time to observe the supernova in ultraviolet (UV) wavelengths, which are otherwise absorbed by the earth’s atmosphere and not observable from ground based telescopes. Thanks to these measurements one can study the immediate surroundings of the supernova, an important part of the puzzle in understanding the progenitor system. Furthermore, the UV observations
are critical to study what it is that absorbs some of the light in the line of sight in the interstellar medium of the host galaxy. This study will have implications for the precision that can be obtained on the measurements of
the properties of dark energy.
The Hubble Space Telescope news center published today the composite image of this supernova explosion, SN2014J, in the galaxy M82.
A detailed paper about SN2014J has been written by Ariel Goobar and collaborators and accepted for publication in the Astrophysical Journal Letters, and we will soon blog again about this exceptional supernova.
Contact: Ariel Goobar firstname.lastname@example.org
Hubble Heritage Realease
Posted on January 14, 2014 | by Serena | No Comments
The Fermi satellite was launched in 2008 and since then it has continuously monitored the sky at gamma-ray energies above 100 MeV. Most of the sources detected at these energies are blazars, Active Galactic Nuclei in which the accretion onto a supermassive black hole also leads to the launching of two opposite relativistic jets. If a jet is pointing close to our line of sight we will see intense high energy emission due to strong Doppler boosting.
Fermi has so far detected well over 1000 blazars. One of these is B0218+357, which is known from optical and radio observations to be gravitationally lensed by a foreground spiral galaxy. The lens forms two closely spaced images of the blazar. The Fermi Large Area Telescope (LAT) can not spatially separate the two images so it can only measure the sum of both. However,
with timing analysis it is still possible to separate the signal of the individual components. This is because the path length from the blazar to us is different for the two images so we measure all blazar variability twice, with some time separation. Read more
Posted on December 23, 2013 | by Lars | No Comments
Hello and Happy Holidays to all friends of the OKC
As the year 2013 is now nearing its end, it is time to recapitulate the main events of the year from the OKC perspective. If I temporarily put on my Nobel hat (being the scientific secretary of the Nobel Committee for Physics) the main event from the Stockholm horizon is without doubt the Nobel Prize to Francois Englert and Peter Higgs for their almost 50-year old prediction from the early 1960’s that was so spectacularly confirmed by the ATLAS and CMS experiments at CERN’s LHC accelerator last year. Hats off for Englert and Higgs, and also for the many clever and hard-working experimentalists, in particular the ATLAS people of OKC such as Jonas Strandberg, who has been directly involved in the discovery of the Higgs particle in ATLAS. Of course we now look forward to the energy upgrade of LHC, which will increase the chances substantially to find the much awaited effects beyond the Standard Model that, hopefully, could give an indication of what the dark matter may consist of. At the Oskar Klein Centre we also have been searching in gamma-ray, positron and neutrino signals, without positive results (yet), but producing some of the best limits.
The OKC has now been in existence for 5 years, and we will soon encounter the international mid-review panel of the Science Council (VR) of Sweden. By September 1st we had to submit our self-assessment report, containing a detailed description This meant a lot of work for me and the OKC Steering Group: Christophe Clement, Jan Conrad, Claes Fransson, Ariel Goobar, Klas Hultquist, Garrelt Mellema, Mark Pearce, Sara Strandberg and Göran Östlin (and of course our great communications manager, Serena Nobili). We hope that we managed to convey our great enthusiasm for the scientific outcome of the OKC during its first 5 years, and that the evaluation committee will agree that it has been a great success. In fact, when we meet them January 30th, we will have quite a number of recent sucesses to report:
- A generous grant of SEK 32 million from the K&A Wallenberg Foundation was given to groups in OKC (with J. Sollerman as PI) for contributing to the Zwicky Transient Facility (with S. Kulkarni of Caltech leading the team).
- OKC Steering Group member Sara Strandberg has obtained both a young researcher’s grant from the VR and a Wallenberg Academy Fellow (WAF) grant – both in very strong competition.
- Jan Conrad (also OKC Steering Group member) has in addition to his previous WAF grant also been given one of the new excellent junior investigator grants from VR. Congratulations to Sara and Jan!
- The IceCube experiment has finally detected high-energy (PeV) cosmological neutrino events, with a surprising energy distribution. This was declared the discovery of the year of the Physics World magazine. Congratulations to the OKC IceCube group (Chad Finley, P.O. Hulth, Klas Hultquist & al.) and the Uppsala group (with present IceCube spokesperson Olga Botner and her colleagues)!
- The Fermi satellite project with large OKC contribution continues to make important discoveries. One concerns the discovery of a gamma-ray spectrum of two supernova remnants which clearly shows a hadronic origin (from decays of neutral pions), and thus is a proof that these sources accelerate protons, and are thus the long-sought-for sources of the Galactic cosmic rays. This was one of the runner-ups for the discovery of the year of Science magazine.
To conclude, with all the interesting science produced by OKC during its first half-life, one may only anticipate with great expectations what will come out of the second half!
Merry Holidays and a Happy New Year to all in the OKC research environment and all our followers!
Posted on December 2, 2013 | by Serena | No Comments
Where have you studied or did research before coming to the OKC?
I did my undergraduate studies at École Polytechnique near Paris. I then completed my Mas ter degree at the theoretical physics department of École Normale Supérieure in Lyon and did my Ph.D. with the IDAPP (International Doctorate on AstroParticle Physics) program both in Annecy and Turin under the supervision of Pierre Salati and Nicolao Fornengo. Autumn 2010, I moved to Madrid to do my first post-doc at the Instituto de Física Teórica (IFT) of the Universidad Autónoma where I stayed for two years. Last year I worked at the Laboratoire d’Annecy-le-Vieux de Physique Théorique (LAPTh) and the Institut d’Astrophysique de Paris (IAP).
What is your field of research?
I work in modelling the propagation of Galactic Cosmic Rays and Dark Matter indirect detection. Cosmic rays are high energy particle that are accelerated by exploding stars, by high magnetised stars called pulsars, and maybe by the annihilation or decay of Dark Matter particles. Even though cosmic rays have been discovered more than 100 years ago we still do not understand precisely where they come from nor how they propagate in the interstellar medium. In spite of being a rather young science, cosmic ray physics are is a wonderful way to look at things in the sky that do not emit light and cannot be probed by usual astronomy.
What I really enjoy in this field is that it is at the intersection of cosmology, astrophysics and particle physics and allows to interact with many people from very different fields.
Posted on November 22, 2013 | by Serena | 1 CommentToday’s issue of Science highlights a breakthrough in astroparticle physics many decades in the making. After tantalizing hints in the past year, the IceCube Collaboration now reports on a follow-up analysis, leading to a larger event sample and compelling evidence that the first high-energy neutrinos from outer space are starting to be seen.
The IceCube Neutrino Observatory is a strange kind of telescope, because it searches for neutrinos—rather than photons—from space. It’s situated at the South Pole, and it consists of thousands of detector modules buried up to 2.5 km deep in the glacial ice there. At that depth, the ice is very clear and very dark. What the modules see is the passage of subatomic particles zipping through the ice, emitting a well-known, faint blue light called Cherenkov light. When enough modules detect this light from a passing particle, the information is sent to the surface where a computer cluster starts crunching the `event’ to make a rough estimate of the direction and energy of the particle.
In the analysis reported today, 28 events are in the final sample, sifted out of over 10ˆ11 (one hundred thousand million) events in total, collected over two years. The overwhelming majority of these events are background particles from cosmic rays striking the atmosphere. Finding the handful of neutrinos that potentially originated in space is extraordinarily challenging. One of the innovations of the new analysis is to use the outermost detector modules as a `veto’, to tag any particle observed coming into the detector through the outer layer as a background event. All that remains are events which first appear, mysteriously, in the middle of the detector. This is the tell-tale signature of a neutrino event. In fact, famous for being “ghost” particles, almost all the neutrinos which pass through the detector never leave a trace at all. But fortunately a tiny fraction do happen to bump into an atom in the ice. When that happens, many other particles (like electrons, and their heavier cousins, muons) are created, and these particles create the Cherenkov light that IceCube detects.
It turns out that this veto design, selecting only those events where the light emission begins inside the detector, is extremely efficient for separating high energy neutrinos from background. Applying this technique and selecting only very energetic events, the two years of data would be expected to boil down to only about ten surviving background events (including some background neutrinos called atmospheric neutrinos). The fact that 28 events survive is thus strongly inconsistent with an explanation purely in terms of background. There are, moreover, many additional details such as their energy distribution and their distribution over the sky that are consistent with an origin in space but not with any known backgrounds.
Posted on November 22, 2013 | by Serena | No CommentsAbout once a day, a gamma-ray burst is detected. When this happens, e-mails get sent around and scientists scramble to detect whatever few photons might have been sent our way. But sometimes things are different…
On April 27th this year, an e-mail alert was sent around signifying the detection of yet another GRB. Yet this event was like no other. Rather than fighting to catch photons, there were suddenly too many to detect! The main emission episode was so bright that the GBM instrument on Fermi became saturated. And not only that – the GeV emission lasted for more than a day!
Posted on October 8, 2013 | by Christophe | 2 Comments
Today’s Nobel Prize awarded jointly to François Englert and Peter W. Higgs “for the theoretical discovery of a mechanism that contributes to our understanding of the origin of mass of subatomic particles, and which recently was confirmed through the discovery of the predicted fundamental particle, by the ATLAS and CMS experiments at CERN’s Large Hadron Collider”.
Here at OKC we are so delighted to see this prize. It confirms the importance of last year’s discovery of the mechanism and the particle imagined by Englert and Higgs. To tell the truth, although the Higgs particle was only discovered recently it has been part of some of our calculations here at OKC for some time. Some theories of dark matter assume the existence of a Higgs particle. So it was important to confirm this with the ATLAS and CMS experiments, since the discovery we know we are on the right track.
But not until a short time before the discovery annoucement did we really know that the Higgs particle existed. Not so long before the discovery some experimentalists and theorists would get a bit nervous, wondering what would we do if no Higgs particle was found… one would have to start from scratch, change the theory, go back to the drawing board, invent something new but what?
Thanks to the hard physical discovery of the Higgs particle at CERN we can now move forward, while many other theories without a Higgs particle have faded away into history.
That’s science at work. The Higgs boson is the last missing piece of the so-called standard model of particle physics. Good we got that sorted out!
But we know that the standard model is not the full story, the Higgs particle does not give mass to the neutrinos, nor do we know what is dark matter, as the standard model does not contain any such particles.
The CERN programme with the ATLAS, CMS and LHC experiments is still to provide about 200 times more data than was needed to find the Higgs particle. This is by no mean a guarantee that we will find something new, but it is only by covering new ground with some ingenious new instruments, that there is a chance to learn something new about Nature. The LHC project and the ATLAS and CMS experiments are just fantastic instruments built for that purpose. It is a great privilege to work on the ATLAS experiment and see the Nobel Prize going to particle physics today, after a bit of excitement, here at OKC, we will go back to analysing the data from the ATLAS experiment and see if we can solve another mystery of Nature.
Christophe Clement – researcher at the Oskar Klein Centre
Posted on October 3, 2013 | by Serena | 1 Comment
It is the Knut och Alice Wallenbergs foundation that grants a 5-year long project for finding and studying supernovae. The OKC are already since the beginning of this year members of the intermediate Palomar
Transient Factory (iPTF) – a supernova search aimed at finding supernovae soon after explosion. This is a pathfinder for the next generation of this project – the Zwicky Transient Facility (ZTF). The 30 million grant from KAW will now enable OKC astronomers and physicists to play a leading role in that project.
Jesper Sollerman, from the department of astronomy, is leading the application:
- Previous supernova surveys have often discovered supernovae days or weeks after explosion. We want to find them on the very first night. In this way we hope to learn more about their progenitors, the stars that actually exploded.
The deaths of massive stars is the focus for the supernova astronomers at the department of astronomy, including both observers such as Sollerman and modelers as co-applicant Claes Fransson.
The supernova group at the department of physics are more interested in thermonuclear supernovae and their use for cosmology. Co-applicant Ariel Goobar: