Fermi/Swift GRB Symposium 2012: Polarisation and thermal emission in GRBs
Posted on May 10, 2012 | by Felix | No Comments
The Fermi/Swift gamma-ray burst Symposium 2012 was held in Munich 7-11 May 2012.
Recent results on the prompt and afterglow emissions in gamma-ray burst were discussed at the Fermi/Swift gamma-ray burst Symposium 2012 which was held in Munich 7-11 May 2012.
Among the most important issues presented was the recent gamma-polarisation measurement with IKAROS-GAP. Significant degrees of polarisation in several bursts have now been detected. In particular, the change in polarisation angle was significantly detected. It was speculated that this is due to variation in emission patches in very narrowly collimated jets.
Another point which gained a lot of attention was on the existence of thermal components in GRB spectra. Previously the leading model for the prompt emission has been optically thin synchrotron emission. However, amounting observational evidence is showing that the photosphere in the relativistic flow is responsible for, at least a part of, the observed emission. Also recent progress in the theory and numerical simulations of relativistic jet was presented, and again thermal emission seems to be unavoidable.
Links:
Featured on www.nature.com/
Conference website
Gamma-ray spectrum of GRB110721A which will soon be presented in a Fermi publication led by Magnus Axelsson. In addition to the dominant broad component, there is a bump at lower energies which is likely emission from the photosphere. The spectrum cannot be explained by synchrotron emission and thus disproves the long-held view that synchrotron emission alone can explain GRB spectra.
Interview with Kanan K. Datta
Posted on March 30, 2012 | by Serena | No Comments
Kanan Datta is one of the OKC fellows working at the Astronomy department since October 2009. He is doing his first postdoc studing the universe reionization, something that probably happened only about 200 million years after the Big Bang. He is originally from India, but he enjoys very much being in Sweden.
How do you like working at the Oskar Klein Centre?
I am quite satisfied. In the beginning it took some time to decide on the projects I want to work on, develop codes etc. So if I judge myself by the number of results I produced here, it is not so impressive. Nevertheless, together with my collaborators here I got some interesting new results and more results are coming up now. Apart from that, I think I learned a lot, developed some new tools which made me more confident than I used to be before I started my postdoc.
Socially, I really enjoy staying in Stockholm. It is a very beautiful city, very nice helpful people all around. This is the first time I am outside my country which made me worry before I came here. Everything was extremely new when I arrived in Stockholm. But I did not find any difficulty to settle here despite huge differences in culture, weather between Sweden and my home country India. I enjoy both very long nights during winter and also the long days in summer because they are new to me. It is also fun to walk on a frozen lake……
Why did you choose the OKC for doing your postdoc?
I always wanted to go outside my country for postdoc to work with experts in my field and learn something new and also for better scientific environment, facilities etc. So I agreed immediately when I got the postdoc offer from OKC. I am happy that I made this choice. I applied here because I wanted to continue my research on the reionization and probing it using 21-cm observations. Read more
The Lithium problem. Primordial, cosmological or stellar?
Posted on March 22, 2012 | by Serena | No Comments
Fabio Iocco is one of the Postdoc working within the OKC on Dark Matter. He is also interested in one of the puzzles keeping astronomers and cosmologists busy: the Lythium problem. Fabio has recently organized a conference dedicated to this mystery and he is getting ready to give the next OKC colloquium, this is why I asked him to tell us a bit more about this topic.
Credit: Belèn Roncoroni
Alright: the “Lithium problem”.
The “Cosmological” Lithium Problem.
The “Primordial” Lithium problem.
We all have heard about it since kindergarden, but would you bet 5000 SEK you know exactly what it is? I did not, so had to look it up. And here is what I have learned.
First of all, let’s play it fair: there’s two stable lithium isotopes, lithium-six and lithium-seven. In the last years it seemed both had problems, but we are talking about the bigger brother here, the one who has had problems for a longer time. Since 1982, 30 years ago -when my brother was born- there have been observations of lithium-seven in metal poor stars of the galactic halo. The most metal poor stars, the smallest mass, therefore the oldest stars to be around. Or at least a good approximation of a lot, a lot old. Ancient, pristine maybe. Ay, there’s the rub: “maybe”. Would you bet they were the first stars to be formed? I would not, but that’s another story. What matters here is that the stars were not the first generation, but the stuff in their atmosphere, what you observe when you take spectra of their surface may have been whatever had been produced “as far back in the past” as we could get with chemistry observations in our galaxy.
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Tags: astrophysics > lithium > star formation > star forming galaxies > stars
Interview with Antje Putze
Posted on February 28, 2012 | by Serena | No Comments
Antje Putze is an Oskar Klein Fellow since october 2009. She is working in cosmic-ray physics and indirect dark matter detection.
You have been an Oskar Klein Fellow for more than 2 year, how is it going so far?
I am very much enjoying working at the OKC. In particular, the inspirational atmosphere within the centre is very fruitful for my work. I adjusted easily to the Swedish climate (especially the short winter days) and I love living in Stockholm.
Why did you choose the OKC for doing a postdoc?
The most compelling feature of the OKC is the broad spectrum of astroparticle physics subjects addressed by the OKC researchers. In particular, the interplay between experimental, phenomenological, and theoretical physics is very appealing to me. My Ph.D. focused on experimental cosmic-ray physics and phenomenology. The OKC gives me the opportunity to continue working in both areas (within the astroparticle group at KTH and the CoPS group at SU) while simultaneously broadening my knowledge base to other fields, such as indirect searches for dark matter.
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New Steering Group and postdocs at the Oskar Klein Centre
Posted on February 17, 2012 | by Lars | No Comments
This week, two major things have happened of importance for the future working of the Oskar Klein Centre. First, a new Steering Group of the Centre has been appointed by the Rektor of Stockholm University, Professor Kåre Bremer. The new Steering Group has 3 new members and consists of:
Lars Bergström (chair), Department of Physics, Stockholm University (SU)
Claes Fransson (vice chair), Department of Astronomy, SU
Christophe Clément (new member), Department of Physics, SU
Jan Conrad (new member), Department of Physics, SU
Ariel Goobar, Department of Physics, SU
Sten Hellman, Department of Physics, SU
Klas Hultqvist, Department of Physics, SU
Garrelt Mellema (new member), Department of Astronomy, SU
Mark Pearce, Department of Physics, Royal Institute of Technology
Göran Östlin, Department of Astronomy, SU
(In addition we have adjoined Christopher Savage as a representative of the OKC postdocs, and Serena Nobili, who among many other things at the Centre also acts as secretary of the meetings of the Steering Group.)
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Interview with Christopher Savage
Posted on February 14, 2012 | by Serena | 1 Comment
Christopher Savage is a Oskar Klein Fellow since the summer of 2009. He is working on direct detection of Dark Matter and seems to be very happy about it! I asked him to tell us more.
Why did you choose the OKC for doing a postdoc?
The broad focus on cosmology, with an emphasis on interaction between different areas, was very appealing. In addition, I had started working on capture of dark matter in stars and there is a lot of expertise in that area here in Stockholm (particularly Joakim Edsjö).
When I was given the offer, I was at a conference in Michigan with four OKC people in attendance (Marcus Berg and Joakim Edsjö plus PhD students Erik Lundström and Sara Rydbeck). That gave me a chance to see what the group was like and it made the decision an easy one.
What is your field of research?
My field of research is in the phenomenology of detecting dark matter, both directly and indirectly. The former case (direct detection) involves looking for interactions (scattering) of dark matter particles inside a detector, while the latter case (indirect detection) involves looking for products of dark matter particles that annihilate elsewhere.
Direct detection has long been a focus of my research and I continue to work in that area here at the OKC. I look at how various issues affect the signals seen in direct detection experiments, which might explain the apparent incompatibility between experiments that observe signals consistent with dark matter (CoGeNT, CRESST, and DAMA) and those that do not (CDMS and XENON, to name a few). The issues include how dark matter couples to ordinary matter, how the dark matter is distributed in the galaxy, and potential systematic issues in the experiments themselves (often involving energy calibrations). In addition, several of us (Yashar Akrami, Pat Scott, Jan Conrad, Joakim Edsjö and I) are looking at how direct detection results constrain supersymmetric models, which provide a natural candidate for a dark matter particle (the neutralino).
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And the ATLAS Thesis Award 2011 goes to Christian Ohm!
Posted on January 27, 2012 | by Serena | No Comments
Christian Ohm in the control rum at Cern during the LHC startup
“It is very exciting!” tells me a radiant Christian when he joins me in my office “if you think that the other four are all Americans, and I am the only European! And they come from places like Harvard, Caltech and Berkeley!”
The five winners were selected by the CB Chair Advisory Committee, which acted as the Thesis Awards Committee, from a selection of 21 nominations received.
My thesis centers around two searches for beyond Standard Model (SM) physics but contains published work of technical nature as well. The two physics analyses I contributed to are both a signature-driven searches for new physics giving rise to so-far unobserved massive long-lived particles. The ATLAS experiment was built primarily to directly detect SM particles, and most searches for new physics rely on the assumption that new states produced in the pp collisions will decay promptly and leave SM particles detectable in the final state. Many extensions of the SM feature new particles with decay lengths on the scale of modern collider experiments, and these two analyses instead search for new physics based on direct detection. Christian explains.
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Interview with a new Oskar Klein Fellow
Posted on January 20, 2012 | by Serena | 1 Comment
Elena Moretti is the first of the about 300 applicants who was selected to become an Oskar Klein Fellow this year. She comes from a little country-side town, called Cartura, on the south of Padua in Italy, where she graduated in physics in 2006. She got her PhD in Trieste where she worked with the AGILE and Fermi experiments on GRBs. She developed a method that was used to calculate the flux upper limits on the GRB emission that was used in both experiments. In 2010 she moved to Stockholm working as a postdoc at the KTH. We ask her to tell us more about herself and the work she will be doing at the Oskar Klein Centre.
Congratulations Elena! You have been offered an Oskar Klein Fellowship. How does it feel?
It feels good! It gives me the opportunity to develop my newborn interest in the polarimetry field. Wen I came here 2 years ago I was working only in the high energy astrophysics field with the 2 gamma-ray experiments Fermi and AGILE. After one year a new interest was tickling me: PoGOLite. I started to work on it as a “side job” on my spare time….well I guess that would change soon.
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End of a good Oskar Klein Centre year
Posted on December 21, 2011 | by Lars | No Comments
This year has been very interesting for the OKC. The highlight was of course the Nobel Prize for Saul Perlmutter, Brian Schmidt and Adam Riess.
The Nobel banquet, waiting for the Laureates and Royalties to arrive. (Photo: Lars Bergström)
The half-day December 12th immediately following the Prize ceremony, organized by Ariel Goobar and Jesper Sollerman, was a great success. I could not be present, unfortunately, but I can recommend the video from the very memorable colloquium session, at http://videos.albanova.se/colloquia/2011/ – it is well worth watching, as is the colloquium the day after on global warming by Rich Muller (who was one of the forefathers of the Supernova Cosmology Project). Read more
An ATLAS art installation at AlbaNova
Posted on December 20, 2011 | by Serena | No Comments
Since early Autumn the ATLAS Art Installation is on the first floor of Stockholm House of Science at AlbaNova.
“In ATLAS we have made rather artistic animations of particle physics. In addition an artist has made the mural painting at CERN on one of the ATLAS buildings. The ATLAS events have also been rather artistic and made it to the many magazines and newspapers. I think that is why the installation is called the ATLAS Art Installation. I prefer to call it the People of ATLAS, as it is very much about the ATLAS people.” says Erik Johansson, professor at the Oskar Klein Centre.
The installation is composed of four video projectors showing different aspects of the ATLAS Experiment at the CERN LHC. “it shows that the people of ATLAS have a lot of other interests than physics. And we are not dressed in white laboratory clothes. We sing and play and climb mountains and many other things – as most people.”
Erik Johansson has been involved as the co-coordinator of ATLAS Education and Outreach group at the time, and he is also responsible to bring it here to Stockholm and House of Science. Read more
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What is dark energy? What and where is the dark matter? What physics lies behind the most energetic processes in the Universe such as supernovae, gamma-ray bursts and black holes?
