The Oskar Klein Centre blog

Cosmology and a bit more

Radioactive glow as smoking gun: cosmic explosions, heavy elements and gravitational waves

Posted on September 16, 2013 | by Serena | No Comments

On June 3rd 2013 at 15:49 UT NASA’s Swift satellite detected an intense flash of γ -rays known as a short γ-ray burst. Follow-up observations by the Hubble Space Telescope revealed infrared emission that was present 9 days after the burst, but had faded away after 30 days. This infrared transient is likely the first ever observed example of a “macro-nova”, emission that is produced by the radioactive decay of very heavy nuclei that have been freshly synthesized in the merger of a compact binary system consisting of either two neutron stars or a neutron star with a black hole. If this interpretation is correct, the observation could have profound consequences for high-energy astrophysics, cosmic nucleosynthesis and detections of gravitational waves.

γ-ray bursts (GRBs) come in two flavors of different duration. Long bursts (longer than about 2 seconds) are produced in the death of a rare breed of massive stars, whereas short bursts (shorter than 2 seconds) are thought to result from compact-binary mergers. To date, we know 10 systems containing two neutron stars— extremely densely packed objects with masses around 1.4 times the mass of the Sun, but only about 12 kilometres in radius, and that consist predominantly of neutrons. As the stars orbit around each other they emit gravitational waves and therefore slowly spiral in towards one another until they finally merge. Such orbital decays have actually been observed2, and they agree remarkably well with the predictions from Einstein’s theory of general relativity.
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PoGOLite landed!

Posted on August 27, 2013 | by Mark | 1 Comment

After a pioneering circumpolar journey lasting almost 14 days, the PoGOLite flight ended on the Siberian tundra. The gondola was cut from the balloon in the early hours of 26th July and touched down by parachute approximately 1 hour later. The gondola landed near, but luckily not in, a lake (this seems to be a recurring theme for us…). The landing site was close to the Siberian city of Norilsk which houses a large nickel and copper mine, as well as good infrastructure for a helicopter-based recovery of the gondola.

PoGOLite flight path 2013

The path followed by PoGOLite during the ~14 day long flight.

Photographs provided by the Russian recovery team show that the gondola is in good shape. Recovery operations are still on-going with the ultimate aim of returning the gondola to Stockholm once customs issues are solved – hopefully during the next couple of weeks. While it was hoped that PoGOLite would make a full circumpolar transit and return to Scandinavia, the stratospheric winds pushed the gondola too far to the North. Read more

A new interesting period for the OKC

Posted on August 21, 2013 | by Lars | No Comments

Hello everybody in the OKC!
Welcome back after a well-deserved vacation for most of you. For OKC this is a rather hectic period, as we have our mid-term evaluation requested from Vetenskaprådet (VR)  just starting. The International Advisory Board (Katie Freese, Bengt Gustafsson, Wolfgang Hillebrandt, Hugh Montgomery, John Peacock and Larus Thorlacius) will visit us August 29 – 30, and you have been informed by Serena about some of the events taking place. 

The review process will take place during the autumn, with a face-to-face meeting during a site visit January 30, 2014. The IAB has promised to act as a “mock panel”, so that we get feedback before submitting our self-evaluation with deadline September 1. When the verdict of the review comes, sometime during spring, we will know whether our Linnaeus Centre OKC gets increased funding (by up to 20 %), decreased funding (by up to the same amount), or a constant budget. It is a zero-sum game between the 20 Linnaeus Centre that received grants in 2008, so if we win some others have to lose, and vice versa. Quite exciting, in other words! Read more

PoGOLite launched!

Posted on July 13, 2013 | by Mark | No Comments

On July 12th at 0818 UTC, PoGOLite was successfully launched from the Esrange Space Centre.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The balloon trajectory can be seen here.

 

Greetings from Esrange,

The PoGOLite team

 

 

54 HST orbits allocated to eLARS

Posted on June 18, 2013 | by Serena | No Comments

In order to celebrate a substantial allocation of time on the Hubble Space Telescope (HST) in cycle 21, the LARS project invited all of OKC for a drink on wednesday 12 june. This time, eLARS, the extension of the LARS project was awarded another 54 spacecraft orbits. In total the LARS project has so far been awarded 110 orbits, and is the biggest Swedish led project on HST ever.

The aim of the LARS project is to improve our understanding of how the Lyman alpha emission line is formed and transported out of galaxies. This is vital since Lyman alpha is the most accessible and most commonly used spectral probe of the distant universe. LARS will make extremely detailed studies of Ly alpha emission from 42 galaxies in the nearby universe, obtaining a physical resolution more than 2 orders of magnitude better than achievable at high redshift. One of the results that have emerged so far is that galaxies appear systematically larger when seen in Lyman alpha than in the continuum or in other recombination lines such as Halpha, a consequence of Lyman alpha photons resonantly scattering on neutral hydrogen atoms.

Image of the first galaxy in the LARS sample (Mkn259). In blue, Lyman alpha is shown, in red H-alpha and in green/yellow the Ultra Violet continuum. The size of the image corresponds to 15 by 15 kpc (approx 50000x50000 light years)

- Göran Östlin – ostlin@astro.su.se

GRB 130427A: a chance not to miss

Posted on May 13, 2013 | by Serena | 1 Comment

Credit NASA, DOE, Fermi LAT Collaboration (click to enlarge and make the GRB explode)

On 27 April, an incredible opportunity was given to GRB science detectives. As the spring was outbursting here in Stockholm the explosion of a distant star almost blinded the Gamma ray Burst Monitor (GBM) detectors on board the Fermi satellite. GRB130427 is the brightest GRB ever detected in the keV – MeV band and the longest lasting in the GeV energy range: Fermi Large Area Telescope (LAT) could detect it for hours after the trigger.

Gamma ray bursts (GRBs) are cosmological flashes of which the prompt emission, lasting for 0.01-100s, is in the gamma ray band. Their late emission can be detected at lower energy ranges like optical and radio. One or two GRBs per day are typically observed, but their origin and the particle acceleration mechanisms involved remain nowadays unknown. The favourite hypothesis on their origin is the collapse of a supermassive star, while there is not a leading hypothesis for the acceleration mechanisms involved in the outflow responsible for the prompt emission.

This burst was also detected by other experiments such as Swift and Integral which allowed a rapid and precise localization which enabled optical, infrared and radio follow-up observations. The redshift was measured within hours from the original trigger and revealed that the outbursting star was quite close (for this kind of objects): z= 0.34.

With nearly 1000 photons per second and square centimeter in the 10-1000 keV band and 14 photons per second per square meter in the 100 MeV – 10 GeV band (see attached figure), this burst is a unique occasion for the scientific community to probe models for particle acceleration and photon emission in the outflow.

source: arXiv:1303.2908

Soon the Fermi and Swift collaborations will publish their papers and hopefully more news and more papers will follow. We expect to be able to take a step further in understanding the physics of the GRB thanks to this record breaker burst. Keep an eye on it!

The figure (source: arXiv:1303.2908) shows the fluence in two energy band of the Fermi LAT detected burst, the star indicate the position this burst would have in this plot.
The event fluence in the first 20 seconds in the 10-1000 keV band is (1.975 +/- 0.003) E-03 erg/cm^2, while in the fluence in the first 140s in the 100 MeV – 10 GeV band is (1.1 +/- 0.1)E-4 erg/cm^2.

For more information: http://www.nasa.gov/topics/universe/features/shocking-burst.html
http://edition.cnn.com/2013/05/06/opinion/urry-gamma-ray-burst/index.html

- Elena Moretti, (OKC fellow) – moretti@particle.kth.se

The missing star or the Supernova 2011dh

Posted on May 13, 2013 | by Serena | 1 Comment

Image credit: Mattias Ergon, Dept of Astronomy, OKC.

A bright supernova appeared in the fairly “nearby” (24 million light years) Whirlpool galaxy (M51) in late August 2011. It was named Supernova 2011dh. Images taken using the Hubble Space Telescope of the galaxy before the explosion showed a star at the position of the supernova, but astronomers argued whether this was indeed the star that exploded. Now we know!

 

New images taken once the supernova has faded reveal that the star is gone. This animation is made of B, V and R band images taken before – and long after – the supernova explosion using the 2.6m Nordic Optical Telescope on La Palma. The zoomed in part is blinked to highlight the star that is now gone (click on the image to enlarge it).

- It is pretty cool that we can spot a single star, among 100 billion stars in a remote galaxy, says Jesper Sollerman, that participated in the study. This is because supernovae come from the most massive and luminous stars we know of.

The paper, lead by M. Ergon, that describes the supernova in some detail is now submitted to Astronomy & Astrophysics, and it is also available from the ArXiv.

Links:

http://www.astronomerstelegram.org/?read=4912
https://ttt.astro.su.se/~maer0651/sn2011dh-progenitor.html

 

Interview with Florian Kühnel

Posted on April 26, 2013 | by Serena | No Comments

Today we publish an interview with one OKC fellow who joined us early this year to work in the Theory group.

Florian Kühnel

Can you tell us a bit of yourself? Where are you from?
I could start with: “It was a warm summer evening in ancient Greece…” (cit.) ;-)
But let’s say: I am 32-years-old German, born and raised in a lovely region of North Rhine-Westphalia, called Lippe. I knew quite early in my life that I would like to be a theoretical physicist, which – with studies at Bielefeld University & École normale supérieure in Paris, work at the LMU in Munich as a postdoc, and now at the Oskar-Klein Centre – worked quite well so far… Besides my professional activities, and if time permits, I very much enjoy (full-frame) photography, writing poems, playing the blues harmonica, and dancing Tango Argentino; Oh, and not to forget my passion for good food… :-)

Where did you study before?
I studied physics at Bielefeld University, with an Intermezzo at École normale supérieure in Paris where I worked on my Diploma thesis (equiv. to MSc. thesis) in the field of condensed matter physics – more specifically, I worked on disordered systems. Then, I changed to cosmology, where I have been fruitfully able to apply condensed-matter methods.
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First results of the AMS-02 experiment

Posted on April 17, 2013 | by Serena | No Comments

The Alpha Magnetic Spectrometer (AMS) collaboration announced its first physics result in Physical Review Letters on 3 April 2013 [AMS Collaboration, Phys. Rev. Lett. 110 (2013)]. This was a long awaited event for the astroparticle physics community. Indeed, this large particle detector was first proposed by Nobel laureate Samuel Ting in 1994, to study primordial cosmic-ray particles in the energy range from 0.5 to 2 TeV. A proof-of-principle spectrometer (AMS-01) flew successfully for 10 days on the space shuttle Discovery during flight STS-91 in June 1998.

AMS-02 is visible at centre of the International Space Station's starboard truss.

The encouraging results have strengthen the undertaking of building the first high-precision astroparticle detector (AMS-02) to be installed on the International Space Station (ISS). Following the loss of the space shuttle Columbia and its crew on 1 February 2003, the space shuttle programme was suspended by NASA, cancelling a number of flights, including the AMS-02 one. On 15 October 2009, hence over six years later, President George W. Bush signs the bill authorising NASA to add another space shuttle to launch AMS-02 on the ISS. On 16 May 2011 the space shuttle Endavour finally takes the AMS detector to space. The crew of the STS-134 mission successfully installed AMS three days later on the ISS S3 truss (see picture), from where AMS is taking continually data ever since.
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Unique study shows how Lyman alpha light travels through starburst galaxies

Posted on April 8, 2013 | by Serena | No Comments

Credit: ESA/Hubble & NASA, M. Hayes

A study of nearby starburst galaxies by a team of scientists lead by OKC professor Göran Östlin, and involving several other OKC members, has been featured as a Hubble Space Telescope Picture of the Week last week. The study, the Lyman-Alpha Reference Sample (LARS), targeted 14 galaxies using the Hubble Space Telescope (HST). The galaxies were observed at many different wavelengths, making it the largest Swedish project ever to carried out on HST. The first publication from the team is now available(astro-ph: http://arxiv.org/abs/1303.0006). The first author of the article, Dr. Matthew Hayes (IRAP, Touolouse, France), will be joining the OKC as a researcher later this year. The main results is the discovery of an extended halo of Lyman-alpha radiation in most of the galaxies in the sample. The size of this halo is significantly larger than the sizes of the galaxies in ultraviolet light. The presence of the extended emission means that the Ly-alpha radiation escapes the galaxies far from the places, the sites with active star formation, where it was produced.

One of the main drivers for the LARS project is to understand how Ly-alpha radiation is produced and reprocessed in star-forming galaxies. By targeting nearby galaxies the study
can give very detailed clues to what is happening in these complicated systems. The knowledge gained by investigating the local galaxies can also be used to try and understand observations of Ly-alpha emitting galaxies much further away (at high redshift). Here are collected images of the all 14 galaxies (but using a different set of filters).
These first results from the LARS project are exciting, but the wealth of data collected by the HST for LARS means that there is much more to come later this year!

- Jens Melinder, OKC postdoc (jens@astro.su.se)

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