Tag Archives: X-rays

Bad news for PoGOLite once again.

PoGOLite launch activities have been terminated at Esrange. We have been waiting to launch since 1st July, but weather conditions have not been good enough. This is very unusual. The low pressure regions which have been oscillating back-and-forth over Esrange have lead to wind conditions which are incompatible with launching a million cubic metre volume balloon. Now, at the end of July, the stratospheric winds are no longer stable enough to support a flight Eastwards towards Canada and beyond.
PoGOLite during tests at Esrange
PoGOLite during tests at Esrange in June
Needless-to-say, we are all extremely disappointed (this is a massive understatement of course!). After last year’s failed launch, we were counting on finally observing the Crab in polarised X-rays. Disassembling, repairing, reassembling, and testing PoGOLite after last year’s failed launch has required a big effort from the team. I would like to thank them all for their dedication and many sacrifices which made this year’s flight attempt a reality.
One thing is already decided. We will try again next year!



A second chance for PoGOLite and some news from PAMELA

Approximately one year ago, the PoGOLite team deployed to the Esrange Space Centre located outside of Kiruna in Northern Sweden. The result of that ill-fated flight attempt is well known to readers of this blog. Time flies (which is more than can be said for our balloon) and the last year has passed quickly. Now we find ourselves back at Esrange with some 6 weeks until PoGOLite is due to be airborne once more. It is a little bizarre to be commuting back-and-forth to 67 degrees N. Just as summer finally seems to be coming to the Stockholm region, there is still snow and chilly days up North.

PoGOLite preparations
Preparing to roll out the X-ray polarimeter for another night of observations at Linköping airport. The long tube is a star tracker - the subject of the test. Mark at the wheel, Mozsi on the hook and MSc student Anders lending a helping hand.

The past year has by no means been a quiet one for the PoGOLite team. During the Autumn, the result of an investigation into the cause of the flight failure was published. The investigation showed that a sudden change of wind speed and wind direction just as the balloon was released was primarily to blame. After licking our wounds, we started the painstaking task of completely disassembling our X-ray polarimeter, repairing damage, reassembling and testing. Much of this work was completed around the start of 2012 and since then we’ve been based in a drafty hangar at Linköping airport for tests together with the attitude control system (which keeps the polarimeter accurately aligned with observation targets), developed with DST Control AB. The team’s obsession with checking weather forecasts in order to pinpoint clear nights for tests of our star trackers lead to colleagues commenting that some of us had truly made the transition from our particle physics pasts.

Hanging the gondola at Esrange. Can we have a larger OKC sticker, please?

On July 1st, the PoGOLite launch window will open. We stand to benefit from a 15 day long flight with corresponding multiple observations of our scientific targets – The Crab and Cygnus X-1. This is very exciting, but we’ll also be somewhat nervous… such a large balloon has never made such a circumpolar traverse before. The balloon will be carried in a Westerly direction by stratospheric winds, flying over Norway, Greenland, Canada and Russia before returning to Scandinavia where the flight will be terminated and our telescope returned to ground by parachute.

More news from PoGOLite as the launch date approaches. In the meantime, if you want to know more why not come to Merlin Kole’s licentiate seminar on May 31st: “PoGoLite: 2011 flight results and 2012 pre-flight predictions“? Although we were aloft for a short time during the 2011 flight, it was still possible to squeeze some very useful information from the data we collected and Merlin will reveal all.

While we’re on the subject of thesis presentations, I would also like to alert you to two PAMELA Ph.D. thesis presentations in the near future. Juan Wu will present her thesis, “Measurements of cosmic ray antiprotons with PAMELA and studies of propagation models“, on Friday June 1st with Fiorenza Donato from Turn University as opponent. Juan has worked closely with Antje Putze, giving this work a true OKC flavour. Laura Rossetto presents her thesis, “PAMELA measurements of high energy cosmic ray positrons“, on May 11th with Tatsuya Nakada as opponent. The particle physicists amongst you may know him as a past Spokesperson for LHCb – you may not know that he is also leading a balloon-borne positron mission called PEBS (cosmic-ray positron measurements up to the TeV scale – something for OKC, maybe?). These will be the final two PAMELA Ph.D. students at KTH. The end of an era! Of course, we’re all waiting with bated-breath for first results from PAMELA’s larger sibling, AMS. I am particularly curious to see their positron results. Now that the PAMELA rise in the positron fraction has been confirmed by an inventive use of the Fermi Gamma-ray Space Telescope, that AMS also sees the rise will not come as much of a surprise. What will be interesting, however, is the maximum energy at which AMS can reliably resolve positrons from the large background of cosmic-ray protons. The Twittersphere was recently awash with congratulatory messages as AMS passed 17 billion triggers – so far, so good. Rumour has it that something ‘interesting’ will be shown at the summer conferences. Stay tuned…


PoGOLite flight cut short

The PoGOLite flight did not turn out as we had hoped. A few hours after the spectacular launch at 2 AM on Thursday 7th July it became clear that the balloon’s altitude was lower than expected. It was soon after determined that the balloon was in fact leaking and that the altitude had started to steadily decrease. Since the balloon was approaching a mountainous region it was decided to terminate the flight – a 5 day flight to Canada was no longer an option. We were, of course, extremely disappointed and frustrated. During our few hours aloft we managed to commission the polarimeter and start pointing exercises with the attitude control system. The first guide stars we selected appeared nicely centred in our field-of-view and we were eagerly awaiting the Crab rising in a couple of hours time.

Happy faces.
The first data download from the polarimeter. Happy faces!

Before shutting down the instrument we did manage to point at Cygnus X-1 and take some data. The pointing worked beautifully, but we were already too low to allow meaningful X-ray observations. The gondola was finally cut from the balloon around 0730 on Thursday morning in the vicinity of Kebnekaise and landed by parachute near to Nikkaluokta. Initial GPS information indicated that it had splashed down in a lake, but fortunately this was not the case. We managed to locate the gondola the day after and were relieved to find it relatively intact.

PoGOLite after flight termination.

So, what happens now? The first step is to understand the status of the polarimeter, attitude control system, star trackers and electronic control systems. Today we have made an initial appraisal and first results are promising. It will take more time to form a proper understanding of the situation however.

Given the excellent performance we experienced during our few hours aloft, we are keen to fly again as soon as possible!








The countdown approaches…

POGOLite is almost ready for launch! As you can see from the photograph, the polarimeter, which once filled our lab at AlbaNova, is now dwarfed by the protective gondola and solar cell arrays. The picture was taken just before Midsummer, during a launch rehearsal. This provided us with a realistic environment to tune-up our pre-flight checklists and confirm that we can operate the polarimeter, pointing system and our satellite communication systems together with the other balloon systems.

PoGOLite hanging on the Hercules launch vehicle
PoGOLite hanging on the Hercules launch vehicle

There are a few items remaining on our ‘to do‘ list and then we’re ready to launch. How long we need to wait will depend on the weather. There are very strict requirements placed on wind speeds at the ground and at altitudes of a few hundred metres. The countdown itself takes about 24 hours once a positive weather prognosis is received. The polyethylene balloon is unpacked at the last moment. Being about as thick as a standard sandwich bag, once unpacked it so fragile that it must either be used or thrown away.

For the latest news updates, you might like to take a look at our recently overhauled web-page.

I’ll post an update here after the launch.

The re-brightening of supernova 1987A

Josefin Larsson is one of the Oskar Klein Center postdocs since august 2009, working at the Astronomy department. Her recent paper, X-ray illumination of the ejecta of supernova 1987A, written in collaboration with several other people from the OKC, has been accepted in Nature and has been published online last week.
I asked Josefin to write something for this blog about the exciting results she found. Here is her account.

Supernova 1987A exploded in our neighbouring galaxy the Large Magellanic Cloud nearly 25 years ago. Due to its proximity it can be studied in much greater detail than any other supernova. This has lead to many important discoveries over the years, and even now, many years later, it continues to surprise us.

SN1987A - Josefin Larsson

The Hubble Space Telescope has observed SN 1987A regularly since the mid-nineties (a selection of images is shown above) and we have recently used these data to measure how the brightness of the ejecta changes over time. Our analysis revealed that the flux declined up to around 2001, or about 5000 days after the explosion, but then started to increase, more than doubling by the end of 2009. By modelling the light curve we found that the declining phase is well explained by energy input from the radioactive decay of 44Ti. However, radioactivity cannot explain the re-brightening, so a new energy source must have started to dominate around 2001.

The brightening turns out to be connected to the interaction Continue reading The re-brightening of supernova 1987A

An update from above the Arctic Circle

In a little over two weeks, just after Midsummer, the launch window for PoGOLite will open. In my last post, I talked about the conclusion of PoGOLite tests at Linköping airport. Since then, PoGOLite has been moved up to the Esrange Space Centre thereby marking the start of the launch campaign. Esrange is located some 40 km east of Kiruna and provides unique opportunities to launch large helium-filled balloons into the stratosphere. We are hoping to make a circumpolar navigation of the North Pole, overflying Norway, Iceland, Greenland, Canada and Russia before landing back in Sweden some 20 days later. Such a long flight will allow repeated observations of our primary science targets, the Crab and Cygnus X-1 and plenty of time to study backgrounds – which is essential for a counting rate anisotropy measurement such as polarisation. Obtaining permission to fly over Russia is a complicated business and we are still on tenterhooks waiting for the green light. If this is not forthcoming, we’ll have to cut the balloon down over Western Canada and strike out into the wilderness to recover the payload and, in particular, the valuable cargo of hard disks.

PoGOLite arrives at Esrange.

There is a lot of activity at Esrange right now with several large balloons being prepared for launch. First up are three NASA-sponsored payloads. The first two, AESOP and LEE, have flown many times before in their quest to monitor the effect of solar modulation on low energy cosmic rays. The relatively high latitude of Esrange means that cosmic rays are not screened by the Earth’s magnetic field. LEE (Low Energy Electrons), has already been launched and landed in Western Canada after 5 days. AESOP (Anti-Electron Sub Orbital Payload) will be launched as soon as weather conditions allow. The final payload in the queue is called Highwind and uses a Fabry-Perot interferometer to probe the upper atmosphere. Interestingly, LEE and AESOP have connections to my ‘other’ experiment PAMELA. You may recall that the low energy part of the well-known PAMELA positron fraction did not agree with the majority of other published balloon-borne data since these measurements were taken during a different solar configuration (polarity and activity). Measurements from AESOP collected around the time PAMELA was launched agreed with the PAMELA observations, however.

Integrating the polarimeter with part of the gondola.

PoGOLite rounds off the summer launch programme for large balloons, with the late date chosen to maximise the angle between the Sun and the Crab. So, how large is large? Well, the balloon which will lift PoGOLite to an altitude of 40 km has a volume of a little over 1 million cubic metres – about twice the volume of the Globen Arena. Such a large balloon is needed since PoGOLite is, in reality, not so light and weighs in at about 2 metric Tonnes.

An exciting few weeks lie ahead at Esrange. On-ground tests of the polarimeter continue, with a polarised radioactive source replacing photons from the Crab. The attitude control system which keeps the polarimeter aligned to targets of interest is also being put through its paces. As PoGOLite drifts Westward, Esrange will eventually drop below the horizon and the only way to contact the balloon is through Iridium satellite links. This requires that the payload can operate autonomously, rather like a satellite. Not always so easy to test realistically on the ground!

For more details about PoGOLite, you may wish to take a look at a paper which was presented a couple of weeks ago at the 20th ESA Symposium on European Rocket & Balloon Programmes (arXiv:1106.1322).