Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

‘Cold’ wind of the Crab pulsar produces very-high-energy gamma-ray pulses

16.02.2012
One of the brightest high-energy gamma-ray sources in the sky is the Crab pulsar, from which recently also pulsed very-high-energy radiation has been discovered.

Scientists around Felix Aharonian from the MPI for Nuclear Physics and the Dublin Institute for Advanced Studies now present an explanation for this radiation. It is based on the abrupt acceleration of an ultrafast wind of “cold” electrons and positrons, taking place at a distance of some Earth’s diameters from the pulsar. (Nature, 15.02.2012 online)


Fig. 1: The Crab nebula (M1) in the Taurus constellation, taken by the Hubble space telescope (lower left). The details to the right are showing a composite of visible light (red) and X-rays (blue) with the pulsar as central star. At the shock front in 0.3 light-years distance from the pulsar, the ultrarelativistic wind of electrons and positrons collides with the surrounding nebula.
Graphics: MPIK, source: NASA


Fig. 2: Schematic evolution of the pulsar wind (electrons and positrons: e–, e+). High-energy gamma quanta (ã) are created in the acceleration zone by inverse Compton scattering of the pulsar wind with X-ray quanta (X) from the magnetosphere as well as at large distance at the shock front to the interstellar medium.
Graphics: MPIK

The Crab pulsar, a fast-rotating, highly magnetized neutron star, is a product of the historical supernova observed in the constellation Taurus in 1054 AD. Its mass amounts to 1.4 to 2 times that of the Sun and its diameter is only 28 to 30 km. Together with its surrounding nebula, it is one of the best investigated astronomical objects (Fig. 1).

The generally accepted paradigm postulates the existence of a relativistic wind of electrons and their antiparticles, positrons, which originates in the pulsar’s magnetosphere and terminates in the interstellar medium. The evolution of the wind is characterized by three consecutive processes (Fig. 2): At a distance of about 1000 km from the pulsar, the pulsar’s rotational energy is transformed into electromagnetic energy, which in turn is converted to kinetic energy of bulk motion, i.e. acceleration of the wind. Finally, the wind terminates by collision with matter in a standing reverse shock about 0.3 light years away. Thereby, the electrons and positrons are accelerated up to extremely high energies, resulting in an extended non-thermal source: the Crab nebula. All three processes need to proceed with incredibly high (close to 100 %) efficiency in order to explain the observational data.

Both the Crab pulsar and the Crab nebula are bright gamma-ray sources. While the pulsar emits in the high energies, the radiation of the nebula is released predominantly at the very-high-energy band. Meanwhile, the third key component, the wind, via which the transfer of energy from the pulsar to the nebula is realized, at first glance seems to be an ‘invisible substance’. Indeed, despite the relativistic speed of the wind, in the frame of the outflow the electrons are ‘cold’, meaning they move together with the wind’s magnetic field and therefore do not emit radiation. The wind, however, can radiate high-energy gamma-rays through the mechanism of inverse Compton scattering in which ultrafast electrons and positrons of the wind are illuminated by X-ray photons originating in the pulsar’s magnetosphere and/or the surface of the neutron star. In a paper published in Nature, Felix Aharonian, Sergey Bogovalov and Dmitry Khangulyan argue that recent reports of the surprise detection of pulsed, very-high-energy gamma radiation from Crab by the VERITAS and MAGIC atmospheric Cherenkov telescopes are best explained by inverse Compton scattering. Pulsed X-ray photons of the pulsar interact with ultrafast electrons of the wind predominantly in their acceleration zone. The wind, therefore, is the source of the pulsed gamma radiation and explains the observations with only three parameters: site of the acceleration of the wind, its final velocity, and the level of anisotropy.

If this interpretation is correct, then detection of the pulsed very-high-energy gamma-ray emission implies the first observational evidence of the formation of a cold ultrafast electron-positron wind from the Crab pulsar. The reported gamma-ray data allow us to localize, with a good precision, the site and estimate the speed with which the electromagnetic energy is transformed into the kinetic energy of the wind’s bulk motion. The results show that the acceleration of the wind to ultrarelativistic velocities should take place abruptly in a narrow cylindrical zone of radius between 20 and 50 thousand kilometers centered on the rotation axis of the pulsar. Although the ultrafast nature of the wind does support the general paradigm of pulsar winds, the requirement of the very fast acceleration of the wind in a narrow zone not very far from the pulsar challenges current models.

Weitere Informationen:
Original publication:
Abrupt acceleration of a 'cold' ultrarelativistic wind from the Crab pulsar
F. A. Aharonian, S. V. Bogovalov and D. Khangulyan
Nature, doi: 10.1038/nature10793
Contact:
Prof. Dr. Felix Aharonian
MPI für Kernphysik
phone: (+49)6221-516-485
e-mail: felix.aharonian (at) mpi-hd.mpg.de

Dr. Bernold Feuerstein | Max-Planck-Institut
Further information:
http://www.mpi-hd.mpg.de

More articles from Physics and Astronomy:

nachricht UNLV study unlocks clues to how planets form
13.12.2018 | University of Nevada, Las Vegas

nachricht Unprecedented Views of the Birth of Planets
13.12.2018 | Universität Heidelberg

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: An energy-efficient way to stay warm: Sew high-tech heating patches to your clothes

Personal patches could reduce energy waste in buildings, Rutgers-led study says

What if, instead of turning up the thermostat, you could warm up with high-tech, flexible patches sewn into your clothes - while significantly reducing your...

Im Focus: Lethal combination: Drug cocktail turns off the juice to cancer cells

A widely used diabetes medication combined with an antihypertensive drug specifically inhibits tumor growth – this was discovered by researchers from the University of Basel’s Biozentrum two years ago. In a follow-up study, recently published in “Cell Reports”, the scientists report that this drug cocktail induces cancer cell death by switching off their energy supply.

The widely used anti-diabetes drug metformin not only reduces blood sugar but also has an anti-cancer effect. However, the metformin dose commonly used in the...

Im Focus: New Foldable Drone Flies through Narrow Holes in Rescue Missions

A research team from the University of Zurich has developed a new drone that can retract its propeller arms in flight and make itself small to fit through narrow gaps and holes. This is particularly useful when searching for victims of natural disasters.

Inspecting a damaged building after an earthquake or during a fire is exactly the kind of job that human rescuers would like drones to do for them. A flying...

Im Focus: Topological material switched off and on for the first time

Key advance for future topological transistors

Over the last decade, there has been much excitement about the discovery, recognised by the Nobel Prize in Physics only two years ago, that there are two types...

Im Focus: Researchers develop method to transfer entire 2D circuits to any smooth surface

What if a sensor sensing a thing could be part of the thing itself? Rice University engineers believe they have a two-dimensional solution to do just that.

Rice engineers led by materials scientists Pulickel Ajayan and Jun Lou have developed a method to make atom-flat sensors that seamlessly integrate with devices...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

ICTM Conference 2019: Digitization emerges as an engineering trend for turbomachinery construction

12.12.2018 | Event News

New Plastics Economy Investor Forum - Meeting Point for Innovations

10.12.2018 | Event News

EGU 2019 meeting: Media registration now open

06.12.2018 | Event News

 
Latest News

Magic number colloidal clusters

13.12.2018 | Life Sciences

UNLV study unlocks clues to how planets form

13.12.2018 | Physics and Astronomy

Live from the ocean research vessel Atlantis

13.12.2018 | Earth Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>