Long (up to Megaparsec scale), highly collimated jets of magnetized plasma emanating from the active nuclei of galaxies pose many astrophysical puzzles - including the mechanism by which those outflows are accelerated to relativistic velocities, and the structure of the jet magnetic field. Recent high resolution X-ray imaging of the jet in famous radio galaxy Pictor A shows some surprising and unexpected variability.
May 5, 2015 | A Flare in the Jet of Pictor A
May 5, 2015 | One Flavor of Quasar Or Two?
A team of KIPAC astrophysicists has applied a rigorous statistical analysis to observations of quasars resulting in an interesting perspective.
An example of a bias arising from data truncation. In this plot of radio luminosity versus redshift (distance) for quasars detected by a survey, inherently faint objects can only be seen if they are close (low redshift).
May 5, 2015 | Does Galactic Dust Twirl and Shine?
The question of whether we receive microwave radiation from spinning dust grains in our Galaxy has been debated for 15 years. A collaboration including a KIPAC scientist has provided valuable data indicating that the answer is probably yes.
The ARCADE 2 instrument being launched on a high altitude balloon. Getting above the atmosphere is important in an absolute atrophysical microwave measurement.
Gamma-ray observations of the Universe by the Fermi Gamma-ray Space Telescope have enabled another astrophysical constraint on the properties of particle dark matter.
The Fermi Gamma-ray Space Telescope continues to bridge astronomy and particle physics.
Simulations of accretion flows around black holes, involving General Relativity and relativistic plasma physics, have led to a new model of how extreme particle acceleration is achieved in the hearts of galaxies, gamma-ray bursts, and elsewhere.
Huge natural thermonuclear explosions, so called stellar novae, are observed in binary systems consisting of a dense compact white dwarf circling a star. The Fermi LAT has for the first time ever detected gamma-ray emission from such an event. This observation indicates particle acceleration in the shock wave produced by the nova explosion to at least GeV energies.
May 5, 2015 | Simulating Stimulating Bursts of Gamma Rays
Using powerful computer simulations, a KIPAC scientist explores the possible mechanisms behind the gamma-ray emission in the super explosions known as gamma-ray bursts.
Artist's conception of a GRB. We see the burst of gamma rays if the jets are oriented so that one points toward us. (Image courtesy of NASA)
Although the Fermi Gamma-ray Space Telescope is primarily a gamma-ray instrument, its most cited paper reports a measurement of the combined electron and positron cosmic-ray spectrum. Now a team, led by KIPAC researchers, has built on this result by using a novel technique to separate the cosmic-ray electrons and positrons and measure the spectrum of each component individually. The result will keep theorists busy thinking about pulsars and dark matter.
May 5, 2015 | Let the Sun Shine (In Gamma Rays) II
Unifying the astronomically near and far, the Fermi Gamma-ray Space Telescope has seen its first signature of cosmic rays interacting with the light from our Sun.
The left panel shows the LAT gamma rays per pixel from near the Sun and the right panel shows the same for another patch of sky. There is a clear large flux from the solar disk and a less dense but extended flux surrounding it.
For several decades now, astrophysicists have known of the existence of powerful jets of particles and magnetic fields that shoot out at nearly the speed of light (that is, “relativistically”) from the centers of certain “active” galaxies. Scientists have learned that the jets originate in the accretion disks surrounding supermassive black holes at the cores of these galaxies. Relativistic jets are sources of strongly beamed radiation characterized by broad and smooth (or “non-thermal”) spectra, therefore their orientation relative to the observer has dramatic effects on the observed characteristics of the active galaxies. In particular, when one of the jets happens to point towards us, the galaxy in which it originates is called a “blazar”.
By Jeff Scargle and Roger Blandford
The Crab Nebula, an old solid and reliable friend -- mostly
By Radek Wojtak
Cosmologists generally assume that we do not sit at any special place in the Universe when extracting properties about our Universe, such as figuring out its expansion history (for which the Nobel Prize in Physics was awarded in 2011).