2 research outputs found
The coupling of an EUV coronal wave and ion acceleration in a Fermi-LAT behind-the-limb solar flare
We present the Fermi-LAT observations of the behind-the-limb (BTL) flare of
July 17, 2021 and the joint detection of this flare by STIX onboard Solar
Orbiter. The separation between Earth and the Solar Orbiter was 99.2
at 05:00 UT, allowing STIX to have a front view of the flare. The location of
the flare was ~S20E140 in Stonyhurst heliographic coordinates making this the
most distant behind-the-limb flare ever detected in 100 MeV gamma-rays. The
LAT detection lasted for 16 minutes, the peak flux was
(10) ph cm s with a significance 15. A coronal
wave was observed from both STEREO-A and SDO in extreme ultraviolet (EUV) with
an onset on the visible disk in coincidence with the LAT onset. A complex type
II radio burst was observed by GLOSS also in coincidence with the onset of the
LAT emission indicating the presence of a shock wave. We discuss the relation
between the time derivative of the EUV wave intensity profile at 193\angstrom\
as observed by STEREO-A and the LAT flux to show that the appearance of the
coronal wave at the visible disk and the acceleration of protons as traced by
the observed 100 MeV gamma-ray emission are coupled. We also report how this
coupling is present in the data from 3 other BTL flares detected by Fermi-LAT
suggesting that the protons driving the gamma-ray emission of BTL solar flares
and the coronal wave share a common origin.Comment: 10 pages, 9 figure
The X-Ray Polarization View of Mrk 421 in an Average Flux State as Observed by the Imaging X-Ray Polarimetry Explorer
Particle acceleration mechanisms in supermassive black hole jets, such as shock acceleration, magnetic reconnection, and turbulence, are expected to have observable signatures in the multiwavelength polarization properties of blazars. The recent launch of the Imaging X-Ray Polarimetry Explorer (IXPE) enables us, for the first time, to use polarization in the X-ray band (2-8 keV) to probe the properties of the jet synchrotron emission in high-synchrotron-peaked BL Lac objects (HSPs). We report the discovery of X-ray linear polarization (degree pi(x) = 15% +/- 2% and electric vector position angle psi (x) = 35 degrees +/- 4 degrees) from the jet of the HSP Mrk 421 in an average X-ray flux state. At the same time, the degree of polarization at optical, infrared, and millimeter wavelengths was found to be lower by at least a factor of 3. During the IXPE pointing, the X-ray flux of the source increased by a factor of 2.2, while the polarization behavior was consistent with no variability. The higher level of pi(x) compared to longer wavelengths, and the absence of significant polarization variability, suggest a shock is the most likely X-ray emission site in the jet of Mrk 421 during the observation. The multiwavelength polarization properties are consistent with an energy-stratified electron population, where the particles emitting at longer wavelengths are located farther from the acceleration site, where they experience a more disordered magnetic field