322 research outputs found
Breaking degeneracy in jet dynamics: multi-epoch joint modelling of the BL Lac PKS 2155-304
Supermassive black holes can launch powerful jets which can be some of the
most luminous multi-wavelength sources; decades after their discovery their
physics and energetics are still poorly understood. The past decade has seen a
dramatic improvement in the quality of available data, but despite this
improvement the semi-analytical modelling of jets has advanced slowly: simple
one-zone models are still the most commonly employed method of interpreting
data, in particular for AGN jets. These models can roughly constrain the
properties of jets but they cannot unambiguously couple their emission to the
launching regions and internal dynamics, which can be probed with simulations.
However, simulations are not easily comparable to observations because they
cannot yet self-consistently predict spectra. We present an advanced
semi-analytical model which accounts for the dynamics of the whole jet,
starting from a simplified parametrization of Relativistic Magnetohydrodynamics
in which the magnetic flux is converted into bulk kinetic energy. To benchmark
the model we fit six quasisimultaneous, multi-wavelength spectral energy
distributions of the BL Lac PKS 2155-304 obtained by the TANAMI program, and we
address the degeneracies inherent to such a complex model by employing a
state-of-the-art exploration of parameter space, which so far has been mostly
neglected in the study of AGN jets. We find that this new approach is much more
effective than a single-epoch fit in providing meaningful constraints on model
parameters.Comment: Accepted for publication on MNRA
Zeolite-dye micro lasers
We present a new class of micro lasers based on nanoporous molecular sieve
host-guest systems. Organic dye guest molecules of
1-Ethyl-4-(4-(p-Dimethylaminophenyl)-1,3-butadienyl)-pyridinium Perchlorat were
inserted into the 0.73-nm-wide channel pores of a zeolite AlPO-5 host. The
zeolitic micro crystal compounds where hydrothermally synthesized according to
a particular host-guest chemical process. The dye molecules are found not only
to be aligned along the host channel axis, but to be oriented as well. Single
mode laser emission at 687 nm was obtained from a whispering gallery mode
oscillating in a 8-m-diameter monolithic micro resonator, in which the
field is confined by total internal reflection at the natural hexagonal
boundaries inside the zeolitic microcrystals.Comment: Accepted for publication in Phys. Rev. Let
Cellular Automata Simulating Experimental Properties of Traffic Flows
A model for 1D traffic flow is developed, which is discrete in space and
time. Like the cellular automaton model by Nagel and Schreckenberg [J. Phys. I
France 2, 2221 (1992)], it is simple, fast, and can describe stop-and-go
traffic. Due to its relation to the optimal velocity model by Bando et al.
[Phys. Rev. E 51, 1035 (1995)], its instability mechanism is of deterministic
nature. The model can be easily calibrated to empirical data and displays the
experimental features of traffic data recently reported by Kerner and Rehborn
[Phys. Rev. E 53, R1297 (1996)].Comment: For related work see
http://www.theo2.physik.uni-stuttgart.de/helbing.html and
http://traffic.comphys.uni-duisburg.de/member/home_schreck.htm
Spin-flip processes and ultrafast magnetization dynamics in Co - unifying the microscopic and macroscopic view of femtosecond magnetism
The femtosecond magnetization dynamics of a thin cobalt film excited with
ultrashort laser pulses has been studied using two complementary pump-probe
techniques, namely spin-, energy- and time-resolved photoemission and
time-resolved magneto-optical Kerr effect. Combining the two methods it is
possible to identify the microscopic electron spin-flip mechanisms responsible
for the ultrafast macroscopic magnetization dynamics of the cobalt film. In
particular, we show that electron-magnon excitation does not affect the overall
magnetization even though it is an efficient spin-flip channel on the sub-200
fs timescale. Instead we find experimental evidence for the relevance of
Elliott-Yafet type spin-flip processes for the ultrafast demagnetization taking
place on a time scale of 300 fs.Comment: 12 pages, 3 figures; accepted by Physical Review Letter
Investigating source confusion in PMN J16034904
PMN J16034904 is a likely member of the rare class of -ray
emitting young radio galaxies. Only one other source, PKS 1718649, has been
confirmed so far. These objects, which may transition into larger radio
galaxies, are a stepping stone to understanding AGN evolution. It is not
completely clear how these young galaxies, seen edge-on, can produce
high-energy -rays. PMN J16034904 has been detected by TANAMI Very
Long Baseline Interferometry (VLBI) observations and has been followed-up with
multiwavelength observations. A Fermi/LAT -ray source has been
associated with it in the LAT catalogs. We have obtained Chandra observations
of the source in order to consider the possibility of source confusion, due to
the relatively large positional uncertainty of Fermi/LAT. The goal was to
investigate the possibility of other X-ray bright sources in the vicinity of
PMN J16034904 that could be counterparts to the -ray emission. With
Chandra/ACIS, we find no other sources in the uncertainty ellipse of Fermi/LAT
data, which includes an improved localization analysis of 8 years of data. We
further study the X-ray fluxes and spectra. We conclude that PMN J16034904
is indeed the second confirmed -ray bright young radio galaxy.Comment: 4 pages, 3 figures, accepted for publication in A&
Black Hole Lightning from the Peculiar Gamma-Ray Loud Active Galactic Nucleus IC 310
The nearby active galaxy IC 310, located in the outskirts of the Perseus
cluster of galaxies is a bright and variable multi-wavelength emitter from the
radio regime up to very high gamma-ray energies above 100 GeV. Originally, the
nucleus of IC 310 has been classified as a radio galaxy. However, studies of
the multi-wavelength emission showed several properties similarly to those
found from blazars as well as radio galaxies. In late 2012, we have organized
the first contemporaneous multi-wavelength campaign including radio, optical,
X-ray and gamma-ray instruments. During this campaign an exceptionally bright
flare of IC 310 was detected with the MAGIC telescopes in November 2012
reaching an averaged flux level in the night of up to one Crab above 1 TeV with
a hard spectrum over two decades in energy. The intra-night light curve showed
a series of strong outbursts with flux-doubling time scales as fast as a few
minutes. The fast variability constrains the size of the gamma-ray emission
regime to be smaller than 20% of the gravitational radius of its central black
hole. This challenges the shock acceleration models, commonly used to explain
gamma-ray radiation from active galaxies. Here, we will present more details on
the MAGIC data and discuss several possible alternative emission models.Comment: 8 pages, 5 figures, Proceedings of the 34th International Cosmic Ray
Conference, 30 July - 6 August, 2015, The Hague, The Netherland
A redshifted Fe K line from the unusual gamma-ray source PMN J1603-4904
Multiwavelength observations have revealed the highly unusual properties of
the gamma-ray source PMN J1603-4904, which are difficult to reconcile with any
other well established gamma-ray source class. The object is either a very
atypical blazar or compact jet source seen at a larger angle to the line of
sight. In order to determine the physical origin of the high-energy emission
processes in PMN J1603-4904, we study the X-ray spectrum in detail. We
performed quasi-simultaneous X-ray observations with XMM-Newton and Suzaku in
2013 September, resulting in the first high signal-to-noise X-ray spectrum of
this source. The 2-10 keV X-ray spectrum can be well described by an absorbed
power law with an emission line at 5.440.05 keV (observed frame).
Interpreting this feature as a K{\alpha} line from neutral iron, we determine
the redshift of PMN J1603-4904 to be z=0.180.01, corresponding to a
luminosity distance of 87254 Mpc. The detection of a redshifted X-ray
emission line further challenges the original BL Lac classification of PMN
J1603-4904. This result suggests that the source is observed at a larger angle
to the line of sight than expected for blazars, and thus the source would add
to the elusive class of gamma-ray loud misaligned-jet objects, possibly a
{\gamma}-ray bright young radio galaxy.Comment: 5 pages, 1 figure, A&A accepte
- …