TY  - JOUR
A1  - Lange, Ilja
A1  - Reiter, Sina
A1  - Kniepert, Juliane
A1  - Piersimoni, Fortunato
A1  - Paetzel, Michael
A1  - Hildebrandt, Jana
A1  - Brenner, Thomas J. K.
A1  - Hecht, Stefan
A1  - Neher, Dieter
T1  - Zinc oxide modified with benzylphosphonic acids as transparent electrodes in regular and inverted organic solar cell structures
JF  - Applied physics letters
N2  - An approach is presented to modify the work function of solution-processed sol-gel derived zinc oxide (ZnO) over an exceptionally wide range of more than 2.3 eV. This approach relies on the formation of dense and homogeneous self-assembled monolayers based on phosphonic acids with different dipole moments. This allows us to apply ZnO as charge selective bottom electrodes in either regular or inverted solar cell structures, using poly(3-hexylthiophene): phenyl-C71-butyric acid methyl ester as the active layer. These devices compete with or even surpass the performance of the reference on indium tin oxide/poly(3,4-ethylenedioxythiophene) polystyrene sulfonate. Our findings highlight the potential of properly modified ZnO as electron or hole extracting electrodes in hybrid optoelectronic devices. (C) 2015 AIP Publishing LLC.
Y1  - 2015
U6  - https://doi.org/10.1063/1.4916182
SN  - 0003-6951
SN  - 1077-3118
VL  - 106
IS  - 11
PB  - American Institute of Physics
CY  - Melville
ER  - 
TY  - JOUR
A1  - Sellberg, Jonas A.
A1  - McQueen, Trevor A.
A1  - Laksmono, Hartawan
A1  - Schreck, Simon
A1  - Beye, Martin
A1  - DePonte, Daniel P.
A1  - Kennedy, Brian
A1  - Nordlund, Dennis
A1  - Sierra, Raymond G.
A1  - Schlesinger, Daniel
A1  - Tokushima, Takashi
A1  - Zhovtobriukh, Iurii
A1  - Eckert, Sebastian
A1  - Segtnan, Vegard H.
A1  - Ogasawara, Hirohito
A1  - Kubicek, Katharina
A1  - Techert, Simone
A1  - Bergmann, Uwe
A1  - Dakovski, Georgi L.
A1  - Schlotter, William F.
A1  - Harada, Yoshihisa
A1  - Bogan, Michael J.
A1  - Wernet, Philippe
A1  - Föhlisch, Alexander
A1  - Pettersson, Lars G. M.
A1  - Nilsson, Anders
T1  - X-ray emission spectroscopy of bulk liquid water in "no-man's land"
JF  - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr
N2  - The structure of bulk liquid water was recently probed by x-ray scattering below the temperature limit of homogeneous nucleation (T-H) of similar to 232 K [J. A. Sellberg et al., Nature 510, 381-384 (2014)]. Here, we utilize a similar approach to study the structure of bulk liquid water below T-H using oxygen K-edge x-ray emission spectroscopy (XES). Based on previous XES experiments [T. Tokushima et al., Chem. Phys. Lett. 460, 387-400 (2008)] at higher temperatures, we expected the ratio of the 1b(1)' and 1b(1)" peaks associated with the lone-pair orbital in water to change strongly upon deep supercooling as the coordination of the hydrogen (H-) bonds becomes tetrahedral. In contrast, we observed only minor changes in the lone-pair spectral region, challenging an interpretation in terms of two interconverting species. A number of alternative hypotheses to explain the results are put forward and discussed. Although the spectra can be explained by various contributions from these hypotheses, we here emphasize the interpretation that the line shape of each component changes dramatically when approaching lower temperatures, where, in particular, the peak assigned to the proposed disordered component would become more symmetrical as vibrational interference becomes more important. (C) 2015 AIP Publishing LLC.
Y1  - 2015
U6  - https://doi.org/10.1063/1.4905603
SN  - 0021-9606
SN  - 1089-7690
VL  - 142
IS  - 4
PB  - American Institute of Physics
CY  - Melville
ER  - 
TY  - JOUR
A1  - Hainich, Rainer
A1  - Pasemann, Diana
A1  - Todt, Helge Tobias
A1  - Shenar, Tomer
A1  - Sander, Andreas Alexander Christoph
A1  - Hamann, Wolf-Rainer
T1  - Wolf-Rayet stars in the Small Magellanic Cloud I. Analysis of the single WN stars
JF  - Astronomy and astrophysics : an international weekly journal
N2  - Context. Wolf-Rayet (WR) stars have a severe impact on their environments owing to their strong ionizing radiation fields and powerful stellar winds. Since these winds are considered to be driven by radiation pressure, it is theoretically expected that the degree of the wind mass-loss depends on the initial metallicity of WR stars.
 Aims. Following our comprehensive studies of WR stars in the Milky Way, M31, and the LMC, we derive stellar parameters and mass-loss rates for all seven putatively single WN stars known in the SMC. Based on these data, we discuss the impact of a low-metallicity environment on the mass loss and evolution of WR stars.
 Methods. The quantitative analysis of the WN stars is performed with the Potsdam Wolf-Rayet (PoWR) model atmosphere code. The physical properties of our program stars are obtained from fitting synthetic spectra to multi-band observations.
 Results. In all SMC WN stars, a considerable surface hydrogen abundance is detectable. The majority of these objects have stellar temperatures exceeding 75 kK, while their luminosities range from 10(5.5) to 10(6.1) L-circle dot. The WN stars in the SMC exhibit on average lower mass-loss rates and weaker winds than their counterparts in the Milky Way, M31, and the LMC.
 Conclusions. By comparing the mass-loss rates derived for WN stars in different Local Group galaxies, we conclude that a clear dependence of the wind mass-loss on the initial metallicity is evident, supporting the current paradigm that WR winds are driven by radiation. A metallicity effect on the evolution of massive stars is obvious from the HRD positions of the SMC WN stars at high temperatures and high luminosities. Standard evolution tracks are not able to reproduce these parameters and the observed surface hydrogen abundances. Homogeneous evolution might provide a better explanation for their evolutionary past.
KW  - stars: Wolf-Rayet
KW  - Magellanic Clouds
KW  - stars: early-type
KW  - stars: atmospheres
KW  - stars: winds, outflows
KW  - stars: mass-loss
Y1  - 2015
U6  - https://doi.org/10.1051/0004-6361/201526241
SN  - 1432-0746
VL  - 581
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Hoffmann, Holger
A1  - Seiss, Martin
A1  - Salo, Heikki
A1  - Spahn, Frank
T1  - Vertical structures induced by embedded moonlets in Saturn's rings
JF  - Icarus : international journal of solar system studies
N2  - We study the vertical extent of propeller structures in Saturn's rings (i) by extending the model of Spahn and Sremcevic (Spahn, F., Sremcevic, M. [2000]. Astron. Astrophys., 358, 368-372) to include the vertical direction and (ii) by performing N-body box simulations of a perturbing moonlet embedded into the rings. We find that the gravitational interaction of ring particles with a non-inclined moonlet does not induce considerable vertical excursions of ring particles, but causes a considerable thermal motion in the ring plane. We expect ring particle collisions to partly convert the lateral induced thermal motion into vertical excursions of ring particles in the course of a quasi-thermalization. The N-body box simulations lead to maximal propeller heights of about 0.6-0.8 Hill radii of the embedded perturbing moonlet. Moonlet sizes estimated by this relation are in good agreement with size estimates from radial propeller scalings for the propellers Bleriot and Earhart. For large propellers, the extended hydrodynamical propeller model predicts an exponential propeller height relaxation, confirmed by N-body box simulations of non-self gravitating ring particles. Exponential cooling constants, calculated from the hydrodynamical propeller model agree fairly well with values from fits to the tail of the azimuthal height decay of the N-body box simulations. From exponential cooling constants, determined from shadows cast by the propeller Earhart and imaged by the Cassini spacecraft, we estimate collision frequencies of about 6 collisions per particle per orbit in the propeller gap region and about 11 collisions per particle per orbit in the propeller wake region. (C) 2015 Elsevier Inc. All rights reserved.
KW  - Planetary rings
KW  - Saturn, rings
KW  - Saturn, satellites
KW  - Disks
Y1  - 2015
U6  - https://doi.org/10.1016/j.icarus.2015.02.003
SN  - 0019-1035
SN  - 1090-2643
VL  - 252
SP  - 400
EP  - 414
PB  - Elsevier
CY  - San Diego
ER  - 
TY  - JOUR
A1  - Aliu, E.
A1  - Archer, A.
A1  - Aune, T.
A1  - Barnacka, Anna
A1  - Behera, B.
A1  - Beilicke, M.
A1  - Benbow, W.
A1  - Berger, K.
A1  - Bird, R.
A1  - Buckley, J. H.
A1  - Bugaev, V.
A1  - Byrum, K.
A1  - Cardenzana, J. V.
A1  - Cerruti, M.
A1  - Chen, Xuhui
A1  - Ciupik, L.
A1  - Connolly, M. P.
A1  - Cui, Wei
A1  - Dickinson, H. J.
A1  - Dumm, J.
A1  - Eisch, J. D.
A1  - Errando, M.
A1  - Falcone, A.
A1  - Federici, Simone
A1  - Feng, Q.
A1  - Finley, J. P.
A1  - Fortin, P.
A1  - Fortson, L.
A1  - Furniss, A.
A1  - Galante, N.
A1  - Gillanders, G. H.
A1  - Griffin, S.
A1  - Griffiths, S. T.
A1  - Grube, J.
A1  - Gyuk, G.
A1  - Hakansson, Nils
A1  - Hanna, D.
A1  - Holder, J.
A1  - Hughes, G.
A1  - Humensky, T. B.
A1  - Johnson, C. A.
A1  - Kaaret, P.
A1  - Kar, P.
A1  - Kertzman, M.
A1  - Khassen, Y.
A1  - Kieda, D.
A1  - Krawczynski, H.
A1  - Krennrich, F.
A1  - Kumar, S.
A1  - Lang, M. J.
A1  - Madhavan, A.
A1  - McArthur, S.
A1  - McCann, A.
A1  - Meagher, K.
A1  - Millis, J.
A1  - Moriarty, P.
A1  - Nieto, Daniel
A1  - Ong, R. A.
A1  - Orr, M.
A1  - Otte, A. N.
A1  - Park, N.
A1  - Perkins, J. S.
A1  - Pohl, Martin
A1  - Popkow, A.
A1  - Prokoph, H.
A1  - Pueschel, Elisa
A1  - Quinn, J.
A1  - Ragan, K.
A1  - Rajotte, J.
A1  - Reyes, L. C.
A1  - Reynolds, P. T.
A1  - Richards, G. T.
A1  - Roache, E.
A1  - Sembroski, G. H.
A1  - Shahinyan, K.
A1  - Staszak, D.
A1  - Telezhinsky, Igor O.
A1  - Tucci, J. V.
A1  - Tyler, J.
A1  - Varlotta, A.
A1  - Vassiliev, V. V.
A1  - Wakely, S. P.
A1  - Weinstein, A.
A1  - Welsing, R.
A1  - Wilhelm, Alina
A1  - Williams, D. A.
A1  - Zitzer, B.
T1  - Veritas observations of the BL LAC OBJECT PG 1553+113
JF  - The astrophysical journal : an international review of spectroscopy and astronomical physics
N2  - We present results from VERITAS observations of the BL Lac object PG 1553+113 spanning the years 2010, 2011, and 2012. The time-averaged spectrum, measured between 160 and 560 GeV, is well described by a power law with a spectral index of 4.33 +/- 0.09. The time-averaged integral flux above 200 GeV measured for this period was (1.69 +/- 0.06) x 10(-11) photons cm(-2) s(-1), corresponding to 6.9% of the Crab Nebula flux. We also present the combined gamma-ray spectrum from the Fermi Large Area Telescope and VERITAS covering an energy range from 100 MeV to 560 GeV. The data are well fit by a power law with an exponential cutoff at 101.9 +/- 3.2 GeV. The origin of the cutoff could be intrinsic to PG 1553+113 or be due to the gamma-ray opacity of our universe through pair production off the extragalactic background light (EBL). Given lower limits to the redshift of z > 0.395 based on optical/UV observations of PG 1553+113, the cutoff would be dominated by EBL absorption. Conversely, the small statistical uncertainties of the VERITAS energy spectrum have allowed us to provide a robust upper limit on the redshift of PG 1553+113 of z <= 0.62. A strongly elevated mean flux of (2.50 +/- 0.14) x10(-11) photons cm(-2) s(-1) (10.3% of the Crab Nebula flux) was observed during 2012, with the daily flux reaching as high as (4.44 +/- 0.71) x10(-11) photons cm(-2) s(-1) (18.3% of the Crab Nebula flux) on MJD 56048. The light curve measured during the 2012 observing season is marginally inconsistent with a steady flux, giving a chi(2) probability for a steady flux of 0.03%.
KW  - BL Lacertae objects: general
Y1  - 2015
U6  - https://doi.org/10.1088/0004-637X/799/1/7
SN  - 0004-637X
SN  - 1538-4357
VL  - 799
IS  - 1
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Pulkkinen, Otto
A1  - Metzler, Ralf
T1  - Variance-corrected Michaelis-Menten equation predicts transient rates of single-enzyme reactions and response times in bacterial gene-regulation
JF  - Scientific reports
N2  - Many chemical reactions in biological cells occur at very low concentrations of constituent molecules. Thus, transcriptional gene-regulation is often controlled by poorly expressed transcription-factors, such as E. coli lac repressor with few tens of copies. Here we study the effects of inherent concentration fluctuations of substrate-molecules on the seminal Michaelis-Menten scheme of biochemical reactions. We present a universal correction to the Michaelis-Menten equation for the reaction-rates. The relevance and validity of this correction for enzymatic reactions and intracellular gene-regulation is demonstrated. Our analytical theory and simulation results confirm that the proposed variance-corrected Michaelis-Menten equation predicts the rate of reactions with remarkable accuracy even in the presence of large non-equilibrium concentration fluctuations. The major advantage of our approach is that it involves only the mean and variance of the substrate-molecule concentration. Our theory is therefore accessible to experiments and not specific to the exact source of the concentration fluctuations.
Y1  - 2015
U6  - https://doi.org/10.1038/srep17820
SN  - 2045-2322
VL  - 5
PB  - Nature Publ. Group
CY  - London
ER  - 
TY  - JOUR
A1  - Pulkkinen, Otto
A1  - Metzler, Ralf
T1  - Variance-corrected Michaelis-Menten equation predicts transient rates of single-enzyme reactions and response times in bacterial gene-regulation
JF  - Scientific reports
N2  - Many chemical reactions in biological cells occur at very low concentrations of constituent molecules. Thus, transcriptional gene-regulation is often controlled by poorly expressed transcription-factors, such as E.coli lac repressor with few tens of copies. Here we study the effects of inherent concentration fluctuations of substrate-molecules on the seminal Michaelis-Menten scheme of biochemical reactions. We present a universal correction to the Michaelis-Menten equation for the reaction-rates. The relevance and validity of this correction for enzymatic reactions and intracellular gene-regulation is demonstrated. Our analytical theory and simulation results confirm that the proposed variance-corrected Michaelis-Menten equation predicts the rate of reactions with remarkable accuracy even in the presence of large non-equilibrium concentration fluctuations. The major advantage of our approach is that it involves only the mean and variance of the substrate-molecule concentration. Our theory is therefore accessible to experiments and not specific to the exact source of the concentration fluctuations.
Y1  - 2015
U6  - https://doi.org/10.1038/srep17820
SN  - 2045-2322
IS  - 5
PB  - Nature Publishing Group
CY  - London
ER  - 
TY  - JOUR
A1  - Dell'Angela, Martina
A1  - Anniyev, Toyli
A1  - Beye, Martin
A1  - Coffee, Ryan
A1  - Föhlisch, Alexander
A1  - Gladh, Jörgen
A1  - Kaya, Sarp
A1  - Katayama, Tetsuo
A1  - Krupin, Oleg
A1  - Nilsson, Anders
A1  - Nordlund, Dennis
A1  - Schlotter, William F.
A1  - Sellberg, Jonas A.
A1  - Sorgenfrei, Florian
A1  - Turner, Joshua J.
A1  - ÖstrÖm, Henrik
A1  - Ogasawara, Hirohito
A1  - Wolf, Martin
A1  - Wurth, Wilfried
T1  - Vacuum space charge effects in sub-picosecond soft X-ray photoemission on a molecular adsorbate layer
JF  - Structural dynamics
N2  - Vacuum space charge induced kinetic energy shifts of O 1s and Ru 3d core levels in femtosecond soft X-ray photoemission spectra (PES) have been studied at a free electron laser (FEL) for an oxygen layer on Ru(0001). We fully reproduced the measurements by simulating the in-vacuum expansion of the photoelectrons and demonstrate the space charge contribution of the high-order harmonics in the FEL beam. Employing the same analysis for 400 nm pump-X-ray probe PES, we can disentangle the delay dependent Ru 3d energy shifts into effects induced by space charge and by lattice heating from the femtosecond pump pulse. (C) 2015 Author(s).
Y1  - 2015
U6  - https://doi.org/10.1063/1.4914892
SN  - 2329-7778
VL  - 2
IS  - 2
PB  - American Institute of Physics
CY  - Melville
ER  - 
TY  - JOUR
A1  - Aleksic, J.
A1  - Ansoldi, S.
A1  - Antonelli, L. A.
A1  - Antoranz, P.
A1  - Babic, A.
A1  - Bangale, P.
A1  - de Almeida, U. Barres
A1  - Barrio, J. A.
A1  - Gonzalez, J. Becerra
A1  - Bednarek, W.
A1  - Bernardini, E.
A1  - Biasuzzi, B.
A1  - Biland, A.
A1  - Blanch Bigas, O.
A1  - Boller, A.
A1  - Bonnefoy, S.
A1  - Bonnoli, G.
A1  - Borracci, F.
A1  - Bretz, T.
A1  - Carmona, E.
A1  - Carosi, A.
A1  - Colin, P.
A1  - Colombo, E.
A1  - Contreras, J. L.
A1  - Cortina, J.
A1  - Covino, S.
A1  - Da Vela, P.
A1  - Dazzi, F.
A1  - De Angelis, A.
A1  - De Caneva, G.
A1  - De Lotto, B.
A1  - Wilhelmi, E. de Ona
A1  - Mendez, C. Delgado
A1  - Prester, Dijana Dominis
A1  - Dorner, D.
A1  - Doro, M.
A1  - Einecke, S.
A1  - Eisenacher, D.
A1  - Elsaesser, D.
A1  - Fonseca, M. V.
A1  - Font, L.
A1  - Frantzen, K.
A1  - Fruck, C.
A1  - Galindo, D.
A1  - Lopez, R. J. Garcia
A1  - Garczarczyk, M.
A1  - Terrats, D. Garrido
A1  - Gaug, M.
A1  - Godinovic, N.
A1  - Munoz, A. Gonzalez
A1  - Gozzini, S. R.
A1  - Hadasch, D.
A1  - Hanabata, Y.
A1  - Hayashida, M.
A1  - Herrera, J.
A1  - Hildebrand, D.
A1  - Hose, J.
A1  - Hrupec, D.
A1  - Hughes, G.
A1  - Idec, W.
A1  - Kadenius, V.
A1  - Kellermann, H.
A1  - Knoetig, M. L.
A1  - Kodani, K.
A1  - Konno, Y.
A1  - Krause, J.
A1  - Kubo, H.
A1  - Kushida, J.
A1  - La Barbera, A.
A1  - Lelas, D.
A1  - Lewandowska, N.
A1  - Lindfors, E.
A1  - Lombardi, S.
A1  - Lopez, M.
A1  - Lopez-Coto, R.
A1  - Lopez-Oramas, A.
A1  - Lorenz, E.
A1  - Lozano, I.
A1  - Makariev, M.
A1  - Mallot, K.
A1  - Maneva, G.
A1  - Mankuzhiyil, N.
A1  - Mannheim, K.
A1  - Maraschi, L.
A1  - Marcote, B.
A1  - Mariotti, M.
A1  - Martinez, M.
A1  - Mazin, D.
A1  - Menzel, U.
A1  - Miranda, J. M.
A1  - Mirzoyan, R.
A1  - Moralejo, A.
A1  - Munar-Adrover, P.
A1  - Nakajima, D.
A1  - Niedzwiecki, A.
A1  - Nilsson, K.
A1  - Nishijima, K.
A1  - Noda, K.
A1  - Orito, R.
A1  - Overkemping, A.
A1  - Paiano, S.
A1  - Palatiello, M.
A1  - Paneque, D.
A1  - Paoletti, R.
A1  - Paredes, J. M.
A1  - Paredes-Fortuny, X.
A1  - Persic, M.
A1  - Moroni, P. G. Prada
A1  - Prandini, E.
A1  - Puljak, I.
A1  - Reinthal, R.
A1  - Rhode, W.
A1  - Ribo, M.
A1  - Rico, J.
A1  - Garcia, J. Rodriguez
A1  - Rugamer, S.
A1  - Saito, T.
A1  - Saito, K.
A1  - Satalecka, K.
A1  - Scalzotto, V.
A1  - Scapin, V.
A1  - Schultz, C.
A1  - Schweizer, T.
A1  - Sun, S.
A1  - Shore, S. N.
A1  - Sillanpaa, A.
A1  - Sitarek, J.
A1  - Snidaric, I.
A1  - Sobczynska, D.
A1  - Spanier, F.
A1  - Stamatescu, V.
A1  - Stamerra, A.
A1  - Steinbring, T.
A1  - Steinke, B.
A1  - Storz, J.
A1  - Strzys, M.
A1  - Takalo, L.
A1  - Takami, H.
A1  - Tavecchio, F.
A1  - Temnikov, P.
A1  - Terzic, T.
A1  - Tescaro, D.
A1  - Teshima, M.
A1  - Thaele, J.
A1  - Tibolla, O.
A1  - Torres, D. F.
A1  - Toyama, T.
A1  - Treves, A.
A1  - Uellenbeck, M.
A1  - Vogler, P.
A1  - Zanin, R.
A1  - Archambault, S.
A1  - Archer, A.
A1  - Beilicke, M.
A1  - Benbow, W.
A1  - Berger, K.
A1  - Bird, R.
A1  - Biteau, Jonathan
A1  - Buckley, J. H.
A1  - Bugaev, V.
A1  - Cerruti, M.
A1  - Chen, Xiaoming
A1  - Ciupik, L.
A1  - Collins-Hughes, E.
A1  - Cui, W.
A1  - Eisch, J. D.
A1  - Falcone, A.
A1  - Feng, Q.
A1  - Finley, J. P.
A1  - Fortin, P.
A1  - Fortson, L.
A1  - Furniss, A.
A1  - Galante, N.
A1  - Gillanders, G. H.
A1  - Griffin, S.
A1  - Gyuk, G.
A1  - Hakansson, Nils
A1  - Holder, J.
A1  - Johnson, C. A.
A1  - Kaaret, P.
A1  - Kar, P.
A1  - Kertzman, M.
A1  - Kieda, D.
A1  - Lang, M. J.
A1  - McArthur, S.
A1  - McCann, A.
A1  - Meagher, K.
A1  - Millis, J.
A1  - Moriarty, P.
A1  - Ong, R. A.
A1  - Otte, A. N.
A1  - Perkins, J. S.
A1  - Pichel, A.
A1  - Pohl, Manuela
A1  - Popkow, A.
A1  - Prokoph, H.
A1  - Pueschel, Elisa
A1  - Ragan, K.
A1  - Reyes, L. C.
A1  - Reynolds, P. T.
A1  - Richards, G. T.
A1  - Roache, E.
A1  - Rovero, A. C.
A1  - Sembroski, G. H.
A1  - Shahinyan, K.
A1  - Staszak, D.
A1  - Telezhinsky, Igor O.
A1  - Tucci, J. V.
A1  - Tyler, J.
A1  - Varlotta, A.
A1  - Wakely, S. P.
A1  - Welsing, R.
A1  - Wilhelm, Alina
A1  - Williams, D. A.
A1  - Buson, S.
A1  - Finke, J.
A1  - Villata, M.
A1  - Raiteri, C.
A1  - Aller, H. D.
A1  - Aller, M. F.
A1  - Cesarini, A.
A1  - Chen, W. P.
A1  - Gurwell, M. A.
A1  - Jorstad, S. G.
A1  - Kimeridze, G. N.
A1  - Koptelova, E.
A1  - Kurtanidze, O. M.
A1  - Kurtanidze, S. O.
A1  - Lahteenmaki, A.
A1  - Larionov, V. M.
A1  - Larionova, E. G.
A1  - Lin, H. C.
A1  - McBreen, B.
A1  - Moody, J. W.
A1  - Morozova, D. A.
A1  - Marscher, A. P.
A1  - Max-Moerbeck, W.
A1  - Nikolashvili, M. G.
A1  - Perri, M.
A1  - Readhead, A. C. S.
A1  - Richards, J. L.
A1  - Ros, J. A.
A1  - Sadun, A. C.
A1  - Sakamoto, T.
A1  - Sigua, L. A.
A1  - Smith, P. S.
A1  - Tornikoski, M.
A1  - Troitsky, I. S.
A1  - Wehrle, A. E.
A1  - Jordan, B.
T1  - Unprecedented study of the broadband emission of Mrk 421 during flaring activity in March 2010
JF  - Astronomy and astrophysics : an international weekly journal
N2  - Context. Because of its proximity, Mrk 421 is one of the best sources on which to study the nature of BL Lac objects. Its proximity allows us to characterize its broadband spectral energy distribution (SED).
 Aims. The goal is to better understand the mechanisms responsible for the broadband emission and the temporal evolution of Mrk 421. These mechanisms may also apply to more distant blazars that cannot be studied with the same level of detail.
 Methods. A flare occurring in March 2010 was observed for 13 consecutive days (from MJD 55 265 to MJD 55 277) with unprecedented wavelength coverage from radio to very high energy (VHE; E > 100 GeV) gamma-rays with MAGIC, VERITAS, Whipple, Fermi-LAT, MAXI, RXTE, Swift, GASP-WEBT, and several optical and radio telescopes. We modeled the day-scale SEDs with one-zone and two-zone synchrotron self-Compton (SSC) models, investigated the physical parameters, and evaluated whether the observed broadband SED variability can be associated with variations in the relativistic particle population.
 Results. The activity of Mrk 421 initially was high and then slowly decreased during the 13-day period. The flux variability was remarkable at the X-ray and VHE bands, but it was minor or not significant at the other bands. The variability in optical polarization was also minor. These observations revealed an almost linear correlation between the X-ray flux at the 2-10 keV band and the VHE gamma-ray flux above 200 GeV, consistent with the gamma-rays being produced by inverse-Compton scattering in the Klein-Nishina regime in the framework of SSC models. The one-zone SSC model can describe the SED of each day for the 13 consecutive days reasonably well, which once more shows the success of this standard theoretical scenario to describe the SEDs of VHE BL Lacs such as Mrk 421. This flaring activity is also very well described by a two-zone SSC model, where one zone is responsible for the quiescent emission, while the other smaller zone, which is spatially separated from the first, contributes to the daily variable emission occurring at X-rays and VHE gamma-rays. The second blob is assumed to have a smaller volume and a narrow electron energy distribution with 3 x 10(4) < gamma < 6 x 10(5), where. is the Lorentz factor of the electrons. Such a two-zone scenario would naturally lead to the correlated variability at the X-ray and VHE bands without variability at the optical/UV band, as well as to shorter timescales for the variability at the X-ray and VHE bands with respect to the variability at the other bands.
 Conclusions. Both the one-zone and the two-zone SSC models can describe the daily SEDs via the variation of only four or five model parameters, under the hypothesis that the variability is associated mostly with the underlying particle population. This shows that the particle acceleration and cooling mechanism that produces the radiating particles might be the main mechanism responsible for the broadband SED variations during the flaring episodes in blazars. The two-zone SSC model provides a better agreement with the observed SED at the narrow peaks of the low-and high-energy bumps during the highest activity, although the reported one-zone SSC model could be further improved by varying the parameters related to the emitting region itself (delta, B and R), in addition to the parameters related to the particle population.
KW  - radiation mechanisms: non-thermal
KW  - galaxies: active
KW  - BL Lacertae objects: individual: Mrk 421
KW  - gamma rays: galaxies
Y1  - 2015
U6  - https://doi.org/10.1051/0004-6361/201424811
SN  - 0004-6361
SN  - 1432-0746
VL  - 578
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Bodrova, Anna S.
A1  - Chechkin, Aleksei V.
A1  - Cherstvy, Andrey G.
A1  - Metzler, Ralf
T1  - Ultraslow scaled Brownian motion
JF  - New journal of physics : the open-access journal for physics
N2  - We define and study in detail utraslow scaled Brownian motion (USBM) characterized by a time dependent diffusion coefficient of the form D(t) similar or equal to 1/t. For unconfined motion the mean squared displacement (MSD) of USBM exhibits an ultraslow, logarithmic growth as function of time, in contrast to the conventional scaled Brownian motion. In a harmonic potential the MSD of USBM does not saturate but asymptotically decays inverse-proportionally to time, reflecting the highly non-stationary character of the process. We show that the process is weakly non-ergodic in the sense that the time averaged MSD does not converge to the regular MSD even at long times, and for unconfined motion combines a linear lag time dependence with a logarithmic term. The weakly non-ergodic behaviour is quantified in terms of the ergodicity breaking parameter. The USBM process is also shown to be ageing: observables of the system depend on the time gap between initiation of the test particle and start of the measurement of its motion. Our analytical results are shown to agree excellently with extensive computer simulations.
KW  - anomalous diffusion
KW  - stochastic processes
KW  - ageing
Y1  - 2015
U6  - https://doi.org/10.1088/1367-2630/17/6/063038
SN  - 1367-2630
VL  - 17
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  -