Abstracts of Interest
Selected by:
Sally Robertson
Abstract: 1805.07765
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Title: $Fermi$-LAT detection of a transient $γ$-ray source in the direction of a distant blazar B3 1428+422 at $z =4.72$
(Submitted on 20 May 2018)
Abstract: We report the detection of a transient $\gamma$-ray source in the direction of B3 1428+422 ($z=4.72$) by analyzing the 110-month $Fermi$-LAT Pass 8 data. The new transient $\gamma$-ray source is rather similar to the known high redshift $\gamma$-ray blazars in many aspects, including the soft spectrum, high luminosity (assuming a redshift of $z=4.72$) as well as significant variability. In view of these facts, we suggest that the newly discovered transient is the $\gamma$-ray counterpart of B3 1428+422, which is thus the $most$ $distant$ GeV source detected so far. The detection of a group of such distant $\gamma-$ray blazars will be helpful to reconstruct the evolution of the luminosity function and to study the extragalactic background light at such high redshifts.
Abstract: 1805.07995
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Title: An upper limit on the strength of the extragalactic magnetic field from ultra-high-energy cosmic-ray anisotropy
(Submitted on 21 May 2018)
Abstract: If ultra-high-energy cosmic rays originate from extragalactic sources, the offsets of their arrival directions from these sources imply an upper limit on the strength of the extragalactic magnetic field. The Pierre Auger Collaboration has recently reported that anisotropy in the arrival directions of cosmic rays is correlated with several types of extragalactic objects. If these cosmic rays originate from these objects, they imply a limit on the extragalactic magnetic field strength of B < 0.7-2.2 x 10^-9 (lambda_B / 1 Mpc)^-1/2 G for coherence lengths lambda_B < 100 Mpc and B < 0.7-2.2 x 10^-10 G at larger scales. This is comparable to existing upper limits at lambda_B = 1 Mpc, and improves on them by a factor 4-12 at larger scales. The principal source of uncertainty in our results is the unknown cosmic-ray composition.
Abstract: 1805.10227
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Title: LOFAR observations of the mode-switching pulsar B0943+10
(Submitted on 22 May 2018)
Abstract: PSR B0943+10 is an old non-recycled pulsar which for decades has been mostly known for its rapid and spontaneous radio mode switching. Recently, Hermsen et al. (2013) discovered correlated changes in the thermal X-ray emission from the polar cap, thus demonstrating that radio modes are not just a product of the local changes in the radio emission region, but a sign of some global magnetospheric transformation. At about the same time, owing to the commissioning of the new generation of low-frequency radio arrays, the broadband observations at the lowest edge of ionospheric transparency window became available. At these radio frequencies profile morphology and the single-pulse properties of PSR B0943+10's emission become very dynamic, providing details not only about the emission itself, but also about the conditions in the polar gap. Here, I will present the recent results of the LOFAR observations of PSR B0943+10 and discuss their contribution to the multiwavelength picture.
Abstract: 1805.09704
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Title: A global analysis for searching neutrinos associated with the black holes merging gravitational wave events
(Submitted on 24 May 2018)
Abstract: Several neutrino observatories have searched for coincident neutrino signals associated with gravitational waves induced by the merging of two black holes.No statistically significant neutrino signal in excess of background level was observed.These experiments use different neutrino detection technologies and are sensitive to various neutrino types.A combined analysis was performed on the KamLAND, Super-Kamiokande and Borexino experimental data with a frequentist statistical approach to achieve a global picture of the associated neutrino fluence.Both monochromatic and Fermi-Dirac neutrino spectra were assumed in the calculation.The final results are consistent with null neutrino signals associated with a binary of black holes merging process.The derived 90\% confidence level upper limits on the fluence and luminosity of various neutrino types are presented for neutrino energy less than 110 MeV.
Abstract: 1805.09343
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Title: GRB and blazar jets shining through their stripes
(Submitted on 23 May 2018)
Abstract: Black-hole driven relativistic astrophysical jets, such as blazars and gamma-ray bursts (GRBs), are powerful sources of electromagnetic radiation. Their emission is powered by some energy dissipation and particle acceleration mechanism operating in-situ at large distances from the black hole. We propose that the formation of the dissipative structures in the jet is controlled by the time variability of the accretion disc. We argue that the open magnetic field lines through the black hole, which drive a strongly magnetized jet, may have their polarity reversing over time-scales related to the growth of the magneto-rotational dynamo in the disc. Consequently, the jet is characterized by an alternating toroidal field polarity along its propagation axis, i.e., it is a "striped jet". Magnetic reconnection in the current sheets that form between the stripes dissipates the alternating-field energy and thus powers further jet acceleration. Here, we consider a jet with a broad distribution of stripe widths $l>l_{\rm min}$, above a dominant scale $l_{\rm min}$. We find that the bulk acceleration of the jet, driven by the annihilation of the stripes, is very gradual. The dissipation rate peaks at a distance $z_{\rm peak}\sim 10^6 R_g\, (\Gamma_\infty/30)^2\, (l_{\rm min}/1000R_g)$, where $R_{g}$ is the black-hole's gravititional radius and $\Gamma_{\infty}$ the jet's asymptotic Lorentz factor, and exhibits a very broad plateau extending by $\sim 4-5$ orders of magnitude in distance. The prolonged energy dissipation accounts for the flat-to-inverted long-wavelength spectra commonly observed in jets. The model can also account for the broad range of flaring timescales of blazars and the fact that their bulk acceleration appears to continue out to ~100 pc scales. In GRB jets, the model predicts comparable power for the photopsheric and Thomson-thin emission components.
Abstract: 1805.08675
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Title: Long-term monitoring of the ANTARES optical module efficiencies using $^{40}\mathrm{K}$ decays in sea water
(Submitted on 22 May 2018)
Abstract: Cherenkov light induced by radioactive decay products is one of the major sources of background light for deep-sea neutrino telescopes such as ANTARES. These decays are at the same time a powerful calibration source. Using data collected by the ANTARES neutrino telescope from mid 2008 to 2017, the time evolution of the photon detection efficiency of optical modules is studied. A modest loss of only 20% in 9 years is observed. The relative time calibration between adjacent modules is derived as well.
This page created: Tue May 29 10:51:58 ACST 2018 by Sally Robertson
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