The radio-loud quasar SDSS J013127.34-032100.1at a redshift z=5.18 is one of
the most distant radio-loud objects. The radio to optical flux ratio (i.e. the
radio-loudness) of the source is large, ...making it a promising blazar candidate.
Its overall spectral energy distribution, completed by the X-ray flux and
spectral slope derived through Target of Opportunity Swift/XRT observations, is
interpreted by a non-thermal jet plus an accretion disc and molecular torus
model. We estimate that its black hole mass is (1.1+-0.2)1e10 Msun. for an
accretion efficiency eta=0.08, scaling roughly linearly with eta. Although
there is a factor ~2 of systematic uncertainty, this black hole mass is the
largest found at these redshifts in a radio loud object. We derive a viewing
angle between 3 and 5 degrees. This implies that there must be other (hundreds)
sources with the same black hole mass of SDSS J013127.34-032100.1, but whose
jets are pointing away from Earth. We discuss the problems posed by the
existence of such large black hole masses at such redshifts, especially in
jetted quasars. In fact, if they are associated to rapidly spinning black
holes, the accretion efficiency is high, implying a slower pace of black hole
growth with respect to radio-quiet quasars.
The physics of the non-thermal Universe provides information on the acceleration mechanisms in extreme environments, such as black holes and relativistic jets, neutron stars, supernovae or clusters ...of galaxies. In the presence of magnetic fields, particles can be accelerated towards relativistic energies. As a consequence, radiation along the entire electromagnetic spectrum can be observed, and extreme environments are also the most likely sources of multi-messenger emission. The most energetic part of the electromagnetic spectrum corresponds to the very-high-energy (VHE, E>100 GeV) gamma-ray regime, which can be extensively studied with ground based Imaging Atmospheric Cherenkov Telescopes (IACTs). The results obtained by the current generation of IACTs, such as H.E.S.S., MAGIC, and VERITAS, demonstrate the crucial importance of the VHE band in understanding the non-thermal emission of extreme environments in our Universe. In some objects, the energy output in gamma rays can even outshine the rest of the broadband spectrum. The Cherenkov Telescope Array (CTA) is the next generation of IACTs, which, with cutting edge technology and a strategic configuration of ~100 telescopes distributed in two observing sites, in the northern and southern hemispheres, will reach better sensitivity, angular and energy resolution, and broader energy coverage than currently operational IACTs. With CTA we can probe the most extreme environments and considerably boost our knowledge of the non-thermal Universe.
We update a flux-limited complete sample of Swift-based SGRBs (SBAT4, D'Avanzo et al. 2014), bringing it to 25 events and doubling its previous redshift range. We then evaluate the column densities ...of the events in the updated sample, in order to compare them with the NH distribution of LGRBs, using the sample BAT6ext (Arcodia et al. 2016). We rely on Monte Carlo simulations of the two populations and compare the computed NH distributions with a two sample Kolmogorov Smirnov (K-S) test. We then study how the K-S probability varies with respect to the redshift range we consider. We find that the K-S probability keeps decreasing as redshift increases until at z\(\sim\)1.8 the probability that short and long GRBs come from the same parent distribution drops below 1\(\%\). This testifies for an observational difference among the two populations. This difference may be due to the presence of highly absorbed LGRBs above z\(\sim\)1.3, which have not been observed in the SGRB sample yet, although this may be due to our inability to detect them, or to the relatively small sample size.
The discovery of gravitational waves, high-energy neutrinos or the very-high-energy counterpart of gamma-ray bursts has revolutionized the high-energy and transient astrophysics community. The ...development of new instruments and analysis techniques will allow the discovery and/or follow-up of new transient sources. We describe the prospects for the Cherenkov Telescope Array (CTA), the next-generation ground-based gamma-ray observatory, for multi-messenger and transient astrophysics in the decade ahead. CTA will explore the most extreme environments via very-high-energy observations of compact objects, stellar collapse events, mergers and cosmic-ray accelerators.
Observations of the prompt afterglow of g-ray burst events are unanimously considered of paramount importance for GRB science and cosmology. Such observations at NIR wavelengths are even more ...promising allowing the monitoring of high-z Ly-a absorbed bursts as well as events occurring in dusty star-forming regions. In these pages we present rapid eye mount (REM), a fully robotized fast slewing telescope equipped with a high throughput NIR (Z, J, H, K) camera dedicated to detecting the prompt IR afterglow. REM can discover objects at extremely high redshift and trigger large telescopes to observe them. The REM telescope will simultaneously feed REM optical slitless spectrograph (ROSS) via a dichroic. ROSS will intensively monitor the prompt optical continuum of GRB afterglows. The synergy between the REM-IR camera and the ROSS spectrograph makes REM a powerful observing tool for any kind of fast transient phenomena. Beside its ambitious scientific goals, REM is also technically challenging since it represent the first attempt to locate a NIR camera on a small telescope providing, with ROSS, unprecedented simultaneous wavelength coverage on a telescope of this size.
We present optical and near-infrared observations of the afterglow of the gamma-ray burst GRB 050904. We derive a photometric redshift $z = 6.3$, estimated from the presence of the Lyman break ...falling between the I and J filters. This is by far the most distant GRB known to date. Its isotropic-equivalent energy is $3.4 \times 10^{53}$ erg in the rest-frame 110-1100 keV energy band. Despite the high redshift, both the prompt and the afterglow emission are not peculiar with respect to other GRBs. We find a break in the J-band light curve at $t_{\rm b} = 2.6 \pm 1.0$ d (observer frame). If we assume this is the jet break, we derive a beaming-corrected energy $E_\gamma \sim (4 \div 12) \times 10^{51}$ erg. This limit shows that GRB 050904 is consistent with the Amati and Ghirlanda relations. This detection is consistent with the expected number of GRBs at $z > 6$ and shows that GRBs are a powerful tool to study the star formation history up to very high redshift.
This white paper briefly summarizes the importance of the study of relativistic cosmic rays, both as a constituent of our Universe, and through their impact on stellar and galactic evolution. The ...focus is on what can be learned over the coming decade through ground-based gamma-ray observations over the 20 GeV to 300 TeV range. The majority of the material is drawn directly from "Science with the Cherenkov Telescope Array", which describes the overall science case for CTA. We request that authors wishing to cite results contained in this white paper cite the original work.
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