The grand challenges of contemporary fundamental physics—dark matter, dark energy, vacuum energy, inflation and early universe cosmology, singularities and the hierarchy problem—all involve gravity as a key component. And of all gravitational phenomena, black holes stand out in their elegant simplicity, while harbouring some of the most remarkable predictions of General Relativity: event horizons, singularities and ergoregions. The hitherto invisible landscape of the gravitational Universe is being unveiled before our eyes: the historical direct detection of gravitational waves by the LIGO-Virgo collaboration marks the dawn of a new era of scientific exploration. Gravitational-wave astronomy will allow us to test models of black hole formation, growth and evolution, as well as models of gravitational-wave generation and propagation. It will provide evidence for event horizons and ergoregions, test the theory of General Relativity itself, and may reveal the existence of new fundamental fields. The synthesis of these results has the potential to radically reshape our understanding of the cosmos and of the laws of Nature. The purpose of this work is to present a concise, yet comprehensive overview of the state of the art in the relevant fields of research, summarize important open problems, and lay out a roadmap for future progress. This write-up is an initiative taken within the framework of the European Action on ‘Black holes, Gravitational waves and Fundamental Physics’.

GRB 980425 and GRB 031203 are apparently two outliers with respect to the correlation between the isotropic equivalent energy E_iso emitted in the prompt radiation phase and the peak frequency E_peak of the spectrum in a vF(v) representation (the so-called Amati relation). We discuss if these two bursts are really different from the others or if their location in the E_iso-E_peak plane is the result of other effects, such as viewing them off-axis, or through a scattering screen, or a misinterpretation of their spectral properties. The latter case seems particularly interesting after GRB 060218, that, unlike GRB 031203 and GRB 980425, had a prompt emission detected both in hard and soft X-rays which lasted ~2800 seconds. This allowed to determine its E_peak and total emitted energy. Although it shares with GRB 031203 the total energetics, it is not an outlier with respect to the Amati correlation. We then investigate if a hard-to-soft spectral evolution in GRB 031203 and GRB 980425, consistent with all the observed properties, can give rise to a time integrated spectrum with an E_peak consistent with the Amati relation.Comment: 13 pages, 9 figures, 2 tables. Accepted for publication in MNRA

We derive the correlation between the peak luminosity Liso and the peak energy of the νFν spectrum Epeak using 25 long gamma‐ray bursts (GRBs) with firm redshift measurements. We find that its slope is similar to that of the correlation between the time‐integrated isotropic emitted energy Eiso and Epeak. For the 16 GRBs in our sample with estimated jet opening angle, we compute the collimation‐corrected peak luminosity Lγ, and find that it correlates with Epeak. This correlation has, however, a scatter larger than that of the correlation between Epeak and Eγ (the time‐integrated emitted energy, corrected for collimation), which we ascribe to the fact that the opening angle is estimated through the global energetics. We have then selected a large sample of 442 GRBs with pseudo‐redshifts, derived through the lag–luminosity relation, to test the existence of the Liso–Epeak correlation. With this sample we also explore the possibility of a correlation between time‐resolved quantities, namely Lpiso and the peak energy at the peak of emission Eppeak.

For a sample of long γ‐ray bursts (GRBs) with known redshift, we study the distribution of the evolutionary tracks on the rest‐frame luminosity‐peak energy Liso−E′p diagram. We are interested in exploring the extension of the ‘Yonetoku’ correlation to any phase of the prompt light curve, and in verifying how the high‐signal prompt duration time, T′f, in the rest frame correlates with the residuals of such correlation. For our purpose, we separately analyse two samples of time‐resolved spectra corresponding to 32 GRBs with peak fluxes Fp > 1.8 phot cm−2 s−1 from the Swift‐BAT detector, and seven bright GRBs from the Compton Gamma‐ray Observatory (CGRO)‐BATSE detector previously processed by Kaneko et al. After constructing the Liso−E′p diagram, we discuss the relevance of selection effects, finding that they could significantly affect the correlation. However, we find that these effects are much less significant in the Liso T′f−E′p diagram, where the intrinsic scatter reduces significantly. We apply further corrections in order to reduce the intrinsic scatter even more. For the subsamples of GRBs (seven from Swift and five from CGRO) with measured jet break time, tj, we analyse the effects of correcting Liso by jet collimation. We find that (i) the scatter around the correlation is reduced, and (ii) this scatter is dominated by the internal scatter of the individual evolutionary tracks. These results suggest that the time‐integrated ‘Amati’ and ‘Ghirlanda’ correlations are consequences of the time‐resolved features, not of selection effects, and therefore call for a physical origin. We finally remark the relevance of looking inside the nature of the evolutionary tracks.

Motivated by the recent observational and theoretical evidence that long gamma-ray bursts (GRBs) are likely associated with low metallicity, rapidly rotating massive stars, we examine the cosmological star formation rate (SFR) below a critical metallicity Z crit ∼ 1/10-1/5 Z , to estimate the event rate of high redshift long GRB progenitors. To this purpose, we exploit a galaxy formation scenario already successfully tested on a wealth of observational data on (proto)spheroids, Lyman break galaxies, Lyman α emitters, submm galaxies, quasars and local early-type galaxies. We find that the predicted rate of long GRBs amounts to about 300 events yr −1 sr −1 , of which about 30 per cent occur at z 6. Correspondingly, the GRB number counts well agree with the bright SWIFT data, without the need for an intrinsic luminosity evolution. Moreover, the above framework enables us to predict the properties of the GRB host galaxies. Most GRBs are associated with low-mass galaxy haloes M H 10 11 M , and effectively trace the formation of small galaxies in such haloes. The hosts are young, with age smaller than 5 × 10 7 yr, gas rich, but poorly extincted (A V 0.1) because of their chemical immaturity; this also implies high specific SFR and quite extreme α-enhancement. Only the minority of hosts residing in large haloes with M H 10 12 M has larger extinction (A V ∼ 0.7 − 1), SFRs exceeding 100 M yr −1 and can be detected at submm wavelengths. Most of the hosts have ultraviolet magnitudes in the range −20 M 1350 −16, and Lyman α luminosity in the range 2 × 10 40 L Lyman α 2 × 10 42 erg s −1 . GRB hosts are thus tracing the faint end of the luminosity function of Lyman break galaxies and Lyman α emitters. Finally, our results imply that the population of 'dark' GRBs occur mostly in faint hosts at high redshift, rather than in dusty hosts at low redshift.

We study seven gamma‐ray bursts (GRBs), detected both by the Burst And Transient Source Experiment (BATSE) instrument, onboard the Compton Gamma‐ray Observatory, and by the Wide Field Camera (WFC), onboard BeppoSAX. These bursts have measured spectroscopic redshifts and are a sizeable fraction of the bursts defining the correlation between the peak energy Epeak (i.e. the peak of the νFν spectrum) and the total prompt isotropic energy Eiso (so‐called ‘Amati’ relation). Recent theoretical interpretations of this correlation assume that blackbody emission dominates the time‐resolved spectra of GRBs, even if, in the time‐integrated spectrum, its presence may be hidden by the change of its temperature and by the dilution of a possible non‐thermal power‐law component. We perform a time‐resolved spectral analysis and show that the sum of a power law and a blackbody gives acceptable fits to the time‐dependent spectra within the BATSE energy range but overpredicts the flux in the WFC X‐ray range. Moreover, a fit with a cut‐off power law plus a blackbody is consistent with the WFC data but the blackbody component contributes a negligible fraction of the total flux. On the contrary, we find that fitting the spectra with a Band model or a simple cut‐off power‐law model yields an X‐ray flux and spectral slope which well matches the WFC spectra.

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We present the updated INTEGRAL catalogue of gamma-ray bursts (GRBs) observed between December 2002 and February 2012. The catalogue contains the spectral parameters for 59 GRBs localized by the INTEGRAL Burst Alert System (IBAS). We used the data from the two main instruments on board the INTEGRAL satellite: the spectrometer SPI (SPectrometer on INTEGRAL) nominally covering the energy range 20 keV−8 MeV, and the imager IBIS (the Imager on Board the INTEGRAL Satellite) operating in the range from 15 keV to 10 MeV. For the spectral analysis we applied a new data extraction technique, developed to explore the energy regions of highest sensitivity for both instruments, SPI and IBIS. It allowed us to analyse the GRB spectra over a broad energy range and to determine the bursts' spectral peak energies. The spectral analysis was performed on the whole sample of GRBs triggered by IBAS, including all the events observed in the period December 2002 to February 2012. The catalogue contains the trigger times, burst coordinates, positional errors, durations, and peak fluxes for 28 unpublished GRBs observed between September 2008 and February 2012. The light curves in the 20−200 keV energy band of these events were derived using IBIS data. We compare the prompt emission properties of the INTEGRAL GRB sample with the BATSE and Fermi samples.