On the optical and X-ray afterglows of gamma ray bursts

We severely criticize the consuetudinary analysis of the afterglows of gamma-ray bursts (GRBs) in the conical-ejection fireball scenarios. We argue that, instead, recent observations imply that the long-duration GRBs and their afterglows are produced by highly relativistic jets of cannonballs (CBs) emitted in supernova explosions. The CBs are heated by their collision with the supernova shell. The GRB is the boosted surface radiation the CBs emit as they reach the transparent outskirts of the shell. The exiting CBs further decelerate by sweeping up interstellar matter (ISM). The early X-ray afterglow is dominated by thermal bremsstrahlung from the cooling CBs, the optical afterglow by synchrotron radiation from the ISM electrons swept up by the CBs. We show that this model fits simply and remarkably well all the measured optical afterglows of the 15 GRBs with known redshift, including that of GRB 990123, for which unusually prompt data are available. We demonstrate that GRB 980425 was a normal GRB produced by SN1998bw, with standard X-ray and optical afterglows. We find that the very peculiar afterglow of GRB 970508 can be explained if its CBs encountered a significant jump in density as they moved through the ISM. The afterglows of the nearest 8 of the known-redshift GRBs show various degrees of evidence for an association with a supernova akin to SN1998bw. In all other cases such an association, even if present, would have been undetectable with the best current photometric sensitivities. This gives strong support to the proposition that most, maybe all, of the long-duration GRBs are associated with supernovae. Though our emphasis is on optical afterglows, we also provide an excellent description of X-ray afterglows.Comment: Includes fits to the and X-ray and optical afterglows of all GRBs with known redshift prior to July 2001 and an alternative interpretation of the peculiar X-ray and optical afterglows of GRB 970508. In press in Astronomy and Astrophysic

On the radio afterglow of gamma ray bursts

We use the cannonball (CB) model of gamma ray bursts (GRBs) to predict the spectral and temporal behaviour of their radio afterglows (AGs). A single simple expression describes the AGs at all times and frequencies; its high-frequency limit reproduces the successful CB model predictions for optical and X-ray AGs. We analyze all of the observed radio AGs of GRBs with known redshifts, including those of the exceptionally close-by GRB 980425. We also study in detail the time-evolution of the AGs' spectral index. The agreement between theory and observations is excellent, even though the CB model is extremely frugal in the number of parameters required to explain the radio observations. We propose to use the scintillations in the radio AGs of GRBs to verify and measure the hyperluminal speed of their jetted CBs, whose apparent angular velocity is of the same order of magnitude as that of galactic pulsars, consistently measured directly, or via scintillations.Comment: Accepted for publication in A&

Review of Speculative "Disaster Scenarios" at RHIC

We discuss speculative disaster scenarios inspired by hypothetical new fundamental processes that might occur in high energy relativistic heavy ion collisions. We estimate the parameters relevant to black hole production; we find that they are absurdly small. We show that other accelerator and (especially) cosmic ray environments have already provided far more auspicious opportunities for transition to a new vacuum state, so that existing observations provide stringent bounds. We discuss in most detail the possibility of producing a dangerous strangelet. We argue that four separate requirements are necessary for this to occur: existence of large stable strangelets, metastability of intermediate size strangelets, negative charge for strangelets along the stability line, and production of intermediate size strangelets in the heavy ion environment. We discuss both theoretical and experimental reasons why each of these appears unlikely; in particular, we know of no plausible suggestion for why the third or especially the fourth might be true. Given minimal physical assumptions the continued existence of the Moon, in the form we know it, despite billions of years of cosmic ray exposure, provides powerful empirical evidence against the possibility of dangerous strangelet production.Comment: 28 pages, REVTeX; minor revisions for publication (Reviews of Modern Physics, ca. Oct. 2000); email to [email protected]

Comparing and contrasting the νμ→ντ\nu_{\mu} \to \nu_{\tau} and νμ→νs\nu_{\mu} \to \nu_s solutions to the atmospheric neutrino problem with SuperKamiokande data

The $\nu_{\mu} \to \nu_{\tau}$ and $\nu_{\mu} \to \nu_s$ solutions to the atmospheric neutrino problem are compared with SuperKamiokande data. The differences between these solutions due to matter effects in the Earth are calculated for the ratio of $\mu$-like to $e$-like events and for up-down flux asymmetries. These quantities are chosen because they are relatively insensitive to theoretical uncertainties in the overall neutrino flux normalisation and detection cross-sections and efficiencies. A $\chi^2$ analysis using these quantities is performed yielding $3\sigma$ ranges which are approximately given by $(0.725 - 1.0, 4 \times 10^{-4} - 2 \times 10^{-2} eV^2)$ and $(0.74 - 1.0, 1 \times 10^{-3} - 2 \times 10^{-2} eV^2)$ for $(\sin^2 2\theta,\Delta m^2)$ for the $\nu_{\mu} \to \nu_{\tau}$ and $\nu_{\mu} \to \nu_s$ solutions, respectively. Values of $\Delta m^2$ smaller than about $2 \times 10^{-3}$ eV$^2$ are disfavoured for the $\nu_{\mu} \to \nu_s$ solution, suggesting that future long baseline experiments should see a positive signal if this scenario is the correct one.Comment: revtex, 22 pages, 12 figure

Four--Neutrino Oscillation Solutions of the Solar Neutrino Problem

We present an analysis of the neutrino oscillation solutions of the solar neutrino problem in the framework of four-neutrino mixing where a sterile neutrino is added to the three standard ones. We perform a fit to the full data set corresponding to the 825-day Super-Kamiokande data sample as well as to Chlorine, GALLEX and SAGE and Kamiokande experiments. In our analysis we use all measured total event rates as well as all Super-Kamiokande data on the zenith angle dependence and the recoil electron energy spectrum. We consider both transitions via the Mikheyev-Smirnov-Wolfenstein (MSW) mechanism as well as oscillations in vacuum (just-so) and find the allowed solutions for different values of the additional mixing angles. This framework permits transitions into active or sterile neutrinos controlled by the additional parameter $\cos^2(\vartheta_{23}) \cos^2(\vartheta_{24})$ . We discuss the maximum allowed values of this additional mixing parameter for the different solutions.Comment: 28 pages Latex file using RevTeX. 8 postscript figures included (bitmapped for compression). Detailed explanation of criterion 3 and lower two graphs of Fig. 8. Misprints corrected in table II.A full version of the paper can be found at http://ific.uv.es/~penya/papers/four

Gamma-ray bursts: optical afterglows in the deep Newtonian phase

Gamma-ray burst remnants become trans-relativistic typically in days to tens of days, and they enter the deep Newtonian phase in tens of days to months, during which the majority of shock-accelerated electrons will no longer be highly relativistic. However, a small portion of electrons are still accelerated to ultra-relativistic speeds and capable of emitting synchrotron radiation. The distribution function for electrons is re-derived here so that synchrotron emission from these relativistic electrons can be calculated. Based on the revised model, optical afterglows from both isotropic fireballs and highly collimated jets are studied numerically, and compared to analytical results. In the beamed cases, it is found that, in addition to the steepening due to the edge effect and the lateral expansion effect, the light curves are universally characterized by a flattening during the deep Newtonian phase.Comment: MNRAS in press (originally submitted in October 2002), 8 pages with 8 eps figures embedded, references update

GRB Fireball Physics: Prompt and Early Emission

We review the fireball shock model of gamma-ray burst prompt and early afterglow emission in light of rapid follow-up measurements made and enabled by the multi-wavelength Swift satellite. These observations are leading to a reappraisal and expansion of the previous standard view of the GRB and its fireball. New information on the behavior of the burst and afterglow on minutes to hour timescales has led, among other results, to the discovery and follow-up of short GRB afterglows, the opening up of the z>6 redshift range, and the first prompt multi-wavelength observations of a long GRB-supernova. We discuss the salient observational results and some associated theoretical issues.Comment: 23 pages. Published in the New Journal of Physics Focus Issue, "Focus on Gamma-Ray Bursts in the Swift Era" (Eds. D. H. Hartmann, C. D. Dermer & J. Greiner). V2: Minor change

Atmospheric Muon Flux at Sea Level, Underground, and Underwater

The vertical sea-level muon spectrum at energies above 1 GeV and the underground/underwater muon intensities at depths up to 18 km w.e. are calculated. The results are particularly collated with a great body of the ground-level, underground, and underwater muon data. In the hadron-cascade calculations, the growth with energy of inelastic cross sections and pion, kaon, and nucleon generation in pion-nucleus collisions are taken into account. For evaluating the prompt muon contribution to the muon flux, we apply two phenomenological approaches to the charm production problem: the recombination quark-parton model and the quark-gluon string model. To solve the muon transport equation at large depths of homogeneous medium, a semi-analytical method is used. The simple fitting formulas describing our numerical results are given. Our analysis shows that, at depths up to 6-7 km w. e., essentially all underground data on the muon intensity correlate with each other and with predicted depth-intensity relation for conventional muons to within 10%. However, the high-energy sea-level data as well as the data at large depths are contradictory and cannot be quantitatively decribed by a single nuclear-cascade model.Comment: 47 pages, REVTeX, 15 EPS figures included; recent experimental data and references added, typos correcte

Habitable Zones in the Universe

Habitability varies dramatically with location and time in the universe. This was recognized centuries ago, but it was only in the last few decades that astronomers began to systematize the study of habitability. The introduction of the concept of the habitable zone was key to progress in this area. The habitable zone concept was first applied to the space around a star, now called the Circumstellar Habitable Zone. Recently, other, vastly broader, habitable zones have been proposed. We review the historical development of the concept of habitable zones and the present state of the research. We also suggest ways to make progress on each of the habitable zones and to unify them into a single concept encompassing the entire universe.Comment: 71 pages, 3 figures, 1 table; to be published in Origins of Life and Evolution of Biospheres; table slightly revise

Gamma Ray Bursts as standard candles to constrain the cosmological parameters

Gamma Ray Bursts (GRBs) are among the most powerful sources in the Universe: they emit up to 10^54 erg in the hard X-ray band in few tens of seconds. The cosmological origin of GRBs has been confirmed by several spectroscopic measurements of their redshifts, distributed in the range 0.1-6.3. These two properties make GRBs very appealing to investigate the far Universe. The energetics implied by the observed fluences and redshifts span at least four orders of magnitudes. Therefore, at first sight, GRBs are all but standard candles. But there are correlations among some observed quantities which allow us to know the total energy or the peak luminosity emitted by a specific burst with a great accuracy. Through these correlations, GRBs become "known" candles to constrain the cosmological parameters. One of these correlation is between the rest frame peak spectral energy E_peak and the total energy emitted in gamma--rays E_gamma, properly corrected for the collimation factor. Another correlation, discovered very recently, relates the total GRB luminosity L_iso, its peak spectral energy E_peak and a characteristic timescale T_0.45, related to the variability of the prompt emission. It is based only on prompt emission properties, it is completely phenomenological, model independent and assumption--free. The constraints found through these correlations on the Omega_M and Omega_Lambda parameters are consistent with the concordance model. The present limited sample of bursts and the lack of low redshift events, necessary to calibrate these correlations, makes the cosmological constraints obtained with GRBs still large compared to those obtained with other cosmological probes (e.g. SNIa or CMB). However, the newly born field of GRB--cosmology is very promising for the future.Comment: 39 pages, 23 figures, 2 tables. Accepted for publication in the New Journal of Physics focus issue, "Focus on Gamma--Ray bursts in the Swift Era" (Eds. D. H. Hartmann, C. D. Dermer, J. Greiner