Structure of Gamma-Ray Burst jets: intrinsic versus apparent properties

With this paper we introduce the concept of apparent structure of a GRB jet, as opposed to its intrinsic structure. The latter is customarily defined specifying the functions epsilon(theta) (the energy emitted per jet unit solid angle) and Gamma(theta) (the Lorentz factor of the emitting material); the apparent structure is instead defined by us as the isotropic equivalent energy E_iso(theta_v) as a function of the viewing angle theta_v. We show how to predict the apparent structure of a jet given its intrinsic structure. We find that a Gaussian intrinsic structure yields a power law apparent structure: this opens a new viewpoint on the Gaussian (which can be understood as a proxy for a realistic narrow, well collimated jet structure) as a possible candidate for a quasi-universal GRB jet structure. We show that such a model (a) is consistent with recent constraints on the observed luminosity function of GRBs; (b) implies fewer orphan afterglows with respect to the standard uniform model; (c) can break out the progenitor star (in the collapsar scenario) without wasting an unreasonable amount of energy; (d) is compatible with the explanation of the Amati correlation as a viewing angle effect; (e) can be very standard in energy content, and still yield a very wide range of observed isotropic equivalent energies.Comment: 10 pages, 8 figures, 1 table. Accepted by MNRA

Afterglows from precursors in Gamma Ray Bursts. Application to the optical afterglow of GRB 091024

About 15% of Gamma Ray Bursts have precursors, i.e. emission episodes preceding the main event, whose spectral and temporal properties are similar to the main emission. We propose that precursors have their own fireball, producing afterglow emission due to the dissipation of the kinetic energy via external shock. In the time lapse between the precursor and the main event, we assume that the central engine is not completely turned off, but it continues to eject relativistic material at a smaller rate, whose emission is below the background level. The precursor fireball generates a first afterglow by the interaction with the external circumburst medium. Matter injected by the central engine during the "quasi-quiescent" phase replenishes the external medium with material in relativistic motion. The fireball corresponding to the main prompt emission episode crashes with this moving material, producing a second afterglow, and finally catches up and merges with the first precursor fireball. We apply this new model to GRB 091024, an event with a precursor in the prompt light curve and two well defined bumps in the optical afterglow, obtaining an excellent agreement with the existing data.Comment: 11 pages, 6 figures, 3 tables. Accepted for publication in MNRAS, Main Journa

Luminosity function and jet structure of Gamma Ray Bursts

The structure of Gamma Ray Burst (GRB) jets impacts on their prompt and afterglow emission properties. The jet of GRBs could be uniform, with constant energy per unit solid angle within the jet aperture, or it could instead be structured, namely with energy and velocity that depend on the angular distance from the axis of the jet. We try to get some insight about the still unknown structure of GRBs by studying their luminosity function. We show that low (1e46-1e48 erg/s) and high (i.e. with L > 1e50 erg/s) luminosity GRBs can be described by a unique luminosity function, which is also consistent with current lower limits in the intermediate luminosity range (1e48-1e50} erg/s). We derive analytical expressions for the luminosity function of GRBs in uniform and structured jet models and compare them with the data. Uniform jets can reproduce the entire luminosity function with reasonable values of the free parameters. A structured jet can also fit adequately the current data, provided that the energy within the jet is relatively strongly structured, i.e. E propto theta^{-k} with k > 4. The classical E propto theta^{-2} structured jet model is excluded by the current data.Comment: 11 pages, 2 tables, 7 figures, submitted to MNRA

Bulk Lorentz factors of Gamma-Ray Bursts

Knowledge of the bulk Lorentz factor $\Gamma_{0}$ of GRBs allows us to compute their comoving frame properties shedding light on their physics. Upon collisions with the circumburst matter, the fireball of a GRB starts to decelerate, producing a peak or a break (depending on the circumburst density profile) in the light curve of the afterglow. Considering all bursts with known redshift and with an early coverage of their emission, we find 67 GRBs with a peak in their optical or GeV light curves at a time $t_{\rm p}$. For another 106 GRBs we set an upper limit $t_{\rm p}^{\rm UL}$. We show that $t_{\rm p}$ is due to the dynamics of the fireball deceleration and not to the passage of a characteristic frequency of the synchrotron spectrum across the optical band. Considering the $t_{\rm p}$ of 66 long GRBs and the 85 most constraining upper limits, using censored data analysis methods, we reconstruct the most likely distribution of $t_{\rm p}$. All $t_{\rm p}$ are larger than the time $t_{\rm p,g}$ when the prompt emission peaks, and are much larger than the time $t_{\rm ph}$ when the fireball becomes transparent. The reconstructed distribution of $\Gamma_0$ has median value $\sim$300 (150) for a uniform (wind) circumburst density profile. In the comoving frame, long GRBs have typical isotropic energy, luminosity, and peak energy $\langle E_{\rm iso}\rangle=3(8)\times 10^{50}$ erg, $\langle L_{\rm iso}\rangle=3(15) \times 10^{47}$ erg s$^{-1}$ , and $\langle E_{\rm peak}\rangle =1(2)$ keV in the homogeneous (wind) case. We confirm that the significant correlations between $\Gamma$ and the rest frame isotropic energy ($E_{\rm iso}$), luminosity ($L_{\rm iso}$) and peak energy ($E_{\rm peak}$) are not due to selection effects. Assuming a typical opening angle of 5 degrees, we derive the distribution of the jet baryon loading which is centered around a few $10^{-6} {\rm M_{\odot}}$.Comment: 19 pages, 11 figures, 6 tables. Accepted for publication on Astronomy & Astrophysic

Airborne Measurements of Gravity Wave Breaking at the Tropopause

2000 FLORIDA AVE NW, WASHINGTON, DC, 2000

Unveiling the population of orphan Gamma Ray Bursts

Gamma Ray Bursts are detectable in the gamma-ray band if their jets are oriented towards the observer. However, for each GRB with a typical theta_jet, there should be ~2/theta_jet^2 bursts whose emission cone is oriented elsewhere in space. These off-axis bursts can be eventually detected when, due to the deceleration of their relativistic jets, the beaming angle becomes comparable to the viewing angle. Orphan Afterglows (OA) should outnumber the current population of bursts detected in the gamma-ray band even if they have not been conclusively observed so far at any frequency. We compute the expected flux of the population of orphan afterglows in the mm, optical and X-ray bands through a population synthesis code of GRBs and the standard afterglow emission model. We estimate the detection rate of OA by on-going and forthcoming surveys. The average duration of OA as transients above a given limiting flux is derived and described with analytical expressions: in general OA should appear as daily transients in optical surveys and as monthly/yearly transients in the mm/radio band. We find that ~ 2 OA yr^-1 could already be detected by Gaia and up to 20 OA yr^-1 could be observed by the ZTF survey. A larger number of 50 OA yr^-1 should be detected by LSST in the optical band. For the X-ray band, ~ 26 OA yr^-1 could be detected by the eROSITA. For the large population of OA detectable by LSST, the X-ray and optical follow up of the light curve (for the brightest cases) and/or the extensive follow up of their emission in the mm and radio band could be the key to disentangle their GRB nature from other extragalactic transients of comparable flux density.Comment: 9 pages, 4 figures, 2 tables. Accepted for publication by Astronomy and Astrophysic

Metilfenidato: influência da notificação de receita A (cor amarela) sobre a prática de prescrição por médicos brasileiros

Four hundred and sixty three brazilian neurologists and 411 brazilian psychiatrists answered a questionnaire aimed at to obtain information on the prescription of methylphenidate for the treatment of the Attention Deficit and Hyperactivity Disorder. The majority of the doctors reported the erratic occurrence of a few non serious adverse reactions such as headache, weight loss, inapetence, hyperexcitability and tachycardia. On the other hand, only six doctors reported cases that cold raise a suspicion of drug dependence, although none of these six cases satisfied the ICD-10 criteria for dependence. The vast majority of the medical doctors manifested the opinion that the especial prescriptions the Notifications A of yellow color, the same used for opiates also, as demanded by the Brazilian Health Authorities, is inadequate as it raises misconceptions in relation to the real patient disease and frightens the parents and relatives. The doctors also claimed the such especial prescription form encumbers the prescription of the medicament making methylphenidate the second choice for the treatment and, for this reason, less available in pharmacies and drugstores. As a consequence the adherence to the treatment is more difficult to attain. The neurologists and psychiatrists agree that a certain control over methylphenidate is necessary, but as it is prescribed mostly by specialists and does not possess an evident abuse potential, the Prescription Notification B, of blue color, would be enough for efficient control. In fact, according to the doctors, the scheduling in Brazil of methylphenidate in the same list as the amphetamines and dronabinol (the active principle of Cannabis sativa) should be reviewed.Oitocentos e noventa e dois médicos, entre eles neurologistas (463) e psiquiatras (411), responderam a um questionário sobre a prescrição do metilfenidato para o transtorno do déficit de atenção e hiperatividade (TDAH). A maioria dos médicos relatou a ocorrência esporádica de reações adversas não-sérias, tais como dor de cabeça, emagrecimento, inapetência, hiperexcitabilidade, taquicardia, etc; apenas seis médicos, entretanto, relataram casos que poderiam levar à suspeita de dependência, embora nenhum deles satisfizesse os critérios da CID-10 para tal. A grande maioria opinou que a exigência da notificação de receita A (amarela) é inadequada, criando preconceitos em relação à condição dos pacientes e amedrontando seus parentes. Relatam ainda que tal classificação dificulta a prescrição do medicamento, fazendo muitas vezes com que o metilfenidato se torne a segunda opção para o tratamento de TDAH, além de tornar o produto pouco disponível nas farmácias e dificultar o trabalho dos profissionais. Isso faz com que a adesão ao tratamento se torne mais difícil, pois, além dos vários entraves burocráticos para se adquirir o medicamento, há também o medo por parte dos familiares e do próprio paciente de estar tomando tal medicação. Neurologistas e psiquiatras argumentam que o controle do metilfenidato deve existir, mas, em se tratando de um medicamento prescrito por especialistas e de não possuir grande potencial de dependência, o receituário azul já seria suficiente para o controle adequado. A classificação do metilfenidato, juntamente com as anfetaminas e com o princípio ativo da maconha (dronabinol), é uma outra questão levantada, sendo tal fato para grande parte dos profissionais uma total incoerência.UNIFESP-EPM Departamento de Psicobiologia Centro Brasileiro de Informações sobre Drogas PsicotrópicasNovartis BiociênciasUNIFESP, EPM, Depto. de Psicobiologia Centro Brasileiro de Informações sobre Drogas PsicotrópicasSciEL

The filtered martingale problem

Abstract Let X be a Markov process characterized as the solution of a martingale problem with generator A, and let Y be a related observation process. The conditional distribution π t of X(t) given observations of Y up to time t satisfies certain martingale properties, and it is shown that any probability-measure-valued process with the appropriate martingale properties can be interpreted as the conditional distribution of X for some observation process. In particular, if Y (t) = γ(X(t)) for some measurable mapping γ, the conditional distribution of X(t) given observations of Y up to time t is characterized as the solution of a filtered martingale problem. Uniqueness for the original martingale problem implies uniqueness for the filtered martingale problem which in turn implies the Markov property for the conditional distribution considered as a probability-measure-valued process. Other applications include a Markov mapping theorem and uniqueness for filtering equations. MSC 2000 subject classifications: 60J25, 93E11, 60G35, 60J35, 60G4

FFAs and QT intervals in obese women with visceral adiposity: Effects of sustained weight loss over 1 year

We evaluated 66 obese patients grouped by waist-to-hip ratio (WHR) into group A (WHR > 0.85, n = 30) and group B (WHR ≤ 0.85, n = 36), before and after 1 yr of diet-induced weight loss compared with 25 nonobese women. Before diet, the longest values of QT intervals and the highest levels of FFA and catecholamines were in group A (P < 0.01). In obese women (both groups), the corrected QT (QTc); interval correlated with plasma FFA (P < 0.01) and catecholamine (P < 0.02) concentrations. After 1 yr of diet, at the same levels of body weight reduction, the decrement of the QTc interval (P < 0.02), FFA (P < 0.01) and catecholamine (P < 0.02) levels were significantly greater in-group A than group B. In multivariate analysis, the decline of the QTc interval after weight loss was associated with changes in plasma FFA independently of changes in WHR and plasma catecholamines. Our data suggest that the QTc interval is tightly correlated with plasma FFA levels; shortening of cardiac repolarization times in the course of long-lasting weight reduction may reduce the risk of ventricular electrical instability, especially in women with abdominal adiposity

Short GRBs at the dawn of the gravitational wave era

We derive the luminosity function and redshift distribution of short Gamma Ray Bursts (SGRBs) using (i) all the available observer-frame constraints (i.e. peak flux, fluence, peak energy and duration distributions) of the large population of Fermi SGRBs and (ii) the rest-frame properties of a complete sample of Swift SGRBs. We show that a steep $\phi(L)\propto L^{-a}$ with a>2.0 is excluded if the full set of constraints is considered. We implement a Monte Carlo Markov Chain method to derive the $\phi(L)$ and $\psi(z)$ functions assuming intrinsic Ep-Liso and Ep-Eiso correlations or independent distributions of intrinsic peak energy, luminosity and duration. To make our results independent from assumptions on the progenitor (NS-NS binary mergers or other channels) and from uncertainties on the star formation history, we assume a parametric form for the redshift distribution of SGRBs. We find that a relatively flat luminosity function with slope ~0.5 below a characteristic break luminosity ~3$\times10^{52}$ erg/s and a redshift distribution of SGRBs peaking at z~1.5-2 satisfy all our constraints. These results hold also if no Ep-Liso and Ep-Eiso correlations are assumed. We estimate that, within ~200 Mpc (i.e. the design aLIGO range for the detection of GW produced by NS-NS merger events), 0.007-0.03 SGRBs yr$^{-1}$ should be detectable as gamma-ray events. Assuming current estimates of NS-NS merger rates and that all NS-NS mergers lead to a SGRB event, we derive a conservative estimate of the average opening angle of SGRBs: $\theta_{jet}$~3-6 deg. Our luminosity function implies an average luminosity L~1.5$\times 10^{52}$ erg/s, nearly two orders of magnitude higher than previous findings, which greatly enhances the chance of observing SGRB "orphan" afterglows. Efforts should go in the direction of finding and identifying such orphan afterglows as counterparts of GW events.Comment: 13 pages, 5 figures, 2 tables. Accepted for publication in Astronomy & Astrophysics. Figure 5 and angle ranges corrected in revised versio