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

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

Structure and nuclear quadrupole coupling interaction in hydroxylamines: The rotational spectrum of N,N-diethyl(2H)hydroxylamine

The ground-state rotational spectrum of N,N-diethyl(2H)hydroxylamine (C2H5-NOD-C2H5) was measured by Fourier transform microwave spectroscopy. Six rotational transition lines were assigned to the most stable conformer with the alkyl chain in the trans arrangement and the hydroxyl trans to the bisector of the CNC angle, that is, with the NOD frame in the bc-symmetry plane. Rotational constants are A= 7210.938(2), B= 2018.628(1), and C= 1739.696(1) MHz. These data together with those previously determined for the parent species and 13C and 15N isotopologues, were used to determine a partial r0 structure. The hyperfine structure due to the nuclear quadrupole coupling (NQC) interaction of both 14N and D nuclei was disentangled allowing to obtain the diagonal NQC-constants. On the basis of the determined geometry, the NQC-tensor values in the electric field-gradient principal axis system were determined (χxxN= 0.71, χyyN= 5.90, χzzN= −6.61 MHz; χxxD= −0.11, χyyD= −0.15, χzzD= 0.26 MHz). Comparison with other amines shows that using ammonia as reference, χzzN can be estimated with an additive model: +0.4 and +1.7 MHz from hydrogen to alkyl and hydroxyl substitution, respectively. From the analysis of the available data on the 1:1 water complex of N,N-diethylhydroxylamine, a 8% electric field gradient decrease at the nitrogen nucleus due to the formation of the hydrogen bond involving the nitrogen lone pair was found

How Water Interacts with the NOH Group: The Rotational Spectrum of the 1:1 N,N-diethylhydroxylamine·Water Complex

The rotational spectrum of the 1:1 N,N-diethylhydroxylamine-water complex has been investigated using pulsed jet Fourier transform microwave spectroscopy in the 6.5–18.5 GHz frequency region. The most stable conformer has been detected as well as the (Formula presented.) C monosubstituted isotopologues in natural abundance and the (Formula presented.) O enriched water species, allowing to determine the nitrogen nuclear quadrupole coupling constants and the molecular structure in the vibrational ground state. The molecule has a (Formula presented.) symmetry and the water lies in the (Formula presented.) symmetry plane forming two hydrogen bonds with the NOH frame with length: (Formula presented.) = 1.974 Å and (Formula presented.) = 2.096 Å. From symmetry-adapted perturbation theory calculations coupled to atoms in molecule approach, the corresponding interaction energy values are estimated to be 24 and 13 kJ·mol (Formula presented.), respectively. The great strength of the intermolecular interaction involving the nitrogen atom is in agreement with the high reactivity of hydroxylamine compounds at the nitrogen site

Efficient three-dimensional survey techniques and their comparison in open software in the archaeological test site of "Ninfeo Maggiore" and "Ninfeo Minore" of Formia (Latina, Italy)

In Europe and beyond, the cultural and archaeological heritage may have considerable extensions of hundreds of square metres if not kilometres. It is then necessary to study highly efficient techniques able , at the same time, to maintain centimetric accuracy. In these contexts, the SLAM technique can be an efficient solution. We tested the latter in a survey of a portion of the so-called Roman Villa of Caposele, also known as Villa Rubino in Formia, (Italy): the "Ninfeo Maggiore"and "Ninfeo Minore"(Major and Minor nymphaeum). The two structures had to be surveyed for both conservation and study purposes and to allow a virtual visit, which is particularly important since they are located inside a private property. The structure is complex, with a succession of rooms and environments in an archaeological complex extending approximately 480 metres in an east-west direction and approximately 50 metres in a south-north direction. We decided to survey both nymphaea with the "GEOSLAM Zeb Horizon", also surveying all the internal connecting rooms and corridors between them. Both nymphaea were also surveyed with a "Faro"terrestrial laser scanning, to allow comparison. To verify the validity of the SLAM on the outside, a survey was carried out using a DJI Matrix drone with laser scanning. The comparison showed very limited deviations whose statistical validation is in progress, demonstrating that the SLAM technique can advantageously be used in such vast archaeological complexes where the efficiency and completeness of the survey is more important than the millimetric accuracy.</p

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

The circumburst environment of a FRED GRB: study of the prompt emission and X-ray/optical afterglow of GRB 051111

We report a multi-wavelength analysis of the prompt emission and early afterglow of GRB051111 and discuss its properties in the context of current fireball models. The detection of GRB051111 by the Burst Alert Telescope on-board Swift triggered early BVRi' observations with the 2-m robotic Faulkes Telescope North in Hawaii, as well as X-ray observations with the Swift X-Ray Telescope. The prompt gamma-ray emission shows a classical FRED profile. The optical afterglow light curves are fitted with a broken power law, with alpha_1=0.35 to alpha_2=1.35 and a break time around 12 minutes after the GRB. Although contemporaneous X-ray observations were not taken, a power law connection between the gamma-ray tail of the FRED temporal profile and the late XRT flux decay is feasible. Alternatively, if the X-ray afterglow tracks the optical decay, this would represent one of the first GRBs for which the canonical steep-shallow-normal decay typical of early X-ray afterglows has been monitored optically. We present a detailed analysis of the intrinsic extinction, elemental abundances and spectral energy distribution. From the absorption measured in the low X-ray band we find possible evidence for an overabundance of some alpha elements such as oxygen, [O/Zn]=0.7+/-0.3, or, alternatively, for a significant presence of molecular gas. The IR-to-X-ray Spectral Energy Distribution measured at 80 minutes after the burst is consistent with the cooling break lying between the optical and X-ray bands. Extensive modelling of the intrinsic extinction suggests dust with big grains or grey extinction profiles. The early optical break is due either to an energy injection episode or, less probably, to a stratified wind environment for the circumburst medium.Comment: accepted to A&A on Nov. 10 (14 pages, 8 figures