A. Galli

Early emission of rising optical afterglows: the case of GRB 060904B and GRB 070420

Aims. We present the time-resolved optical emission of gamma-ray bursts GRB 060904B and GRB 070420 during their prompt and early afterglow phases. Methods. We used time resolved photometry from optical data taken by the TAROT telescope and time resolved spectroscopy at high energies from the Swift spacecraft instrument. Results. The optical emissions of both GRBs are found to increase from the end of the prompt phase, passing to a maximum of brightness at tpeak = 9.2 min and 3.3 min for GRB 060904B and GRB 070420 respectively and then decrease. GRB 060904B presents a large optical plateau and a very large X-ray flare. We argue that the very large X-flare occurring near tpeak is produced by an extended internal engine activity and is only a coincidence with the optical emission. GRB 070420 observations would support this idea because there was no X-flare during the optical peak. The nature of the optical plateau of GRB 060904B is less clear and might be related to the late energy injection.

Long-term flaring activity of XRF 011030 observed with BeppoSAX

We present the spectral and temporal analysis of the X-ray flash XRF 011030 observed with BeppoSAX. This event is characterized by a very long X-ray bursting activity that lasts about 1500 s, one of the longest ever observed by BeppoSAX. In particular, a precursor and a late flare are present in the light curve.
We connect the late X-ray flare observed at about 1300 s to the afterglow emission observed by Chandra and associate it with the onset of the afterglow emission in the framework of external shock by a long duration engine activity. We find that the late X-ray flare and the broadband afterglow data, including optical and radio measurements, are consistent either with a fireball expanding in a wind environment or with a jetted fireball in an ISM.

On the nature of X-ray flashes in the SWIFT era

Aims. X-Ray Flashes (XRFs) are soft gamma-ray bursts whose nature is not clear. Their soft spectrum can be due to cosmological effects (high redshift), an off-axis view of the jet or can be intrinsic to the source. We use SWIFT observations to investigate different scenarios proposed to explain their origin. Methods. We have made a systematic analysis of the afterglows of XRFs with known redshift observed by SWIFT. We derive their redshift and luminosity distributions, and compare their properties with a sample of normal GRBs observed by the same instrument. Results. The high distance hypothesis is ruled out by the redshift distribution of our sample of XRFs, indicating that, at least for our sample, the off-axis and sub-energetic hypotheses are preferred. Of course, this does not exclude that some XRFs without known redshift could be at high distance. However we find that taking into account the sensitivity of the BAT instrument, XRFs cannot be detected by SWIFT beyond ≈ 3. The luminosity distribution of XRF afterglows is similar to the GRB one. This would rule out most off-axis models, but for the homogeneous jet model. However this model predicts a GRB rate uncomfortably near the observed rate of supernovae. This implies that XRFs, at least those of our sample, are intrinsically soft.

GIARPS@TNG: GIANO-B and HARPS-N together for a wider wavelength range spectroscopy

Abstract.Since 2012, thanks to the installation of the high-resolution echelle spectrograph in the optical range HARPS-N, the Italian telescope TNG (La Palma) became one of the key facilities for the study of the extrasolar planets. In 2014 TNG also offered GIANO to the scientific community, providing a near-infrared (NIR) cross-dispersed echelle spectroscopy covering 0.97-2.45μm at a resolution of 50000. GIANO, although designed for direct light-feed from the telescope at the Nasmyth-B focus, was provisionally mounted on the rotating building and connected via fibers to only available interface at the Nasmyth-A focal plane. The synergy between these two instruments is particularly appealing for a wide range of science cases, especially for the search of exoplanets around young and active stars and the characterisation of their atmosphere. Through the funding scheme “WOW” (a Way to Others Worlds), the Italian National Institute for Astrophysics (INAF) proposed to position GIANO at the focal station for which it was originally designed and the simultaneous use of these spectrographs with the aim to achieve high-resolution spectroscopy in a wide wavelength range (0.383-2.45μm) obtained in a single exposure, giving rise to the project called GIARPS (GIANO-B & HARPS-N). Because of its characteristics, GIARPS can be considered the first and unique worldwide instrument providing not only high resolution in a large wavelength band, but also a high-precision radial velocity measurement both in the visible and in the NIR arm, since in the next future GIANO-B will be equipped with gas absorption cells.

GIARPS: the unique VIS-NIR high precision radial velocity facility in this world

GIARPS (GIAno and haRPS) is a project devoted to have on the same focal station of the Telescopio Nazionale Galileo (TNG) both the high resolution spectrographs HARPS-N (VIS) and GIANO (NIR) working simultaneously. This could be considered the first and unique worldwide instrument providing cross-dispersed echelle spectroscopy at a high resolution (R=115,000 in the visual and R=50,000 in the IR) and over in a wide spectral range (0.383 - 2.45 μm) in a single exposure. The science case is very broad, given the versatility of such an instrument and the large wavelength range. A number of outstanding science cases encompassing mainly extra-solar planet science starting from rocky planet search and hot Jupiters, atmosphere characterization can be considered. Furthermore both instrument can measure high precision radial velocity by means the simultaneous thorium technique (HARPS - N) and absorbing cell technique (GIANO) in a single exposure. Other science cases are also possible. Young stars and proto- planetary disks, cool stars and stellar populations, moving minor bodies in the solar system, bursting young stellar objects, cataclysmic variables and X-ray binary transients in our Galaxy, supernovae up to gamma-ray bursts in the very distant and young Universe, can take advantage of the unicity of this facility both in terms of contemporaneous wide wavelength range and high resolution spectroscopy.

From Single Pulse to Multi‐Pulse: looking for Gamma‐ray Bursts intimate properties

We report on spectral and temporal analysis, of prompt and afterglow emission, of two samples of object that show different time profile: Single and Multi‐pulse GRBs. We compare their observational properties in order to evaluate the possibility that they could be described by the same emitting scenario.

Relativistic interaction of a high intensity photon beam with a plasma: a possible GRB emission mechanism

A long duration photon beam can induce macroscopic coherent effects on a plasma by single photon electron scattering if the probability of the interaction approaches 1 in a volume of unit surface and length equal to the plasma typical wavelength and the induced electron oscillations become relativistic in few plasma cycles. A fraction of the plasma electrons is accelerated through the Wakefield mechanism by the cavities created by the photon‐electron interactions and radiates through boosted betraton emission in the same cavities. The resulting emission in this framework is very similar to the typical GRB radiation. Several comparisons with GRB light curves and spectral‐energy correlations will be presented.

X‐ray and GeV Flares in GRB Light Curves

Observations are showing that X‐ray flares are very common features in Gamma‐Ray Burst light curves. X‐ray flares occur from hundred to thousands of seconds after the burst, when the prompt‐to‐afterglow transition takes place. Flares present a variety of spectral and temporal behaviours, thus several models have been proposed in the literature to explain this phenomenon. In particular we study flares in the framework of external shocks. In this context X‐ray flares are produced by synchrotron emission as thick shell fireballs collide with the external medium and represent the onset of the afterglow emission. The X‐ray flare photons are expected to be Inverse Compton (IC) scattered by the afterglow electrons producing high energy counterparts that potentially will be detected by the Large Area Telescope on board GLAST. The existence of high energy flares is supported by the delayed GeV emission detected by EGRET in GRB 940217. We investigate the contribution of the IC emission associated with X‐ray flares ...

GeV flares observations with GLAST LAT

Early X‐ray afterglow observations show that X‐ray flares are very common features in GRB light curves. X‐ray flares may reflect long duration central engine activity. The delayed flare photons are expected to interact with relativistic electrons by Inverse Compton giving delayed high energy counterparts that potentially will be detected by GLAST LAT, which could observe GRB from 20 MeV to more than 300 GeV. The nature oh high energy spectral components from GRB detected by EGRET is still debated. Observations with GLAST LAT will give useful information to constrain the origin of X‐ray flares. In this work we simulate a set of possible GeV emitting flares in the context of External Shock model to study the capability of GLAST LAT to detect GeV flares at different intensities and durations.