Fabrizio Vitali

REM observations of GRB 060418 and GRB 060607A: the onset of the afterglow and the initial fireball Lorentz factor determination

Context. Gamma-ray burst (GRB) emission is believed to originate in highly relativistic fireballs. Aims. Currently, only lower limits were securely set to the initia l fireball Lorentz factor 0. We aim to provide a direct measure of 0. Methods. The early-time afterglow light curve carries information about 0, which determines the time of the afterglow peak. We have obtained early observations of the near-infrared afte rglows of GRB 060418 and GRB 060607A with the REM robotic telescope. Results. For both events, the afterglow peak could be clearly singled out, allowing a firm determination of the fireball Lorentz of 0∼ 400, fully confirming the highly relativistic nature of GRB fi reballs. The deceleration radius was inferred to be Rdec≈ 10 17 cm. This is much larger than the internal shocks radius (believed to power the prompt emission), thus providing further evidence for a different origin of the prompt and afterglow stages of the GRB.E. Molinari, S.D. Vergani , D. Malesani , S. Covino, P. D’Avanzo, G. Chincarini , F.M. Zerbi, L.A. Antonelli, P. Conconi , V. Testa, G. Tosti , F. Vitali, F. D’Alessio, G. Malaspina, L. Nicastro, E. Palazzi , D. Guetta, S. Campana , P. Goldoni , N. Masetti , E.J.A. Meurs, A. Monfardini, L. Norci, E. Pian, S. Piranomonte , D. Rizzuto, M. Stefanon, L. Stella, G. Tagliaferri , P.A. Ward, G. Ihle, L. Gonzalez, A. Pizarro, P. Sinclair, J. Valenzuela 15

Ground-based and Airborne Instrumentation for Astronomy IV

MOONS is a new conceptual design for a Multi-Object Optical and Near-infrared Spectrograph for the Very Large Telescope (VLT), selected by ESO for a Phase A study. The baseline design consists of ~1000 fibers deployable over a field of view of ~500 square arcmin, the largest patrol field offered by the Nasmyth focus at the VLT. The total wavelength coverage is 0.8μm-1.8μm and two resolution modes: medium resolution and high resolution. In the medium resolution mode (R~4,000-6,000) the entire wavelength range 0.8μm-1.8μm is observed simultaneously, while the high resolution mode covers simultaneously three selected spectral regions: one around the CaII triplet (at R~8,000) to measure radial velocities, and two regions at R~20,000 one in the J-band and one in the H-band, for detailed measurements of chemical abundances. The grasp of the 8.2m Very Large Telescope (VLT) combined with the large multiplex and wavelength coverage of MOONS – extending into the near-IR – will provide the observational power necessary to study galaxy formation and evolution over the entire history of the Universe, from our Milky Way, through the redshift desert and up to the epoch of re-ionization at z<8-9. At the same time, the high spectral resolution mode will allow astronomers to study chemical abundances of stars in our Galaxy, in particular in the highly obscured regions of the Bulge, and provide the necessary follow-up of the Gaia mission. Such characteristics and versatility make MOONS the long-awaited workhorse near-IR MOS for the VLT, which will perfectly complement optical spectroscopy performed by FLAMES and VIMOS.

The REM telescope: detecting the near infra-red counterparts of Gamma-Ray Bursts and the prompt behavior of their optical continuum

Observations of the prompt afterglow of Gamma Ray Burst (GRB) events are unanimously considered of paramount importance for GRB science and related cosmology. Such observations at NIR wavelengths are even more promis- ing allowing one to monitor high-z Ly- absorbed bursts as well as events occurring in dusty star-forming regions. In these pages we present REM (Rapid Eye Mount), a fully robotized fast slewing telescope equipped with a high throughput NIR (Z, J, H, K) camera dedicated to detecting the prompt IR afterglow. REM can discover objects at extremely high redshift and trigger large telescopes to observe them. The REM telescope will simultaneously feed ROSS (REM Optical Slitless Spectrograph) via a dichroic. ROSS will intensively monitor the prompt optical continuum of GRB afterglows. The synergy between REM-IR cam and ROSS makes REM a powerful observing tool for any kind of fast transient phenomena.

A rapid and dramatic outburst in Blazar 3C 454.3 during May 2005 - Optical and infrared observations with REM and AIT

The flat-spectrum radio quasar 3C454.3 is well known to be a highly active and variable source with outbursts occurring across the whole electromagnetic spectrum over the last decades. In spring 2005, 3C454.3 has been reported to exhibit a strong optical outburst which subsequently triggered multi-frequency observations of the source covering the radio up to γ-ray bands. Here, we present first results of our near-IR/optical (V, R, I, H band) photometry performed between May 11 and August 5, 2005 with the Rapid Eye Mount (REM) at La Silla in Chile and the Automatic Imaging Telescope (AIT) of the Perugia University Observatory. 3C454.3 was observed during an exceptional and historical high state with a subsequent decrease in brightness over our 86 days observing period. The continuum spectral behaviour during the flaring and declining phase suggests a synchrotron peak below the near-IR band as well as a geometrical origin of the variations e.g. due to changes in the direction of forward beaming.

Near-Infrared H2 and [Fe II] Imaging and Spectroscopy of New Jets in the Vela Molecular Clouds*

We present narrowband imaging in the 2.122 μm transition of H2 and in the 1.644 μm transition of [Fe II] of a sample of 12 protostellar candidates and three Herbig-Haro (HH) objects belonging to the Vela molecular ridge (VMR). Out of the 15 investigated fields, we detected H2 emission in IRS 63, 17, 19, 21, and 8 (according to our catalog), while [Fe II] was observed toward only one source (IRS 8), where a counterjet has been identified for the first time. H2 and [Fe II] images have been combined to trace the different shock conditions along this jet. In addition, a new pure molecular H2 jet was discovered in IRS 17, which results in about 20 knots of emission extending up to 0.3 pc from the central driving source. IR spectroscopy (1.55-2.55 μm) at a resolution of ≈600 of the most prominent knots has revealed a large number of H2 emission lines, which were used to evaluate both the extinction and the excitation temperature along the flow. The observed increase of the excitation temperature with the distance from the central source was interpreted as being due to a decrease of the flow velocity with time or, alternatively, to the fact that internal knots travel in a medium already put into motion by previous shock events. Comparisons with model predictions indicate nondissociative C-shocks as the most likely mechanism for line excitation. Finally, the presence of a common alignment of the detected flows with the Galactic plane indicates that the Galactic B field affects the star formation on large scales in VMR.

Star formation in the Vela Molecular Clouds: A new protostar powering a bipolar jet

We have performed a detailed study of the star-forming region associated with the IRAS source 08448-4343 in the cloud D of the Vela Molecular Ridge. Our investigation covers a wide spectral range from the near IR, through the thermal IR to the mm-band exploiting both imaging and spectroscopic facilities in each spectral regime. A picture emerges of a dust structure which hosts a near IR cluster and multiple well-collimated H2 jets; these jets originate from different sources lying in a compact region at the cluster centre. The peak of the 1.2 mm map does not coincide with the IRAS peak, thus tracing a less evolved and denser region with a colder dust with respect to that traced by IRAS. This view is also confirmed by the observations of CS transitions from J = 2− 1t oJ = 7−6. The mm peak can be associated with the position of a red object, already proposed in previous studies as the driving source of the main jet in the field. This jet, extended along more than 0.3 pc, is composed of individual knots whose radial velocities decrease with increasing distance from the central source, which is resolved into at least six 2 µm peaks. The reddest and coldest of these peaks is well aligned with the inner knots of the jet. The spectral energy distribution of the central source resembles that of an intermediate luminosity, Class I protostar, whose youth is discussed in terms of the efficiency of the energy transfer into the jet.

The commissioning of the REM-IR camera at La Silla

During the early Summer 2003, the REM telescope has been installed at La Silla, together with the near infrared camera REM-IR and the optical spectrograph. ROSS. The REM project is a fully automated instrument to follow-up Gamma Ray Burst, triggered mainly by satellites, such as HETE II, INTEGRAL, AGILE and SWIFT. REM-IR will perform high efficiency imaging of the prompt infrared afterglow of GRB and, together with the optical spectrograph ROSS, will cover simultaneously a wide wavelength range, allowing a better understanding of the intriguing scientific case of GRB. In this paper we present the result of the commissioning phase of the near infrared camera REM-IR, lasted for an extended period of time and currently under the final fine tuning.

Simultaneous swift and rem monitoring of the blazar PKS 0537-441 in 2005

The blazar PKS 0537-441 has been observed with all instruments of the Swift satellite between the end of 2004 and 2005 November. The BAT monitored it recurrently for a total of 2.7 Ms, and the XRT and UVOT pointed it on seven occasions for a total of 67 k. The automatic optical and near-infrared telescope REM has monitored simultaneously the source at all times. In 2005 January-February, PKS 0537-441 was detected at its brightest in optical and X-rays: more than a factor of 2 brighter in X-rays and about a factor of 60 brighter in the optical than observed in 2004 December. The 2005 July observation recorded a fainter X-ray state, albeit still brighter than the historical average. The simultaneous optical state is comparable to the one recorded in early 2005 January, before the outburst. In 2005 November, the source subsided both in X-rays and optical to a quiescent state. The optical and X-ray variations are well correlated, with no measurable time lag larger than about 1 month. On intraday timescales there is no obvious correlation between X-ray and optical variations, but the former tend to be more pronounced, opposite to what is observed on monthly timescales. The widely different amplitude of the long-term variability in optical and X-rays is very unusual. The spectral energy distributions are interpreted in terms of the synchrotron and inverse Compton mechanisms within a jet where the plasma radiates via internal shocks and the dissipation depends on the distance of the emitting region from the central engine.

REM near-IR and optical multiband observations of PKS 2155-304 in 2005 ⋆

Context. Spectral variability is the main tool for constraining emis sion models of BL Lac objects. Aims. By means of systematic observations of the BL Lac prototype PKS 2155-304 in the infrared-optical band, we explore variability on the scales of months, days and hours. Methods. We made our observations with the robotic 60 cm telescope REM located at La Silla, Chile. VRIJHK filters were used. Results. PKS 2155-304 was observed from May to December 2005. The wavelength interval explored, the total number of photometric points and the short integration time render our photometry substantially superior to previous ones for this source. On the bas is of the intensity and colour we distinguish three different states of the source, each of duration of months, which include all those described in the literature. In particular, we report the highest state ever detected in the H band. The source varied by a factor of 4 in this band, much more than in the V band (a factor ≈ 2). The source softened with increasing intensity, contrar y to the general pattern observed in the UV-X-ray bands. On fiv e nights of November we had nearly continuous monitoring for 2-3 hours. A variability episode with a time scale of τ ≈24 h is well documented, a much more rapid flare with τ=1-2 h, is also apparent, but is supported by relatively few points. Conclusions. The overall spectral energy distribution of PKS 2155-304 is commonly described by a synchrotron-self-Compton model. The optical infrared emission is however in excess of the expectation of the model, in its original formulation. This can be explained by a variation of the frequency of the synchrotron peak, which is not unprecedented in BL Lacs.

SWIRCAM: a NIR imager-spectrometer to search for extragalactic supernovae

We present the main characteristics and astronomical results of SWIRCAM, a NIR imager-spectrometer mainly devoted to the search for extragalactic Supernovae, in the frame of the SWIRT project, a joint scientific collaboration among the Astronomical Observatories of Rome, Teramo and Pulkovo. The camera is currently at the focal plane of the AZT-24 1.1 m telescope at the Observing Station of Campo Imperatore, operated by the Astronomical Observatory of Rome. SWIRCAM saw its first light during December 1998 and it is currently employed for both the SWIRT operative phase and other institutional projects.