Vincenzo Testa - Academia.edu (original) (raw)

Papers by Vincenzo Testa

Astronomy & Astrophysics, 2003

We use infrared Color Magnitude Diagrams from the 2-Micron All-Sky Survey (2MASS) to search for s... more We use infrared Color Magnitude Diagrams from the 2-Micron All-Sky Survey (2MASS) to search for stars belonging to the tidal stream of the Sagittarius dwarf spheroidal galaxy (Sgr dSph) around selected Galactic globular clusters. Statistically significant detections are presented for the cases of Pal 12 and NGC 4147, strongly supporting the idea that these clusters are associated with the Sgr

We present a wide-field photometric study of globular cluster systems in 3 early-type galaxies (N... more We present a wide-field photometric study of globular cluster systems in 3 early-type galaxies (NGC4406 NGC4365 NGC3115) based on BVR observations with the WFI at the 2.2m ESO/MPG telescope. Candidates globular clusters were selected on the basis of shape parameters and (B-R) colors. For the samples of bona-fide candidate globular clusters the luminosity functions and color distributions were derived and

The projected multiplicity function of galaxies gives (per square degree) the density of galaxy a... more The projected multiplicity function of galaxies gives (per square degree) the density of galaxy aggregates formed by N members. We use the CRoNaRio matched catalogues to derive the low N (N<15) multiplicity function from D-POSS data. The van Albada (1982) algorithm was implemented and used to identify candidate groups in the CRoNaRio catalogues. In absence of redshift surveys complete down

Astronomy & Astrophysics, 2009

We report optical B-band observations with the Large Binocular Telescope (LBT) of the isolated ne... more We report optical B-band observations with the Large Binocular Telescope (LBT) of the isolated neutron star RBS1774. The stacked image with a total exposure of 2fh5 reveals a candidate optical counterpart at mB = 26.96 ± 0.20 at position alpha (2000) = 21^h43^m03fs40, delta(2000) = +06degr54^prime17farcs5, within the joint Chandra and XMM-Newton error circles. We analyse archival XMM-Newton observations and

We used HST-WFPC2 and the 1.54 Danish ESO-telescope at La Silla (Chile) to obtain photometry for ... more We used HST-WFPC2 and the 1.54 Danish ESO-telescope at La Silla (Chile) to obtain photometry for stars located within 200 arcsec from the center of the cluster NGC 6101. HST-WFPC2 data for 1 field centered on the cluster, have been collected during HST-cycle 6. The resulting V, V-I photometry reach a limiting magnitude of V~25.5. Ground observations have been collected on July 1995. The resulting photometry containing the stars simultaneously detected in the V, B and I filters, is characterized by a limiting magnitude of V~22.5. (2 data files).

Astronomy & Astrophysics, 2004

We present (V, V-I) VLT-FORS1 observations of the Galactic Globular Cluster NGC 6397. We derive a... more We present (V, V-I) VLT-FORS1 observations of the Galactic Globular Cluster NGC 6397. We derive accurate color-magnitude diagrams and luminosity functions (LFs) of the cluster Main Sequence (MS) for two fields extending from a region near the centre of the cluster out to ~=10 arcmin. The photometry of these fields produces a narrow MS extending down to V ~= 27,

Astrophysical Journal - ASTROPHYS J, 2006

We present deep J, H, and Ks photometry and accurate color magnitude diagrams down to K~18.5 for ... more We present deep J, H, and Ks photometry and accurate color magnitude diagrams down to K~18.5 for a sample of 13 globular clusters in the Large Magellanic Cloud. This data set combined with the previous sample of six clusters published by our group gives the opportunity to study the properties of giant stars in clusters with different ages (ranging from ~80 Myr up to 3.5 Gyr). Quantitative estimates of star population ratios (by number and luminosity) in the asymptotic giant branch (AGB), the red giant branch (RGB), and the He clump have been obtained and compared with theoretical models in the framework of probing the so-called phase transitions. The AGB contribution to the total luminosity starts to be significant at ~200 Myr and reaches its maximum at 500-600 Myr, when the RGB phase transition is starting. At ~900 Myr the full development of an extended and well-populated RGB has been completed. The occurrences of both the AGB and RGB phase transitions are sharp events, lasting a ...

The Astrophysical Journal, 2010

We have gathered optical photometry data on a large sample of Swift-era gamma-ray burst (GRB) aft... more We have gathered optical photometry data on a large sample of Swift-era gamma-ray burst (GRB) afterglows. We analyzed their light curves and derive spectral energy distributions for the sample with the best data quality, allowing us to derive the host galaxy extinction. We transform the afterglow light curves into an extinction-corrected z = 1 system and compare their luminosities with a sample of pre-Swift afterglows. We find that the luminosity distribution of the two afterglow samples are very similar, and that a fainter sample can be explained by a moderate amount of line-of-sight host extinction. We derive bolometric isotropic energies for all GRBs in our sample, and find only a tentative correlation between the prompt energy release and the optical afterglow luminosity. Furthermore, we propose the existence of an upper ceiling on afterglow luminosities and study the luminosity distribution at early times, which was not accessible before the advent of the Swift satellite. Finally, we postulate the existence of an intermediate class of long GRBs which lie between the typical high-luminosity, high-redshift events described in the rest of the paper and nearby low-luminosity events associated with spectroscopic SNe in terms of energetics and redshift distribution.

The Astrophysical Journal, 2008

We observed the nearby, low-density globular cluster M71 (NGC 6838) with the Chandra X-ray Observ... more We observed the nearby, low-density globular cluster M71 (NGC 6838) with the Chandra X-ray Observatory to study its faint X-ray populations. Five X-ray sources were found inside the cluster core radius, including the known eclipsing binary millisecond pulsar (MSP) PSR J1953+1846A. The X-ray light curve of the source coincident with this MSP shows marginal evidence for periodicity at the binary period of 4.2 h. Its hard X-ray spectrum and luminosity resemble those of other eclipsing binary MSPs in 47 Tuc, suggesting a similar shock origin of the X-ray emission. A further 24 X-ray sources were found within the halfmass radius, reaching to a limiting luminosity of 1.5 × 10 30 ergs s −1 (0.3-8 keV). From a radial distribution analysis, we find that 18 ± 6 of these 29 sources are associated with M71, somewhat more than predicted, and that 11 ± 6 are background sources, both galactic and extragalactic. M71 appears to have more X-ray -2sources between L X = 10 30 -10 31 ergs s −1 than expected by extrapolating from other studied clusters using either mass or collision frequency. We explore the spectra and variability of these sources, and describe the results of ground-based optical counterpart searches. Subject headings: globular clusters: individual (M71, NGC 6838) -pulsars: individual (PSR J1953+1846A, M71A) -X-rays: stars, binaries 1 See

The Astrophysical Journal, 2007

We present a deep, wide-field photometric survey of the newly discovered Hercules dwarf spheroida... more We present a deep, wide-field photometric survey of the newly discovered Hercules dwarf spheroidal galaxy (dSph), based on data from the Large Binocular Telescope. Images in B, V, and r were obtained with the Large Binocular Camera covering a field of view to a magnitude of ∼25.5 (5 j). This permitted the construction 23 # 23 of color-magnitude diagrams that reach approximately 1.5 mag below the Hercules main-sequence turnoff. Threefilter photometry allowed us to preferentially select probable Hercules member stars and to examine the structure of this system at a previously unattained level. We find that the Hercules dwarf is highly elongated ( ), 3 : 1 considerably more so than any other dSph satellite of the Milky Way, except the disrupting Sagittarius dwarf. Although we cannot rule out that the unusual structure is intrinsic to Hercules as an equilibrium system, our results suggest tidal disruption as a likely cause of this highly elliptical structure. Given the relatively large galactocentric distance of this system ( kpc), signs of tidal disruption would require the Hercules dwarf 132 ‫ע‬ 12 to be on a highly eccentric orbit around the Milky Way.

Astronomy and Astrophysics, 2001

We have used ESO telescopes at La Silla and the Hubble Space Telescope (HST) in order to obtain a... more We have used ESO telescopes at La Silla and the Hubble Space Telescope (HST) in order to obtain accurate B,V,I CCD photometry for the stars located within 200 ′′ (≃ 2 half-mass radii, r h = 1.71 ′ ) from the center of the cluster NGC 6101. Color-Magnitude Diagrams (CMDs) extending from the red-giant tip to about 5 magnitudes below the main-sequence turnoff MSTO (V = 20.05 ± 0.05) have been constructed. The following results have been obtained from the analysis of the CMDs: a) The overall morphology of the main branches confirms previous results from the literature, in particular the existence of a sizeable population of 73 "blue stragglers" (BSS), which had been already partly detected . They are considerably more concentrated than either the subgiant branch (SGB) or the main sequence (MS) stars, and have the same spatial distribution as the horizontal branch (HB) stars (84 % probability from K-S test). An hypothesis on the possible BSS progeny is also presented. b) The HB is narrow and the bulk of stars is blue, as expected for a typical metal-poor globular cluster. c) The derived magnitudes for the HB and the MSTO, VZAHB = 16.59 ± 0.10, VTO = 20.05 ± 0.05, coupled with the values E(B-V) = 0.1, [Fe/H] = -1.80, Y = 0.23 yield a distance modulus (m − M )V = 16.23 and an age similar to other "old" metal-poor globular clusters. In particular, from the comparison with theoretical isochrones, we derive for this cluster an age of 13 Gyrs. d) By using the large statistical sample of Red Giant Branch (RGB) stars, we detected with high accuracy the position of the bump in the RGB luminosity function. This observational feature has been compared with theoretical prescriptions, yielding a good agreement within the current theoretical and observational uncertainties.

Astronomy and Astrophysics, 2007

Context. Gamma-ray burst (GRB) emission is believed to originate in highly relativistic fireballs... more Context. Gamma-ray burst (GRB) emission is believed to originate in highly relativistic fireballs. Aims. Currently, only lower limits were securely set to the initial fireball Lorentz factor Γ 0 . We aim to provide a direct measure of Γ 0 . Methods. The early-time afterglow light curve carries information about Γ 0 , which determines the time of the afterglow peak. We have obtained early observations of the near-infrared afterglows 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 Γ 0 ∼ 400, fully confirming the highly relativistic nature of GRB fireballs. The deceleration radius was inferred to be R dec ≈ 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.

Astronomy and Astrophysics, 2010

Context. Multiwavelength observations of gamma-ray burst prompt and afterglow emission are a key ... more Context. Multiwavelength observations of gamma-ray burst prompt and afterglow emission are a key tool to disentangle the various possible emission processes and scenarios proposed to interpret the complex gamma-ray burst phenomenology. Aims. We collected a large dataset on GRB 060908 in order to carry out a comprehensive analysis of the prompt emission as well as the early and late afterglow. Methods. Data from Swift-BAT, -XRT and -UVOT together with data from a number of different ground-based optical/NIR and millimeter telescopes allowed us to follow the afterglow evolution from about a minute from the high-energy event down to the host galaxy limit. We discuss the physical parameters required to model these emissions. Results. The prompt emission of GRB 060908 was characterized by two main periods of activity, spaced by a few seconds of low intensity, with a tight correlation between activity and spectral hardness. Observations of the afterglow began less than one minute after the high-energy event, when it was already in a decaying phase, and it was characterized by a rather flat optical/NIR spectrum which can be interpreted as due to a hard energy-distribution of the emitting electrons. On the other hand, the X-ray spectrum of the afterglow could be fit by a rather soft electron distribution. Conclusions. GRB 060908 is a good example of a gamma-ray burst with a rich multi-wavelength set of observations. The availability of this dataset, built thanks to the joint efforts of many different teams, allowed us to carry out stringent tests for various interpretative scenarios showing that a satisfactorily modeling of this event is challenging. In the future, similar efforts will enable us to obtain optical/NIR coverage comparable in quality and quantity to the X-ray data for more events, therefore opening new avenues to progress gamma-ray burst research. arXiv:1007.4769v1 [astro-ph.HE]

Astronomy and Astrophysics, 2005

We present optical and near-infrared observations of the afterglow of the gamma-ray burst GRB 050... more We present optical and near-infrared observations of the afterglow of the gamma-ray burst GRB 050904. We derive a photometric redshift z = 6.3, estimated from the presence of the Lyman break falling between the I and J filters. This is by far the most distant GRB known to date. Its isotropic-equivalent energy is 3.4×10 53 erg in the rest-frame 110-1100 keV energy band. Despite the high redshift, both the prompt and the afterglow emission are not peculiar with respect to other GRBs. We find a break in the J-band light curve at t b = 2.6 ± 1.0 d (observer frame). If we assume this is the jet break, we derive a beaming-corrected energy E γ ∼ (4 ÷ 12) × 10 51 erg. This limit shows that GRB 050904 is consistent with the Amati and Ghirlanda relations. This detection is consistent with the expected number of GRBs at z > 6 and shows that GRBs are a powerful tool to study the star formation history up to very high redshift.

Gamma-ray burst are thought to be produced by highly relativistic outflows. Although upper and lo... more Gamma-ray burst are thought to be produced by highly relativistic outflows. Although upper and lower limits for the outflow initial Lorentz factor Γ 0 are available, observational efforts to derive a direct determination of Γ 0 have so far failed or provided ambiguous results. As a matter of fact, the shape of the early-time afterglow light curve is strongly sensitive on Γ 0 which determines the time of the afterglow peak, i.e. when the outflow and the shocked circumburst material share a comparable amount of energy. We now comment early-time observations of the near-infrared afterglows of GRB 060418 and GRB 060607A performed by the REM robotic telescope. For both events, the afterglow peak was singled out and allowed us to determine the initial fireball Lorentz, Γ 0 ∼ 400.

Advances in Astronomy, 2010

We present the result of a year-long effort to think, design, build, realize, and manage the robo... more We present the result of a year-long effort to think, design, build, realize, and manage the robotic, autonomous REM observatory, placed since June 2003 on the cerro La Silla, ESO Chile. The various aspects of the management and control are here surveyed, with the nice ideas and the wrong dead ends we encountered under way. Now REM is offered to the international astronomical community, a real, schedulable telescope, automatic for the People.

Following the refined radio position of SGR 1806-20 (Gaensler et al., astro-ph/0502393; Cameron e... more Following the refined radio position of SGR 1806-20 (Gaensler et al., astro-ph/0502393; Cameron et al., astro-ph/0502428), about 0.5" away from the preliminary one (Kouveliotou et al. 2005, GCN #2929), we note that the possible counterpart we tentatively identified (Israel et al., ATel #378) is not anymore included in the radio positional uncertainty region. Only one relatively faint object falls within the refined radio position regions, while two additional objects are just outside.

Following the recent radio detection of SGR 1806-20 (Gaensler et al. 2005, GCN 2929) which provid... more Following the recent radio detection of SGR 1806-20 (Gaensler et al. 2005, GCN 2929) which provided an unprecedented positional accuracy (at the level of 0.1"), we re-analysed all the VLT NACO images of the field (in J, H and Ks bands) we collected in 2004 after the X-ray burst activity from the source detected during March, June, August and October 2004.