11 research outputs found
A Large Catalog of Homogeneous Ultra-Violet/Optical GRB Afterglows: Temporal and Spectral Evolution
We present the second Swift Ultra-Violet/Optical Telescope (UVOT) gamma-ray
burst (GRB) afterglow catalog, greatly expanding on the first Swift UVOT GRB
afterglow catalog. The second catalog is constructed from a database containing
over 120,000 independent UVOT observations of 538 GRBs first detected by Swift,
the High Energy Transient Explorer 2 (HETE2), the INTErnational Gamma-Ray
Astrophysics Laboratory (INTEGRAL), the Interplanetary Network (IPN), Fermi,
and Astro-rivelatore Gamma a Immagini Leggero (AGILE). The catalog covers GRBs
discovered from 2005 Jan 17 to 2010 Dec 25. Using photometric information in
three UV bands, three optical bands, and a `white' or open filter, the data are
optimally co-added to maximize the number of detections and normalized to one
band to provide a detailed light curve. The catalog provides positional,
temporal, and photometric information for each burst, as well as Swift Burst
Alert Telescope (BAT) and X-Ray Telescope (XRT) GRB parameters. Temporal slopes
are provided for each UVOT filter. The temporal slope per filter of almost half
the GRBs are fit with a single power-law, but one to three breaks are required
in the remaining bursts. Morphological comparisons with the X-ray reveal that
approximately 75% of the UVOT light curves are similar to one of the four
morphologies identified by Evans et al. (2009). The remaining approximately 25%
have a newly identified morphology. For many bursts, redshift and extinction
corrected UV/optical spectral slopes are also provided at 2000, 20,000, and
200,000 seconds.Comment: 44 pages, 14 figures, to be published in Astrophysical Journal
Supplementa
THE SWIFT UVOT STARS SURVEY. I. METHODS AND TEST CLUSTERS
We describe the motivations and background of a large survey of nearby stel-
lar populations using the Ultraviolet Optical Telescope (UVOT) aboard the Swift
Gamma-Ray Burst Mission. UVOT, with its wide field, NUV sensitivity, and 2.3
spatial resolution, is uniquely suited to studying nearby stellar populations
and providing insight into the NUV properties of hot stars and the contribution
of those stars to the integrated light of more distant stellar populations. We
review the state of UV stellar photometry, outline the survey, and address
problems spe- cific to wide- and crowded-field UVOT photometry. We present
color-magnitude diagrams of the nearby open clusters M 67, NGC 188, and NGC
2539, and the globular cluster M 79. We demonstrate that UVOT can easily
discern the young- and intermediate-age main sequences, blue stragglers, and
hot white dwarfs, pro- ducing results consistent with previous studies. We also
find that it characterizes the blue horizontal branch of M 79 and easily
identifies a known post-asymptotic giant branch star.Comment: 35 pages, 8 figures, accepted for publication in Astronomical Journa
A Quasar Catalog with Simultaneous UV, Optical and X-ray Observations by Swift
We have compiled a catalog of optically-selected quasars with simultaneous
observations in UV/optical and X-ray bands by the Swift Gamma Ray Burst
Explorer. Objects in this catalog are identified by matching the Swift
pointings with the Sloan Digital Sky Survey Data Release 5 quasar catalog. The
final catalog contains 843 objects, among which 637 have both UVOT and XRT
observations and 354 of which are detected by both instruments. The overall
X-ray detection rate is ~60% which rises to ~85% among sources with at least 10
ks of XRT exposure time. We construct the time-averaged spectral energy
distribution for each of the 354 quasars using UVOT photometric measurements
and XRT spectra. From model fits to these SEDs, we find that the big blue bump
contributes about 0.3 dex to the quasar luminosity. We re-visit the
alpha_ox-L_uv relation by selecting a clean sample with only type 1 radio-quiet
quasars; the dispersion of this relation is reduced by at least 15% compared to
studies that use non-simultaneous UV/optical and X-ray data. We only found a
weak correlation between L/L_Edd and alpha_uv. We do not find significant
correlations between alpha_x and alpha_ox, alpha_ox and alpha_uv, and alpha_x
and Log L(0.3-10 keV). The correlations between alpha_uv and alpha_x, alpha_ox
and alpha_x, alpha_ox and alpha_uv, L/L_Edd and alpha_x, and L/L_Edd and
alpha_ox are stronger amongst low-redshift quasars, indicating that these
correlations are likely driven by the changes of SED shape with accretion
state.Comment: 63 pages, 22 figures, accepted by ApJ