A Method to Measure Photometries of Moderately-Saturated UVOT Sources
arXiv:2308.10171 · doi:10.3847/1538-4365/acf20a
Abstract
For bright transients such as Gamma-Ray Bursts (GRBs), the Ultra-Violet/Optical Telescope (UVOT) operates under event mode at early phases, which records incident positions and arrival time for each photon. The event file is able to be screened into many exposures to study the early light curve of GRBs with a high time resolution, including in particular the rapid brightening of the UV/Optical emission. Such a goal, however, is hampered for some extremely bright GRBs by the saturation in UVOT event images. For moderately saturated UVOT sources, in this work we develop the method proposed in Jin et al. (2023) to recover their photometries. The basic idea is to assume a stable point spread function (PSF) of UVOT images, for which the counts in the core region (i.e., an aperture of a radius of 5 arcsec) and the wing region (i.e., an annulus ranging from 15 arcsec to 25 arcsec) should be a constant and the intrinsic flux can be reliably inferred with data in the ring. We demonstrate that in a given band, a tight correlation does hold among the background-removed count rates in the core and the wing. With the new method, the bright limit of measuring range for UVOT V and B bands increases ~ 1.7 mag, while only ~ 0.7 mag for U band due to the lack of bright calibration sources. Systematic uncertainties are ~ 0.2 mag for V, B and U bands.
arXiv comment27 pages, 19 figures, 3 tables, accepted to ApJS
References in corpus (15)
- The Swift Ultra-Violet/Optical Telescope
- Photometric Calibration of the Swift Ultraviolet/Optical Telescope
- Paper II: Calibration of the Swift ultraviolet/optical telescope
- Spectrophotometric Libraries, Revised Photonic Passbands and Zero-points for UBVRI, Hipparcos and Tycho Photometry
- Observations of the Naked-Eye GRB 080319B: Implications of Nature's Brightest Explosion
- GRB 130427A: a Nearby Ordinary Monster
- No X-rays from the very nearby Type Ia SN2014J: constraints on its environment
- Gaia Data Release 3: The Galaxy in your preferred colours. Synthetic photometry from Gaia low-resolution spectra
- Gamma-Ray Burst at the extreme: "the naked-eye burst" GRB 080319B
- The Swift-UVOT ultraviolet and visible grism calibration
- Swift-UVOT captures the earliest ultraviolet spectrum of a Gamma Ray Burst
- The use and calibration of read-out streaks to increase the dynamic range of the Swift Ultraviolet/Optical Telescope
- A cross-calibration between Tycho-2 photometry and HST spectrophotometry
- Accurate Photometry of Saturated Stars Using the Point-Spread-Function Wing Technique with Spitzer
- An optical-ultraviolet flare with absolute AB magnitude of -39.4 detected in GRB 220101A