ABSTRACT We verified the off-axis jet model of X-ray flashes (XRFs) and examined a discovery of off-axis orphan gamma-ray burst (GRB) afterglows. The XRF sample was selected on the basis of the ...following three factors: (1) a constraint on the lower peak energy of the prompt spectrum , (2) redshift measurements, and (3) multicolor observations of an earlier (or brightening) phase. XRF 020903 was the only sample selected on the basis of these criteria. A complete optical multicolor afterglow light curve of XRF 020903 obtained from archived data and photometric results in the literature showed an achromatic brightening around 0.7 days. An off-axis jet model with a large observing angle (0.21 rad, which is twice the jet opening half-angle, ) can naturally describe the achromatic brightening and the prompt X-ray spectral properties. This result indicates the existence of off-axis orphan GRB afterglow light curves. Events with a larger viewing angle ( ) could be discovered using an 8 m class telescope with wide-field imagers such as the Subaru Hyper-Suprime-Cam and the Large Synoptic Survey Telescope.
We report the first detection of radio polarization of a gamma-ray burst (GRB) afterglow with the first intensive combined use of telescopes in the millimeter and submillimeter ranges for GRB ...171205A. The linear polarization degree in the millimeter band at the subpercent level (0.27% 0.04%) is lower than those observed in late-time optical afterglows (weighted average of ∼1%). The Faraday depolarization by nonaccelerated, cool electrons in the shocked region is one of the possible mechanisms for the low value. This scenario requires a total energy that is larger by a factor of ∼10 than ordinary estimates without considering nonaccelerated electrons. The polarization position angle varies by at least 20° across the millimeter band, which is not inconsistent with this scenario. This result indicates that polarimetry in the millimeter and submillimeter ranges is a unique tool for investigating GRB energetics, and coincident observations with multiple frequencies or bands would provide more accurate measurements of the nonaccelerated electron fraction.
We present the first radio polarimetric observations of a fast-rising blue optical transient, AT2018cow. Two epochs of polarimetry with additional coincident photometry were performed with the ...Atacama Large Millimeter/submillimeter Array. The overall photometric results based on simultaneous observations in the 100 and 230 GHz bands are consistent with the nonthermal radiation model reported by Ho et al. and indicate that the spectral peaks (∼110 GHz at the first epoch and ∼67 GHz at the second epoch) represent the synchrotron self-absorption frequency. The non-detection of linear polarization with <0.15% in the 230 GHz band at the phase when the effect of synchrotron self-absorption was quite small in the band may be explained by internal Faraday depolarization with high circumburst density and strong magnetic field. This result supports the stellar explosion scenario rather than the tidal disruption model. The maximum energy of accelerating particles at the shocks of AT2018cow-like objects is also discussed.
Abstract
We investigated the radio properties of the host galaxy of X-ray flash, XRF 020903, which is the best example for investigating the off-axis origin of gamma-ray bursts (GRBs). Dust continuum ...at 233 GHz and CO are observed using the Atacama Large millimeter/submillimeter array. The molecular gas mass derived by applying the metallicity-dependent CO-to-H
2
conversion factor matches the global trend along the redshift and stellar mass of the GRB host galaxies. The estimated gas depletion timescale (pertaining to the potential critical characteristics of GRB host galaxies) is equivalent to those of GRBs and super-luminous supernova hosts in the same redshift range. These properties of the XRF 020903 host galaxy observed in radio resemble those of GRB host galaxies, thereby supporting the identical origin of XRF 020903 and GRBs.
Abstract
Hyper Suprime-Cam (HSC) is a wide-field imaging camera on the prime focus of the 8.2-m Subaru telescope on the summit of Mauna Kea in Hawaii. A team of scientists from Japan, Taiwan, and ...Princeton University is using HSC to carry out a 300-night multi-band imaging survey of the high-latitude sky. The survey includes three layers: the Wide layer will cover 1400 deg2 in five broad bands (grizy), with a 5 σ point-source depth of r ≈ 26. The Deep layer covers a total of 26 deg2 in four fields, going roughly a magnitude fainter, while the UltraDeep layer goes almost a magnitude fainter still in two pointings of HSC (a total of 3.5 deg2). Here we describe the instrument, the science goals of the survey, and the survey strategy and data processing. This paper serves as an introduction to a special issue of the Publications of the Astronomical Society of Japan, which includes a large number of technical and scientific papers describing results from the early phases of this survey.
Planned rapid submillimeter (submm) gamma-ray-bursts (GRBs) follow-up observations conducted using the Greenland Telescope (GLT) are presented. The GLT is a 12-m submm telescope to be located at the ...top of the Greenland ice sheet, where the high altitude and dry weather porvide excellent conditions for observations at submm wavelengths. With its combination of wavelength window and rapid responding system, the GLT will explore new insights on GRBs. Summarizing the current achievements of submm GRB follow-ups, we identify the following three scientific goals regarding GRBs: (1) systematic detection of bright submm emissions originating from reverse shock (RS) in the early afterglow phase, (2) characterization of forward shock and RS emissions by capturing their peak flux and frequencies and performing continuous monitoring, and (3) detections of GRBs at a high redshift as a result of the explosion of first generation stars through systematic rapid follow-ups. The light curves and spectra calculated by available theoretical models clearly show that the GLT could play a crucial role in these studies.
Abstract
The Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) is a three-layered imaging survey aimed at addressing some of the most important outstanding questions in astronomy today, including ...the nature of dark matter and dark energy. The survey has been awarded 300 nights of observing time at the Subaru Telescope, and it started in 2014 March. This paper presents the first public data release of HSC-SSP. This release includes data taken in the first 1.7 yr of observations (61.5 nights), and each of the Wide, Deep, and UltraDeep layers covers about 108, 26, and 4 square degrees down to depths of i ∼ 26.4, ∼26.5, and ∼27.0 mag, respectively (5 σ for point sources). All the layers are observed in five broad bands (grizy), and the Deep and UltraDeep layers are observed in narrow bands as well. We achieve an impressive image quality of 0${^{\prime\prime}_{.}}$6 in the i band in the Wide layer. We show that we achieve 1%–2% point spread function (PSF) photometry (root mean square) both internally and externally (against Pan-STARRS1), and ∼10 mas and 40 mas internal and external astrometric accuracy, respectively. Both the calibrated images and catalogs are made available to the community through dedicated user interfaces and database servers. In addition to the pipeline products, we also provide value-added products such as photometric redshifts and a collection of public spectroscopic redshifts. Detailed descriptions of all the data can be found online. The data release website is https://hsc-release.mtk.nao.ac.jp.
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