arXiv subjects

Josh S. Bloom

Publications and source records attributed to Josh S. Bloom.

4 recordsLinked to original sources

arXiv2024

ZTF SN Ia DR2: Overview

We present the first homogeneous release of several thousand Type Ia supernovae (SNe Ia), all having spectroscopic classification, and spectroscopic redshifts for half the sample. This release, named the "DR2", contains 3628 nearby (z < 0.3) SNe Ia discovered, followed and classified by the Zwicky Transient Facility survey between March 2018 and December 2020. Of these, 3000 have good-to-excellent sampling and 2667 pass standard cosmology light-curve quality cuts. This release is thus the largest SN Ia release to date, increasing by an order of magnitude the number of well characterized low-redshift objects. With the "DR2", we also provide a volume-limited (z < 0.06) sample of nearly a thousand SNe Ia. With such a large, homogeneous and well controlled dataset, we are studying key current questions on SN cosmology, such as the linearity SNe Ia standardization, the SN and host dependencies, the diversity of the SN Ia population, and the accuracy of the current light-curve modeling. These, and more, are studied in detail in a series of articles associated with this release. Alongside the SN Ia parameters, we publish our force-photometry gri-band light curves, 5138 spectra, local and global host properties, observing logs, and a python tool to ease use and access of these data. The photometric accuracy of the "DR2" is not yet suited for cosmological parameter inference, which will follow as "DR2.5" release. We nonetheless demonstrate that the multi-thousand SN Ia Hubble Diagram has a typical 0.15 mag scatter.

astro-ph.CO↗

arXiv2018

LSST: from Science Drivers to Reference Design and Anticipated Data Products

(Abridged) We describe here the most ambitious survey currently planned in the optical, the Large Synoptic Survey Telescope (LSST). A vast array of science will be enabled by a single wide-deep-fast sky survey, and LSST will have unique survey capability in the faint time domain. The LSST design is driven by four main science themes: probing dark energy and dark matter, taking an inventory of the Solar System, exploring the transient optical sky, and mapping the Milky Way. LSST will be a wide-field ground-based system sited at Cerro Pachón in northern Chile. The telescope will have an 8.4 m (6.5 m effective) primary mirror, a 9.6 deg$^2$ field of view, and a 3.2 Gigapixel camera. The standard observing sequence will consist of pairs of 15-second exposures in a given field, with two such visits in each pointing in a given night. With these repeats, the LSST system is capable of imaging about 10,000 square degrees of sky in a single filter in three nights. The typical 5$σ$ point-source depth in a single visit in $r$ will be $\sim 24.5$ (AB). The project is in the construction phase and will begin regular survey operations by 2022. The survey area will be contained within 30,000 deg$^2$ with $δ<+34.5^\circ$, and will be imaged multiple times in six bands, $ugrizy$, covering the wavelength range 320--1050 nm. About 90\% of the observing time will be devoted to a deep-wide-fast survey mode which will uniformly observe a 18,000 deg$^2$ region about 800 times (summed over all six bands) during the anticipated 10 years of operations, and yield a coadded map to $r\sim27.5$. The remaining 10\% of the observing time will be allocated to projects such as a Very Deep and Fast time domain survey. The goal is to make LSST data products, including a relational database of about 32 trillion observations of 40 billion objects, available to the public and scientists around the world.

astro-ph↗

arXiv2011

Circumstellar Material in Type Ia Supernovae via Sodium Absorption Features

Type Ia supernovae are key tools for measuring distances on a cosmic scale. They are generally thought to be the thermonuclear explosion of an accreting white dwarf in a close binary system. The nature of the mass donor is still uncertain. In the single-degenerate model it is a main-sequence star or an evolved star, whereas in the double-degenerate model it is another white dwarf. We show that the velocity structure of absorbing material along the line of sight to 35 type Ia supernovae tends to be blueshifted. These structures are likely signatures of gas outflows from the supernova progenitor systems. Thus many type Ia supernovae in nearby spiral galaxies may originate in single-degenerate systems.

astro-ph.HE↗

arXiv2006

GRB Afterglows as a New Probe of the ISM and IGM at High Redshift

We summarize results from a study of the metallicity, relative abundances, gas density, and kinematics of dense media in the host environment of two Swift bursts, GRB050730 at z=3.968 and GRB051111 at z=1.549. Both GRB hosts exhibit strong absorption features from excited Si+ and Fe+ ions, indicating an extreme ISM environment that is similar to what is found around massive stars like luminous blue variables (LBV) and Wolf-Rayet stars. The extreme ISM properties have never been observed in intervening quasar absorption line systems beyond the local universe.

astro-ph↗