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Sheila McBreen

Publications and source records attributed to Sheila McBreen.

6 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2022

In Search of Short Gamma-ray Burst Optical Counterparts with the Zwicky Transient Facility

The Fermi Gamma-ray Burst Monitor (GBM) triggers on-board in response to∼40 short gamma-ray bursts (SGRBs) per year; however, their large localization regions have made the search for optical counterparts a challenging endeavour. We have developed and executed an extensive program with the wide field of view of the Zwicky Transient Facility (ZTF) camera, mounted on the Palomar 48 inch Oschin telescope (P48), to perform target-of-opportunity (ToO) observations on 10Fermi-GBM SGRBsduring 2018 and 2020-2021. Bridging the large sky areas with small field of view optical telescopesin order to track the evolution of potential candidates, we look for the elusive SGRB afterglows andkilonovae (KNe) associated with these high-energy events. No counterpart has yet been found, eventhough more than 10 ground based telescopes, part of the Global Relay of Observatories WatchingTransients Happen (GROWTH) network, have taken part in these efforts. The candidate selectionprocedure and the follow-up strategy have shown that ZTF is an efficient instrument for searchingfor poorly localized SGRBs, retrieving a reasonable number of candidates to follow-up and showingpromising capabilities as the community approaches the multi-messenger era. Based on the medianlimiting magnitude of ZTF, our searches would have been able to retrieve a GW170817-like event upto∼200 Mpc and SGRB afterglows to z = 0.16 or 0.4, depending on the assumed underlying energymodel. Future ToOs will expand the horizon to z = 0.2 and 0.7 respectively.

Tomas Ahumada↗
NASA NTRS2021

Discovery and Confirmation of the Shortest Gamma-Ray Burst from a Collapsar

Gamma-ray bursts (GRBs) are among the brightest and most energetic events in the Universe. The duration and hardness distribution of GRBs has two clusters, now understood to reflect (at least) two different progenitors. Short-hard GRBs (SGRBs; T(sub 90) < 2 s) arise from compact binary mergers, and long-soft GRBs (LGRBs; T(sub 90) > 2 s) have been attributed to the collapse of peculiar massive stars (collapsars). The discovery of SN 1998bw/GRB 980425 marked the first association of an LGRB with a collapsar, and AT 2017gfo/GRB 170817A/GW170817 marked the first association of an SGRB with a binary neutron star merger, which also produced a gravitational wave. Here, we present the discovery of ZTF20abwysqy (AT2020scz), a fast-fading optical transient in the Fermi satellite and the Interplanetary Network localization regions of GRB 200826A; X-ray and radio emission further confirm that this is the afterglow. Follow-up imaging (at rest-frame 16.5 days) reveals excess emission above the afterglow that cannot be explained as an underlying kilonova, but which is consistent with being the supernova. Although the GRB duration is short (rest-frame T90 of 0.65 s), our panchromatic follow-up data confirm a collapsar origin. GRB 200826A is the shortest LGRB found with an associated collapsar; it appears to sit on the brink between a successful and a failed collapsar. Our discovery is consistent with the hypothesis that most collapsars fail to produce ultra-relativistic jets.

High-energy astrophysics↗
NASA NTRSDate not supplied

Transient Science with LEAP

The LargE Area burst Polarimeter (LEAP) will investigate the nature of gamma-ray burst jets by making via the first high-fidelity polarization and spectroscopy measurements of the prompt gamma-ray emission from a large sample of gamma-ray bursts (GRBs). LEAP is a proposed International Space Station (ISS) payload with a three-year mission designed to answer the following science questions. Are the jet magnetic fields randomly oriented or are their directions ordered? Are the jets dominated by matter or magnetic fields? Is the energy dissipated within the jet by internal shocks or by magnetic reconnection? Is the non-thermal emission mechanism synchrotron radiation, and what portion of the signal is of thermal photospheric origin? LEAP's baseline mission requires observation of at least 65 GRBs with a sensitivity defined by a minimum detectable polarization (MDP) of 30%. The current LEAP design is expected to trigger on approximately 400 GRBs, with about 86 of those having an MDP <30%. LEAP will enable rapid community follow-up to better understand GRBs and their environments. The LEAP design enables a broad range of secondary science while achieving its baseline mission. During overlap between LIGO's A+ configuration, approximately 3 joint GW/GRB detections per year are expected with LEAP. LEAP will also be sensitive to magnetar bursts, which have recently been associated with Fast Radio Bursts and will potentially measure polarization for bright individual bursts or stacked collections of bursts. LEAP will extend pulse flux and spin frequency histories for accreting pulsars with a sensitivity similar to Fermi GBM, and will potentially measure polarization for their brightest outbursts. The LEAP mission is scheduled during the declining phase of Solar Cycle 25, during which many intense flares are likely to occur; LEAP will make the most sensitive measurements to date of solar flare polarization. LEAP will open a new window into the nature of the most energetic phenomena in the universe with gamma-ray polarization.

N/A↗