226 research outputs found
Probing Kilonova Ejecta Properties Using a Catalog of Short Gamma-Ray Burst Observations
The discovery of GW170817 and GRB 170817A in tandem with AT 2017gfo cemented
the connection between neutron star mergers, short gamma-ray bursts (GRBs), and
kilonovae. To investigate short GRB observations in the context of diverse
kilonova behavior, we present a comprehensive optical and near-infrared (NIR)
catalog of 85 bursts discovered over 2005-2020 on timescales of
days. The sample includes previously unpublished observations of 23 bursts, and
encompasses both detections and deep upper limits. We identify 11.8% and 15.3%
of short GRBs in our catalog with upper limits that probe luminosities lower
than those of AT 2017gfo and a fiducial NSBH kilonovae model (for pole-on
orientations), respectively. We quantify the ejecta masses allowed by the
deepest limits in our catalog, constraining blue and `extremely blue' kilonova
components of 14.1% of bursts to . The
sample of short GRBs is not particularly constraining for red kilonova
components. Motivated by the large catalog as well as model predictions of
diverse kilonova behavior, we investigate altered search strategies for future
follow-up to short GRBs. We find that ground-based optical and NIR observations
on timescales of days can play a significant role in constraining
more diverse outcomes. We expect future short GRB follow up efforts, such as
from the {\it James Webb Space Telescope}, to expand the reach of kilonova
detectability to redshifts of .Comment: 33 pages, 7 figures, 3 tables. Submitted to Ap
SAGUARO: Time-domain Infrastructure for the Fourth Gravitational-wave Observing Run and Beyond
We present upgraded infrastructure for Searches after Gravitational Waves
Using ARizona Observatories (SAGUARO) during LIGO, Virgo, and KAGRA's fourth
gravitational-wave (GW) observing run (O4). These upgrades implement many of
the lessons we learned after a comprehensive analysis of potential
electromagnetic counterparts to the GWs discovered during the previous
observing run. We have developed a new web-based target and observation manager
(TOM) that allows us to coordinate sky surveys, vet potential counterparts, and
trigger follow-up observations from one centralized portal. The TOM includes
software that aggregates all publicly available information on the light curves
and possible host galaxies of targets, allowing us to rule out potential
contaminants like active galactic nuclei, variable stars, solar-system objects,
and preexisting supernovae, as well as to assess the viability of any plausible
counterparts. We have also upgraded our image-subtraction pipeline by
assembling deeper reference images and training a new neural network-based
real-bogus classifier. These infrastructure upgrades will aid coordination by
enabling the prompt reporting of observations, discoveries, and analysis to the
GW follow-up community, and put SAGUARO in an advantageous position to discover
kilonovae in the remainder of O4 and beyond. Many elements of our open-source
software stack have broad utility beyond multimessenger astronomy, and will be
particularly relevant in the "big data" era of transient discoveries by the
Vera C. Rubin Observatory.Comment: submitted to AAS Journal
The Broad-band Counterpart of the Short GRB 200522A at :A Luminous Kilonova or a Collimated Outflow with a Reverse Shock?
We present the discovery of the radio afterglow and near-infrared (NIR)
counterpart of the Swift short GRB 200522A, located at a small projected offset
of kpc from the center of a young, star-forming host galaxy at
. The radio and X-ray luminosities of the afterglow are consistent
with those of on-axis cosmological short GRBs. The NIR counterpart, revealed by
our HST observations at a rest-frame time of days, has a
luminosity of erg s. This is
substantially lower than on-axis short GRB afterglow detections, but is a
factor of - more luminous than the kilonova of GW170817, and
significantly more luminous than any kilonova candidate for which comparable
observations exist. The combination of the counterpart's color (; rest-frame) and luminosity cannot be explained by standard radioactive
heating alone. We present two scenarios to interpret the broad-band behavior of
GRB 200522A: a synchrotron forward shock with a luminous kilonova (potentially
boosted by magnetar energy deposition), or forward and reverse shocks from a
, relativistic () jet. Models which
include a combination of enhanced radioactive heating rates, low-lanthanide
mass fractions, or additional sources of heating from late-time central engine
activity may provide viable alternate explanations. If a stable magnetar was
indeed produced in GRB 200522A, we predict that late-time radio emission will
be detectable starting - years after the burst for a deposited
energy of erg. Counterparts of similar luminosity to GRB
200522A associated with gravitational wave events will be detectable with
current optical searches to Mpc.Comment: 33 pages, 13 figures, 5 tables. Submitted to AAS Journal
The Broad-band Counterpart of the Short GRB 200522A at :A Luminous Kilonova or a Collimated Outflow with a Reverse Shock?
We present the discovery of the radio afterglow and near-infrared (NIR) counterpart of the Swift short GRB 200522A, located at a small projected offset of kpc from the center of a young, star-forming host galaxy at . The radio and X-ray luminosities of the afterglow are consistent with those of on-axis cosmological short GRBs. The NIR counterpart, revealed by our HST observations at a rest-frame time of days, has a luminosity of erg s. This is substantially lower than on-axis short GRB afterglow detections, but is a factor of - more luminous than the kilonova of GW170817, and significantly more luminous than any kilonova candidate for which comparable observations exist. The combination of the counterpart's color (; rest-frame) and luminosity cannot be explained by standard radioactive heating alone. We present two scenarios to interpret the broad-band behavior of GRB 200522A: a synchrotron forward shock with a luminous kilonova (potentially boosted by magnetar energy deposition), or forward and reverse shocks from a , relativistic () jet. Models which include a combination of enhanced radioactive heating rates, low-lanthanide mass fractions, or additional sources of heating from late-time central engine activity may provide viable alternate explanations. If a stable magnetar was indeed produced in GRB 200522A, we predict that late-time radio emission will be detectable starting - years after the burst for a deposited energy of erg. Counterparts of similar luminosity to GRB 200522A associated with gravitational wave events will be detectable with current optical searches to Mpc
The Demographics, Stellar Populations, and Star Formation Histories of Fast Radio Burst Host Galaxies: Implications for the Progenitors
We present a comprehensive catalog of observations and stellar population properties for 23 highly secure host galaxies of fast radio bursts (FRBs). Our sample comprises 6 repeating FRBs and 17 apparent nonrepeaters. We present 82 new photometric and 8 new spectroscopic observations of these hosts. Using stellar population synthesis modeling and employing nonparametric star formation histories (SFHs), we find that FRB hosts have a median stellar mass of ≈109.9M⊙, mass-weighted age ≈5.1 Gyr, and ongoing star formation rate ≈1.3 M⊙ yr−1 but span wide ranges in all properties. Classifying the hosts by degree of star formation, we find that 87% (20 of 23 hosts) are star-forming, two are transitioning, and one is quiescent. The majority trace the star-forming main sequence of galaxies, but at least three FRBs in our sample originate in less-active environments (two nonrepeaters and one repeater). Across all modeled properties, we find no statistically significant distinction between the hosts of repeaters and nonrepeaters. However, the hosts of repeating FRBs generally extend to lower stellar masses, and the hosts of nonrepeaters arise in more optically luminous galaxies. While four of the galaxies with the clearest and most prolonged rises in their SFHs all host repeating FRBs, demonstrating heightened star formation activity in the last ≲100 Myr, one nonrepeating host shows this SFH as well. Our results support progenitor models with short delay channels (i.e., magnetars formed via core-collapse supernova) for most FRBs, but the presence of some FRBs in less-active environments suggests a fraction form through more delayed channels
Mutation in utp15 Disrupts Vascular Patterning in a p53-Dependent Manner in Zebrafish Embryos
Angiogenesis is the process by which the highly branched and functional vasculature arises from the major vessels, providing developing tissues with nutrients, oxygen, and removing metabolic waste. During embryogenesis, vascular patterning is dependent on a tightly regulated balance between pro- and anti-angiogenic signals, and failure of angiogenesis leads to embryonic lethality. Using the zebrafish as a model organism, we sought to identify genes that influence normal vascular patterning.In a forward genetic screen, we identified mutant LA1908, which manifests massive apoptosis during early embryogenesis, abnormal expression of several markers of arterial-venous specification, delayed angiogenic sprouting of the intersegmental vessels (ISV), and malformation of the caudal vein plexus (CVP), indicating a critical role for LA1908 in cell survival and angiogenesis. Genetic mapping and sequencing identified a G to A transition in the splice site preceding exon 11 of utp15 in LA1908 mutant embryos. Overexpression of wild type utp15 mRNA suppresses all observed mutant phenotypes, demonstrating a causative relationship between utp15 and LA1908. Furthermore, we found that injecting morpholino oligonucleotides inhibiting p53 translation prevents cell death and rescues the vascular abnormalities, indicating that p53 is downstream of Utp15 deficiency in mediating the LA1908 phenotypes.Taken together, our data demonstrate an early embryonic effect of Utp15 deficiency on cell survival and the normal patterning of the vasculature and highlight an anti-angiogenic role of p53 in developing embryos
Differentiating Protein-Coding and Noncoding RNA: Challenges and Ambiguities
The assumption that RNA can be readily classified into either protein-coding or non-protein–coding categories has pervaded biology for close to 50 years. Until recently, discrimination between these two categories was relatively straightforward: most transcripts were clearly identifiable as protein-coding messenger RNAs (mRNAs), and readily distinguished from the small number of well-characterized non-protein–coding RNAs (ncRNAs), such as transfer, ribosomal, and spliceosomal RNAs. Recent genome-wide studies have revealed the existence of thousands of noncoding transcripts, whose function and significance are unclear. The discovery of this hidden transcriptome and the implicit challenge it presents to our understanding of the expression and regulation of genetic information has made the need to distinguish between mRNAs and ncRNAs both more pressing and more complicated. In this Review, we consider the diverse strategies employed to discriminate between protein-coding and noncoding transcripts and the fundamental difficulties that are inherent in what may superficially appear to be a simple problem. Misannotations can also run in both directions: some ncRNAs may actually encode peptides, and some of those currently thought to do so may not. Moreover, recent studies have shown that some RNAs can function both as mRNAs and intrinsically as functional ncRNAs, which may be a relatively widespread phenomenon. We conclude that it is difficult to annotate an RNA unequivocally as protein-coding or noncoding, with overlapping protein-coding and noncoding transcripts further confounding this distinction. In addition, the finding that some transcripts can function both intrinsically at the RNA level and to encode proteins suggests a false dichotomy between mRNAs and ncRNAs. Therefore, the functionality of any transcript at the RNA level should not be discounted
Judah Folkman, a pioneer in the study of angiogenesis
More than 30 years ago, Judah Folkman found a revolutionary new way to think about cancer. He postulated that in order to survive and grow, tumors require blood vessels, and that by cutting off that blood supply, a cancer could be starved into remission. What began as a revolutionary approach to cancer has evolved into one of the most exciting areas of scientific inquiry today. Over the years, Folkman and a growing team of researchers have isolated the proteins and unraveled the processes that regulate angiogenesis. Meanwhile, a new generation of angiogenesis research has emerged as well, widening the field into new areas of human disease and deepening it to examine the underlying biological processes responsible for those diseases
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