35 research outputs found
The Host Galaxy of GRB 060505: Host ISM Properties
We investigate the ISM environment of GRB 060505. Using optical emission-line
diagnostic ratios, we compare the ISM properties of the GRB 060505 host region
with the hosts of unambiguous long- and short-duration GRBs. We show that the
metallicity, ionization state, and star formation rate of the GRB 060505
environment are more consistent with short-duration GRBs than with
long-duration GRBs. We compare the metallicity and star formation rates of the
GRB 060505 region with four other star-forming regions within the GRB 060505
host galaxy. We find no significant change in metallicity or star formation
rate between the GRB 060505 region and the other four host regions. Our results
are consistent with a compact-object-merger progenitor for GRB 060505.Comment: 7 pages, two figures; accepted for publication in ApJ
MMT Extremely Metal Poor Galaxy Survey I. An Efficient Technique to Identify Metal Poor Galaxies
We demonstrate a successful strategy for identifying extremely metal poor
galaxies. Our preliminary survey of 24 candidates contains 10 metal poor
galaxies of which 4 have 12+log(O/H)<7.65, some of the lowest metallicity blue
compact galaxies known to date. Interestingly, our sample of metal poor
galaxies have systematically lower metallicity for their luminosity than
comparable samples of blue compact galaxies, dIrrs, and normal star-forming
galaxies. Our metal poor galaxies share very similar properties, however, with
the host galaxies of nearby long-duration gamma-ray bursts (GRBs), including
similar metallicity, stellar ages, and star formation rates. We use H\beta to
measure the number of OB stars present in our galaxies and estimate a
core-collapse supernova rate of ~10^-3 yr^-1. A larger sample of metal poor
galaxies may provide new clues into the environment where GRBs form and may
provide a list of potential GRB hosts.Comment: Accepted to AJ, 8 pages using emulateap
The Host Galaxies of Gamma-Ray Bursts I: ISM Properties of Ten Nearby Long-Duration GRB Hosts
We present the first observations from a large-scale survey of nearby (z < 1)
long-duration gamma-ray burst (LGRB) host galaxies, which consist of eight
rest-frame optical spectra obtained at Keck and Magellan. Along with two host
galaxy observations from the literature, we use optical emission line
diagnostics to determine metallicities, ionization parameters, young stellar
population ages, and star formation rates. We compare the LGRB host
environments to a variety of local and intermediate-redshift galaxy
populations, as well as the newest grid of stellar population synthesis and
photoionization models generated with the Starburst99/Mappings codes. With
these comparisons we investigate whether the GRB host galaxies are consistent
with the properties of the general galaxy population, and therefore whether
they may be used as reliable tracers of star formation. We find that LGRB host
galaxies generally have low-metallicity ISM environments out to z ~ 1. The ISM
properties of our GRB hosts, including metallicity, ionization parameter, and
young stellar population age, are significantly different from the general
galaxy population, host galaxies of nearby broad-lined Type Ic supernovae, and
nearby metal-poor galaxies.Comment: 29 pages, 19 figures, 5 tables, accepted for publication in A
No Correlation Between Host Galaxy Metallicity and Gamma-Ray Energy Release for Long-Duration Gamma-Ray Bursts
We compare the redshifts, host galaxy metallicities, and isotropic
(E_gamma,iso) and beaming-corrected (E_gamma) gamma-ray energy release of 16
long-duration gamma-ray bursts (LGRBs) at z < 1. From this comparison, we find
no statistically significant correlation between host metallicity and redshift,
E_gamma,iso, or E_gamma. These results are at odds with previous theoretical
and observational predictions of an inverse correlation between gamma-ray
energy release and host metallicity, as well as the standard predictions of
metallicity-driven wind effects in stellar evolutionary models. We consider the
implications that these results have for LGRB progenitor scenarios, and discuss
our current understanding of the role that metallicity plays in the production
of LGRBs.Comment: 13 pages, 1 figure; accepted to Astrophysical Journa
GRB 090426: The Environment of a Rest-Frame 0.35-second Gamma-Ray Burst at Redshift z=2.609
We present the discovery of an absorption-line redshift of z = 2.609 for GRB
090426, establishing the first firm lower limit to a redshift for a gamma-ray
burst with an observed duration of <2 s. With a rest-frame burst duration of
T_90z = 0.35 s and a detailed examination of the peak energy of the event, we
suggest that this is likely (at >90% confidence) a member of the short/hard
phenomenological class of GRBs. From analysis of the optical-afterglow spectrum
we find that the burst originated along a very low HI column density sightline,
with N_HI < 3.2 x 10^19 cm^-2. Our GRB 090426 afterglow spectrum also appears
to have weaker low-ionisation absorption (Si II, C II) than ~95% of previous
afterglow spectra. Finally, we also report the discovery of a blue, very
luminous, star-forming putative host galaxy (~2 L*) at a small angular offset
from the location of the optical afterglow. We consider the implications of
this unique GRB in the context of burst duration classification and our
understanding of GRB progenitor scenarios.Comment: Submitted to MNRA
Investigation of two Fermi-LAT gamma-ray blazars coincident with high-energy neutrinos detected by IceCube
After the identification of the gamma-ray blazar TXS 0506+056 as the first
compelling IceCube neutrino source candidate, we perform a systematic analysis
of all high-energy neutrino events satisfying the IceCube realtime trigger
criteria. We find one additional known gamma-ray source, the blazar GB6
J1040+0617, in spatial coincidence with a neutrino in this sample. The chance
probability of this coincidence is 30% after trial correction. For the first
time, we present a systematic study of the gamma-ray flux, spectral and optical
variability, and multi-wavelength behavior of GB6 J1040+0617 and compare it to
TXS 0506+056. We find that TXS 0506+056 shows strong flux variability in the
Fermi-LAT gamma-ray band, being in an active state around the arrival of
IceCube-170922A, but in a low state during the archival IceCube neutrino flare
in 2014/15. In both cases the spectral shape is statistically compatible () with the average spectrum showing no indication of a significant
relative increase of a high-energy component. While the association of GB6
J1040+0617 with the neutrino is consistent with background expectations, the
source appears to be a plausible neutrino source candidate based on its
energetics and multi-wavelength features, namely a bright optical flare and
modestly increased gamma-ray activity. Finding one or two neutrinos originating
from gamma-ray blazars in the given sample of high-energy neutrinos is
consistent with previously derived limits of neutrino emission from gamma-ray
blazars, indicating the sources of the majority of cosmic high-energy neutrinos
remain unknown.Comment: 22 pages, 11 figures, 2 Table
A pregnancy lifestyle intervention to prevent gestational diabetes risk factors in overweight Hispanic women: a feasibility randomized controlled trial
AIMS: To pilot the feasibility of a prenatal lifestyle intervention to modify physical activity and diet among pregnant overweight and obese Hispanic women, with the aim of reducing risk factors for gestational diabetes mellitus.
METHODS: Women were randomized either to a lifestyle intervention (n = 33, 48.5%), consisting of a culturally and linguistically modified, motivationally targeted, individually tailored 6-month prenatal programme, or to standard care (n = 35, 51.5%). Bilingual and bicultural health educators encouraged women to achieve guidelines for physical activity, decrease saturated fat and increase dietary fibre. Outcomes included gestational weight gain, infant birth weightand biomarkers associated with insulin resistance.
RESULTS: Patient retention up to delivery was 97% in both study groups. The lifestyle intervention attenuated the pregnancy-associated decline in moderate-intensity physical activity, but differences between groups were not significant (mean +/- se -23.4 +/- 16.6 vs -27.0 +/- 16.2 metabolic equivalent of task h/week; P = 0.88). Vigorous-intensity activity increased during the course of pregnancy in the lifestyle intervention group (mean +/- se 1.6 +/- 0.8 metabolic equivalent of task h/week) and declined in the standard care group (-0.8 +/- 0.8 metabolic equivalent of task h/week; P = 0.04). The lifestyle intervention group also had slightly lower gestational weight gain and infant birth weights compared with the standard care group; however, these differences were not statistically significant. There were no statistically significant differences in biomarkers of insulin resistance between groups.
CONCLUSIONS: Findings suggest that a motivationally matched lifestyle intervention is feasible and may help attenuate pregnancy-related decreases in vigorous physical activity in a population of overweight and obese Hispanic women. The intervention protocol can readily be translated into clinical practice in underserved and minority populations
Measured metallicities at the sites of nearby broad-lined type Ic supernovae and implications for the supernovae gamma-ray burst connection
We compare the chemical abundances at the sites of 12 nearby (z < 0.14) Type Ic supernovae (SN Ic) that showed broad lines, but had no observed gamma-ray burst (GRB), with the chemical abundances in five nearby (z < 0.25) galaxies at the sites of GRBs where broad-lined SN Ic were seen after the fireball had faded. It has previously been noted that GRB hosts are low in luminosity and low in their metal abundances. If low metallicity is sufficient to force the evolution of massive stars to end their lives as GRBs with an accompanying broad-lined SN Ic, then we would expect higher metal abundances for the broad-lined SN Ic that have no detected GRBs. This is what we observe, and this trend is independent of the choice of metallicity calibration we adopt and the mode of SN survey that found the broad-lined SN Ic. A unique feature of this analysis is that we present new spectra of the host galaxies and analyze all measurements of both samples in the same set of methods, using the galaxy emission-line measurements corrected for extinction and stellar absorption, via independent metallicity diagnostics of Kewley & Dopita, McGaugh, and Pettini & Pagel. In our small sample, the boundary between galaxies that have GRBs accompanying their broad-lined SN Ic and those that have broad-lined SN Ic without GRBs lies at an oxygen abundance of 12 + log(O/H)KD02 8.5, which corresponds to 0.2-0.6 Z⊙ depending on the adopted metallicity scale and solar abundance value. Even when we limit the comparison to SN Ic that were found in untargeted supernova surveys, the environment of every broad-lined SN Ic that had no GRB is more metal rich than the site of any broad-lined SN Ic where a GRB was detected