10 research outputs found
Variable Sodium Absorption in a Low-Extinction Type Ia Supernova
Recent observations have revealed that some Type Ia supernovae exhibit
narrow, time-variable Na I D absorption features. The origin of the absorbing
material is controversial, but it may suggest the presence of circumstellar gas
in the progenitor system prior to the explosion, with significant implications
for the nature of the supernova progenitors. We present the third detection of
such variable absorption, based on six epochs of high-resolution spectroscopy
of the Type Ia supernova SN 2007le from Keck and the HET. The data span ~3
months, from 5 days before maximum light to 90 days after maximum. We find that
one component of the Na D absorption lines strengthened significantly with
time, indicating a total column density increase of ~2.5 x 10^12 cm^-2. The
changes are most prominent after maximum light rather than at earlier times
when the UV flux from the SN peaks. As with SN 2006X, we detect no change in
the Ca II H&K lines over the same time period, rendering line-of-sight effects
improbable and suggesting a circumstellar origin for the absorbing material.
Unlike the previous two SNe exhibiting variable absorption, SN 2007le is not
highly reddened (E_B-V = 0.27 mag), also pointing toward circumstellar rather
than interstellar absorption. Photoionization models show that the data are
consistent with a dense (10^7 cm^-3) cloud or clouds of gas located ~0.1 pc
from the explosion. These results broadly support the single-degenerate
scenario previously proposed to explain the variable absorption, with mass loss
from a nondegenerate companion star responsible for providing the circumstellar
gas. We also present tentative evidence for narrow Halpha emission associated
with the SN, which will require followup observations at late times to confirm.
[abridged]Comment: 16 pages, 10 figures (8 in color), 5 tables. Accepted for publication
in Ap
A Type Ia Supernova at Redshift 1.55 in Hubble Space Telescope Infrared Observations from CANDELS
We report the discovery of a Type Ia supernova (SNIa) at redshift z=1.55 with
the infrared detector of the Wide Field Camera 3 (WFC3-IR) on the Hubble Space
Telescope (HST). This object was discovered in CANDELS imaging data of the
Hubble Ultra Deep Field, and followed as part of the CANDELS+CLASH Supernova
project, comprising the SN search components from those two HST multi-cycle
treasury programs. This is the highest redshift SNIa with direct spectroscopic
evidence for classification. It is also the first SN Ia at z>1 found and
followed in the infrared, providing a full light curve in rest-frame optical
bands. The classification and redshift are securely defined from a combination
of multi-band and multi-epoch photometry of the SN, ground-based spectroscopy
of the host galaxy, and WFC3-IR grism spectroscopy of both the SN and host.
This object is the first of a projected sample at z>1.5 that will be discovered
by the CANDELS and CLASH programs. The full CANDELS+CLASH SN Ia sample will
enable unique tests for evolutionary effects that could arise due to
differences in SN Ia progenitor systems as a function of redshift. This high-z
sample will also allow measurement of the SN Ia rate out to z~2, providing a
complementary constraint on SN Ia progenitor models.Comment: 10 pages, 6 figures, accepted for publication in Ap
The Carnegie Supernova Project: Second Photometry Data Release of Low-Redshift Type Ia Supernovae
The Carnegie Supernova Project (CSP) was a five-year observational survey
conducted at Las Campanas Observatory that obtained, among other things,
high-quality light curves of ~100 low-redshift Type Ia supernovae (SNe Ia).
Presented here is the second data release of nearby SN Ia photometry consisting
of 50 objects, with a subset of 45 having near-infrared follow-up observations.
Thirty-three objects have optical pre-maximum coverage with a subset of 15
beginning at least 5 days before maximum light. In the near-infrared, 27
objects have coverage beginning before the epoch of B-band maximum, with a
subset of 13 beginning at least 5 days before maximum. In addition, we present
results of a photometric calibration program to measure the CSP optical
(uBgVri)bandpasses with an accuracy of ~1%. Finally, we report the discovery of
a second SN Ia, SN 2006ot, similar in its characteristics to the peculiar SN
2006bt.Comment: 115 pages, 7 figures, 7 tables. To be published in the Astronomical
Journal. Comments welcom
Rivaroxaban or aspirin for patent foramen ovale and embolic stroke of undetermined source: a prespecified subgroup analysis from the NAVIGATE ESUS trial
Background: Patent foramen ovale (PFO) is a contributor to embolic stroke of undetermined source (ESUS). Subgroup analyses from previous studies suggest that anticoagulation could reduce recurrent stroke compared with antiplatelet therapy. We hypothesised that anticoagulant treatment with rivaroxaban, an oral factor Xa inhibitor, would reduce the risk of recurrent ischaemic stroke compared with aspirin among patients with PFO enrolled in the NAVIGATE ESUS trial. Methods: NAVIGATE ESUS was a double-blinded, randomised, phase 3 trial done at 459 centres in 31 countries that assessed the efficacy and safety of rivaroxaban versus aspirin for secondary stroke prevention in patients with ESUS. For this prespecified subgroup analysis, cohorts with and without PFO were defined on the basis of transthoracic echocardiography (TTE) and transoesophageal echocardiography (TOE). The primary efficacy outcome was time to recurrent ischaemic stroke between treatment groups. The primary safety outcome was major bleeding, according to the criteria of the International Society of Thrombosis and Haemostasis. The primary analyses were based on the intention-to-treat population. Additionally, we did a systematic review and random-effects meta-analysis of studies in which patients with cryptogenic stroke and PFO were randomly assigned to receive anticoagulant or antiplatelet therapy. Findings: Between Dec 23, 2014, and Sept 20, 2017, 7213 participants were enrolled and assigned to receive rivaroxaban (n=3609) or aspirin (n=3604). Patients were followed up for a mean of 11 months because of early trial termination. PFO was reported as present in 534 (7·4%) patients on the basis of either TTE or TOE. Patients with PFO assigned to receive aspirin had a recurrent ischaemic stroke rate of 4·8 events per 100 person-years compared with 2·6 events per 100 person-years in those treated with rivaroxaban. Among patients with known PFO, there was insufficient evidence to support a difference in risk of recurrent ischaemic stroke between rivaroxaban and aspirin (hazard ratio [HR] 0·54; 95% CI 0·22–1·36), and the risk was similar for those without known PFO (1·06; 0·84–1·33; pinteraction=0·18). The risks of major bleeding with rivaroxaban versus aspirin were similar in patients with PFO detected (HR 2·05; 95% CI 0·51–8·18) and in those without PFO detected (HR 2·82; 95% CI 1·69–4·70; pinteraction=0·68). The random-effects meta-analysis combined data from NAVIGATE ESUS with data from two previous trials (PICSS and CLOSE) and yielded a summary odds ratio of 0·48 (95% CI 0·24–0·96; p=0·04) for ischaemic stroke in favour of anticoagulation, without evidence of heterogeneity. Interpretation: Among patients with ESUS who have PFO, anticoagulation might reduce the risk of recurrent stroke by about half, although substantial imprecision remains. Dedicated trials of anticoagulation versus antiplatelet therapy or PFO closure, or both, are warranted. Funding: Bayer and Janssen