59 research outputs found
Near IR Astrometry of Magnetars
We report on the progress of our five-year program for astrometric monitoring of magnetars using high-resolution NIR observations using the laser guide star adaptive optics (LGS-AO) supported NIRC2 camera on the 10-meter Keck telescope. We have measured the proper motion of two of the youngest magnetars, SGR 1806–20 and SGR 1900+14, which have counterparts with K ~21 mag, and have placed a preliminary upper limit on the motion of the young AXP 1E 1841–045. The precision of the proper motion measurement is at the milliarcsecond per year level. Our proper motion measurements now provide evidence to link SGR 1806–20 and SGR 1900+14 with neighboring young star clusters. At the distances of these magnetars, their proper motion corresponds to transverse space velocities of 350 ± 100 km s^(−1) and 130 ± 30 km s^(−1) respectively. The upper limit on the proper motion of AXP 1E 1841–045 is 160 km s^(−1). With the sample of proper motions available, we conclude that the kinematics of the magnetar family are not distinct from that of pulsars
Proper Motions and Origins of SGR 1806–20 and SGR 1900+14
We present results from high-resolution infrared observations of magnetars SGR 1806–20 and SGR 1900+14 over 5 years using laser-supported adaptive optics at the 10 m Keck Observatory. Our measurements of the proper motions of these magnetars provide robust links between magnetars and their progenitors and provide age estimates for magnetars. At the measured distances of their putative associations, we measure the linear transverse velocity of SGR 1806–20 to be 350 ± 100 km s^(–1) and of SGR 1900+14 to be 130 ± 30 km s^(–1). The transverse velocity vectors for both magnetars point away from the clusters of massive stars, solidifying their proposed associations. Assuming that the magnetars were born in the clusters, we can estimate the braking index to be ~1.8 for SGR 1806–20 and ~1.2 for SGR 1900+14. This is significantly lower than the canonical value of n = 3 predicted by the magnetic dipole spin-down suggesting an alternative source of dissipation such as twisted magnetospheres or particle winds
Proper Motions and Origins of AXP 1E 2259+586 and AXP 4U 0142+61
Using high-resolution NIR images supported by laser guide star adaptive optics from the Keck II telescope from 2005 to 2012, we have measured the proper motions of two anomalous X-ray pulsars, AXP 1E 2259+586 and AXP 4U 0142+61. The proper motion of AXP 1E 2259+586 in the sky frame is (μ_α, μ_δ) = (– 6.4 ± 0.6, –2.3 ± 0.6) mas yr^(–1) and that of AXP 4U 0142+61 is (μ_α, μ_δ) = (– 4.1 ± 1, 1.9 ± 1) mas yr^(–1). After correcting for the velocity of the progenitors, we calculate the tangential ejection velocities of the magnetars to be 157 ± 17 km s^(–1) and 102 ± 26 km s^(–1) respectively. The proper motion vector of AXP 1E 2259+586 is directed away from the putative center of the supernova remnant CTB 109 that has long been proposed to be associated with AXP 1E 2259+586. This is significant evidence for linking the pulsar with CTB 109. We comment on the possible movement of CTB 109 after the explosion. We narrow the search cone for the birthsite or remnant of AXP 4U 0142+61 to an opening angle of 24°. However, we are unable to find any suitable association
Probabilistic Association of Transients to their Hosts (PATH)
We introduce a new method to estimate the probability that an extragalactic
transient source is associated with a candidate host galaxy. This approach
relies solely on simple observables: sky coordinates and their uncertainties,
galaxy fluxes and angular sizes. The formalism invokes Bayes' rule to calculate
the posterior probability P(O_i|x) from the galaxy prior P(O), observables x,
and an assumed model for the true distribution of transients in/around their
host galaxies. Using simulated transients placed in the well-studied COSMOS
field, we consider several agnostic and physically motivated priors and offset
distributions to explore the method sensitivity. We then apply the methodology
to the set of 13~fast radio bursts (FRBs) localized with an uncertainty of
several arcseconds. Our methodology finds nine of these are securely associated
to a single host galaxy, P(O_i|x)>0.95. We examine the observed and intrinsic
properties of these secure FRB hosts, recovering similar distributions as
previous works. Furthermore, we find a strong correlation between the apparent
magnitude of the securely identified host galaxies and the estimated cosmic
dispersion measures of the corresponding FRBs, which results from the Macquart
relation. Future work with FRBs will leverage this relation and other measures
from the secure hosts as priors for future associations. The methodology is
generic to transient type, localization error, and image quality. We encourage
its application to other transients where host galaxy associations are critical
to the science, e.g. gravitational wave events, gamma-ray bursts, and
supernovae. We have encoded the technique in Python on GitHub:
https://github.com/FRBs/astropath.Comment: In press, ApJ; comments still welcome; Visit
https://github.com/FRBs/astropath to use and build PAT
PTF10iya: a short-lived, luminous flare from the nuclear region of a star-forming galaxy
We present the discovery and characterization of PTF10iya, a short-lived (Δt≈ 10 d, with an optical decay rate of ∼0.3 mag d^(−1)), luminous (M_(g') ≈ -21) transient source found by the Palomar Transient Factory. The ultraviolet/optical spectral energy distribution is reasonably well fitted by a blackbody with T≈ (1–2) × 10^4 K and peak bolometric luminosity LBB≈ (1–5) × 10^(44) erg s^(−1) (depending on the details of the extinction correction). A comparable amount of energy is radiated in the X-ray band that appears to result from a distinct physical process. The location of PTF10iya is consistent with the nucleus of a star-forming galaxy (z= 0.224 05 ± 0.000 06) to within 350 mas (99.7 per cent confidence radius), or a projected distance of less than 1.2 kpc. At first glance, these properties appear reminiscent of the characteristic ‘big blue bump’ seen in the near-ultraviolet spectra of many active galactic nuclei (AGNs). However, emission-line diagnostics of the host galaxy, along with a historical light curve extending back to 2007, show no evidence for AGN-like activity. We therefore consider whether the tidal disruption of a star by an otherwise quiescent supermassive black hole may account for our observations. Though with limited temporal information, PTF10iya appears broadly consistent with the predictions for the early ‘super-Eddington’ phase of a solar-type star being disrupted by a ∼10^7 M_⊙ black hole. Regardless of the precise physical origin of the accreting material, the large luminosity and short duration suggest that otherwise quiescent galaxies can transition extremely rapidly to radiate near the Eddington limit; many such outbursts may have been missed by previous surveys lacking sufficient cadence
Robotic Laser-Adaptive-Optics Imaging of 715 Kepler Exoplanet Candidates using Robo-AO
The Robo-AO Kepler Planetary Candidate Survey is designed to observe every
Kepler planet candidate host star with laser adaptive optics imaging to search
for blended nearby stars, which may be physically associated companions and/or
responsible for transit false positives. In this paper we present the results
from the 2012 observing season, searching for stars close to 715 representative
Kepler planet candidate hosts. We find 53 companions, 44 of which are new
discoveries. We detail the Robo-AO survey data reduction methods including a
method of using the large ensemble of target observations as mutual
point-spread-function references, along with a new automated
companion-detection algorithm designed for large adaptive optics surveys. Our
survey is sensitive to objects from 0.15" to 2.5" separation, with contrast
ratios up to delta-m~6. We measure an overall nearby-star-probability for
Kepler planet candidates of 7.4% +/- 1.0%, and calculate the effects of each
detected nearby star on the Kepler-measured planetary radius. We discuss
several KOIs of particular interest, including KOI-191 and KOI-1151, which are
both multi-planet systems with detected stellar companions whose unusual
planetary system architecture might be best explained if they are "coincident
multiple" systems, with several transiting planets shared between the two
stars. Finally, we detect 2.6-sigma evidence for <15d-period giant planets
being 2-3 times more likely be found in wide stellar binaries than smaller
close-in planets and all sizes of further-out planets.Comment: Accepted by ApJ. Minor updates & improved statistical analysis; no
changes to results. 15 pages, 13 figure
The Robo-AO software: fully autonomous operation of a laser guide star adaptive optics and science system
Robo-AO is the first astronomical laser guide star adaptive optics (AO) system designed to operate completely
independent of human supervision. A single computer commands the AO system, the laser guide star, visible and
near-infrared science cameras (which double as tip-tip sensors), the telescope, and other instrument functions.
Autonomous startup and shutdown sequences as well as concatenated visible observations were demonstrated in
late 2011. The fully robotic software is currently operating during a month long demonstration of Robo-AO at
the Palomar Observatory 60-inch telescope
Non-detection of CHIME/FRB sources with the Arecibo Observatory
In this work, we present follow-up observations of two known repeating fast
radio bursts (FRBs) and seven non-repeating FRBs with complex morphology
discovered with CHIME/FRB. These observations were conducted with the Arecibo
Observatory 327 MHz receiver. We detected no additional bursts from these
sources, nor did CHIME/FRB detect any additional bursts from these sources
during our follow-up program. Based on these non-detections, we provide
constraints on the repetition rate, for all nine sources. We calculate
repetition rates using both a Poisson distribution of repetition and the
Weibull distribution of repetition presented by Oppermann et al. (2018). For
both distributions, we find repetition upper limits of the order for all sources. These rates are much lower
than those recently published for notable repeating FRBs like FRB 20121102A and
FRB 20201124A, suggesting the possibility of a low-repetition sub-population.Comment: 12 pages, 4 figures, 5 tables; submitted to Ap
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