We present the first laser guide star adaptive optics (LGSAO) observations of the Galactic center. LGSAO has dramatically improved the quality and robustness with which high angular resolution ...infrared images of the Galactic center can be obtained with the Keck II 10 m telescope. Specifically, Strehl ratios of 0.7 and 0.3 at L' (3.8 km) and K' (2.1 km), respectively, are achieved in these LGSAO images; these are at least a factor of 2 higher and a factor of 4-5 more stable against atmospheric fluctuations than the Strehl ratios delivered thus far with the Keck natural guide star AO system on the Galactic center. Furthermore, these observations are the first that cover a large area (76 x 76) surrounding the central black hole at diffraction-limited resolution for an 8-10 m class telescope. During our observations, the infrared counterpart to the central supermassive black hole, Sgr A*-IR, showed significant infrared intensity variations, with observed L' magnitudes ranging from 12.6 to 14.5 mag and a decrease in flux density of a factor of 2 over an 8 minute interval. The faintest end of our L' detections, 1.3 mJy (dereddened), is the lowest level of emission yet observed for this source by a factor of 3. No significant variation in the location of Sgr A*-IR is detected as a function of either wavelength or intensity. Previous claims of such positional variations are easily attributable to a nearby (0.09 or 720 AU, projected), extended, very red source, which we suggest arises from a locally heated dust feature. Near a peak in its intensity, we obtained the first measurement of Sgr A*-IR's K'- L' color; its K' - L' of 3.0 c 0.2 mag (observed) or 1.4 c 0.2 (dereddened) corresponds to an intrinsic spectral index of a = -0.5 c 0.3 for F sub( )8 super(a). This is significantly bluer than other recent infrared measurements from the literature, which suggest a = -4 c 1. Because our measurement was taken at a time when Sgr A* was 66 times brighter in the infrared than the other measurements, we posit that the spectral index of the emission arising from the vicinity of our Galaxy's central black hole may depend on the strength of the flare, with stronger flares giving rise to a higher fraction of high-energy electrons in the emitting region.
Design of the ALPS II optical system Diaz Ortiz, M.; Gleason, J.; Grote, H. ...
PHYSICS OF THE DARK UNIVERSE,
03/2022, Letnik:
35
Journal Article
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The Any Light Particle Search II (ALPSII) is an experiment currently being built at DESY in Hamburg, Germany, that will use a light-shining-through-a-wall (LSW) approach to search for axion-like ...particles. ALPSII represents a significant step forward for these types of experiments as it will use 24 superconducting dipole magnets, along with dual, high-finesse, 122m long optical cavities. This paper gives the first comprehensive recipe for the realization of the idea, proposed over 30 years ago, to use optical cavities before and after the wall to increase the power of the regenerated photon signal. The experiment is designed to achieve a sensitivity to the coupling between axion-like particles and photons down to gαγγ=2×10−11GeV−1 for masses below 0.1meV, more than three orders of magnitude beyond the sensitivity of previous laboratory experiments. The layout and main components that define ALPSII are discussed along with plans for reaching design sensitivity. An accompanying paper (Hallal et al., (2021)) offers a more in-depth description of the heterodyne detection scheme, the first of two independent detection systems that will be implemented in ALPSII.
ABSTRACT A gravitational-wave (GW) transient was identified in data recorded by the Advanced Laser Interferometer Gravitational-wave Observatory (LIGO) detectors on 2015 September 14. The event, ...initially designated G184098 and later given the name GW150914, is described in detail elsewhere. By prior arrangement, preliminary estimates of the time, significance, and sky location of the event were shared with 63 teams of observers covering radio, optical, near-infrared, X-ray, and gamma-ray wavelengths with ground- and space-based facilities. In this Letter we describe the low-latency analysis of the GW data and present the sky localization of the first observed compact binary merger. We summarize the follow-up observations reported by 25 teams via private Gamma-ray Coordinates Network circulars, giving an overview of the participating facilities, the GW sky localization coverage, the timeline, and depth of the observations. As this event turned out to be a binary black hole merger, there is little expectation of a detectable electromagnetic (EM) signature. Nevertheless, this first broadband campaign to search for a counterpart of an Advanced LIGO source represents a milestone and highlights the broad capabilities of the transient astronomy community and the observing strategies that have been developed to pursue neutron star binary merger events. Detailed investigations of the EM data and results of the EM follow-up campaign are being disseminated in papers by the individual teams.
Neurons within the spinal cord are sensitive to environmental relations and can bring about a behavioral modification without input from the brain. For example, rats that have undergone a thoracic ...(T2) transection can learn to maintain a hind leg in a flexed position to minimize exposure to a noxious electrical stimulation (shock). Inactivating neurons within the spinal cord with lidocaine, or cutting communication between the spinal cord and the periphery (sciatic transection), eliminates the capacity to learn, which implies that it depends on spinal neurons. Here we show that these manipulations have no effect on the maintenance of the learned response, which implicates a peripheral process. EMG showed that learning augments the muscular response evoked by motoneuron output and that this effect survives a sciatic transection. Quantitative fluorescent imaging revealed that training brings about an increase in the area and intensity of ACh receptor labeling at the neuromuscular junction (NMJ). It is hypothesized that efferent motoneuron output, in conjunction with electrical stimulation of the tibialis anterior muscle, strengthens the connection at the NMJ in a Hebbian manner. Supporting this, paired stimulation of the efferent nerve and tibialis anterior generated an increase in flexion duration and augmented the evoked electrical response without input from the spinal cord. Evidence is presented that glutamatergic signaling contributes to plasticity at the NMJ. Labeling for vesicular glutamate transporter is evident at the motor endplate. Intramuscular application of an NMDAR antagonist blocked the acquisition/maintenance of the learned response and the strengthening of the evoked electrical response.
The neuromuscular junction (NMJ) is designed to faithfully elicit a muscular contraction in response to neural input. From this perspective, encoding environmental relations (learning) and the maintenance of a behavioral modification over time (memory) are assumed to reflect only modifications upstream from the NMJ, within the CNS. The current results challenge this view. Rats were trained to maintain a hind leg in a flexed position to avoid noxious stimulation. As expected, treatments that inhibit activity within the CNS, or disrupt peripheral communication, prevented learning. These manipulations did not affect the maintenance of the acquired response. The results imply that a peripheral modification at the NMJ contributes to the maintenance of the learned response.
A gravitational-wave (GW) transient was identified in data recorded by the Advanced Laser Interferometer Gravitational-wave Observatory (LIGO) detectors on 2015 September 14. The event, initially ...designated G184098 and later given the name GW150914, is described in detail elsewhere. By prior arrangement, preliminary estimates of the time, significance, and sky location of the event were shared with 63 teams of observers covering radio, optical, near-infrared, X-ray, and gamma-ray wavelengths with ground- and space-based facilities. In this Letter we describe the low-latency analysis of the GW data and present the sky localization of the first observed compact binary merger. We summarize the follow-up observations reported by 25 teams via private Gamma-ray Coordinates Network circulars, giving an overview of the participating facilities, the GW sky localization coverage, the timeline, and depth of the observations. As this event turned out to be a binary black hole merger, there is little expectation of a detectable electromagnetic (EM) signature. Nevertheless, this first broadband campaign to search for a counterpart of an Advanced LIGO source represents a milestone and highlights the broad capabilities of the transient astronomy community and the observing strategies that have been developed to pursue neutron star binary merger events. Detailed investigations of the EM data and results of the EM follow-up campaign are being disseminated in papers by the individual teams.
As a backend to the first station of the Long Wavelength Array (LWA1), the Prototype All Sky Imager has been imaging the sky >-26degrees declination during 34 gamma-ray bursts (GRBs) between 2012 ...January and 2013 May. Using this data, we were able to put the most stringent limits to date on prompt low-frequency emission from GRBs. While our limits depend on the zenith angle of the observed GRB, we estimate a 1sigma rms sensitivity of 68, 65, and 70 Jy for 5 s integrations at 37.9, 52.0, and 74.0MHz at zenith. These limits are relevant for pulses > or =, slanted5 s and are limited by dispersion smearing. For 5 s pulses, we are limited to dispersion measures (DMs) < or =, slant 220, 570, and 1600 pc cm super(-3) for the frequencies above. For pulses lasting longer than 5 s, the DM limits increase linearly with the duration of the pulse. We also report two interesting transients, which are, as of yet, of unknown origin and are not coincident with any known GRBs. For general transients, we give rate density limits of < or =, slant 7.5 x 10 super(-3), 2.9 x 10 super(-2), and 1.4 x 10 super(-2) yr super(-1) deg super(-2) with pulse energy densities > 1.3 x 10 super(-22), 1.1 x 10 super(-22), and 1.4 x 10 super(-22) J m super(-2) Hz super(-1) and pulse widths of 5 s at the frequencies given above.
Natural history models of breast cancer progression provide an opportunity to evaluate and identify optimal screening scenarios. This paper describes a detailed Markov model characterising breast ...cancer tumour progression.
Breast cancer is modelled by a 13-state continuous-time Markov model. The model differentiates between indolent and aggressive ductal carcinomas in situ tumours, and aggressive tumours of different sizes. We compared such aggressive cancers, that is, which are non-indolent, to those which are non-growing and regressing. Model input parameters and structure were informed by the 1978-1984 Ostergotland county breast screening randomised controlled trial. Overlaid on the natural history model is the effect of screening on diagnosis. Parameters were estimated using Bayesian methods. Markov chain Monte Carlo integration was used to sample the resulting posterior distribution.
The breast cancer incidence rate in the Ostergotland population was 21 (95% CI: 17-25) per 10 000 woman-years. Accounting for length-biased sampling, an estimated 91% (95% CI: 85-97%) of breast cancers were aggressive. Larger tumours, 21-50 mm, had an average sojourn of 6 years (95% CI: 3-16 years), whereas aggressive ductal carcinomas in situ took around half a month (95% CI: 0-1 month) to progress to the invasive ≤10 mm state.
These tumour progression rate estimates may facilitate future work analysing cost-effectiveness and quality-adjusted life years for various screening strategies.
Satellites of the Largest Kuiper Belt Objects Brown, M. E; van Dam, M. A; Bouchez, A. H ...
Astrophysical journal/The Astrophysical journal,
03/2006, Letnik:
639, Številka:
1
Journal Article
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We have searched the four brightest objects in the Kuiper Belt for the presence of satellites using the newly commissioned Keck Observatory Laser Guide Star Adaptive Optics system. Satellites are ...seen around three of the four objects: Pluto (whose satellite Charon is well-known and whose recently discovered smaller satellites are too faint to be detected), 2003 EL61 (where a second satellite is seen in addition to the previously known satellite), and 2003 UB313 (where a satellite is seen for the first time). The object 2005 FY9, the brightest Kuiper Belt object (KBO) after Pluto, does not have a satellite detectable within 0 4 with a brightness of more than 1% of the primary. The presence of satellites around three of the four brightest KBOs is inconsistent with the fraction of satellites in the Kuiper Belt at large at the 99.2% confidence level, suggesting a different formation mechanism for these largest KBO satellites. The two satellites of 2003 EL61, and the one satellite of 2003 UB313, with fractional brightnesses of 5% and 1.5%, and 2%, of their primaries, respectively, are significantly fainter relative to their primaries than other known KBO satellites, again pointing to possible differences in their origin.
DETECTION OF RADIO EMISSION FROM FIREBALLS Obenberger, K S; Taylor, G B; Hartman, J M ...
Astrophysical journal. Letters,
06/2014, Letnik:
788, Številka:
2
Journal Article
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We present the findings from the Prototype All-Sky Imager, a back end correlator of the first station of the Long Wavelength Array, which has recorded over 11,000 hr of all-sky images at frequencies ...between 25 and 75 MHz. In a search of this data for radio transients, we have found 49 long-duration (10 s of seconds) transients. Ten of these transients correlate both spatially and temporally with large meteors (fireballs), and their signatures suggest that fireballs emit a previously undiscovered low frequency, non-thermal pulse. This emission provides a new probe into the physics of meteors and identifies a new form of naturally occurring radio transient foreground.
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