59 research outputs found
The Search for Signatures Of Transient Mass Loss in Active Stars
The habitability of an exoplanet depends on many factors. One such factor is
the impact of stellar eruptive events on nearby exoplanets. Currently this is
poorly constrained due to heavy reliance on solar scaling relationships and a
lack of experimental evidence. Potential impacts of Coronal Mass Ejections
(CMEs), which are a large eruption of magnetic field and plasma from a star,
are space weather and atmospheric stripping. A method for observing CMEs as
they travel though the stellar atmosphere is the type II radio burst, and the
new LOw Frequency ARray (LOFAR) provides a means for detection. We report on 15
hours of observation of YZ Canis Minoris (YZ CMi), a nearby M dwarf flare star,
taken in LOFAR's beam-formed observation mode for the purposes of measuring
transient frequency-dependent low frequency radio emission. The observations
utilized Low-Band Antenna (10-90 MHz) or High-Band Antenna (110-190 MHz) for
five three-hour observation periods. In this data set, there were no confirmed
type II events in this frequency range. We explore the range of parameter space
for type II bursts constrained by our observations Assuming the rate of shocks
is a lower limit to the rate at which CMEs occur, no detections in a total of
15 hours of observation places a limit of shocks/hr for YZ CMi due to the stochastic nature of the events and
limits of observational sensitivity. We propose a methodology to interpret
jointly observed flares and CMEs which will provide greater constraints to CMEs
and test the applicability of solar scaling relations
A deep campaign to characterize the synchronous radio/X-ray mode switching of PSR B0943+10
We report on simultaneous X-ray and radio observations of the mode-switching
pulsar PSR B0943+10 obtained with the XMM-Newton satellite and the LOFAR, LWA
and Arecibo radio telescopes in November 2014. We confirm the synchronous
X-ray/radio switching between a radio-bright (B) and a radio-quiet (Q) mode, in
which the X-ray flux is a factor ~2.4 higher than in the B-mode. We discovered
X-ray pulsations, with pulsed fraction of 38+/-5% (0.5-2 keV), during the
B-mode, and confirm their presence in Q-mode, where the pulsed fraction
increases with energy from ~20% up to ~65% at 2 keV. We found marginal evidence
for an increase in the X-ray pulsed fraction during B-mode on a timescale of
hours. The Q-mode X-ray spectrum requires a fit with a two-component model
(either a power-law plus blackbody or the sum of two blackbodies), while the
B-mode spectrum is well fit by a single blackbody (a single power-law is
rejected). With a maximum likelihood analysis, we found that in Q-mode the
pulsed emission has a thermal blackbody spectrum with temperature ~3.4x10^6 K
and the unpulsed emission is a power-law with photon index ~2.5, while during
B-mode both the pulsed and unpulsed emission can be fit by either a blackbody
or a power law with similar values of temperature and photon index. A Chandra
image shows no evidence for diffuse X-ray emission. These results support a
scenario in which both unpulsed non-thermal emission, likely of magnetospheric
origin, and pulsed thermal emission from a small polar cap (~1500 m^2) with a
strong non-dipolar magnetic field (~10^{14} G), are present during both radio
modes and vary in intensity in a correlated way. This is broadly consistent
with the predictions of the partially screened gap model and does not
necessarily imply global magnetospheric rearrangements to explain the mode
switching.Comment: To be published on The Astrophysical Journa
Simultaneous Radio And X-Ray Observations Of Psr B0611+22
We report results from simultaneous radio and X-ray observations of PSR B0611+22 which is known to exhibit bursting in its single-pulse emission. The pulse phase of the bursts vary with radio frequency. The bursts are correlated in 327/150 MHz data sets while they are anti-correlated, with bursts at one frequency associated with normal emission at the other, in 820/150 MHz data sets. Also, the flux density of this pulsar is lower than expected at 327 MHz assuming a power law. We attribute this unusual behaviour to the pulsar itself rather than absorption by external astrophysical sources. Using this data set over an extensive frequency range, we show that the bursting phenomenon in this pulsar exhibits temporal variance over a span of few hours. We also show that the bursting is quasi-periodic over the observed band. The anti-correlation in the phase offset of the burst mode at different frequencies suggests that the mechanisms responsible for phase offset and flux enhancement have different dependencies on the frequency. We did not detect the pulsar with XMM-Newton and place a 99 per cent confidence upper limit on the X-ray efficiency of 10-5
GMRT radio observations of the transiting extrasolar planet HD189733b at 244 and 614 MHz
We report a sensitive search for meter-wavelength emission at 244 and 614 MHz
from HD189733b, the nearest known extrasolar transiting planet of `hot-Jupiter'
type. To discriminate any planetary emission from possible stellar or
background contributions, we observed the system for 7.7 hours encompassing the
planet's eclipse behind the host star. These GMRT observations provide very low
(3 sigma) upper limits of 2 mJy at 244 MHz and 160 micro-Jy at 614 MHz. These
limits are, respectively, about 40 and 500 times deeper than those reported
recently at a nearby frequency of 340 MHz. Possible explanations of our
non-detection include: (1) the Earth being outside the planet's emission beam;
(2) its highly variable emission with more rapid flaring than the temporal
sampling in our observations; (3) the planetary emission being intrinsically
too weak; or more likely, (4) the emission being predominantly at lower
frequencies because of a weak planetary magnetic field. We briefly discuss
these possibilities and the constraints on this exo-planetary system
environment.Comment: Accepted for publication in A&A letter
Optimized Trigger for Ultra-High-Energy Cosmic-Ray and Neutrino Observations with the Low Frequency Radio Array
When an ultra-high energy neutrino or cosmic ray strikes the Lunar surface a
radio-frequency pulse is emitted. We plan to use the LOFAR radio telescope to
detect these pulses. In this work we propose an efficient trigger
implementation for LOFAR optimized for the observation of short radio pulses.Comment: Submitted to Nuclear Instruments and Methods in Physics Research
Section
GMRT search for 150 MHz radio emission from the transiting extrasolar planets HD189733b and HD209458b
We report a sensitive search for meter-wavelength emission at 150 MHz from
two prominent transiting extrasolar planets, HD189733b and HD209458b. To
distinguish any planetary emission from possible stellar or background
contributions, we monitored these systems just prior to, during, and after the
planet's eclipse behind the host star. No emission was detected from HD209458b
with a 3-sigma upper limit of 3.6 mJy. For HD189733b we obtain a 3-sigma upper
limit of 2.1 mJy and a marginal 2.7-sigma detection of about 1.9+/-0.7 mJy from
a direction just 13" from the star's coordinates (i.e., within the beam), but
its association with the planet remains unconfirmed. Thus, the present GMRT
observations provide unprecedentedly tight upper limits for meter wavelengths
emissions from these nearest two transiting type exoplanets. We point out
possible explanations of the non-detections and briefly discuss the resulting
constraints on these systems.Comment: To be published in Astronomy & Astrophysic
Mass estimates from optical modelling of the new TRAPUM redback PSR J1910−5320
Spider pulsars continue to provide promising candidates for neutron star mass measurements. Here we present the discovery of PSR J1910−5320, a new millisecond pulsar discovered in a MeerKAT observation of an unidentified Fermi-LAT gamma-ray source. This pulsar is coincident with a recently identified candidate redback binary, independently discovered through its periodic optical flux and radial velocity. New multicolour optical light curves obtained with ULTRACAM/New Technology Telescope in combination with MeerKAT timing and updated SOAR/Goodman spectroscopic radial velocity measurements allow a mass constraint for PSR J1910−5320. icarus optical light curve modelling, with streamlined radial velocity fitting, constrains the orbital inclination and companion velocity, unlocking the binary mass function given the precise radio ephemeris. Our modelling aims to unite the photometric and spectroscopic measurements available by fitting each simultaneously to the same underlying physical model, ensuring self-consistency. This targets centre-of-light radial velocity corrections necessitated by the irradiation endemic to spider systems. Depending on the gravity darkening prescription used, we find a moderate neutron star mass of either 1.6 ± 0.2 or 1.4 ± 0.2 M⊙. The companion mass of either 0.45 ± 0.04 or M⊙ also further confirms PSR J1910−5320 as an irradiated redback spider pulsar
Method to observe Jupiter’s radio emissions at high resolution using multiple LOFAR stations: a first case study of the Io-decametric emission using the Irish IE613, French FR606 and German DE604 stations
The Low Frequency Array (LOFAR) is an international radio telescope array, consisting of 38 stations in the Netherlands and 14 international stations spread over Europe. Here we present an observation method to study the jovian decametric radio emissions from several LOFAR stations (here Birr Castle in Ireland, Nançay in France and Postdam in Germany), at high temporal and spectral resolution. This method is based on prediction tools, such as radio emission simulations and probability maps, and data processing. We report an observation of Io-induced decametric emission from June 2021, and a first case study of the substructures that compose the macroscopic emissions (called millisecond bursts). The study of these bursts make it possible to determine the electron populations at the origin of these emissions. We then present several possible future avenues for study based on these observations. The methodology and study perspectives described in this paper can be applied to new observations of jovian radio emissions induced by Io, but also by Ganymede or Europa, or jovian auroral radio emissions
Channelopathies in Cav1.1, Cav1.3, and Cav1.4 voltage-gated L-type Ca2+ channels
Voltage-gated Ca2+ channels couple membrane depolarization to Ca2+-dependent intracellular signaling events. This is achieved by mediating Ca2+ ion influx or by direct conformational coupling to intracellular Ca2+ release channels. The family of Cav1 channels, also termed L-type Ca2+ channels (LTCCs), is uniquely sensitive to organic Ca2+ channel blockers and expressed in many electrically excitable tissues. In this review, we summarize the role of LTCCs for human diseases caused by genetic Ca2+ channel defects (channelopathies). LTCC dysfunction can result from structural aberrations within their pore-forming α1 subunits causing hypokalemic periodic paralysis and malignant hyperthermia sensitivity (Cav1.1 α1), incomplete congenital stationary night blindness (CSNB2; Cav1.4 α1), and Timothy syndrome (Cav1.2 α1; reviewed separately in this issue). Cav1.3 α1 mutations have not been reported yet in humans, but channel loss of function would likely affect sinoatrial node function and hearing. Studies in mice revealed that LTCCs indirectly also contribute to neurological symptoms in Ca2+ channelopathies affecting non-LTCCs, such as Cav2.1 α1 in tottering mice. Ca2+ channelopathies provide exciting disease-related molecular detail that led to important novel insight not only into disease pathophysiology but also to mechanisms of channel function
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