180 research outputs found
How else can we detect Fast Radio Bursts?
We discuss possible electromagnetic signals accompanying Fast Radio Bursts
(FRBs) that are expected in the scenario where FRBs originate in neutron star
magnetospheres. For models involving Crab-like giant pulses, no appreciable
contemporaneous emission is expected at other wavelengths. Magnetar giant
flares, driven by the reconfiguration of the magnetosphere, however, can
produce both contemporaneous bursts at other wavelengths as well as
afterglow-like emission. We conclude that the best chances are: (i) prompt
short GRB-like emission; (ii) a contemporaneous optical flash that can reach
naked eye peak luminosity (but only for a few milliseconds); (iii) a high
energy afterglow emission. Case (i) could be tested by coordinated radio and
high-energy experiments. Case (ii) could be seen in a coordinated radio-optical
surveys, \eg\ by the Palomar Transient Factory in a 60-second frame as a
transient object of magnitude with an expected optical detection rate
of about 0.1~hr, an order of magnitude higher than in radio. Shallow,
but large-area sky surveys such as ASAS-SN and EVRYSCOPE could also detect
prompt optical flashes from the more powerful Lorimer-burst clones. The best
constraints on the optical-to-radio power for this kind of emission could be
provided by future observations with facilities like LSST. Case (iii) might be
seen in relatively rare cases that the relativistically ejected magnetic blob
is moving along the line of sight
Flares from Galactic centre pulsars: a new class of X-ray transients?
Despite intensive searches, the only pulsar within 0.1 pc of the central
black hole in our Galaxy, Sgr A*, is a radio-loud magnetar. Since magnetars are
rare among the Galactic neutron star population, and a large number of massive
stars are already known in this region, the Galactic centre (GC) should harbor
a large number of neutron stars. Population syntheses suggest several thousand
neutron stars may be present in the GC. Many of these could be highly energetic
millisecond pulsars which are also proposed to be responsible for the GC
gamma-ray excess. We propose that the presence of a neutron star within 0.03~pc
from Sgr~A* can be revealed by the shock interactions with the disk around the
central black hole. As we demonstrate, these interactions result in observable
transient non-thermal X-ray and gamma-ray emission over timescales of months,
provided that the spin down luminosity of the neutron star is L_{sd}~10^{35}
erg/s. Current limits on the population of normal and millisecond pulsars in
the GC region suggest that a number of such pulsars are present with such
luminosities.Comment: 4 pages, 4 figure
The detectability of eccentric binary pulsars
Studies of binary pulsars provide insight into various theories of physics.
Detection of such systems is challenging due to the Doppler modulation of the
pulsed signal caused by the orbital motion of the pulsar. We investigated the
loss of sensitivity in eccentric binary systems for different types of
companions. This reduction of sensitivity should be considered in future
population synthesis models for binary pulsars. This loss can be recovered
partially by employing the `acceleration search' algorithm and even better by
using the `acceleration-jerk search' algorithm.Comment: 2 pages. To appear in the proceeding of "The Metrewavelength Sky
Conference" held at NCRA-TIFR, Pune, from December 9-13 2013, to mark 50
years of radio astronomy research at the Tata Institute of Fundamental
Research (TIFR), as well as 10 years of operation of the Giant Metrewave
Radio Telescope (GMRT) as an international observator
On gigahertz spectral turnovers in pulsars
Pulsars are known to emit non-thermal radio emission that is generally a
power-law function of frequency. In some cases, a turnover is seen at
frequencies around 100~MHz. Kijak et al. have reported the presence of a new
class of ''Gigahertz Peaked Spectrum'' (GPS) pulsars that show spectral
turnovers at frequencies around 1 GHz. We apply a model based on free-free
thermal absorption to explain these turnovers in terms of surrounding material
such as the dense environments found in HII regions, Pulsar Wind Nebulae
(PWNe), or in cold, partially ionized molecular clouds. We show that the
turnover frequency depends on the electron temperature of the environment close
to the pulsar, as well as the emission measure along the line of sight. We
fitted this model to the radio fluxes of known GPS pulsars and show that it can
replicate the GHz turnover. From the thermal absorption model, we demonstrate
that normal pulsars would exhibit a GPS-like behaviour if they were in a dense
environment. We discuss the application of this model in the context of
determining the population of neutron stars within the central parsec of the
Galaxy. We show that a non-negligible fraction of this population might exhibit
high-frequency spectral turnovers, which has implications on the detectability
of these sources in the Galactic centre.Comment: 7 pages, 3 figures, Accepted for publication in MNRA
Variability of the Pulsed Radio Emission from the Large Magellanic Cloud Pulsar PSR J0529-6652
We have studied the variability of PSR J0529-6652, a radio pulsar in the LMC,
using observations conducted at 1390 MHz with the Parkes 64-m telescope. PSR
J0529-6652 is detectable as a single pulse emitter, with amplitudes that
classify the pulses as giant pulses. This makes PSR J0529-6652 the second known
giant pulse emitter in the LMC, after PSR B0540-69. The fraction of the emitted
pulses detectable from PSR J0529-6652 at this frequency is roughly two orders
of magnitude greater than it is for either PSR B0540-69 or the Crab pulsar (if
the latter were located in the LMC). We have measured a pulse nulling fraction
of 83.3 \pm 1.5% and an intrinsic modulation index of 4.07 \pm 0.29 for PSR
J0529-6652. The modulation index is significantly larger than values previously
measured for typical radio pulsars but is comparable to values reported for
members of several other neutron star classes. The large modulation index,
giant pulses, and large nulling fraction suggest that this pulsar is
phenomenologically more similar to these other, more variable sources, despite
having spin and physical characteristics that are typical of the unrecycled
radio pulsar population. The large modulation index also does not appear to be
consistent with the small value predicted for this pulsar by a model of polar
cap emission outlined by Gil & Sendyk (2000). This conclusion depends to some
extent on the assumption that PSR J0529-6652 is exhibiting core emission, as
suggested by its simple profile morphology, narrow profile width, and
previously measured profile polarization characteristics.Comment: 24 pages, including 7 figures and 2 tables. Accepted to the
Astrophysical Journa
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