26 research outputs found
Constraints on Dark Energy Models Including Gamma Ray Bursts
In this paper we analyze the constraints on the property of dark energy from
cosmological observations. Together with SNe Ia Gold sample, WMAP, SDSS and
2dFGRS data, we include 69 long Gamma-Ray Bursts (GRBs) data in our study and
perform global fitting using Markov Chain Monte Carlo (MCMC) technique. Dark
energy perturbations are explicitly considered. We pay particular attention to
the time evolution of the equation of state of dark energy parameterized as
with the scale factor of the universe, emphasizing
the complementarity of high redshift GRBs to other cosmological probes. It is
found that the constraints on dark energy become stringent by taking into
account high redshift GRBs, especially for , which delineates the
evolution of dark energy.Comment: 7 pages and 3 figures. Replaced with version accepted for publication
in Phys. Lett.
An Intermediate-field Fast Radio Burst Model and the Quasi-periodic Oscillation
Quasi-periodic oscillation (QPO) signals are discovered in some fast radio
bursts (FRBs) such as FRB 20191221A, as well as in the X-ray burst associated
with the galactic FRB from SGR 1935+2154. We revisit the intermediate-field FRB
model where the radio waves are generated as fast-magnetosonic waves through
magnetic reconnection near the light cylinder. The current sheet in the
magnetar wind is compressed by a low frequency pulse emitted from the inner
magnetosphere to trigger magnetic reconnection. By incorporating the wave
dynamics of the magnetosphere, we demonstrate how the FRB frequency, the single
pulse width, and luminosity are determined by the period, magnetic field, QPO
frequency and quake energetics of the magnetar. We find that this model can
naturally and self-consistently interpret the X-ray/radio event from SGR
1935+2154 and the QPO in FRB 20191221A. It can also explain the observed wide
energy range of repeating FRBs in a narrow bandwidth.Comment: 10 pages, 1 figure, accepted to RAA, Figure 1 is updated with a
clearer description of the mode
Sub-second periodic radio oscillations in a microquasar
Powerful relativistic jets are one of the ubiquitous features of accreting
black holes in all scales. GRS 1915+105 is a well-known fast-spinning
black-hole X-ray binary with a relativistic jet, termed as a ``microquasar'',
as indicated by its superluminal motion of radio emission. It exhibits
persistent x-ray activity over the last 30 years, with quasi-periodic
oscillations of Hz and 34 and 67 Hz in the x-ray band. These
oscillations likely originate in the inner accretion disk, but other origins
have been considered. Radio observations found variable light curves with
quasi-periodic flares or oscillations with periods of minutes.
Here we report two instances of 5 Hz transient periodic oscillation
features from the source detected in the 1.05-1.45 GHz radio band that occurred
in January 2021 and June 2022, respectively. Circular polarization was also
observed during the oscillation phase.Comment: The author version of the article which will appear in Nature on 26
July 2023, 32 pages including the extended data. The online publication
version can be found at the following URL:
https://www.nature.com/articles/s41586-023-06336-
Prompt-to-afterglow transition of optical emission in a long gamma-ray burst consistent with a fireball
Long gamma-ray bursts (GRBs), which signify the end-life collapsing of very
massive stars, are produced by extremely relativistic jets colliding into
circumstellar medium. Huge energy is released both in the first few seconds,
namely the internal dissipation phase that powers prompt emissions, and in the
subsequent self-similar jet-deceleration phase that produces afterglows
observed in broad-band electromagnetic spectrum. However, prompt optical
emissions of GRBs have been rarely detected, seriously limiting our
understanding of the transition between the two phases. Here we report
detection of prompt optical emissions from a gamma-ray burst (i.e. GRB 201223A)
using a dedicated telescope array with a high temporal resolution and a wide
time coverage. The early phase coincident with prompt {\gamma}-ray emissions
show a luminosity in great excess with respect to the extrapolation of
{\gamma}-rays, while the later luminosity bump is consistent with onset of the
afterglow. The clearly detected transition allows us to differentiate physical
processes contributing to early optical emissions and to diagnose the
composition of the jetComment: Authors' version of article published in Nature Astronomy, see their
website for official versio
Atypical radio pulsations from magnetar SGR 1935+2154
Magnetars are neutron stars with extremely strong magnetic fields, frequently
powering high-energy activity in X-rays. Pulsed radio emission following some
X-ray outbursts have been detected, albeit its physical origin is unclear. It
has long been speculated that the origin of magnetars' radio signals is
different from those from canonical pulsars, although convincing evidence is
still lacking. Five months after magnetar SGR 1935+2154's X-ray outburst and
its associated Fast Radio Burst (FRB) 20200428, a radio pulsar phase was
discovered. Here we report the discovery of X-ray spectral hardening associated
with the emergence of periodic radio pulsations from SGR 1935+2154 and a
detailed analysis of the properties of the radio pulses. The complex radio
pulse morphology, which contains both narrow-band emission and frequency
drifts, has not been seen before in other magnetars, but is similar to those of
repeating FRBs - even though the luminosities are many orders of magnitude
different. The observations suggest that radio emission originates from the
outer magnetosphere of the magnetar, and the surface heating due to the
bombardment of inward-going particles from the radio emission region is
responsible for the observed X-ray spectral hardening.Comment: 47 pages, 11 figure
Sciences for The 2.5-meter Wide Field Survey Telescope (WFST)
The Wide Field Survey Telescope (WFST) is a dedicated photometric survey
facility under construction jointly by the University of Science and Technology
of China and Purple Mountain Observatory. It is equipped with a primary mirror
of 2.5m in diameter, an active optical system, and a mosaic CCD camera of 0.73
Gpix on the main focus plane to achieve high-quality imaging over a field of
view of 6.5 square degrees. The installation of WFST in the Lenghu observing
site is planned to happen in the summer of 2023, and the operation is scheduled
to commence within three months afterward. WFST will scan the northern sky in
four optical bands (u, g, r, and i) at cadences from hourly/daily to
semi-weekly in the deep high-cadence survey (DHS) and the wide field survey
(WFS) programs, respectively. WFS reaches a depth of 22.27, 23.32, 22.84, and
22.31 in AB magnitudes in a nominal 30-second exposure in the four bands during
a photometric night, respectively, enabling us to search tremendous amount of
transients in the low-z universe and systematically investigate the variability
of Galactic and extragalactic objects. Intranight 90s exposures as deep as 23
and 24 mag in u and g bands via DHS provide a unique opportunity to facilitate
explorations of energetic transients in demand for high sensitivity, including
the electromagnetic counterparts of gravitational-wave events detected by the
second/third-generation GW detectors, supernovae within a few hours of their
explosions, tidal disruption events and luminous fast optical transients even
beyond a redshift of 1. Meanwhile, the final 6-year co-added images,
anticipated to reach g about 25.5 mag in WFS or even deeper by 1.5 mag in DHS,
will be of significant value to general Galactic and extragalactic sciences.
The highly uniform legacy surveys of WFST will also serve as an indispensable
complement to those of LSST which monitors the southern sky.Comment: 46 pages, submitted to SCMP