4 research outputs found
An Observationally-Derived Kick Distribution for Neutron Stars in Binary Systems
Understanding the natal kicks received by neutron stars (NSs) during
formation is a critical component of modelling the evolution of massive
binaries. Natal kicks are an integral input parameter for population synthesis
codes, and have implications for the formation of double NS systems and their
subsequent merger rates. However, many of the standard observational kick
distributions that are used are obtained from samples created only from
isolated NSs. Kick distributions derived in this way overestimate the intrinsic
NS kick distribution. For NSs in binaries, we can only directly estimate the
effect of the natal kick on the binary system, instead of the natal kick
received by the NS itself. Here, for the first time, we present a binary kick
distribution for NSs with low-mass companions. We compile a catalogue of 145
NSs in low-mass binaries with the best available constraints on proper motion,
distance, and systemic radial velocity. For each binary, we use a
three-dimensional approach to estimate its binary kick. We discuss the
implications of these kicks on system formation, and provide a parametric model
for the overall binary kick distribution, for use in future theoretical
modelling work. We compare our results with other work on isolated NSs and NSs
in binaries, finding that the NS kick distributions fit using only isolated
pulsars underestimate the fraction of NSs that receive low kicks. We discuss
the implications of our results on modelling double NS systems, and provide
suggestions on how to use our results in future theoretical works.Comment: Accepted for publication in MNRAS. 28 pages, 19 figures, 8 table
Precise Measurements of Self-absorbed Rising Reverse Shock Emission from Gamma-ray Burst 221009A
The deaths of massive stars are sometimes accompanied by the launch of highly
relativistic and collimated jets. If the jet is pointed towards Earth, we
observe a "prompt" gamma-ray burst due to internal shocks or magnetic
reconnection events within the jet, followed by a long-lived broadband
synchrotron afterglow as the jet interacts with the circum-burst material.
While there is solid observational evidence that emission from multiple shocks
contributes to the afterglow signature, detailed studies of the reverse shock,
which travels back into the explosion ejecta, are hampered by a lack of
early-time observations, particularly in the radio band. We present rapid
follow-up radio observations of the exceptionally bright gamma-ray burst GRB
221009A which reveal an optically thick rising component from the reverse shock
in unprecedented detail both temporally and in frequency space. From this, we
are able to constrain the size, Lorentz factor, and internal energy of the
outflow while providing accurate predictions for the location of the peak
frequency of the reverse shock in the first few hours after the burst.Comment: 11 figures, 4 table
Constraining black hole natal kicks with high-precision radio astrometry
Studying the motion of black hole systems in our Galaxy allows us to constrain the distances and velocities of these systems. We used radio telescopes around the globe to measure these motions and report the first observationally determined birth velocity distribution for black holes, helping us understand how these objects are born. We used the motion of unclassified radio sources to identify a new subpopulation of possible Galactic black hole candidates
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Precise measurements of self-absorbed rising reverse shock emission from gamma-ray burst 221009A
The deaths of massive stars are sometimes accompanied by the launch of highly relativistic and collimated jets. If the jet is pointed towards Earth, we observe a ‘prompt’ gamma-ray burst due to internal shocks or magnetic reconnection events within the jet, followed by a long-lived broadband synchrotron afterglow as the jet interacts with the circumburst material. While there is solid observational evidence that emission from multiple shocks contributes to the afterglow signature, detailed studies of the reverse shock, which travels back into the explosion ejecta, are hampered by a lack of early-time observations, particularly in the radio band. We present rapid follow-up radio observations of the exceptionally bright gamma-ray burst GRB 221009A that reveal in detail, both temporally and in frequency space, an optically thick rising component from the reverse shock. From this, we are able to constrain the size, Lorentz factor and internal energy of the outflow while providing accurate predictions for the location of the peak frequency of the reverse shock in the first few hours after the burst. These observations challenge standard gamma-ray burst models describing reverse shock emission