## The 999th Swift Gamma-Ray Burst: some like it thermal. (arXiv:1604.08204v1 [astro-ph.HE])

### April 29th, 2016

We present a multiwavelength study of GRB 151027A. This is the 999th GRB
detected by the Swift satellite and it has a densely sampled emission in the
X-ray and optical band and has been observed and detected in the radio up to
140 days after the prompt. The multiwavelength light curve from 500 s to 140
days can be modelled through a standard forward shock afterglow but requires an
additional component to reproduce the early X-ray and optical emission. We
present TNG and LBT optical observations performed 19.6, 33.9 and 92.3 days
after the trigger which show a bump with respect to a standard afterglow flux
decay and are possibly interpreted as due to the underlying SN and host galaxy
(of 0.4 uJy in the R band). Radio observations, performed with SRT, Medicina,
EVN and VLBA between day 4 and 140, suggest that the burst exploded in an
environment characterised by a density profile scaling with the distance from
the source (wind profile). A remarkable feature of the prompt emission is the
presence of a bright flare 100 s after the trigger, lasting 70 seconds in the
soft X-ray band, which was simultaneously detected from the optical band up to
the MeV energy range. By combining Swift-BAT/XRT and Fermi-GBM data, the
broadband (0.3-1000 keV) time resolved spectral analysis of the flare reveals
the coexistence of a non-thermal (power law) and thermal blackbody components.
The BB component contributes up to 35% of the luminosity in the 0.3-1000 keV
band. The gamma-ray emission observed in Swift-BAT and Fermi-GBM anticipates
and lasts less than the soft X-ray emission as observed by Swift-XRT, arguing
against a Comptonization origin. The BB component could either be produced by
an outflow becoming transparent or by the collision of a fast shell with a
slow, heavy and optically thick fireball ejected during the quiescent time
interval between the initial and later flares of the burst.

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## Investigation of Primordial Black Hole Bursts using Interplanetary Network Gamma-ray Bursts. (arXiv:1512.01264v2 [astro-ph.HE] UPDATED)

### April 29th, 2016

The detection of a gamma-ray burst (GRB) in the solar neighborhood would have
very important implications for GRB phenomenology. The leading theories for
cosmological GRBs would not be able to explain such events. The final bursts of
evaporating Primordial Black Holes (PBHs), however, would be a natural
explanation for local GRBs. We present a novel technique that can constrain the
distance to gamma-ray bursts using detections from widely separated,
non-imaging spacecraft. This method can determine the actual distance to the
burst if it is local. We applied this method to constrain distances to a sample
of 36 short duration GRBs detected by the Interplanetary Network (IPN) that
show observational properties that are expected from PBH evaporations. These
bursts have minimum possible distances in the 10^13-10^18 cm (7-10^5 AU) range,
consistent with the expected PBH energetics and with a possible origin in the
solar neighborhood, although none of the bursts can be unambiguously
demonstrated to be local. Assuming these bursts are real PBH events, we
estimate lower limits on the PBH burst evaporation rate in the solar
neighborhood.

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## Search for high energy gamma-ray emission from tidal disruption events with the Fermi Large Area Telescope. (arXiv:1601.02734v2 [astro-ph.HE] UPDATED)

### April 28th, 2016

Massive black holes at galaxy center may tear apart a star when the star
passes occasionally within the disruption radius, which is the so-called tidal
disruption event(TDE). Most TDEs radiate with thermal emission resulted from
the accretion disk, but three TDEs have been detected in bright non-thermal
X-ray emission, which is interpreted as arising from the relativistic jets.
Search for high-energy gamma-ray emission from one relativistic TDE (Swift
J164449.3+573451) with the \textsl{Fermi} Large Area Telescope (LAT) has
yielded non-detection. In this paper, we report the search for high energy
emission from the other two relativistic TDEs (Swift J2058.4+0516 Swift
J1112.2-8238) during the flare period. No significant GeV emission is found,
with an upper limit fluence in LAT energy range being less than $1\%$ of that
in X-rays. Compared with gamma-ray bursts (GRBs) and blazars, these TDEs have
the lowest flux ratio between GeV emission and X-ray emission. The
non-detection of high-energy emission from relativistic TDEs could be due to
that the high-energy emission is absorbed by soft photons in the source. Based
on this hypothesis, upper limits on the bulk Lorentz factors, $\Gamma\la 30$,
are then obtained for the jets in these TDEs. We also search for high-energy
gamma-ray emission from the nearest TDE discovered to date, ASASSN-14li. No
significant GeV emission is found and an upper limit of $L(\rm 0.1-10 GeV)\le 4.4\times 10^{42}$ erg s$^{-1}$ (at $95\%$ confidence level) is obtained for
the first $10^{7}$ s after the disruption.

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## A fundamental plane for gamma-ray bursts with X-ray plateaus. (arXiv:1604.06840v1 [astro-ph.HE])

### April 26th, 2016

A class of long Gamma-Ray Bursts (GRBs) presenting light curves with an
extended plateau phase in their X-ray afterglows obeys a correlation between
the rest frame end time of the plateau, $T_a$, and its corresponding X-ray
luminosity, $L_{a}$, Dainotti et al. (2008). In this work we perform an
analysis of a total sample of 176 {\it Swift} GRBs with known redshifts,
exhibiting afterglow plateaus. By adding a third parameter, that is the peak
luminosity in the prompt emission, $L_{peak}$, we discover the existence of a
new three parameter correlation, a GRB fundamental plane'. The scatter of data
This sample of 122 GRBs is selected from the total sample by excluding GRBs
with associated Supernovae (SNe), X-ray flashes and short GRBs with extended
emission. Moreover, we further limit our analysis to GRBs with lightcurves
having good data coverage and almost flat plateaus, 40 GRBs forming our gold
sample'. The intrinsic scatter, $\sigma_{int}=0.27 \pm 0.04$, for the
three-parameter correlation for this last subclass is more than twice smaller
than the value for the $L_{a}-T_a$ one, making this the tightest three
parameter correlation involving the afterglow plateau phase. Finally, we also
show that a slightly less tight correlation is present between $L_{peak}$ and a
proxy for the total energy emitted during the plateau phase, $L_a T_a$,
confirming the existence of an energy scaling between prompt and afterglow
phases.

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## On the gamma-ray burst — gravitational wave association in GW150914. (arXiv:1604.07132v1 [astro-ph.HE])

### April 26th, 2016

The data from the Fermi Gamma-ray Burst Monitor (GBM) satellite suggest that
the recently discovered gravitational wave source, a pair of two coalescing
black holes, was related to a gamma-ray burst. The electromagnetic radiation in
high energy (above 50 keV) originated from a weak transient source and lasted
for about 1 second. Its localization is consistent with the direction to
GW150914. We speculate on the possible scenario for the formation of a
gamma-ray burst accompanied by the GW signal. Our model invokes a close binary
system consisting of a massive star and a black hole, which leads to triggering
of a collapse of the star's nucleus, formation of a second black hole, and
finally to the binary black hole merger. For the most-likely configuration of
the binary spin vectors with respect to the orbital angular momentum in the
GW150914 event, the recoil velocity acquired by the final black hole through
gravitational waves emission allows it to take only a small fraction of matter
from the host star. The gamma-ray burst is produced on the cost of accretion of
this remnant matter onto the final black hole. The moderate spin of the final
black hole accounts for the gamma-ray burst jet to be powered by a weak
neutrino emission rather than the Blandford-Znajek mechanism, and hence
explains low power available for the observed GRB signal.

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## High Energy Neutrinos from the Gravitational Wave event GW150914 possibly associated with a short Gamma-Ray Burst. (arXiv:1602.08436v2 [astro-ph.HE] UPDATED)

### April 26th, 2016

High-energy neutrino (HEN) and gravitational wave (GW) can probe
astrophysical sources in addition to electromagnetic observations.
Multimessenger studies can reveal nature of the sources which may not be
discerned from one type of signal alone. We discuss HEN emission in connection
with the Advanced Laser Interferometer Gravitational-wave Observatory (ALIGO)
event GW150914 which could be associated with a short gamma-ray burst (GRB)
detected by the $Fermi$ Gamma-ray Burst Monitor (GBM) 0.4 s after the GW event
and within localization uncertainty of the GW event. We calculate HEN flux from
this short GRB, GW150914-GBM, and show that non-detection of a high-energy
starting event (HESE) by the IceCube Neutrino Observatory can constrain the
total isotropic-equivalent jet energy of this short burst to be less than
$3\times 10^{52}$ erg.

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## Modeling the Multi-Band Afterglow of GRB 130831A: Evidence for a Spinning-Down Magnetar Dominated by Gravitational Wave Losses?. (arXiv:1604.04817v1 [astro-ph.HE])

### April 19th, 2016

The X-ray afterglow of GRB 130831A shows an “internal plateau” with a decay
slope of $\sim$ 0.8, followed by a steep drop at around $10^5$ s with a slope
of $\sim$ 6. After the drop, the X-ray afterglow continues with a much
shallower decay. The optical afterglow exhibits two segments of plateaus
separated by a luminous optical flare, followed by a normal decay with a slope
basically consistent with that of the late-time X-ray afterglow. The decay of
the internal X-ray plateau is much steeper than what we expect in the simplest
magnetar model. We propose a scenario in which the magnetar undergoes
gravitational-wave-driven r-mode instability, and the spin-down is dominated by
gravitational wave losses up to the end of the steep plateau, so that such a
relatively steep plateau can be interpreted as the internal emission of the
magnetar wind and the sharp drop can be produced when the magnetar collapses
into a black hole. This scenario also predicts an initial X-ray plateau lasting
for hundreds of seconds with an approximately constant flux which is compatible
with observation. Assuming that the magnetar wind has a negligible contribution
in the optical band, we interpret the optical afterglow as the forward shock
emission by invoking the energy injection from a continuously refreshed shock
following the prompt emission phase. It is shown that our model can basically
describe the temporal evolution of the multi-band afterglow of GRB 130831A.

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## Modelling the Multi-band Afterglow of GRB 091127: Evidence of a Hard Electron Energy Spectrum with an Injection Break. (arXiv:1604.04847v1 [astro-ph.HE])

### April 19th, 2016

The afterglow of GRBs is believed to originate from the synchrotron emission
of shock-accelerated electrons produced by the interaction between the outflow
and the external medium. The accelerated electrons are usually assumed to
follow a power law energy distribution with an index of $p$. Observationally,
although most GRB afterglows have a $p$ larger than 2, there are still a few
GRBs suggestive of a hard ($p<2$) electron spectrum. GRB 091127, with
well-sampled broad-band afterglow data, shows evidence of a hard electron
spectrum and strong spectral evolution, with a spectral break moving from high
to lower energies. The spectral break evolves very fast and cannot be explained
by the cooling break in the standard afterglow model, unless evolving
microphysical parameters are assumed. Besides, the multi-band afterglow light
curves show an achromatic break at around 33 ks. Based on the model of a hard
electron spectrum with an injection break, we interpret the observed spectral
break as the synchrotron frequency corresponding to the injection break, and
the achromatic break as a jet break caused by the jet-edge effect. It is shown
that the spectral evolution and the multi-band afterglow light curves of GRB
091127 can be well reproduced by this model.

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## The Progenitor of GW 150914. (arXiv:1603.00511v2 [astro-ph.HE] UPDATED)

### April 19th, 2016

The spectacular detection of gravitational waves (GWs) from GW 150914 and its
reported association with a gamma-ray burst (GRB) offer new insights into the
evolution of massive stars. Here it is shown that no single star of any mass
and credible metallicity is likely to produce the observed GW signal. Stars
with helium cores in the mass range 35 to 133 solar masses encounter the pair
instability and either explode or pulse until the core mass is less than 40
solar masses, smaller than the combined mass of the observed black holes. The
rotation of more massive helium cores is either braked by interaction with a
slowly rotating hydrogen envelope, if one is present, or by mass loss, if one
is not. The very short interval between the GW signal and the observed onset of
the putative GRB in GW 150914 is also too short to have come from a single
star. A more probable model for making the gravitational radiation is the
delayed merger of two black holes made by 70 and 90 solar mass stars in a
binary system. The more massive component was a pulsational-pair instability
supernova before making the first black hole.

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## The Observer&apos;s Guide to the Gamma-Ray Burst-Supernova Connection. (arXiv:1604.03549v1 [astro-ph.HE])

### April 14th, 2016

In this review we present a progress report of the connection between
long-duration gamma-ray bursts (GRBs) and their accompanying supernovae (SNe).
The analysis is from the point of view of an observer, with much of the
emphasis placed on how observations, and the modelling of observations, have
constrained what we known about GRB-SNe. We discuss their photometric and
spectroscopic properties, their role as cosmological probes, including their
measured luminosity$-$decline relationships, and how they can be used to
measure the Hubble constant. We present a statistical analysis of their
bolometric properties, and use this to determine the properties of the
“average” GRB-SNe: which has a kinetic energy of $E_{\rm K} \approx 2.5\times10^{52}$ erg, an ejecta mass of $M_{\rm ej} \approx 6$ M$_{\odot}$, a
nickel mass of $M_{\rm Ni} \approx 0.4$ M$_{\odot}$, a peak photospheric
velocity of $v_{\rm ph} \approx 21,000$ km s$^{-1}$, a peak bolometric
luminosity of $L_{\rm p} \approx 1\times10^{43}$ erg s$^{-1}$, and it reaches
peak bolometric light in $t_{\rm p} \approx 13$ days. We discuss their
geometry, consider the various physical processes that are thought to power the
luminosity of GRB-SNe, and whether differences exist between GRB-SNe and the
SNe associated with ultra-long duration GRBs. We discuss how observations of
the environments of GRB-SNe further constrain the physical properties of their
progenitor stars, and give an overview of the current theoretical paradigms of
their suspected central engines. We also present an overview of the
radioactively powered transients that have been photometrically associated with
short-duration GRBs. We conclude the review by discussing what additional
research is needed to further our understanding of GRB-SNe, in particular the
role of binary-formation channels and the connection of GRB-SNe with
superluminous SNe (abridged).

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