1,536 research outputs found
A common stochastic process rules gamma-ray burst prompt emission and X-ray flares
Prompt gamma-ray and early X-ray afterglow emission in gamma-ray bursts
(GRBs) are characterized by a bursty behavior and are often interspersed with
long quiescent times. There is compelling evidence that X-ray flares are linked
to prompt gamma-rays. However, the physical mechanism that leads to the complex
temporal distribution of gamma-ray pulses and X-ray flares is not understood.
Here we show that the waiting time distribution (WTD) of pulses and flares
exhibits a power-law tail extending over 4 decades with index ~2 and can be the
manifestation of a common time-dependent Poisson process. This result is robust
and is obtained on different catalogs. Surprisingly, GRBs with many (>=8)
gamma-ray pulses are very unlikely to be accompanied by X-ray flares after the
end of the prompt emission (3.1 sigma Gaussian confidence). These results are
consistent with a simple interpretation: an hyperaccreting disk breaks up into
one or a few groups of fragments, each of which is independently accreted with
the same probability per unit time. Prompt gamma-rays and late X-ray flares are
nothing but different fragments being accreted at the beginning and at the end,
respectively, following the very same stochastic process and likely the same
mechanism.Comment: 11 pages, 7 figures, accepted by Ap
Constraints on the environment and energetics of the Broad-Line Ic SN2014ad from deep radio and X-ray observations
Broad-line type Ic Supernovae (BL-Ic SNe) are characterized by high ejecta
velocity ( km s) and are sometimes associated with the
relativistic jets typical of long duration ( s) Gamma-Ray Bursts
(L-GRBs). The reason why a small fraction of BL-Ic SNe harbor relativistic jets
is not known. Here we present deep X-ray and radio observations of the BL-Ic
SN2014ad extending from to days post explosion. SN2014ad was not
detected at either frequency and has no observational evidence of a GRB
counterpart. The proximity of SN2014ad ( Mpc) enables very deep
constraints on the progenitor mass-loss rate and on the total energy
of the fast ejecta . We consider two synchrotron emission scenarios for a
wind-like circumstellar medium (CSM): (i) uncollimated non-relativistic ejecta,
and (ii) off-axis relativistic jet. Within the first scenario our observations
are consistent with GRB-less BL-Ic SNe characterized by a modest energy budget
of their fast ejecta ( erg), like SNe 2002ap and 2010ay.
For jetted explosions, we cannot rule out a GRB with erg
(beam-corrected) with a narrow opening angle ()
observed moderately off-axis () and
expanding in a very low CSM density ( M
yr). Our study shows that off-axis low-energy jets expanding in a
low-density medium cannot be ruled out even in the most nearby BL-Ic SNe with
extensive deep observations, and might be a common feature of BL-Ic SNe.Comment: 9 pages, 5 figures, accepted in Ap
Endurance of SN 2005ip after a decade: X-rays, radio, and H-alpha like SN 1988Z require long-lived pre-supernova mass loss
SN2005ip was a TypeIIn event notable for its sustained strong interaction
with circumstellar material (CSM), coronal emission lines, and IR excess,
interpreted as shock interaction with the very dense and clumpy wind of an
extreme red supergiant. We present a series of late-time spectra of SN2005ip
and a first radio detection of this SN, plus late-time X-rays, all of which
indicate that its CSM interaction is still strong a decade post-explosion. We
also present and discuss new spectra of geriatric SNe with continued CSM
interaction: SN1988Z, SN1993J, and SN1998S. From 3-10 yr post-explosion,
SN2005ip's H-alpha luminosity and other observed characteristics were nearly
identical to those of the radio-luminous SN1988Z, and much more luminous than
SNe1993J and 1998S. At 10 yr after explosion, SN2005ip showed a drop in
H luminosity, followed by a quick resurgence over several months. We
interpret this variability as ejecta crashing into a dense shell located at
around 0.05 pc from the star, which may be the same shell that caused the IR
echo at earlier epochs. The extreme H-alpha luminosities in SN2005ip and
SN1988Z are still dominated by the forward shock at 10 yr post-explosion,
whereas SN1993J and SN1998S are dominated by the reverse shock at a similar
age. Continuous strong CSM interaction in SNe~2005ip and 1988Z is indicative of
enhanced mass loss for about 1e3 yr before core collapse, longer than Ne, O, or
Si burning phases. Instead, the episodic mass loss must extend back through C
burning and perhaps even part of He burning.Comment: 14 pages, 8 figs. accepted in MNRA
One thousand days of SN 2015bn: HST imaging shows a light curve flattening consistent with magnetar predictions
We present the first observations of a Type I superluminous supernova (SLSN)
at days after maximum light. We observed SN 2015bn using the
Hubble Space Telescope Advanced Camera for Surveys in the F475W, F625W and
F775W filters at 721 days and 1068 days. SN 2015bn is clearly detected and
resolved from its compact host, allowing reliable photometry. A galaxy template
constructed from these data further enables us to isolate the SLSN flux in deep
ground-based imaging. We measure a light curve decline rate at days of
mag (100 d), much shallower than the earlier evolution,
and slower than previous SLSNe (at any phase) or the decay rate of Co.
Neither additional radioactive isotopes nor a light echo can consistently
account for the slow decline. A spectrum at 1083 days shows the same [O I] and
[Ca II] lines as seen at days, with no new features to indicate
strong circumstellar interaction. Radio limits with the Very Large Array rule
out an extended wind for mass-loss rates M yr (where is the wind velocity in
units of 10 km s). The optical light curve is consistent with , which we show is expected for magnetar spin-down with inefficient
trapping; furthermore, the evolution matches predictions from earlier magnetar
model fits. The opacity to magnetar radiation is constrained at
cm g, consistent with photon-matter pair-production over a broad
GeV-TeV range. This suggests the magnetar spectral energy distribution,
and hence the 'missing energy' leaking from the ejecta, may peak in this range.Comment: Accepted for publication in ApJL, updated to match accepted versio
Relativistic supernovae have shorter-lived central engines or more extended progenitors: the case of SN\,2012ap
Deep late-time X-ray observations of the relativistic, engine-driven, type Ic
SN2012ap allow us to probe the nearby environment of the explosion and reveal
the unique properties of relativistic SNe. We find that on a local scale of
~0.01 pc the environment was shaped directly by the evolution of the progenitor
star with a pre-explosion mass-loss rate <5x10^-6 Msun yr-1 in line with GRBs
and the other relativistic SN2009bb. Like sub-energetic GRBs, SN2012ap is
characterized by a bright radio emission and evidence for mildly relativistic
ejecta. However, its late time (t~20 days) X-ray emission is ~100 times fainter
than the faintest sub-energetic GRB at the same epoch, with no evidence for
late-time central engine activity. These results support theoretical proposals
that link relativistic SNe like 2009bb and 2012ap with the weakest observed
engine-driven explosions, where the jet barely fails to breakout. Furthermore,
our observations demonstrate that the difference between relativistic SNe and
sub-energetic GRBs is intrinsic and not due to line-of-sight effects. This
phenomenology can either be due to an intrinsically shorter-lived engine or to
a more extended progenitor in relativistic SNe.Comment: Version accepted to ApJ. Significantly broadened discussio
iPTF15eqv: Multi-wavelength Expos\'e of a Peculiar Calcium-rich Transient
The progenitor systems of the class of "Ca-rich transients" is a key open
issue in time domain astrophysics. These intriguing objects exhibit unusually
strong calcium line emissions months after explosion, fall within an
intermediate luminosity range, are often found at large projected distances
from their host galaxies, and may play a vital role in enriching galaxies and
the intergalactic medium. Here we present multi-wavelength observations of
iPTF15eqv in NGC 3430, which exhibits a unique combination of properties that
bridge those observed in Ca-rich transients and Type Ib/c supernovae. iPTF15eqv
has among the highest [Ca II]/[O I] emission line ratios observed to date, yet
is more luminous and decays more slowly than other Ca-rich transients. Optical
and near-infrared photometry and spectroscopy reveal signatures consistent with
the supernova explosion of a < 10 solar mass star that was stripped of its
H-rich envelope via binary interaction. Distinct chemical abundances and ejecta
kinematics suggest that the core collapse occurred through electron capture
processes. Deep limits on possible radio emission made with the Jansky Very
Large Array imply a clean environment ( 0.1 cm) within a radius of
cm. Chandra X-ray Observatory observations rule out alternative
scenarios involving tidal disruption of a white dwarf by a black hole, for
masses > 100 solar masses). Our results challenge the notion that
spectroscopically classified Ca-rich transients only originate from white dwarf
progenitor systems, complicate the view that they are all associated with large
ejection velocities, and indicate that their chemical abundances may vary
widely between events.Comment: 24 pages, 16 figures. Closely matches version published in The
Astrophysical Journa
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