The measurement of the period and period derivative, and the canonical model of dipole radiation have provided a method to estimate the low superficial magnetic fields in the so-called central ...compact objects (CCOs). In the present work, a scenario is introduced in order to explain the magnetic behavior of such CCOs. Based on magnetohydrodynamic simulations of the post core-collapse supernova phase during the hypercritical accretion episode, we argue that the magnetic field of a newborn neutron star could have been early buried. During this phase, thermal neutrinos are created mainly by the pair annihilation, plasmon decay, photo-neutrino emission and other processes. We study the dynamics of these neutrinos in this environment and also estimate the number expected of the neutrino events with their flavor ratios on Earth. The neutrino burst is the only viable observable that could provide compelling evidence of the hypercritical phase and therefore, the hidden magnetic field mechanism as the most favorable scenario to explain the anomalous low magnetic fields estimated for CCOs.
ABSTRACT
We present optical and near-infrared (NIR) photometric observations of GRB 191016 with the COATLI,DDOTI, and RATIR ground-based telescopes over the first three nights. We present the ...temporal evolution of the optical afterglow and describe five different stages that were not completely characterized in previous works, mainly due to scarcity of data points to accurately fit the different components of the optical emission. After the end of the prompt gamma-ray emission, we observed the afterglow rise slowly in the optical and NIR wavelengths and peak at around T + 1450 s in all filters. This was followed by an early decay, a clear plateau from T + 5000 s to T + 11 000 s, and then a regular late decay. We also present evidence of the jet break at later times, with a temporal index in good agreement with the temporal slope obtained from X-ray observations. Although many of the features observed in the optical light curves of gamma-ray bursts are usually well explained by a reverse shock (RS) or forward shock (FS), the shallowness of the optical rise and enhanced peak emission in the GRB 191016A afterglow is not well fitted by only a FS or a RS. We propose a theoretical model which considers both of these components and combines an evolving FS with a later embedded RS and a subsequent late energy injection from the central engine activity. We use this model to successfully explain the temporal evolution of the light curves and discuss its implications on the fireball properties.
Whale lice (Cyamidae) are ectoparasitic amphipods exclusive to cetaceans. Data on their epidemiology usually come from species infecting baleen whales, which are large, slow‐moving hosts. In this ...study, we provide data on infection parameters, population structure and microhabitat selection in a whale louse exclusive to delphinids, Syncyamus aequus, with the aim of comparing them with those from cyamid species from large whales. A total of 176 striped dolphins Stenella coeruleoalba stranded along the Mediterranean coast of Spain during 1980–2016 were examined. The prevalence of S. aequus was 27.3% (95% CI: 20.9–34.3), and populations were sparse, with a mean number of whale lice per infected host of just 4.5 (3.4–6.7). The parasites were found on the head, with a clearly nested pattern, with the blowhole being the most frequently occupied site, followed by the mouth corner and eyes. Single‐male or single‐female populations were found on as much as 39.6% of infected dolphins. The sex ratio did not significantly depart from 1:1. Females were significantly larger than males and exhibited low fecundity (<10 eggs). The sex or the age class of the dolphins did not significantly affect the abundance or population structure of S. aequus. The patterns here obtained are in sharp contrast with those reported for whale lice infecting large whales. The small, streamlined body of dolphins creates strong current flows that would restrict the amount of suitable microhabitats and the body size of their associated cyamids. This would limit population growth, which in turn would lower the chances of host‐to‐host transmission upon body contacts, as well as male competition for the access to females.
We studied the infection parameters, population structure and microhabitat selection of the whale louse Syncyamus aequus, exclusive to delphinids. The data were obtained from stranded striped dolphins, Stenella coeruleoalba, from the Western Mediterranean. The small, streamlined bodies of dolphins create strong current flows that would restrict the amount of suitable microhabitats for the parasite and might impose constraints on their size and population growth. This, in turn, could influence key aspects such as sex ratio, reproductive potential or sexual dimorphism in S. aequus.
The early optical emission of gamma-ray bursts (GRBs) gives an opportunity to understand the central engine and first stages of these events. About 30% of GRBs present flares whose origin is still a ...subject of discussion. We present optical photometry of GRB 180620A with the COATLI telescope and RATIR instrument. COATLI started to observe from the end of prompt emission at T + 39.3 s and RATIR from T + 121.4 s. We supplement the optical data with the X-ray light curve from Swift/XRT. We observe an optical flare from T + 110 s to T + 550 s, with a temporal index decay O,decay = 1.32 0.01, and Δt/t = 1.63, which we interpret as the signature of a reverse shock component. After the initial normal decay the light curves show a long plateau from T + 500 s to T + 7800 s in both X-rays and the optical before decaying again after an achromatic jet break at T + 7800 s. Fluctuations are seen during the plateau phase in the optical. Adding to the complexity of GRB afterglows, the plateau phase (typically associated with the coasting phase of the jet) is seen in this object after the "normal" decay phase (associated with the deceleration phase of the jet), and the jet break phase occurs directly after the plateau. We suggest that this sequence of events can be explained by a rapid deceleration of the jet with td 40 s due to the high density of the environment ( 100 cm−3) followed by reactivation of the central engine, which causes the flare and powers the plateau phase.
Cassiopeia A, the youngest supernova remnant known in the Milky Way, is one of the brightest radio sources in the sky and a unique laboratory for supernova physics. Although its compact remnant was ...discovered in 1999 by the Chandra X-Ray Observatory, nowadays it is widely accepted that a neutron star lies in the centre of this supernova remnant. In addition, new observations suggest that such a neutron star with a low magnetic field and evidence of a carbon atmosphere could have suffered a hypercritical accretion phase seconds after the explosion. Considering this hypercritical accretion episode, we compute the neutrino cooling effect, the number of events and neutrino flavour ratios expected on Hyper-Kamiokande Experiment. The neutrino cooling effect (the emissivity and luminosity of neutrinos) is obtained through numerical simulations performed in a customized version of the flash code. Based on these simulations, we forecast that the number of events expected on the Hyper-Kamiokande Experiment is around 3195. Similarly, we estimate the neutrino flavour ratios to be detected considering the neutrino effective potential due to the thermal and magnetized plasma and thanks to the envelope of the star. It is worth noting that our estimates correspond to the only trustworthy method for verifying the hypercritical phase and although this episode took place 330 years ago, at present supernova remnants with these similarities might occur thus confirming our predictions for this phase.
We present optical photometry of the afterglow of the long GRB 180205A with the COATLI telescope from 217 s to about 5 days after the Swift/BAT trigger. We analyze this photometry in conjunction with ...the X-ray light curve from Swift/XRT. The late-time light curves and spectra are consistent with the standard forward-shock scenario. However, the early-time optical and X-ray light curves show atypical behavior; the optical light curve exhibits a flat plateau while the X-ray light curve shows a flare. We explore several scenarios and conclude that the most likely explanation for the early behavior is late activity of the central engine.
GRB 980923 was one of the brightest bursts observed by the Burst and Transient Source Experiment. Previous studies have detected two distinct components in addition to the main prompt episode, which ...is well described by a Band function. The first of these is a tail with a duration of Asymptotically = to400 s, while the second is a high-energy component lasting Asymptotically = to2 s. We summarize the observations and argue for a unified model in which the tail can be understood as the early gamma -ray afterglow from forward shock synchrotron emission, while the high-energy component arises from synchrotron self-Compton from the reverse shock. Consistency between the main assumption of thick shell emission and agreement between the observed and computed values for fluxes, break energies, starting times, and spectral indices leads to a requirement that the ejecta must be highly magnetized.
The transition from prompt to afterglow emission is one of the most exciting and least understood phases in gamma-ray bursts (GRBs). Correlations among optical, X-ray, and gamma-ray emission in GRBs ...have been explored, to attempt to answer whether the earliest optical emission comes from internal and/or external shocks. We present optical photometric observations of GRB 180325A collected with the TAROT and RATIR ground-based telescopes. These observations show two strong optical flashes with separate peaks at ∼50 and ∼120 s, followed by a temporally extended optical emission. We also present X-rays and gamma-ray observations of GRB 180325A, detected by the Burst Alert Telescope and X-ray Telescope, on the Neil Gehrels Swift observatory, which both observed a narrow flash at ∼80 s. We show that the prompt gamma-ray and X-ray early emission shares similar temporal and spectral features consistent with internal dissipation within the relativistic outflow (e.g., by internal shocks or magnetic reconnection), while the early optical flashes are likely generated by the reverse shock that decelerates the ejecta as it sweeps up the external medium.
Abstract
The High Altitude Water Cherenkov (HAWC) Gamma-Ray Observatory surveys the very high-energy sky in the 300 GeV to >100 TeV energy range. HAWC has detected two blazars above 11
σ
, Markarian ...421 (Mrk 421) and Markarian 501 (Mrk 501). The observations are comprised of data taken in the period between 2015 June and 2018 July, resulting in ∼1038 days of exposure. In this work, we report the time-averaged spectral analyses for both sources, above 0.5 TeV. Taking into account the flux attenuation due to the extragalactic background light, the intrinsic spectrum of Mrk 421 is described by a power law with an exponential energy cutoff with index
α
=
2.26
±
0.12
stat
−
0.2
+
0.17
sys
and energy cutoff
E
c
=
5.1
±
1.6
stat
−
2.5
+
1.4
sys
TeV, while the intrinsic spectrum of Mrk 501 is better described by a simple power law with index
α
=
2.61
±
0.11
stat
−
0.07
+
0.01
sys
. The maximum energies at which the Mrk 421 and Mrk 501 signals are detected are 9 and 12 TeV, respectively. This makes these some of the highest energy detections to date for spectra averaged over years-long timescales. Since the observation of gamma radiation from blazars provides information about the physical processes that take place in their relativistic jets, it is important to study the broadband spectral energy distributions (SEDs) of these objects. For this purpose, contemporaneous data in the gamma-ray band to the X-ray range, and literature data in the radio to UV range, were used to build time-averaged SEDs that were modeled within a synchrotron-self Compton leptonic scenario.
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