729 research outputs found
The nuclear starburst in Arp 299-A: From the 5.0 GHz VLBI radio light-curves to its core-collapse supernova rate
The nuclear region of the Luminous Infra-red Galaxy Arp 299-A hosts a recent
( Myr), intense burst of massive star formation which is expected to
lead to numerous core-collapse supernovae (CCSNe). Previous VLBI observations,
carried out with the EVN at 5.0 GHz and with the VLBA at 2.3 and 8.4 GHz,
resulted in the detection of a large number of compact, bright, non-thermal
sources in a region \lsim150 pc in size. We aim at establishing the nature of
all non-thermal, compact components in Arp 299-A, as well as estimating its
core-collapse supernova rate. We use multi-epoch European VLBI Network (EVN)
observations taken at 5.0 GHz to image with milliarcsecond resolution the
compact radio sources in the nuclear region of Arp 299-A. We also use one
single-epoch 5.0 GHz Multi-Element Radio Linked Interferometer Network (MERLIN)
observation to image the extended emission in which the compact radio sources
--traced by our EVN observations-- are embedded. Twenty-six compact sources are
detected, 8 of them are new objects not previously detected. The properties of
all detected objects are consistent with them being a mixed population of CCSNe
and SNRs. We find clear evidence for at least two new CCSNe, implying a lower
limit to the CCSN rate of \nu_{\rm SN}\gsim0.80 SN/yr indicating that the
bulk of the current star formation in Arp 299-A is taking place in the
innermost pc. Our MERLIN observations trace a region of diffuse,
extended emission which is co-spatial to the region where all compact sources
are found. From this diffuse, non-thermal radio emission we obtain an
independent estimate for the core-collapse supernova rate, which is in the
range - 0.65 SN/yr, roughly in agreement with previous
estimates and our direct estimate of the CCSN rate from the compact radio
emission.Comment: 13 pages, 5 figures, accepted for publication on Astronomy &
Astrophysic
GRB 221009A: A light dark matter burst or an extremely bright Inverse Compton component?
Gamma-ray bursts (GRBs) have been considered as potential very high-energy
photon emitters due to the large amount of energy released as well as the
strong magnetic fields involved in their jets. However, the detection of TeV
photons is not expected from bursts beyond a redshift of due to
their attenuation with the extragalactic background light (EBL). For these
reasons, the recent observation of photons with energies of 18 and 251 TeV from
GRB 221009A (z=0.151) last October 9th, 2022 has challenged what we know about
the TeV-emission mechanisms and the extragalactic background. In order to
explain the TeV observations, recent works exploring candidates of dark matter
have started to appear. In this paper, we discuss the required conditions and
limitations within the most plausible scenario, synchrotron-self Compton (SSC)
radiation in the GRB afterglow, to interpret the one 18-TeV photon observation
besides the EBL. To avoid the Klein-Nishina effect, we find an improbable value
of the microphysical magnetic parameter below for a circumburst
medium value (expected in the collapsar scenario).
Therefore, we explore possible scenarios in terms of ALPs and dark photon
mechanisms to interpret this highly-energetic photon and we discuss the
implications in the GRB energetics. We find that the ALPs and dark photon
scenarios can explain the 18 TeV photon but not the 251 TeV photon.Comment: 15 pages, 5 figures, 4 table
Wheat Straw Open Burning: Emissions and Impact on Climate Change
The state of Baja California, Mexico, is the second national wheat producer. Mexicali, the capital of Baja California, is the primary wheat producer, and it represents the most significant crop in the valley, with 90,609 ha of a cultivated surface by 2015; it leads to a wheat production of 585,334 t and a generation of 661,446 t of wheat straw as agricultural residue. The 15% of this waste has various uses. The 85% of wheat straw is open burnt in situ to prepare the farmland for the next agricultural cycle. Through the development of an emissions and energy model on iThink®, the emissions of 6,185 t of PM, 35,983 t of CO, and 1,125 t of CH4 considering a headfire burning or 3,373 t of PM, 30,360 t of CO, and 731 t of CH4 by backfire burning were estimated. Also, the wheat straw wasted energy was estimated at 8.15 PJ by 2015, with a lower heating value of 14.50 MJ/kg determined experimentally. The results highlight that for each hectare of harvested wheat, 6.205 t of wheat straw are generated and burnt. It represents the emission of pollutants and 89,972.50 MJ of wasted energy
In vitro antileishmanial activity and iron superoxide dismutase inhibition of arylamine Mannich base derivatives
Leishmaniasis is one of the world’s most neglected diseases, and it has a worldwide prevalence of 12 million. There are no effective human vaccines for its prevention, and treatment is hampered by outdated drugs. Therefore, research aiming at the development of new therapeutic tools to fight Leishmaniasis remains a crucial goal today. With this purpose in mind, we present twenty arylaminoketone derivatives with a very interesting in vitro and in vivo efficacy against Trypanosoma cruzi that have now been studied against promastigote and amastigote forms of L. infantum, L. donovani and L. braziliensis strains. Six out of the twenty Mannich base-type derivatives showed Selectivity Index between 39 and 2337 times higher in the amastigote form than the reference drug glucantime. These six derivatives affected the parasite infectivity rates; the result was lower parasite infectivity rates than glucantime tested at a IC25 dose. In addition, these derivatives were substantially more active against the three Leishmania species tested than glucantime. The mechanism of action of these compounds has been studied, showing a greater alteration in glucose catabolism and leading to greater levels of Fe-SOD (iron superoxide dismutase) inhibition. These molecules could be potential candidates for Leishmaniasis chemotherapy
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