Catalogue Search | MBRL
Are you sure you want to remove the book from the shelf?
{{itemTitle}}
4,065,006
result(s) for
"B"
Sort by:
A magnetar-powered X-ray transient as the aftermath of a binary neutron-star merger
Mergers of neutron stars are known to be associated with short γ-ray bursts
1
–
4
. If the neutron-star equation of state is sufficiently stiff (that is, the pressure increases sharply as the density increases), at least some such mergers will leave behind a supramassive or even a stable neutron star that spins rapidly with a strong magnetic field
5
–
8
(that is, a magnetar). Such a magnetar signature may have been observed in the form of the X-ray plateau that follows up to half of observed short γ-ray bursts
9
,
10
. However, it has been expected that some X-ray transients powered by binary neutron-star mergers may not be associated with a short γ-ray burst
11
,
12
. A fast X-ray transient (CDF-S XT1) was recently found to be associated with a faint host galaxy, the redshift of which is unknown
13
. Its X-ray and host-galaxy properties allow several possible explanations including a short γ-ray burst seen off-axis, a low-luminosity γ-ray burst at high redshift, or a tidal disruption event involving an intermediate-mass black hole and a white dwarf
13
. Here we report a second X-ray transient, CDF-S XT2, that is associated with a galaxy at redshift
z
= 0.738 (ref.
14
). The measured light curve is fully consistent with the X-ray transient being powered by a millisecond magnetar. More intriguingly, CDF-S XT2 lies in the outskirts of its star-forming host galaxy with a moderate offset from the galaxy centre, as short γ-ray bursts often do
15
,
16
. The estimated event-rate density of similar X-ray transients, when corrected to the local value, is consistent with the event-rate density of binary neutron-star mergers that is robustly inferred from the detection of the gravitational-wave event GW170817.
Observations of an X-ray transient associated with a galaxy at redshift 0.738 suggest that the X-ray transient is powered by a millisecond magnetar and that it is the remnant of a merger between two neutron stars.
Journal Article
The lost cousins
\"Grandad realizes the children have never met their cousins who are scattered across the globe. It's time to head off on an adventure to go visit them--but finding the long-lost cousins is harder than it sounds! \"-- Provided by publisher.
Book
A peculiar low-luminosity short gamma-ray burst from a double neutron star merger progenitor
Double neutron star (DNS) merger events are promising candidates of short gamma-ray burst (sGRB) progenitors as well as high-frequency gravitational wave (GW) emitters. On August 17, 2017, such a coinciding event was detected by both the LIGO-Virgo gravitational wave detector network as GW170817 and Gamma-Ray Monitor on board NASA’s
Fermi
Space Telescope as GRB 170817A. Here, we show that the fluence and spectral peak energy of this sGRB fall into the lower portion of the distributions of known sGRBs. Its peak isotropic luminosity is abnormally low. The estimated event rate density above this luminosity is at least
19
0
-
160
+
440
Gpc
−3
yr
−1
, which is close to but still below the DNS merger event rate density. This event likely originates from a structured jet viewed from a large viewing angle. There are similar faint soft GRBs in the
Fermi
archival data, a small fraction of which might belong to this new population of nearby, low-luminosity sGRBs.
A short-duration gamma-ray burst was detected along with a double neutron start merger gravitational wave by LIGO-Virgo on August 17th 2017. Here, the authors show that the fluence and spectral peak energy of this event fall into the lower portion of the distribution of known short-duration gamma-ray bursts.
Journal Article
The afterglow and elliptical host galaxy of the short γ-ray burst GRB 050724
Hard evidence
Gamma-ray bursts (GRBs) are either ‘long and soft’, or ‘short and hard’. It is now clear that the long-duration type are caused by explosions of massive stars in distant star-forming galaxies. Only in recent months, with the Swift satellite latching onto bursts as soon as they happen, has it been possible to collect data on short bursts that may lead to similar certainty as to their cause. GRB 050724 burst onto the scene on 24 July, and has all the properties needed to solve the mystery of short GRBs. The new evidence supports the merging compact object model of short GRBs, involving either a neutron star–neutron star merger, or a neutron star–black hole binary system as progenitor.
Despite a rich phenomenology, γ-ray bursts (GRBs) are divided
1
into two classes based on their duration and spectral hardness—the long-soft and the short-hard bursts. The discovery of afterglow emission from long GRBs was a watershed event, pinpointing
2
their origin to star-forming galaxies, and hence the death of massive stars, and indicating
3
an energy release of about 10
51
erg. While theoretical arguments
4
suggest that short GRBs are produced in the coalescence of binary compact objects (neutron stars or black holes), the progenitors, energetics and environments of these events remain elusive despite recent
5
,
6
,
7
,
8
localizations. Here we report the discovery of the first radio afterglow from the short burst GRB 050724, which unambiguously associates it with an elliptical galaxy at a redshift
9
z
= 0.257. We show that the burst is powered by the same relativistic fireball mechanism as long GRBs, with the ejecta possibly collimated in jets, but that the total energy release is 10–1,000 times smaller. More importantly, the nature of the host galaxy demonstrates that short GRBs arise from an old (> 1 Gyr) stellar population, strengthening earlier suggestions
5
,
6
and providing support for coalescing compact object binaries as the progenitors.
Journal Article
The lost house : a seek and find book
\"A brother and sister want to go to the playground with their grandfather, but they can't leave until they find everything they need to take with them, in his colorful house. Help Grandad find all of his belongings in this search and find!\"-- Provided by publisher.
Book
A trade-off between plant and soil carbon storage under elevated CO2
Terrestrial ecosystems remove about 30 per cent of the carbon dioxide (CO
2
) emitted by human activities each year
1
, yet the persistence of this carbon sink depends partly on how plant biomass and soil organic carbon (SOC) stocks respond to future increases in atmospheric CO
2
(refs.
2
,
3
). Although plant biomass often increases in elevated CO
2
(eCO
2
) experiments
4
–
6
, SOC has been observed to increase, remain unchanged or even decline
7
. The mechanisms that drive this variation across experiments remain poorly understood, creating uncertainty in climate projections
8
,
9
. Here we synthesized data from 108 eCO
2
experiments and found that the effect of eCO
2
on SOC stocks is best explained by a negative relationship with plant biomass: when plant biomass is strongly stimulated by eCO
2
, SOC storage declines; conversely, when biomass is weakly stimulated, SOC storage increases. This trade-off appears to be related to plant nutrient acquisition, in which plants increase their biomass by mining the soil for nutrients, which decreases SOC storage. We found that, overall, SOC stocks increase with eCO
2
in grasslands (8 ± 2 per cent) but not in forests (0 ± 2 per cent), even though plant biomass in grasslands increase less (9 ± 3 per cent) than in forests (23 ± 2 per cent). Ecosystem models do not reproduce this trade-off, which implies that projections of SOC may need to be revised.
A synthesis of elevated carbon dioxide experiments reveals that when plant biomass is strongly stimulated by elevated carbon dioxide levels, soil carbon storage declines, and where biomass is weakly stimulated, soil carbon accumulates.
Journal Article
Economic development in provincial China : the central Shaanxi since 1930
The economic development of Central Shaanxi province from 1930 until today illustrates the effects of famine, war, & construction under Chinese communism. It portrays the growing pains of a frontier economy & discusses the natural barriers to agricultural expansion. An extensive economic survey of counties in hill & plain areas based on data from local governments & the author's own observation shows great regional differences, in the past as well as the present.
Book
A large and ubiquitous source of atmospheric formic acid
Formic acid (HCOOH) is one of the most abundant acids in the atmosphere, with an important influence on precipitation chemistry and acidity. Here we employ a chemical transport model (GEOS-Chem CTM) to interpret recent airborne and ground-based measurements over the US Southeast in terms of the constraints they provide on HCOOH sources and sinks. Summertime boundary layer concentrations average several parts-per-billion, 2–3× larger than can be explained based on known production and loss pathways. This indicates one or more large missing HCOOH sources, and suggests either a key gap in current understanding of hydrocarbon oxidation or a large, unidentified, direct flux of HCOOH. Model-measurement comparisons implicate biogenic sources (e.g., isoprene oxidation) as the predominant HCOOH source. Resolving the unexplained boundary layer concentrations based (i) solely on isoprene oxidation would require a 3× increase in the model HCOOH yield, or (ii) solely on direct HCOOH emissions would require approximately a 25× increase in its biogenic flux. However, neither of these can explain the high HCOOH amounts seen in anthropogenic air masses and in the free troposphere. The overall indication is of a large biogenic source combined with ubiquitous chemical production of HCOOH across a range of precursors. Laboratory work is needed to better quantify the rates and mechanisms of carboxylic acid production from isoprene and other prevalent organics. Stabilized Criegee intermediates (SCIs) provide a large model source of HCOOH, while acetaldehyde tautomerization accounts for ~ 15% of the simulated global burden. Because carboxylic acids also react with SCIs and catalyze the reverse tautomerization reaction, HCOOH buffers against its own production by both of these pathways. Based on recent laboratory results, reaction between CH3O2 and OH could provide a major source of atmospheric HCOOH; however, including this chemistry degrades the model simulation of CH3OOH and NOx : CH3OOH. Developing better constraints on SCI and RO2 + OH chemistry is a high priority for future work. The model neither captures the large diurnal amplitude in HCOOH seen in surface air, nor its inverted vertical gradient at night. This implies a substantial bias in our current representation of deposition as modulated by boundary layer dynamics, and may indicate an HCOOH sink underestimate and thus an even larger missing source. A more robust treatment of surface deposition is a key need for improving simulations of HCOOH and related trace gases, and our understanding of their budgets.
Journal Article