384 research outputs found
Acoustic characteristics of synthesized signals of Chinese bahaba (Bahaba taipingensis)
As a member of Sciaenidae, Chinese bahaba (Bahaba taipingensis) generate sounds using sonic muscles to drive the swim bladder. In this study, the drumming sounds of Chinese bahaba in two groups differing in body size were recorded in an indoor aquarium and an outdoor pond. A piecewise exponential oscillation function was developed to synthesize the signals with a good agreement. Statistical comparisons found that the oscillation frequency and damping coefficient (part 1) of synthesized signals from larger-sized fish were lower. The results suggest that the acoustic characteristics of Chinese bahaba signals are related to fish morphology as the physiological age alters
Multiwavelength observations of Mkn 501 during the 1997 high state
During the observation period 1997, the nearby Blazar Mkn 501 showed
extremely strong emission and high variability. We examine multiwavelength
aspects of this event using radio, optical, soft and hard X-ray and TeV data.
We concentrate on the medium-timescale variability of the broadband spectra,
averaged over weekly intervals.
We confirm the previously found correlation between soft and hard X-ray
emission and the emission at TeV energies, while the source shows only minor
variability at radio and optical wavelengths. The non-linear correlation
between hard X-ray and TeV fluxes is consistent with a simple analytic estimate
based on an SSC model in which Klein-Nishina effects are important for the
highest-energy electrons in the jet, and flux variations are caused by
variations of the electron density and/or the spectral index of the electron
injection spectrum.
The time-averaged spectra are fitted with a Synchrotron Self-Compton (SSC)
dominated leptonic jet model, using the full Klein-Nishina cross section and
following the self-consistent evolution of relativistic particles along the
jet, accounting for gamma-gamma absorption and pair production within the
source as well as due to the intergalactic infrared background radiation. The
contribution from external inverse-Compton scattering is tightly constrained by
the low maximum EGRET flux and found to be negligible at TeV energies. We find
that high levels of the X-ray and TeV fluxes can be explained by a hardening of
the energy spectra of electrons injected at the base of the jet, in remarkable
contrast to the trend found for gamma-ray flares of the flat-spectrum radio
quasar PKS 0528+134.Comment: accepted for publication in ApJ, 31 pages, 11 figure
IPN localizations of Konus short gamma-ray bursts
Between the launch of the \textit{GGS Wind} spacecraft in 1994 November and
the end of 2010, the Konus-\textit{Wind} experiment detected 296 short-duration
gamma-ray bursts (including 23 bursts which can be classified as short bursts
with extended emission). During this period, the IPN consisted of up to eleven
spacecraft, and using triangulation, the localizations of 271 bursts were
obtained. We present the most comprehensive IPN localization data on these
events. The short burst detection rate, 18 per year, exceeds that of many
individual experiments.Comment: Published versio
Investigation of Primordial Black Hole Bursts using Interplanetary Network Gamma-ray Bursts
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.Comment: Accepted to the Astrophysical Journal (9 Figures, 3 Tables
Rest-frame properties of 32 gamma-ray bursts observed by the Fermi Gamma-Ray Burst Monitor
Aims: In this paper we study the main spectral and temporal properties of
gamma-ray bursts (GRBs) observed by Fermi/GBM. We investigate these key
properties of GRBs in the rest-frame of the progenitor and test for possible
intra-parameter correlations to better understand the intrinsic nature of these
events. Methods: Our sample comprises 32 GRBs with measured redshift that were
observed by GBM until August 2010. 28 of them belong to the long-duration
population and 4 events were classified as short/hard bursts. For all of these
events we derive, where possible, the intrinsic peak energy in the spectrum (\eprest), the duration in the rest-frame, defined as the
time in which 90% of the burst fluence was observed (\tninetyrest) and the
isotropic equivalent bolometric energy (\eiso). Results: The distribution of
\eprest has mean and median values of 1.1 MeV and 750 keV, respectively. A
log-normal fit to the sample of long bursts peaks at ~800 keV. No high-\ep
population is found but the distribution is biased against low \ep values. We
find the lowest possible \ep that GBM can recover to be ~ 15 keV. The
\tninetyrest distribution of long GRBs peaks at ~10 s. The distribution of
\eiso has mean and median values of erg and erg, respectively. We confirm the tight correlation between \eprest
and \eiso (Amati relation) and the one between \eprest and the 1-s peak
luminosity () (Yonetoku relation). Additionally, we observe a parameter
reconstruction effect, i.e. the low-energy power law index gets softer
when \ep is located at the lower end of the detector energy range. Moreover, we
do not find any significant cosmic evolution of neither \eprest nor
\tninetyrest.Comment: accepted by A&
Agile Detection of Delayed Gamma-Ray Emission from the Short Gamma-Ray Burst GRB 090510
Short gamma-ray bursts (GRBs), typically lasting less than 2 s, are a special
class of GRBs of great interest. We report the detection by the AGILE satellite
of the short GRB 090510 which shows two clearly distinct emission phases: a
prompt phase lasting ~ 200 msec and a second phase lasting tens of seconds. The
prompt phase is relatively intense in the 0.3-10 MeV range with a spectrum
characterized by a large peak/cutoff energy near 3 MeV, in this phase, no
significant high-energy gamma-ray emission is detected. At the end of the
prompt phase, intense gamma-ray emission above 30 MeV is detected showing a
power-law time decay of the flux of the type t^-1.3 and a broad-band spectrum
remarkably different from that of the prompt phase. It extends from sub-MeV to
hundreds of MeV energies with a photon index alpha ~ 1.5. GRB 090510 provides
the first case of a short GRB with delayed gamma-ray emission. We present the
timing and spectral data of GRB 090510 and briefly discuss its remarkable
properties within the current models of gamma-ray emission of short GRBs.Comment: Accepted by the Astrophysical Journal Letters on September 11, 200
The Burst and Transient Source Experiment (BATSE) Earth Occultation Catalog of Low-Energy Gamma-Ray Sources
The Burst and Transient Source Experiment (BATSE), aboard the Compton Gamma
Ray Observatory (CGRO), provided a record of the low-energy gamma-ray sky
(20-1000 keV) between 1991 April and 2000 May (9.1y). Using the Earth
Occultation Technique to extract flux information, a catalog of sources using
data from the BATSE large area detectors has been prepared. The first part of
the catalog consists of results from the monitoring of 58 sources, mostly
Galactic. For these sources, we have included tables of flux and spectral data,
and outburst times for transients. Light curves (or flux histories) have been
placed on the world wide web. We then performed a deep-sampling of 179 objects
(including the aforementioned 58 objects) combining data from the entire 9.1y
BATSE dataset. Source types considered were primarily accreting binaries, but a
small number of representative active galaxies, X-ray-emitting stars, and
supernova remnants were also included. The deep sample results include definite
detections of 83 objects and possible detections of 36 additional objects. The
definite detections spanned three classes of sources: accreting black hole and
neutron star binaries, active galaxies and supernova remnants. Flux data for
the deep sample are presented in four energy bands: 20-40, 40-70, 70-160, and
160-430 keV. The limiting average flux level (9.1 y) for the sample varies from
3.5 to 20 mCrab (5 sigma) between 20 and 430 keV, depending on systematic
error, which in turn is primarily dependent on the sky location. To strengthen
the credibility of detection of weaker sources (5-25 mCrab), we generated Earth
occultation images, searched for periodic behavior using FFT and epoch folding
methods, and critically evaluated the energy-dependent emission in the four
flux bands.Comment: 64 pages, 17 figures, abstract abridged, Accepted by ApJ
Panchromatic Observations of SN 2011dh Point to a Compact Progenitor Star
We report the discovery and detailed monitoring of X-ray emission associated
with the Type IIb SN 2011dh using data from the Swift and Chandra satellites,
placing it among the best studied X-ray supernovae to date. We further present
millimeter and radio data obtained with the SMA, CARMA, and EVLA during the
first three weeks after explosion. Combining these observations with early
optical photometry, we show that the panchromatic dataset is well-described by
non-thermal synchrotron emission (radio/mm) with inverse Compton scattering
(X-ray) of a thermal population of optical photons. In this scenario, the shock
partition fractions deviate from equipartition by a factor, (e_e/e_B) ~ 30. We
derive the properties of the shockwave and the circumstellar environment and
find a shock velocity, v~0.1c, and a progenitor mass loss rate of ~6e-5
M_sun/yr. These properties are consistent with the sub-class of Type IIb SNe
characterized by compact progenitors (Type cIIb) and dissimilar from those with
extended progenitors (Type eIIb). Furthermore, we consider the early optical
emission in the context of a cooling envelope model to estimate a progenitor
radius of ~1e+11 cm, in line with the expectations for a Type cIIb SN.
Together, these diagnostics are difficult to reconcile with the extended radius
of the putative yellow supergiant progenitor star identified in archival HST
observations, unless the stellar density profile is unusual. Finally, we
searched for the high energy shock breakout pulse using X-ray and gamma-ray
observations obtained during the purported explosion date range. Based on the
compact radius of the progenitor, we estimate that the breakout pulse was
detectable with current instruments but likely missed due to their limited
temporal/spatial coverage. [Abridged]Comment: (27 pages, 5 figures, 2 tables, final version to appear in ApJ
Primary recovery factor as a function of production rate: implications for conventional reservoirs with different drive mechanisms
This study evaluates the dependency of production rate on the recovery of hydrocarbon from conventional reservoirs using MBAL simulator. The results indicated that the recoveries are sensitive to the production rate in almost all hydrocarbon reservoirs. It was also found that the recovery of volumetric gas drive reservoirs is not impacted by the production rate. In fact, any increase in the production rate improves gas recovery in weak and strong water drive reservoirs. Moreover, increasing the production rate in oil reservoirs decreases the recovery with a significant effect observed in the weak water drive reservoirs. The results of this study demonstrate the need for implementing an effective reservoir management in order to obtain a maximum recovery
The High-Metallicity Explosion Environment of the Relativistic Supernova 2009bb
We investigate the environment of the nearby (d ~ 40Mpc) broad-lined Type Ic
supernova SN 2009bb. This event was observed to produce a relativistic outflow
likely powered by a central accreting compact object. While such a phenomenon
was previously observed only in long-duration gamma-ray bursts (LGRBs), no LGRB
was detected in association with SN 2009bb. Using an optical spectrum of the SN
2009bb explosion site, we determine a variety of ISM properties for the host
environment, including metallicity, young stellar population age, and star
formation rate. We compare the SN explosion site properties to observations of
LGRB and broad-lined SN Ic host environments on optical emission line ratio
diagnostic diagrams. Based on these analyses, we find that the SN 2009bb
explosion site has a very high metallicity of ~2x solar, in agreement with
other broad-lined SN Ic host environments and at odds with the low-redshift
LGRB host environments and recently proposed maximum metallicity limits for
relativistic explosions. We consider the implications of these findings and the
impact that SN 2009bb's unusual explosive properties and environment have on
our understanding of the key physical ingredient that enables some SNe to
produce a relativistic outflow.Comment: 7 pages, 4 figures, 1 table; accepted for publication in ApJ Letters
(replaced to include missing figure
- …