409 research outputs found
X-ray Emission from the Type Ic Supernova 1994I Observed with Chandra
We present two high-resolution Chandra X-ray observations of supernova (SN)
1994I which show, for the first time, that the interaction of the blast wave
from a Type Ic SN with its surrounding circumstellar material (CSM) can give
rise to soft X-ray emission. Given a 0.3-2 keV band X-ray luminosity of L_x ~ 1
x 10^{37} ergs/s between six and seven years after the outburst of SN 1994I,
and assuming the X-ray emission arises from the shock-heated CSM, we derive a
pre-SN mass-loss rate of \dot{M} ~ 1 x 10^{-5} M_sun/yr (v_w/10 km/s).
Combining the results with earlier ROSAT observations, we construct the X-ray
lightcurve of SN 1994I. A best-fit X-ray rate of decline of L_x \propto t^{-s}
with index s~1 and a CSM density profile of rho_csm \propto r^{-1.9\pm0.1} are
inferred, consistent with what is expected for a constant mass-loss rate and
constant wind velocity profile for the SN progenitor (rho_csm \propto r^{-2}).Comment: 5 pages, 3 figures, accepted for publication in the Astrophysical
Journal Letter
SN 1996cr: Confirmation of a Luminous Type IIn Supernova in the Circinus Galaxy
We have recently confirmed SN 1996cr as a late-time type IIn supernova (SN)
via VLT spectroscopy and isolated its explosion date to ~1 yr using archival
optical imaging. We briefly touch upon here the wealth of optical, X-ray, and
radio archival observations available for this enigmatic source. Due to its
relative proximity (3.8 +/-0.6 Mpc), SN 1996cr ranks among the brightest X-ray
and radio SNe ever detected and, as such, may offer powerful insights into the
structure and composition of type IIn SNe. We also find that SN 1996cr is
matched to GRB 4B 960202 at a 2-3 sigma confidence level, making it perhaps the
third GRB to be significantly associated with a type II SN. We speculate on
whether SN 1996cr could be an off-axis or ``failed'' GRB.Comment: 3 pages, 1 figure, poster proceeding for "Supernova 1987A: 20 Years
After: Supernovae and Gamma-Ray Bursters" AIP, New York, eds. S. Immler, K.W.
Weiler, and R. McCra
Chandra and ASCA X-ray Observations of the Radio Supernova SN1979C IN NGC 4321
We report on the X-ray observation of the radio selected supernova SN1979C
carried out with ASCA in 1997 December and serendipitously available from a
Chandra Guaranteed Time Observation in 1999 November. The supernova, of type SN
II-Linear (SN IIL), was first observed in the optical and occurred in the
weakly barred, almost face on spiral galaxy NGC 4321 (M100). The galaxy, a
member of the Virgo S cluster, is at a distance of 17.1 Mpc, and contains at
least three other supernovae discovered in this century. The useful exposure
time was ~25 ks for the Solid-State Imaging Spectrometer (SIS), ~28 ks for the
Gas Scintillation Imaging Spectrometer (GIS), and ~2.5 ks for Chandra's
Advanced CCD Imaging Spectrometer (ACIS). No point source was detected at the
radio position of SN1979C in a 3' diameter half power response circle in the
ASCA data. The background and galaxy subtracted SN signal had a 3sigma upper
limit to the flux of 6.3x10^-14 ergs/s/cm^-2 in the full ASCA SIS band
(0.4-10.0 keV) and a 3sigma upper limit of <3-4x10^-14 erg/s/cm^2 in the 2-10
keV band. In the Chandra data, a source at the position of SN1979C is
marginally detected at energies below 2 keV at a flux consistent with the ROSAT
HRI detection in 1995. At energies above 2 keV, no source is detected with an
upper limit of ~3x10^-14 erg/s/cm^-2. These measurements give the first ever
x-ray flux limit of a Type IIL SN above 2 keV which is an important diagnostic
of the outgoing shock wave ploughing through the circumstellar medium.Comment: 8 pages, 2 figures, accepted A
Detecting z > 2 Type IIn Supernovae
Type IIn supernovae (SNe IIn) dominate the brightest supernova events in
observed FUV flux (~1200-2000A). We show that multi-band, multi-epoch optical
surveys complete to m_r = 27 can detect the FUV emission of ~25 z > 2 SNe IIn
deg^-2 yr^-1 rest-frame (~10 SNe IIn deg^-2 yr^-1 observed-frame) to 4 sigma
using a technique monitoring color-selected galaxies. Moreover, the strength
and evolution of the bright emission lines observed in low redshift SNe IIn
imply that the Ly-a emission features in ~70% of z > 2 SNe IIn are above
8m-class telescope spectroscopic thresholds for ~2 yr rest-frame. As a result,
existing facilities have the capability to both photometrically detect and
spectroscopically confirm z > 2 SNe IIn and pave the way for efficient searches
by future 8m-class survey and 30m-class telescopes. The method presented here
uses the sensitivities and wide-field capabilities of current optical
instruments and exploits (1) the efficiency of z > 2 galaxy color-selection
techniques, (2) the intrinsic brightness distribution ( = -19.0 +/-0.9)
and blue profile of SNe IIn continua, (3) the presence of extremely bright,
long-lived emission features, and (4) the potential to detect blueshifted SNe
Ly-a emission shortward of host galaxy Ly-a features.Comment: 26 pages (pre-print), 6 figures, accepted Ap
Recommended from our members
Sanitation Realities in Peri-Urban Communities: Unfreedoms, Capabilities and the Conscious Mind - A Case of Chennai, India
This thesis assesses sanitation realities experienced by peri-urban slum dwellers in Chennai, India, to investigate whether rapid economic growth translates into pervasive safe sanitation, otherwise a threat to human security. This is in line with the Sustainable Development Goals of âleaving no one behindâ. The empirical methodology consists of qualitative comparative case studies approached through rapid appraisal. At least 5 interviews at each of the 10 different slum settlement locations within the Chennai Metropolitan area were conducted. Both the locations and the settlers were conveniently sampled. The settlements were chosen as they mostly lay in a rapidly urbanizing area. The selection of interviewee was determined by availability, yet leaning towards women who are more vulnerable when lacking safe sanitation facilities, and who are the primary caregivers in the household. The research found that out of the 10 settlements visited, 5 habitually practiced open defecation, as no sanitation facilities were available. Hence some settlers were restricted in their freedom to be safe from emotional or physical harm: threatened by dangerous pathogens released into the environment, and insecurities due to lack of privacy. Conceptually the thesis applies an understanding of how affecting influences in individual history and living environment impact upon an individualâs conscious mind, connecting the capability approach to consciousness research. The thesis argues how settlers, overlooked by public services, and subjected to the dangerous and humiliating practice of open defecation, are faced with mental health issues and a diminished likelihood to productively engage, and exercise agency for human growth
The evolution of sperm morphometry in pheasants
Postcopulatory sexual selection is thought to be a potent evolutionary force driving the
diversification of sperm shape and function across species. In birds, insemination and
fertilisation are separated in time and sperm storage increases the duration of sperm
female interaction and hence the opportunity for sperm competition and cryptic female
choice. We performed a comparative study of 24 pheasant species (Phasianidae,
Galliformes) to establish the relative importance of sperm competition and the duration of
sperm storage for the evolution of sperm morphometry (i.e. size of different sperm traits).
We found that sperm size traits were negatively associated with the duration of sperm
storage but were independent of the risk of sperm competition estimated from relative
testis mass. Our study emphasises the importance of female reproductive biology for the
evolution of sperm morphometry particularly in sperm storing taxa
Constraints on supernova progenitors from spatial correlations with H-alpha emission
We have attempted to constrain the progenitors of all supernova types,
through correlations of the positions of historical supernovae with recent star
formation, as traced by H-alpha emission. Through pixel statistics we have
found that a large fraction of the SNII population do not show any association
with current star formation, which we put down to a 'runaway' fraction of these
progenitors. The SNIb/c population accurately traces the H-alpha emission, with
some suggestion that the SNIc progenitors show a higher degree of correlation
than the SNIb, suggesting higher mass progenitors for the former. Overall the
SNIa population only show a weak correlation to the positions of HII regions,
but as many as a half may be associated with a young stellar population.Comment: To appear in conference proceedings: "Supernova 1987A: 20 Years After
-- Supernovae & Gamma-Ray Bursters", held in Aspen, February 200
A Catalog of Candidate Intermediate-luminosity X-ray Objects
ROSAT, and now Chandra, X-ray images allow studies of extranuclear X-ray
point sources in galaxies other than our own. X-ray observations of normal
galaxies with ROSAT and Chandra have revealed that off-nuclear, compact,
Intermediate-luminosity (Lx[2-10 keV] >= 1e39 erg/s) X-ray Objects (IXOs,
a.k.a. ULXs [Ultraluminous X-ray sources]) are quite common. Here we present a
catalog and finding charts for 87 IXOs in 54 galaxies, derived from all of the
ROSAT HRI imaging data for galaxies with cz <= 5000 km/s from the Third
Reference Catalog of Bright Galaxies (RC3). We have defined the cutoff Lx for
IXOs so that it is well above the Eddington luminosity of a 1.4 Msun black hole
(10^38.3 erg/s), so as not to confuse IXOs with ``normal'' black hole X-ray
binaries. This catalog is intended to provide a baseline for follow-up work
with Chandra and XMM, and with space- and ground-based survey work at
wavelengths other than X-ray. We demonstrate that elliptical galaxies with IXOs
have a larger number of IXOs per galaxy than non-elliptical galaxies with IXOs,
and note that they are not likely to be merely high-mass X-ray binaries with
beamed X-ray emission, as may be the case for IXOs in starburst galaxies.
Approximately half of the IXOs with multiple observations show X-ray
variability, and many (19) of the IXOs have faint optical counterparts in DSS
optical B-band images. Follow-up observations of these objects should be
helpful in identifying their nature.Comment: 29 pages, ApJS, accepted (catalog v2.0) (full resolution version of
paper and future releases of catalog at http://www.xassist.org/ixocat_hri
Chandra X-Ray Point Sources, including Supernova 1979C, in the Spiral Galaxy M100
Six x-ray point sources, with luminosities of in the 0.4--7 keV band, were detected in Chandra
observations of the spiral galaxy M100. One source is identified with supernova
SN 1979C and appears to have roughly constant x-ray flux for the period 16--20
years after the outburst. The x-ray spectrum is soft, as would be expected if
the x-ray emission is due to the interaction of supernova ejecta with
circumstellar matter. Most of the other sources are variable either within the
Chandra observation or when compared to archival data. None are coincident with
the peak of the radio emission at the nucleus. These sources have harder
spectra than the supernova and are likely x-ray binaries. M100 has more bright
x-ray sources than typical for spiral galaxies of its size. This is likely
related to active star formation occurring in the galaxy.Comment: accepted by the Astrophysical Journal, 7 page
SN 2007od: A Type IIP SN with Circumstellar Interaction
SN 2007od exhibits characteristics that have rarely been seen in a Type IIP
supernova (SN). Optical V band photometry reveals a very steep brightness
decline between the plateau and nebular phases of ~4.5 mag, likely due to SN
2007od containing a low mass of 56Ni. The optical spectra show an evolution
from normal Type IIP with broad Halpha emission, to a complex, four component
Halpha emission profile exhibiting asymmetries caused by dust extinction after
day 232. This is similar to the spectral evolution of the Type IIn SN 1998S,
although no early-time narrow (~200 km s-1) Halpha component was present in SN
2007od. In both SNe, the intermediate-width Halpha emission components are
thought to arise in the interaction between the ejecta and its circumstellar
medium (CSM). SN 2007od also shows a mid-IR excess due to new dust. The
evolution of the Halpha profile and the presence of the mid-IR excess provide
strong evidence that SN 2007od formed new dust before day 232. Late-time
observations reveal a flattening of the visible lightcurve. This flattening is
a strong indication of the presence of a light echo, which likely accounts for
much of the broad, underlying Halpha component seen at late-times. We believe
the multi-peaked Halpha emission is consistent with the interaction of the
ejecta with a circumstellar ring or torus (for the inner components at \pm1500
km s-1), and a single blob or cloud of circumstellar material out of the plane
of the CSM ring (for the outer component at -5000 km s-1). The most probable
location for the formation of new dust is in the cool dense shell created by
the interaction between the expanding ejecta and its CSM. Monte Carlo radiative
transfer modeling of the dust emission from SN 2007od implies that up to 4x
10-4Msun of new dust has formed. This is similar to the amounts of dust formed
in other CCSNe such as SNe 1999em, 2004et, and 2006jc.Comment: 35 pages, 6 figures. Accepted for publication in Ap
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