29 research outputs found
Chandra's insights into SN 2023ixf
We report Chandra-ACIS observations of SN 2023ixf in M101 on day 13 and 86
since the explosion. The X-rays in both epochs are characterized by high
temperature plasma from the forward shocked region as a result of circumstellar
interaction. We are able to constrain the absorption column density at both
Chandra epochs, which is much larger than that due to the Galactic and host
absorption column, and we attribute it to absorption by the circumstellar
matter in the immediate vicinity of SN 2023ixf. Combining our column density
measurements with the published measurement on day 4, we show that the column
density declines as between day 4 to day 13 and then evolves as
. The unabsorbed keV luminosity evolves as during the
Chandra epochs. On day 13 Chandra observation we detect the Fe K
fluorescent line at 6.4 keV indicating presence of cold material in the
vicinity of the SN. The line is absent on day 86, consistent with the decreased
column density by a factor of 7 between the two epochs. Our analysis indicates
that during 10 years to 1.5 years before explosion, the progenitor was evolving
with a constant mass-loss rate of M yr.Comment: Accepted for publication in ApJ Letter
Oscillation Effects On Neutrinos From The Early Phase Of a Nearby Supernova
Neutrinos emitted during stellar core collapse leading to a supernova are
primarily of the electron neutrino type at source which may undergo oscillation
between flavor eigenstates during propagation to an earth-bound detector.
Although the number of neutrinos emitted during the pre-bounce collapse phase
is much smaller than that emitted in the post-bounce phase (in which all
flavors of neutrinos are emitted), a nearby supernova event may nevertheless
register a substantial number of detections from the pre-bounce phase at
SuperKamiokande (SK) and the Sudbury Neutrino Observatory (SNO). The
calorimetric measurement of the supernova neutrino fluence from this stage via
the charge current and neutral current detection channels in SNO and the
corresponding distortion of detected spectrum in SK over the no-oscillation
spectrum, can probe information about neutrino mass difference and mixing which
are illustrated here in terms of two- and three-flavor oscillation models
Discussion on a possible neutrino detector located in India
We have identified some important and worthwhile physics opportunitites with
a possible neutrino detector located in India. Particular emphasis is placed on
the geographical advantage with a stress on the complimentary aspects with
respect to other neutrino detectors already in operation.Comment: 9 pages; arXiv copy of published proceedings contributio
Chandra's tryst with SN 1995N
We present the spectroscopic and imaging analysis of a type IIn supernova SN
1995N observed with the Chandra X-ray observatory on 2004 March 27. We compare
the spectrum obtained from our Chandra observation with that of the previous
observation with ASCA in 1998. We find the presence of Neon lines in the
Chandra spectrum that were not reported in the ASCA observation. We see no
evidence of Iron in both epochs. The observed absorption column depth indicates
an extra component over and above the galactic absorption component and is
possibly due to a cool dense shell between the reverse-shock and the contact
discontinuity in the ejecta. The ASCA and the ROSAT observations suggested a
non-linear behavior of the X-ray light curve. However, with the higher spatial
resolution and sensitivity of Chandra, we separate out many nearby sources in
the supernova field-of-view that had additionally contributed to the supernova
flux due to the large Point Spread Function of the ASCA. Taking out the
contribution of those nearby sources, we find that the light curves are
consistent with a linear decline profile. We consider the light curve in the
high energy band separately. We discuss our results in the context of models of
nucleosynthesis and the interaction of the shock waves with the circumstellar
medium in core collapse supernovae.Comment: 35 pages, 12 figures, accepted for publication in Astrophysical
Journa
Type IIP Supernova SN 2004et: A Multi-Wavelength Study in X-Ray, Optical and Radio
We present X-ray, broad band optical and low frequency radio observations of
the bright type IIP supernova SN 2004et. The \cxo observed the supernova at
three epochs, and the optical coverage spans a period of 470 days since
explosion. The X-ray emission softens with time, and we characterise the X-ray
luminosity evolution as \Lx \propto t^{-0.4}. We use the observed X-ray
luminosity to estimate a mass-loss rate for the progenitor star of \sim
\ee{2}{-6} M_\odot \mathrm{yr}^{-1}. The optical light curve shows a
pronounced plateau lasting for about 110 days. Temporal evolution of
photospheric radius and color temperature during the plateau phase is
determined by making black body fits. We estimate the ejected mass of Ni
to be 0.06 0.03 M. Using the expressions of Litvinova &
Nad\"{e}zhin (1985) we estimate an explosion energy of (0.98 0.25)
erg. We also present a single epoch radio observation of SN
2004et. We compare this with the predictions of the model proposed by Chevalier
et al. (2006). These multi-wavelength studies suggest a main sequence
progenitor mass of 20 M for SN 2004et.Comment: 13 Figures, Accepted for Publication in MNRA
Results from an extensive simultaneous broadband campaign on the underluminous active nucleus M81*: further evidence for mass-scaling accretion in black holes
We present the results of a broadband simultaneous campaign on the nearby
low-luminosity active galactic nucleus M81*. From February through August 2005,
we observed M81* five times using the Chandra X-ray Observatory with the
High-Energy Transmission Grating Spectrometer, complemented by ground-based
observations with the Giant Meterwave Radio Telescope, the Very Large Array and
Very Large Baseline Array, the Plateau de Bure Interferometer at IRAM, the
Submillimeter Array and Lick Observatory. We discuss how the resulting spectra
vary over short and longer timescales compared to previous results, especially
in the X-rays where this is the first ever longer-term campaign at spatial
resolution high enough to nearly isolate the nucleus (17pc). We compare the
spectrum to our Galactic center weakly active nucleus Sgr A*, which has
undergone similar campaigns, as well as to weakly accreting X-ray binaries in
the context of outflow-dominated models. In agreement with recent results
suggesting that the physics of weakly-accreting black holes scales predictably
with mass, we find that the exact same model which successfully describes hard
state X-ray binaries applies to M81*, with very similar physical parameters.Comment: 58 pages (preprint version), 22 figures, accepted for publication in
the Astrophysical Journa
A MISSING-LINK IN THE SUPERNOVA-GRB CONNECTION: THE CASE OF SN 2012ap
Gamma Ray Bursts (GRBs) are characterized by ultra-relativistic outflows,
while supernovae are generally characterized by non-relativistic ejecta. GRB
afterglows decelerate rapidly usually within days, because their low-mass
ejecta rapidly sweep up a comparatively larger mass of circumstellar material.
However supernovae, with heavy ejecta, can be in nearly free expansion for
centuries. Supernovae were thought to have non-relativistic outflows except for
few relativistic ones accompanied by GRBs. This clear division was blurred by
SN 2009bb, the first supernova with a relativistic outflow without an observed
GRB. Yet the ejecta from SN 2009bb was baryon loaded, and in nearly-free
expansion for a year, unlike GRBs. We report the first supernova discovered
without a GRB, but with rapidly decelerating mildly relativistic ejecta, SN
2012ap. We discovered a bright and rapidly evolving radio counterpart driven by
the circumstellar interaction of the relativistic ejecta. However, we did not
find any coincident GRB with an isotropic fluence of more than a sixth of the
fluence from GRB 980425. This shows for the first time that central engines in
type Ic supernovae, even without an observed GRB, can produce both relativistic
and rapidly decelerating outflows like GRBs.Comment: 8 pages, 5 figures, 1 table, accepted for publication in Ap