1,096 research outputs found
Discovery of a new photometric sub-class of faint and fast classical novae
We present photometric and spectroscopic follow-up of a sample of
extragalactic novae discovered by the Palomar 60-inch telescope during a search
for "Fast Transients In Nearest Galaxies" (P60-FasTING). Designed as a fast
cadence (1-day) and deep (g < 21 mag) survey, P60-FasTING was particularly
sensitive to short-lived and faint optical transients. The P60-FasTING nova
sample includes 10 novae in M31, 6 in M81, 3 in M82, 1 in NGC2403 and 1 in
NGC891. This significantly expands the known sample of extragalactic novae
beyond the Local Group, including the first discoveries in a starburst
environment. Surprisingly, our photometry shows that this sample is quite
inconsistent with the canonical Maximum Magnitude Rate of Decline (MMRD)
relation for classical novae. Furthermore, the spectra of the P60-FasTING
sample are indistinguishable from classical novae. We suggest that we have
uncovered a sub-class of faint and fast classical novae in a new phase space in
luminosity-timescale of optical transients. Thus, novae span two orders of
magnitude in both luminosity and time. Perhaps, the MMRD, which is
characterized only by the white dwarf mass, was an over-simplification. Nova
physics appears to be characterized by quite a rich four-dimensional parameter
space in white dwarf mass, temperature, composition and accretion rate.Comment: Submitted to ApJ, 12 pages. High resolution version at
http://www.astro.caltech.edu/~mansi/msFasting.pd
Spitzer Observations of Large Amplitude Variables in the LMC and IC 1613
The 3.6 and 4.5 micron characteristics of AGB variables in the LMC and IC1613
are discussed. For C-rich Mira variables there is a very clear
period-luminosity-colour relation, where the [3.6]-[4.5] colour is associated
with the amount of circumstellar material and correlated with the pulsation
amplitude. The [4.5] period-luminosity relation for dusty stars is
approximately one mag brighter than for their naked counterparts with
comparable periods.Comment: 5 pages, 4 figures, to appear in Proceedings of "Wide-Field
Variability Surveys: A 21st Century Perspective
Calcium-rich Gap Transients: Solving the Calcium Conundrum in the Intracluster Medium
X-ray measurements suggest the abundance of Calcium in the intracluster
medium is higher than can be explained using favored models for core-collapse
and Type Ia supernovae alone. We investigate whether the Calcium conundrum in
the intracluster medium can be alleviated by including a contribution from the
recently discovered subclass of supernovae known as Calcium-rich gap
transients. Although the Calcium-rich gap transients make up only a small
fraction of all supernovae events, we find that their high Calcium yields are
sufficient to reproduce the X-ray measurements found for nearby rich clusters.
We find the goodness-of-fit metric improves from 84 to 2 by
including this new class. Moreover, Calcium-rich supernovae preferentially
occur in the outskirts of galaxies making it easier for the nucleosynthesis
products of these events to be incorporated in the intracluster medium via
ram-pressure stripping. The discovery of a Calcium-rich gap transients in
clusters and groups far from any individual galaxy suggests supernovae
associated with intracluster stars may play an important role in enriching the
intracluster medium. Calcium-rich gap transients may also help explain
anomalous Calcium abundances in many other astrophysical systems including
individual stars in the Milky Way, the halos of nearby galaxies and the
circumgalactic medium. Our work highlights the importance of considering the
diversity of supernovae types and corresponding yields when modeling the
abundance of the intracluster medium and other gas reservoirs
PTF 11kx: A Type Ia Supernova with a Symbiotic Nova Progenitor
There is a consensus that type Ia supernovae (SNe Ia) arise from the thermonuclear explosion of white dwarf stars that accrete matter from a binary companion. However, direct observation of SN Ia progenitors is lacking, and the precise nature of the binary companion remains uncertain. A temporal series of high-resolution optical spectra of the SN Ia PTF 11kx reveals a complex circumstellar environment that provides an unprecedentedly detailed view of the progenitor system. Multiple shells of circumstellar material are detected, and the SN ejecta are seen to interact with circumstellar material starting 59 days after the explosion. These features are best described by a symbiotic nova progenitor, similar to RS Ophiuchi
PTF 10bzf (SN 2010ah): A Broad-Line Ic Supernova Discovered by the Palomar Transient Factory
We present the discovery and follow-up observations of a broad-line Type Ic supernova (SN), PTF 10bzf (SN 2010ah), detected by the Palomar Transient Factory (PTF) on 2010 February 23. The SN distance is ≅218 Mpc, greater than GRB 980425/SN 1998bw and GRB 060218/SN 2006aj, but smaller than the other SNe firmly associated with gamma-ray bursts (GRBs). We conducted a multi-wavelength follow-up campaign with Palomar 48 inch, Palomar 60 inch, Gemini-N, Keck, Wise, Swift, the Allen Telescope Array, Combined Array for Research in Millimeter-wave Astronomy, Westerbork Synthesis Radio Telescope, and Expanded Very Large Array. Here we compare the properties of PTF 10bzf with those of SN 1998bw and other broad-line SNe. The optical luminosity and spectral properties of PTF 10bzf suggest that this SN is intermediate, in kinetic energy and amount of ^(56)Ni, between non-GRB-associated SNe like 2002ap or 1997ef, and GRB-associated SNe like 1998bw. No X-ray or radio counterpart to PTF 10bzf was detected. X-ray upper limits allow us to exclude the presence of an underlying X-ray afterglow as luminous as that of other SN-associated GRBs such as GRB 030329 or GRB 031203. Early-time radio upper limits do not show evidence for mildly relativistic ejecta. Late-time radio upper limits rule out the presence of an underlying off-axis GRB, with energy and wind density similar to the SN-associated GRB 030329 and GRB 031203. Finally, by performing a search for a GRB in the time window and at the position of PTF 10bzf, we find that no GRB in the interplanetary network catalog could be associated with this SN
Explosive Outflows from Forming Massive Stars
AO imaging of the near IR [Fe ii] and H_2 lines and ALMA CO J = 2 − 1 data confirms the explosive nature of the BN/KL outflow in Orion. N-body interactions in compact groups may be responsible for the production of powerful, explosive protostellar outflows and luminous infrared flares. The Orion event may have been triggered by a protostellar merger. First results of a search for Orion-like events in 200 nearby galaxies with the SPitzer InfraRed Intensive Transients Survey (SPIRITS) are briefly discussed
The first direct double neutron star merger detection: implications for cosmic nucleosynthesis
The astrophysical r-process site where about half of the elements heavier
than iron are produced has been a puzzle for several decades. Here we discuss
the role of neutron star mergers (NSMs) in the light of the first direct
detection of such an event in both gravitational (GW) and electromagnetic (EM)
waves. We analyse bolometric and NIR lightcurves of the first detected double
neutron star merger and compare them to nuclear reaction network-based
macronova models. The slope of the bolometric lightcurve is consistent with the
radioactive decay of neutron star ejecta with (but not
larger), which provides strong evidence for an r-process origin of the
electromagnetic emission. This rules out in particular "nickel winds" as major
source of the emission. We find that the NIR lightcurves can be well fitted
either with or without lanthanide-rich ejecta. Our limits on the ejecta mass
together with estimated rates directly confirm earlier purely theoretical or
indirect observational conclusions that double neutron star mergers are indeed
a major site of cosmic nucleosynthesis. If the ejecta mass was {\em typical},
NSMs can easily produce {\em all} of the estimated Galactic r-process matter,
and --depending on the real rate-- potentially even more. This could be a hint
that the event ejected a particularly large amount of mass, maybe due to a
substantial difference between the component masses. This would be compatible
with the mass limits obtained from the GW-observation. The recent observations
suggests that NSMs are responsible for a broad range of r-process nuclei and
that they are at least a major, but likely the dominant r-process site in the
Universe.Comment: 11 pages, 8 figures; accepted for A \&
A Very Large Array Search for 5 GHz Radio Transients and Variables at Low Galactic Latitudes
We present the results of a 5 GHz survey with the Very Large Array (VLA) and the expanded VLA, designed to search for short-lived (≾1 day) transients and to characterize the variability of radio sources at milli-Jansky levels. A total sky area of 2.66 deg^2, spread over 141 fields at low Galactic latitudes (b≅6-8 deg), was observed 16 times with a cadence that was chosen to sample timescales of days, months, and years. Most of the data were reduced, analyzed, and searched for transients in near real-time. Interesting candidates were followed up using visible light telescopes (typical delays of 1-2 hr) and the X-ray Telescope on board the Swift satellite. The final processing of the data revealed a single possible transient with a peak flux density of f_ν≅2.4 mJy. This implies a transient's sky surface density of κ(f_ν > 1.8 mJy) = 0.039^(+0.13 +0.18)_(–0.032,–0.038) deg^(–2) (1σ, 2σ confidence errors). This areal density is roughly consistent with the sky surface density of transients from the Bower et al. survey extrapolated to 1.8 mJy. Our observed transient areal density is consistent with a neutron star's origin for these events. Furthermore, we use the data to measure the source variability on timescales of days to years, and we present the variability structure function of 5 GHz sources. The mean structure function shows a fast increase on ≈1 day timescale, followed by a slower increase on timescales of up to 10 days. On timescales between 10 and 60 days, the structure function is roughly constant. We find that ≳30% of the unresolved sources brighter than 1.8 mJy are variables at the >4σ confidence level, presumably mainly due to refractive scintillation
Background-Limited Imaging in the Near-Infrared with Warm InGaAs Sensors: Applications for Time-Domain Astronomy
We describe test observations made with a customized 640 x 512 pixel Indium
Gallium Arsenide (InGaAs) prototype astronomical camera on the 100" DuPont
telescope. This is the first test of InGaAs as a cost-effective alternative to
HgCdTe for research-grade astronomical observations. The camera exhibits an
instrument background of 113 e-/sec/pixel (dark + thermal) at an operating
temperature of -40C for the sensor, maintained by a simple thermo-electric
cooler. The optical train and mechanical structure float at ambient temperature
with no cold stop, in contrast to most IR instruments which must be cooled to
mitigate thermal backgrounds. Measurements of the night sky using a reimager
with plate scale of 0.4 arc seconds / pixel show that the sky flux in Y is
comparable to the dark current. At J the sky brightness exceeds dark current by
a factor of four, and hence dominates the noise budget. The sensor read noise
of ~43e- falls below sky+dark noise for exposures of t>7 seconds in Y and 3.5
seconds in J. We present test observations of several selected science targets,
including high-significance detections of a lensed Type Ia supernova, a type
IIb supernova, and a z=6.3 quasar. Deeper images are obtained for two local
galaxies monitored for IR transients, and a galaxy cluster at z=0.87. Finally,
we observe a partial transit of the hot JupiterHATS34b, demonstrating the
photometric stability required over several hours to detect a 1.2% transit
depth at high significance. A tiling of available larger-format sensors would
produce an IR survey instrument with significant cost savings relative to
HgCdTe-based cameras, if one is willing to forego the K band. Such a camera
would be sensitive for a week or more to isotropic emission from r-process
kilonova ejecta similar to that observed in GW170817, over the full 190 Mpc
horizon of Advanced LIGO's design sensitivity for neutron star mergers.Comment: 13 pages, 12 figures, submitted to A
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