1,202 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
On Discovering Electromagnetic Emission from Neutron Star Mergers: The Early Years of Two Gravitational Wave Detectors
We present the first simulation addressing the prospects of finding an
electromagnetic (EM) counterpart to gravitational wave detections (GW) during
the early years of only two advanced interferometers. The perils of such a
search may have appeared insurmountable when considering the coarse ring-shaped
GW localizations spanning thousands of deg^2 using time-of-arrival information
alone. We show that leveraging the amplitude and phase information of the
predicted GW signal narrows the localization to arcs with a median area of only
~250 deg^2, thereby making an EM search tractable. Based on the locations and
orientations of the two LIGO detectors, we find that the GW sensitivity is
limited to one polarization and thus to only two sky quadrants. Thus, the rates
of GW events with two interferometers is only ~40% of the rate with three
interferometers of similar sensitivity. Another important implication of the
sky quadrant bias is that EM observatories in North America and Southern Africa
would be able to systematically respond to GW triggers several hours sooner
than Russia and Chile. Given the larger sky areas and the relative proximity of
detected mergers, 1m-class telescopes with very wide-field cameras are well
positioned for the challenge of finding an EM counterpart. Identification of
the EM counterpart amidst the even larger numbers of false positives further
underscores the importance of building a comprehensive catalog of foreground
stellar sources, background AGN and potential host galaxies in the local
universe.Comment: Submitted to ApJL, 8 pages, 4 figures, 1 tabl
NSV 11749: Symbiotic Nova, Not a Born-Again Red Giant
NSV 11749 is a little-studied variable star, discovered by W. J. Luyten,
which had a long-duration outburst around the year 1903, reaching blue
magnitude 12.5 at maximum. Following the outburst, it has apparently been
quiescent at about blue magnitude 17 for the past century. It was recently
suggested that NSV 11749 may have been a low- or intermediate-mass star that
underwent a final helium shell flash, making it temporarily a "born-again" red
giant. If so, it would be only the fourth known member of this class, along
with V605 Aql, FG Sge, and V4334 Sgr. However, our newly obtained optical and
near-IR spectra of the object show that it is instead a symbiotic binary, with
strong Balmer and He I-II emission lines, combined with a cool red-giant
companion of spectral type M1-2 III. The 1903 outburst was most likely a
symbiotic nova event, of which less than a dozen are known at present.Comment: 13 pages, 3 figures, Accepted for publication in PAS
Intermediate Palomar Transient Factory: Realtime Image Subtraction Pipeline
A fast-turnaround pipeline for realtime data reduction plays an essential
role in discovering and permitting follow-up observations to young supernovae
and fast-evolving transients in modern time-domain surveys. In this paper, we
present the realtime image subtraction pipeline in the intermediate Palomar
Transient Factory. By using high-performance computing, efficient database, and
machine learning algorithms, this pipeline manages to reliably deliver
transient candidates within ten minutes of images being taken. Our experience
in using high performance computing resources to process big data in astronomy
serves as a trailblazer to dealing with data from large-scale time-domain
facilities in near future.Comment: 18 pages, 6 figures, accepted for publication in PAS
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
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
First Detection of Mid-Infrared Variability from an Ultraluminous X-Ray Source Holmberg II X-1
We present mid-infrared (IR) light curves of the Ultraluminous X-ray Source
(ULX) Holmberg II X-1 from observations taken between 2014 January 13 and 2017
January 5 with the \textit{Spitzer Space Telescope} at 3.6 and 4.5 m in
the \textit{Spitzer} Infrared Intensive Transients Survey (SPIRITS). The mid-IR
light curves, which reveal the first detection of mid-IR variability from a
ULX, is determined to arise primarily from dust emission rather than from a jet
or an accretion disk outflow. We derived the evolution of the dust temperature
( K), IR luminosity (
), mass (
), and equilibrium temperature radius
( AU). A comparison of X-1 with a sample
spectroscopically identified massive stars in the Large Magellanic Cloud on a
mid-IR color-magnitude diagram suggests that the mass donor in X-1 is a
supergiant (sg) B[e]-star. The sgB[e]-interpretation is consistent with the
derived dust properties and the presence of the [Fe II] (
m) emission line revealed from previous near-IR studies of X-1. We
attribute the mid-IR variability of X-1 to increased heating of dust located in
a circumbinary torus. It is unclear what physical processes are responsible for
the increased dust heating; however, it does not appear to be associated with
the X-ray flux from the ULX given the constant X-ray luminosities provided by
serendipitous, near-contemporaneous X-ray observations around the first mid-IR
variability event in 2014. Our results highlight the importance of mid-IR
observations of luminous X-ray sources traditionally studied at X-ray and radio
wavelengths.Comment: 9 page, 4 figures, 1 table, Accepted to ApJ Letter
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 â
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
Infrared emission from kilonovae: the case of the nearby short hard burst GRB 160821B
We present constraints on Ks-band emission from one of the nearest short hard
gamma-ray bursts, GRB 160821B, at z=0.16, at three epochs. We detect a reddened
relativistic afterglow from the jetted emission in the first epoch but do not
detect any excess kilonova emission in the second two epochs. We compare upper
limits obtained with Keck I/MOSFIRE to multi-dimensional radiative transfer
models of kilonovae, that employ composition-dependent nuclear heating and LTE
opacities of heavy elements. We discuss eight models that combine toroidal
dynamical ejecta and two types of wind and one model with dynamical ejecta
only. We also discuss simple, empirical scaling laws of predicted emission as a
function of ejecta mass and ejecta velocity. Our limits for GRB 160821B
constrain the ejecta mass to be lower than 0.03 Msun for velocities greater
than 0.1c. At the distance sensitivity range of advanced LIGO, similar
ground-based observations would be sufficiently sensitive to the full range of
predicted model emission including models with only dynamical ejecta. The color
evolution of these models shows that I-K color spans 7--16 mag, which suggests
that even relatively shallow infrared searches for kilonovae could be as
constraining as optical searches.Comment: Accepted for Publication in Astrophysical Journal Letter
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