11 research outputs found
A search for rapidly pulsating hot subdwarf stars in the GALEX survey
NASA's Galaxy Evolution Explorer (GALEX) provided near- and far-UV
observations for approximately 77 percent of the sky over a ten-year period;
however, the data reduction pipeline initially only released single NUV and FUV
images to the community. The recently released Python module gPhoton changes
this, allowing calibrated time-series aperture photometry to be extracted
easily from the raw GALEX data set. Here we use gPhoton to generate light
curves for all hot subdwarf B (sdB) stars that were observed by GALEX, with the
intention of identifying short-period, p-mode pulsations. We find that the
spacecraft's short visit durations, uneven gaps between visits, and dither
pattern make the detection of hot subdwarf pulsations difficult. Nonetheless,
we detect UV variations in four previously known pulsating targets and report
their UV pulsation amplitudes and frequencies. Additionally, we find that
several other sdB targets not previously known to vary show promising signals
in their periodograms. Using optical follow-up photometry with the Skynet
Robotic Telescope Network, we confirm p-mode pulsations in one of these
targets, LAMOST J082517.99+113106.3, and report it as the most recent addition
to the sdBVr class of variable stars.Comment: 11 Pages, 8 Figures, Accepted for publication in the Astrophysical
Journa
Signatures of an eruptive phase before the explosion of the peculiar core-collapse SN 2013gc
We present photometric and spectroscopic analysis of the peculiar
core-collapse SN 2013gc, spanning seven years of observations. The light curve
shows an early maximum followed by a fast decline and a phase of almost
constant luminosity. At +200 days from maximum, a brightening of 1 mag is
observed in all bands, followed by a steep linear luminosity decline after +300
d. In archival images taken between 1.5 and 2.5 years before the explosion, a
weak source is visible at the supernova location, with mag20. The
early supernova spectra show Balmer lines, with a narrow (560 km
s) P-Cygni absorption superimposed on a broad (3400 km s)
component, typical of type IIn events. Through a comparison of colour curves,
absolute light curves and spectra of SN 2013gc with a sample of supernovae IIn,
we conclude that SN 2013gc is a member of the so-called type IId subgroup. The
complex profile of the H line suggests a composite circumstellar medium
geometry, with a combination of lower velocity, spherically symmetric gas and a
more rapidly expanding bilobed feature. This circumstellar medium distribution
has been likely formed through major mass-loss events, that we directly
observed from 3 years before the explosion. The modest luminosity
( near maximum) of SN 2013gc at all phases, the very small amount
of ejected Ni (of the order of M), the major
pre-supernova stellar activity and the lack of prominent [O I] lines in
late-time spectra support a fall-back core-collapse scenario for the massive
progenitor of SN~2013gc.Comment: 20 pages, 11 figures, 8 tables, accepted by MNRA
Sloan Digital Sky Survey Multicolor Observations of GRB010222
The discovery of an optical counterpart to GRB010222 (detected by BeppoSAX;
Piro 2001) was announced 4.4 hrs after the burst by Henden (2001a). The Sloan
Digital Sky Survey's 0.5m photometric telescope (PT) and 2.5m survey telescope
were used to observe the afterglow of GRB010222 starting 4.8 hours after the
GRB. The 0.5m PT observed the afterglow in five, 300 sec g' band exposures over
the course of half an hour, measuring a temporal decay rate in this short
period of F_nu \propto t^{-1.0+/-0.5}. The 2.5m camera imaged the counterpart
nearly simultaneously in five filters (u' g' r' i' z'), with r' = 18.74+/-0.02
at 12:10 UT. These multicolor observations, corrected for reddening and the
afterglow's temporal decay, are well fit by the power-law F_nu \propto
nu^{-0.90+/-0.03} with the exception of the u' band UV flux which is 20% below
this slope. We examine possible interpretations of this spectral shape,
including source extinction in a star forming region.Comment: 8 pages, 4 figures, accepted for publication in ApJ. Two figures
added, minor changes to text in this draft. Related material can be found at:
http://sdss.fnal.gov:8000/grb
The Rapidly Flaring Afterglow of the Very Bright and Energetic GRB 070125
We report on multi-wavelength observations, ranging from the X-ray to radio
wave bands, of the IPN-localized gamma-ray burst GRB 070125. Spectroscopic
observations reveal the presence of absorption lines due to O I, Si II, and C
IV, implying a likely redshift of z = 1.547. The well-sampled light curves, in
particular from 0.5 to 4 days after the burst, suggest a jet break at 3.7 days,
corresponding to a jet opening angle of ~7.0 degrees, and implying an intrinsic
GRB energy in the 1 - 10,000 keV band of around E = (6.3 - 6.9)x 10^(51) erg
(based on the fluences measured by the gamma-ray detectors of the IPN network).
GRB 070125 is among the brightest afterglows observed to date. The spectral
energy distribution implies a host extinction of Av < 0.9 mag. Two
rebrightening episodes are observed, one with excellent time coverage, showing
an increase in flux of 56% in ~8000 seconds. The evolution of the afterglow
light curve is achromatic at all times. Late-time observations of the afterglow
do not show evidence for emission from an underlying host galaxy or supernova.
Any host galaxy would be subluminous, consistent with current GRB host-galaxy
samples. Evidence for strong Mg II absorption features is not found, which is
perhaps surprising in view of the relatively high redshift of this burst and
the high likelihood for such features along GRB-selected lines of sight.Comment: 50 pages, 9 figures, 5 tables Accepted to the Astrophysical Journa
GRB Afterglows and Other Transients in the SDSS
The Sloan Digital Sky Survey (SDSS) will image one quarter of the sky centered on the northern galactic cap and produce a 3âD map of galaxies and quasars found in the sample. An additional 225 deg2 southern survey will be imaged repeatedly on varying timescales. Here we discuss both archival searches in the SDSS catalog (such as SDSS J24602.54+011318.8) and active searches with the SDSS instruments (such as for GRB 010222) for GRB afterglows and other transient objects. © 2003 American Institute of PhysicsPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87288/2/349_1.pd
Mapping the Milky Way: A Radio Astronomy-Directed Investigation for Lecture-Based Astro 101 Courses
The Green Bank 20-meter radio telescope integrated into the Skynet Robotic Telescope Network offers a unique opportunity to engage learners in investigations that are not possible with optical telescopes. Radio investigation of the Milky Way using the neutral hydrogen (HI) 1420.41 MHz emission line have a long history with the educators at Green Bank Observatory and through the Skynet team. The project discussed considers how best to adapt these investigations into a large-enrollment, general education, introductory college astronomy course (âAstro 101â). Astro 101 courses serve over 250,000 students nationwide each year. To conduct a class-wide investigation of the Milky Way, we first have each student collect a 60-second radio spectral scan of the HI emission line for a single portion of the galactic disk. Once this class data over a wide range of galactic longitudes is combined, the students can use simple geometry and Doppler information to determine that we live in a spiral galaxy and that we orbit the galactic center clockwise (if looking down on the Galactic North Pole). Together with archived data of the Large and Small Magellanic Clouds, a galactic rotation curve and an enclosed mass curve can be created to illustrate the âmissing massâ problem as evidence for existence of dark matter. Results from a formative assessment illustrate that this project helps students connect concepts learned in class and gain confidence in their abilities to do scientific research. Activity lecture slides and data spreadsheets are freely available
New Pulse Timing Measurements of the sdBV Star CS 1246
CS 1246 is a hot subdwarf B star discovered in 2009 to exhibit a single, large-amplitude radial pulsation. An O-C diagram constructed from this mode revealed reflex motion due to the presence of a low-mass M dwarf, as well as a long-term trend consistent with a decrease in the pulsational period. The orbital reflex motion was later confirmed with radial velocity measurements. Using eight years of data collected with the Skynet Robotic Telescope Network, we show that the pulsation amplitude of CS 1246 is decaying nonlinearly. We also present an updated O-C diagram, which might now indicate a positive áč and a new 2.09 ± 0.05 yr oscillation consistent with orbital reflex motion of the entire inner sdB+dM binary, possibly due to the gravitational influence of a circumbinary planet with minimum mass . However, unlike the presence of the M dwarf, we hesistate to claim this object as a definitive detection since intrinsic variability of the pulsation phase could theoretically produce a similar effect
Grb 051022: Physical parameters and extinction of a prototype dark burst
GRB 051022 was undetected to deep limits in early optical observations, but precise astrometry from radio and X-rays showed that it most likely originated in a galaxy at z approximate to 0.8. We report radio, optical, near-infrared, and X-ray observations of GRB 051022. Using the available X-ray and radio data, we model the afterglow and calculate its energetics, finding it to be an order of magnitude lower than that of the prompt emission. The broadband modeling also allows us to precisely define various other physical parameters and the minimum required amount of extinction to explain the absence of an optical afterglow. Our observations suggest a high extinction, at least 2.3 mag in the infrared (J) and at least 5.4 mag in the optical (U) in the host-galaxy rest frame. Such high extinctions are unusual for GRBs and likely indicate a geometry where our line of sight to the burst passes through a dusty region in the host that is not directly colocated with the burst itself