58 research outputs found
A Direct Measurement of the Dust Extinction Curve in an Intermediate-Redshift Galaxy
We present a proof-of-concept study that dust extinction curves can be
extracted from the infrared (IR), optical, ultraviolet (UV) and X-ray afterglow
observations of GRBs without assuming known extinction laws. We focus on GRB
050525A (z = 0.606), for which we also present IR observations from the Spitzer
Space Telescope at about 2.3 days post-burst. We construct the spectral energy
distribution (SED) of the afterglow and use it to derive the dust extinction
curve of the host galaxy in 7 optical/UV wavebands. By comparing our derived
extinction curve to known templates, we see that the Galactic or Milky Way
extinction laws are disfavored versus the Small and Large Magellanic Cloud (SMC
and LMC) ones, but that we cannot rule out the presence of a LMC-like 2175
angstrom bump in our extinction curve. The dust-to-gas ratio present within the
host galaxy of GRB 050525A is similar to that found in the LMC, while about 10
to 40% more dust is required if the SMC template is assumed. Our method is
useful to observatories that are capable of simultaneously observing GRB
afterglows in multiple wavebands from the IR to the X-ray.Comment: 9 pages, 5 figures. Accepted by ApJ. Minor changes to 2nd Paragraph
of Introductio
Real-Time Detection and Rapid Multiwavelength Follow-up Observations of a Highly Subluminous Type II-P Supernova from the Palomar Transient Factory Survey
The Palomar Transient Factory (PTF) is an optical wide-field variability
survey carried out using a camera with a 7.8 square degree field of view
mounted on the 48-in Oschin Schmidt telescope at Palomar Observatory. One of
the key goals of this survey is to conduct high-cadence monitoring of the sky
in order to detect optical transient sources shortly after they occur. Here, we
describe the real-time capabilities of the PTF and our related rapid
multiwavelength follow-up programs, extending from the radio to the gamma-ray
bands. We present as a case study observations of the optical transient
PTF10vdl (SN 2010id), revealed to be a very young core-collapse (Type II-P)
supernova having a remarkably low luminosity. Our results demonstrate that the
PTF now provides for optical transients the real-time discovery and
rapid-response follow-up capabilities previously reserved only for high-energy
transients like gamma-ray bursts.Comment: ApJ, in press; all spectroscopic data available from the Weizmann
Institute of Science Experimental Astrophysics Spectroscopy System (WISEASS;
http://www.weizmann.ac.il/astrophysics/wiseass/
Rapid UBVRI Follow-up of the Highly Collimated Optical Afterglow of GRB010222
(Abridged) We present the earliest optical observations of the optical
counterpart to the GRB 010222, obtained with the FLWO 1.2-m telescope in UBVRI
passbands, starting 3.64 hours after the burst. We also present late R-band
observations of the afterglow obtained with the 1.8-m VATT ~25 days after the
burst. The temporal analysis of our data joined with published data indicates a
steepening decay, independent of wavelength, asymptotically approaching
t^{-0.80+/-0.05} at early times (t << 1 day) and t^{-1.30+/-0.05} at late
times, with a sharp break at t_b=0.72+/-0.1 days. This is the second earliest
observed break of any afterglow (after GRB 980519), which clearly indicates the
importance of rapid multi-band follow-up for GRB afterglow research. The
optical spectral energy distribution, corrected for small Galactic reddening,
can be fit fairly well by a single power-law with a slope of -1.07+/-0.09.
However, when we fit using our BVRI data only, we obtain a shallower slope of
-0.88+/- 0.1, in excellent agreement with the slope derived from our
low-resolution spectrum (-0.89 +/- 0.03). The spectral slope and light curve
decay slopes we derive are not consistent with a jet model despite the presence
of a temporal break. Significant host dust extinction with a star-burst
reddening law would flatten the spectral index to match jet predictions and
still be consistent with the observed spectral energy distribution. We derive
an opening angle of 2.1 deg, smaller than any listed in the recent compilation
of Frail et al. The total beamed energy corrected for the jet geometry is
4x10^50 erg, very close to the ``standard'' value of 5x10^50 erg found by Frail
et al. for a number of other bursts with light-curve breaks.Comment: revised version (minor changes only) to be published in the ApJ Part
1, 12 pages, 4 figures; all data used for the fits and our CCD frames
available at ftp://cfa-ftp.harvard.edu/pub/kstanek/GRB010222/ and through WWW
at http://cfa-www.harvard.edu/cfa/oir/Research/GRB
PTF11eon/SN2011dh: Discovery of a Type IIb Supernova From a Compact Progenitor in the Nearby Galaxy M51
On May 31, 2011 UT a supernova (SN) exploded in the nearby galaxy M51 (the
Whirlpool Galaxy). We discovered this event using small telescopes equipped
with CCD cameras, as well as by the Palomar Transient Factory (PTF) survey, and
rapidly confirmed it to be a Type II supernova. Our early light curve and
spectroscopy indicates that PTF11eon resulted from the explosion of a
relatively compact progenitor star as evidenced by the rapid shock-breakout
cooling seen in the light curve, the relatively low temperature in early-time
spectra and the prompt appearance of low-ionization spectral features. The
spectra of PTF11eon are dominated by H lines out to day 10 after explosion, but
initial signs of He appear to be present. Assuming that He lines continue to
develop in the near future, this SN is likely a member of the cIIb (compact
IIb; Chevalier and Soderberg 2010) class, with progenitor radius larger than
that of SN 2008ax and smaller than the eIIb (extended IIb) SN 1993J progenitor.
Our data imply that the object identified in pre-explosion Hubble Space
Telescope images at the SN location is possibly a companion to the progenitor
or a blended source, and not the progenitor star itself, as its radius (~10^13
cm) would be highly inconsistent with constraints from our post-explosion
photometric and spectroscopic data
The Araucaria Project: The distance to the Fornax Dwarf Galaxy from near-infrared photometry of RR Lyrae stars
We have obtained single-phase near-infrared (NIR) magnitudes in the J- and K-bands for 77 RR Lyrae (RRL) stars in the Fornax Dwarf Spheroidal Galaxy. We have used different theoretical and empirical NIR period-luminosity-metallicity calibrations for RRL stars to derive their absolute magnitudes, and found a true, reddening-corrected distance modulus of 20.818 +/- 0.015 (statistical) +/- 0.116 (systematic) mag. This value is in excellent agreement with the results obtained within the Araucaria Project from the NIR photometry of red clump stars (20.858 +/- 0.013 mag), the tip of the red giant branch (20.84 +/- 0.04 +/- 0.14 mag), as well as with other independent distance determinations to this galaxy. The effect of metallicity and reddening is substantially reduced in the NIR domain, making this method a robust tool for accurate distance determination at the 5 percent level. This precision is expected to reach the level of 3 percent once the zero points of distance calibrations are refined thanks to the Gaia mission. NIR period-luminosity-metallicity relations of RRL stars are particularly useful for distance determinations to galaxies and globular clusters up to 300 kpc, that lack young standard candles, like Cepheids
A Deep Search with HST for Late Time Supernova Signatures in the Hosts of XRF 011030 and XRF 020427
X-ray Flashes (XRFs) are, like Gamma-Ray Bursts (GRBs), thought to signal the
collapse of massive stars in distant galaxies. Many models posit that the
isotropic equivalent energies of XRFs are lower than those for GRBs, such that
they are visible from a reduced range of distances when compared with GRBs.
Here we present the results of two epoch Hubble Space Telescope imaging of two
XRFs. These images taken approximately 45 and 200 days post burst reveal no
evidence for an associated supernova in either case. Supernovae such as SN
1998bw would have been visible out to z ~1.5 in each case, while fainter
supernovae such as SN 2002ap would have been visible to z ~ 1. If the XRFs lie
at such large distances, their energies would not fit the observed correlation
between the GRB peak energy and isotropic energy release, in which soft bursts
are less energetic. We conclude that, should these XRFs reside at low redshifts
(), either their line of sight is heavily extinguished, or they are
associated with extremely faint supernovae, or, unlike GRBs, these XRFs do not
have temporally coincident supernovae.Comment: 12 Pages, 4 Figures, accepted for publication in Ap
The Highly Energetic Expansion of SN2010bh Associated with GRB 100316D
We present the spectroscopic and photometric evolution of the nearby (z =
0.059) spectroscopically confirmed type Ic supernova, SN 2010bh, associated
with the soft, long-duration gamma-ray burst (X-ray flash) GRB 100316D.
Intensive follow-up observations of SN 2010bh were performed at the ESO Very
Large Telescope (VLT) using the X-shooter and FORS2 instruments. Owing to the
detailed temporal coverage and the extended wavelength range (3000--24800 A),
we obtained an unprecedentedly rich spectral sequence among the hypernovae,
making SN 2010bh one of the best studied representatives of this SN class. We
find that SN 2010bh has a more rapid rise to maximum brightness (8.0 +/- 1.0
rest-frame days) and a fainter absolute peak luminosity (L_bol~3e42 erg/s) than
previously observed SN events associated with GRBs. Our estimate of the ejected
(56)Ni mass is 0.12 +/- 0.02 Msun. From the broad spectral features we measure
expansion velocities up to 47,000 km/s, higher than those of SNe 1998bw (GRB
980425) and 2006aj (GRB 060218). Helium absorption lines He I lambda5876 and He
I 1.083 microm, blueshifted by ~20,000--30,000 km/s and ~28,000--38,000 km/s,
respectively, may be present in the optical spectra. However, the lack of
coverage of the He I 2.058 microm line prevents us from confirming such
identifications. The nebular spectrum, taken at ~186 days after the explosion,
shows a broad but faint [O I] emission at 6340 A. The light-curve shape and
photospheric expansion velocities of SN 2010bh suggest that we witnessed a
highly energetic explosion with a small ejected mass (E_k ~ 1e52 erg and M_ej ~
3 Msun). The observed properties of SN 2010bh further extend the heterogeneity
of the class of GRB supernovae.Comment: 37 pages and 12 figures (one-column pre-print format), accepted for
publication in Ap
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