arXiv subjects

T. Matheson

Publications and source records attributed to T. Matheson.

At least 73 records · Page 4Linked to original sources

arXiv2003

The Type Ic Hypernova SN 2003dh/GRB 030329

The spectra of SN 2003dh, identified in the afterglow of GRB030329, are modeled using radiation transport codes. It is shown that SN 2003dh had a high explosion kinetic energy ($\sim 4 \times 10^{52}$ erg in spherical symmetry), making it one of the most powerful hypernovae observed so far, and supporting the case for association between hypernovae and Gamma Ray Bursts. However, the light curve derived from fitting the spectra suggests that SN 2003dh was not as bright as SN 1998bw, ejecting only $\sim 0.35\Msun$ of \Nifs. The spectra of SN 2003dh resemble those of SN 1998bw around maximum, but later they look more like those of the less energetic hypernova SN 1997ef. The spectra and the inferred light curve can be modeled adopting a density distribution similar to that used for SN 1998bw at $ v > 25,000$\kms but more like that of SN 1997ef at lower velocities. The mass of the ejecta is $\sim 8\Msun$, somewhat less than in the other two hypernovae. The progenitor must have been a massive star ($M \sim 35-40\Msun$), as for other hypernovae. The need to combine different one-dimensional explosion models strongly indicates that SN 2003dh was an asymmetric explosion.

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arXiv2003

Photometry and Spectroscopy of GRB 030329 and Its Associated Supernova 2003dh: The First Two Months

We present extensive optical and infrared photometry of the afterglow of gamma-ray burst (GRB) 030329 and its associated supernova (SN) 2003dh over the first two months after detection (2003 March 30-May 29 UT). Optical spectroscopy from a variety of telescopes is shown and, when combined with the photometry, allows an unambiguous separation between the afterglow and supernova contributions. The optical afterglow of the GRB is initially a power-law continuum but shows significant color variations during the first week that are unrelated to the presence of a supernova. The early afterglow light curve also shows deviations from the typical power-law decay. A supernova spectrum is first detectable ~7 days after the burst and dominates the light after ~11 days. The spectral evolution and the light curve are shown to closely resemble those of SN 1998bw, a peculiar Type Ic SN associated with GRB 980425, and the time of the supernova explosion is close to the observed time of the GRB. It is now clear that at least some GRBs arise from core-collapse SNe.

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arXiv2003

Spectroscopic Discovery of the Supernova 2003dh Associated with GRB 030329

We present early observations of the afterglow of the Gamma-Ray Burst (GRB) 030329 and the spectroscopic discovery of its associated supernova SN 2003dh. We obtained spectra of the afterglow of GRB 030329 each night from March 30.12 (0.6 days after the burst) to April 8.13 (UT) (9.6 days after the burst). The spectra cover a wavelength range of 350 nm to 850 nm. The early spectra consist of a power-law continuum (F_nu ~ nu^{-0.9}) with narrow emission lines originating from HII regions in the host galaxy, indicating a low redshift of z=0.1687. However, our spectra taken after 2003 Apr. 5 show broad peaks in flux characteristic of a supernova. Correcting for the afterglow emission, we find the spectrum of the supernova is remarkably similar to the type Ic `hypernova' SN 1998bw. While the presence of supernovae have been inferred from the light curves and colors of GRB afterglows in the past, this is the first direct, spectroscopic confirmation that a subset of classical gamma-ray bursts originate from supernovae.

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arXiv2003

Optical Spectra of the Type Ia Supernova 1998aq

We present 29 optical spectra of the normal Type Ia SN 1998aq, ranging from 9 days before to 241 days after the time of maximum brightness. This spectroscopic data set, together with photometric data presented elsewhere, makes SN 1998aq one of the best observed Type Ia supernova at optical wavelengths. We use the parameterized supernova synthetic-spectrum code SYNOW to study line identifications in the early photospheric-phase spectra. The results include evidence for lines of singly ionized carbon, at ejection velocities as low as 11,000 km/sec. Implications for explosion models are discussed.

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arXiv2002

The Spectroscopic Variability of GRB 021004

We present spectra of the optical transient (OT) associated with GRB 021004. The spectra show a blue continuum with superposed absorption features and one emission line. We confirm two intervening metal-line systems at z = 1.380 and z = 1.602 and one very strong absorption system at a redshift of z = 2.323. Ly_alpha emission is also seen at this redshift. While the spectrum of the OT overall cannot be simply described with a power law, the spectral index over the range 5500-8850 A is steep, F_nu ~ nu^(-0.96 +/- 0.03). Comparison of spectra from multiple epochs shows a distinct color evolution with the OT becoming redder with time over the first three days. This is the first clear example of color change in an OT detected spectroscopically.

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arXiv2002

The unusual optical afterglow of the gamma-ray burst GRB 021004: Color changes and short-time-scale variability

We report UBVRI observations of the optical afterglow of the gamma-ray burst GRB 021004. We observed significant (10-20%) deviations from a power law decay on several time scales, ranging from a few hours down to 20-30 minutes. We also observed a significant color change starting ~1.5 days after the burst, confirming the spectroscopic results already reported by Matheson et al. (2002). We discuss these results in the context of several models that have recently been proposed to account for the anomalous photometric behavior of this event.

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arXiv2002

Discovery of the Low-Redshift Optical Afterglow of GRB 011121 and Its Progenitor Supernova 2001ke

We present the discovery and follow-up observations of the afterglow of the GRB 011121 and its associated supernova SN 2001ke. Images were obtained with the OGLE 1.3m telescope in BVRI passbands, starting 10.3 hours after the burst. The temporal analysis of our early data indicates a steep decay, independent of wavelength with power-law index alpha=-1.72+/-0.05. There is no evidence for a break in the light curve earlier than 2.5 days after the burst. The spectral energy distribution determined from the early broad-band photometry is a power-law with index beta=-0.66+/-0.13 after correcting for a large reddening. Spectra, obtained with the Magellan 6.5m Baade telescope, reveal narrow emission lines from the host galaxy which provide a redshift of z=0.362+/-0.001 to the GRB. We also present late R and J-band observations of the afterglow between 7-17 days after the burst. The late-time photometry shows a large deviation from the initial decline and our data combined with Hubble Space Telescope photometry provide strong evidence for a supernova peaking about 12 rest-frame days after the GRB. The first spectrum ever obtained of a GRB supernova at cosmological distance revealed a blue continuum. SN 2001ke was more blue near maximum than SN 1998bw and faded more quickly which demonstrates that a range of properties are possible in supernovae which generate GRB. The blue color is consistent with a supernova interacting with circumstellar gas and this progenitor wind is also evident in the optical afterglow. This is the best evidence to date that classical, long gamma-ray bursts are generated by core-collapse supernovae.

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arXiv2002

The Type IIn SN 1995G: Interaction with the CSM

We present the photometric and spectroscopic evolution of the type IIn SN 1995G in NGC 1643, on the basis of 4 years of optical and infrared observations. This supernova shows very flat optical light curves similar to SN 1988Z, with a slow decline rate at all times. The spectra are characterized by strong Balmer lines with multiple components in emission and with a P-Cygni absorption component blueshifted by only 700 km/s. This feature indicates the presence of a slowly expanding shell above the SN ejecta as in the case of SNe 1994aj and 1996L. As in other SNe IIn the slow luminosity decline cannot be explained only with a radioactive energy input and an additional source of energy is required, most likely that produced by the interaction between supernova ejecta and a pre--existent circumstellar medium. It was estimated that the shell material has a density n(H) >> 10^8 cm^-3, consistent with the absence of forbidden lines in the spectra. About 2 years after the burst the low velocity shell is largely overtaken by the SN ejecta and the luminosity drops at a faster rate.

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arXiv2000

Exploring the Structure of Distant Galaxies with Adaptive Optics on the Keck-II Telescope

We report on the first observation of cosmologically distant field galaxies with an high order Adaptive Optics (AO) system on an 8-10 meter class telescope. Two galaxies were observed at 1.6 microns at an angular resolution as high as 50 milliarcsec using the AO system on the Keck-II telescope. Radial profiles of both objects are consistent with those of local spiral galaxies and are decomposed into a classic exponential disk and a central bulge. A star-forming cluster or companion galaxy as well as a compact core are detected in one of the galaxies at a redshift of 0.37+/-0.05. We discuss possible explanations for the core including a small bulge, a nuclear starburst, or an active nucleus. The same galaxy shows a peak disk surface brightness that is brighter than local disks of comparable size. These observations demonstrate the power of AO to reveal details of the morphology of distant faint galaxies and to explore galaxy evolution.

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arXiv2000

Optical Spectroscopy of Supernova 1993J During Its First 2500 Days

We present 42 low-resolution spectra of Supernova (SN) 1993J, our complete collection from the Lick and Keck Observatories, from day 3 after explosion to day 2454, as well as one Keck high-dispersion spectrum from day 383. SN 1993J began as an apparent SN II, albeit an unusual one. After a few weeks, a dramatic transition took place, as prominent helium lines emerged in the spectrum. SN 1993J had metamorphosed from a SN II to a SN IIb. Nebular spectra of SN 1993J closely resemble those of SNe Ib and Ic, but with a persistent H_alpha line. At very late times, the H_alpha emission line dominated the spectrum, but with an unusual, box-like profile. This is interpreted as an indication of circumstellar interaction.

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arXiv1999

A Black Hole in the X-Ray Nova Velorum 1993

We have obtained 17 moderate-resolution (~2.5 A) optical spectra of the Galactic X-ray Nova Velorum 1993 in quiescence with the Keck-II telescope. The orbital period (P) is 0.285206 +/- 0.0000014 d, and the semiamplitude (K_2) is 475.4 +/- 5.9 km/s. Our derived mass function, f(M_1) = PK_2^3 /2 pi G = 3.17 +/- 0.12 M_sun, is close to the conventional absolute limiting mass for a neutron star (~ 3.0-3.2 M_sun) -- but if the orbital inclination i is less than 80 degrees (given the absences of eclipses), then M_1 is greater than 4.2-4.4 M_sun for nominal secondary-star masses of 0.5 M_sun (M0) to 0.65 M_sun (K6). The primary star is therefore almost certainly a black hole rather than a neutron star. The velocity curve of the primary from H-alpha emission has a semiamplitude (K_1) of 65.3 +/- 7.0 km/s, but with a phase offset by 237 degrees (rather than 180 degrees) from that of the secondary star. The nominal mass ratio q = M_2/M_1 = K_1/K_2 = 0.137 +/- 0.015, and hence for M_2 = 0.5-0.65 M_sun we derive M_1 = 3.64-4.74 M_sun. An adopted mass M_1 ~ 4.4 M_sun is significantly below the typical value of ~ 7 M_sun found for black holes in other low-mass X-ray binaries. Keck observations of MXB 1659-29 (V2134 Oph) in quiescence reveal a probable optical counterpart at R = 23.6 +/- 0.4 mag.

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arXiv1998

Cosmology from Type Ia Supernovae

This presentation reports on first evidence for a low-mass-density/positive-cosmological-constant universe that will expand forever, based on observations of a set of 40 high-redshift supernovae. The experimental strategy, data sets, and analysis techniques are described. More extensive analyses of these results with some additional methods and data are presented in the more recent LBNL report #41801 (Perlmutter et al., 1998; accepted for publication in Ap.J.), astro-ph/9812133 . This Lawrence Berkeley National Laboratory reprint is a reduction of a poster presentation from the Cosmology Display Session #85 on 9 January 1998 at the American Astronomical Society meeting in Washington D.C. It is also available on the World Wide Web at http://supernova.LBL.gov/ This work has also been referenced in the literature by the pre-meeting abstract citation: Perlmutter et al., B.A.A.S., volume 29, page 1351 (1997).

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arXiv1998

Measurements of Omega and Lambda from 42 High-Redshift Supernovae

We report measurements of the mass density, Omega_M, and cosmological-constant energy density, Omega_Lambda, of the universe based on the analysis of 42 Type Ia supernovae discovered by the Supernova Cosmology Project. The magnitude-redshift data for these SNe, at redshifts between 0.18 and 0.83, are fit jointly with a set of SNe from the Calan/Tololo Supernova Survey, at redshifts below 0.1, to yield values for the cosmological parameters. All SN peak magnitudes are standardized using a SN Ia lightcurve width-luminosity relation. The measurement yields a joint probability distribution of the cosmological parameters that is approximated by the relation 0.8 Omega_M - 0.6 Omega_Lambda ~= -0.2 +/- 0.1 in the region of interest (Omega_M <~ 1.5). For a flat (Omega_M + Omega_Lambda = 1) cosmology we find Omega_M = 0.28{+0.09,-0.08} (1 sigma statistical) {+0.05,-0.04} (identified systematics). The data are strongly inconsistent with a Lambda = 0 flat cosmology, the simplest inflationary universe model. An open, Lambda = 0 cosmology also does not fit the data well: the data indicate that the cosmological constant is non-zero and positive, with a confidence of P(Lambda > 0) = 99%, including the identified systematic uncertainties. The best-fit age of the universe relative to the Hubble time is t_0 = 14.9{+1.4,-1.1} (0.63/h) Gyr for a flat cosmology. The size of our sample allows us to perform a variety of statistical tests to check for possible systematic errors and biases. We find no significant differences in either the host reddening distribution or Malmquist bias between the low-redshift Calan/Tololo sample and our high-redshift sample. The conclusions are robust whether or not a width-luminosity relation is used to standardize the SN peak magnitudes.

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arXiv1998

Steps Toward Determination of the Size and Structure of the Broad-Line Region in Active Galactic Nuclei. XV. Long-Term Optical Monitoring of NGC 5548

We present the results of three years of ground-based observations of the Seyfert 1 galaxy NGC 5548, which combined with previously reported data, yield optical continuum and broad-line H-beta light curves for a total of eight years. The light curves consist of over 800 points, with a typical spacing of a few days between observations. During this eight-year period, the nuclear continuum has varied by more than a factor of seven, and the H-beta emission line has varied by a factor of nearly six. The H-beta emission line responds to continuum variations with a time delay or lag of 10-20 days, the precise value varying somewhat from year to year. We find some indications that the lag varies with continuum flux in the sense that the lag is larger when the source is brighter.

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arXiv1997

Measurements of the Cosmological Parameters Omega and Lambda from the First 7 Supernovae at z >= 0.35

We have developed a technique to systematically discover and study high-redshift supernovae that can be used to measure the cosmological parameters. We report here results based on the initial seven of >28 supernovae discovered to date in the high-redshift supernova search of the Supernova Cosmology Project. We find a dispersion in peak magnitudes of sigma_{M_B} = 0.27 this dispersion narrows to sigma_{M_B,corr} = 0.19 after "correcting" the magnitudes using the light-curve "width-luminosity" relation found for nearby (z <= 0.1) type Ia supernovae from the Calan/Tololo survey (Hamuy et al. 1996). Comparing lightcurve-width-corrected magnitudes as a function of redshift of our distant (z = 0.35-0.46) supernovae to those of nearby type Ia supernovae yields a global measurement of the mass density, Omega_M = 0.88^{+0.69}_{-0.60} for a Lambda = 0 cosmology. For a spatially flat universe (i.e., Omega_M +Omega_Lambda = 1), we find Omega_M = 0.94 ^{+0.34}_{-0.28} or, equivalently, a measurement of the cosmological constant, Omega_Lambda = 0.06 ^{+0.28}_{-0.34} (<0.51 at the 95% confidence level). For the more general Friedmann-Lemaitre cosmologies with independent Omega_M and Omega_Lambda, the results are presented as a confidence region on the Omega_M-Omega_Lambda plane. This region does not correspond to a unique value of the deceleration parameter q_0. We present analyses and checks for statistical and systematic errors, and also show that our results do not depend on the specifics of the width-luminosity correction. The results for Omega_Lambda-versus-Omega_M are inconsistent with Lambda-dominated, low density, flat cosmologies that have been proposed to reconcile the ages of globular cluster stars with higher Hubble constant values.

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arXiv1997

Implications For The Hubble Constant from the First Seven Supernovae at z >= 0.35

The Supernova Cosmology Project has discovered over twenty-eight supernovae (SNe) at 0.35 = 0.2, we find that H_0^G < 70 km/s/Mpc in a Lambda=0 universe and H_0^G < 78 km/s/Mpc in a flat universe, correcting the distant and local SN apparent magnitudes for light curve width. Lower results for H_0^G are obtained if the magnitudes are not width corrected.

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arXiv1996

Scheduled Discoveries of 7+ High-Redshift Supernovae: First Cosmology Results and Bounds on q_0

Our search for high-redshift Type Ia supernovae discovered, in its first years, a sample of seven supernovae. Using a "batch" search strategy, almost all were discovered before maximum light and were observed over the peak of their light curves. The spectra and light curves indicate that almost all were Type Ia supernovae at redshifts z = 0.35 -- 0.5. These high-redshift supernovae can provide a distance indicator and "standard clock" to study the cosmological parameters q_0, Lambda, Omega_0, and H_0. This presentation and the following presentations of Kim et al. (1996), Goldhaber et al. (1996), and Pain et al. (1996) will discuss observation strategies and rates, analysis and calibration issues, the sources of measurement uncertainty, and the cosmological implications, including bounds on q_0, of these first high-redshift supernovae from our ongoing search.

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arXiv1996

K Corrections For Type Ia Supernovae and a Test for Spatial Variation of the Hubble Constant

Cross-filter K corrections for a sample of "normal" Type Ia supernovae (SNe) have been calculated for a range of epochs. With appropriate filter choices, the combined statistical and systematic K correction dispersion of the full sample lies within 0.05 mag for redshifts z<0.7. This narrow dispersion of the calculated K correction allows the Type Ia to be used as a cosmological probe. We use the K corrections with observations of seven SNe at redshifts 0.3 < z <0.5 to bound the possible difference between the locally measured Hubble constant (H_L) and the true cosmological Hubble constant (H_0).

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