SN 2011dh Research Articles

Supernova 2006aj and the associated X-Ray Flash 060218

We have studied the afterglow of the gamma-ray burst (GRB) of February 18, 2006. This is a nearby long GRB, with a very low peak energy, and is therefore classified as an X-ray Flash (XRF). XRF 060218 is clearly associated with a supernova -- dubbed SN 2006aj. We present early spectra for SN 2006aj as well as optical lightcurves reaching out to 50 days past explosion. Our optical lightcurves define the rise times, the lightcurve shapes and the absolute magnitudes in the U, V and R bands, and we compare these data with data for other relevant supernovae. SN 2006aj evolved quite fast, somewhat similarly to SN 2002ap, but not as fast as SN 1994I. Our spectra show the evolution of the supernova over the peak, when the U-band portion of the spectrum rapidly fades due to extensive line blanketing. We compare to similar spectra of very energetic Type Ic supernovae. Our first spectra are earlier than spectra for any other GRB-SN. The spectrum taken 12 days after burst in the rest frame is similar to somewhat later spectra of both SN 1998bw and SN 2003dh, implying a rapid early evolution. This is consistent with the fast lightcurve. From the narrow emission lines from the host galaxy we derive a redshift of z=0.0331+-0.0007. This makes XRF 060218 the second closest gamma-ray burst detected. The flux of these emission lines indicate a high-excitation state, and a modest metallicity and star formation rate of the host galaxy.

Supernovae in helium star-compact object binaries: a possibleγ-ray burst mechanism

Helium star-compact object binaries, and helium star-neutron star binaries in particular, are widely believed to be the progenitors of the observed double-neutron-star systems. In these, the second neutron star is presumed to be the compact remnant of the helium star supernova. In this paper, the observational implications of such a supernova are discussed, and in particular are explored as a candidate γ-ray burst mechanism. In this scenario, the supernova results in a transient period of rapid accretion on to the compact object, extracting via magnetic torques its rotational energy at highly super-Eddington luminosities in the form of a narrowly beamed, strongly electromagnetically dominated jet. Compton scattering of supernova photons advected within the ejecta, and photons originating at shocks driven into the ejecta by the jet, will cool the jet and can produce the observed prompt emission characteristics, including the peak-inferred isotropic energy relation, X-ray flash characteristics, subpulse light curves, energy-dependent time lags and subpulse broadening, and late time spectral softening. The duration of the burst is limited by the rate of Compton cooling of the jet, eventually creating an optically thick, moderately relativistically expanding fireball that can produce the afterglow emission. If the black hole or neutron star stays bound to a compact remnant, late term light curve variability may be observed as in SN 2003dh.

Gamma‐Ray Burst Dust Echoes Revisited: Expectations at Early Times

Gamma-ray burst (GRB) dust echoes were first proposed as an alternative explanation for the supernova-like (SN-like) components to the afterglows of GRB 980326 and GRB 970228. However, the spectroscopic identification of Type Ic SN 2003dh associated with GRB 030329, as well as the identification of SN-like components to the afterglows of other GRBs, appears to have confirmed the GRB/SN paradigm. However, the likely progenitors of Type Ic SNe are Wolf-Rayet WC stars, and late-type WC stars have been observed to be surrounded by dust, at a distance of 10^14 -- 10^15 cm from the star. Consequently, we revisit the possibility of GRB dust echoes, not on a timescale of weeks after the burst but on a timescale of minutes to hours. We find that if the optical flash is sufficiently bright and the jet sufficiently wide, GRB afterglows may be accompanied by chromatic variations on this timescale. From these signatures, such model parameters as the inner radius of the dust distribution, the initial opening angle of the jet, etc., may be deduced. With rapid and regular localizations of GRBs by HETE-2, Integral, and now Swift, and new and improved robotic telescope systems, these early-time GRB dust echoes may soon be detected. We describe one such robotic telescope system, called PROMPT, that the University of North Carolina at Chapel Hill is building at the Cerro Tololo Inter-American Observatory in greater detail.

Low Frequency Radio and X-ray Properties of Core-Collapse Supernovae

SummaryRadio and X-ray studies of young supernovae probe the interaction between the supernova shock waves and the surrounding medium and give clues to the nature and past of the progenitor star. Here we discuss the early emission from type Ic SN 2002ap and argue that repeated Compton boosting of optical photons by hot electrons presents the most natural explanation of the prompt X-ray emission. We describe the radio spectrum of another type Ic SN 2003dh (GRB030329) obtained with combined GMRT and VLA data. We report on the low frequency radio monitoring of SN 1995N and our objectives of distinguishing between competing models of X-ray emission from this SN and the nature of its progenitor by X-ray spectroscopy. Radio studies on SN 2001gd, SN 2001ig and SN 2002hh are mentioned.

The color evolution of the optical afterglow of GRB 030329 and the implications for the underlying supernova SN 2003dh

We find that the color indices $(B-V)_{0}$, $(V-R)_{0}$, $(R-I)_{0}$, $(I-J)_{0}$ in the observer frame of the optical afterglow (OA) of GRB 030329 during $t-T_{0} R magnitude of this event $M_{R_0}\approx -26.6$ mag in the rest frame at $(t-T_{\rm 0})_{\rm rest}= 0.25$ days is in good agreement with the typical brightness of the OAs analyzed by Simon et al. ([CITE]). We detected large color variations of the OA of GRB 030329 only for $t-T_{0}>12$ days, which suggest a rapid evolution of the spectrum of the underlying SN 2003dh. We compare it with the individual type Ic SNe and find that its color evolution is plausibly matched only by that of SN 1998bw although the indices still reveal spectral differences between the two objects. The agreement is particularly good only at $t-T_{0}= 26$ and 27 days. The evolution of SN 2003dh becomes faster than that of SN 1998bw later on and SN 2003dh develops an excess light in the red/IR spectral region. We also emphasize the discordance with other type Ic SNe which are not associated with GRBs.

The J -Band Light Curve of SN 2003lw, Associated with GRB 031203

At z=0.1055, the gamma-ray burst GRB 031203 is one of the two nearest GRBs known. Using observations from the Very Large Array (VLA) and Chandra X-ray Observatory, we derive sub-arcsecond localizations of the radio and X-ray afterglow of this GRB. We present near-infrared observations of the supernova SN 2003lw, which exploded in the host galaxy of the GRB 031203. Our deep, high resolution Magellan/PANIC data establish that this SN is spatially coincident with the radio and X-ray localizations of the afterglow of GRB 031203 to sub-arcsecond precision, and is thus firmly associated with the GRB. We use image differencing to subtract the bright emission from the host galaxy, and measure the time evolution of the SN between ~5 and ~50 days after the GRB. The resulting light curve has a shape which is quite different from that of the two SNe previously associated with GRBs, SN 1998bw and SN 2003dh. With SN 2003lw securely associated with this burst, we confirm that all three GRBs with redshifts z<0.3 were accompanied by SN explosions.

Spectral Evolution of the GRB 030329 Afterglow: Detection of the Supernova Nebular Phase Emissions

Abstract GRB 030329 is the first Gamma-ray burst event for which a connection with a supernova (SN 2003dh) has been confirmed spectroscopically in its early phase. We present optical spectroscopy of this object 40 and 85 days after the burst (35 and 73 rest-frame days, respectively) obtained with the Subaru 8.2-m telescope. After subtracting the host galaxy template spectrum, the second-epoch spectrum shows nebular-phase emission lines emerging from the dominated photospheric-phase spectrum. The transition from the photospheric phase to the nebular phase has just started, or was slowly progressing at the time of our second-epoch observations. Our spectral analysis of the nebular-phase emission lines suggests that the explosion of the progenitor of the GRB 030329 was aspherical, and that the axis of an asphericity is well aligned to both the GRB relativistic jet and our line of sight. Although the decay index and the color evolution in the rest frame during our two epochs are very consistent with those of the Type Ic supernovae SN 1998bw and SN 1997ef, the nebular-phase lines emerged slightly earlier than in the case of these supernovae. These results infer that the most important factor that distinguishes SNe with GRB from SNe without GRB is the scale of the jet activity, or a viewing-angle effect, or both of them.

Hypernovae/Gamma-Ray Bursts in the Galactic Center as Possible Sources of Galactic Positrons

The observation of a strong and extended positron-electron line annihilation emission in the central regions of the Galaxy by the SPectrometer on the International Gamma-Ray Astrophysical Laboratory (INTEGRAL/SPI), consistent with the Galactic bulge geometry and without any counterpart in the gamma-ray range, neither at high energy nor in the 1809 keV 26Al decay line, is challenging. Leaving aside the geometrical question, we address the problem of the adequate positron sources, showing the potentiality of a new category of Type Ic supernovae (SNe Ic), exemplified by SN 2003dh, that is associated with a gamma-ray burst (GRB). This kind of supernova/hypernova/GRB event is interpreted as the result of a bipolar Wolf-Rayet explosion, which produces a large amount of 56Ni and ejects it at high velocity along the rotation axis. The bulk of positrons resulting from 56Co decay escapes in the surrounding medium as a result of the rapid thinning of the ejecta in the polar direction. We show that a rate of about 0.02 SN 2003dh-like events per century in the central region of the Galaxy is sufficient to explain the positron flux detected by INTEGRAL/SPI. In order to explain this flux by SN Ia events alone, a rate of 0.5 per century is necessary, much higher than indicated by Galactic evolutionary models applied to the bulge. Further observations of late light curves of SNe Ia and SNe Ic in the bulge of spiral galaxies, together with three-dimensional hydrodynamic calculations of anisotropic ejections of 56Ni in SN Ic/GRB events, will allow us to estimate the separate contributions of SNe Ia and SNe Ic to positron injection.

Nucleosynthesis in Outflows from the Inner Regions of Collapsars

We consider nucleosynthesis in outflows originating from the inner regions of viscous accretion disks formed after the collapse of a rotating massive star. We show that windlike outflows driven by viscous and neutrino heating can efficiently synthesize Fe group elements moving at near-relativistic velocities. The mass of 56Ni synthesized and the asymptotic velocities attained in our calculations are in accord with those inferred from observations of SN 1998bw and SN 2003dh. These steady windlike outflows are generally proton-rich, characterized by only modest entropies, and consequently synthesize essentially nothing heavier than the Fe group elements. We also discuss bubble-like outflows resulting from rapid energy deposition in localized regions near or in the accretion disk. These intermittent ejecta emerge with low electron fraction and are a promising site for the synthesis of the A = 130 r-process peak elements.

Neutrino signatures of the supernova: Gamma ray burst relationship

We calculate the TeV-PeV neutrino fluxes of gamma-ray bursts associated with supernovae, based on the observed association between GRB 030329 and supernova SN 2003dh. The neutrino spectral flux distributions can test for possible delays between the supernova and gamma-ray burst events down to much shorter time scales than what can be resolved with photons. As an illustrative example, we calculate the probability of neutrino induced muon and electron cascade events in a km scale under-ice detector at the South Pole, from the GRB 030329. Our calculations demonstrate that km scale neutrino telescopes are expected to detect signals that will allow us to constrain supernova-GRB models.

Properties of SN 2003dh Associated with GRB 030329

GRB 030329 has provided solid evidence for the Gamma-Ray Burst-Supernova connection. We construct an ejecta model to reproduce spectra of SN 2003dh, by combining the respective density structures of SNe 1998bw and 1997ef.The energetic model is confirmed though light, curve fitting. The model parameters are M e j = 8M (M m s ∼ 35 - 40M) E k i n = 4 × 10 5 2 ergs, and M( 5 6 Ni) = 0.35M.

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.

A Radio Survey of Type Ib and Ic Supernovae: Searching for Engine‐driven Supernovae

The association of ?-ray bursts (GRBs) and core-collapse supernovae (SNe) of Type Ib and Ic was motivated by the detection of SN 1998bw in the error box of GRB 980425 and the now secure identification of SN 2003dh in the cosmological GRB 030329. The bright radio emission from SN 1998bw indicated that it possessed some of the unique attributes expected of GRBs, namely, a large reservoir of energy in (mildly) relativistic ejecta and variable energy input. The two popular scenarios for the origin of SN 1998bw are a typical cosmological burst observed off-axis or a member of a new distinct class of supernova explosions. In the former, about 0.5% of local Type Ib/c SNe are expected to be similar to SN 1998bw; for the latter no such constraint exists. Motivated thus, we began a systematic program of radio observations of most reported Type Ib/c SNe accessible to the Very Large Array. Of the 33 SNe observed from late 1999 to the end of 2002, at most one is as bright as SN 1998bw. From this we conclude that the incidence of such events is 3%. Furthermore, analysis of the radio emission indicates that none of the observed SNe exhibit clear engine signatures. Finally, a comparison of the SN radio emission to that of GRB afterglows indicates that none of the SNe could have resulted from a typical GRB, independent of the initial jet orientation. Thus, while the nature of SN 1998bw remains an open question, there appears to be a clear dichotomy between the majority of hydrodynamic and engine-driven explosions.

The Earliest Optical Observations of GRB 030329

We present the earliest optical imaging observations of the gamma-ray burst GRB 030329 related to SN 2003dh. The burst was detected by the High Energy Transient Explorer 2 satellite on 2003 March 29, at 11:37:14.67 UT. Our wide-field monitoring started 97 minutes before the trigger, and the burst position was continuously observed. We found no precursor or contemporaneous flare brighter than V = 5.1 (V = 5.5) in the 32 s (64 s) timescale between 10:00 and 13:00 UT. Follow-up time series photometries started at 12:51:39 UT (75 s after position notice through the GRB Coordinates Network) and continued for more than 5 hr. The afterglow was RC = 12.35 ± 0.07 at t = 74 minutes after burst. Its fading between 1.2 and 6.3 hr is well characterized by a single power law of the form f(mJy) = [1.99 ± 0.02 (statistic) ± 0.14 (systematic)](t/1 day)-0.890 ± 0.006 (statistic) ± 0.010 (systematic) in the RC band. No significant flux variation was detected, and upper limits are derived as (Δf/f)rms = 3%-5% in minute-to-hour timescales and (Δf/f)rms = 35%-5% in second-to-minute timescales. Such a featureless light curve is explained by the smooth distribution of the circumburst medium. Another explanation is that the optical band was above the synchrotron cooling frequency where the emergent flux is insensitive to the ambient density contrasts. Extrapolation of the afterglow light curve to the burst epoch excludes the presence of an additional flare component at t < 10 minutes as seen in GRB 990123 and GRB 021211.

The Nature of GRB 980425 and the Search for Off‐Axis Gamma‐Ray Burst Signatures in Nearby Type Ib/c Supernova Emission

The identification of Type Ib/c supernovae (SNe Ib/c) as gamma-ray burst (GRB) progenitors is motivated by the association of GRB 980425 with SN 1998bw and of GRB 030329 with SN 2003dh. While the gamma-ray luminosity of GRB 030329 was typical to cosmological GRBs, the luminosity of the nearby (40 Mpc) GRB 980425 was ~5 orders of magnitude lower. The large luminosity difference is commonly explained by hypothesizing either that SNe Ib/c produce two different classes of GRBs or that GRB 980425 was a typical cosmological GRB jet viewed off-axis. In the latter scenario, strong radio emission, Lν ~ 1030ν ergs s-1 Hz-1, is expected at ~1 yr delay as a result of jet deceleration to subrelativistic speed, as observed from GRB 970508. The radio luminosity of SN 1998bw was 3 orders of magnitude lower than this value. We show that the low radio flux may be consistent with the off-axis jet interpretation, if the density of the wind surrounding the progenitor is lower than typically expected, ≡ (/10-5 M☉ yr-1)/(vw/103 km s-1) 0.1 instead of 1. The lower value of is consistent with the observed radio emission from the SN shock driven into the wind. This interpretation predicts transition to subrelativistic expansion at ~10 yr delay, with current ≈1 mJy 10 GHz flux and mV ≈ 23 optical flux, and with ≈10 mas angular source size. It also implies that in order to search for the signature of off-axis GRBs associated with nearby SNe Ib/c, follow-up observations should be carried out on a multiyear timescale.

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.