Search

We present the late-time Hubble Space Telescope observations of two Gamma Ray Burst (GRB) associated supernovae (SNe), GRB 030329/SN 2003dh and XRF 060218/SN 2006aj. Using the multi-color data up to ~320 days after the burst, we constrain the late-time decay nature of these SNe. The decay rates of SN 2003dh are steeper than SN 2006aj. A comparison with two other GRB SNe, GRB 980425/SN 1998bw and the SN associated with XRF 020903, shows that the decay rates of SN 2003dh are similar to XRF 020903 and those of SN 2006aj are similar to SN 1998bw. The late-time decay rates are steeper than the 56Co→56Fe radioactive decay rate indicating that there is some leakage of gamma-rays. We also compare the late-time decay rates of nine type Ic SNe, including the SNe of long GRBs, Ic broad lined and normal Ics. The decay rates of the SNe sample show a remarkable similarity in I band at late-times with a scatter of ~10%.

We present a search for late-time rebrightening of radio emission from three supernovae (SNe) with associated gamma-ray bursts (GRBs). It has been previously proposed that the unusually energetic SNe associated with GRBs should enter the Sedov-Taylor phase decades after the stellar explosion, and this SN "remnant" emission will outshine the GRB radio afterglow and be detectable at significant distances. We place deep limits on the radio luminosity of GRB 980425/SN 1998bw, GRB 030329/SN 2003dh and GRB 060218/SN 2006aj, 10-18 years after explosion, with our deepest limit being $L_��$ $< 4 \times 10^{26}$ erg s$^{-1}$ Hz$^{-1}$ for GRB 980425/SN 1998bw. We put constraints on the density of the surrounding medium for various assumed values of the microphysical parameters related to the magnetic field and synchrotron-emitting electrons. For GRB 060218/SN 2006aj and GRB 980425/SN 1998bw, these density limits have implications for the density profile of the surrounding medium, while the non-detection of GRB 030329/SN 2003dh implies that its afterglow will not be detectable anymore at GHz frequencies., 9 pages, 4 figures

In: Dwarf galaxies: from the deep universe to the present; edited by:McQuinn, KBW; Stierwalt, S.; ISBN:978-1-108-47161-9.--Conference: 344th Symposium of the International-Astronomical-Union (IAU), Vienna, Austria, Aug 20-24, 2018., The hosts of long Gamma-ray bursts (GRBs) are places of intense star-formation, which, at low redshift, are primarily low-mass dwarf starburst galaxies. Spatially resolved studies of these galaxies are still sparse, even more so at high spectral resolution where we can probe gas kinematics, in- and outflows and differences in abundance between different components. Here we present the first high resolution IFU sample of six low redshift GRB hosts, all dwarf starbursts. All galaxies in our sample show evidence for excess emission or broad emission components, with velocities of 100-200 kms(-1). For GRB 030329, outflowing gas had also been observed in absorption in spectra of the GRB afterglow. The high velocity emission is usually blue shifted, connected to the brightest star-forming regions and more metal rich than the narrow component associated with the emission of the general host ISM. This gives strong indications that the excess emission/broad component is indeed associated to a starburst wind as observed in many field star-burst galaxies and a sign for the intense ongoing star-formation in those galaxies.

Long duration gamma-ray bursts are a rare subclass of stripped-envelope core-collapse supernovae that launch collimated relativistic outflows (jets). All gamma-ray-burst-associated supernovae are spectroscopically of Type Ic with broad lines, but the fraction of broad-lined Type Ic supernovae harboring low-luminosity gamma-ray-burst remains largely unconstrained. Some supernovae should be accompanied by off-axis $\gamma$-ray burst jets that remain invisible initially, but then emerge as strong radio sources (as the jets decelerate). However, this critical prediction of the jet model for gamma-ray bursts has yet to be verified observationally. Here, we present K. G. Jansky Very Large Array observations of 15 broad-lined supernovae of Type Ic discovered by the Palomar Transient Factory in an untargeted manner. Most of the supernovae in our sample exclude radio emission observationally similar to that of the radio-loud, relativistic SN\,1998bw. We constrain the fraction of 1998bw-like broad-lined Type Ic supernovae to be, Comment: 20 pages, 10 figures; accepted for publication in ApJ. This version addresses Referee's comments

GRB 030329 displayed one of the brightest optical afterglows ever. We have followed the radio afterglow of GRB 030329 for over 5 years using the GMRT and WSRT at low radio frequencies. This is the longest as well as the lowest frequency follow up of any GRB afterglow ever.Radio observations of a GRB afterglow provide a unique probe of the physics of the blast wave at late times, when the expansion of the fireball slows down to non‐relativistic speeds. Our GMRT‐WSRT observations suggest that the afterglow of GRB030329 entered the non‐relativistic phase around 60 days after the burst. The estimate of the fireball energy content, ∼1051 erg, in this near‐isotropic phase is much less susceptible to the collimation‐related uncertainties arising in the relativistic phase. We have also been closely monitoring the evolution of the afterglow to look for possible signatures of emission from a counter jet, but no conclusive evidence has so far been found.

The long-duration gamma-ray burst (GRB) 030329, associated with supernova (SN) 2003dh, occurred inside a star-forming dwarf galaxy at redshift $z=0.1685$. The low redshift, and a rich set of archival Hubble Space Telescope (HST) images, makes this GRB well-suited for a detailed study of the stellar population in the immediate vicinity of the explosion. Since the lifetime of a star is directly tied to its mass, the age of the stellar population can be used to put constraints on the GRB and SN progenitor mass. From the HST images we extract the colours of the precise site from which the GRB originated, and find that the colours are significantly different from those of the overall host galaxy and the surrounding starburst environment. We have used spectral evolutionary models, including nebular emission, to carefully constrain the age of the stellar population, and hence the progenitor, at the very explosion site. For instantaneous burst models we find that a population age of 5 Myr best matches the data, suggesting a very massive (M > 50 M_sun) star as the progenitor, with an upper limit of 8 Myr (M > 25 M_sun). For more extended star formation scenarios, the inferred progenitor age is in most cases still very young (age < 7 Myr, implying M > 25 M_sun), with an upper limit of 20 Myr (M > 12 M_sun). These age estimates are an order of magnitude lower than the ages inferred from the overall host galaxy colours, indicating that progenitor mass estimates based on data for spatially unresolved GRB host galaxies will in general be of limited use. Our results are consistent with the collapsar scenario., Accepted to MNRAS

We present a series of early UVES/VLT high resolution spectra of the afterglow of GRB 030329 at redshift z=0.16867+-0.00001. In contrast to other spectra from this burst, both emission and absorption lines were detected. None of them showed any temporal evolution. From the emission lines, we determine the properties of the host galaxy which has a star formation rate (SFR) of 0.198 M_solar yr^-1 and a low metallicity of 1/7 Z_solar. Given the low total stellar host mass M_star=10^7.75+-0.15 M_solar and an absolute luminosity m_V=-16.37, we derive specific SFRs (SSFR) of log SFR/M = -8.5 yr^-1 and SFR/L = 14.1 M_solar yr^-1 L_*^-1. This fits well into the picture of GRB hosts as being low mass, low metallicity, actively star forming galaxies. The MgII and MgI absorption lines from the host show multiple narrow (Doppler width b=5-10 km/s) components spanning a range of v about 260 km/s, mainly blueshifted compared to the redshift from the emission lines. These components are likely probing outflowing material of the host galaxy, which could arise from former galactic superwinds, driven by supernovae from star forming regions. Similar features have been observed in QSO spectra. The outflowing material is mainly neutral with high column densities of log N(MgII)=14.0+-0.1 cm^-2 and log N(MgI)=12.3+-0.1 cm^-2., Comment: 11 pages, 4 figures, submitted to ApJ

Radio observations of gamma-ray burst (GRB) afterglows are essential for our understanding of the physics of relativistic blast waves, as they enable us to follow the evolution of GRB explosions much longer than the afterglows in any other wave band. We have performed a three-year monitoring campaign of GRB 030329 with the Westerbork Synthesis Radio Telescopes (WSRT) and the Giant Metrewave Radio Telescope (GMRT). Our observations, combined with observations at other wavelengths, have allowed us to determine the GRB blast wave physical parameters, such as the total burst energy and the ambient medium density, as well as investigate the jet nature of the relativistic outflow. Further, by modeling the late-time radio light curve of GRB 030329, we predict that the Low-Frequency Array (LOFAR, 30-240 MHz) will be able to observe afterglows of similar GRBs, and constrain the physics of the blast wave during its non-relativistic phase., Comment: 5 pages, 2 figures, Phil. Trans. R. Soc. A, vol.365, p.1241, proceedings of the Royal Society Scientific Discussion Meeting, London, September 2006

A distinguishing feature of GRB 030329 is the obvious rebrightening of its optical afterglow at around t ∼1.6 d. We have re-examined the event numerically in light of three candidate models. Both the density-jump model and the two-component jet model fail to produce any significant rebrightening at the right moment. The energy-injection model seems to be the most preferred choice. By engaging a sequence of energy-injection events, it provides an acceptable fit to the rebrightening at t ∼1.6 d, as well as the whole observed light curve that extends to t ∼80 d.

The gamma-ray burst (GRB) jet powers the afterglow emission by shocking the surrounding medium, and radio afterglow can now be routinely observed to almost a year after the explosion. Long-duration GRBs are accompanied by supernovae (SNe) that typically contain much more energy than the GRB jet. Here we consider the fact that the SN blast wave will also produce its own afterglow (supernova remnant emission), which will peak at much later time (since it is non-relativistic), when the SN blast wave transitions from a coasting phase to a decelerating Sedov-Taylor phase. We predict that this component will peak generally a few tens of years after the explosion and it will outshine the GRB powered afterglow well-before its peak emission. In the case of GRB 030329, where the external density is constrained by the $\sim 10$-year coverage of the radio GRB afterglow, the radio emission is predicted to start rising over the next decade and to continue to increase for the following decades up to a level of $\sim$ mJy. Detection of the SN-powered radio emission will greatly advance our knowledge of particle acceleration in $ \sim 0.1$c shocks., Comment: 8 pages, 4 figures, 1 table, MNRAS accepted; added equation, added references, expanded Discussion

Long duration gamma-ray bursts (GRBs) and broad-line, type Ic supernovae (SNe) are strongly connected. We aim at characterizing SN 2013dx, associated with GRB\,130702A, through sensitive and extensive ground-based observational campaigns in the optical-IR band. We monitored the field of the Swift GRB 130702A (redshift z = 0.145) using the 8.2-m VLT, the 3.6-m TNG and the 0.6-m REM telescopes during the time interval between 4 and 40 days after the burst. Photometric and spectroscopic observations revealed the presence of the associated Type Ic SN 2013dx. Our multi-band photometry allowed the construction of a bolometric light curve.} The bolometric light curve of SN 2013dx resembles that of 2003dh (associated with GRB 030329), but is ~10% faster and ~25% dimmer. From this we infer a synthesized 56Ni mass of ~0.2 solar masses. The multi-epoch optical spectroscopy shows that the SN 2013dx behavior is best matched by SN 1998bw, among the other well-known low-redshift SNe associated with GRBs and XRFs, and by SN 2010ah, an energetic Type Ic SN not associated with any GRB. The photospheric velocity of the ejected material declines from ~2.7X10^4 km/s at 8 rest frame days from the explosion, to ~3.5X10^3 km/s at 40 days. These values are extremely close to those of SN1998bw and 2010ah. We deduce for SN 2013dx a kinetic energy of ~35X10^51 erg, and an ejected mass of ~7 solar masses. This suggests that the progenitor of SN2013dx had a mass of ~25 solar masses, i.e., 15-20% less massive than that of SN 1998bw. Finally, we performed a study of the SN 2013dx environment, through spectroscopy of the closeby galaxies. 9 out of the 14 inspected galaxies lie within 0.03 in redshift from z=0.145, indicating that the host of GRB 130702A/SN 2013dx belongs to a group of galaxies, an unprecedented finding for a GRB-associated SN and, to our knowledge, for long GRBs in general., 14 pages, 11 figures, 6 tables, accepted for publication in Astronomy and Astrophysics

The remnants of two gamma-ray bursts, GRB 030329 and GRB 041227, have been resolved by Very Long Baseline Interferometry observations. The radio counterparts were observed to expand with time. These observations provide an important way to test the dynamics of the standard fireball model. We show that the observed size evolution of these two events cannot be explained by a simple jet model, rather, it can be satisfactorily explained by the two-component jet model. It strongly hints that gamma-ray burst ejecta may have complicated structures.

We present multicolor optical observations of the nearby (z=0.1685) GRB 030329 obtained with the same instrumentation over a time period of 6 hours for a total of an unprecedented 475 quasi-simultaneous BVR observations. The achromatic steepening in the optical, which occurs at t~0.7 days, provides evidence for a dynamic transition of the source, and can be most readily explained by models in which the GRB ejecta are collimated into a jet. Since the current state-of-the-art modeling of GRB jets is still flawed with uncertainties, we use these data to critically assess some classes of models that have been proposed in the literature. The data, especially the smooth decline rate seen in the optical afterglow, are consistent with a model in which GRB 030329 was a homogeneous, sharp-edged jet, viewed near its edge interacting with a uniform external medium, or viewed near its symmetry axis with a stratified wind-like external environment. The lack of short timescale fluctuations in the optical afterglow flux down to the 0.5 per cent level puts stringent constraints on possible small scale angular inhomogeneities within the jet or fluctuations in the external density.

A new procedure for smoothing a gamma-ray burst (GRB) lightcurve and calculating its variability is presented. Applying the procedure to a sample of 25 long GRBs, we have obtained a very tight correlation between the variability and the peak luminosity. The only significant outlier in the sample is GRB 030329. With this outlier excluded, the data scatter is reduced by a factor of \sim 3 compared to that of Guidorzi et al. (2005), measured by the deviation of fit. Possible causes for the outlier are discussed., Comment: 9 pages, including 7 figure. Expanded as requested by referee. An error in Fig. 1 was corrected (the two 1-sigma lines in the old version were wrong). Accepted for publication by MNRAS

The best-sampled afterglow light curves are available for GRB 030329. A distinguishing feature of this event is the obvious rebrightening at around 1.6 days after the burst. Proposed explanations for the rebrightening mainly include the two-component jet model and the refreshed shock model, although a sudden density-jump in the circumburst environment is also a potential choice. Here we re-examine the optical afterglow of GRB 030329 numerically in light of the three models. In the density-jump model, no obvious rebrightening can be produced at the jump moment. Additionally, after the density jump, the predicted flux density decreases rapidly to a level that is significantly below observations. A simple density-jump model thus can be excluded. In the two-component jet model, although the observed late afterglow (after 1.6 days) can potentially be explained as emission from the wide-component, the emergence of this emission actually is too slow and it does not manifest as a rebrightening as previously expected. The energy-injection model seems to be the most preferred choice. By engaging a sequence of energy-injection events, it provides an acceptable fit to the rebrightening at $\sim 1.6$ d, as well as the whole observed light curve that extends to $\sim 80$ d. Further studies on these multiple energy-injection processes may provide a valuable insight into the nature of the central engines of gamma-ray bursts., 18 pages, 3 figures; a few references added and minor word changes; now accepted for publication in ApJ

We present our centimeter wavelength (1.4, 2.3 and 4.8 GHz) light curves of the afterglow of GRB 030329, which were obtained with the Westerbork Synthesis Radio Telescope. Modeling the data according to a collimated afterglow results in a jet-break time of 10 days. This is in accordance with earlier results obtained at higher radio frequencies. However, with respect to the afterglow model, some additional flux at the lower frequencies is present when these light curves reach their maximum after 40-80 days. We show that this additional flux can be modeled with two or more components with progressively later jet breaks. From these results we infer that the jet is in fact a structured or a layered jet, where the ejecta with lower Lorentz factors produce additional flux that becomes visible at late times in the lowest frequency bands. We show that a transition to non-relativistic expansion of the fireball at late times can also account for the observed flux excess, except for the lowest frequency (1.4 GHz) data., 7 pages, 2 figures, accepted for publication in ApJ

We present broad band photometry and spectroscopic observations of the host galaxy of GRB 030329. Analysis of the spectral emission lines shows that the host is likely a low metallicity galaxy (Z~0.004). The spectral energy distribution (SED) constructed with the photometric points has been fitted using synthetic and observational templates. The best SED fit is obtained with a starburst template with an age of ~150 Myr and an extinction Av~0.6. We find that the GRB 030329 host galaxy is a subluminous galaxy (L~0.016 L*) with a stellar mass of >~10^8 Mo. Three independent diagnostics, based on the restframe UV continuum, the [OII], and the Balmer emission lines, provide a consistent unextincted star formation rate of ~0.6 Mo yr^-1, implying a high unextincted specific star formation rate (~34 Mo yr^-1 (L/L*)^-1). We estimate that the unextincted specific star formation rate of the GRB 030329 host is higher than ~93.5% of the galaxies at a similar redshift., 11 pages, 4 figures. Accepted for publication in A&A

The net optical light curves and spectra of the supernova (SN) 2003dh are obtained from the published spectra of GRB 030329, covering about 6 days before SN maximum to about 60 days after. The bulk of the U-band flux is subtracted from the observed spectra using early-time afterglow templates, because strong line blanketing greatly depresses the UV and U-band SN flux in a metal-rich, fast-moving SN atmosphere. The blue-end spectra of the gamma-ray burst (GRB)connected hypernova SN 1998bw is used to determine the amount of subtraction. The subtraction of a host galaxy template affects the late-time results. The derived SN 2003dh light curves are narrower than those of SN 1998bw, rising as fast before maximum, reaching a possibly fainter maximum, and then declining ~ 1.2-1.4 times faster. We then build UVOIR bolometric SN light curve. Allowing for uncertainties, it can be reproduced with a spherical ejecta model of Mej ~ 7+/-3 Msun, KE ~ (3.5+/-1.5)E52 ergs, with KE/Mej ~ 5 following previous spectrum modelling, and M(Ni56) ~ (0.4 +0.15/-0.1) Msun. This suggests a progenitor main-sequence mass of about 25-40 Msun, lower than SN 1998bw but significantly higher than normal Type Ic SNe and the GRB-unrelated hypernova SN 2002ap., 18 pages, 7 figures, published by ApJ

Nobeyama Millimeter Array was used to observe millimeter-wave afterglow of GRB 030329 at 93 GHz and 141 GHz from 2003 April 6 to 2003 May 30. A sensitive search for CO(J=1-0) emission/absorption from the host galaxy of GRB 030329 was also carried out. Unresolved millimeter continuum emission at the position of GRB 030329 was detected until 2003 April 21. We found a steep decline of continuum flux (\propto t^{-2.0}) during this period, in accord with a previous report. Moreover, our data implies that the decay was accompanied by possible plateaus phases, or bumps, on a time scale of several days. From an integrated spectrum, produced by summing up the data from 2003 April 10 to 2003 May 30, we found a possible emission feature, which could be a redshifted CO(J=1-0) line. Its position and redshift coincide well with those of GRB 030329, though further observations are required to confirm the detection. If the emission feature is real, the observed CO flux is 1.4 +/- 0.52 Jy km/s, corresponding to a large molecular gas mass of M(H_2) > 10^9 Mo. This implies that the host galaxy, which is optically faint, is highly obscured due to a rich interstellar medium., 13 pages, 4 figures, 1 table, to appear in PASJ

We use data on the image size of the radio afterglow of GRB 030329 (Taylor et al. 2004) to constrain the physical parameters of this explosion. Together with the observed broad band spectrum, this data over-constrains the physical parameters, thus enabling to test different GRB jet models for consistency. We consider two extreme models for the lateral spreading of the jet: model 1 with relativistic expansion in the local rest frame, and model 2 with little lateral expansion as long as the jet is highly relativistic. We find that both models are consistent with the data for a uniform external medium, while for a stellar wind environment model 1 is consistent with the data but model 2 is disfavored by the data. Our derivations can be used to place tighter constraints on the dynamics and structure of GRB jets in future afterglows, following a denser monitoring campaign for the temporal evolution of their image size., 12 pages, 6 figues; submitted to ApJ

Study of radio supernovae (SNe) over the past 25 years includes two dozen detected objects and more than 100 upper limits. From this work it is possible to identify classes of radio properties, demonstrate conformance to and deviations from existing models, estimate the density and structure of the circumstellar material and, by inference, the evolution of the presupernova stellar wind, and reveal the last stages of stellar evolution before explosion. It is also possible to detect ionized hydrogen along the line of sight, to demonstrate binary properties of the stellar system, and to show clumpiness of the circumstellar material. Since 1997 the afterglow of γ-ray bursting sources (GRBs) has occasionally been detected in the radio, as well in other wavelength bands. In particular, the interesting and unusual γ-ray burst GRB 980425, almost certainly related to the radio supernova SN 1998bw, and the more recent SN 2003dh/GRB 030329 are links between the two classes of objects. Analyzing the extensive radio emission data available for SN 1998bw, one can describe its time evolution within the well established framework available for the analysis of radio emission from supernovae. This then allows relatively detailed description of a number of physical properties of the object. The radio emission can best be explained as the interaction of a mildly relativistic (Γ ∼ 1.6) shock with a dense pre-explosion stellar wind-established circumstellar medium that is highly structured both azimuthally, in clumps or filaments, and radially, with observed density enhancements. From this we can support the conclusion that at least some members of the slow-soft class of GRBs are related to type Ib/c SNe and can be attributed to the explosion of a massive star in a dense, highly structured CSM that was presumably established by the pre-explosion stellar system. However, due to the lack of sensitivity of current radio telescopes, most supernovae cannot be studied if they are more distant than the Virgo Cluster (∼20 Mpc) or, for exceptionally luminous Type IIn supernovae, beyond ∼100 Mpc. While the GRBs are up to 4 orders-of-magnitude more radio luminous, they are also generally much more distant because of their small probability of detection in smaller volumes of space and most are at z ∼ 1. Those which are radio detected rarely exceed peak flux densities of ∼100 − 300 μJy. Such low flux densities mean that detailed study of their radio “light curves” and, derived from those light curves, the energetics and dynamics of the explosions and the properties of their progenitors and the circumburst medium is very difficult and severely limited in scope. The increased capability of the SKA to attack these problems will significantly advance the field.

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 central engine of gamma-ray bursts (GRBs) is believed to eject double-sided ultra-relativistic jets. For an observed GRB, one of the twin jets should point toward us, and is responsible for the prompt gamma-ray and subsequent afterglow emission. We consider in this Letter the other receding jet, which will give rise to late-time radio re-brightening (RRB) when it becomes non-relativistic (NR) and radiative isotropic. The RRB peaks at a time $5t_{NR}=2(E_{j,51}/n)^{1/3}$ yr after the GRB, where $t_{NR}$ is the observed NR timescale for the preceding jet, $E_j$ is the jet energy and $n$ is the ambient medium density. The peak flux is comparable to the preceding-jet emission at $t_{NR}$. We expect the RRB of GRB 030329 1.7 yr after the burst with a flux $\sim0.6$ mJy at 15 GHz. The cases of GRBs 970508 and 980703 have also been discussed. The detection of RRB, which needs dense monitoring campaign even a few years after a GRB, will be the direct evidence for the existence of double-sided jets in GRBs, and prove the black hole-disk system formation in the cores of progenitors., Comment: 5 pages, 1 figure, minor changes, ApJL accepted

We have developed a robotic telescope at Tokyo Institute of Technology (Tokyo Tech) to perform rapid follow-up observations of early optical afterglows of gamma-ray bursts (GRBs). Our system was primarily designed to respond quickly to the GRB locations notified by the High Energy Transient Explorer 2 (HETE-2) satellite, but it can also respond to all the notifications provided by the GRB Coordinates Network (GCN). In order to cover the error circle of the HETE-2 wide-field and thermo-electrically cooled CCD camera is equipped on the focus of a small 30 cm telescope. A field of view of our system is 44 arcminutes which can cover the most error circles of the HETE-2. The rapid response (less than 15 sec after the notice) and slew speeds (6 deg/sec) make our system appropriate for observing GRB afterglows. Using this convenient system, we detected the optical afterglow of GRB 030329. Observation was started 67 minutes after the burst, which was one of the earliest detection in the world. We report the performance of our telescope coupled to CCD camera, and estimate the limiting magnitude of our system. Although our system is located in a region affected by strong city lights, the limiting magnitude is approximately 17.3 mag.

We present the radio observations of the afterglow from the intense cosmic gamma-ray burst GRB 030329 performed with the radio telescopes of the Institute of Applied Astronomy, Russian Academy of Sciences, at the Svetloe (λ=3.5 cm) and Zelenchuk (λ=6 cm) Observatories. The difference between the fluxes measured in two different polarization modes suggests the existence of a circular polarization in the radio afterglow from GRB 030329. However, since the measurement errors of the fluxes with different circular polarizations are large, we cannot draw a firm conclusion about its detection; we can only set an upper limit on its value. An analysis of the possible generation mechanisms for the circular polarization of the relativistic jet suggests that there is a helical magnetic field in the jet. The existence of significant flux densities at various wavelengths during a long (≥10 days) period leads us to conclude that the hydrodynamic evolution of the relativistic bow shock takes place in the stellar wind, not in the interstellar medium. We have estimated the total GRB energy (E=1051 erg) (under the assumption of isotropic radiation) and the plasma density of the stellar wind from the presupernova (n=3 cm−3). The magnetic-field strength in the relativistic jet can be estimated as B≈100 G.

We explore the prospects for simultaneous, broad-band, multiwavelength polarimetric observations of GRB afterglows. We focus on the role of cosmic dust in GRB host galaxies on the observed percentage polarization of afterglows in the optical/near-infrared bands as a function of redshift. Our driving point is the afterglow of GRB 030329, for which we obtained polarimetric data in the R band and K band simultaneously about 1.5 days after the burst. We argue that polarimetric observations can be very sensitive to dust in a GRB host, because dust can render the polarization of an afterglow wavelength-dependent. We discuss the consequences for the interpretation of observational data and emphasize the important role of very early polarimetric follow-up observations in all bands, when afterglows are still bright, to study the physical properties of dust and magnetic fields in high-z galaxies., Comment: accepted for publication in Astronomy & Astrophysics

The finding of a Type Ic supernova connected with GRB 030329 showed a massive star origin for this burst, supporting evidence for this association in previous bursts with lightcurve bumps at the appropriate time for a supernova. Here, we explore the possibility that all long bursts have massive star progenitors, interacting with either the freely expanding wind of the progenitor or the shocked wind. We present models for the afterglows of GRB 020405 and GRB 021211, which are a challenge to wind interaction models. Considering sources for which wind interaction models are acceptable, a range of wind densities is required, from values typical of Galactic Wolf-Rayet stars to values ~100 times smaller. The reason for the low densities is unclear, but may involve low progenitor masses and/or low metallicities. If mass is a factor, a low density event should be associated with a low mass supernova. The interpretation of bursts apparently interacting with constant density media as interaction with a shocked wind requires both a range of mass loss densities and a range of external pressures. The highest pressures, p/k > 10^8 cm^{-3} K, may be due to an extreme starburst environment, which would imply that the burst is superposed on an active star forming region. Although the range of observed events can be accomodated by the shocked wind theory, special circumstances are necessary to bring this about. Finally, we consider the high velocity, high ionization absorption features observed in some afterglow spectra. If the features are circumstellar, the presence of the burst in a starburst region may be important for the formation of clumps near the burst.

We present the results of the radio observations of the afterglow of GRB 030329 with the Nobeyama 45-m telescope. The observations were made at 23.5 GHz, 43 GHz, and 90 GHz. The light curves show steep decline after constant phase. The start time of the decline depends on frequency. Namely, the decline started earlier at higher frequency. The spectrum has a peak at mm wavelength range. The peak frequency and the peak flux decreased with time. These results are consistent with the expectation from fireball model., Comment: 4 pages, 3 figures, to be published in PASJ Vol.56, No.2

We report on the optical light curve of the afterglow of GRB 030329. Our observation combined with publicly available data sets revealed that the light curve was rich in unexpectedly complicated structures throughout ∼ 6d ays after the burst. Our early observation indicates that the light curve can be described by a single power-law model with bumps until a supernova component became dominant. The bumps superimposed on a fading trend had roughly constant amplitudes and colors. The long-lived, large-amplitude variations indicate that additional energy was supplied for the shock region. The refreshed shock scenario is most plausible. The observed slopes of the bumps during early times, however, contradict the prediction of this model.

Extensive X-ray, optical and radio observations of the bright afterglow of the Gamma Ray Burst GRB 030329 are used to construct the multi-frequency evolution of the event. The data are fitted using the standard fireball shock model to provide estimates of the initial energy, epsilon = 6.8 x 10^52 ergs sr^-1, the density of the ambient medium, n_0 = 1 cm^-3, the electron and magnetic energy density fractions, epsilon_e = 0.24 & epsilon_B = 0.0017, the power law index of the relativistic electron spectrum, p = 2.25, and the opening angle of the jet, theta_j = 3 degrees. Deviations from the standard model seen in the optical and radio are most likely attributable to the concurrent hypernova SN2003dh. Peaks at 0.23 and 1.7 days in the R-band are much brighter than expected from a standard SN, and there is a large radio excess over the expected afterglow flux for t>2 days. No deviation from the best-fit afterglow model is seen in the X-ray decline, indicating that the excess optical and radio flux from 1-5 days arises from a later injection of slower electrons by the central engine., References have been corrected; paper accepted for publication in MNRAS

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.

Past studies have suggested that long-duration gamma-ray bursts have a 'standard' energy of E(gamma) approximately 10(51) erg in the ultra-relativistic ejecta, after correcting for asymmetries in the explosion ('jets'). But a group of sub-energetic bursts, including the peculiar GRB980425 associated with the supernova SN1998bw (E(gamma) approximately 10(48) erg), has recently been identified. Here we report radio observations of GRB030329 that allow us to undertake calorimetry of the explosion. Our data require a two-component explosion: a narrow (5 degrees opening angle) ultra-relativistic component responsible for the gamma-rays and early afterglow, and a wide, mildly relativistic component that produces the radio and optical afterglow more than 1.5 days after the explosion. The total energy release, which is dominated by the wide component, is similar to that of other gamma-ray bursts, but the contribution of the gamma-rays is energetically minor. Given the firm link of GRB030329 with SN2003dh, our result indicates a common origin for cosmic explosions in which, for reasons not yet understood, the energy in the highest-velocity ejecta is extremely variable.

We report on XMM-Newton and Rossi-XTE observations of the bright (fluence $\sim$ 10$^{-4}$ erg cm$^{-2}$) and nearby (z=0.1685) Gamma-Ray Burst GRB030329 associated to SN2003dh. The first Rossi-XTE observation, 5 hours after the burst, shows a flux decreasing with time as a power law with index 0.9$\pm$0.3. Such a decay law is only marginally consistent with a further Rossi-XTE measurement (at t-t$_{GRB}\sim$30 hr). Late time observations of this bright afterglow at X-ray wavelengths have the advantage, compared to optical observations, of not being affected by contributions from the supernova and host galaxy. A first XMM-Newton observation, at t-t$_{GRB}\sim$37 days, shows a flux of 4$\times10^{-14}$ erg cm$^{-2}$ s$^{-1}$ (0.2-10 keV). The spectrum is a power law with photon index $\Gamma$=1.9 and absorption $, Comment: 5 pages, 5 figures, accepted for publication in A&A

We calculate the time evolution of the flux, apparent size, and image centroid motion of gamma-ray burst (GRB) radio jets and show that they can be resolved by the Very Long Baseline Array (VLBA) at distances of hundreds of megaparsecs. We find that GRB 030329, which showed spectroscopic evidence for an associated Type Ic supernova (SN) at a distance of ≈800 Mpc, might just be resolvable by VLBA after several months. The prospects are much better for jets that are oriented sideways in similar SNe with no GRB counterpart; in particular, the motion of the flux centroid in such jets can be detected by the VLBA up to , even when the z ∼ 1 jet cannot be resolved. If most GRBs are accompanied by a Type Ib/c SN, then there should be a few SN/GRB jets per year within a distance 200 Mpc, and most of them would be oriented sideways with no gamma-ray or X-ray precursor. Detection of these jets can be used to calibrate the fraction of all core-collapse SNe that produce relativistic outflows and determine the local GRB rate. Overall, the rate of Type Ib/c SNe that do not produce a GRB at all, but rather make relativistic radio jets with an initial Lorentz factor of a few, may be larger by up to 2 orders of magnitude than the rate of those that produce GRBs. Subject headings: gamma rays: bursts — ISM: jets and outflows — supernovae: general On-line material: color figures

Over the past five years evidence has mounted that long-duration (> 2 s) gamma-ray bursts (GRBs)--the most brilliant of all astronomical explosions--signal the collapse of massive stars in our Universe. This evidence was originally based on the probable association of one unusual GRB with a supernova, but now includes the association of GRBs with regions of massive star formation in distant galaxies, the appearance of supernova-like 'bumps' in the optical afterglow light curves of several bursts and lines of freshly synthesized elements in the spectra of a few X-ray afterglows. These observations support, but do not yet conclusively demonstrate, the idea that long-duration GRBs are associated with the deaths of massive stars, presumably arising from core collapse. Here we report evidence that a very energetic supernova (a hypernova) was temporally and spatially coincident with a GRB at redshift z = 0.1685. The timing of the supernova indicates that it exploded within a few days of the GRB, strongly suggesting that core-collapse events can give rise to GRBs, thereby favouring the 'collapsar' model., 19 pages, 3 figures

Photometric and spectroscopic data of the energetic Type Ic supernova (SN) 2002ap are presented, and the properties of the SN are investigated through models of its spectral evolution and its light curve. The SN is spectroscopically similar to the hypernova SN 1997ef. However, its kinetic energy [~(4-10) ? 1051 ergs] and the mass ejected (2.5-5 M?) are smaller, resulting in a faster evolving light curve. The SN synthesized ~0.07 M? of 56Ni, and its peak luminosity was similar to that of normal SNe. Brightness alone should not be used to define a hypernova, whose defining character, namely very broad spectral features, is the result of high kinetic energy. The likely main-sequence mass of the progenitor star was 20-25 M?, which is also lower than that of both hypernovae SN 1997ef and SN 1998bw. SN 2002ap appears to lie at the low-energy and low-mass end of the hypernova sequence as it is known so far. Observations of the nebular spectrum, which is expected to dominate by the summer of 2002, are necessary to confirm these values.

We extend our calculation of physical parameters of gamma-ray burst (GRB) jets by modeling the broadband emission of the afterglows 970508, 980519, 991208, 000926, 000418, and 010222. Together with 990123, 990510, 991216, and 000301c, there are 10 well-observed afterglows for which the initial opening angle of the GRB jet can be constrained. The jet energies (after the GRB phase) obtained for this set of afterglows are within one decade around 5 × 1050 ergs. With the exception of 000418, which requires a jet wider than rad, the jet initial half-angle in the other cases ranges from 2? to 20?. We find that in half of the cases, a homogeneous ambient medium accommodates the afterglow emission better than the windlike r-2 profile medium expected around massive stars. The two types of media give fits of comparable quality in four cases, with a wind medium providing a better description only for 970508. The circumburst densities we obtain are in the 0.1-100 cm-3 range, with the exception of 990123, for which it is below 10-2 cm-3. If in all 10 cases the observed GRB durations are a good measure of the ejecta deceleration timescale, then the parameters obtained here lead to jet Lorentz factors at the deceleration radius between 70 and 300, anticorrelated with the jet initial aperture, and jet masses around 10-6 M? . Our results on the jet energy, opening Lorentz factor, and evacuation of material until breakout provide constraints on theoretical models of GRB jets.

We present VLBI and archival Karl G. Jansky Very Large Array (VLA) and Westerbork Synthesis Radio Telescope (WSRT) observations of the radio afterglow from the gamma-ray burst (GRB) of 2003 March 29 (GRB 030329) taken between 672 and 2,032 days after the burst. The VLA and WSRT data suggest a simple power law decay in the flux at 5 GHz, with no clear signature of any rebrightening from the counter jet. We report an unresolved source at day 2,032 of size 1. 18 ± 0. 13 mas, which we use in conjunction with the expansion rate of the burst to argue for the presence of a uniform, ISM-like circumburst medium. A limit of < 0. 067 mas year−1 is placed on the proper motion, supporting the standard afterglow model for gamma-ray bursts.

We perform calorimetry on the bright gamma-ray burst (GRB) 030329 by fitting simultaneously the broadband radio afterglow and the observed afterglow image size to a semi-analytic hydrodynamics and afterglow emission model. Our semi-analytic method is valid in both the relativistic and non-relativistic regimes, and incorporates a model of the interstellar scintillation that substantially effects the broadband afterglow below 10 GHz. The model is fitted to archival measurements of the afterglow flux from 1 day to 8.3 years after the burst. Values for the initial burst parameters are determined and the nature of the circumburst medium is explored. Additionally, direct measurements of the lateral expansion rate of the radio afterglow image size allow us to estimate the initial Lorentz factor of the jet.

We present and discuss the photometric and spectroscopic evolution of the peculiar SN1998bw, associated with GRB980425, through an analysis of optical and near IR data collected at ESO-La Silla. The spectroscopic data, spanning the period from day -9 to day +376 (relative to B maximum), have shown that this SN was unprecedented, although somewhat similar to SN1997ef. Maximum expansion velocities as high as 3x10^4 km/s to some extent mask its resemblance to other Type Ic SNe. At intermediate phases, between photospheric and fully nebular, the expansion velocities (~10^4 km/s) remained exceptionally high compared to those of other recorded core-collapse SNe at a similar phase. The mild linear polarization detected at early epochs suggests the presence of asymmetry in the emitting material. The degree of asymmetry, however, cannot be decoded from these measurements alone. The HeI 1.083 mu and 2.058 mu lines are identified and He is suggested to lie in an outer region of the envelope. The temporal behavior of the fluxes and profiles of emission lines of MgI]4571A, [OI]6300,6364A and a feature ascribed to Fe are traced to stimulate future modeling work., Comment: 32 pages, 19 figures; ps file including figures at http://www.eso.org/~fpatat/sn98bw

We present the first systematic investigation of spectral properties of 17 Type Ic Supernovae (SNe Ic), 10 broad-lined SNe Ic (SNe Ic-bl) without observed Gamma-Ray Bursts (GRBs) and 11 SNe Ic-bl with GRBs (SN-GRBs) as a function of time in order to probe their explosion conditions and progenitors. We analyze a total of 407 spectra, which were drawn from published spectra of individual SNe as well as from the densely time-sampled spectra data of Modjaz et al. (2014). In order to quantify the diversity of the SN spectra as a function of SN subtype, we construct average spectra of SNe Ic, SNe Ic-bl without GRBs and SNe Ic-bl with GRBs. We find that SN 1994I is not a typical SN Ic, in contrast to common belief, while the spectra of SN 1998bw/GRB 980425 are representative of mean spectra of SNe Ic-bl. We measure the ejecta absorption and width velocities using a new method described here and find that SNe Ic-bl with GRBs, on average, have quantifiably higher absorption velocities, as well as broader line widths than SNe without observed GRBs. In addition, we search for correlations between SN-GRB spectral properties and the energies of their accompanying GRBs. Finally, we show that the absence of clear He lines in optical spectra of SNe Ic-bl, and in particular of SN-GRBs, is not due to them being too smeared out due to the high velocities present in the ejecta. This implies that the progenitor stars of SN-GRBs are probably He-free, in addition to being H-free, which puts strong constraints on the stellar evolutionary paths needed to produce such SN-GRB progenitors at the observed low metallicities., Released all code and data products on our github pages https://github.com/nyusngroup/SESNtemple and https://github.com/nyusngroup/SESNspectraLib . Accepted by ApJ. Total of 27 pages, 13 figures, 6 Tables, Appendix

Cosmic gamma-ray bursts (GRBs) have been firmly established as one of the most powerful phenomena in the Universe, releasing electromagnetic energy approaching the rest-mass energy of a neutron star in a few seconds. The two currently popular models for GRB progenitors are the coalescence of two compact objects (such as neutron stars or black holes) or collapse of a massive star. An unavoidable consequence of the latter model is that a bright supernovae should accompany the GRB. The emission from this supernova competes with the much brighter afterglow produced by the relativistic shock that gives rise to the GRB itself. Here we present evidence for an unusual light curve for GRB 980326 based on new optical observations. The transient brightened ~3 weeks after the burst to a flux sixty times larger than that extrapolated from the rapid decay seen at early time. Furthermore, the spectrum changed dramatically and became extremely red. We argue that the new source is the underlying supernova. If our hypothesis is true then this would be the first evidence for a supernova connection with GRBs at cosmological distances. We suggest that GRBs with long durations are associated with death of massive stars.

In several GRBs afterglows, rapid temporal decay is observed which is inconsistent with spherical (isotropic) blast-wave models. In particular, GRB 980519 had the most rapidly fading of the well-documented GRB afterglows, with t^{-2.05\pm 0.04} in optical as well as in X-rays. We show that such temporal decay is more consistent with the evolution of a jet after it slows down and spreads laterally, for which t^{-p} decay is expected (where p is the index of the electron energy distribution). Such a beaming model would relax the energy requirements on some of the more extreme GRBs by a factor of several hundreds. It is likely that a large fraction of the weak (or no) afterglow observations are also due to the common occurrence of beaming in GRBs, and that their jets have already transitioned to the spreading phase before the first afterglow observations were made. With this interpretation, a universal value of p~2.5 is consistent with all data.

Data accumulated over the past year strongly favour the idea that γ-ray bursts lie at cosmological distances, although the nature of the power source remains unclear. Here we report radio observations of the supernova SN1998bw, which exploded at about the same time, and in about the same direction, as the γ-ray burst GRB980425. At its peak, the supernova was unusually luminous at radio wavelengths. A simple interpretation of the data requires that the source expanded with an apparent velocity of at least twice the speed of light, indicating that the supernova was accompanied by a shock wave moving at relativistic speeds (the ejects of supernovae are typically characterized by non-relativistic velocities). The energy of the shock is at least 10^(49)erg, with an inferred ejecta mass of 10^(-5) solar masses, and we suggest that the early phase of this shock wave produced the burst of γ-rays. Although in general the properties of supernovae are very different from those of γ-ray bursts, we argue that this unusual supernova establishes a second class of γ-ray burst, which is distinctly different from the cosmological kind.

We discuss the afterglows from the evolution of both spherical and anisotropic fireballs decelerating in an inhomogeneous external medium. We consider both the radiative and adiabatic evolution regimes and analyze the physical conditions under which these regimes can be used. Afterglows may be expected to differ widely among themselves, depending on the angular anisotropy of the fireball and the properties of the environment. They may be entirely absent or may be detected without a corresponding gamma -ray event. A tabulation of different representative light curves is presented, covering a wide range of behaviors that resemble what is currently observed in the gamma -ray bursts (GRBs) GRB 970228, GRB 970508, and other objects.

Long-duration gamma-ray bursts (GRBs) are associated with type Ic supernovae that are more luminous than average and that eject material at very high velocities. Less-luminous supernovae were not hitherto known to be associated with GRBs, and therefore GRB-supernovae were thought to be rare events. Whether X-ray flashes - analogues of GRBs, but with lower luminosities and fewer gamma-rays - can also be associated with supernovae, and whether they are intrinsically 'weak' events or typical GRBs viewed off the axis of the burst, is unclear. Here we report the optical discovery and follow-up observations of the type Ic supernova SN 2006aj associated with X-ray flash XRF 060218. Supernova 2006aj is intrinsically less luminous than the GRB-supernovae, but more luminous than many supernovae not accompanied by a GRB. The ejecta velocities derived from our spectra are intermediate between these two groups, which is consistent with the weakness of both the GRB output and the supernova radio flux. Our data, combined with radio and X-ray observations, suggest that XRF 060218 is an intrinsically weak and soft event, rather than a classical GRB observed off-axis. This extends the GRB-supernova connection to X-ray flashes and fainter supernovae, implying a common origin. Events such as XRF 060218 are probably more numerous than GRB-supernovae., Final published version

We perform calorimetry on the bright gamma ray burst (GRB) 030329 by fitting simultaneously the broadband radio afterglow and the observed afterglow image size to a semi-analytic magnetohydrodynamical (MHD) and afterglow emission model. Our semi-analytic method is valid in both the relativistic and non-relativistic regimes, and incorporates a model of the interstellar scintillation that substantially effects the broadband afterglow below 10 GHz. The model is fitted to archival measurements of the afterglow flux from 1 day to 8.3 years after the burst. Values for the initial burst parameters are determined and the nature of the circumburst medium is explored. Additionally, direct measurements of the lateral expansion rate of the radio afterglow image size allow us to estimate the initial Lorentz factor of the jet., Comment: 8 pages, 4 figures. Accepted for publication by Astrophysical Journal