---
abstract: |
    We present late-time radio observations of 68 local Type Ibc supernovae, including six events with broad optical absorption lines (“hypernovae”). None of these objects exhibit radio emission attributable to off-axis gamma-ray burst jets spreading into our line-of-sight. Comparison with our afterglow models reveals the following conclusions: (1) Less than $\sim 10\%$ of Type Ibc supernovae are associated with typical gamma-ray bursts initially directed away from our line-of-sight; this places an empirical constraint on the GRB beaming factor of $\langle f_b^{-1}\rangle
    \lesssim 10^4$ corresponding to an average jet opening angle, $\theta_j \gtrsim 0.8$ degrees. (2) This holds in particular for the broad-lined supernovae (SNe 1997dq, 1997ef, 1998ey, 2002ap, 2002bl and 2003jd) which have been argued to host GRB jets. Our observations reveal no evidence for typical (or even sub-energetic) GRBs and rule out the scenario in which every broad-lined SN harbors a GRB at the $84\%$ confidence level. Their large photospheric velocities and asymmetric ejecta (inferred from spectropolarimetry and nebular spectroscopy) appear to be characteristic of the non-relativistic supernova explosion and do not necessarily imply the existence of associated GRB jets.
author:
- 'A. M. Soderberg , E. Nakar , E. Berger , S. R. Kulkarni'
title: |
    Late-time Radio Observations of 68 Type Ibc Supernovae:\
    Strong Constraints on Off-Axis Gamma-ray Bursts
---

Introduction
============

It is now generally accepted that long duration gamma-ray bursts (GRBs) give rise to engine-driven relativistic jets as well as non-relativistic spherical supernova (SN) explosions. The first example of this GRB-SN connection came with the discovery of the Type Ic supernova, SN1998bw, associated with GRB980425 ($d\sim 36$ Mpc; @gvv+98 [@paa+00]). The unusually fast photospheric velocities and exceptionally bright radio emission of SN1998bw indicated $\sim
10^{52}$ erg of kinetic energy and mildly relativistic ejecta (bulk Lorentz factor, $\Gamma\sim 3$; @kfw+98 [@imn+98; @lc99; @wes99]). In comparison with other core-collapse events ($E_{KE}\sim 10^{51}$ erg and ejecta speeds, $v\lesssim 0.1c$), SN1998bw was considered a hyper-energetic supernova (“hypernova”; @imn+98). Broad optical absorption lines were also observed in the Type Ic SNe 2003dh and 2003lw, associated with the cosmological GRBs 030329 and 031203, indicative of comparably large photospheric velocities [@mgs+03; @mtc+04]. Together, these observations appear to suggest that broad spectral features are characteristic of GRB-associated SNe.

In addition to events with prompt gamma-ray emission, the GRB-SN connection also implies the existence of “orphan” supernovae whose relativistic jets are initially beamed away from our line of sight [@rho99; @pac01]. Since the discovery of SN1998bw, several broad-lined SNe have been identified locally ($d\lesssim 100$ Mpc) and are currently estimated to represent $\sim 5\%$ of the Type Ibc supernova (SNe Ibc) population [@pmn+04]. Given their spectral similarity to the GRB-associated SNe, it has been argued that local broad-lined supernovae can be used as signposts for GRBs.

Thus, associations with poorly-localized BATSE bursts have been invoked for the broad-lined SNe 1997cy, 1997ef and 1999E [@grs+00; @tsm+00; @ww98; @min00; @rtb+03]. In addition, association with off-axis GRBs have also been claimed. In the case of SN2002ap, broad optical absorption lines and evidence for mildly asymmetric ejecta (based on spectropolarimetry measurements) were interpreted to support an off-axis GRB jet (@kji+02 [@tot03], but see @lfc+02).

More recently, an off-axis GRB model has been proposed for SN2003jd, for which photospheric velocities upward of 40,000 $\rm km~s^{-1}$ were measured at early time [@ffs03; @mck+03]. More intriguingly, late-time ($t\sim 400$ days) spectra showed double-peaked emission lines of light-elements, attributed to an asymmetric explosion [@kmd+04]. @mkm+05 argue that these observations can be understood if SN2003jd was accompanied by a highly collimated GRB jet initially directed $\sim 70$ degrees away from our line-of-sight.

Regardless of viewing angle, however, strong afterglow emission eventually becomes visible as the decelerating GRB jets spread laterally and the emission becomes effectively isotropic. As the jets spread into our line-of-sight, a rapid increase of broadband synchrotron emission is observed on a timescale of a few weeks to several years. This late-time emission is most easily detected at long wavelengths [@pl98; @low+02; @wax04]. Targeting local Type Ibc supernovae with late-time radio observations has thus become the preferred method to search for evidence of off-axis GRBs [@svw+03; @sfw04].

Using early radio observations ($t\lesssim 100$ days) we have already limited the fraction of SNe Ibc harboring on-axis (or mildly off-axis) GRBs to be $\lesssim 3\%$ [@bkf+03]. In this paper, we present late-time ($t\sim 0.5$ to 20 yr) radio observations for 68 local Type Ibc supernovae, including SN2003jd and five additional broad-lined events, making this the most comprehensive study of late-time radio emission from SNe Ibc. We use these data to constrain the SN fraction associated with GRB jets regardless of viewing angle assumptions, constraining even those initially beamed perpendicular to our line-of-sight.

Radio Observations {#sec:obs}
==================

Type Ic SN2003jd
----------------

SN2003jd was discovered on 2003 October 25.2 UT within host galaxy MCG -01-59-021 ($d_L\sim 81$ Mpc; @bsl+03). In Table \[tab:SN2003jd\] we summarize our radio observations for SN2003jd, spanning $8-569$ days after the explosion. All observations were conducted with the Very Large Array (VLA) in the standard continuum mode with a bandwidth of $2\times 50$ MHz centered at 4.86, 8.46 or 22.5 GHz. We used 3C48 and 3C147 (J0137+331 and J0542+498) for flux calibration, while J2323-032 was used to monitor the phase. Data were reduced using standard packages within the Astronomical Image Processing System (AIPS).

No radio emission was detected at the optical SN position during our early observations. Our radio limits imply that SN2003jd was a factor of $\gtrsim 100$ less luminous than SN1998bw on a comparable timescale. We conclude that SN2003jd, like the majority of SNe Ibc, did not produce relativistic ejecta along our line-of-sight.

We re-observed SN2003jd at $t\sim 1.6$ yrs to search for radio emission from an off-axis GRB jet. No emission was detected, implying a limit of $F_{\nu} < 45~\mu$Jy ($3\sigma$) at 8.46 GHz.

Late-time data on Local Type Ibc Supernovae
-------------------------------------------

We supplement these data with late-time ($t\sim 0.5-20$ year) radio observations for 67 local ($d_L\lesssim 200$ Mpc) SNe Ibc, summarized in Table \[tab:vla\]. Eleven objects were observed at moderately late-time as part of our on-going VLA program to characterize the early ($t\lesssim 100$ days) radio emission from SNe Ibc (Soderberg [*et al.*]{}, in prep). The remaining 54 objects were observed on a later timescale ($t\gtrsim 1$ year) and were taken from the VLA archive. We note that five of these supernovae (SNe 1997dq, 1997ef, 1998ey, 2002ap, 2002bl) were spectroscopically observed to have broad optical absorption lines, similar to SN1998bw.

All VLA observations were conducted at 8.46 GHz (except for SN1991D at 4.86 GHz) in the standard continuum mode with a bandwidth of $2\times 50$ MHz. Data were reduced using AIPS, and the resulting flux density measurements for this sample of SNe Ibc is given in Table \[tab:vla\]. With the exception of SN2001em, from which radio emission from the non-relativistic, spherical supernova ejecta is still detected at late-time (@sks+05 [@bb05], but see @gr04), none of the SNe Ibc show radio emission above our average detection limit of $\sim 0.15$ mJy ($3\sigma$). In comparison with SN1998bw, only SN2001em shows a comparable radio luminosity on this timescale. These results are consistent with the earlier report by @svw+03.

In Figure \[fig:lum\_limits\_oa\] we plot the radio observations for this sample of SNe Ibc, in addition to late-time radio data for SN1954A [@ecb02] and SN1984L [@sfw04].

Off-Axis Models for Gamma-ray Bursts {#sec:model}
====================================

An Analytic Approach {#sec:waxman}
--------------------

@wax04 present an analytic model for the late-time radio emission from a typical GRB viewed significantly away from the collimation axis. In this model, the GRB jet is initially characterized by a narrow opening angle, $\theta_j\sim$ few degrees, while the viewing angle is assumed to be large, $\theta_{\rm
obs}\gtrsim 1$ radian. As the jet sweeps up circumstellar material (CSM) and decelerates, it eventually undergoes a dynamical transition to sub-relativistic expansion [@fwk00]. The timescale for this non-relativistic transition is estimated at $t_{NR}\approx 0.2
(E_{51}/n_0)^{1/3}$ yr ($\approx 0.3 E_{51}/A_*$ yr) in the case of a homogeneous (wind-stratified) medium [@wax04]. Here, $E_{51}$ is the beaming-corrected ejecta energy normalized to $10^{51}$ erg and $n_0$ is the circumstellar density of the homogeneous medium (interstellar medium; ISM) normalized to 1 particle cm$^{-3}$. For a wind-stratified medium, $A_*$ defines the circumstellar density in terms of the progenitor mass loss rate, $\dot{M}$, and wind velocity, $v_w$, such that $\dot{M}/4\pi v_w=5\times 10^{11} A_*~\rm g~cm^{-1}$, and thus $A_*=1$ for $\dot{M}=10^{-5}~M_{\odot}~\rm yr^{-1}$ and $v_w=10^{3}~\rm km~s^{-1}$ [@lc99].

Once sub-relativistic, the jets spread sideways, rapidly intersecting our line-of-sight as the ejecta approach spherical symmetry. At this point the afterglow emission is effectively isotropic and appears similar to both on-axis and off-axis observers. The broadband emission observed from the sub-relativistic ejecta is described by a standard synchrotron spectrum, characterized by three break frequencies: the synchrotron self-absorption frequency, $\nu_a$, the characteristic synchrotron frequency, $\nu_m$, and the synchrotron cooling frequency, $\nu_c$. On timescales comparable to the non-relativistic transition, $\nu_a$ and $\nu_m$ are typically below the radio band while $\nu_c$ is generally near the optical [@fwk00; @bkf04; @fsk+05]. Making the usual assumption that the kinetic energy is partitioned between relativistic electrons and magnetic fields ($\epsilon_e$ and $\epsilon_B$, respectively), and that these fractions are constant throughout the evolution of the jet, @wax04 estimate the radio luminosity of the sub-relativistic, isotropic emission to be

$$\begin{aligned}
L_{\nu} & \approx & 8.0\times 10^{29} \left(\frac{\epsilon_e}{0.1}\right) \left(\frac{\epsilon_B}{0.1}\right)^{3/4} n_0^{3/4} E_{51} \\
& & \times \left(\frac{\nu}{\rm 10 GHz}\right)^{-1/2} \left(\frac{t}{t_{\rm NR}}\right)^{-9/10}~\rm erg~s^{-1}~Hz^{-1} \nonumber\end{aligned}$$

for the ISM case, while for a wind-stratified medium

$$\begin{aligned}
L_{\nu} & \approx & 2.1\times 10^{29} \left(\frac{\epsilon_e}{0.1}\right) \left(\frac{\epsilon_B}{0.1}\right)^{3/4} A_*^{9/4} E_{51}^{-1/2} \\
& & \times \left(\frac{\nu}{\rm 10 GHz}\right)^{-(p-1)/2} \left(\frac{t}{t_{\rm NR}}\right)^{-3/2}~\rm erg~s^{-1}~Hz^{-1}. \nonumber\end{aligned}$$

Here it is assumed that the electrons are accelerated into a power-law distribution, $N(\gamma) \propto \gamma^{-p}$ with $p=2.0$. These equations reveal that the strength of the non-relativistic emission is strongly dependent on the density of the circumstellar medium (especially in the case of a wind) and is best probed at low frequencies.

While this analytic model provides robust predictions for the afterglow emission at $t>t_{\rm NR}$, it does not describe the early evolution or the transition from relativistic to sub-relativistic expansion. At early time, the observed emission from an off-axis GRB is strongly dependent on the viewing angle and dynamics of the jet. To investigate this early afterglow evolution and the transition to sub-relativistic expansion, we developed a detailed semi-analytic model, described below.

A Semi-analytic Model {#sec:our_model}
---------------------

In modeling the afterglow emission from an off-axis GRB jet, we adopt the standard framework for a adiabatic blastwave expanding into either a uniform or wind stratified medium [@sar97; @gs02]. We assume a uniform, sharp-edged jet such that Lorentz factor and energy are constant over the jet surface. The hydrodynamic evolution of the jet is fully described in @onp04. As the bulk Lorentz factor of the ejecta approaches $\Gamma\sim 1$, the jets begin to spread laterally at the sound speed . Our off-axis light-curves are obtained by integrating the afterglow emission over equal arrival time surface. We note that these resulting light-curves are in broad agreement with Model 2 of @gpk+02 and are consistent with Waxman’s analytic model (§\[sec:waxman\]) on timescales, $t\gtrsim t_{\rm NR}$.

Over-plotted in Figure \[fig:lum\_limits\_oa\] are our off-axis models calculated for both wind-stratified and homogeneous media at an observing frequency of $\nu_{\rm obs}=8.46$ GHz. We assume standard GRB parameters of $E_{51}=A_*=n=1$, $\epsilon_B=\epsilon_e=0.1$, $p=2.2$ and $\theta_j=5^{\rm o}$, consistent with the typical values inferred from broadband modeling of GRBs [@pk02; @yhs+03; @clf04]. We compute model light-curves for off-axis viewing angles between 30 and 90 degrees. As clearly shown in the figure, the majority of our late-time SNe Ibc limits are significantly fainter than [*all*]{} of the model light-curves, constraining even the extreme case where $\theta_{\rm obs}=90^{\rm o}$.

SN2003jd: Constraints on the off-axis jet {#sec:SN2003jd}
=========================================

Based on the double-peaked profiles observed for the nebular lines of neutral oxygen and magnesium, @mkm+05 argue that SN2003jd was an aspherical, axisymmetric explosion viewed near the equatorial plane. They suggest that this asymmetry may be explained if the SN explosion was accompanied by a tightly collimated and relativistic GRB jet, initially directed $\sim 70$ degrees from our line-of-sight. This hypothesis is consistent with the observed lack of prompt gamma-ray emission [@hcm+03] as well as the absence of strong radio and X-ray emission at early time [@skf03; @wpr+03].

Our radio observation of SN2003jd at $t\sim 1.6$ years imposes strong constraints on the putative off-axis GRB jet. While the early data constrain only mildly off-axis jets ($\theta_{\rm obs}\lesssim
30^{\rm o}$), our late-time epoch constrains even those jets initially directed perpendicular to our line-of-sight. As shown in Figure \[fig:lum\_limits\_oa\], our radio limit is a factor of $\gtrsim 200$ ($\gtrsim 20$) fainter than that predicted for a typical GRB expanding into a homogeneous (wind-stratified) medium, even in the extreme case where $\theta_{\rm obs}\sim 90^{\rm o}$. Given the assumption of typical GRB parameters, we conclude that our late-time radio limit is inconsistent with the presence of an off-axis GRB jet. We note that the model assumptions and physical parameters of our off-axis afterglow light-curves are identical to those adopted by @mkm+05.

We next explore the range of parameters ruled out by our deep radio limits. As shown in Equations 1 and 2, the luminosity of the late-time emission is a function of the ejecta energy, the density of the circumstellar medium and the equipartition fractions. To investigate the effect of energy and density on the late-time radio luminosity, we fix the equipartition fractions to $\epsilon_e=\epsilon_B=0.1$, chosen to be consistent with the values typically inferred from afterglow modeling of cosmological GRBs [@pk02; @yhs+03]. In Figure \[fig:SN2003jd\_ed\], we illustrate how each radio epoch for SN2003jd maps to a curve within the two-dimensional parameter space of kinetic energy and circumstellar density for an off-axis GRB. Here we adopt our semi-analytic model (§\[sec:our\_model\]) for a wind-stratified medium, along with a typical electron index of $p=2.2$ and a viewing angle of $\theta_{\rm obs}=90^{\rm o}$; the faintest model for a given set of equipartition fractions. By comparing the luminosity limit for SN2003jd at a particular epoch with the off-axis model prediction for that time, we exclude the region of parameter space [ *rightward*]{} of the curve since this region produces a jet which is [*brighter*]{} than the observed limit. The union of these regions represents the total parameter space ruled out for an associated GRB. As shown in this figure, the total excluded parameter space extends from $A_*\gtrsim 0.03$ and $E \sim 10^{47}$ to $10^{52}$.

We compare these constraints with the beaming-corrected kinetic energies and CSM densities for 18 cosmological GRBs (Table \[tab:grb\]). Here we make the rough approximation that $A_*\approx n_0$; a reasonable assumption for circumstellar radii near $\sim 10^{18}$ cm. As shown in Figure \[fig:SN2003jd\_ed\], these GRBs span the region of parameter space roughly bracketed by $A_*\sim
0.002$ to 100 and $E\sim 2\times 10^{49}$ to $4\times 10^{51}$. The majority of the bursts (13 out of 18) fall within the excluded region of parameter space for SN2003jd. We conclude that SN2003jd was not likely associated with a typical GRB at a confidence level of $\sim 72\%$.

Local Type Ibc Supernovae: Further Constraints {#sec:SNe}
==============================================

While physical parameters atypical of the cosmological GRB population can be invoked to hide an off-axis GRB for SN2003jd, it is exceedingly unlikely for atypical parameters to dominate a large statistical sample of SNe Ibc. Motivated thus, we searched for off-axis GRBs in the 67 local Type Ibc SNe for which we have compiled late-time ($t\sim 0.5-30$ yr) radio observations. Applying the method described in §\[sec:SN2003jd\] we produce exclusion regions in the $E_{51}-A_*$ parameter space for each SN. Figure \[fig:all\_ed\] shows the resulting contours for all 68 SNe, including SN2003jd and five broad-lined events. For the twenty SNe with early radio limits [@bkf+03; @bkc02] we combine late- and early-time data to provide further constraints.

In Figure \[fig:confidence\_ed\] we compile all 68 exclusion regions to quantify the $E_{51}-A_*$ parameter space constrained by this statistical sample. Contours map the regions excluded by incremental fractions of our sample. As in the case of SN2003jd, all curves rule out bursts with $A_*\gtrsim 1$ and $E\gtrsim 10^{50}$ erg. Moreover, 50% exclude $A_* \gtrsim 0.1$ and $E \gtrsim 10^{49}$ erg. For comparison, the mean ejecta energy and CSM density values for cosmological GRBs are $E \approx 4.4\times 10^{50}$ erg and $A_*=n_0\approx 1.2$.

Focusing on the subsample of broad-lined SNe, we emphasize that our deep limits rule out both putative GRB jets directed along our line-of-sight (e.g. SN1997ef) as well as those which are initially beamed off-axis (e.g. SN2002ap and SN2003jd). In particular, the large exclusion region for SN2002ap (see Figure \[fig:all\_ed\]) implies that an extremely low CSM density, less than $A_*\sim 3\times
10^{-3}$, is needed to suppress the emission from an associated GRB. This is a factor of $\sim 10$ below the density inferred from modeling of the early radio emission [@bkc02] and we therefore conclude that an off-axis GRB model is inconsistent with our late-time observations of SN2002ap. In Figure \[fig:confidence\_ed\] we show that this entire sample of six broad-lined SNe rule out bursts with energies $E\gtrsim 10^{49}$ erg, and 50% even rule out $E\sim 10^{47}$ erg (all assuming a typical $A_*=1$).

We next address the limits on an association with GRBs defined by the cosmological sample (Table \[tab:grb\]). For each SN in our sample we calculate the fraction of observed GRBs that lie in its exclusion region. We then determine the probability of finding null-detections for our entire sample by calculating the product of the individual probabilities. We find that the probability that [*every*]{} Type Ibc supernova has an associated GRB is $1.1\times 10^{-10}$. We further rule out a scenario in which one in ten SNe Ibc is associated with a GRB at a confidence level of $\sim 90\%$. For the broad-lined events alone we rule out the scenario that every event is associated with a GRB at a confidence level of $\sim 84\%$. Confidence levels are shown as a function of GRB/SN fraction in Figure \[fig:binomial\_prob\].

Discussion and Conclusions {#sec:disc}
==========================

We present late-time radio observations for 68 local Type Ibc supernovae, including six broad-lined SNe (“hypernovae”), making this the most comprehensive study of late-time radio emission from SNe Ibc. None of these objects show evidence for bright, late-time radio emission that could be attributed to off-axis jets coming into our line-of-sight. Comparison with our most conservative off-axis GRB afterglow models reveals the following conclusions:

\(1) Less than $\sim 10\%$ of Type Ibc supernovae are associated with GRBs. These data impose an empirical constraint on the GRB beaming factor, $\langle f_b^{-1}\rangle$, where $f_b=(1-{\rm cos}~\theta_j)$. Assuming a local GRB rate of $\sim 0.5~\rm Gpc^{-3}~yr^{-1}$ [@sch01; @psf03; @gpw05] and an observed SNe Ibc rate of $\sim
4.8\times 10^{4}~\rm Gpc^{-3}~yr^{-1}$ [@mdp+98; @cet99; @frp+99], we constrain the GRB beaming factor to be $\langle
f_b^{-1}\rangle\lesssim \times 10^{4}$. Adopting a lower limit of $\langle f_b^{-1}\rangle > 13$ [@low+02], the beaming factor is now observationally bound by $\langle f_b^{-1}\rangle\approx
[13-10^4]$, consistent with the observed distribution of jet opening angles [@fks+01; @gpw05].

\(2) Despite predictions that most or all broad-lined SNe Ibc harbor GRB jets [@pmn+04], our radio observations for six broad-lined events (SNe 1997dq, 1997ef, 1998ey, 2002ap, 2002bl and 2003jd) reveal no evidence for association with typical (or even sub-energetic) GRBs. While unusual physical parameters can suppress the radio emission from off-axis jets in any one SN, it is unlikely that all six broad-lined events host atypical GRBs. We observationally rule out the scenario in which every broad-lined SN harbors GRB jets with a confidence level of $\sim 84\%$.

\(3) While low CSM densities (e.g. $A_* \lesssim 0.1$) can suppress the emission from off-axis GRB jets, such values are inconsistent with the mass loss rates measured from local Wolf-Rayet stars ($0.6-9.5\times 10^{-5}~\rm M_{\odot}~yr^{-1}$; @cgv04), thought to be the progenitors of long-duration gamma-ray bursts.

\(4) While we have so far considered only the signature from a highly collimated GRB jet, these late-time radio data also impose constraints on the presence of broader jets and/or jet cocoons. As demonstrated by GRBs 980425 and 030329, the fraction of energy coupled to mildly relativistic and mildly collimated ejecta can dominate the total relativistic energy budget [@kfw+98; @bkp+03]. Less sensitive to to the effects of beaming and viewing geometry, broad jets are more easily probed at early time ($t\sim 100$ days) when the emission is brightest. Still, we note that the majority of our late-time radio limits are significantly fainter than GRBs 980425 and 030329 on a comparable timescale, thus constraining even mildly relativistic ejecta.

These conclusions, taken together with the broad spectral features observed for GRB-associated SNe 1998bw, 2003dh and 2003lw, motivate the question: what is the connection between GRBs and local Type Ibc supernovae? While current optical data suggest that all GRB-SNe are broad-lined, our late-time radio observations clearly show that the inverse is [*not*]{} true: broad optical absorption lines do not serve as a reliable proxy for relativistic ejecta. This suggests that their observed large photospheric velocities and asymmetric ejecta are often merely characteristics of the non-relativistic SN explosion and thus manifestations of the diversity within SNe Ibc.

The authors thank Doug Leonard, Paolo Mazzali, Dale Frail, Brian Schmidt and Avishay Gal-Yam for helpful discussions. As always, the authors thank Jochen Greiner for maintaining his GRB page. A.M.S. is supported by the NASA Graduate Student Research Program. E.B. is supported by NASA through Hubble Fellowship grant HST-HF-01171.01 awarded by the STScI, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS 5-26555.

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[lrrrr]{} 2003 Oct 29 & 8 & $\pm 52$ & $\pm 34$ & $\pm 58$\
2003 Nov 4 & 14 & & $\pm 77$ &\
2003 Nov 15 & 25 & & $\pm 74$ &\
2005 May 12 & 569 & & $\pm 15$ &\
\[tab:SN2003jd\]

[llrcclrr]{} 1983N & NGC 5236 & 7.2 & 1983 Jun 26 & 3835 & 2003 Oct 17 & 7416 & $\pm 124$\
1985F & NGC 4618 & 7.7 & 1985 May 14 & 4042 & 2003 Oct 17 & 6730 & $\pm 37$\
1987M & NGC 2715 & 18.9 & 1987 Aug 31 & 4451 & 2003 Oct 17 & 5891 & $\pm 34$\
1990B & NGC 4568 & 32.0 & 1989 Dec 23-1990 Jan 20 & 4949 & 2003 Oct 17 & 5032 & $\pm 24$\
1990U & NGC 7479 & 33.7 & 1990 Jun 28-Jul 27 & 5063 & 2003 Oct 17 & 4845 & $\pm 44$\
1991A & IC 2973 & 45.5 & 1990 Dec 6-13 & 5178 & 2003 Oct 17 & 4695 & $\pm 35$\
1991D & Anon. & 173 & 1991 Jan 16 & 5153 & 1992 Oct 11 & 633 & $\pm 49$\
1991N & NGC 3310 & 14.0 & 1991 Feb 20-Mar 29 & 5227 & 2003 Oct 17 & 4604 & $\pm 59$\
1991ar & IC 49 & 65.0 & 1991 Aug 3 & 5334 & 2003 Oct 17 & 4458 & $\pm 30$\
1994I & NGC 5194 & 6.5 & 1994 Apr 1-2 & 5961 & 2003 Oct 17 & 3486 & $\pm 42$\
1994ai & NGC 908 & 21.3 & 1994 Dec 8-16 & 6120 & 2003 Oct 17 & 3336 & $\pm 40$\
1996D & NGC 1614 & 68.1 & 1996 Jan 28 & 6317 & 2003 Oct 15 & 2818 & $\pm 153$\
1996N & NGC 1398 & 19.7 & 1996 Feb 16-Mar 13 & 6351 & 2003 Oct 15 & 2787 & $\pm 36$\
1996aq & NGC 5584 & 23.2 & 1996 Jul 30 & 6465 & 2003 Oct 17 & 2635 & $\pm 32$\
1997B & IC 438 & 44.3 & 1996 Dec 14 & 6535 & 2003 Oct 15 & 2498 & $\pm 33$\
1997C & NGC 3160 & 99.2 & 1996 Dec 18-1997 Jan 14 & 6536 & 2003 Oct 17 & 2481 & $\pm 37$\
1997X & NGC 4691 & 15.7 & 1997 Jan 16-Feb 2 & 6552 & 2003 Oct 17 & 2457 & $\pm 22$\
1997dc & NGC 7678 & 49.6 & 1997 Jul 22 & 6715 & 2003 Oct 17 & 2278 & $\pm 36$\
1997dq & NGC 3810 & 14.0 & 1997 Oct 16 & 6770 & 2003 Oct 17 & 2192 & $\pm 30$\
1997ef & UGC 4107 & 49.8 & 1997 Nov 16-26 & 6778 & 2003 Oct 17 & 2156 & $\pm 33$\
1998T & NGC 3690 & 44.3 & 1998 Feb 8-Mar 3 & 6830 & 2003 Oct 17 & 2066 & $\pm 482$\
1998ey & NGC 7080 & 69.0 & 1998 Nov 1-Dec 5 & 6830 & 2003 Oct 17 & 1794 & $\pm 32$\
1999bc & UGC 4433 & 90.2 & 1999 Jan 30 & 7133 & 2003 Oct 15 & 1721 & $\pm 25$\
1999di & NGC 776 & 70.2 & 1999 Jul 6 & 7234 & 2003 Oct 17 & 1564 & $\pm 35$\
1999dn & NGC 7714 & 39.7 & 1999 Aug 10-20 & 7241 & 2003 Oct 17 & 1524 & $\pm 42$\
1999ec & NGC 2207 & 38.9 & 1999 Aug 24 & 7268 & 2003 Oct 15 & 1515 & $\pm 45$\
1999eh & NGC 2770 & 27.6 & 1999 Jul 26 & 7282 & 2003 Oct 17 & 1544 & $\pm 19$\
2000C & NGC 2415 & 53.8 & 1999 Dec 30-2000 Jan 4 & 7348 & 2003 Oct 17 & 1385 & $\pm 35$\
2000F & IC 302 & 84.5 & 1999 Dec 30-2000 Jan 10 & 7353 & 2003 Oct 15 & 1383 & $\pm 26$\
2000S & MCG -01-27-2 & 85.8 & 1999 Oct 9 & 7384 & 2003 Oct 17 & 1469 & $\pm 30$\
2000de & NGC 4384 & 35.6 & 2000 Jul 13 & 7478 & 2003 Oct 17 & 1191 & $\pm 40$\
2000ds & NGC 2768 & 19.4 & 2000 May 28 & 7507 & 2003 Oct 17 & 1237 & $\pm 34$\
2000dv & UGC 4671 & 57.7 & 2000 Jul 4 & 7510 & 2003 Oct 17 & 1200 & $\pm 32$\
2001B & IC 391 & 22.0 & 2000 Dec 25-2001 Jan 4 & 7555 & 2003 Oct 15 & 1021 & $\pm 30$\
2001M & NGC 3240 & 50.6 & 2001 Jan 3-21 & 7568 & 2003 Oct 17 & 1008 & $\pm 54$\
2001bb & IC 4319 & 66.3 & 2001 Apr 15-29 & 7614 & 2003 Oct 17 & 908 & $\pm 35$\
2001ch & MCG -01-54-1 & 41.6 & 2001 Mar 23 & 7637 & 2003 Oct 17 & 938 & $\pm 32$\
2001ci & NGC 3079 & 15.8 & 2001 Apr 17-25 & 7638 & 2003 Oct 17 & 909 & $\pm 188$\
2001ef & IC 381 & 35.1 & 2001 Aug 29-Sep 9 & 7710 & 2003 Oct 17 & 774 & $\pm 33$\
2001ej & UGC 3829 & 57.4 & 2001 Aug 30 & 7719 & 2003 Oct 15 & 778 & $\pm 36$\
2001em & UGC 11794 & 83.6 & 2001 Sep 10-15 & 7722 & 2003 Oct 17 & 765 & $907\pm 58$\
2001is & NGC 1961 & 56.0 & 2001 Dec 14-23 & 7782 & 2003 Oct 15 & 668 & $\pm 31$\
2002J & NGC 3464 & 53.0 & 2002 Jan 15-21 & 7800 & 2003 Oct 17 & 637 & $\pm 23$\
2002ap & NGC 628 & 9.3 & 2002 Jan 28-29 & 7810 & 2003 Oct 17 & 626 & $\pm 29$\
2002bl & UGC 5499 & 67.8 & 2002 Jan 31 & 7845 & 2003 Oct 17 & 624 & $\pm 39$\
2002bm & MCG -01-32-1 & 78.0 & 2002 Jan 16-Mar 6 & 7845 & 2003 Oct 17 & 630 & $\pm 39$\
2002cp & NGC 3074 & 73.4 & 2002 Apr 11-28 & 7887 & 2003 Oct 17 & 547 & $\pm 29$\
2002hf & MCG -05-3-20 & 80.2 & 2002 Oct 22-29 & 8004 & 2003 Oct 17 & 357 & $\pm 48$\
2002ho & NGC 4210 & 38.8 & 2002 Sep 24 & 8011 & 2003 Oct 17 & 389 & $\pm 35$\
2002hy & NGC 3464 & 53.0 & 2002 Oct 13-Nov 12 & 8016 & 2003 Oct 17 & 354 & $\pm 23$\
2002hz & UGC 12044 & 77.8 & 2002 Nov 2-12 & 8017 & 2003 Oct 17 & 344 & $\pm 29$\
2002ji & NGC 3655 & 20.8 & 2002 Oct 20 & 8025 & 2003 Oct 17 & 362 & $\pm 18$\
2002jj & IC 340 & 60.1 & 2002 Oct 22 & 8026 & 2003 Oct 15 & 360 & $\pm 30$\
2002jp & NGC 3313 & 52.7 & 2002 Oct 20 & 8031 & 2003 Oct 17 & 362 & $\pm 37$\
2003A & UGC 5904 & 94.4 & 2002 Nov 23-2003 Jan 5 & 8041 & 2003 Jun 15 & 182 & $\pm 69$\
2003I & IC 2481 & 76.0 & 2002 Dec 14 & 8046 & 2003 Jun 15 & 183 & $\pm 60$\
2003aa & NGC 3367 & 43.1 & 2003 Jan 24-31 & 8063 & 2003 Jun 15 & 138 & $\pm 70$\
2003bm & UGC 4226 & 113.7 & 2003 Feb 20-Mar 3 & 8086 & 2003 Jun 15 & 109 & $\pm 57$\
2003bu & NGC 5393 & 86.1 & 2003 Feb 10-Mar 11 & 8092 & 2003 Jun 15 & 110 & $\pm 71$\
2003cr & UGC 9639 & 155.2 & 2003 Feb 24-Mar 31 & 8103 & 2003 Nov 2 & 233 & $\pm 59$\
2003dg & UGC 6934 & 79.1 & 2003 Mar 24-Apr 8 & 8113 & 2003 Nov 2 & 215 & $\pm 90$\
2003dr & NGC 5714 & 31.7 & 2003 Apr 8-12 & 8117 & 2003 Nov 2 & 206 & $\pm 58$\
2003ds & NGC 3191 & 132.9 & 2003 Mar 25-Apr 14 & 8120 & 2003 Nov 2 & 212 & $\pm 67$\
2003el & NGC 5000 & 80.2 & 2003 Apr 19-May 22 & 8135 & 2003 Nov 2 & 180 & $\pm 65$\
2003ev & Anonymous & 103.3 & 2003 Apr 9-Jun 1 & 8140 & 2003 Nov 2 & 180 & $\pm 61$\
2003jd & MCG -01-59-21 & 80.8 & 2003 Oct 16-25 & 8232 & 2005 May 12 & 569 & $\pm 15$\
. . \[tab:vla\]

[lrrrcc]{} 970508 & 0.835 & $2.4^{+1.4}_{-0.9}$ & $2.4^{+1.4}_{-0.9}$ & ISM & 1\
980329 & $\lesssim 3.9$ & $1.1^{+0.26}_{-0.46}$ & $20^{+10}_{-10}$ & ISM & 2\
980425 & 0.0085 & 0.012 & 0.04 & Wind & 3\
980519 & 1 & $0.41^{+0.48}_{-0.14}$ & $0.14^{+0.48}_{-0.14}$ & ISM & 4\
980703 & 0.966 & $3.5^{+1.26}_{-0.42}$ & $28^{+8}_{-6}$ & ISM & 2\
990123 & 1.60 & $0.15^{+0.33}_{-0.04}$ & $0.0019^{+0.0005}_{-0.0015}$ & ISM & 4\
990510 & 1.619 & $0.14^{0.49}_{-0.05}$ & $0.29^{+0.11}_{-0.15}$ & ISM & 4\
991208 & 0.706 & $0.24^{+0.28}_{-0.22}$ & $18^{+22}_{-6}$ & ISM & 4\
991216 & 1.02 & $0.11^{+0.1}_{-0.04}$ & $4.7^{+6.8}_{-1.8}$ & ISM & 4\
000301c & 2.03 & $0.33^{+0.03}_{-0.05}$ & $27^{+5}_{-5}$ & ISM & 4\
000418 & 1.118 & 3.4 & 0.02 & ISM & 5\
000926 & 2.066 & $2.0^{+0.34}_{-0.2}$ & $16^{+6}_{-6}$ & ISM & 2\
010222 & 1.477 & 0.51 & 1.7 & ISM & 4\
011121 & 0.36 & 0.2 & 0.015 & Wind & 6\
020405 & 0.69 & 0.3 & $\lesssim 0.07$ & Wind & 6\
020903 & 0.251 & 0.4 & 100 & ISM & 7\
030329 & 0.168 & 0.67 & 3.0 & ISM & 8\
031203 & 0.105 & 0.017 & 0.6 & ISM & 9\
\[tab:grb\]
