A tale of two GRB-SNe at a common redshift of z=0.54

We present early-time ground-based optical follow-up observations of GRB 180418A, which was discovered by both Swift/BAT and Fermi/GBM. Its broadband afterglow was well monitored by Swift/XRT and ground-based optical telescopes. The optical light curve of GRB 180418A can be modeled by forward shock (FS) plus reverse shock (RS). We fit the light curves with standard external shock models and derive the physical properties of the outflow. It is found that the ratio R B ≡ ε B,r /ε B,f is 11.22, indicating a moderate degree of magnetization in the RS region. The reported duration of GRB 180418A, T 90, lies in the intermediate region between short and long gamma-ray bursts (GRBs). We further discuss the classification of GRB 180418A, and calculate ε = E γ,iso,52/E p,z,2 values of 0.026 and 0.018 (assuming the redshift z is 1.0 and 1.5, respectively), which is closer to short GRBs (SGRBs) in the ε-T 90,z plane. If GRB 180418A is an SGRB, it is the only reported SGRB thus far with RS emission in optical light curves. In order to compare the properties of GRB 180418A, we collected three SGRBs that may have RS emission (GRBs 060313, 090426, and 210207B) and also 22 long GRBs (LGRBs) with RS emission. We find that the parameters of LGRBs are in a wider range than those of SGRBs. Also, SGRBs appear to have very small R B values, but the results are generally similar to those of LGRBs. The fitting parameters of GRB 180418A are generally consistent with those of the other three SGRBs, implying that GRB 180418A may belong to the category of SGRBs.

Astronomy & Astrophysics manuscript no. (will be inserted by hand later) arXiv:astro-ph/0504050v1 3 Apr 2005 A possible bright blue SN in the afterglow of GRB 020305 ⋆ J. Gorosabel 1,2 , J.P.U. Fynbo 3 , A. Fruchter 2 , A. Levan 4 , J. Hjorth 3 , P. Nugent 5 , A.J. Castro-Tirado 1 , J.M. Castro Cer´on 2,3 , J. Rhoads 2 , D. Bersier 2 , and I. Burud 2 Instituto de Astrof´isica de Andaluc´ia (IAA-CSIC), P.O. Box 03004, E-18080 Granada, Spain Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, DK-2100 Kobenhavn O, Denmark Department of Physics and Astronomy, University of Leicester, University Road, Leicester, LE1 7RH, UK Lawrence Berkeley National Laboratory, MS 50-F, 1 Cyclotron Road, Berkeley, CA 94720, USA Received ; accepted Abstract. We report on ground-based and HST(+STIS) imaging of the afterglow and host galaxy of the Gamma-Ray Burst (GRB) of March 5 2002. The GRB occurred in a R = 25.17 ± 0.14 galaxy, which apparently is part of an interacting system. The lightcurve of the optical afterglow shows a rebrightening, or at least a plateau, 12–16 days after the gamma-ray event. U BV RIK ′ multi-band imaging of the afterglow ∼12 days after the GRB reveals a blue spectral energy distribution (SED). The SED is consistent with a power-law with a spectral index of β = −0.63 ± 0.16, but there is tentative evidence for deviations away from a power-law. Unfortunately, a spectroscopic redshift has not been secured for GRB 020305. From the SED we impose a redshift upper limit of z . 2.8, hence excluding the pseudo redshift of 4.6 reported for this burst. We discuss the possibilities for explaining the lightcurve, SED and host galaxy properties for GRB 020305. The most natural interpretation of the lightcurve and the SED is an associated supernova (SN). Our data can not precisely determine the redshift of the GRB. The most favoured explanation is a low redshift (z ∼ 0.2) SN, but a higher redshift (z & 0.5) SN can not be excluded. We also discuss less likely scenarios not based on SNe, like a burst occurring in a z = 2.5 galaxy with an extinction curve similar to that of the Milky Way. Key words. gamma rays: bursts – techniques: photometric 1. Introduction For long duration GRBs the relation with supernovae (SNe) became firmly established with the discovery of the type Ic su- pernova SN 2003dh associated with GRB 030329 (Stanek et al. 2003; Hjorth et al. 2003). This result lends strong support to the collapsar model (Woosley 1993), but a SN is also an ingredient in other models (e.g. Dado et al. 2003; Fryer & Heger 2004). However, the associated SNe follow a broad distribution of op- tical luminosities (Zeh et al. 2004). Furthermore the connection of GRBs with SNe of other types than Ic can not be excluded, motivated by the two possible associations of GRBs and II type SNe (SN 1997cy, Germany et al. 2000; SN 1999E, Rigon et al. 2003). Therefore, the afterglow lightcurves and SEDs around the SN peak are far from being described by an universal SN template. In this study we present ground and space-based opti- cal observations of GRB 020305 carried out from 11.5 to 321.2 days after the burst. Send offprint requests to: J. Gorosabel Based on observations made with the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden. Correspondence to: jgu@iaa.es GRB 020305 was localised by the HETE-II satellite on March 5.4968 UT (Ricker et al. 2002). The high-energy emis- sion as seen by the Interplanetary network (IPN) consisted in two broad pulses, with a total GRB duration of ∼280s (Hurley et al. 2002), placing it in the long-soft burst category. Price et al. (2002) reported the presence of a transient optical source in the HETE-II/IPN error box in images taken ∼20 hours after the GRB. Further imaging confirmed the fading behaviour of the candidate (Lee et al. 2002; Ohyama et al. 2002). The paper is structured as follows: Sect. 2 details the ob- servations and the data reduction, Sect. 3 reports the results on the SED, lightcurve and host galaxy, Sect. 4 discusses several interpretations of the results, and finally Sect. 5 draws the con- clusions of this study. 2. Observations and data reduction 2.1. NOT observations We observed the field of GRB 020305 from the ground with the 2.56-m Nordic Optical Telescope (NOT) on 2002 March 16.95–22.18 UT, i.e. 11.45–16.68 days after the GRB. The in- strument used was the Andaluc´ia Faint Object Spectrograph (ALFOSC) equipped with a 2048 2 pixel Loral CCD having a

XRF 030723 is the first X-ray flash (XRF) to show in its optical light curve (LC) a bump that has been interpreted as the signature of a supernova (SN). After subtracting the afterglow component from the observed optical LC of the XRF counterpart, the properties of the putative SN are constrained by means of synthetic LCs of core-collapse SNe. For the redshift range $z \sim 0.3$ -- 1, all possible models require a rather small mass of synthesized \Nifs, i.e. $M$(\Nifs) $\sim$ 0.01 -- 0.3 $\Msun$. The models used to describe the energetic SNe Ic associated with gamma-ray bursts (SNe 1998bw and 2003dh) are too massive for the observed LC. If the relation between ejected \Nifs mass and total ejecta mass established from models of various Type Ic SNe also holds for the putative SN in XRF 030723, the ejecta mass is constrained to be $\sim$ 1 -- 3 $\Msun$ and the kinetic energy $\lsim 1\times 10^{52}$ erg. This corresponds to a progenitor with $15\Msun \lesssim M_{\rm MS}\lesssim 25\Msun$. The SN therefore appears to have properties intermediate between a normal SN Ic like SN 1994I and a more energetic object like SN 2002ap.

GRB 060614 is a remarkable gamma-ray burst (GRB) observed by Swift with puzzling properties, which challenge current progenitor models. In particular, the lack of any bright supernova (SN) down to very strict limits and the vanishing spectral lags during the whole burst are typical of short GRBs, strikingly at odds with the long (102 s) duration of this event. Here we present detailed spectral and temporal analysis of the Swift observations of GRB 060614. We show that the burst presents standard optical, ultraviolet and X-ray afterglows, detected beginning 4 ks after the trigger. An achromatic break is observed simultaneously in the optical and X-ray bands, at a time consistent with the break in the R-band light curve measured by the VLT. The achromatic behaviour and the consistent postbreak decay slopes make GRB 060614 one of the best examples of a jet break for a Swift burst. The optical and ultraviolet afterglow light curves have also an earlier break at 29.7 ± 4.4 ks, marginally consistent with a corresponding break at 36.6 ± 2.4 ks observed in the X-rays. In the optical, there is strong spectral evolution around this break, suggesting the passage of a break frequency through the optical/ultraviolet band. The very blue spectrum at early times suggests this may be the injection frequency, as also supported by the trend in the light curves: rising at low frequencies, and decaying at higher energies. The early X-ray light curve (from 97 to 480 s) is well interpreted as the X-ray counterpart of the burst extended emission. Spectral analysis of the BAT and XRT data in the ∼80 s overlap time interval show that the peak energy of the burst has decreased to as low as 8 keV at the beginning of the XRT observation. Spectral analysis of following XRT data shows that the peak energy of the burst continues to decrease through the XRT energy band and exits it at about 500 s after the trigger. The average peak energy Ep of the burst is likely below the BAT energy band (<24 keV at the 90% confidence level) but larger than 8 keV. The initial group of peaks observed by BAT (∼5 s) is however distinctly harder than the rest of the prompt emission, with a peak energy of about 300 keV as measured by Konus Wind. Considering the time-averaged spectral properties, GRB 060614 is consistent with the Eiso − E rest , Eγ − E rest ,a ndLp,iso − E rest correlations.

We present optical, radio, and X-ray observations of SN 2020bvc (=ASASSN-20bs, ZTF 20aalxlis), a nearby ( z = 0.0252 ; d = 114 Mpc) broad-line (BL) Type Ic supernova (SN) and the first double-peaked Ic-BL discovered without a gamma-ray burst (GRB) trigger. Our observations show that SN 2020bvc shares several properties in common with the Ic-BL SN 2006aj, which was associated with the low-luminosity gamma-ray burst (LLGRB) 060218. First, the 10 GHz radio luminosity ( L radio ≈ 10 37 erg s − 1 ) is brighter than ordinary core-collapse SNe but fainter than LLGRB SNe such as SN 1998bw (associated with LLGRB 980425). We model our VLA observations (spanning 13–43 days) as synchrotron emission from a mildly relativistic (v ≳ 0.3c) forward shock. Second, with Swift and Chandra, we detect X-ray emission (L X ≈ 1041 erg s − 1 ) that is not naturally explained as inverse Compton emission or part of the same synchrotron spectrum as the radio emission. Third, high-cadence (6× night–1) data from the Zwicky Transient Facility (ZTF) show a double-peaked optical light curve, the first peak from shock cooling of extended low-mass material (mass M e &lt; 10 − 2 M ⊙ at radius R e &gt; 1012 cm) and the second peak from the radioactive decay of 56 Ni . SN 2020bvc is the first double-peaked Ic-BL SN discovered without a GRB trigger, so it is noteworthy that it shows X-ray and radio emission similar to LLGRB SNe. For four of the five other nearby (z ≲ 0.05) Ic-BL SNe with ZTF high-cadence data, we rule out a first peak like that seen in SN 2006aj and SN 2020bvc, i.e., that lasts ≈1 day and reaches a peak luminosity M ≈ −18. Follow-up X-ray and radio observations of Ic-BL SNe with well-sampled early optical light curves will establish whether double-peaked optical light curves are indeed predictive of LLGRB-like X-ray and radio emission.

Context. More than 60 broad-lined type Ic (Ic-BL) supernovae (SNe) are associated with a long gamma-ray burst (GRB). However, many type Ic-BL SNe exhibit no sign of an associated GRB. On average, the expansion velocities of GRB-associated type Ic-BL SNe (GRB-SNe) are greater than those of type Ic-BL SNe without an associated GRB. It has been proposed that this is the result of energy transfer between the ultra-relativistic GRB jet and the SN ejecta. However, this cannot fully explain the discrepancy, as some type Ic-BL SNe without a GRB detection (ordinary type Ic-BL SNe) may also harbour GRB jets. Aims. This work presents the largest spectroscopic sample of type Ic-BL SNe with and without GRBs to date, consisting of 61 ordinary type Ic-BL SNe and 13 GRB-SNe, comprising a total of 875 spectra. The goal of this work is to compare the evolution of SN expansion velocities in cases where an ultra-relativistic jet has been launched (GRB-SNe) and cases where no GRB jet is inferred from observations (ordinary type Ic-BL SNe). This will help us understand whether the presence of the jet affects the evolution of the expansion velocity, possibly allowing us to infer the existence of jets in cases where GRB emission is not detected. Methods. We measured the expansion velocities of the Fe II [5169 Å] and Si II [6355 Å] features observed in the spectra of type Ic-BL SNe using a spline fitting method. We fit the expansion velocity evolution with single and broken power laws. In each analysis, we compared two populations: ordinary type Ic-BL SNe and GRB-SNe. Results. The expansion velocities of the Fe II and Si II features revealed considerable overlap between the two populations. Although some GRB-SNe expand more rapidly than ordinary type Ic-BL SNe, the difference between the population medians is not statistically significant. Our analysis confirms that type Ic-BL SNe and GRB-SNe generally expand more rapidly than type Ic SNe. The marginalised Fe II and Si II power law indices indicate that GRB-SNe decline at similar rates to ordinary type Ic-BL SNe. Broken power law evolution appears to be more common for the Si II feature, which always follows a shallow-steep decay. In contrast, the broken power law Fe II decays are predominantly steep-shallow. The Si II velocity evolution of PTF12gzk and SN2016coi (engine-driven SNe) are similar to GRB060218-SN2006aj, with both showing broken power law decay. This observation may hint at a two-component ejecta model, such as a GRB jet or a cocoon. Conclusions. Neither the velocities nor their evolution can be used to distinguish between ordinary type Ic-BL SNe and GRB-SNe. Velocities consistent with broken power law evolution may indicate the presence of a GRB jet in some of these ordinary type Ic-BL SNe, but this is likely not as robust as late-time radio surveys. These results suggest that GRB-SNe and ordinary type Ic-BL SNe are drawn from the same underlying population of events.

We present a comprehensive analysis of the optical and X-ray light curves (LCs) and spectral energy distributions (SEDs) of a large sample of gamma-ray burst (GRB) afterglows to investigate the relationship between the optical and X-ray emission after the prompt phase. We collected the optical data from the literature and determined the shapes of the optical LCs. Then, using previously presented X-ray data we modeled the optical/X-ray SEDs. We studied the SED parameter distributions and compared the optical and X-ray LC slopes and shapes. The optical and X-ray spectra become softer as a function of time while the gas-to-dust ratios of GRBs are higher than the values calculated for the Milky Way and the Large and Magellanic Clouds. For 20% of the GRBs the difference between the optical and X-ray slopes is consistent with 0 or 1=4 within the uncertainties (we did it not consider the steep decay phase), while in the remaining 80% the optical and X-ray afterglows show significantly different temporal behaviors. Interestingly, we find an indication that the onset of the forward shock in the optical LCs (initial peaks or shallow phases) could be linked to the presence of the X-ray flares. Indeed, when X-ray flares are present during the steep decay, the optical LC initial peak or end plateau occurs during the steep decay; if instead the X-ray flares are absent or occur during the plateau, the optical initial peak or end plateau takes place during the X-ray plateau. The forward-shock model cannot explain all features of the optical (e.g. bumps, late re-brightenings) and X-ray (e.g. flares, plateaus) LCs. However, the synchrotron model is a viable mechanism for GRBs at late times. In particular, we found a relationship between the presence of the X-ray flares and the shape of the optical LC that indicates a link between the prompt emission and the optical afterglow.

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.

We present ground-based and Hubble Space Telescope optical observations of the X-ray flash (XRF) 020903, covering 300 days. The afterglow showed a very rapid rise in the first day, followed by a relatively slow decay in the next few days. There was a clear bump in the light curve after ~25 days, accompanied by a drastic change in the spectral energy distribution. The light curve and the spectral energy distribution are naturally interpreted as the emergence -- and subsequent decay -- of a supernova (SN), similar to SN 1998bw. At peak luminosity, the SN is estimated to be 0.8 +/- 0.1 mag fainter than SN1998bw. This argues in favor of the existence of a supernova associated with this X-ray flash. A spectrum obtained 35 days after the burst shows emission lines from the host galaxy. We use this spectrum to put an upper limit on the oxygen abundance of the host at [O/H] < -0.6 dex. We also discuss a possible trend between the softness of several bursts and the early behavior of the optical afterglow, in the sense that XRFs and X-ray rich GRBs seem to have a plateau phase or even a rising light curve. This can be naturally explained in models where XRFs are similar to GRBs but seen off the jet axis.

We present the results of an optical and near-infrared (NIR) monitoring campaign of the counterpart of Gamma-Ray Burst (GRB) 000911, located at redshift , from 5 days to more than 13 months after explosion. Our extensive dataset is a factor of 2 larger and spans a time interval ~4 times longer than the ones considered previously for this GRB afterglow; this allows a more thorough analysis of its light curve and of the GRB host galaxy properties. The afterglow light curves show a single power-law temporal decline, modified at late times by light from a host galaxy with moderate intrinsic extinction, and possibly by an emerging supernova (SN). The afterglow evolution is interpreted within the classical “fireball” scenario as a weakly collimated adiabatic shock propagating in the interstellar medium. The presence of a SN light curve superimposed on the non-thermal afterglow emission is investigated: while in the optical bands no significant contribution to the total light is found from a SN, the NIR J-band data show an excess which is consistent with a SN as bright as the known hypernova SN1998bw. If the SN interpretation is true, this would be the farthest GRB-associated SN, as well as the farthest core-collapse SN, discovered to date. However, other possible explanations of this NIR excess are also investigated. Finally, we studied the photometric properties of the host, and found that it is likely to be a slightly reddened, subluminous, extreme starburst compact galaxy, with luminosity ~0.1 , an age of ~0.5 Gyr and a specific Star Formation Rate (SFR) of ≈30 yr-1 ()-1. This is the highest specific SFR value for a GRB host inferred from optical/NIR data.

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

A class of long gamma-ray bursts (GRBs) presenting light curves with an extended plateau phase in their X-ray afterglows obeys a correlation between the rest-frame end-time of the plateau, T a , and its corresponding X-ray luminosity, L a , (Dainotti et al). In this work we perform an analysis of a total sample of 176 Swift GRBs with known redshifts, exhibiting afterglow plateaus. By adding a third parameter that is the peak luminosity in the prompt emission, L peak, we discover the existence of a new three-parameter correlation. The scatter of data about this plane becomes smaller when a class-specific GRB sample is defined. This sample of 122 GRBs is selected from the total sample by excluding GRBs with associated supernovae (SNe), X-ray flashes and short GRBs with extended emission. With this sample the three-parameter correlation identifies a GRB “fundamental plane.” Moreover, we further limit our analysis to GRBs with light curves with good data coverage and almost flat plateaus, 40 GRBs forming our “gold sample.” The intrinsic scatter, , for the three-parameter correlation for this last sub-class is more than two times smaller than the value for the one, making this the tightest three-parameter correlation that involves the afterglow plateau phase. Finally, we also show that a slightly less tight correlation is present between L peak and a proxy for the total energy emitted during the plateau phase, , confirming the existence of an energy scaling between the prompt and afterglow phases.

We have sub-classified short and long-duration gamma-ray bursts (GRBs) into seven families according to the binary nature of their progenitors. Short GRBs are produced in mergers of neutron-star binaries (NS-NS) or neutron star-black hole binaries (NS-BH). Long GRBs are produced via the induced gravitational collapse (IGC) scenario occurring in a tight binary system composed of a carbon-oxygen core (COcore) and a NS companion. The COcore explodes as type Ic supernova (SN) leading to a hypercritical accretion process onto the NS: if the accretion is sufficiently high the NS reaches the critical mass and collapses forming a BH, otherwise a massive NS is formed. Therefore long GRBs can lead either to NS-BH or to NS-NS binaries depending on the entity of the accretion. We discuss for the above compact-object binaries: 1) the role of the NS structure and the nuclear equation of state; 2) the occurrence rates obtained from X and gamma-rays observations; 3) the predicted annual number of detections by the Advanced LIGO interferometer of their gravitational-wave emission.

We present optical and near-infrared follow-up observations of the X-ray flash (XRF) of 2003 July 23. Our observations in the R band cover the temporal range from 4.2 hr to 64 days after the high-energy event. We also present the results of multicolor imaging extending to the K band on three epochs. The light curve of the R-band afterglow the first week after the burst is similar to the light curve for long-duration gamma-ray bursts (GRBs), i.e., a broken power law with a late time slope of � � 2: 0( F� / t � � ). Furthermore, the spectral energy distribution (SED) has a power-law (F� / � � � ) shape with slope � � 1:0. However, the decay slope at t < 1d ay is shallow, consistent with zero. This is in qualitative agreement with the prediction that XRFs are off-axis classical GRBs. After the first week there is a strong bump in the light curve, which peaks at around 16 days. The SED after the peak becomes significantly redder. We discuss the possible interpretations of this bump and conclude that an underlying supernova is the most likely explanation since no other model appears consistent with the evolution of the SED. Finally, we present deep spectroscopy of the burst both in the afterglow and in the bump

There is significant interest in the models for production of short gamma-ray bursts (GRBs). Until now, the number of known short GRBs with multi-wavelength afterglows has been small. While the Fermi GRB Monitor detects many GRBs relative to the Neil Gehrels Swift Observatory, the large localization regions makes the search for counterparts difficult. With the Zwicky Transient Facility (ZTF) recently achieving first light, it is now fruitful to use its combination of depth (mAB ∼ 20.6), field of view (≈47 square degrees), and survey cadence (every ∼3 days) to perform Target of Opportunity observations. We demonstrate this capability on GRB 180523B, which was recently announced by the Fermi GRB Monitor as a short GRB. ZTF imaged ≈2900 square degrees of the localization region, resulting in the coverage of 61.6% of the enclosed probability over two nights to a depth of mAB ∼ 20.5. We characterized 14 previously unidentified transients, and none were found to be consistent with a short GRB counterpart. This search with the ZTF shows it is an efficient camera for searching for coarsely localized short GRB and gravitational-wave counterparts, allowing for a sensitive search with minimal interruption to its nominal cadence.