We present LOw Frequency ARray (LOFAR) studies of supernovae SN 1979C, SN 1986J, and SN 2006X, focusing on new observations from the LOFAR Two-metre Sky Survey (LoTSS) and the International LOFAR Telescope (ILT). For Type Ia supernovae (SNe Ia) SN 2006X, we derive a 3 σ upper limit of 0.7 mJy at 0.146 GHz, and using radio emission models based on the CS15DD2 explosion model, we constrain the circumstellar density to n _H ≲ 10 cm ^−3 for the microphysical parameters ϵ _rel = ϵ _B = 0.01. SN 1979C is clearly detected in the LoTSS image with a flux density of 4.6 ± 0.36 mJy nearly 40 yr postexplosion. Modeling its radio evolution suggests a steep flux decay ( F _ν ∝ t ^−2.1 ) between 22 and 42 yr, a break in the spectrum near 1.5 GHz possibly due to synchrotron cooling, a progenitor mass of ∼13 M _⊙ , and a progressive steepening with velocity for the density slope of the supernova ejecta. Our findings for SN 1979C contradict scenarios involving central compact object emission, and we obtain X-ray temperatures close to those derived from recent observations. For SN 1986J, we present the first ILT image showing a flux density of 6.77 ± 0.2 mJy at 0.146 GHz. The spectral index of the shell emission is found to be 0.66 ± 0.03, consistent with previous estimates, although variations at low frequencies warrant further investigation. Our results highlight the power of LOFAR for studying long-term radio evolution in supernovae.

We present multiwavelength observations and analysis of six luminous fast blue optical transients (LFBOTs) discovered in Zwicky Transient Facility (ZTF) survey data. We identified these LFBOTs from their fast light-curve evolution (t_1/2≤ 12d), blue colors at peak brightness (g-r≤-0.5mag), a visible host galaxy, high optical luminosity (M_g<-20), and an X-ray or radio detection. With the exception of AT2024aehp (ZTF24abygbss), these transients exhibit peaks in their 10GHz radio light curves at t_rest≈ 50-100 d, with peak radio luminosities ranging from 10^38-10^40 erg s^-1. Modeling the radio emission as synchrotron radiation indicates a fast (v=0.1-0.3c) shock in a dense (n_e≈10^3-10^4 cm^-3) medium. The X-ray emission varies by ≈2 orders of magnitude in luminosity (10^42-10^44 erg s^-1) at t_rest∼20d. Analysis of the host-galaxy photometry and spectroscopy for each transient shows that they are predominantly nonnuclear (a few kpc offset) with star-forming host galaxies of stellar masses 10^9-10^11 ,M_⊙. Unlike all other LFBOTs to date, AT2024aehp exhibited a luminous (M<-19mag) plateau in the optical light curve; spectra during this plateau phase showed a featureless blue continuum. The 6-15 GHz radio emission of AT2024aehp brightened by over an order of magnitude from t_rest≈70d to t_rest≈130d. The mostly consistent radio behavior between optically selected LFBOTs implies a similar circumburst medium, leading us to prefer a progenitor scenario in which mass is lost in a consistent way shortly prior to the terminal event, such as a massive star merging with a compact object.

Calcium-strong transients (CaSTs) are a subclass of faint and rapidly evolving supernovae (SNe) that exhibit strong calcium features and notably weak oxygen features. The small but growing population of CaSTs exhibits some aspects similar to thermonuclear SNe but others similar to massive star core-collapse events, leading to intriguing questions on their physical origins. SN 2025coe is one of the nearest CaSTs discovered to date, and our coordinated multiwavelength observations obtained days to weeks postexplosion reveal new insights into these enigmatic transients. With the most robust near-IR (NIR) spectroscopic time series of a CaST collected to date, SN 2025coe shows spectral signatures characteristic of Type Ib SNe (SNe Ib; i.e., He-rich stripped-envelope SNe (SESNe)). SN 2025coe is the third X-ray-detected CaST and our analysis of Neil Gehrels Swift Observatory X-ray data suggests interaction with 0.12 +/- 0.11 M circle dot of circumstellar material (CSM) extending to at least 2 & times; 1015 cm (similar to 30,000 R circle dot), while our analysis of the 1-240 GHz radio nondetections gives an outer radius of that CSM of at most similar to 5 & times; 1015 cm. This inferred nearby high-density CSM extending out to (3.5 +/- 1.5) & times; 1015 cm is similar to that seen in the other two X-ray-detected CaSTs, and its presence suggests that either intensive mass loss from a massive star or some exotic pre-SN mass ejection may be a common feature of this subclass. Our work also expands upon recent studies of the optical properties of SN 2025coe and explores our current understanding of different progenitor systems that could possibly produce CaSTs.

Observable properties of core-collapse supernovae (CCSNe) depend sensitively on the circumstellar material (CSM) formed by pre-explosion mass loss from the progenitor star. Since a large fraction of CCSN progenitors reside in binaries, both the progenitor structure and surrounding CSM can be significantly impacted by binary interaction. Yet, its impact on the observed CCSN landscape remains poorly constrained. In this work, we investigate CCSNe from binary systems undergoing stable Roche lobe overflow. We construct a suite of binary evolution models in with a fixed initial primary mass (16M_⊙), exploring secondary masses in the range 12-15M_⊙ and initial orbital periods >500 days. We generate three-dimensional (3D) CSM structures from the resulting mass-loss histories and orbital dynamics, extract angle-dependent density profiles along three lines of sight, and compute multi-band light curves with the radiation-hydrodynamics code . We find that binary-driven CSM develops highly aspherical morphologies, governed by the orbital period and the mass ratio. Interaction between SN ejecta and this structured medium produces pronounced viewing-angle dependence in the light curves, with peak luminosities differing by factors of ∼5 and late-time B-V colors varying by ∼1.5 mag depending on observer orientation. We further show that interpreting such events with one-dimensional frameworks assuming isolated progenitors and spherical winds can introduce biases up to 50% for inferred explosion properties and >200% for inferred mass-loss rates. Our results are consistent with a substantial fraction of interacting Type II SN diversity arising from binary-shaped asymmetric CSM and viewing-angle effects, motivating multidimensional approaches to interpreting these transients.

This chapter presents the science potential of the Square Kilometre Array (SKA) for studying all classes of supernovae and their environments. It substantially updates and extends the earlier work of Perez-Torres et al. (2015), originally published in the 2015 Advancing Astrophysics with the SKA (AASKA14) volume, reflecting the dramatic progress in time-domain astronomy and radio instrumentation over the past decade. We outline how SKA1 and its pathfinders will transform the radio study of core-collapse supernovae (CCSNe) through sensitive, commensal wide-field surveys capable of discovering hundreds of events per year, providing a dust-unbiased census of massive-star deaths and direct measurements of the volumetric CCSN rate. The same data will probe ejecta-circumstellar medium (CSM) interaction, shock microphysics, and progenitor mass-loss histories. Deep, triggered observations of thermonuclear supernovae (SNe Ia) will allow the SKA to test competing progenitor scenarios by detecting – or definitively excluding – the prompt radio emission expected from single-degenerate systems. The chapter further explores superluminous supernovae (SLSNe), delayed interaction supernovae and synergies with facilities such as ALMA, ngVLA, CTA, IceCube-Gen2, and ULTRASAT. Collectively, these studies will turn radio supernova astrophysics from a discovery-limited field into one governed by population statistics.

The final life stages of the massive star progenitors of stripped-envelope supernovae (SESNe) are still an open question, especially when it comes to the timing and magnitude of the progenitor stripping. Observing SESNe across the electromagnetic spectrum allows for the most direct constraints on mass loss in the final stages of progenitor evolution. In this work, we present radio (GMRT+VLA) and X-ray (Swift+Chandra) observations of SN 2019yvr obtained from 18-1784 days post-explosion. SN 2019yvr was a type Ib supernova (SN Ib, with strong helium but no or little optical hydrogen features) that transitioned into a type IIn supernova (SN IIn, with shock-driven hydrogen features) at ∼ 100 days post-explosion. The radio evolution is best-fit by a synchrotron self-absorbed model with a ρ∝ r^-1.65 ± 0.25 CSM density profile, suggesting a decreasing mass-loss rate from the progenitor in the years leading up to the explosion. The radio-derived shock speed is high, more than 30,000 km/s at early times, suggesting a compact progenitor star. The combined radio and X-ray data probe CSM that extends from less than 10^16 cm up to ∼ 20×10^16 cm and was created by mass-loss from ∼ 1-3 ×10^-5M_⊙ yr^-1 (assuming a CSM speed of 100 km/s). The combined dataset rules out any dramatic jump in CSM density (which was seen in the optical analog SN 2014C) associated with the emergence of optical hydrogen emission in SN 2019yvr. We place SN 2019yvr in context with similar transitional SNe and discuss implications for the progenitor.

We present a comprehensive multiwavelength study of a bright gamma-ray burst GRB 230204B, analyzing both prompt and afterglow emissions. This GRB is highly energetic, with an isotropic equivalent energy emission of Eiso similar to 2.2 & times; 1054 erg released during the prompt emission. The GROWTH-India Telescope discovered a bright afterglow (mr = 15.55) that fades rapidly (proportional to t-1.82). The prompt emission shows a strong thermal photospheric emission along with a nonthermal high-energy component. We explore the evolution of these components and find them to be consistent with the theoretical expectations of the fireball model. Afterglow modeling reveals an energetic jet (E gamma greater than or similar to 1052 erg) expanding into a wind-type medium viewed nearly on-axis, suggesting a massive star progenitor with strong winds. We also explore correlations between the prompt emission and afterglow that may help to place GRB 230204B within the broader context of the long GRB population.

On 2025 August 18, the LIGO-Virgo-KAGRA collaboration reported S250818k, a sub-threshold gravitational-wave (GW) candidate consistent with a binary neutron star (NS) merger potentially involving a sub-solar-mass NS. Optical follow-up by the Zwicky Transient Facility identified AT2025ulz, a transient temporally coincident with the GW trigger that initially resembled a kilonova but was later classified as a young stripped-envelope Type IIb supernova (SN), dubbed SN 2025ulz. A key question is whether SN 2025ulz harbors fast, possibly collimated, non-thermal ejecta indicative of a central engine, as invoked in "superkilonova" scenarios linking sub-solar-mass NSs to accretion-disk fragmentation or core fission. We present early-to-late-time multi-band radio observations of SN 2025ulz obtained with the Karl G. Jansky Very Large Array as part of the JAGWAR program, complemented by observations with the upgraded Giant Metrewave Radio Telescope and MeerKAT. We detect a faint but significant radio counterpart to SN 2025ulz at 6-10 GHz. The data are consistent with non-thermal emission from SN ejecta interacting with circumstellar material, favoring a compact progenitor and relatively fast ejecta akin to those of Type cIIb SNe. Our data are also consistent with emission from an off-axis jet peaking at about 50-100 days after the GW trigger. Overall, our radio detection is compatible with a superkilonova scenario and would motivate future systematic multi-wavelength follow-up of core-collapse events coincident with sub-solar NS GW candidates, should the association between S250818k and SN 2025ulz be supported by offline GW analyses.

Supernovae characterized by enduring narrow optical hydrogen emission lines (SNe IIn) are believed to result primarily from the core-collapse of massive stars undergoing sustained interaction with a dense circumstellar medium (CSM). While the properties of SN IIn progenitors have relatively few direct constraints, the ongoing ejecta-CSM interaction provides unique information about late-stage stellar mass-loss preceding core collapse. We present late-time X-ray and radio observations of four >= 3000 day old SNe IIn: SN 2013L, SN 2014ab, SN 2015da, and KISS15s. The radio and X-ray emission from KISS15s indicate a mass-loss rate of M similar to 4 & times;10(-3)M(circle dot)yr(-1 )at similar to 450 yr pre-SN-2 orders of magnitude below earlier optical estimates (which probed the mass loss immediately preceding the SN). We find hints of a spectral inversion in the radio spectral energy distribution of KISS15s; a possible signature of a secondary shock due to a binary system or the emergence of a pulsar wind. For SN 2013L, we obtain a mass-loss rate of M similar to 2 & times;10(-3)M(circle dot)yr(-1 ) at similar to 400 yr preexplosion based on the X-ray detection. For SN 2014ab and SN 2015da, we find upper limits on the mass-loss rates of M<2 & times;10(-3)M(circle dot)yr(-1 )explosion at similar to 300 and 250 yr preexplosion, respectively. All four objects display mass-loss rates lower than estimates from earlier optical analyses by at least 1-2 orders of magnitude, necessitating a rapidly evolving progenitor process over the last centuries preexplosion. Our analysis reveals how X-ray and radio observations can elucidate progenitor evolution when these objects have faded at optical wavelengths.

We report the discovery of a slowly evolving, extragalactic radio transient, ASKAP J005512.2-255834 (hereafter ASKAP J0055-2558), identified using the Australian SKA Pathfinder in a search for orphan afterglows associated with archival gravitational-wave events. Although discovered in this context, there is no evidence that the transient is associated with any known gravitational-wave event. Nonetheless, this source exhibits a 20-fold increase in flux density over <250 days, and it remains in a declining yet detectable state more than 1000 days after the initial detection. Follow-up observations from 0.3 to 9 GHz reveal an evolving spectrum consistent with synchrotron emission. ASKAP J0055-2558 is spatially coincident with a low-mass, star-forming galaxy at redshift z = 0.116 (d(L) = 543 Mpc), placing its peak radio luminosity at nu L-nu similar to 10(39) erg s(-1). Analysis of its radio light curve, inferred blast-wave velocity, energetics, host-galaxy properties, and the absence of counterparts at other wavelengths suggests that ASKAP J0055-2558 is most consistent with either the late-time phase of an orphan long gamma-ray burst afterglow or a tidal disruption event involving an intermediate-mass black hole spatially offset from the galaxy nucleus. The radio discovery of either of these phenomena is extremely rare, with only a few or no confirmed examples to date.

CU Vir, a magnetic hot star, is the first discovered Main-sequence Radio Pulse emitter (MRP) characterized by its ability to produce periodic radio pulses via electron cyclotron maser emission. Although significant advancements have been made in understanding MRPs, their temporal properties remain mostly unexplored. To overcome this limitation, we conducted a pilot study with the Australia Telescope Compact Array, in which we observed pulses from CU Vir at 36 epochs over 1-3 GHz. In this frequency range, CU Vir produces two ≈ 100% circularly polarized pulses, called `leading' and `trailing' pulses per rotation period. We find significant differences in the variability indices exhibited by the two pulses as a function of frequencies, with the leading pulse showing higher variability throughout our observing band. This result could be explained in the scenario of centrifugal breakout events in the magnetosphere of an oblique rotator causing correlated fluctuations across frequencies, along with intrinsic instabilities associated with coherent emission. In addition, we discover jittering in the arrival phases of pulses that must be considered in future monitoring campaigns. The pulses also exhibit a systematic shift to later arrival times during the course of our observing campaign, allowing us to refine the rotation period to 0.5206882 days. Finally, we estimate that ∼ 30 pulses will be needed to extract global pulse properties for the leading or trailing pulses. This relatively small number strongly motivates more extensive monitoring campaigns of MRPs, both to validate our results, and also to pinpoint the origin of the observed temporal variations.

While the subclass of interacting supernovae (SNe) with narrow hydrogen emission lines (Type IIn supernovae (SNe IIn)) consists of some of the longest-lasting and brightest supernovae (SNe) ever discovered, their progenitors are still not well understood. Investigating SNe IIn as they emit across the electromagnetic spectrum is the most robust way to understand the progenitor evolution before the explosion. This work presents X-ray, optical, infrared, and radio observations of the strongly interacting Type IIn supernova, SN 2020ywx, covering a period >1200 days after discovery. Through multiwavelength modeling, we find that the progenitor of 2020ywx was losing mass at ∼10 ^−2 –10 ^−3 M _⊙ yr ^−1 for at least 100 yr pre-explosion using the circumstellar medium (CSM) speed of 120 km s ^−1 measured from optical and near-infrared (NIR) spectra. Despite the similar magnitude of mass loss measured in different wavelength ranges, we find discrepancies between the X-ray and optical/radio-derived mass-loss evolution, which suggest asymmetries in the CSM. Furthermore, we find evidence for dust formation due to the combination of a growing blueshift in optical emission lines and NIR continuum emission which we fit with blackbodies at ∼1000 K. Based on the observed elevated mass loss over more than 100 yr and the configuration of the CSM inferred from the multiwavelength observations, we invoke binary interaction as the most plausible mechanism to explain the overall mass-loss evolution. SN 2020ywx is thus a case that may support the growing observational consensus that SNe IIn mass loss is explained by binary interaction.

We present the long-term photometric and spectroscopic analysis of a transitioning SN IIn/Ibn from -10.8 d to 150.7 d post V-band maximum. SN 2021foa shows prominent He i lines comparable in strength to the H alpha line around peak, placing SN 2021foa between the SN IIn and SN Ibn populations. The spectral comparison shows that it resembles the SN IIn population at pre-maximum, becomes intermediate between SNe IIn/Ibn, and at post-maximum matches with SN IIn 1996al. The photometric evolution shows a precursor at -50 d and a light curve shoulder around 17 d. The peak luminosity and colour evolution of SN 2021foa are consistent with most SNe IIn and Ibn in our comparison sample. SN 2021foa shows the unique case of an SN IIn where the narrow P-Cygni in H alpha becomes prominent at 7.2 d. The H alpha profile consists of a narrow (500-1200 km s(-1)) component, intermediate width (3000-8000 km s(-1)) and broad component in absorption. Temporal evolution of the H alpha profile favours a disc-like CSM geometry. Hydrodynamical modelling of the light curve well reproduces a two-component CSM structure with different densities (rho proportional to r(-2)-rho proportional to r(-5)), mass-loss rates (10(-3)-10(-1) M-circle dot yr(-1)) assuming a wind velocity of 1000 km s(-1) and having a CSM mass of 0.18 M-circle dot. The overall evolution indicates that SN 2021foa most likely originated from an LBV star transitioning to a WR star with the mass-loss rate increasing in the period from 5 to 0.5 yr before the explosion or it could be due to a binary interaction.

We present multiwavelength analysis of ZTF23abelseb (AT 2023sva), an optically discovered fast-fading (Delta m(r)=2.2 mag in Delta t=0.74 d), luminous (M-r similar to-30.0 mag), and red (g-r=0.50 mag) transient at z=2.28 with accompanying luminous radio emission. AT 2023sva does not possess a gamma-ray burst (GRB) counterpart to an isotropic equivalent energy limit of E-gamma,(iso)<1.6x10(52) erg, determined through searching gamma-ray satellite archives between the last non-detection and first detection, making it the sixth example of an optically discovered afterglow with a redshift measurement and no detected GRB counterpart. We analyse AT 2023sva's optical, radio, and X-ray observations to characterize the source. From radio analyses, we find the clear presence of strong interstellar scintillation (ISS) 72 d after the initial explosion, allowing us to place constraints on the source's angular size and bulk Lorentz factor. When comparing the source sizes derived from ISS of orphan events to those of the classical GRB population, we find orphan events have statistically smaller source sizes. We also utilize Bayesian techniques to model the multiwavelength afterglow. Within this framework, we find evidence that AT 2023sva possesses a shallow power-law structured jet viewed slightly off-axis (theta(v)=0.07 +/- 0.02) just outside of the jet's core opening angle (theta(c)=0.06 +/- 0.02). We determine this is likely the reason for the lack of a detected GRB counterpart, but also investigate other scenarios. AT 2023sva's evidence for possessing a structured jet stresses the importance of broadening orphan afterglow search strategies to a diverse range of GRB jet angular energy profiles, to maximize the return of future optical surveys.

In this paper, we report auroral radio emission from a magnetic B star HD 142990 using the MeerKAT radio telescope at 900–1670 MHz. This star is known to produce such emission (observed as periodic radio pulses) via electron cyclotron maser emission (ECME). However, past studies on ECME from this star were confined to observations at specific rotational phase ranges where one expects to see such pulses. We, for the first time, observed the star for its one complete rotation cycle and discovered that the star also produces “off-pulse” emission, which we term as secondary enhancements. Two such enhancements were observed, one of which is left circularly polarized (LCP) and the other is right circularly polarized, the latter is confirmed to be persistent. Using simulation, we infer that such pulses are likely related to the large misalignment between the stellar rotation and magnetic dipole axes (>80°), leading to the formation of highly complex magnetospheric plasma distribution. In addition, by extracting dynamic spectra for the primary pulses, we discovered prominent fine structures in one of the LCP pulses, with timescales as small as the instrumental time resolution (8 s). This is the first time that such structures are seen from a magnetic hot star, and has the potential to reveal detailed information about how the emission is driven, and the nature of the elementary sources of radiation. To pinpoint the origin of these fine structures and their significance, higher time and spectral resolution observations should be conducted in the future.

We present the results from our extensive hard-to-soft X-ray (NuSTAR, Swift-XRT, XMM-Newton, Chandra) and meter-to-millimeter-wave radio (Giant Metrewave Radio Telescope, Very Large Array, NOEMA) monitoring campaign of the very nearby ( d = 6.9 Mpc) Type II supernova (SN) 2023ixf spanning ≈4–165 days post-explosion. This unprecedented data set enables inferences on the explosion’s circumstellar medium (CSM) density and geometry. In particular, we find that the luminous X-ray emission is well modeled by thermal free–free radiation from the forward shock with rapidly decreasing photoelectric absorption with time. The radio spectrum is dominated by synchrotron radiation from the same shock. Similar to the X-rays, the level of free–free absorption affecting the radio spectrum rapidly decreases with time as a consequence of the shock propagation into the dense CSM. While the X-ray and the radio modeling independently support the presence of a dense medium corresponding to an effective mass-loss rate M ̇ ≈ 1 0 − 4 M ⊙ yr − 1 at R = (0.4–14) × 10 15 cm (for v w = 25 km s −1 ), our study points at a complex CSM density structure with asymmetries and clumps. The inferred densities are ≈10–100 times those of typical red supergiants, indicating an extreme mass-loss phase of the progenitor in the ≈200 yr preceding core collapse, which leads to the most X-ray luminous Type II SN and the one with the most delayed emergence of radio emission. These results add to the picture of the complex mass-loss history of massive stars on the verge of collapse and demonstrate the need for panchromatic campaigns to fully map their intricate environments.

In the past few years, the improved sensitivity and cadence of wide-field optical surveys have enabled the discovery of several afterglows without associated detected gamma-ray bursts (GRBs). We present the identification, observations, and multiwavelength modeling of a recent such afterglow (AT 2023lcr), and model three literature events (AT 2020blt, AT 2021any, and AT 2021lfa) in a consistent fashion. For each event, we consider the following possibilities as to why a GRB was not observed: (1) the jet was off-axis; (2) the jet had a low initial Lorentz factor; and (3) the afterglow was the result of an on-axis classical GRB (on-axis jet with physical parameters typical of the GRB population), but the emission was undetected by gamma-ray satellites. We estimate all physical parameters using afterglowpy and Markov Chain Monte Carlo methods from emcee . We find that AT 2023lcr, AT 2020blt, and AT 2021any are consistent with on-axis classical GRBs, and AT 2021lfa is consistent with both on-axis low Lorentz factor (Γ _0 ≈ 5–13) and off-axis ( θ _obs = 2 θ _jet ) high Lorentz factor (Γ _0 ≈ 100) jets.

Supernovae that interact with hydrogen-poor, helium-rich circumstellar material (CSM), known as type Ibn supernovae (SNe Ibn), present a unique opportunity to probe mass-loss processes in massive stars. In this work, we report the first radio detection of an SN Ibn, SN 2023fyq, and characterize the mass-loss history of its stellar progenitor using the radio and X-ray observations obtained over 18 months post-explosion. We find that the radio emission from 58 to 185 days is best modeled by synchrotron radiation attenuated by free–free absorption from a CSM of density ∼10 −18 g cm −3 (∼10 6 ρ ISM ) at a radius of 10 16 cm, corresponding to a mass-loss rate of ∼4 × 10 −3 M ⊙ yr −1 (for a CSM velocity of 1700 km s −1 from optical spectroscopy) from 0.7 to 3 yr before the explosion. This timescale is consistent with the time frame over which pre-explosion optical outbursts were observed. However, our late-time observations at 525 days post-explosion yield nondetections, and the 3 σ upper limits (along with an X-ray nondetection) allow us to infer a drop in the progenitor mass-loss rate at 5–10 yr pre-explosion with M ̇ < 2.5 × 10 −3 M ⊙ yr −1 . These results suggest a shell-like CSM from at most 4 × 10 15 to 2 × 10 16 cm (∼10 5 R ⊙ ), with a CSM density that is roughly consistent with predictions from a merger model for this object. Future radio observations of a larger sample of SNe Ibn will provide key details on the extent and density of their helium-rich CSM.

We present a comprehensive multi-wavelength study of a bright gamma-ray burst GRB 230204B, analyzing both prompt and afterglow emissions. This GRB is highly energetic, with an isotropic equivalent energy emission E_iso∼ 2.2 × 10^54 erg, released during the prompt emission. The GROWTH-India Telescope discovered a bright afterglow (m_r = 15.55) that faded rapidly (∝ t^-1.82). The prompt emission shows strong thermal photospheric emission, along with a non-thermal high-energy component. We explore the evolution of these components and find them to be consistent with theoretical expectations. Afterglow modeling reveals an energetic jet E_tot≳ 10^52 erg expanding into a wind-type medium viewed nearly on-axis, suggesting a massive star progenitor with strong winds. We also explore correlations between the prompt emission and afterglow that may help to understand the complete picture of GRB progenitors.

The interaction of post-explosion supernova ejecta with the surrounding circumstellar medium creates emissions across the electromagnetic spectrum. Since the circumstellar medium is created by the mass lost from the progenitor star, it carries tell-tale signatures of the progenitor. Consequently, observations and modeling of radiation produced by the interaction in various types of supernovae have provided valuable insights into their progenitors. Detailed studies have shown that the interaction in supernovae begins and sustains over various timescales and lengthscales, with differing mass-loss rates in distinct sub-classes. This reveals diverse progenitor histories for these stellar explosions. This review paper summarizes various supernova subtypes, linking them to stellar death pathways, and presents an updated supernova classification diagram. We then present a multi-wavelength study of circumstellar interaction in different supernova classes. We also present unpublished X-ray as well as radio observations of a type IIn supernova, SN 2010jl, which allow us to extend its circumstellar interaction studies to about 7 years post-explosion. The new data indicates that the extreme mass-loss rate (∼0.1 M⊙ yr−1) in SN 2010jl, reported by Chandra et al. commenced within the last 300 years before the explosion. We summarize the current status of the field and argue that via detailed studies of the circumstellar interaction, a.k.a. “Time Machine” technique, one of the big mysteries of stellar evolution, i.e., mapping supernovae progenitors to their explosive outcomes can be solved.