Surface activity of rapidly rotating stars from simultaneous X-ray and UV observations with AstroSat

Our study focuses on analysing the coronal, transition and chromospheric activity of four rapidly rotating stars located within 50 pc in the solar neighbourhood. We have used the multi-wavelength capabilities of AstroSat, to investigate the outer atmospheres of AB Dor, BO Mic, DG CVn and GJ 3331. These stars, classified as M and K type active stars, are known for their short rotation periods, leading to increased surface magnetic activity. Our soft X-ray observations provide the coronal properties such as emission measures, temperatures and elemental coronal abundances. We report the detection of X-ray flares from AB Dor, BO Mic, and DG CVn, while UV light curves reveal flares in both BO Mic and DG CVn.Comment: Accepted for publication in Journal of Astrophysics and Astronom

Far-Ultraviolet to Near-Infrared Observations of SN 2023ixf: A high energy explosion engulfed in complex circumstellar material

We present early-phase panchromatic photometric and spectroscopic coverage spanning far-ultraviolet (FUV) to the near-infrared (NIR) regime of the nearest hydrogen-rich core-collapse supernova in the last 25 years, SN~2023ixf. We observe early `flash' features in the optical spectra due to a confined dense circumstellar material (CSM). We observe high-ionization absorption lines Fe II, Mg II in the ultraviolet spectra from very early on. We also observe a multi-peaked emission profile of H-alpha in the spectrum beginning ~16 d, which indicates ongoing interaction of the SN ejecta with a pre-existing shell-shaped CSM having an inner radius of ~ 75 AU and an outer radius of ~140 AU. The shell-shaped CSM is likely a result of enhanced mass loss ~ 35 - 65 years before the explosion assuming a standard Red-Supergiant wind. Spectral modeling of the FUV, NUV, and the optical spectra during 9-12 d, using the radiative transfer spectrum synthesis code TARDIS indicates that the supernova ejecta could be well represented by a progenitor elemental composition greater than solar abundances. Based on early light curve models of Type II SNe, we infer that the nearby dense CSM confined to ~7+-3e14~cm(~45 AU) is a result of enhanced mass loss ~1e-(3.0+-0.5) Msol/yr two decades before the explosion.Comment: Submitted to AAS Journals, 4 figures, 2 table

Characterizing the Ordinary Broad-lined Type Ic SN 2023pel from the Energetic GRB 230812B

International audienceWe report observations of the optical counterpart of the long gamma-ray burst (LGRB) GRB 230812B, and its associated supernova (SN) SN 2023pel. The proximity ($z = 0.36$) and high energy ($E_{\gamma, \rm{iso}} \sim 10^{53}$ erg) make it an important event to study as a probe of the connection between massive star core-collapse and relativistic jet formation. With a phenomenological power-law model for the optical afterglow, we find a late-time flattening consistent with the presence of an associated SN. SN 2023pel has an absolute peak $r$-band magnitude of $M_r = -19.46 \pm 0.18$ mag (about as bright as SN 1998bw) and evolves on quicker timescales. Using a radioactive heating model, we derive a nickel mass powering the SN of $M_{\rm{Ni}} = 0.38 \pm 0.01$$\rm{M_\odot}$, and a peak bolometric luminosity of $L_{\rm{bol}} \sim 1.3 \times 10^{43}$$\rm{erg}$$\rm{s^{-1}}$. We confirm SN 2023pel's classification as a broad-lined Type Ic SN with a spectrum taken 15.5 days after its peak in $r$ band, and derive a photospheric expansion velocity of $v_{\rm{ph}} = 11,300 \pm 1,600$$\rm{km}$$\rm{s^{-1}}$ at that phase. Extrapolating this velocity to the time of maximum light, we derive the ejecta mass $M_{\rm{ej}} = 1.0 \pm 0.6$$\rm{M_\odot}$ and kinetic energy $E_{\rm{KE}} = 1.3^{+3.3}_{-1.2} \times10^{51}$$\rm{erg}$. We find that GRB 230812B/SN 2023pel has SN properties that are mostly consistent with the overall GRB-SN population. The lack of correlations found in the GRB-SN population between SN brightness and $E_{\gamma, \rm{iso}}$ for their associated GRBs, across a broad range of 7 orders of magnitude, provides further evidence that the central engine powering the relativistic ejecta is not coupled to the SN powering mechanism in GRB-SN systems