[Paper Review] Photometric observations and modeling of type IIb supernova 2008ax

D. Yu. Tsvetkov, I. M. Volkov+3 more|ArXiv.org|Oct 22, 2009

Gamma-ray bursts and supernovae1 references3 citations

TL;DR

This study presents extensive UBVRI photometric observations of Type IIb supernova SN 2008ax over 320 days, modeling its light curves using the STELLA code with a hydrodynamical model based on a 13 M⊙ progenitor that lost most of its hydrogen envelope. The model reproduces the observed peak luminosity and light curve shape well, particularly in the V band, though early-time and U/B-band discrepancies suggest room for refinement, confirming SN 2008ax as a typical Type IIb SN with absolute V-magnitude peak of -17.45 mag.

ABSTRACT

CCD UBVRI photometry is presented for type IIb SN 2008ax for about 320 days. The photometric behavior is typical for core-collapse SNe with low amount of hydrogen. The main photometric parameters are derived and the comparison with SNe of similar types is reported. Preliminary modeling is carried out, and the results are compared to the observed light curves. The main parameters of the hydrodynamical models are close to those used for SN IIb 1993J.

Motivation & Objective

• To obtain and analyze high-cadence UBVRI photometric light curves of Type IIb supernova SN 2008ax over 320 days post-explosion.
• To compare the photometric behavior of SN 2008ax with other Type IIb, Ib, and Ic supernovae to assess its typicality within the class.
• To model the observed light curves using the STELLA code with a hydrodynamical model based on a 13 M⊙ progenitor that lost most of its H-envelope.
• To evaluate the consistency of the model parameters—such as 56Ni mass, explosion energy, and progenitor radius—with those of well-known SNe like 1993J.
• To investigate the implications of the light curve evolution, including the UV dip and color changes, for progenitor evolution and explosion mechanisms.

Proposed method

• CCD UBVRI photometry was collected using multiple telescopes (50–100 cm) at observatories in Slovakia, Russia, and the U.S., including the 2-m Faulkes Telescope North.
• Image subtraction was applied using archival ING images of NGC 4490 as templates due to strong, non-uniform galaxy background.
• PSF-fitting photometry was performed relative to a sequence of local standard stars with calibrated magnitudes in UBVRI bands.
• The photometric data were cross-validated with P08 and R09 data, with Sloan-to-Johnson-Cousins transformations applied for filter consistency.
• Light curves were modeled using the STELLA code, which couples implicit hydrodynamics with time-dependent, multi-group non-equilibrium radiative transfer.
• A hydrodynamical model (Model 13C of Woosley et al. 1994) with 3.8 M⊙ total mass, 600 R⊙ radius, 0.11 M⊙ 56Ni, and 1.5×10⁵¹ erg explosion energy was used for synthetic light curve computation.

Experimental results

Research questions

• RQ1 How does the photometric evolution of SN 2008ax compare to other Type IIb supernovae in terms of light curve shape, peak luminosity, and color evolution?
• RQ2 To what extent does the hydrodynamical model based on a 13 M⊙ progenitor with significant H-envelope loss reproduce the observed UBVRI light curves of SN 2008ax?
• RQ3 What are the key photometric parameters (e.g., peak magnitude, decline rate, color evolution) of SN 2008ax, and how do they compare to SN 1993J and SN 2002ap?
• RQ4 Why are there discrepancies between the observed and modeled early-time light curves, particularly in the U and B bands?
• RQ5 What does the UV dip and subsequent rise in the light curve suggest about the progenitor's structure or explosion mechanism?

Key findings

• SN 2008ax reached an absolute V-band peak magnitude of -17.45 mag, placing it among the typical luminosities of Type IIb supernovae, slightly fainter than SN 1993J and SN 1999ex, but similar to SN 2002ap.
• The model light curves reproduce the observed V-band maximum luminosity and shape very well, with the best agreement in the V band and reasonable fit in R and I bands.
• The computed early-time peak in U and B bands is brighter than observed, indicating a mismatch in the early evolution, possibly due to model assumptions or opacity effects.
• The color evolution shows a rapid reddening after maximum, with B-V and V-R becoming nearly constant after ~100 days, while R-I shows only a slight reddening, consistent with a declining but stable post-maximum phase.
• The U-band light curve shows a dip followed by a rise, similar to SN 1993J, suggesting a common physical mechanism related to the recombination of H and He in the ejecta.
• The comparison with P08 and R09 data shows good agreement in R and I bands, moderate differences in U and B bands likely due to filter transformation errors from Sloan to Johnson-Cousins systems.