skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: THE TRANSITIONAL STRIPPED-ENVELOPE SN 2008ax: SPECTRAL EVOLUTION AND EVIDENCE FOR LARGE ASPHERICITY

Abstract

Supernova (SN) 2008ax in NGC 4490 was discovered within hours after shock breakout, presenting the rare opportunity to study a core-collapse SN beginning with the initial envelope-cooling phase immediately following shock breakout. We present an extensive sequence of optical and near-infrared spectra, as well as three epochs of optical spectropolarimetry. Our initial spectra, taken two days after shock breakout, are dominated by hydrogen Balmer lines at high velocity. However, by maximum light, He I lines dominated the optical and near-infrared spectra, which closely resembled those of normal Type Ib supernovae (SNe Ib) such as SN 1999ex. This spectroscopic transition defines Type IIb SNe, but the strong similarity of SN 2008ax to normal SNe Ib beginning near maximum light, including an absorption feature near 6270 A due to H{alpha} at high velocities, suggests that many objects classified as SNe Ib in the literature may have ejected similar amounts of hydrogen as SN 2008ax, roughly a few x 0.01 M{sub sun}. Only the unusually early discovery of SN 2008ax allowed us to observe the spectroscopic signatures of the hydrogen-rich outer ejecta. Early-time spectropolarimetry (six and nine days after shock breakout) revealed strong line polarization modulations of 3.4% across H{alpha}, indicating the presencemore » of large asphericities in the outer ejecta and possibly that the spectrum of SN 2008ax could be dependent on the viewing angle. After removal of interstellar polarization, the continuum shares a common polarization angle with the hydrogen, helium, and oxygen lines, while the calcium and iron absorptions are oriented at different angles. This is clear evidence of deviations from axisymmetry even in the outer ejecta. Intrinsic continuum polarization of 0.64% only nine days after shock breakout shows that the outer layers of the ejecta were quite aspherical. A single epoch of late-time spectropolarimetry as well as the shapes of the nebular line profiles demonstrate that asphericities extended from the outermost layers all the way down to the center of this core-collapse SN. SN 2008ax may in some ways be an extragalactic analog of the explosion giving rise to Cassiopeia A, which has recently been determined to be a remnant of an SN IIb.« less

Authors:
; ; ; ; ;  [1];  [2];  [3];  [4];  [5];  [6];  [7];  [8]; ; ;  [9]; ;  [10];  [11];  [12]
  1. Department of Astronomy, University of California, Berkeley, CA 94720-3411 (United States)
  2. The George P. and Cynthia W. Mitchell Institute for Fundamental Physics and Astronomy, Texas A and M University, Department of Physics and Astronomy, 4242 TAMU, College Station, TX 77843-4242 (United States)
  3. Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States)
  4. Department of Physics, and Center for Astrophysics and Space Sciences, University of California, San Diego, La Jolla, CA 92093-0424 (United States)
  5. Kavli Institute for Cosmology and Institute of Astronomy, Cambridge CB3 0HA (United Kingdom)
  6. Department of Physics, University of California, Davis, CA 95616 (United States)
  7. Physics Department, University of Notre Dame, Notre Dame, IN 46556 (United States)
  8. Institute of Astronomy, University of Cambridge, Cambridge CB3 0HA (United Kingdom)
  9. Aerospace Corporation, Mail Stop M2-266, Los Angeles, CA 90009-2957 (United States)
  10. Centre for Astrophysics and Supercomputing, Swinburne University of Technology, Victoria 3122 (Australia)
  11. Astronomy Department, Wesleyan University, Middletown, CT 06459 (United States)
  12. Institute for Astronomy, University of Hawaii, Honolulu, HI 96822 (United States)
Publication Date:
OSTI Identifier:
21587502
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 739; Journal Issue: 1; Other Information: DOI: 10.1088/0004-637X/739/1/41; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0004-637X
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABSORPTION; BALMER LINES; HELIUM; HYDROGEN; INFRARED SPECTRA; NEAR INFRARED RADIATION; OXYGEN; POLARIZATION; SUPERNOVAE; BINARY STARS; ELECTROMAGNETIC RADIATION; ELEMENTS; ERUPTIVE VARIABLE STARS; FLUIDS; GASES; INFRARED RADIATION; NONMETALS; RADIATIONS; RARE GASES; SORPTION; SPECTRA; STARS; VARIABLE STARS

Citation Formats

Chornock, R., Filippenko, A. V., Li, W., Modjaz, M., Silverman, J. M., Steele, T. N., Marion, G. H., Foley, R. J., Rafelski, M., Becker, G. D., De Vries, W. H., Garnavich, P., Jorgenson, R. A., Lynch, D. K., Rudy, R. J., Russell, R. W., Malec, A. L., Murphy, M. T., Moran, E. C., and Stockton, A., E-mail: rchornock@cfa.harvard.edu. THE TRANSITIONAL STRIPPED-ENVELOPE SN 2008ax: SPECTRAL EVOLUTION AND EVIDENCE FOR LARGE ASPHERICITY. United States: N. p., 2011. Web. doi:10.1088/0004-637X/739/1/41; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA).
Chornock, R., Filippenko, A. V., Li, W., Modjaz, M., Silverman, J. M., Steele, T. N., Marion, G. H., Foley, R. J., Rafelski, M., Becker, G. D., De Vries, W. H., Garnavich, P., Jorgenson, R. A., Lynch, D. K., Rudy, R. J., Russell, R. W., Malec, A. L., Murphy, M. T., Moran, E. C., & Stockton, A., E-mail: rchornock@cfa.harvard.edu. THE TRANSITIONAL STRIPPED-ENVELOPE SN 2008ax: SPECTRAL EVOLUTION AND EVIDENCE FOR LARGE ASPHERICITY. United States. doi:10.1088/0004-637X/739/1/41; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA).
Chornock, R., Filippenko, A. V., Li, W., Modjaz, M., Silverman, J. M., Steele, T. N., Marion, G. H., Foley, R. J., Rafelski, M., Becker, G. D., De Vries, W. H., Garnavich, P., Jorgenson, R. A., Lynch, D. K., Rudy, R. J., Russell, R. W., Malec, A. L., Murphy, M. T., Moran, E. C., and Stockton, A., E-mail: rchornock@cfa.harvard.edu. Tue . "THE TRANSITIONAL STRIPPED-ENVELOPE SN 2008ax: SPECTRAL EVOLUTION AND EVIDENCE FOR LARGE ASPHERICITY". United States. doi:10.1088/0004-637X/739/1/41; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA).
@article{osti_21587502,
title = {THE TRANSITIONAL STRIPPED-ENVELOPE SN 2008ax: SPECTRAL EVOLUTION AND EVIDENCE FOR LARGE ASPHERICITY},
author = {Chornock, R. and Filippenko, A. V. and Li, W. and Modjaz, M. and Silverman, J. M. and Steele, T. N. and Marion, G. H. and Foley, R. J. and Rafelski, M. and Becker, G. D. and De Vries, W. H. and Garnavich, P. and Jorgenson, R. A. and Lynch, D. K. and Rudy, R. J. and Russell, R. W. and Malec, A. L. and Murphy, M. T. and Moran, E. C. and Stockton, A., E-mail: rchornock@cfa.harvard.edu},
abstractNote = {Supernova (SN) 2008ax in NGC 4490 was discovered within hours after shock breakout, presenting the rare opportunity to study a core-collapse SN beginning with the initial envelope-cooling phase immediately following shock breakout. We present an extensive sequence of optical and near-infrared spectra, as well as three epochs of optical spectropolarimetry. Our initial spectra, taken two days after shock breakout, are dominated by hydrogen Balmer lines at high velocity. However, by maximum light, He I lines dominated the optical and near-infrared spectra, which closely resembled those of normal Type Ib supernovae (SNe Ib) such as SN 1999ex. This spectroscopic transition defines Type IIb SNe, but the strong similarity of SN 2008ax to normal SNe Ib beginning near maximum light, including an absorption feature near 6270 A due to H{alpha} at high velocities, suggests that many objects classified as SNe Ib in the literature may have ejected similar amounts of hydrogen as SN 2008ax, roughly a few x 0.01 M{sub sun}. Only the unusually early discovery of SN 2008ax allowed us to observe the spectroscopic signatures of the hydrogen-rich outer ejecta. Early-time spectropolarimetry (six and nine days after shock breakout) revealed strong line polarization modulations of 3.4% across H{alpha}, indicating the presence of large asphericities in the outer ejecta and possibly that the spectrum of SN 2008ax could be dependent on the viewing angle. After removal of interstellar polarization, the continuum shares a common polarization angle with the hydrogen, helium, and oxygen lines, while the calcium and iron absorptions are oriented at different angles. This is clear evidence of deviations from axisymmetry even in the outer ejecta. Intrinsic continuum polarization of 0.64% only nine days after shock breakout shows that the outer layers of the ejecta were quite aspherical. A single epoch of late-time spectropolarimetry as well as the shapes of the nebular line profiles demonstrate that asphericities extended from the outermost layers all the way down to the center of this core-collapse SN. SN 2008ax may in some ways be an extragalactic analog of the explosion giving rise to Cassiopeia A, which has recently been determined to be a remnant of an SN IIb.},
doi = {10.1088/0004-637X/739/1/41; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA)},
journal = {Astrophysical Journal},
issn = {0004-637X},
number = 1,
volume = 739,
place = {United States},
year = {2011},
month = {9}
}