SN 1998bw

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SN 1998bw
SN 1998bw.jpg
Event typeSupernova
Type Ic
Date26 April 1998
Constellation Telescopium
Right ascension 19h 35m 03.17s [1]
Declination −52° 50′ 46.1″ [1]
Galactic coordinates 344.99°, −27.72° [2]
Redshift 0.0085  OOjs UI icon edit-ltr-progressive.svg
Host ESO 184-G82
[ edit on Wikidata]

SN 1998bw was a rare broad-lined Type Ic [3] gamma ray burst supernova detected on 26 April 1998 in the ESO 184-G82 spiral galaxy, which some astronomers believe may be an example of a collapsar (hypernova). [4] The hypernova has been linked to GRB 980425 , which was detected on 25 April 1998, the first time a gamma-ray burst has been linked to a supernova. [5] The hypernova is approximately 140 million light years away, very close for a gamma ray burst source. [6]

Contents

The region of the galaxy where the supernova occurred hosts stars 5-8 million years old and is relatively free from dust. A nearby region hosts multiple Wolf-Rayet stars less than 3 million years old, but it is unlikely that the supernova progenitor could be a runaway from that region. The implication is that the progenitor was a star originally 25-40 M☉ if it exploded as a single star at the end of its life. [7]

Observations

On 25 April 1998, a gamma ray burst was detected by the BeppoSAX satellite and assigned the identifier GRB 980425. The event lasted for 30 seconds, [8] and was about average in terms of burst flux. [9] A check of images from the ESO New Technology Telescope showed a rapidly brightening point source within the error box of GRB 980425. It was located in the face-on spiral galaxy ESO 184-G82, in a spiral arm at an offset from the nucleus. This candidate supernova event lacked spectral lines of hydrogen, ruling out a normal core-collapse Type II supernova, and it was a missing line of silicon that indicated it is not a typical Type Ia supernova. [10]

A few weeks after full light, the spectrum of supernova SN 1998bw showed no clear indications of helium. This suggested the event be classed as a Type Ic supernova, although it showed some peculiarities compared to other supernovae of this type. The expansion velocity measured from calcium lines was measured as 11,700 km/s, and 9,100 km/s from silicon lines. [11] The maximum recorded expansion velocities reached 3×104 km/s. [12] Energy emissions from the supernova showed polarization, which supported a core-collapse scenario with asymmetry. [13]

Radio measurements of the supernova showed that is was unusually luminous in this band. The data suggested a shock wave moving at a relativistic velocity, whereas most supernovae ejecta are non-relativistic. [14] This was the first evidence found for a relativistic shock from a supernova. [15] The supernova light curves from radio to X-ray bands also indicated a blast wave that was highly relativistic. The data was consistent with a physical association between SN 1998bw and GRB 980425, [16] [17] and supported the idea of a hypernova or collapsar event. This scenario results in the formation of a black hole from the collapse of a massive star. [16] [18] Spherically-symmetrical models failed to reproduce an event with this energy level, indicating a highly asymmetrical explosion that produced the gamma-ray burst from a relativistic jet. [19] In this case, only a fraction of the progenitor's stellar mass was ejected, with the remainder collapsing to form a black hole. [3]

The supernova transitioned to the nebular phase around 100 days after the explosion. [20] Expansion velocities remained very high compared to other core-collapse supernovae at similar phases. [12] The unusual spectrum observed during the nebular phase matched a model for a strongly aspherical explosion observed from near the direction of a relativistic jet. [21] [22] The radio emission from the supernova can best be explained by interaction between the relativistic shock and clumpy circumstellar medium previously ejected by a strong stellar wind. [23] Observations from the Chandra X-ray Observatory in 2004 found X-ray emission that supported this scenario. [24] It also lent support to the idea that the supernova and gamma-ray burst were the same event. [25]

Environment

Observations with the Hubble Space Telescope indicated that the host for the supernova event is a sub-luminous galaxy with a morphological classification of SBc. This indicates ESO 184-G82 is a barred spiral galaxy with loosely-wound spiral arms. The galaxy is undergoing strong star formation and the supernova occurred in an active star forming area that includes an H II region. This environment is fairly typical for Type II supernovae. The supernova afterglow was about a magnitude brighter than expected from a radioactive decay model, suggesting a contribution from a surrounding stellar cluster. [26]

The host galaxy appears morphologically disturbed, which suggests interaction from nearby galaxies. This could explain the amplified star forming process. [26] Six galaxies lie within the field of ESO 184-G82 but none of them have a matching redshift of 0.0087±0.0006. Thus, it appears to be an isolated dwarf galaxy and another explanation is needed for the star formation. [27] A 2020 study with the Atacama Large Millimeter Array discovered the galaxy has a ring of dense neutral hydrogen, which includes clumps of gas. One of these clumps was the host of SN 1998bw. The presence of a ring indicates a past collision with a companion galaxy. [28]

References

  1. 1 2 Barbon, R.; et al. (2008). "Asiago Supernova Catalogue". VizieR On-line Data Catalog. 2008-Mar. Bibcode:2008yCat.2283....0B.
  2. ↑ "SN 1998bw", SIMBAD , Centre de données astronomiques de Strasbourg , retrieved 20 March 2025.
  3. 1 2 Woosley, S. E.; et al. (1999). "Gamma-ray bursts and Type Ic supernova: SN 1998bw". The Astrophysical Journal. 516 (2): 788–796. arXiv: astro-ph/9806299 . Bibcode:1999ApJ...516..788W. doi:10.1086/307131. hdl:1885/94504. S2CID   17690696.
  4. ↑ Greiner, Jochen. "Gamma-ray burst 980425". Max-Planck-Institute for Extraterrestrial Physics. Retrieved 11 June 2017.
  5. ↑ Vreeswijk, P.; et al. (2000). "Gamma-ray burst afterglows: surprises from the sky". The ING Newsletter. 2: 5. Bibcode:2000INGN....2....5V.
  6. ↑ "A strange supernova with a gamma-ray burst". European Southern Observatory. 15 October 1998. Retrieved 14 November 2015.
  7. ↑ Krühler, Thomas; et al. (2017). "Hot gas around SN 1998bw - Inferring the progenitor from its environment". Astronomy & Astrophysics. 602 (85): A85. arXiv: 1702.05430 . Bibcode:2017A&A...602A..85K. doi:10.1051/0004-6361/201630268. S2CID   54903796.
  8. ↑ Soffitta, P.; et al. (26 April 1998). "GRB 980425". IAU Circulars. 6884. Central Bureau for Astronomical Telegrams: 1. Retrieved 22 March 2025.
  9. ↑ Wang, Lifan; Wheeler, J. Craig (September 1998). "The Supernova-Gamma-Ray Burst Connection". The Astrophysical Journal. 504 (2): L87 –L90. arXiv: astro-ph/9806212 . Bibcode:1998ApJ...504L..87W. doi:10.1086/311580.
  10. ↑ Galama, T. J.; et al. (7 May 1998). "GRB 980425". IAU Circulars. 6895. Central Bureau for Astronomical Telegrams: 1. Retrieved 22 March 2025.
  11. ↑ Patat, F.; Piemonte, A. (May 1998). Green, D. W. E. (ed.). "Supernova 1998bw in ESO 184-G82". IAU Circulars. 6918: 1. Bibcode:1998IAUC.6918....1P.
  12. 1 2 Patat, Ferdinando; et al. (July 2001). "The metamorphosis of SN 1998bw". The Astrophysical Journal. 555 (2): 900–917. arXiv: astro-ph/0103111 . Bibcode:2001ApJ...555..900P. doi:10.1086/321526.
  13. ↑ Kay, L. E.; et al. (July 1998). Green, D. W. E. (ed.). "Supernova 1998bw in ESO 184-G82". IAU Circulars. 6969: 1. Bibcode:1998IAUC.6969....1K.
  14. ↑ Kulkarni, S. R.; et al. (October 1998). "Radio emission from the unusual supernova 1998bw and its association with the γ-ray burst of 25 April 1998". Nature. 395 (6703): 663–669. Bibcode:1998Natur.395..663K. doi:10.1038/27139.
  15. ↑ Wieringa, M. H.; et al. (September 1999). "SN 1998bw: The case for a relativistic shock". Astronomy and Astrophysics Supplement. 138 (3): 467–468. arXiv: astro-ph/9906070 . Bibcode:1999A&AS..138..467W. doi:10.1051/aas:1999312.
  16. 1 2 Iwamoto, Koichi (February 1999). "On the Radio-to-X-Ray Light Curves of SN 1998bw and GRB 980425". The Astrophysical Journal. 512 (1): L47 –L50. arXiv: astro-ph/9810400 . Bibcode:1999ApJ...512L..47I. doi:10.1086/311867.
  17. ↑ Li, Zhi-Yun; Chevalier, Roger A. (December 1999). "Radio Supernova SN 1998bw and Its Relation to GRB 980425". The Astrophysical Journal. 526 (2): 716–726. arXiv: astro-ph/9903483 . Bibcode:1999ApJ...526..716L. doi:10.1086/308031.
  18. ↑ Woosley, S. E.; MacFadyen, A. I. (2000). "Gamma-ray bursts, supernovae, and SN 1998bw". Memorie della Societa Astronomica Italiana. 71: 357–363. Bibcode:2000MmSAI..71..357W.
  19. ↑ Höflich, Peter; et al. (August 1999). "Aspherical Explosion Models for SN 1998BW/GRB-980425". The Astrophysical Journal. 521 (1): 179–189. arXiv: astro-ph/9808086 . Bibcode:1999ApJ...521..179H. doi:10.1086/307521.
  20. ↑ Maeda, K.; et al. (April 2006). "Nebular spectra of SN 1998bw revisited: detailed study by one- and two-dimensional models". The Astrophysical Journal. 640 (2): 854–877. arXiv: astro-ph/0508373 . Bibcode:2006ApJ...640..854M. doi:10.1086/500187.
  21. ↑ Maeda, Keiichi; et al. (January 2002). "Explosive nucleosynthesis in aspherical hypernova explosions and late-time spectra of SN 1998bw". The Astrophysical Journal. 565 (1): 405–412. Bibcode:2002ApJ...565..405M. doi:10.1086/324487.
  22. ↑ Mazzali, Paolo A.; et al. (October 2001). "The nebular spectra of the hypernova SN 1998bw and evidence for asymmetry". The Astrophysical Journal. 559 (2): 1047–1053. arXiv: astro-ph/0106095 . Bibcode:2001ApJ...559.1047M. doi:10.1086/322420.
  23. ↑ Weiler, Kurt W.; et al. (December 2001). "SN 1998bw/GRB 980425 and radio supernovae". The Astrophysical Journal. 562 (2): 670–678. arXiv: astro-ph/0106131 . Bibcode:2001ApJ...562..670W. doi:10.1086/322359.
  24. ↑ Waxman, Eli (April 2004). "Does the detection of X-Ray emission from SN 1998bw support its association with GRB 980425?". The Astrophysical Journal. 605 (2): L97 –L100. arXiv: astro-ph/0401551 . Bibcode:2004ApJ...605L..97W. doi:10.1086/420846.
  25. ↑ Kouveliotou, C.; et al. (June 2004). "Chandra observations of the X-Ray environs of SN 1998bw/GRB 980425". The Astrophysical Journal. 608 (2): 872–882. arXiv: astro-ph/0401184 . Bibcode:2004ApJ...608..872K. doi:10.1086/420878.
  26. 1 2 Fynbo, J. U.; et al. (October 2000). "HST/STIS imaging of the host galaxy of GRB980425/SN1998bw". The Astrophysical Journal. 542 (2): L89 –L93. arXiv: astro-ph/0009014 . Bibcode:2000ApJ...542L..89F. doi:10.1086/312942.
  27. ↑ Foley, S.; et al. (March 2006). "The galaxies in the field of the nearby GRB 980425/SN 1998bw". Astronomy and Astrophysics. 447 (3): 891–895. arXiv: astro-ph/0510813 . Bibcode:2006A&A...447..891F. doi:10.1051/0004-6361:20054382.
  28. ↑ Arabsalmani, M.; et al. (August 2020). "Local starburst conditions and formation of GRB 980425/SN 1998bw within a collisional ring". The Astrophysical Journal. 899 (2). id. 165. arXiv: 2007.01317 . Bibcode:2020ApJ...899..165A. doi: 10.3847/1538-4357/aba3c0 .

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