{
  "eventId": "SN 2001em",
  "body": "A. M. Soderberg, A. Gal-Yam and S. R. Kulkarni, report on behalf of\na larger Caltech/Carnegie collaboration:\n\n\"We report optical spectroscopy of the type Ic SN 2001em (Papenkova et al.,\nIAUC 7722, Filippenko & Chornock, IAUC 7737) in UGC 11794 (d=84 Mpc).\nThis supernova was recently shown to have a rising radio luminosity (Stockdale\net al., IAUC 8282) and bright X-ray emission (Pooley & Lewin, IAUC 8323),\nboth of which are atypical for a type Ic supernova at t > 2 years. An off-axis\nGRB jet was proposed as an explanation for this behavior (Granot &\nRamirez-Ruiz, astro-ph/0403421).\n\nThe optical spectrum is highly unusual for a type Ic SN, and is dominated by\na broad (FWHM of 40 angstrom = 1800 km/s) H-alpha emission line. The strong\nnebular features of oxygen and calcium, characteristic of old (>1 year)\nSNe Ic, including SN 1998bw and SN 2002ap (e.g., Foley et al. 2003,\nPASP, 115, 1220), are not detected.\nThe spectrum is suggestive of strong interaction with the circumstellar medium\nand is similar in shape to spectra of strongly interacting type IIn\nSNe at a similar age (e.g., SN 1998S, Pozzo et al. 2004, astro-ph/0404533).\n\nThis interpretation is consistent with the report by Pooley & Lewin\nthat the X-ray emission can be well fit with a thermal bremsstrahlung\nmodel.  A dense circumstellar medium would also explain the bright\nradio emission, as was proposed by Soderberg, Frail & Wieringa (2004,\nApJ, 607, L13).\n\nA comparison between our spectrum of SN 2001em and those of type IIn SN 1994Y\n(age 180 day; Filippenko 1997, ARA&A, 35, 309) and the type Ic SN 1998bw\n(age 376 days; Patat et al. 2001, ApJ, 555, 900), taken from the data base\npresented by Poznanski et al. (2002, PASP, 114, 833) and Gal-Yam et al. (2004,\nastro-ph/0403296) is posted at:\n\nhttp://www.astro.caltech.edu/~ams/SN2001em.gif \"\n\nThis message may be cited.",
  "submitter": "Alicia Soderberg at Caltech  <ams@astro.caltech.edu>",
  "version": 2,
  "editedBy": "Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov>",
  "email": "ams@astro.caltech.edu",
  "bibcode": "2004GCN..2586....1S",
  "circularId": 2586,
  "createdOn": 1083948880000,
  "subject": "Type Ic SN2001em (off-axis GRB jet?), optical spectrum",
  "editedOn": 1777052975839
}