Long-Term X-Ray Spectral Variability of the Nucleus of M81

Giovanni Peres, Kim, Nicastro, Fabbiano, Elvis, Giovanni Peres, La Parola

Research output: Contribution to journalArticlepeer-review

11 Citations (Scopus)

Abstract

We have analyzed the soft X-ray emission from the nuclear source of the nearby spiral galaxy M81, using the available data collected with ROSAT, ASCA, BeppoSAX, and Chandra. The source flux is highly variable (sometimes dramatic: a factor of 4 in 20 days), showing variability at different timescales, from 2 days to 4 yr, and in particular a steady increase of the flux by a factor of greater than or similar to2 over 4 yr, broken by rapid flares. After accounting for the extended component resolved by Chandra, the nuclear soft X-ray spectrum (from ROSAT/PSPC, BeppoSAX/LECS, and Chandra data) cannot be fitted well with a single absorbed power-law model. Acceptable fits are obtained by adding an extra component, either a multicolor blackbody (MCBB) or an absorption feature. In the MCBB case, the inner accretion disk would be far smaller than the Schwartzchild radius for the 3-60x10(6) M-circle dot nucleus, requiring a strictly edge-on inclination of the disk, even if the nucleus is a rotating Kerr black hole. The temperature is 0.27 keV, larger than expected from the accretion disk of a Schwartzchild black hole but consistent with that expected from a Kerr black hole. In the power law+absorption feature model, we have either high-velocity (0.3c) infalling C V clouds or neutral C I absorption at rest. In both cases the C:O overabundance is a factor of 10.
Original languageEnglish
Pages (from-to)831-844
Number of pages14
JournalTHE ASTROPHYSICAL JOURNAL
Volume601
Publication statusPublished - 2004

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Fingerprint

Dive into the research topics of 'Long-Term X-Ray Spectral Variability of the Nucleus of M81'. Together they form a unique fingerprint.

Cite this