Volume 389, Number 3, July III 2002
|Page(s)||752 - 760|
|Section||Cosmology (including clusters of galaxies)|
|Published online||01 July 2002|
RXTE view of the starburst galaxies M 82 and NGC 253
School of Physics and Astronomy, Tel Aviv University, Tel Aviv, Israel
2 Center for Astrophysics and Space Sciences, University of California, San Diego, USA
Corresponding author: Y. Rephaeli, firstname.lastname@example.org
Accepted: 25 March 2002
The two nearby starburst galaxies M 82 and NGC 253 were observed for ∼100 ksec over a 10-month period in 1997. An increase of the M 82 flux by a factor ∼2 was measured during the period July-November, when compared with the flux measured earlier in 1997. The flux measured in the field centered on M 82 includes ∼38% of the emission from the Seyfert 1 galaxy M 81. The best-fitting model for the earlier emission from M 82 is thermal with . In the high flux state, the emission additionally includes either an absorbed second thermal component or absorbed power-law component, with the former providing a much better fit. A likely origin for the temporal variability is a single source in M 82. The flux of NGC 253, which did not vary significantly during the period of observations, can be well fit by either a thermal spectrum with keV, or by a power law with photon index of . We have also attempted fitting the measurements to more realistic composite models with thermal and power-law components, such as would be expected from a dominant contribution from binary systems, or Compton scattering of (far) IR radiation by radio emitting electrons. However, the addition of any amount of a power-law component, even with cutoff at 20 keV, only increases chi-square. The 90% confidence upper limit for power law emission with (photon) index 1.5 is only 2.4% of the 2–10 keV flux of M 82; the corresponding limit for NGC 253, with index 2.0, is 48%.
Key words: galaxies: starburst / galaxies: individual: M 82, NGC 253 / X-rays: galaxies / radiation mechanisms: non-thermal
© ESO, 2002
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.