Volume 479, Number 1, February III 2008
|Page(s)||35 - 40|
|Published online||20 November 2007|
The 26 year-long X-ray light curve and the X-ray spectrum of the BL Lacertae object 1E 1207.9+3945 in its brightest state
Dipartimento di Fisica, Università La Sapienza, Piazzale A. Moro 2, 00185 Roma, Italy e-mail: email@example.com
2 Agenzia Spaziale Italiana, Unità Osservazione dell'Universo, Viale Liegi 26, 00198 Roma, Italy
3 ASI Science Data Center, ESRIN, via G. Galilei, 00044 Frascati, Italy
4 Dipartimento di Fisica, Università Tor Vergata, via della Ricerca Scientifica 1, 00133 Roma, Italy
Accepted: 24 September 2007
Aims.We studied the temporal and spectral evolution of the synchrotron emission from the high energy peaked BL Lac object 1E 1207.9+3945.
Methods.Two recent observations have been performed by the XMM-Newton and Swift satellites; we carried out X-ray spectral analysis for both of them, and photometry in optical-ultraviolet filters for the Swift one. Combining the results thus obtained with archival data we built the long-term X-ray light curve, spanning a time interval of 26 years, and the Spectral Energy Distribution (SED) of this source.
Results.The light curve shows a large flux increasing, by about a factor of six, in a time interval of a few years. After reaching its maximum in coincidence with the XMM-Newton pointing in December 2000 the flux decreased in later years, as revealed by Swift. The very good statistics available in the 0.5-10 keV XMM-Newton X-ray spectrum reveals a highly significant deviation from a single power law. A log-parabolic model with a best fit curvature parameter of 0.25 and a peak energy at ~1 keV describes well the spectral shape of the synchrotron emission. The simultaneous fit of Swift UVOT and XRT data provides a milder curvature () and a peak at higher energies (~15 keV), suggesting a different state of source activity. In both cases UVOT data support the scenario of a single synchrotron emission component extending from the optical/UV to the X-ray band.
Conclusions.New X-ray observations are important to monitor the temporal and spectral evolution of the source; new generation γ-ray telescopes like AGILE and GLAST may for the first time detect its inverse Compton emission.
Key words: radiation mechanisms: non-thermal / galaxies: active / X-rays: individuals: 1E 1207.9+3945 / X-rays: galaxies
© ESO, 2008
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.