X-ray hiccups from Sagittarius A* observed by XMM-Newton: The second brightest flare and three moderate flares caught in half a day

D. Porquet, N. Grosso, P. Predehl, G. Hasinger, F. Yusef-Zadeh, B. Aschenbach, G. Trap, Fulvio Melia, R. S. Warwick, A. Goldwurm, G. Bélanger, Y. Tanaka, R. Genzel, K. Dodds-Eden, M. Sakano, P. Ferrando

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Abstract

Context. Our Galaxy hosts at its dynamical center SgrA*, the closest supermassive black hole. Surprisingly, its luminosity is several orders of magnitude lower than the Eddington luminosity. However, the recent observations of occasional rapid X-ray flares from SgrA* provide constraints on the accretion and radiation mechanisms at work close to its event horizon.Aims. Our aim is to investigate the flaring activity of SgrA* and to constrain the physical properties of the X-ray flares.Methods. In Spring 2007, we observed SgrA* with XMM-Newton with a total exposure of ~230 ks. We have performed timing and spectral analysis of the new X-ray flares detected during this campaign. To study the range of flare spectral properties, in a consistent manner, we have also reprocessed, using the same analysis procedure and the latest calibration, archived XMM-Newton data of previously reported rapid flares. The dust scattering was taken into account during the spectral fitting. We also used Chandra archived observations of the quiescent state of SgrA* for comparison.Results. On April 4, 2007, we observed for the first time within a time interval of roughly half a day, an enhanced incidence rate of X-ray flaring, with a bright flare followed by three flares of more moderate amplitude. The former event represents the second brightest X-ray flare from Sgr A* on record with a peak amplitude of about 100 above the quiescent luminosity. This new bright flare exhibits similar light-curve shape (nearly symmetrical), duration (~3 ks) and spectral characteristics to the very bright flare observed in October 3, 2002 by XMM-Newton. The measured spectral parameters of the new bright flare, assuming an absorbed power law model taken into account dust scattering effect, are = cm and = 2.3 0.3 calculated at the 90% confidence level. The spectral parameter fits of the sum of the three following moderate flares, while lower ( = cm and ), are compatible within the error bars with those of the bright flares. The column density found, for a power-law model taking into account the dust scattering, during the flares is at least two times higher than the value expected from the (dust) visual extinction toward SgrA* ( ~ 25 mag), i.e., 4.5 10 cm. However, our fitting of the SgrA* quiescent spectra obtained with Chandra, for a power-law model taking into account the dust scattering, shows that an excess of column density is already present during the non-flaring phase.Conclusions. The two brightest X-ray flares observed so far from SgrA* exhibited similar soft spectra.

Original languageEnglish (US)
Pages (from-to)549-557
Number of pages9
JournalAstronomy and Astrophysics
Volume488
Issue number2
DOIs
StatePublished - Sep 2008

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Keywords

  • Galaxy: center
  • Radiation mechanisms: general
  • X-rays: general
  • X-rays: individuals: SgrA

ASJC Scopus subject areas

  • Space and Planetary Science

Cite this

Porquet, D., Grosso, N., Predehl, P., Hasinger, G., Yusef-Zadeh, F., Aschenbach, B., Trap, G., Melia, F., Warwick, R. S., Goldwurm, A., Bélanger, G., Tanaka, Y., Genzel, R., Dodds-Eden, K., Sakano, M., & Ferrando, P. (2008). X-ray hiccups from Sagittarius A* observed by XMM-Newton: The second brightest flare and three moderate flares caught in half a day. Astronomy and Astrophysics, 488(2), 549-557. https://doi.org/10.1051/0004-6361:200809986