Large Flare from Sgr A* Detected by Swift

ATel #5006; N. Degenaar, M. T. Reynolds, J. M. Miller (Michigan), J. A. Kennea (Penn State), R Wijnands (Amsterdam)
on 25 Apr 2013; 00:54 UT
Credential Certification: Mark Reynolds (markrey@umich.edu)

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We report the detection of a large X-ray flare from a position consistent with Sgr A* during regular monitoring observations of the Galactic center with Swift.

In a 1ks observation on 2013-04-24 (17:34UT) a large flare is detected. Using an 10" radius extraction region centred on the known radio position, we measure a count rate of 0.11+/-0.1 ct/s. Comparing to the long term X-ray lightcurve of Sgr A* accumulated by Swift from 2006-2011 (Degenaar et al., 2013), the flare is consistent with the largest count rate detected from Sgr A* by Swift to date.

A total of 122 counts are detected during the observation facilitating basic spectral fitting. Assuming a fixed column density of 9.1e22 cm^-3 (see Degenaar et al. 2013) and fitting with a power-law in the 2 - 10 keV bandpass, we measure

Gamma: 2.1+/-0.5
norm: 0.018 +0.019 -0.01

where the errors are at the 90% confidence level, resulting in an absorbed flux of 2.1e-11 erg/s/cm^2 (2-10 keV), or a luminosity of ~ 1.6e35 erg/s for an assumed distance of 8 kpc. These properties are consistent with the most luminous X-ray flares previously observed from Sgr A*, e.g., Degenaar et al. (2013), Nowak et al. (2012), Porquet et al. (2003, 2008), Baganoff et al. (2001).

Swift is carrying out a daily monitoring campaign throughout 2013 to study the evolution of the X-ray properties of Sgr A* as it interacts with the G2 cloud (Gillessen et al., 2012, 2013). All observations are promptly analyzed and the resulting X-ray lightcurve will be made publicly available at the link below. Bright flares (Lx > 1e35 erg/s) will be reported to the community in further telegrams.

If you would like to receive an automated email update of large flares, please email swift.sgra 'at' gmail.com to be added to the mailing list.

Swift Sgr A* Monitoring Campaign Website