Swift observations confirm a bright new outburst of MAXI J1957+032
ATel #9572; J. A. Kennea (PSU), P. A. Evans, A. P. Beardmore (U Leicester), H. A. Krimm (CRESST/GSFC/USRA), P. Romano (INAF-IASFPA), K. Yamaoka (AGU), M. Serino (RIKEN) and H. Negoro (Nihon U.)
on 30 Sep 2016; 03:16 UT
Credential Certification: Jamie A. Kennea (kennea@astro.psu.edu)
Starting 16:36UT on September 29th, 2016, Swift took a 1ks target-of-opportunity observation of MAXI J1957+032 (AKA IGR J19566+0326), which has been reported, by MAXI, to be in a new outburst (Negoro et al., ATEL #9565). Swift XRT data were taken automatically in Windowed Timing (WT) mode, due to the presence of a bright source in the field of view. A source consistent with the previously reported Swift position of this X-ray transient (Cherepashchuk et al., ATEL #7506), at a count rate of 26.1 +/- 0.3 XRT count/s. We note that this is significantly brighter than any previous detection of MAXI J1957+032 by Swift/XRT.
The XRT WT spectrum is well fit by an absorbed power-law model, with NH = 1.3 +/- 0.1 x 1021 cm-2 and photon index of 1.81 +/- 0.01. The 0.5-10 keV flux, uncorrected for absorption, is 9.4 +/- 0.2 x 10-10 erg/s/cm2, and approximately 1.14 +/- 0.02 x 10-9 erg/s/cm2 when corrected for absorption.
This flux is approximately 20 times brighter than seen in by Swift XRT in the previously reported outburst observed on October 9th, 2015 (Kennea et al., ATEL #8146). Spectrally MAXI J1957+032 is also significantly harder (photon index = 1.8 vs 2.8 seen in the October 2015 observation).
We have requested Swift monitoring of MAXI J1957+032 in order to track this outburst. Multi-wavelength observations are requested in order to determine the nature of this transient.
