Swift observation of the rebrightening in MAXI J1820+070

ATel #12573; A. Bahramian (Curtin), S. Motta (Oxford), P. Atri, J. Miller-Jones (Curtin)
on 13 Mar 2019; 12:32 UT
Credential Certification: Arash Bahramian (arash.bahramian@curtin.edu.au)

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Following the detection of optical rebrightening in MAXI J1820+070 (ASASSN-18ey, ATel #12567), we observed the system with the Neil Gehrels Swift Observatory on 2019-03-12 17:36:24 (UT) for 1 ks. The source is clearly detected in XRT with a net count rate of ~0.03 ct/s.

We extracted an X-ray spectrum in the 0.3-10 keV range and fitted the spectrum with an absorbed powerlaw (using Xspec, with C-stats, assuming NH~1.5e21 cm^-2; ATel #11423). We measure an unabsorbed X-ray flux of 1.1(+0.4/-0.3)e-12 erg/s/cm2 (in the 1-10 keV band) with a photon index of 2.2(+/-0.3). Analysis of the previous Swift observation of the source, taken on 2019-03-10 05:21:35 UT for 2 ks, indicates an unabsorbed X-ray flux of 3(+/-1)e-13 erg/s/cm2 with a photon index of 2.3(+/-0.4). Thus we confirm that MAXI 1820+070 is rebrightening in the X-rays as well.

We also analyzed the Swift/UVOT data from both Swift observations on March 10th and March 12th, and we measured Vega magnitudes of 16.75(+/-0.04) and 15.59(+/-0.04) respectively (in the UM2 filter), indicating an increase in brightness by ~1.1 magnitude in this band.

Further observations have been requested and multi-wavelength follow up is encouraged. We thank the Swift team for rapidly scheduling these observations.