XB-NEWS detection of a new outburst of MAXI J1348-630

ATel #13451; Saarah F. Pirbhoy, Maria Cristina Baglio, David M. Russell, D. M. Bramich, Payaswini Saikia, Aisha Al Yazeedi (NYU Abu Dhabi), Fraser Lewis (Faulkes Telescope Project & Astrophysics Research Institute, LJMU)
on 5 Feb 2020; 18:14 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Maria Cristina Baglio (cristina.baglio@brera.inaf.it)

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The black hole candidate X-ray binary, MAXI J1348-630 was discovered by the MAXI X-ray telescope in 2019 January (ATel #12425). We have been monitoring the source since the start of the outburst with Las Cumbres Observatory (LCO) 2-m and 1-m robotic telescopes. After an initial outburst peak, an optical and X-ray brightening was reported in 2019 May-June (peaking on MJD ~58640; ATel #12829, #12838).

The source then faded at optical wavelengths until the end of August (MJD 58725), then after a week, started to brighten. In ATel #13188 we reported the most recent LCO magnitudes that indicate the brightening, with g' = 19.98 +- 0.28, i' = 17.70 +- 0.072 on 2019 Sep 12 (MJD 58738.9). The source then became Sun constrained until recently.

We now have a real-time data analysis pipeline, the ''X-ray Binary New Early Warning System (XB-NEWS)'' for our incoming LCO images. The pipeline automatically downloads new images of our targets from the LCO archive and their associated calibration data, performs several quality control steps, computes an astrometric solution on each image using Gaia DR2 positions, and flux calibrates the images using the ATLAS-REFCAT2 catalogue (which includes PanSTARRS DR1, APASS, and other catalogues). The pipeline then produces a light curve with near real-time measurements (for more details see Russell et al. 2019).

Since MAXI J1348-630 has come out of Sun constraint, XB-NEWS has detected a new brightening of the source, going from i'= 19.62+-0.04, g'>21.10 on 2020 Jan 24 (MJD 58872) to the peak magnitudes i' = 16.83 +- 0.01, g' = 18.44 +- 0.01 on 2020 Feb 3 (~MJD 58882.04). It has brightened by 2.8 and >2.7 magnitude, in i' and g', respectively, in 10 days. The most recent magnitudes (MJD 58882.96) are: g' = 18.51 +- 0.01 and i' = 16.93 +- 0.01 which suggest that the optical flux is starting to decay. The optical monitoring with LCO is ongoing. The X-ray coverage of the re-brightening will be guaranteed thanks to an approved dedicated Swift/XRT ToO.

The LCO observations are part of an on-going monitoring campaign of ~ 40 low-mass X-ray binaries (Lewis et al. 2008) with LCO and the Faulkes Telescopes. We aim to announce any new outbursts of these sources detected by XB-NEWS in near real-time at the onset of the outburst, and any other light curve morphological changes worth reporting. This work makes use of observations from the Las Cumbres Observatory (LCO). We acknowledge the support of the NYU Abu Dhabi Research Enhancement Fund under grant RE124.

Optical LCO light curves of MAXI J1348-630