The flux of 2S1417-624 is still rising

ATel #14394; J. Knies, S. Saeedi (ECAP/FAU), V. Doroshenko (IAAT), A. Semena, A. Lutovinov, I. Mereminskiy, S. Molkov (IKI), I. Kreykenbohm, P. Weber, J. Wilms (ECAP/FAU), A. Santangelo (IAAT)
on 16 Feb 2021; 15:17 UT
Credential Certification: Joern Wilms (j.wilms@sternwarte.uni-erlangen.de)

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On 2021-02-09 (MJD 59254.92) during the third consecutive all-sky survey, the eROSITA and Mikhail Pavlinsky ART-XC instruments on board the SRG observatory detected renewed activity from the X-ray pulsar 2S 1417-624 (RA: 215.303 deg, Dec: -62.699 deg), as also already reported based on Swift, MAXI, and GBM data (ATel #14349). The source started to brighten in the second week of January 2021. BAT, GBM, and MAXI lightcurves suggest that this trend continues (http://integral.esac.esa.int/bexrbmonitor/Plots/sim_plot_2S1417-624.html), which explains the relatively high flux observed by SRG.

In particular, the source was detected in eight consequent eROSITA scans with a stable count rate of 6.87(+/-0.15) counts/s. Assuming an absorbed powerlaw, we obtain an absorbed flux of 4.11(+/-0.2)E-10 (erg/s/cm^2) and unabsorbed flux of 3.66(+/-0.14)E-10 (erg/s/cm^2) in the 0.5-10.0 keV energy band. The source was also detected with high significance up to 20keV with ART-XC, with a 4-12keV flux of 7.46(+/-0.37)e-10 cgs and an indication of steepening above 10keV.

The SRG-measured flux is comparable to the estimate based on the current (MJD 59256) SWIFT/BAT count rate of ~0.02cps which implies broadband flux of ~2e-9 cgs (assuming the count-rate to flux conversion factor of 1.13E-7 cgs reported by Ji et al, 2019, MNRAS, 491, 1851). Assuming same spectral model as the above paper, the flux observed by SRG implies a broadband flux of ~2e-9 cgs in the 0.5-100keV band. For an assumed distance of 10kpc (Ji et al, 2019, MNRAS, 491, 1851), this corresponds to a luminosity of 2.4e37 erg/s.

We note that current flux is by a factor of three lower than the expected peak flux, and thus the outburst is still in its rising phase. Based on the observed flux evolution in previous outbursts it is expected to peak some time mid-March 2021, although we note that the three earlier outbursts showed rather different light curves and there is a large uncertainty in the expected outburst peak time, rate, duration of the outburst, and possibly other parameters.

Further multi-wavelength monitoring is encouraged.