A new outburst of IGR J06074+2205

ATel #16525; Roberto Nesci (INAF/IAPS), Mariateresa Fiocchi (INAF/IAPS), Antonio Vagnozzi (MPC589)
on 12 Mar 2024; 22:00 UT
Credential Certification: Roberto Nesci (roberto.nesci@inaf.it)

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IGR J06074+2205 is a B0.5Ve HMXB with a pulsar companion of 374 ms period (Nakajima et al. ATel #16401), discovered by INTEGRAL in 2003 (Chenevez, ATel #223). After many years of quiescence the star underwent some X-ray outbursts (Nakajima et al., ATel#15294; Semena, ATel #16267; Nakajima et al., ATel #16351; Sguera, ATel #16277; Chenevez et al., ATel #16278). It was also detected by Fermi-LAT (Malacaria et al., ATel #16307). Based on these observations a probable period of 80 +/-2 days was suggested by Mihara et al., ATel #16351 and Nakajima et al. ATel #16394, with the next outburst expected around March 15 2024. Spectroscopic follow-up by Nesci et al. (ATel #16512) since January 2024 indicated that the H-alpha emission line was always strong, suggesting that a new outburst should occur at the predicted time. Following these indications, we performed a ToO observation with Swft-XRT on 2024-03-12T lasting 1176 s. A quick look photometry showed clearly the source at 0.88 +- 0.03 c/s. In the previous outbursts, the maximum detected count rate was 1.31 c/s on 2023-10-14, 5 days after the outburst on 2023-10-09, so it is likely that the source will become even brighter in the next days. The average X-ray spectrum (0.5-10.0 keV) is well described by an absorbed power-law model (reduced chi^2=0.9 for 206 d.o.f.) with an equivalent hydrogen column of (1.7 +/- 0.4)E22 cm^-2, a photon index of 1.0+/-0.3 and an absorbed flux of 9.5E-11 erg cm^-2 s^-1 (unabsorbed flux of 1.2 E-10 erg cm^-2 s^-1) in the 0.5-10 keV energy range. This is the first time that an outburst of IGR J06074+2205 is catched by Swift based on a predicted ephemeris. Further Swift pointings have been requested in the next days to follow the outburst evolution.