MAXI/GSC observations of weak X-ray outbursts from the Be/X-ray binary pulsar IGR J06074+2205 and the possible binary orbital period

ATel #16351; T. Mihara (RIKEN), M. Nakajima, H. Negoro, K. Kobayashi, M. Tanaka, Y. Soejima, Y. Kudo (Nihon U.), T. Kawamuro, S. Yamada, T. Tamagawa, N. Kawai, M. Matsuoka (RIKEN), T. Sakamoto, M. Serino, S. Sugita, H. Hiramatsu, H. Nishikawa, A. Yoshida (AGU), Y. Tsuboi, S. Urabe, S. Nawa, N. Nemoto, E. Goto (Chuo U.), M. Shidatsu (Ehime U.), I. Takahashi, M. Niwano, S. Sato, N. Higuchi, Y. Yatsu (Tokyo Tech), S. Nakahira, S. Ueno, H. Tomida, M. Ishikawa, S. Ogawa, T. Kurihara (JAXA), Y. Ueda, K. Setoguchi, T. Yoshitake, Y. Nakatani, Y. Okada (Kyoto U.), M. Yamauchi, Y. Hagiwara, Y. Umeki, Y. Otsuki (Miyazaki U.), K. Yamaoka (Nagoya U.), Y. Kawakubo (LSU), M. Sugizaki (NAOC), W. Iwakiri (Chiba U.)
on 29 Nov 2023; 05:27 UT
Credential Certification: Motoki Nakajima (nakajima.motoki@nihon-u.ac.jp)

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IGR J06074+2205 is the Be/X-ray binary of the 373.2 s pulsar and a B0.5Ve star (Reig et al. 2018). Since its discovery in 2003 (ATel#223), the source has been in a quiescent state for about two decades, and the binary properties remain unclear. There is no detailed observation of the outburst peak.

In the last two years, two X-ray outbursts were detected on 2022 March (ATel#15294) and 2023 October (ATel#16267, #16277, #16278, and #16307). In addition to these, MAXI/GSC detected another weak X-ray outburst on 2022 June 10 (MJD 59740). Using the recent three outbursts and the first one in 2003, we search for the possible periodicity of the X-ray outburst of this binary system.

The summary of the observed and assumed outburst peak dates are as follows:
No.1: 2003 Feb 12 (MJD 52682): 7 ± 2 mCrab (3-10keV);
No.2: 2022 Mar 23 (MJD 59661): 18 ± 5 mCrab (4-10keV);
No.3: 2022 Jun 10 (MJD 59740): 11 ± 5 mCrab (4-10keV);
No.4: 2023 Oct 9 (MJD 60226): 30 ± 16 mCrab (4-10keV);
Because all the peaks have a similar flux and duration of the outbursts (several days with MAXI 1-day sensitivity), we consider that all of them are normal (Type-I) outbursts.
(Note: Based on the observed light curve of the outburst, we predicted that the peak of the 2003 outburst was two days before the source discovery.)

First, we took the shortest interval between No. 2 and No. 3 as the X-ray outburst period and then considered the intervals of each of the four outbursts. We found that 80 +- 2 days is the probable outburst period. Or, those divided by an integer (80/n days, n=1,2,3...) can be solutions. Assuming that the observed outbursts were normal outbursts, the obtained period corresponds to the orbital period of the binary. The combination of the derived orbital period of 80 days and its pulse period of 373.2 s is consistent with the position of the distribution of the Be/X-ray binaries in the Corbet diagram. A larger n deviates further from the distribution.

If the B0.5Ve companion star is still active, the next outburst peak will be expect around December 28, 2023. Since No. 2 and No. 3 were successive, X-ray observations of the next outburst are recommended.

The latest X-ray light curve can be checked on the following pages;
MAXI ( http://maxi.riken.jp/v7l3h/J0607+220/index.html ),
Swift/BAT ( https://swift.gsfc.nasa.gov/results/transients/weak/IGRJ06074p2205/ ),
Fermi/GBM ( https://gammaray.msfc.nasa.gov/gbm/science/pulsars/lightcurves/igrj06074.html ), and
the BeXRB monitor page ( https://integral.esac.esa.int/bexrbmonitor/Plots/sim_plot_IGRJ06074+2205.html ).