Abstract
We report on NICER observations of the Be X-ray binary 4U 0115+63 during the rise of the source's current historic outburst, which began around 2023 March 28 and is the brightest recorded in 27 years. The rise of the outburst is still ongoing. The NICER observations were performed on 2023 March 30 (MJD 60033.66) at a count rate of 185.7+/-0.2 counts s^-1 and with a total exposure of 10.8 ks. The current 5-12 keV flux as measured by MAXI has reached 715+/-43 mCrab on 2023 April 3 (ATel #15975). The current 15-50 keV flux as measured by the Swift BAT is 342.9 mCrab (https://integral.esac.esa.int/bexrbmonitor/webpage_oneplot.php, see also http://integral.esac.esa.int/flashes-plots/H%200115+634_plot.html ) and the trend is still rising.
We fit the 0.5-10 keV NICER spectrum with a simple power law with a photon index of 0.42+/-0.03 modified by a neutral hydrogen absorption column of (1.07+/-0.03)x10^22 cm^-2. Prominent emission lines are detected at 6.4, 6.7, 6.97 and 7.1 keV, corresponding to the neutral Fe K-alpha, Fe XXV, Fe XXVI and neutral Fe K beta lines. The unabsorbed 1-10 keV X-ray flux is (2.80+/-0.02)x10^-9 erg cm^-2 s^-1. Based on the distance of 5.8 kpc as measured by Gaia (Fabricius et al. 2021), this corresponds to a 1-10 keV luminosity of (1.123+/-0.008)x10^37 erg s^-1.
Our preliminary timing analysis of the barycenter-corrected light curves yields a neutron star rotation period of 3.613+/-0.001 s, consistent with Fermi/GBM detection of the (orbitally corrected) source pulsations at 3.614316(5) at MJD 60032.5. The 1-10 keV pulse profile is single peaked, but a prominent notch that may be tied to absorption is observed. We find the 1-10 keV pulsed fraction to be 24.5+/-0.7%.
Multiwavelength follow-up observations are encouraged.
NICER is a 0.2-12 keV X-ray telescope operating on the International Space Station. The NICER mission and portions of the NICER science team activities are funded by NASA
We fit the 0.5-10 keV NICER spectrum with a simple power law with a photon index of 0.42+/-0.03 modified by a neutral hydrogen absorption column of (1.07+/-0.03)x10^22 cm^-2. Prominent emission lines are detected at 6.4, 6.7, 6.97 and 7.1 keV, corresponding to the neutral Fe K-alpha, Fe XXV, Fe XXVI and neutral Fe K beta lines. The unabsorbed 1-10 keV X-ray flux is (2.80+/-0.02)x10^-9 erg cm^-2 s^-1. Based on the distance of 5.8 kpc as measured by Gaia (Fabricius et al. 2021), this corresponds to a 1-10 keV luminosity of (1.123+/-0.008)x10^37 erg s^-1.
Our preliminary timing analysis of the barycenter-corrected light curves yields a neutron star rotation period of 3.613+/-0.001 s, consistent with Fermi/GBM detection of the (orbitally corrected) source pulsations at 3.614316(5) at MJD 60032.5. The 1-10 keV pulse profile is single peaked, but a prominent notch that may be tied to absorption is observed. We find the 1-10 keV pulsed fraction to be 24.5+/-0.7%.
Multiwavelength follow-up observations are encouraged.
NICER is a 0.2-12 keV X-ray telescope operating on the International Space Station. The NICER mission and portions of the NICER science team activities are funded by NASA
| Original language | English |
|---|---|
| Publication date | 4 Apr 2023 |
| Publication status | Published - 4 Apr 2023 |
| Series | The Astronomer's telegram |
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| Number | ATel #15978 |
Keywords
- X-ray
- Binary
- Neutron Star
- Transient
- Pulsar