MAXI J1810-298 detected by INTEGRAL at hard X-rays

ATel #14598; V. Sguera (INAF-OAS Bologna, Italy), L. Sidoli (INAF-IASF Milano, Italy)
on 4 May 2021; 18:14 UT
Credential Certification: Vito Sguera (sguera@iasfbo.inaf.it)

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MAXI J1803-298 is a new X-ray transient discovered on 1 May 2021 (ATel #14587). Rapid follow-up observations (at X-rays and optical waveband) were performed to identify its nature (ATels #14588, #14591, #14594, #14597).

The sky region of MAXI J1803-298 was covered by INTEGRAL observations of the Galactic Center region carried out from 2 May 2021 at 21:40 UTC to 4 May 2021 at 04:15 UTC. The transient source was particularly bright, being detected by IBIS/ISGRI in the energy band 25-60 keV at 103 sigma level (6.5 ks on source exposure). Significant detections were also achieved at higher energies, i.e. 28 sigma at 60-100 keV and 6 sigma at 100-200 keV. The measured fluxes are 241.1+/-2.3 mCrab (25-60 keV), 170.5+/-6.1mCrab (60-100 keV) and 103.0+/-17.1 mCrab (100-200 keV).

From a preliminary spectral analysis, the 30-200 keV spectrum is reasonably fitted by a cut-off power law model with hard photon index of 1.1+/-0.2 and energy cut-off equal to 37(+9,-6) keV. The broad band 20-200 keV X-ray flux is 3.7 x 10^-9 erg cm^-2 s^-1. In other bands, fluxes are 2 x 10^-9 erg cm^-2 s^-1 (25-60 keV), 7.8 x 10^-10 erg cm^-2 s^-1 (60-100 keV) and 3.4 x 10^-10 erg cm^-2 s^-1 (100-200 keV).