INTEGRAL IBIS detection of PKS 1830-211 during the GeV gamma-ray outburst observed by the Fermi LAT

ATel #12659; Stefano Ciprini (1. INFN Roma Tor Vergata; 2. ASI Space Science Data Center; Roma, Italy, [*]); Mariateresa Fiocchi (3. INAF-IAPS Roma, Italy [**]); Francesca Onori (3. INAF-IAPS Roma, Italy [**]); Sara Buson (4. Univ. of Wuerzburg Germany; 5. Univ. Maryland Baltimore County, USA, [*]); Celia Sanchez Fernandez (6. ESA ESAC, INTEGRAL Science Operations Centre, Madrid, Spain [**]); Pietro Ubertini (3. INAF-IAPS Roma, Italy [**]); David John Thompson (6. NASA Goddard Space Flight Center, Greenbelt, MD, USA, [*]); [*] on behalf of the Fermi Large Area Telescope Collaboration; [**] on behalf of the INTErnational Gamma-Ray Astrophysics Laboratory Collaboration.
on 12 Apr 2019; 21:26 UT
Credential Certification: Stefano Ciprini (stefano.ciprini@ssdc.asi.it)

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PKS 1830-211 is a peculiar MeV-peaked flat spectrum radio quasar at redshift z=2.507 (Lidman et al. 1999, ApJ, 514, L57), with absorption features and subject to strong gravitational lensing. PKS 1830-211 has been detected in a extremely bright (E>100MeV) gamma-ray state since October 2018 by the Fermi Large Area Telescope, LAT (for example ATel#12136, ATel#12252, ATel#12601) and by AGILE GRID (for example ATel#12541, ATel#12594, ATel#12603, ATel#12622). At the beginning of April 2019 the source rapidly approached and exceeded a daily gamma-ray flux (E>100MeV) of 10^-5 ph cm^-2 s^-1.

Timely ToO observations of PKS 1830-211 were performed by the ESA's INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL), with start time April 3, 2019, 05:45:58 UTC and end time April 5, 2019, 11:04:20 UTC. PKS 1830-211 is detected by INTEGRAL IBIS/ISGRI at about 7 sigma significance, with an effective exposure time of 35 ks and a hard X-ray flux of (6.3±0.9)x10^-11 erg cm^-2 s^-1 in the 25-100 keV energy band. This corresponds to about a factor of 4.5 times the IBIS flux integrated in the period from November 2002 to April 2008 reported in Donnarumma et al. 2011, ApJ, 736, L30. The INTEGRAL data are Near Real Time and have been analyzed using the Offline Software Analysis version 11.0 (OSA11).

Fermi LAT preliminary analysis indicates that from the start of the INTEGRAL observation (Apr. 3, 2019) to the date of Apr. 11, 2019 the daily averaged gamma-ray flux (E>100MeV) measured by the LAT varied from a minimum flux level of (9.8±0.5)x10^-6 to a maximum of (1.75±0.06)x10^-5 ph cm^-2 s^-1 (errors are statistical only), the latter measured on Apr. 11, 2019. The peak 6-hour interval flux (E>100MeV) of (2.2±0.1)x10^-5 ph cm^-2 s^-1 was detected by the LAT on Apr. 11, 2019, and corresponds to about double the 4FGL catalog averaged flux of the Vela pulsar, the brightest persistent MeV-GeV gamma-ray source in the sky.

The PI of this ToO program, SC, and collaborators thank the INTEGRAL Science Operations Center (ISOC) at ESA European Space Astronomy Centre (ESAC), Villanueva de la Cañada, Madrid, Spain, for the scheduling of these observations. This note is based on observations with INTEGRAL, an ESA project with instruments and science data centre funded by ESA member states (especially the PI countries: Denmark, France, Germany, Italy, Switzerland, Spain), and with the participation of the Russian Federation and the USA.

Because Fermi normally operates in an all-sky scanning mode, regular monitoring of PKS 1830-211 will continue. In consideration of its ongoing activity we strongly encourage multiwavelength observations. For this source the Fermi LAT contact persons are S. Ciprini (stefano.ciprini@ssdc.asi.it) and S. Buson (sara.buson@astro.uni-wuerzburg.de). The Fermi-LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden.