Fermi-LAT detection of a GeV flare from high-synchrotron-peaked blazar TXS 1515-273

ATel #12532; Sara Cutini (INFN Perugia), on behalf of the Fermi Large Area Telescope Collaboration
on 26 Feb 2019; 19:12 UT
Credential Certification: Sara Buson (sara.buson@gmail.com)

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The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed gamma-ray flaring activity from a source positionally consistent with the blazar TXS 1515-273 also known as WISE J151803.59-273131.1 with radio coordinates, R.A.: 15h18m03.610s Dec.: -27d31m31.40s Equatorial J2000.0 (Healey, S. et al. 2007; ApJS, 171, 61). This high-synchrotron-peaked gamma-ray blazar was detected in the general Fermi-LAT catalogues as 3FGL J1518.0-2732 (Acero, F. et al. 2015; ApJS, 218, 23), 2FGL J1518.2-2733 (Nolan, P. L. et al 2012; ApJS, 199, 31) and 4FGL J1518.0-2731 (recently released on FSSC website, https://fermi.gsfc.nasa.gov/ssc/data/access/lat/8yr_catalog/) and the high energy catalogues as 3FHL J1518.0-2731 (Ajello, M. et al 2017; ApJS, 232, 18) and 2FHL J1517.9-2732 (Ackermann, M. et al 2016; ApJS, 222, 5). It has a photometric redshift upper limit of 1.1 (Kaur, A. et al. 2018; ApJ, 859, 80).

Preliminary analysis indicates that TXS 1515-273 was in a high state on 2019 February 24 and February 25 with an average gamma-ray flux (E>100MeV) of (0.27+/-0.05) x 10^-6 photons cm^-2 s^-1 (statistical uncertainty only), about 10 times greater than the average flux reported in the third Fermi-LAT catalog (3FGL). It was detected also in weekly time scale with lower integrated flux. During this high state it shows an hardening of the spectral index respect the general catalogues, from 2.05+/- 0.04 (4FGL) to 1.5+/0.1 (daily time scale). Because Fermi operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. In consideration of the ongoing activity of this source we encourage multiwavelength observations. For this source the Fermi-LAT contact persons is S. Cutini (sara.cutini@pg.infn.it).

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.