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Recent Swift Observations of the Blazar TXS 1515-273

ATel #12691; N. Kebede, S. Ali, M. Balakrishnan, J. Chen, J. M. Miller, M. T. Reynolds, B. E. Tetarenko, D. Vozza (Univ. of Michigan)
on 25 Apr 2019; 14:53 UT
Credential Certification: Mark Reynolds (markrey@umich.edu)

Subjects: Radio, Optical, Ultra-Violet, X-ray, Gamma Ray, >GeV, TeV, AGN, Black Hole, Blazar

The high-synchrotron-peaked blazar TXS 1515-273 detected by Fermi-LAT on February 26, 2019 (ATel #12532) had a gamma ray flaring event in which it encouraged multi-wavelength observations of this source. On February 28, 2019 (ATel #12537), the Neil Gehrels Swift Observatory made follow up observations of TXS 1515-273. These showed an increase in flux for the XRT and UVOT data collected on February 26. Three subsequent observations between March 5 and March 18 have been made showing further activity. TXS 1515-273 has a photo-metric redshift upper limit of 1.1 (ATel #12537).

The Swift XRT telescope took three observations with an exposure of ~1.2 ks each. The X-ray spectrum (0.3 - 10.0 keV) can be fit by an absorbed power law model (redshift assumed to be z=1) with an HI column density of N_H = 8.5e20 cm^-2 (ATel #12537). The photon index reached a maximum of 3.0 +/ 0.7 in the observation on March 18, 2019 (OBSID:00046518008). This corresponds to a 0.3 - 10.0 keV (observed frame) flux of (6.9 +/- 0.9)e-12 erg/cm^2/s. At its lowest measured flux on March 5, 2019 (OBSID:00046518005), the data shows a photon index of (2.5 +/- 0.4), corresponding to a flux of (1.1 +/- 0.5)e-12 erg/cm^2/s. On March 9, 2019 the photon index is measured to be 3.0 +\-1.2 and a flux of (2.4 +\- 0.7)e-12 erg/cm^2/s. These compare to a maximum flux of (10.9 +/- 0.7)e-12 erg/cm^2/s measured on February 29 (ATel #12537). All errors are at the 90% confidence level.

The Swift UVOT observations on March 9, 2019 show the U band magnitude of (15.74 +/- 0.05). This is 0.8 mag brighter than the magnitude recorded on January 5, 2019 of (U = 16.56 +/- 0.07) and 0.1 mag brighter than on February 27, 2019 (15.89 +/- 0.07). The B band magnitude was brightest on March 5, 2019 (16.33 +/- 0.05). On March 18, 2019 the B band magnitude was (16.44 +/- 0.08). All magnitudes are in the Vega photometric system.

As this source has been varying in flux for the month of March, additional observations would provide further constraints on its evolution.

We would like to thank the Neil Gehrels Swift Observatory team for making these observations possible.