NuSTAR and XMM-Newton follow-up of the blazar TXS 1515-273

ATel #12565; Vandad Fallah Ramazani (Tuorla observatory, University of Turku, Finland), Armin Nabizadeh (Tuorla observatory, University of Turku, Finland), Elina Lindfors (FINCA, University of Turku, Finland)
on 10 Mar 2019; 19:34 UT
Credential Certification: Vandad Fallah Ramazani (vafara@utu.fi)

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The blazar TXS 1515-273 (RA=15 18 03.610, Dec= -27 31 31.40, J2000.0) has been showing flaring activity in gamma-rays (>100 MeV), X-ray (0.3-10.0 keV) and NIR bands (ATels #12532, #12537, #12552). The first time detection of sub-TeV gamma-ray (E>100 GeV) emission from this source was reported by MAGIC telescopes (ATel #12538). NuSTAR and XMM-Newton performed follow-up observations on this source. We assumed fixed equivalent hydrogen column density of 8.49e20 cm^-2 (Kalberla et al., 2005, A&A , 440, 775) in our analysis.

The NuSTAR observations carried out between MJD 58544.59 and 58545.31 with ~34 ks exposure time. The data were reduced by performing the standard data reduction procedure described in the NuSTAR user guide (https://nustar.ssdc.asi.it/news.php#) using the NuSTAR Data Analysis Software nustardas v1.8.0 with a caldb version 20180419 and assuming 75 arc-seconds circle as the source region. Comparing the log parabola model with power-law, power-law with exponential cut-off and broken power-law models, our preliminary analysis shows that the hard X-ray spectrum (4.0-79.0 keV) of the source can be described better by log parabola model (chi^2/DOF= 93.89/79). The spectral index of the model is 2.26+/-0.20 and the curvature parameter is 0.21+/-0.12. The corresponding flux in range of 4.0 to 79.0 keV is (7.18+/-0.31)e-12 erg/cm^2/s.

The XMM-Newton performed follow-up observations between MJD 58543.95 and 58544.24 with ~19 ks exposure time. The data were analysed using the XMM-Newton Science Analysis System SAS version 17.0.0 with the latest available calibration files. In order to use well-calibrated and cleaned data, the standard filtering expressions were applied to the observation, in which the circular regions of 35 arc-seconds were used to extract the source and background X-ray spectra. Our preliminary analysis shows that the soft X-ray spectrum (0.4-10.0 keV) can be described by log-parabola model (chi^2/DOF= 541/473). The spectral index of the model is 2.04+/-0.01 and the curvature parameter is 0.54+/-0.03. The corresponding flux in range of 0.4 to 10.0 keV is (7.99+/-0.06)e-12 erg/cm^2/s. The observed flux on MJD 58541.64 over the same energy range was 1.76e-11 erg/cm^2/s (Swift-XRT observation). This indicates that the soft X-ray flux is halved in time scale of ~56 h.

We thank the XMM-Newton and NuSTAR science operations teams for fast response and scheduling of our ToO observations.