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Optical Spectrum of TXS 0506+056 (possible counterpart to IceCube-170922A)

ATel #10799; I. A. Steele (Liverpool JMU)
on 29 Sep 2017; 13:00 UT
Credential Certification: Iain Steele (iainsteele@mac.com)

Subjects: Optical, Neutrinos

Referred to by ATel #: 10817, 10830, 10838, 10840, 10844, 10890

I obtained a 900 second exposure spectrum of TXS 0506+056 (PMN J0509+0541) on the night of 2017 Sept 28 using the SPRAT spectrograph of the 2.0m Liverpool Telescope on La Palma, Canary Islands.

The object is a possible counterpart to IceCube-170922A and is currently reported as showing high optical and Gamma ray emission (ATel #10773, #10787, #10791, #10792, #10794).

The spectrum is in the range 4000-8000 Angstroms with a resolution R~350. The spectrum is typical of a BL Lac object - apart from telluric features, it shows a smooth continuum. The only line feature seen is attributable to Galactic interstellar NaI absorption with EW~1 Angstroms. No redshift measurement is possible from the optical spectrum.

I note a preliminary flux calibration indicates the current spectrum is considerably bluer than the (similarly featureless) spectrum presented by Halpern et al. (2003, AJ, 125, 572), indicating a likely "bluer-when-brighter" behaviour.

Liverpool Telescope