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The near-infrared counterpart of GRO J1744-28

ATel #5999; N. Masetti (INAF/IASF, Bologna), P. D'Avanzo (INAF/Oss. Astron. Brera), N. Blagorodnova (IoA, Cambridge) and E. Palazzi (INAF/IASF, Bologna)
on 22 Mar 2014; 12:14 UT
Credential Certification: Nicola Masetti (masetti@iasfbo.inaf.it)

Subjects: Infra-Red, X-ray, Neutron Star, Star, Transient, Pulsar

Within a multiwavelength observational effort to monitor the behaviour of the source GRO J1744-28 during its ongoing outburst started on January 18, 2014 (ATels #5790, #5810, #5845, #5858, #5883, #5997), we observed its field in the near-infrared bands J, H and Ks.

Observations were acquired under an average seeing of 0.7 arcsec with the 3.58-metre ESO-NTT telescope equipped with SofI on March 10, 2014, starting at 07:53 UT and for a total exposure time of 6 min for each filter.

Our PSF-fitting photometry reveals that source 'a' of Gosling et al. (2007; MNRAS, 380, 1511), located at RA = 17:44:33.07 and Dec = -28:44:26.9 (J2000), has magnitudes J = 18.15 +- 0.06, H = 15.29 +- 0.05 and Ks = 13.85 +- 0.15. This means that its near-infrared magnitudes on March 10, 2014 were 0.4 to 0.8 mag brighter (depending on the chosen filter) than on July 26, 2003, when it was observed with ESO-VLT plus ISAAC. A quick inspection of these latter data, published in Gosling et al. (ibid.), confirms the brightening of this source.

On the contrary, object 'b' of that paper is consistent with having the same JHKs magnitudes in the two data sets.

Therefore, we conclude that source 'a' is the actual near-infrared counterpart of GRO J1744-28.

We thank the ESO Director and staff for the quick reaction to the submission of our Director's Discretionary Time request for observations, and the PESSTO team for the timely acquisition and reduction of the data. Observations presented here were obtained under ESO programme 292.D-5038 and from the (ESO archive).