//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25616 SUBJECT: LIGO/Virgo S190901ap: Candidates from the Zwicky Transient Facility DATE: 19/09/02 14:32:28 GMT FROM: Mansi M. Kasliwal at Caltech/Carnegie Erik Kool (OKC), Robert Stein (DESY), Yashvi Sharma (Caltech), Viraj Karambelkar (Caltech), Mansi Kasliwal (Caltech), Daniel Perley (LJMU), Valery Brinnel (HU Berlin), Jakob Nordin (HU Berlin), Shreya Anand (Caltech), Michael Coughlin (Caltech), Leo P. Singer (NASA GSFC), Igor Andreoni (Caltech), Gaurav Waratkar (IITB), Harsh Kumar (IITB), Maitreya Khandagale (IITB), Kunal Deshmukh (IITB), Varun Bhalerao (IITB), G. C. Anupama (IIA), Dougal Dobie (USyd/CSIRO), Brad Cenko (NASA GSFC), Tomas Ahmuda (UMD), Eric Bellm (UW), Albert Kong (NTHU), Anna Franckowiak (DESY), Pradip Gatkine (UMD) On behalf of the Zwicky Transient Facility (ZTF) and Global Relay of Observatories Watching Transients Happen (GROWTH) collaborations We observed the localization region of the gravitational wave trigger S190901ap (LVC et al. GCN 25606, GCN 25614) with the Palomar 48-inch telescope equipped with the 47 square degree ZTF camera (Bellm et al. 2019, Graham et al. 2019). The tiling was optimally determined and triggered using the GROWTH Target of Opportunity marshal (Coughlin et al. 2019a, Kasliwal et al. 2019b). We started obtaining target-of-opportunity observations in the g-band and r-band beginning at UT 2019-09-02 03:08 UT. We covered 44% of the enclosed probability based on the new lalinference map (38% of the enclosed probability based on the initial bayestar map) in 6500 sq deg mapped before we had to close due to clouds. Each exposure was 30s with a typical depth of 20.7 mag. The images were processed in real-time through the ZTF reduction and image subtraction pipelines at IPAC to search for potential counterparts (Masci et al. 2019). AMPEL (Nordin et al. 2019) was used to search the alerts database for candidates. After rejecting stellar sources (Tachibana and Miller 2018) and moving objects and applying machine learning algorithms (Mahabal et al. 2019), and after removing candidates with history of variability prior to the merger time, the following high-significance transient candidates were identified by our pipeline in the 95% localization of the new lalinference map (LVC et al. GCN 25614). ------------------------------------------------------------------------ ZTF Name | RA (deg) | DEC (deg) | Filter | Mag | Magerr ------------------------------------------------------------------------ ZTF19abvizsw | 279.472820 | +61.497984 | r | 19.45 | 0.11 ZTF19abvixoy | 279.552972 | +27.420935 | r | 19.22 | 0.10 ZTF19abvjnsm | 267.202697 | +44.693203 | r | 20.23 | 0.20 ZTF19abvionh | 253.750924 | +14.051330 | g | 20.73 | 0.31 ------------------------------------------------------------------------ ZTF19abvizsw has a red color (g-r ~ 0.5 mag), no underlying host in the reference image and is on the outer periphery of the new LVC sky localization. ZTF has observed this field every night for the past month as part of routine survey operations and the first detections of this transient are only after the binary neutron star merger time. ZTF19abvixoy has an upper limit from Aug 30 UT and possibly a faint counterpart in PS1. ZTF19abvjnsm has an upper limit from Sep 1 UT but its host galaxy has too high a phot-z estimate from SDSS of 0.51 +/- 0.11. The host galaxy of ZTF19abvionh has a consistent SDSS phot-z (0.064 +/- 0.016) but the two detections last night are separated by only a short baseline of 7 minutes (a moving object in our solar system cannot be ruled out for this candidate). We encourage spectroscopic and photometric follow-up to discern the nature of these transients. ZTF and GROWTH are worldwide collaborations comprising Caltech, USA; IPAC, USA, WIS, Israel; OKC, Sweden; JSI/UMd, USA; U Washington, USA; DESY, Germany; MOST, Taiwan; UW Milwaukee, USA; LANL USA; Tokyo Tech, Japan; IIT-B, India; IIA, India; LJMU, UK; TTU, USA; SDSU, USA and USyd, Australia. ZTF acknowledges the generous support of the NSF under AST MSIP Grant No 1440341. GROWTH acknowledges generous support of the NSF under PIRE Grant No 1545949. Alert distribution service provided by DIRAC@UW (Patterson et al. 2019). Alert database searches are done by AMPEL (Nordin et al. 2019). Alert filtering and follow-up co-ordination is being undertaken by the GROWTH marshal system (Kasliwal et al. 2019). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25639 SUBJECT: LIGO/Virgo S190901ap: Keck I LRIS spectroscopy of ZTF19abvizsw DATE: 19/09/04 00:27:15 GMT FROM: Mansi M. Kasliwal at Caltech/Carnegie Kevin Burdge (Caltech), Daniel A. Perley (LJMU) and Mansi M. Kasliwal (Caltech) report on behalf of the GROWTH collaboration: We obtained a Keck I LRIS spectrum of ZTF19abvizsw (Kool et al. GCN 25616). The reduced spectrum shows a featureless continuum superimposed with a number of narrow absorption lines, including Mg II, Mg I, and Fe II at a consistent redshift of z=1.26. This is far beyond the GW distance constraints on S190901ap (LVC et al. GCN 25614, GCN 25606) and demonstrates that this source is unrelated to the LIGO/Virgo source. It could be a flaring AGN or blazar, but there is no counterpart in PS1 or WISE and only a dim, marginal object at this location in the Legacy Survey. It may also be a GRB afterglow. Our conclusions disagree with those of Salmaso et al. (GCN 25618), who reported an M- or K-dwarf spectrum for this object. We note that there is a bright, red star less than 2 arcsec away from the transient position and it is possible that the spectrum reported in GCN 25618 may correspond to that object. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25640 SUBJECT: LIGO/Virgo S190901ap : SVOM/GWAC-F60A observation of transient ZTFabvizsw DATE: 19/09/04 01:42:35 GMT FROM: Liping Xin at NAOC, SVOM J. Y. Wei (NAOC), L. P. Xin (NAOC), S. Antier (CNRS/APC), J. Wang (GXU), N. Leroy (CNRS/LCL), D. Turpin (NAOC) on behalf of the SVOM Multi Messenger Astronomy and GWAC teams: http://www.svom.fr/en/svom-mma-and-gwac-team We used the 60cm SVOM/GWAC-F60A telescope to observe the transient found by the Zwicky Transient Facility ZTF19abvizsw (Kool et al. GCN 25616) localized in the region of the gravitational wave trigger S190901ap (LVC et al. GCN 25606, GCN 25614) during 17:28:07 and 18:45:07 UT on 02th, Sep. 2019. After stacking the images for 31*150 sec, the source was detected with a brightness of R=20.53+/-0.16 mag calibrated by nearby USNO R2 magnitudes. Comparing with the reported by Kool et al., GCN 25616, the source was fading for about one magnitude. Considering its fast decay, a featureless continuum superimposed with a number of narrow absorption lines and the large distance of z=1.26 (Burdge et al., GCN 25639), it is possible an orphan GRB afterglow. The stacked image observed by GWAC-F60A is shown here, http://cmm.svom.cn/gwpub/O3/S190901ap/ZTF19abvizsw_F60_findingchart.png (user:svomo3 pwd:gwo3) SVOM/GWAC-F60A is a dedicated telescope for follow-ups of SVOM/GWAC system, and is operated by Guangxi university and NAOC, CAS, at Xinglong observatory, China. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25643 SUBJECT: Liverpool Telescope observations of ZTF19abvizsw, a candidate untriggered GRB afterglow DATE: 19/09/04 04:50:36 GMT FROM: Daniel Perley at Liverpool JMU D. A. Perley (LJMU), A. Y. Q. Ho (Caltech), and C. M. Copperwheat (LJMU) report on behalf of the GROWTH collaboration: We obtained Liverpool Telescope IO:O imaging observations of ZTF19abvizsw/AT2019pim (Kool et al., GCN 25616), initially reported as a candidate counterpart to S190901ap but recently shown (Burdge et al., GCN 25639) to be an unrelated luminous transient at high redshift. Three r-band images of 150 seconds each were acquired between UT 20:28 and 20:35, followed by a griz sequence (3x150s per filter) between 22:33 and 23:08. The transient is well-detected in all four bands, but has faded substantially since the ZTF discovery epoch (see also Wei et al., GCN 15640). We report the following photometry (times given as UT midpoints): Time (UT) filter mag(AB) unc ------------------- ------ ------ ---- 2019-09-03 22:37:50 r 21.62 0.09 2019-09-03 22:46:33 g 22.02 0.10 2019-09-03 22:55:16 i 21.16 0.07 2019-09-03 23:03:57 z 20.87 0.12 After correcting for Galactic extinction (Schlafly et al. 2011, ApJ 737 103) the SED is well-fit by to a power-law in frequency with spectral index (F_nu ~ nu^beta) of beta ~ -1.4. As noted in GCN 25616, this field was imaged by ZTF every night during the 30 days prior to the ZTF discovery. No source was detected in any of these observations, with the most recent nondetection corresponding to 2019-09-01 UT 07:35, 0.86 days prior to the ZTF discovery observation. The fast rise, red power-law spectrum, and fast decline are consistent with observations of known GRB optical afterglows. However, we searched the Fermi GBM subthreshold GRB catalog over the window between the last ZTF detection and the discovery observation and found no GRB consistent with the location of the transient over time window. Further observations, including multiwavelength observations, have been requested. Important Notice: the information in this email and any attachments is for the sole use of the intended recipient(s). If you are not an intended recipient, or a person responsible for delivering it to an intended recipient, you should delete it from your system immediately without disclosing its contents elsewhere and advise the sender by returning the email or by telephoning a number contained in the body of the email. No responsibility is accepted for loss or damage arising from viruses or changes made to this message after it was sent. The views contained in this email are those of the author and not necessarily those of Liverpool John Moores University. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25683 SUBJECT: ZTF19abvizsw: AbAO and CrAO photometry DATE: 19/09/07 14:05:41 GMT FROM: Alexei Pozanenko at IKI, Moscow S. Belkin (IKI), A. Pozanenko (IKI), R. Ya. Inasaridze (AbAO), V. Rumyantsev (CrAO), A. Volnova (IKI), E. Mazaeva (IKI), I. Molotov (KIAM) report on behalf of IKI GRB FuN collaboration: We observed the ZTF19abvizsw/AT2019pim (Kool et al., GCN 25616; Burdge et al., GCN 25639; Wei et al., GCN 15640; Perley et al., GCN 25643; Levan et al., GCN 25653; Becerra et al., GCN 25655;) with AS-32 (0.7m) telescope of Abastumani Observatory and ZTSh telescope of CrAO. Preliminary photometry of the the optical transients is following. date UT start MJD Filter Exp. OT OT_err Obs./Tel. (mid, d) (s) 2019-09-04 16:54:07 58730.723 R 54*60 21.27 0.16 AbAO/AS-32 2019-09-05 21:49:03 58731.923 R 20*120 21.33 0.14 CrAO/ZTSh The photometry of the latest epoch of 2019-09-05 might be slightly contaminated by red southward star (see also Burdge et al., GCN 25639). We note the flattening of the initial decay previously reported by Becerra (GCN 25655). The photometry is based on nearby USNO-B1.0 stars USNO-B1.0_id R2 1514-0239703 18.81 1514-0239806 19.68 //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25684 SUBJECT: ZTF19abvizsw: 15GHz observations with AMI DATE: 19/09/07 14:29:10 GMT FROM: Lauren Rhodes at Oxford L. Rhodes, R. Fender, D. Williams, J. Bright (Oxford), K. Mooley (NRAO, Caltech; Jansky Fellow), A. Horesh (The Hebrew University of Jerusalem), D. Green, D. Titterington (MRAO) and the JAGWAR collaboration. We observed the position of ZTF19abvizsw/AT2019pim (Kool et al., GCN 25616) with the AMI Large Array at 15GHz. Initially reported as a potential counterpart to S190901ap, ZTF19abvizsw/AT2019pim has been shown to be an unrelated transient. We started observing on 5th September 2019 at 15:40:41UT. A 4hr observation showed a point source at the phase centre with a flux of 404 +/- 10 uJy/beam. The rms noise in the field is 30uJy. There are two 2MASS sources within the AMI clean beam (~40"x20"). We thank the MRAO staff for scheduling these observations. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25686 SUBJECT: ZTF19abvizsw/AT2019pim, search for GRB in SPI-ACS/INTEGRAL data DATE: 19/09/08 15:12:03 GMT FROM: Alexei Pozanenko at IKI, Moscow I. Chelovekov, A. Pozanenko, P. Minaev, S. Grebenev on behalf of the IKI GRB FuN collaboration report: Using SPI-ACS/INTEGRAL data we performed a search for a possible GRB which can be a source of the orphan transient ZTF19abvizsw discovered and observed in optic (Kool et al., GCN 25616; Burdge et al., GCN 25639; Wei et al., GCN 15640; Perley et al., GCN 25643; Belkin GCN 25683). The search was performed in a time window between the last ZTF non-detection (2019-09-01 UT 07:35) and the discovery of ZTF19abvizsw/AT2019pim (2019-09-02 03:08). The SPI-ACS was switch off at low orbit radiation belts pass between 2019-09-01 09:09:36 - 2019-09-01 19:28:44, and operating normally in other time intervals. A blind search for impulsed events was performed on two time scales, 1s and 5 s. We found following candidates for long duration GRBs. Below we present UTC time of the trigger, light curve figure and comment. Some event data is also presented in the figures. 1. UTC: 2019-09-01T07:24:05 ref: http://193.232.11.154/ZTF19abvizsw_binned/png/213100540010.000_acs_lc_T1__00452_00515.png 2019-09-01T07:24:05 comment: not visible in GBM 2. UTC: 2019-09-01T21:24:43 ref: http://193.232.11.154/ZTF19abvizsw_binned/png/213200030010.000_acs_lc_T1__00043_00071.png comment: might be coinciding with the tail of GBM trigger bn190901890 at 2019-09-01 21:19:37.514 3. UTC: 2019-09-02T01:36:16 ref: http://193.232.11.154/ZTF19abvizsw_binned/png/213200070010.000_acs_lc_T1__01320_01395.png comment: no GBM data yet comment: the event is also triggered IBAS One more triggered event at 2019-09-01T19:32:19 is most probably geophysical origin because of coincidence with IREM channel of e- with energies more than 500 keV. We also note the absence of any trigger in GBM data at that time. We do not consider it as a candidate, we plot it only for the reference. ref: http://193.232.11.154/ZTF19abvizsw_binned/png/213200010010.000_acs_lc_T1__00205_00256.png //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25982 SUBJECT: TESS Detection of the Optical Emission from the Possible Untriggered GRB Associated with ZTF19abvizsw DATE: 19/10/08 14:16:56 GMT FROM: Roland Vanderspek at MIT M. M. Fausnaugh, R. Vanderspek, on behalf of the TESS team TESS observed the location of the optical transient ZTF19abvizsw (Kool et al. 2019, GCN 25616) and associated new X-ray source (Ho et al. 2019, GCN 25658) nearly continuously during Sector 15 from 2019-08-15 to 2019-09-10 in Camera 2, CCD 2. The location was imaged in nearly 2400 30-minute full-frame images (FFIs) over that period. A light curve for ZTF19abvizsw was constructed from the FFIs using difference imaging. First, we constructed a reference image by median stacking 20 FFIs with low background levels. We then subtracted the reference image from each epoch using the ISIS software (Alard & Lupton 1998; Alard 2000), which solves for a spatially variable kernel that matches the PSF of the reference image to individual FFIs. This procedure removes systematic errors due to pointing shifts/jitter and thermal variations. We extracted a light curve by fitting a model of the PSF to the difference images at the predicted location of the transient in the FFIs based on the coordinates of ZTF19abvizsw reported to the Transient Name Server, and subtracted a local background based on the median of pixel values in an annulus of inner/outer radius 8/12 pixels. Uncertainties were estimated from the photon noise of the source and the observed scatter of the light curve at early times. We flux-calibrated the differential light curve by shifting the baseline before the transient to zero. We estimated the 3-sigma TESS limiting magnitude at each epoch by taking a factor of 3 times the flux uncertainty at each epoch and converting to TESS magnitudes (the TESS passband spans 600-1000 nm). The average 3-sigma limiting magnitude during the time of the transient is 19.11 and is dominated by the background flux in each FFI. ZTF19abvizsw was seen to brighten above the limiting magnitude in the FFI centered at UT 2019-09-02 03:15 - - one hour before the ZTF measurement at 2019-09-02 04:19:12 (https://wis-tns.weizmann.ac.il/object/2019pim ) - - and peak at a TESS magnitude of 18.37 +/- 0.18 at in the FFI centered at UT 2019-09-02 04:15. The discrepancy between this measurement and the ZTF r-band magnitude of 19.45 may be due to the redness of the source (Kool et al. 2019, GCN 25616) or brightness variations within the 30-minute FFI integration. The light curve has a sharp rise and a slower decline. The duration (T90) of the transient over the background limit is 1.44 days, and the integrated S/N of the transient was 10.4. We also fit a fast rise/exponential decay model to the light curve, from which we estimate the rise time to be 1.21 +/- 0.30 hours. The fit yields a peak magnitude of 18.40 +/- 0.07 at 2019-09-02 04:19:29. This is in family with the measured early brightness of optical counterparts of GRBs with redshifts near the measured redshift of ZTF19abvizsw of 1.26 (Levan et al. 2019, GCN 25653). The differenced image is seen at approximately RA=18:37:53.57, Dec=+61:29:55.58, with an estimated error of 3 arcseconds, based on the flux-weighted centroid. This position is in excellent agreement with the discovery coordinates of ZTF19abvizsw. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 26197 SUBJECT: ZTF19abvizsw: Upper limits from Konus-Wind observations DATE: 19/11/07 08:18:07 GMT FROM: Anna Kozlova at Ioffe Institute A. Ridnaia, S. Golenetskii, R. Aptekar, D. Frederiks, M. Ulanov, D. Svinkin, A. Tsvetkova, A. Lysenko, and T. Cline on behalf of the Konus-Wind team, report: Konus-Wind (KW) was observing the whole sky during a day before discovery of ZTF19abvizsw (2019-09-02 04:19:12 UTC; Kool et al., GCN Circ. 25616) including the time of TESS detection (2019-09-02 03:15 UTC, hereafter T0; Fausnaugh et al., GCN Circ. 25982) One triggered and one waiting-mode KW events were detected during ~1-day interval before T0. The burst localizations are inconsistent with the ZTF19abvizsw. For the interval excluding the KW events, we estimate an upper limit (90% conf.) on the 20 - 1500 keV fluence to 6.3x10^-7 erg/cm^2 for a burst lasting less than 2.944 s and having a typical KW short GRB spectrum (an exponentially cut off power law with alpha =-0.5 and Ep=500 keV). For a typical long GRB spectrum (the Band function with alpha=-1, beta=-2.5, and Ep=300 keV), the corresponding limiting peak flux is 1.3x10^-7 erg/cm^2/s (20 - 1500 keV, 2.944 s scale). Assuming the redshift z=1.26 (Burdge et al. GCN circ. 25639) and a standard cosmology model with H_0 = 67.3 km/s/Mpc, Omega_M = 0.315, and Omega_Lambda = 0.685 (Planck Collaboration, 2014), we estimate an upper limit on a long GRB peak luminosity L_iso ~ 1.3x10^51 erg/s. All the quoted values are preliminary.