//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 33229 SUBJECT: ZTF23aabmzlp/AT2023azs: Zwicky Transient Facility discovery of a fast optical transient DATE: 23/01/28 18:10:55 GMT FROM: Igor Andreoni at JSI Igor Andreoni (JSI), Harsh Kumar (IITB), Michael Coughlin (UMN), Gaurav Waratkar (IITB), Eric Burns (LSU), Daniel Perley (LJMU) We report the discovery of the very fast optical transient ZTF23aabmzlp/AT2023azs with the Zwicky Transient Facility (ZTF, Bellm et al. 2019, Graham et al. 2019) at coordinates: RA = 11:30:16.49 (172.5687149d) Dec = +65:51:10.01 (65.8527808d) ZTF23aabmzlp was first detected on 2023-01-28 06:14 UT at r = 17.42 ± 0.04 mag. ZTF23aabmzlp faded by 2.3 magnitudes in 6.2 hours in the r-band. The last ZTF upper limit before the first detection was measured on 2023-01-28 05:55 UT in g-band, which is about 19 minutes before the first detection. There is no pre-detection at the transient location in 1,736 images of the field previously acquired by the ZTF survey. ZTF photometry is reported in the following table: ---------------------------------- MJD | mag AB ---------------------------------- 59972.24688660 | g > 19.7 59972.25979170 | r = 17.42 +- 0.04 59972.36381940 | g = 19.20 +- 0.11 59972.43465280 | g = 19.60 +- 0.15 59972.51854170 | r = 19.72 +- 0.20 ---------------------------------- Extinction on the line of sight is negligible, with E(B-V)=0.01 mag. The transient is located at high Galactic latitude b=49.2 deg. There is no cataloged source at the transient location in deep Legacy Survey DR9 and Pan-STARRS (Chambers et al., 2016) archival images. No gamma-ray triggers have been reported so far in the time window between the last ZTF upper limit and the first detection. However, it is possible that ZTF23aabmzlp/AT2023azs is a relativistic afterglow. Follow-up observations are strongly encouraged. ZTF23aabmzlp was discovered by the ‘‘ZTF Realtime Search and Triggering’’ project (ZTFReST; Andreoni & Coughlin et al., 2021) within the ZTF Collaboration. Based on observations obtained with the Samuel Oschin Telescope 48-inch and the 60-inch Telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. ZTF is supported by the National Science Foundation under Grant No. AST-2034437 and a collaboration including Caltech, IPAC, the Weizmann Institute for Science, the Oskar Klein Center at Stockholm University, the University of Maryland, Deutsches Elektronen-Synchrotron and Humboldt University, the TANGO Consortium of Taiwan, the University of Wisconsin at Milwaukee, Trinity College Dublin, Lawrence Livermore National Laboratories, and IN2P3, France. Operations are conducted by COO, IPAC, and UW. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 33230 SUBJECT: ZTF23aabmzlp/AT2023azs: GIT confirmation of the likely afterglow DATE: 23/01/28 19:08:22 GMT FROM: Harsh Kumar at Indian Inst of Tech,Bombay H. Kumar (IITB), V. Swain (IITB), R. Norbu (IAO), G. Waratkar (IITB), V. Bhalerao (IITB), G. C. Anupama(IIA), S. Barway (IIA) report on behalf of the GIT team: We observed ZTF23aabmzlp/AT2023azs discovered by Zwicky Transient Facility (Andreoni et al., GCN #33229), with 0.7m GROWTH-India Telescope (GIT). We obtained three exposures of 300sec each in the g', r', and i' filters. We clearly detected the candidate in our stacked images. The photometric results follow as:- ------------------------------------------------------------------- JD (mid) | Filter | Magnitude (AB) | ------------------------------------------------------------------- 2459973.224114 | g' | 20.48 +/- 0.07 | 2459973.235212 | r' | 20.31 +/- 0.06 | 2459973.248096 | i' | 19.79 +/- 0.20 | ------------------------------------------------------------------- GIT observations imply that the source continues fading and is redder in colour. Comparing our g' and r' observations with ZTF (Andreoni et al., GCN #33229), we compute a power-law decay index of ~0.7, further strengthening the claim that the candidate is an afterglow. Candidate follow-up is encouraged. The magnitudes are calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected for Galactic extinction. The GROWTH India Telescope (GIT; Kumar et al. 2022 ) is a 70-cm telescope with a 0.7-degree field of view, set up by the Indian Institute of Astrophysics (IIA) and the Indian Institute of Technology Bombay (IITB) with funding from DST-SERB and IUSSTF. It is located at the Indian Astronomical Observatory (Hanle), operated by IIA. We acknowledge funding by the IITB alumni batch of 1994, which partially supports operations of the telescope. Telescope technical details are available at https://sites.google.com/view/growthindia/. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 33237 SUBJECT: ZTF23aabmzlp/AT2023azs: 1.3m DFOT optical observations DATE: 23/01/30 19:26:14 GMT FROM: Rahul Gupta at ARIES, India Rahul Gupta, Amit K. Ror, S. B. Pandey, A. Aryan, A. Ghosh, Kiran Wani, Dimple, and K. Misra (ARIES) report: We observed the fast optical transient ZTF23aabmzlp/AT2023azs discovery by Zwicky Transient Facility (Andreoni et al. 2023, GCN 33229) using the 1.3m Devasthal Fast Optical Telescope (DFOT) located at the Devasthal observatory of Aryabhatta Research Institute of Observational Sciences (ARIES), Nainital, India. We have taken multiple frames having an exposure time of 120 sec in the R filter. We stacked the images after the alignment. We clearly detected the ZTF23aabmzlp/AT2023azs in the stacked image. The estimated preliminary magnitude is the following: Date_Start_UT T_start-T0 (days) Filter Exp time (sec) Magnitude ============================================================== 2023-01-28 18:42:44 ~0.52 R 120 sec*10 20.21 +/- 0.07 Where T0 is the ZTF first detection time of the transient. Our optical detection is consistent with Kumar et al. 2023, GCN 33230. The temporal decay behaviour of ZTF23aabmzlp/AT2023azs suggests an afterglow candidate, although multiwavelength follow-up observations are required to confirm. The magnitude is not corrected for the Galactic extinction in the direction of the transient. Photometric calibration is performed using the standard stars from the USNO-B1.0 catalog. This circular may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 33239 SUBJECT: ZTF23aabmzlp/AT2023azs: Mondy and AbAO optical observations DATE: 23/01/31 15:17:33 GMT FROM: Alexei Pozanenko at IKI, Moscow N. Pankov (HSE), A. Pozanenko (IKI), E. Klunko (ISTP), R. Ya. Inasaridze (AbAO), and S. Belkin (IKI) report on behalf of GRB IKI FuN: We observed the optical transient of ZZTF23aabmzlp/AT2023azs (Andreoni et al., GCN 33229) with AZT-33IK telescope of Mondy observatory starting on 2023-01-29 (UT) 21:25:32 and AS-32 Abastumani observatory (AbAO) on 2023-01-30 (UT) 17:04:08. We detect the transient (Andreoni et al., GCN 33229; Kumar et al., GCN 33230; Gupta et al., GCN 33237) with AZT-33IK and obtained an upper limit with AS-32. Preliminary photometry of the transient is following Date UT start MJD Filter Exp. OT Err. UL Telescope (mid, days) (s) 2023-01-29 21:25:32 59973.9136 R 30*120 21.63 0.11 23.2 AZT-33IK 2023-01-30 17:04:08 59974.7112 R 145*60 n/d n/d 20.3 AS-32 The photometry is based on the nearby USNO-B1.0 stars USNO-B1.0 RA Dec R2 172.5551 65.8488 18.68 172.5424 65.7999 17.05 172.4866 65.8507 15.58 //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 33241 SUBJECT: ZTF23aabmzlp/AT2023azs: LCOGT Optical Detection DATE: 23/01/31 20:23:25 GMT FROM: Robert Strausbaugh at University of Minnesota R. Strausbaugh (University of Minnesota), A. Cucchiara (NASA) report on behalf of a larger collaboration: We observed the ZTF23aabmzlp/AT2023azs (Andreoni et al., GCN 33229) field with the LCOGT 1-meter Sinistro instrument at the McDonald Observatory, TX, USA site, on January 29, from 09:46 to 10:02 UT (corresponding to 27.53 to 27.80 hours after ZTF first detection) with the SDSS r filter. We performed a series of 3x300s exposures in r band. We marginally (2-sigma) detect a source at the candidate coordinates with evidence for continued fading from previous optical observations (Kumar et al., GCN 33230; Gupta et al., GCN 33237; Pankov et al., GCN 33239). The following magnitude is calculated using the PanSTARRS catalog as reference: r = 22.07 +/- 0.13 These magnitudes are not corrected for galactic extinction. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 33251 SUBJECT: ZTF23aabmzlp/AT2023azs: AMI-LA radio upper limit DATE: 23/02/02 12:49:13 GMT FROM: Lauren Rhodes at Oxford Lauren Rhodes (Oxford), Itai Sfaradi (HUJI), Joe Bright (Oxford), Rob Fender (Oxford), Assaf Horesh (HUJI), David Green (Cambridge), Paul Scott (Cambridge), David Titterington (Cambridge) report: We observed the field of the candidate optical afterglow ZTF23aabmzlp (AT2023azs) (Andreoni et al., GCN 33229) with the Arcminute Microkelvin Imager Large-Array (AMI-LA) at 15.5 GHz beginning at UT 00:29:41 on 02-02-2023 for a total of 4 hours. The flux standard 3c286 was used to calibrate the bandpass response and flux scale of the AMI-LA and J1048+7143 was used as an interleaved complex gain calibrator. We do not detect any radio emission at the position reported in GCN 33229 and report a 3sigma upper limit of 128uJy/beam. Further observations are planned, and any future radio detection will be reported. We thank the staff at the Mullard Radio Astronomy Observatory for carrying out these observations and operating the AMI-LA. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 33253 SUBJECT: ZTF23aabmzlp/AT2023azs: VLA radio detection DATE: 23/02/02 16:00:45 GMT FROM: Daniel Perley at Liverpool JMU D. A. Perley (LJMU) reports on behalf of a larger collaboration: We observed the location of the fast optical transient ZTF23aabmzlp/AT2023azs (Andreoni et al., GCN 33229) using the Karl G. Jansky Very Large Array (VLA) on 2023 January 31 between 04:49 and 05:23 (UT). Observations were carried out using the X-band receivers at a mean frequency of 10 GHz. We detect a source at a location of RA = 11:30:16.468, Dec=+65:51:10.007 (J2000; RMS statistical accuracy +/- 0.02"), consistent with the optical position. The flux density is 136 (+/- 6) microJy at 9 GHz and 76 (+/- 7) microJy at 11 GHz. The mean observation time is approximately 59975.22, 2.96 days after the first reported optical detection. The detection of radio emission supports the conclusion that the source is the afterglow of a relativistic explosion at cosmological distance. The unusual spectral index is likely due to interstellar scintillation. We thank the VLA staff for rapidly scheduling and executing these observations. DisclaimerNone //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 33255 SUBJECT: ZTF23aabmzlp/AT2023azs: Lulin 1m LOT optical observations DATE: 23/02/03 15:40:58 GMT FROM: Ting-Wan Chen at MPE S. Yang (Stockholm), T.-W. Chen (TUM/MPA), H.-Y. Hsiao, Y.-C. Pan, C.-C. Ngeow, W.-J. Hou, C.-S. Lin, H.-C. Lin, and J.-K. Guo (IANCU) report: We observed the field of ZTF23aabmzlp/AT2023azs (Andreoni et al., GCN 33229), using the Lulin One-meter Telescope (LOT) at Lulin Observatory, Taiwan, to obtain g,r,i-band images as part of the Kinder collaboration (Chen et al., AstroNote 2021-92). The first epoch of observations started at 20:51 UT on 28 of January 2023 (MJD = 59972.869), 0.61 days after the first detection from ZTF. The images were combined from 3 frames with 300 sec exposure time for g and r bands, and 2 frames with 300 sec exposure time for i band, taken under poor seeing conditions (4".0 average) and at a median airmass of 1.5. The second epoch was performed at 20:38 UT on 29 of January 2023 (MJD = 59973.860). The images were combined from 2 frames with 300 sec exposure time for each band, taken under variable seeing conditions (1".8 average) and at a median airmass of 1.5. We used PSF photometry to measure the transient brightness with template subtraction using the SDSS images, and derived the following preliminary magnitudes and 3-sigma limits (all in the AB system): 2023-01-28: g > 20.18 mag, r > 19.21 mag, and i > 19.13 mag. 2023-01-29: g > 21.82 mag, r = 21.78 +/- 0.15 mag, and i = 21.34 +/- 0.13 mag. Given magnitudes are calibrated against SDSS field stars and are not corrected for the expected Galactic foreground extinction corresponding to a reddening of E_(B-V) = 0.01 mag in the direction of the counterpart (Schlafly & Finkbeiner 2011). Our measurements of the photometric evolution of ZTF23aabmzlp/AT2023azs are consistent with previous optical observations reported from Kumar et al., GCN 33230; Gupta et al., GCN 33237; Pankov et al., GCN 33239; Strausbaugh et al., GCN 33241. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 33297 SUBJECT: ZTF23aabmzlp/AT2023azs: Neil Gehrels Swift Observatory X-ray observations DATE: 23/02/07 15:14:32 GMT FROM: Igor Andreoni at JSI Igor Andreoni (JSI/UMD/NASA-GSFC) reports on behalf of a larger collaboration Follow-up observations of the optical fast transient ZTF23aabmzlp/AT2023azs (Andreoni et al., GCN #33229, AstroNote 2023-21) were carried out with the Neil Gehrels Swift Observatory starting on 2023-01-29 09:54 UT. The total exposure time on target was 1.9ks. A faint source is tentatively detected in Swift XRT data at the location of ZTF23aabmzlp/AT2023azs in the 0.3-10 keV energy range. The source has a background-subtracted count rate of (2.5 +- 1.1) * 10^(-3) ct/s, which was obtained using an aperture with a radius of 18 arcsec. Using WebPIMMS [1], we converted the count rate to flux assuming a powerlaw model with a photon index of 2 and Galactic NH of 9.85E19 cm^(-2) [2]. The resulting flux in the 0.3-10 keV band is (8.6 +- 3.8) * 10^(-14) erg/s/cm^2. The possible detection of an X-ray counterpart and the detection of a radio counterpart with VLA (Perley et al., GCN #33253) further suggest that the fast optical transient ZTF23aabmzlp/AT2023azs is a cosmological afterglow. We thank the Swift team for approving and scheduling ToO observations of this source (target ID 15860). [1] https://heasarc.gsfc.nasa.gov/cgi-bin/Tools/w3pimms/w3pimms.pl [2] HI4PI Collaboration, N. Ben Bekhti, L. Floer, et al., 2016, Astronomy & Astrophysics, 594, A116 (HI4PI Map).