GRB150424A

This page lists all entries on GRB150424A in GRBweb

Summary IPN Swift GCN 17743 GCN 17745 GCN 17749 GCN 17751 GCN 17752 GCN 17756 GCN 17757 GCN 17758 GCN 17759 GCN 17760 GCN 17761 GCN 17762 GCN 17804 GCN 18100

Summary table
Variable Value Source
T0 7:42:57 UTC GCN_circulars,Swift Det
ra 152.3057° Swift
decl -26.6309° Swift
pos_error 7.77e-05° Swift
T90 91.0 s Swift
T90_start 7:42:57 UTC Swift
fluence 1.50e-06 erg/cm² Swift
redshift 1.0000 GCN_circulars,correction
T100 91.0 s
GBM_located False
mjd 57136.321493055555 GCN_circulars,Swift Det
IPN table
GRB_name GRB150424A
ra 152.3125°
decl -26.6500°
pos_error 5.00e-02°
Swift table
GRB_name GRB150424A
t_trigger 7:42:57 UTC
ra 152.3057°
decl -26.6309°
pos_error 7.77e-05°
T90 91.0 s
fluence 1.50e-06 erg/cm²
redshift 3.0000
GCN 17743 table
GRB_name GRB150424A
GCN_number 17743
Detection_method Swift Det
t_trigger 7:42:57 UTC
ra 152.3120°
decl -26.6470°
Circular_text TITLE: GCN CIRCULAR NUMBER: 17743 SUBJECT: GRB 150424A: Swift detection of a short burst DATE: 15/04/24 07:58:55 GMT FROM: David Palmer at LANL A. P. Beardmore (U Leicester), K. L. Page (U Leicester), D. M. Palmer (LANL) and T. N. Ukwatta (LANL) report on behalf of the Swift Team: At 07:42:57 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 150424A (trigger=638946). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 152.312, -26.647 which is RA(J2000) = 10h 09m 15s Dec(J2000) = -26d 38' 47" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a single structure with a duration of about 0.5 sec. The peak count rate was ~55000 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began observing the field at 07:44:24.7 UT, 87.9 seconds after the BAT trigger. Using promptly downlinked data we find a bright, fading, uncatalogued X-ray source with an enhanced position: RA, Dec 152.3061, -26.6310 which is equivalent to: RA(J2000) = 10h 09m 13.46s Dec(J2000) = -26d 37' 51.6" with an uncertainty of 2.4 arcseconds (radius, 90% containment). This location is 60 arcseconds from the BAT onboard position, within the BAT error circle. This position may be improved as more data are received; the latest position is available at http://www.swift.ac.uk/sper. A power-law fit to a spectrum formed from promptly downlinked event data gives a column density in excess of the Galactic value (6.03 x 10^20 cm^-2, Willingale et al. 2013), with an excess column of 4.8 (+3.00/-2.59) x 10^21 cm^-2 (90% confidence). The initial flux in the 2.5 s image was 2.87e-09 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 150 seconds with the White filter starting 99 seconds after the BAT trigger. No credible afterglow candidate has been found in the initial data products. The 2.7'x2.7' sub-image covers 100% of the XRT error circle. The typical 3-sigma upper limit has been about 19.6 mag. The 8'x8' region for the list of sources generated on-board covers 100% of the XRT error circle. The list of sources is typically complete to about 18 mag. No correction has been made for the expected extinction corresponding to E(B-V) of 0.06. Burst Advocate for this burst is A. P. Beardmore (apb AT star.le.ac.uk). Please contact the BA by email if you require additional information regarding Swift followup of this burst. In extremely urgent cases, after trying the Burst Advocate, you can contact the Swift PI by phone (see Swift TOO web site for information: http://www.swift.psu.edu/too.html.)
GCN 17745 table
GRB_name GRB150424A
GCN_number 17745
Detection_method Optical
Circular_text TITLE: GCN CIRCULAR NUMBER: 17745 SUBJECT: GRB 150424A: Keck detection of optical afterglow DATE: 15/04/24 10:19:56 GMT FROM: Daniel Perley at Caltech D. A. Perley (Caltech) and N. J. McConnell (IfA) report: We observed the field of short-duration GRB 150424A (Beardmore et al., GCN 17743) with the Low Resolution Imaging Spectrometer (LRIS) on the Keck I 10m telescope. Three 120-second imaging exposures in g- and R-bands were acquired between 09:15 and 09:26 UT (approximately 1.6 hours after the GRB trigger), at low elevation through moderate cloud cover. In both filters we detect a bright (R~20 mag) source, not visible in DSS, at the following location inside the XRT error circle: RA = 10:09:13.381 dec = -26:37:51.50 (+/- 0.5" or less) We suggest this as the optical afterglow of GRB 150424A. We also note the presence of a large galaxy (resolved in DSS) 5 arcsec to the southwest.
GCN 17749 table
GRB_name GRB150424A
GCN_number 17749
Detection_method Swift-XRT Det
ra 152.3057°
decl -26.6309°
Circular_text TITLE: GCN CIRCULAR NUMBER: 17749 SUBJECT: GRB 150424A: Enhanced Swift-XRT position DATE: 15/04/24 14:17:39 GMT FROM: Phil Evans at U of Leicester M.R. Goad, J.P. Osborne, A.P. Beardmore and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team. Using 3164 s of XRT Photon Counting mode data and 6 UVOT images for GRB 150424A, we find an astrometrically corrected X-ray position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 152.30569, -26.63092 which is equivalent to: RA (J2000): 10h 09m 13.37s Dec (J2000): -26d 37' 51.3" with an uncertainty of 1.7 arcsec (radius, 90% confidence). This position may be improved as more data are received. The latest position can be viewed at http://www.swift.ac.uk/xrt_positions. Position enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans et al. (2009, MNRAS, 397, 1177). This circular was automatically generated, and is an official product of the Swift-XRT team.
GCN 17751 table
GRB_name GRB150424A
GCN_number 17751
Detection_method Swift-UVOT Det
ra 152.3057°
decl -26.6309°
Circular_text TITLE: GCN CIRCULAR NUMBER: 17751 SUBJECT: GRB 150424A: Swift/UVOT Observations DATE: 15/04/24 15:03:18 GMT FROM: Frank Marshall at GSFC F. E. Marshall (NASA/GSFC) and A. P. Beardmore (U. Leicester) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 150424A 99 s after the BAT trigger (Beardmore et al., GCN Circ. 17743). A source consistent with the position of the suggested optical afterglow (Perley and McConnell, GCN Circ. 17745) is detected in the initial UVOT exposures. The source remains nearly constant in 6 exposures with the white filter starting 99 s after the trigger and ending 6786 s after the trigger. The magnitude is approximately that reported by Perley and McConnell. This may be a detection of the host galaxy. The preliminary UVOT position is: RA (J2000) = 10:09:13.38 = 152.30577 (deg.) Dec (J2000) = -26:37:51.1 = -26.63086 (deg.) with an estimated uncertainty of 0.6 arcsec. (radius, 90% confidence). Preliminary detections and 3-sigma upper limit using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white 99 6786 609 20.38 +/- 0.07 v 641 5881 432 >19.8 b 567 6701 432 20.71 +/- 0.21 u 311 5061 462 20.13 +/- 0.20 w1 690 6291 413 20.00 +/- 0.24 m2 4452 6086 393 19.91 +/- 0.29 w2 616 5677 216 20.03 +/- 0.31 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.06 in the direction of the burst (Schlegel et al. 1998). [GCN OPS NOTE(24apr15): Per author's request the missing minus sign on the hh:mm:ss format of the value was added; the decimal-deg value was correct.]
GCN 17752 table
GRB_name GRB150424A
GCN_number 17752
Detection_method Konus-Wind Det
t_trigger 7:43:01.073 UTC
Circular_text TITLE: GCN CIRCULAR NUMBER: 17752 SUBJECT: Konus-Wind observation of GRB 150424A DATE: 15/04/24 16:56:48 GMT FROM: Dmitry Svinkin at Ioffe Institute S. Golenetskii, R. Aptekar, D. Frederiks, V. Pal'shin, P. Oleynik, M. Ulanov, D. Svinkin, A. Tsvetkova, A. Lysenko, and T. Cline on behalf of the Konus-Wind team, report: The short-duration, intense GRB 150424A (Swift/BAT detection: Beardmore et al., GCN Circ. 17743). triggered Konus-Wind at T0=27781.073 s UT (07:43:01.073). The burst light curve shows a multipeak structure with a total duration of ~0.4 s. The emission is seen up to 4 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB150424_T27781/ As observed by Konus-Wind, the burst had a fluence of 1.81(-0.11,+0.11)x10^-5 erg/cm2, and a 2-ms peak flux, measured from T0+0.212 s, of 1.85(-0.48,+0.48)x10^-4 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-averaged spectrum of the burst (measured from T0 to T0+0.256 s) is best fit in the 20 keV - 10 MeV range by a power law with exponential cutoff model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -0.37(-0.09,+0.10) and Ep = 919(-76,+82) keV (chi2 = 66/57 dof). Fitting by a GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -3.8 (chi2 = 66/56 dof) All the quoted errors are at the 90% confidence level. All the quoted values are preliminary.
GCN 17756 table
GRB_name GRB150424A
GCN_number 17756
Detection_method Optical
ra 152.2962°
decl -26.6162°
Circular_text TITLE: GCN CIRCULAR NUMBER: 17756 SUBJECT: GRB 150424A: NOT optical observations DATE: 15/04/24 23:08:53 GMT FROM: Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst D. Malesani (DARK/NBI), D. Xu (NAOC/CAS), D. J. Watson (DARK/NBI), and P. Blay (IAC/NOT), report on behalf of a larger collaboration: We observed the optical counterpart (Perley, GCN 17745; Marshall & Beardmore, GCN 17751) of the short GRB 150424A (Beardmore et al., GCN Circ. 17743), using the Nordic Optical Telescope equipped with the AlFOSC camera. The first 300-s R-band exposure was taken starting at 20:57 UT (13.2 hr after the GRB) We clearly detect the counterpart with a magnitude R = 20.67 +- 0.06 (assuming R = 16.27 for the USNO star at RA = 10:09:11.09, Dec = -26:36:58.4). This magnitude is just slightly fainter than the value reported by Perley (GCN 17745) 1.6 hr after the trigger, indicating a very slow decay - consistent with the UVOT report. The brightness of the afterglow is unprecedented for a short GRB this late after the GRB. Such a behaviour is unusual and we encourage further observations.
GCN 17757 table
GRB_name GRB150424A
GCN_number 17757
Detection_method GROND
Circular_text TITLE: GCN CIRCULAR NUMBER: 17757 SUBJECT: GRB 150424A: GROND detects strong fading DATE: 15/04/24 23:55:22 GMT FROM: Alexander Kann at TLS Tautenburg D. A. Kann (TLS Tautenburg), M. Tanga, and J. Greiner (both MPE Garching) report on behalf of the GROND team: We observed the field of the extremely bright short GRB 150424A (Swift trigger 638946; Beardmore et al., GCN #17743) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008, PASP 120, 405) mounted at the 2.2 m MPG telescope at ESO La Silla Observatory (Chile). Observations started at 23:09 UT on 2015-04-24, 15.4 hrs after the GRB trigger. They were performed at an average seeing of 1".2 and at an average airmass of 1.1. We detect the optical afterglow (Perley & McConnell, GCN # 17745; Malesani et al., GCN # 17756). Based on 7.7 min of total exposure time in g'r'i'z' and 8.0 min in JHK, centered 15.54 hrs after the GRB, we estimate the following preliminary magnitudes (all in AB system): g' = 22.0 +/- 0.2 mag, r' = 21.6 +/- 0.1 mag, i' = 21.4 +/- 0.1 mag, z' = 21.1 +/- 0.1 mag, J = 20.4 +/- 0.5 mag, and H > 19.9 mag. Compared to the NOT detection about two hours earlier, the afterglow has faded by 0.7 magnitudes, indicating the transition to a very rapid decay. Given magnitudes are calibrated against GROND zero points (g'r'i'z') as well as 2MASS field stars and are not corrected for the expected Galactic foreground extinction corresponding to a reddening of E_(B-V)=0.06 mag in the direction of the burst (Schlegel et al. 1998).
GCN 17758 table
GRB_name GRB150424A
GCN_number 17758
Detection_method Konus-Wind Det
redshift 0.3000
Circular_text TITLE: GCN CIRCULAR NUMBER: 17758 SUBJECT: GRB 150424A: 10.4m GTC spectroscopy DATE: 15/04/25 01:34:57 GMT FROM: Alberto Castro-Tirado at Inst.de Astro. de Andalucia A. J. Castro-Tirado (IAA-CSIC, ISA-UMA), R. Sanchez-Ramirez (UPV/EHU, IAA-CSIC), G. Lombardi (IAC, ULL, GRANTECAN) and M. A. Rivero (GRANTECAN), on behalf of a larger collaboration, report: Following the detection of the short-duration GRB 150424A by Swift/BAT (Beardmore et al. 2015, GCNC 17743) and Konus-Wind (Golenetskii et al. GCNC 17752), we have obtained an optical spectrum (2 x 900s) with the 10.4m GTC telescope (+OSIRIS) in La Palma (Spain), starting on Apr 24, 21:30 UT (i.e. 13.8 hr postburst), covering the 3700-10000 wavelength range. The slit included the position of the proposed optical afterglow (Perley and McConnell, GCNC 17745; Marshall and Beardmore, GCNC 17751; Malesani et al., GCNC 17756; Kann et al. GCNC 17757) as well as the extended galaxy 5 arcsec to the southwest (Perley and McConnell GCNC 17745). At the position of the optical afterglow, we see no obvious absorption features with the continuum extending to 3700 A (implying an upper limit of z < 3 to the redshift of the GRB). At the position of the nearby galaxy, we detect [O II] and H-alpha in emission at a redshift z = 0.30. At this redshift, 5 arcsec corresponds to 22.5 kpc. A more detailed data reduction is ongoing. We acknowledge D. Perley for providing the corresponding ID-chart.
GCN 17759 table
GRB_name GRB150424A
GCN_number 17759
Detection_method Swift-BAT Det
Circular_text TITLE: GCN CIRCULAR NUMBER: 17759 SUBJECT: GRB 150424A: spectral lag, extended-time emission DATE: 15/04/25 01:52:26 GMT FROM: Jay R. Cummings at NASA/GSFC/Swift J. P. Norris (BSU), S. D. Barthelmy (GSFC), J. R. Cummings (GSFC/UMBC), and N. Gehrels (GSFC) report: We report spectral lag and extended emission measurements for the intense, short GRB 150424A (trigger=638946; GCN Circ. 17743, 17745 & 17756) based on Swift-BAT data. Using a 4-ms binned light curve, the lag for the 25-50 keV to 100-350 keV bands is estimated as 0.6 (+0.6/-1.0) ms; and -2.4 (+1.3/-0.7) ms for the 15-25 keV to 50-100 keV bands. A Bayesian Block analysis of the mask-tagged data reveals one significant block of duration ~ 106 seconds at a level of 0.006 counts/det/s, following the intense, initial pulse complex. This extended emission component is three orders of magnitude lower than the peak intensity of the burst, ~ 5.3 counts/pixel/s.
GCN 17760 table
GRB_name GRB150424A
GCN_number 17760
Detection_method Swift-XRT Other
Circular_text TITLE: GCN CIRCULAR NUMBER: 17760 SUBJECT: GRB 150424A: Swift-XRT refined Analysis DATE: 15/04/25 07:59:05 GMT FROM: Phil Evans at U of Leicester A. Melandri (INAF-OAB), P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC), D.N. Burrows (PSU), J.A. Kennea (PSU), B. Sbarufatti (INAF-OAB/PSU), P.A. Evans (U. Leicester), A. Amaral-Rogers (U. Leicester) and A.P. Beardmore report on behalf of the Swift-XRT team: We have analysed 5.1 ks of XRT data for GRB 150424A (Beardmore et al. GCN Circ. 17743), from 77 s to 29.7 ks after the BAT trigger. The data comprise 206 s in Windowed Timing (WT) mode (the first 9 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Goad et al. (GCN Circ. 17749). The light curve can be modelled with a series of power-law decays. The initial decay index is alpha=1.22 (+0.13, -0.29). At T+168 s the decay steepens to an alpha of 2.75 (+0.14, -0.19) before breaking again at T+676 s to a final decay with index alpha=0.64 (+0.08, -0.10). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.60 (+/-0.07). The best-fitting absorption column is 9.4 (+2.7, -2.5) x 10^20 cm^-2, in excess of the Galactic value of 6.0 x 10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 2.00 (+0.19, -0.18) and a best-fitting absorption column of 1.1 (+0.6, -0.5) x 10^21 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.3 x 10^-11 (4.2 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 1.1 (+0.6, -0.5) x 10^21 cm^-2 Galactic foreground: 6.0 x 10^20 cm^-2 Excess significance: 1.8 sigma Photon index: 2.00 (+0.19, -0.18) If the light curve continues to decay with a power-law decay index of 0.64, the count rate at T+24 hours will be 0.022 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 7.4 x 10^-13 (9.2 x 10^-13) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00638946. This circular is an official product of the Swift-XRT team.
GCN 17761 table
GRB_name GRB150424A
GCN_number 17761
Detection_method Swift-BAT Det
ra 152.3050°
decl -26.6460°
Circular_text TITLE: GCN CIRCULAR NUMBER: 17761 SUBJECT: GRB 150424A: Swift-BAT refined analysis DATE: 15/04/25 15:46:23 GMT FROM: Tilan Ukwatta at LANL S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), A. P. Beardmore (U Leicester), J. R. Cummings (GSFC/UMBC), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC), D. M. Palmer (LANL), T. Sakamoto (AGU), M. Stamatikos (OSU), T. N. Ukwatta (LANL) (i.e. the Swift-BAT team): Using the data set from T-240 to T+963 sec from the recent telemetry downlink, we report further analysis of BAT GRB 150424A (trigger #638946) (Beardmore, et al., GCN Circ. 17743). The BAT ground-calculated position is RA, Dec = 152.305, -26.646 deg which is RA(J2000) = 10h 09m 13.2s Dec(J2000) = -26d 38' 45.7" with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment). The partial coding was 69%. BAT light curve shows a bright multi-peaked episode starting around T-0.05 sec, and ending around T+0.5 sec. Very weak extended emission can be seen up to about T+100 sec as mentioned in Norris, et al., GCN Circ. 17759. T90 (15-350 keV) is 91 +- 22 sec (estimated error including systematics). The time-averaged spectrum from T-0.06 to T+106.32 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.23 +- 0.15. The fluence in the 15-150 keV band is 1.5 +- 0.1 x 10^-06 erg/cm2. The 1-sec peak photon flux measured from T-0.06 sec in the 15-150 keV band is 12.0 +- 0.4 ph/cm2/sec. All the quoted errors are at the 90% confidence level. The results of the batgrbproduct analysis are available at http://gcn.gsfc.nasa.gov/notices_s/638946/BA/
GCN 17762 table
GRB_name GRB150424A
GCN_number 17762
Detection_method Swift-BAT Det
Circular_text TITLE: GCN CIRCULAR NUMBER: 17762 SUBJECT: GRB 150424A: RATIR Observations DATE: 15/04/25 17:26:07 GMT FROM: Nat Butler at Az State U Nat Butler (ASU), Alan M. Watson (UNAM), Alexander Kutyrev (GSFC), William H. Lee (UNAM), Michael G. Richer (UNAM), Chris Klein (UCB), Ori Fox (UCB), J. Xavier Prochaska (UCSC), Josh Bloom (UCB), Antonino Cucchiara (ORAU/GSFC), Eleonora Troja (GSFC), Owen Littlejohns (ASU), Enrico Ramirez-Ruiz (UCSC), Jos A. de Diego (UNAM), Leonid Georgiev (UNAM), Jess Gonzlez (UNAM), Carlos Romn-Ziga (UNAM), Neil Gehrels (GSFC), and Harvey Moseley (GSFC) report: We observed the field of the short-duration GRB 150424A (Beardmore, et al., GCN 17743) with the Reionization and Transients Infrared Camera (RATIR; www.ratir.org) on the 1.5m Harold Johnson Telescope at the Observatorio Astronmico Nacional on Sierra San Pedro Mrtir from 2015/04 25.14 to 2015/04 25.28 UTC (19.54 to 23.05 hours after the BAT trigger), obtaining a total of 2.4 hours exposure in the r, i, and z bands. The optical afterglow (Perley, GCN 17745; Marshall & Beardmore, GCN 17751; Malesani, et al., GCN 17756; Kann, et al., GCN 17757) is well-detected. In comparison with 2MASS and the USNO-B1 catalog, we obtain the following detections and upper limit (3-sigma): r 21.92 +/- 0.11 i 21.65 +/- 0.09 z > 20.17 These magnitudes are in the AB system and are not corrected for Galactic extinction in the direction of the GRB. Compared to the earlier NOT and GROND observations, the source appears to be continuing its strong fade (Kann, et al. GCN 17757). We thank the staff of the Observatorio Astronmico Nacional in San Pedro Mrtir.
GCN 17804 table
GRB_name GRB150424A
GCN_number 17804
Detection_method VLA Det
ra 152.3057°
decl -26.6310°
Circular_text TITLE: GCN CIRCULAR NUMBER: 17804 SUBJECT: GRB 150424A: 9.8 GHz VLA detection DATE: 15/05/07 17:03:52 GMT FROM: Wen-fai Fong at U of Arizona W. Fong (Univ. of Arizona) reports: "We observed the position of the short-duration GRB 150424A (Beardmore et al., GCN 17743) with the Karl G. Jansky Very Large Array (VLA) beginning on 2015 Apr 25.073 UT (18.02 hr post-burst) at a mean frequency of 9.8 GHz. In 1 hour of observations, we detect a faint radio source at the position: RA(J2000) = 10:09:13.37 Dec(J2000) = -26:37:51.49 with an uncertainty of 0.5" in each coordinate. This position is coincident with the position of the X-ray afterglow (Goad et al., GCN 17749) as well as the position of the optical afterglow (Perley and McConnell., GCN 17745; Malesani et al., GCN 17756; Kann et al., GCN 17757; Butler et al., GCN 17762). We measure a 9.8 GHz flux density of ~31 microJy. To assess the nature of this radio source, we obtained two additional sets of VLA observations starting at 4.67 and 7.88 days after the burst. The source is no longer detected in each of these observations, as well as a deep, combined image, to 3-sigma limits of 29 microJy and 20 microJy, respectively. Due to the fading of the radio source, as well as the positional coincidence with the X-ray and optical afterglows, we consider this source to be the radio afterglow of GRB 150424A. We thank the VLA staff for quickly executing these observations."
GCN 18100 table
GRB_name GRB150424A
GCN_number 18100
Detection_method correction
redshift 1.0000
Circular_text TITLE: GCN CIRCULAR NUMBER: 18100 SUBJECT: GRB 150424A: HST imaging DATE: 15/07/31 21:13:57 GMT FROM: Nial Tanvir at U.Leicester N. R. Tanvir (U. Leicester), A. J. Levan (U. Warwick), A. S. Fruchter (STScI), J. Hjorth, D. Watson (DARK), D. Perley (Caltech), J. Greiner (MPE), A. de Ugarte Postigo, C. Thoene (IAA-CSIC), R. A. Hounsell (Illinois), S. Rosswog (U. Stockholm) report: We observed the optical/nIR counterpart of short-GRB 150424A (Perley et al. GCN 17745) with HST at three epochs, roughly 6.7, 9.3 and 13.9 days post-trigger. On each occasion we obtained imaging with the WFC3/UVIS F606W and the WFC3/IR F125W and F160W filters. The optical transient is visible at all epochs, fading from J(AB)=25.3 to J(AB)=26.9 over the course of the observations. There is a suggestion of a colour change, from r-H(AB)~1.1 to r-H(AB)~2 between the first and last epoch, although the errors are large (and in particular suffer a rather uncertain background correction - see below). Significantly, the OT is superimposed on a faint source that is extended over about 1 arcsec. We propose that this extended source is most likely the host galaxy of the burst, rather than the bright nearby spiral whose redshift (z=0.3) was reported by Castro-Tirado et al. (GCN 17758). Our current best estimates of the magnitude of this source are r(AB)=26.8, J(AB)=26.1 and H(AB)=25.7, although we note that much of the flux in the r-band is due to a single blue knot of emission, whereas the nIR is more diffuse. Given the luminosity, size and colour of the proposed host, it is likely to be at z>0.7, where the 4000A break would help explain the red r-J colour of most of this galaxy. If the burst was at z=0.3 (e.g. if the faint extended source is a satellite of the spiral, or just a background galaxy aligned by chance), then we place limits on any kilonova/macronova emission of M_J(AB)>~-14.7 at 7 days post-burst in the rest frame. A more likely redshift of z~1, for example, would mean that our reddest filter only corresponds to the rest-frame I-band, here providing a limit of M_I(AB)>~-17.0 at 7 days in the rest-frame (i.e. ~1 mag fainter than typical for a collapsar-produced supernova at the same time). Further analysis is in progress.