Gamma-ray Burst 241115D = EP 241115a

(All information courtesy of the instrument teams.)

Previous IAU Circulars

• none

• GCN Circular #38239
  J. W. Hu (NAO, CAS), M. Q. Huang, Z. Y. Liu (USTC), C. Y. Dai (NJU), Y. J. Zhang (THU), C. X. Zhang (HUST), Y. Liu (NAO, CAS) on behalf of the Einstein Probe team
  We report on the detection of a fast X-ray transient, designated EP241115a, by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission. The transient was detected at=C2=A02024-11-15 05:47:20 (UTC) and lasted for around 500 seconds. The WXT position of EP241115a=C2=A0is R.A.=3D= =C2=A019.416=C2=A0deg, DEC =3D -17.954 deg (J2000) with an uncertainty of 2.6 arcmin (radius, 90% C.L. statistical and systematic).=C2=A0 It has a peak flux of ~1 x 10^-9 erg/s/cm^2 in the 0.5-4 keV band. The average 0.5-4 keV spectrum can be fitted with an absorbed power law with a photon index of 0.56(+0.54/-0.51) (with a column density fixed at the Galactic one of 1.6 x 10^20 cm^-2). The derived average unabsorbed 0.5-4 keV flux is 1.42(+0.6/-0.4) x 10^(-10) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters.
  No previously known bright X-ray sources are found within the error circle around the source position. Further follow-up observations are encouraged to identify the nature of this X-ray transient.
  Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics).
• GCN Circular #38242
  V.Lipunov, E.Gorbovskoy, N.Tiurina, P.Balanutsa, , D.Vlasenko, I.Panchenko, A.Kuznetsov, G.Antipov, A.Sankovich, A.Sosnovskij, Yu.Tselik, M.Gulyaev, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity) D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory)
  MASTER-SAAO robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa (South African Astronomical Observatory) was pointed to the EP241115a ( EP Team et al., GCN 38239) errorbox 8625 sec after notice time and 45587 sec after trigger time at 2024-11-15 18:27:07 UT, with upper limit up to 18.6 mag. Observations started at twilight. The observations began at zenith distance = 28 deg. The sun altitude is -14.1 deg.
  The galactic latitude b = -78 deg., longitude l = 159 deg.
  Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2671161
  We obtain a following upper limits.

  Tmid-T0  |      Date Time      |          Site       |             Coord (J2000)          |Filt.| Expt. | Limit| Comment
  _________|_____________________|_____________________|____________________________________|_____|_______|_______|________
  
     45617 | 2024-11-15 18:27:07 |         MASTER-SAAO | (01h 16m 06.64s , -18d 19m 58.1s) |   C |    60 | 18.6 |        
  

  Filter C is a clear (unfiltred) band.
  The observation and reduction will continue. The message may be cited.
• GCN Circular #38250
  SVOM/GRM team: Chen-Wei Wang, Shi-Jie Zheng, Yong-Wei Dong, Jiang-Tao Liu, Jian-Chao Sun, Yue Huang, Jiang He, Min Gao, Hao-Xuan Guo, Lu Li, Yong-Ye Li, Hong-Wei Liu, Xin Liu, Hao-Li Shi, Li-Ming Song, You-Li Tuo, Wen-Long Zhang, Wen-Jun Tan, Hao-Xi Wang, Jin Wang, Jin-Zhou Wang, Ping Wang, Rui-Jie Wang, Yu-Xi Wang, Bo-Bing Wu, Shao-Lin Xiong, Jian-Ying Ye, Yi-Tao Yin, Wen-Hui Yu, Fan Zhang, Li Zhang, Peng Zhang, Shuang-Nan Zhang, Yan-Qiu Zhang, Yan-Ting Zhang, Shu-Min Zhao, Xiao-Yun Zhao, Chao Zheng (IHEP), Maria-Grazia Bernardini (LUPM/INAF-OAB), Laurent Bouchet (IRAP), David Corre (CEA), Tais Maiolino (LUPM), Frédéric Piron (LUPM), Stéphane Schanne (CEA), Jingwei Wang (IAP), JeanLuc Attéia (IRAP)
  SVOM JSWG: Jian-Yan Wei (NAOC), Bertrand Cordier (CEA), Shuang-Nan Zhang (IHEP), Stéphane Basa (LAM), Arnaud Claret (CEA), Zi-Gao Dai (USTC), Frédéric Daigne (IAP), Jin-Song Deng (NAOC), Olivier Godet (IRAP), Andrea Goldwurm (APC), Diego Götz (CEA), Xu-Hui Han (NAOC), Cyril Lachaud (APC), En-Wei Liang (GXU), Yu-Lei Qiu (NAOC), Susanna Vergani (Obs.Paris), Jing Wang (NAOC), Chao Wu (NAOC), Li-Ping Xin (NAOC), Shao-Lin Xiong (IHEP), Bing Zhang (UNLV)
  report on behalf of the SVOM team:
  During the commissioning phase, the SVOM/GRM was triggered in-flight by GRB 241115D / EP 241115a at 2024-11-15T05:45:36 UT (T0). The time and localization are in consistent with EP241115a (J. W. Hu et al., GCN 38239).
  The real-time alert data and light curves of SVOM/GRM were downlinked to the ground through the VHF system with low latency. With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of multiple pulses with a T90 of 45 +3/-4 s.
  The GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb241115D.png
  This burst is located at about 60 degrees from the SVOM optical axis, and outside the ECLAIRs field of view. At the time of the burst, ECLAIRs was not collecting data.
  The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS.
  The SVOM point of contact for this burst is: Chen-Wei Wang (IHEP)(cwwang@ihep.ac.cn)
  
• GCN Circular #38251
  C. Y. Dai (NJU),M. Q. Huang, Z. Y. Liu (USTC), Y. J. Zhang (THU), C. X. Zhang (HUST), J. W. Hu, Y. Liu (NAO, CAS) on behalf of the Einstein Probe team
  Following up on the new X-ray transient EP241115a detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Hu et al., GCN 38239), which was associated with the GRB 241115D (Wang et al., GCN 38250), we performed a target of opportunity observation with Swift about 24 hours later. The Swift XRT observation began at 2024-11-16 at 06:00:03 (UTC) with an exposure time of 1448 seconds in the Photon Counting mode. An uncatalogued X-ray source was detected at R.A. =3D 19.4188 deg, DEC =3D -17.9596 deg (J2000) with an uncertainty of about 4.3 arcsec (radius, 90% C.L. statistical and systematic) and a signal-to-noise (S/N) ratio of 6.98, which is consistent with the position of the WXT transient within the uncertainties. We suggest that this XRT source is most likely associated with EP241115a.
  The average XRT spectrum can be fitted with an absorbed power law with a photon index of 1.50(+/-0.38) (with a column density fixed at the Galactic one of 1.6 x 10^20 cm^-2). The derived average unabsorbed 0.3-10 keV flux is 2.1(+0.9/-0.5) x 10^(-12) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters.
  We thank the Neil Gehrels Swift Observatory team for making the X-ray observation possible.
• GCN Circular #38254
  L. L. Fan (HNAS), A. Aryan, T.-W. Chen, H.-Y. Hsiao (all NCU), A. K. H. Kong (NTHU), J. Gillanders (Oxford), S. J. Smartt (Oxford/QUB), Y. J. Yang, A. Sankar. K, Y.-C. Pan, C.-C. Ngeow, M.-H. Lee, H.-C. Lin, C.-H. Lai, W.-J. Hou, C.-S. Lin, J.-K. Guo (all NCU), S. Yang, Z. N. Wang, G. H. Sun (all HNAS), H.-W. Lin (UMich), H. F. Stevance, S. Srivastav, L. Rhodes (all Oxford), M. Nicholl, M. Fulton, T. Moore, K. W. Smith, C. Angus, A. Aamer (all QUB), A. Schultz and M. Huber (both IfA, Hawaii) report:
  We observed the field of the fast X-ray transient EP241115a/GRB 241115D (Hu et al., GCN 38239; Dai et al., GCN 38251; Lipunov et al., GCN 38242; SVOM/GRM team + SVOM JSWG, GCN 38250) using the 40cm SLT and 1m LOT at Lulin Observatory in Taiwan as part of the Kinder collaboration (Chen & Yang et al., 2024arXiv240609270C).
  We utilized the astroalign (Beroiz et al. 2020, A&C, 32, 100384) and astropy (Astropy Collaboration et al. 2022, ApJ, 935, 167) packages to align and stack the individual frames. We do not find any new and uncataloged optical source in the stacked frames within the 4.3-arcsecond error circle of the Swift-XRT localization (Dai et al., GCN 38251).
  Moreover, we utilized the Python-based package AutoPhOT (Brennan & Fraser, 2022, A&A, 667, A62) to perform the PSF photometry on our stacked frames. The details of the observations and measured 3-sigma upper limit (in the AB system) are as follows:
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  The first SLT epoch of observations started at 12:26 UTC on the 16th of November 2024 (MJD = 60630.518), 1.28d after the EP WXT trigger.

  Telescope | Filter | MJD (start) | t-t0 (d) | Exposure (s) | Magnitude | avg. Seeing | med. Airmass
  SLT | r | 60630.518 | 1.28 | 300 * 6 | > 20.5 | 2".45 | 1.36
  

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  The first LOT epoch of observations started at 13:06 UTC on the 16th of November 2024 (MJD = 60630.546), 1.30d after the EP WXT trigger.

  Telescope | Filter | MJD (start) | t-t0 (d) | Exposure (s) | Magnitude | avg. Seeing | med. Airmass
  LOT | r | 60630.546 | 1.30 | 300 * 6 | > 21.7 | 1".44 | 1.33
  

  The presented magnitudes are calibrated using the field stars from the Pan-STARRS1 catalog and are not corrected for the expected Galactic foreground extinction corresponding to a reddening of E(B-V) = 0.02 mag in the direction of the transient (Schlafly & Finkbeiner 2011).
• GCN Circular #38323
  D. Svinkin, D. Frederiks, A. Lysenko, A. Ridnaia, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report:
  The long-duration GRB 241115D / EP 241115a (EP-WXT detection: Hu et al., GCN 38239; SVOM-GRM detection: Wang et al., GCN 38250) was detected by Konus-Wind (KW) in the waiting mode at T0(GRM) ~20736 s UT (05:45:36).
  A Bayesian block analysis of the KW waiting mode data in the 20-300 keV band reveals a >30 sigma count rate increase in the interval from T0(GRM)-68 s to ~T0(GRM)+35 s. The total burst duration is ~103 s.
  The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB241115D/
  The total burst fluence is 1.54(-0.21,+0.24)x10^-5 erg/cm^2, and the 2.944 s peak energy flux, measured from T0-0.138 s, is 7.10(-1.8,+1.4)x10^-7 erg/cm^2. (both in the 20 keV - 10 MeV energy range).
  The time-integrated spectrum of the burst, measured from T0-68 s to T0+35 s, can be described by a power law with exponential cutoff (CPL) model dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -1.74(-0.19,+0.53) and Ep = 102(-38,+24) keV.
  The spectrum near the peak count rate, measured from T0-3.082 s to T0+2.806 s, can be described by a CPL model with alpha ~-1.3 and Ep = 121(-22,+29) keV.
  All the quoted errors are estimated at the 68% confidence level. All the presented results are preliminary.