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GCN Circulars

GCN Circulars are rapid astronomical bulletins submitted by and distributed to community members worldwide. They are used to share discoveries, observations, quantitative near-term predictions, requests for follow-up observations, or future observing plans related to high-energy, multi-messenger, and variable or transient astrophysical events. See the documentation for help with subscribing to or submitting Circulars.

Search for Circulars by submitter, subject, or body text (e.g. 'Fermi GRB').
To navigate to a specific circular, enter the associated Circular ID (e.g. 'gcn123', 'Circular 123', or '123').
Advanced Search

To narrow the search results, use advanced search syntax. This allows for specifying which circular field to search (submitter, subject, and/or body). For additional information, refer to the advanced search documentation.

Advanced Search Examples (click to copy):

subject:"Swift"
body:"GRB"
submitter:"Judith Racusin"
  1. GRB 250717B: Swift-XRT observations
  2. GRB 250718B: Fermi GBM Final Real-time Localization
  3. Swift Trigger 1334535 / GRB 250718A: COLIBRÍ optical upper limits
  4. Swift Trigger 1334535: a possible GRB 250718A
  5. Swift GRB250718.01: Global MASTER-Net observations report
  6. GRB 250717B: Fermi GBM Observation
  7. GRB 250717B: Swift/BAT-GUANO arcminute localization of a burst
  8. Konus-Wind detection of GRB 250716A
  9. GRB 250717A: Fermi GBM Final Real-time Localization
  10. GRB 250716A: Swift ToO observations
  11. GRB 250716A: GOTO tentative optical counterpart candidate
  12. GRB 250716A: Fermi GBM Observation
  13. Fermi GRB 250716A: Global MASTER-Net observations report
  14. EP250702a / GRB 250702B,D,E: Hubble Space Telescope Observations
  15. GRB 250702B,D,E / EP250702a: H.E.S.S. very-high-energy gamma-ray observations
  16. GRB 250713A: Mephisto optical upper limits
  17. GRB 250713A: NOT optical upper limits
  18. GRB 250713A: OHP/T193 upper limit
  19. GRB 250713A: SVOM/C-GFT upper limit
  20. GRB 250714A: Fermi GBM Final Real-time Localization
  21. GRB 250713A: EP-FXT counterpart detection
  22. GRB 250706A: Swift-BAT refined analysis
  23. GRB 250628A: Swift-BAT refined analysis
  24. GRB 250713A: JinShan optical upper limits
  25. GRB 250711A: DDOTI Optical Upper Limit
  26. EP250711a: COLIBRÍ refined photometry and optical confirmation of the candidate (duplicate submission)
  27. EP250711a: COLIBRÍ refined photometry and optical confirmation of the candidate
  28. EP250711a: NOT optical counterpart candidate
  29. EP250711a: EP-WXT detection and FXT follow-up observation of a fast X-ray transient
  30. EP250702a: gamma-ray upper limits from joint observations by the LST-1 and MAGIC telescopes
  31. GRB 250704A: GRANDMA observations
  32. GRB 250711A: BALROG localization (Fermi Trigger 773937617 / GRB 250711611)
  33. GRB 250702B,D,E / EP250702a: ALMA detection
  34. LIGO/Virgo/KAGRA S250629ae: Upper limits from Swift/BAT-GUANO
  35. IceCube-250708A: No Candidates from WINTER
  36. GRB 250702B,D,E/EP250702A: MeerKAT radio observations at 1.28GHz
  37. GRB 250702B,D,E / EP250702a: 10 GHz detection with the VLA
  38. IceCube-250708A: Upper limits from a search for additional neutrino events in IceCube
  39. GRB 250709A: Fermi GBM Final Localization
  40. GRB 250706B/C: Insight-HXMT detection
  41. EP/WXT 01709181970: GOTO observations confirm stellar variability
  42. The EP-WXT trigger 01709181970 is likely a flaring star
  43. GRB250702 B,D,E / EP250702a: MOSFIRE imaging of the afterglow
  44. LIGO/Virgo/KAGRA S250704ab: NED Galaxies in the 4-Update Localization Volume
  45. IceCube-250706A: No Candidates from WINTER
  46. IceCube-250708A - IceCube observation of a high-energy neutrino candidate track-like event
  47. GRB 250704B / EP250704a: VLA radio detection
  48. Fermi GRB 250708A: Global MASTER-Net observations report
  49. LIGO/Virgo/KAGRA S250705cb: Updated Sky localization
  50. LIGO/Virgo/KAGRA S250704ab: Updated Sky localization and EM Bright Classification
  51. LIGO/Virgo/KAGRA S250702n: Updated Sky localization
  52. LIGO/Virgo/KAGRA S250701bq: Updated Sky localization
  53. EP250704a/GRB250704B : HCT optical and NIR upper limits
  54. LIGO/Virgo/KAGRA S250701bp: Updated Sky localization
  55. GRB 250706B/C: Konus-Wind analysis of the prompt emission
  56. GRB 250704B: CALET Gamma-Ray Burst Monitor detection
  57. GRB 250704B / EP250704a: Mondy and AbAO optical observations
  58. GRB 250702F: radio detection with the VLA
  59. GRB 250706B/C: VLT/X-shooter redshift z = 0.942
  60. Fermi-LAT Gamma-ray Observations of IceCube-250706A
  61. IceCube-250706A: Global MASTER-Net observations report
  62. GRB 250704A: SVOM/COLIBRÍ (FM-GFT) optical observations
  63. EP250702a/ GRB 250702B: NuSTAR X-ray Observations
  64. GRB 250706C: Konus-Wind detection of a very bright GRB ~1200 s before GRB 250706B
  65. GRB 250704A: Swift/BAT-GUANO localization skymap of a burst
  66. GRB 250702F: GRANDMA observations
  67. GRB 250706A: Swift-XRT refined Analysis
  68. GRB 250706B: refined SVOM/MXT data analysis
  69. GRB 250706A: Swift/UVOT Upper Limits
  70. GRB 250706B: REM optical observations
  71. GRB 250706A: REM optical/NIR observations
  72. IceCube-250706A: COLIBRÍ optical upper limits
  73. GRB 250706A: JinShan optical upper limits
  74. GRB 250706A: SAO RAS optical observations
  75. EP250704A: NOWT Detection
  76. GRB 250706A: SVOM/C-GFT upper limit in eary phase
  77. GRB250706B: Swift-XRT counterpart detection
  78. GRB 250706B: iTelescope optical observations
  79. EP250704a / GRB 250704B: end of optical plateau phase and rapid fading of the counterpart
  80. GRB 250706B: TRT bright optical counterpart detection
  81. GRB 250706A: GROWTH-India Telescope optical upper limit
  82. GRB 250706B: SVOM detection of a long burst
  83. GRBs 250702B,C,D,E / EP250702a: J band upper limit by SYSU 80cm infrared telescope
  84. EP250702a/GRB250702 B,E,D: MeerKAT radio counterpart
  85. GRB 250703A: EIRSAT-1 GMOD Detection
  86. GRB 250704B: Swift/UVOT Upper Limits
  87. GRB 250704A: Swift/UVOT Detection
  88. LIGO/Virgo/KAGRA S250705cb: Identification of a GW compact binary merger candidate
  89. Radio observation of GRBs 250702B,C,E / EP250702a with the Allen Telescope Array
  90. Konus-Wind detection of GRB 250703A
  91. IPN triangulation of GRB 250703A
  92. EP250704a/GRB 250704B: GSP observations of the optical counterpart
  93. EP250704a/GRB 250704B VLT/HAWK-I NIR afterglow detection
  94. GRB 250702F: Kilonova-Catcher optical afterglow detection
  95. EP250704a / GRB 250704B: VLT/X-shooter spectroscopic redshift z = 0.661
  96. EP250704a / GRB 250704B: JinShan optical observations
  97. GRB 250704A: SVOM/VT optical observation
  98. EP250704a / GRB 250704B: SAO RAS optical observations
  99. EP250704a / GRB 250704B : GROWTH-India Telescope optical observations
  100. GRBs 250702B,D,E / EP250702a: fast fading, extremely red counterpart

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