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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"

5369 results found.

  1. EP250730a: SVOM/VT optical upper limit
  2. LIGO/Virgo/KAGRA S250727dc: DECam GW-MMADS candidates
  3. LIGO/Virgo/KAGRA S250727dc: DECam DESGW Epoch 1 Candidates
  4. EP250730a: Global MASTER-Net observations report
  5. EP250730a: Einstein Probe detection of an X-ray transient
  6. LIGO/Virgo/KAGRA S250727dc: DECam GW-MMADS upper limits of AT 2025smm
  7. GRB 250728A: Fermi GBM Observation
  8. GRB 250727A: AST3-2 Upper limit
  9. LIGO/Virgo/KAGRA S250725j: Identification of a GW compact binary merger candidate
  10. GRB 250721A: Fermi GBM Observation
  11. SVOM J195836+32283/sb25072103: NIR observations with WINTER
  12. GRB 250722A: Fermi GBM Final Real-time Localization
  13. The SVOM alert sb25072103 is not due to a GRB, but to a new galactic transient SVOM J195836+32283.
  14. GRB 250721A: MAXI/GSC detection
  15. GRB 250721A: Fermi GBM Final Localization
  16. Fermi trigger No 774730635: Global MASTER-Net observations report
  17. GRB 250717B: COLIBRÍ optical upper limit
  18. GRB 250716A: Lesedi Detection of Fading Optical Transient GOTO25eyp
  19. GRB 250713A: SVOM/VT optical upper limit
  20. GRB 250713A: SVOM/C-GFT upper limit
  21. EP250711a: COLIBRÍ refined photometry and optical confirmation of the candidate
  22. LIGO/Virgo/KAGRA S250711q: Identification of a GW compact binary merger candidate
  23. GRB 250702B,D,E/EP250702A: JCMT sub-mm observations at 350 GHz
  24. GRB 250702B,D,E / EP250702a: ALMA detection
  25. IceCube-250708A: No Candidates from WINTER
  26. IceCube-250708A: No Candidate Transients from the Zwicky Transient Facility
  27. IceCube-250708A: Upper limits from a search for additional neutrino events in IceCube
  28. GRB 250709A: Fermi GBM Final Localization
  29. LIGO/Virgo/KAGRA S250704ab: NED Galaxies in the 4-Update Localization Volume
  30. GRB 250704B / EP250704a: VLA radio detection
  31. Fermi-LAT Gamma-ray Observations of IceCube-250706A
  32. EP250702a/ GRB 250702B: NuSTAR X-ray Observations
  33. GRB 250703A: EIRSAT-1 GMOD Detection
  34. Konus-Wind detection of GRB 250703A
  35. IPN triangulation of GRB 250703A
  36. GRB 250702F: Calapai Observatory, Massa S. Giorgio (Messina), optical observation.
  37. LIGO/Virgo/KAGRA S250704ab: NED Galaxies in the 3-Initial Localization Volume
  38. GRB 250702A: CALET Gamma-Ray Burst Monitor detection
  39. Fermi GBM Analysis of GRB 250702B (formerly B,D,E); dissociation of C burst
  40. Fermi GRB 250703A: Global MASTER-Net observations report
  41. GRB 250702B,C,D,E/EP250702a: COLIBRÍ optical upper limit
  42. GRB 250703A: DDOTI Optical Upper Limit
  43. GRB 250702B,C,D,E / EP 250702a: MAXI/GSC detection
  44. GRB 250703A: Fermi GBM Final Real-time Localization
  45. GRB 250702D, C, E: Swift/BAT-GUANO localization skymap of a burst or galactic transient
  46. Fermi GRB 250702F: Global MASTER-Net observations report
  47. GRB 250702F: Swift detection of a burst with an optical counterpart
  48. Fermi GBM Triggers 250702B, C, D and E are likely from the same source
  49. GRB 250702A: Fermi GBM Detection
  50. GRB 250702D: Fermi GBM Final Localization Correction
  51. GRB 250702A: BALROG localization (Fermi Trigger 773142852 / GRB 250702413)
  52. GRB 250702A: Fermi GBM Final Real-time Localization
  53. Fermi Gamma-ray Burst Monitor trigger 772981768/250630548 is not a GRB
  54. Fermi GRB 250626A: Global MASTER-Net observations report
  55. GRB 250625A: AbAO and INASAN Kislovodsk Optical Observations
  56. GRB 250625A: GTC/OSIRIS+ spectroscopic observations of the potential host galaxy
  57. GRB 250625A: ABObservatory afterglow detection
  58. GRB 250521A: VZLUSAT-2 detection
  59. Fermi trigger No 772190032: Global MASTER-Net observations report
  60. GRB 250620C: Fermi GBM Final Real-time Localization
  61. Fermi trigger No 772128434: Global MASTER-Net observations report
  62. GRB 250617B: Nickel telescope optical observations
  63. GRB 250617B: COLIBRÍ optical observations
  64. GRB 250617B: NUTTelA-TAO early time optical observations
  65. GRB 250617A: Fermi GBM Final Real-time Localization
  66. EP#01709178975: Swift-XRT counterpart detection
  67. GRB 250615A: DDOTI Optical Upper Limit
  68. Fermi trigger No 771752663: Global MASTER-Net observations report
  69. IceCube alert 141029_8144692 retraction
  70. EP250610a: Global MASTER-Net observations report
  71. EP250610a: REM optical/NIR observations
  72. GRB 250609A: Fermi GBM Observation
  73. Fermi trigger No 771072240: Global MASTER-Net observations report
  74. The EP-WXT trigger 01709178283 is likely a flaring star
  75. Fermi trigger No 770867684: Global MASTER-Net observations report
  76. Fermi GRB 250601A: Global MASTER-Net observations report
  77. EP#01709177494: SVOM/VT optical observations
  78. GRB 250530C: BOOTES-7 optical upper limit
  79. GRB 250521C (short): Zwicky Transient Facility identification of a possible fast optical transient counterpart
  80. Fermi trigger No 770047117: Global MASTER-Net observations report
  81. Fermi trigger No 769611916: Global MASTER-Net observations report
  82. Fermi GRB 250522B: Global MASTER-Net observations report
  83. Fermi GRB 250521D: Global MASTER-Net observations report
  84. GRB 250521D: DDOTI Optical Upper Limit
  85. GRB 250520A: 10 GHz VLA radio source
  86. GRB 250516A: COLIBRÍ optical upper limit
  87. Fermi GRB 250516A: Global MASTER-Net observations report
  88. Fermi GRB 250512A: Global MASTER-Net observations report
  89. GRB 250507B: AstroSat CZTI detection
  90. EP250512a: Global MASTER-Net observations report
  91. GRB 250507B: GRBAlpha detection
  92. EP250511a: COLIBRÍ optical counterpart candidate
  93. EP250511a: BOOTES-5 optical upper limit
  94. Fermi GRB 250510C: Global MASTER-Net observations report
  95. GRB 250509A: Fermi GBM Observation
  96. Fermi GRB 250509A: Global MASTER-Net observations report
  97. Swift GRB 250509A: Global MASTER-Net observations report
  98. GRB 250509A: Swift detection of a burst
  99. Fermi-LAT Gamma-ray Observations of IceCube-250506A
  100. IceCube Alert 250506.59: Global MASTER-Net observations report

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