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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 Localization Correction
  3. GRB 250718B: Fermi GBM Final Real-time Localization
  4. Swift Trigger 1334535 / GRB 250718A: COLIBRÍ optical upper limits
  5. Swift Trigger 1334535: a possible GRB 250718A
  6. Swift GRB250718.01: Global MASTER-Net observations report
  7. GRB 250717B: Swift ToO observations
  8. GRB 270713A: Kitab and AbAO Optical Observations
  9. GRB 250717B: Fermi GBM Observation
  10. GRB 250717B: Swift/BAT-GUANO arcminute localization of a burst
  11. Konus-Wind detection of GRB 250716A
  12. GRB 250716A: Swift-XRT afterglow detection
  13. GRB 250717B: Fermi GBM Final Real-time Localization
  14. GRB 250716A: Lesedi Detection of Fading Optical Transient GOTO25eyp
  15. GRB 250717A: Fermi GBM Final Real-time Localization
  16. GRB 250716A: Swift ToO observations
  17. GRB 250716A: GOTO tentative optical counterpart candidate
  18. GRB 250716A: Fermi GBM Observation
  19. GRB 250714A: SVOM/GRM observation
  20. Fermi GRB 250716A: Global MASTER-Net observations report
  21. GRB 250716A: Fermi GBM Final Real-time Localization
  22. Fermi GRB 250715A: Global MASTER-Net observations report
  23. GRB 250715A: Fermi GBM Final Real-time Localization
  24. EP250702a / GRB 250702B,D,E: Hubble Space Telescope Observations
  25. GRB 250702B,D,E / EP250702a: H.E.S.S. very-high-energy gamma-ray observations
  26. GRB 250713A: Mephisto optical upper limits
  27. Fermi GRB 250714A: Global MASTER-Net observations report
  28. GRB 250713A: SVOM/VT optical upper limit
  29. GRB 250713A: NOT optical upper limits
  30. GRB 250713A: OHP/T193 upper limit
  31. GRB 250713A: SVOM/C-GFT upper limit
  32. GRB 250714A: Fermi GBM Final Real-time Localization
  33. GRB 250706B/C: 7DT Follow-up Observations
  34. GRB 250713A: Swift-XRT observations
  35. GRB 250713A: EP-FXT counterpart detection
  36. EP250711a: COLIBRÍ continuous optical observations
  37. GRB 250706A: Swift-BAT refined analysis
  38. GRB 250702F: Swift-BAT refined analysis
  39. GRB 250628A: Swift-BAT refined analysis
  40. LIGO/Virgo/KAGRA S250712cd: Updated Sky localization
  41. GRB 250713A: JinShan optical upper limits
  42. GRB 250713A: SVOM detection of a long burst
  43. EP250711a: Global MASTER-Net observations report
  44. GRB 250711A: DDOTI Optical Upper Limit
  45. LIGO/Virgo/KAGRA S250712cd: Identification of a GW compact binary merger candidate
  46. EP250711a: COLIBRÍ refined photometry and optical confirmation of the candidate (duplicate submission)
  47. EP250711a: COLIBRÍ refined photometry and optical confirmation of the candidate
  48. GRB 250711A: SVOM/GRM observation
  49. EP250711a: NOT optical counterpart candidate
  50. EP250711a: EP-WXT detection and FXT follow-up observation of a fast X-ray transient
  51. EP candidate (ID=08500000365): COLIBRÍ optical Upper limit
  52. Fermi GRB 250711A: Global MASTER-Net observations report
  53. EP250702a: gamma-ray upper limits from joint observations by the LST-1 and MAGIC telescopes
  54. GRB 250704A: GRANDMA observations
  55. GRB 250711A: BALROG localization (Fermi Trigger 773937617 / GRB 250711611)
  56. GRB 250711A: Fermi GBM Final Real-time Localization
  57. GRB 250704A: SVOM/ECLAIRs refined analysis
  58. LIGO/Virgo/KAGRA S250711q: Identification of a GW compact binary merger candidate
  59. GRB 250702B,D,E/EP250702A: JCMT sub-mm observations at 350 GHz
  60. GRB 250704B / EP250704a: 1.3 GHz MeerKAT Detection
  61. GRB 250702B,D,E / EP250702a: ALMA detection
  62. LIGO/Virgo/KAGRA S250629bs: Upper limits from Swift/BAT-GUANO
  63. LIGO/Virgo/KAGRA S250629ae: Upper limits from Swift/BAT-GUANO
  64. IceCube-250708A: No Candidates from WINTER
  65. IceCube-250708A: No Candidate Transients from the Zwicky Transient Facility
  66. GRB 250702B,D,E/EP250702A: MeerKAT radio observations at 1.28GHz
  67. GRB 250702B,D,E / EP250702a: 10 GHz detection with the VLA
  68. IceCube-250708A: Upper limits from a search for additional neutrino events in IceCube
  69. GRB 250709A: Fermi GBM Final Localization
  70. IPN triangulation of GRB 250704B (short/hard, consistent with EP 250704a)
  71. GRB 250706B/C: Insight-HXMT detection
  72. EP/WXT 01709181970: GOTO observations confirm stellar variability
  73. EP-WXT trigger 01709181970. confirmation of a stellar flare by BOOTES-6
  74. EP250704a/GRB 250704B: 10 GHz VLA detection
  75. The EP-WXT trigger 01709181970 is likely a flaring star
  76. GRB250702 B,D,E / EP250702a: MOSFIRE imaging of the afterglow
  77. LIGO/Virgo/KAGRA S250704ab: NED Galaxies in the 4-Update Localization Volume
  78. IceCube-250706A: No Candidates from WINTER
  79. IPN triangulation of GRB 250706C (consistent with the GRB 250706B)
  80. IceCube-250706A: No Candidates from the Zwicky Transient Facility
  81. IceCube-250708A - IceCube observation of a high-energy neutrino candidate track-like event
  82. GRB 250704B / EP250704a: VLA radio detection
  83. Fermi GRB 250708A: Global MASTER-Net observations report
  84. IceCube-250708A: Global MASTER-Net observations report
  85. IceCube-250706A: Upper limits from a search for additional neutrino events in IceCube
  86. LIGO/Virgo/KAGRA S250705cb: Updated Sky localization
  87. LIGO/Virgo/KAGRA S250704ab: Updated Sky localization and EM Bright Classification
  88. LIGO/Virgo/KAGRA S250702n: Updated Sky localization
  89. LIGO/Virgo/KAGRA S250701bq: Updated Sky localization
  90. EP250704a/GRB250704B : HCT optical and NIR upper limits
  91. LIGO/Virgo/KAGRA S250701bp: Updated Sky localization
  92. GRB 250708A: Fermi GBM Final Real-time Localization
  93. GRB 250706B/C: Konus-Wind analysis of the prompt emission
  94. GRB 250706B: SVOM observations interpreted as the afterglow of GRB 250706C
  95. GRB 250704B: CALET Gamma-Ray Burst Monitor detection
  96. GRB 250704B / EP250704a: Mondy and AbAO optical observations
  97. GRB 250702F: radio detection with the VLA
  98. GRB 250706B/C: VLT/X-shooter redshift z = 0.942
  99. IceCube-250706A: EP-FXT follow-up observations
  100. Fermi-LAT Gamma-ray Observations of IceCube-250706A

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