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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 250309B: Fermi GBM Observation
  2. Fermi GRB 250309B: Global MASTER-Net observations report
  3. Fermi GRB 250309A: Global MASTER-Net observations report
  4. GRB250309B: One candidate counterpart from the Zwicky Transient Facility
  5. IceCube-250309A: No candidates from the Zwicky Transient Facility
  6. Fermi-LAT gamma-ray observations of IceCube-250309A
  7. GRB 250308A: SVOM/GRM detection of QPO in the tail emission
  8. GRB 250309B: Fermi GBM Final Localization
  9. Correction to GCN 39633 - Swift is observing GRB 250309B/IceCube-250309A!
  10. GRB 230509B: Tiled Swift observations
  11. GRB 250308A: SVOM/GRM observation of a bright short burst
  12. IceCube-250309A - IceCube observation of a high-energy neutrino candidate track-like event
  13. IceCube Alert 250309.32: Global MASTER-Net observations report
  14. GRB 250309B: BALROG localization (Fermi Trigger 763198715 / GRB 250309318)
  15. EP250308a: Global MASTER-Net observations report
  16. EP250308a: GSP optical upper limit
  17. EP250308a: FTW optical and NIR upper limits
  18. EP250308a: Einstein Probe detection of an X-ray transient
  19. EP250308a: NOT optical upper limit
  20. GRB 250309A: Fermi GBM Final Real-time Localization
  21. GRB 250306A: EIRSAT-1 GMOD detection
  22. The EP-WXT trigger 01709132387 is likely a flaring star
  23. Fermi GRB 250307A: Global MASTER-Net observations report
  24. Konus-Wind detection of GRB 250306A
  25. GRB 250307A: Fermi GBM Final Real-time Localization
  26. GRB 250306A: Swift-BAT refined analysis
  27. GRB 250306A: NuSTAR detection of the prompt emission
  28. EP250304a: MeerKAT detection of a possible radio counterpart
  29. IceCube-241016A: MASTER flaring blazar 5BZU J073038.29-320820.2 with Zhirkov effect
  30. GRB 250305A: AstroSat CZTI detection
  31. EP250302a:Xinglong optical observations
  32. GRB 250306A: AstroSat CZTI detection
  33. Fermi trigger No 762963055: Global MASTER-Net observations report
  34. Fermi Gamma-ray Burst Monitor trigger 762963055/250306591 is not a GRB
  35. Swift GRB 250306A: Global MASTER-Net observations report
  36. LIGO/Virgo/KAGRA S250207bg: Update-5 NED Galaxies in the Localization Volume
  37. GRB 250306A: Swift detection of a burst
  38. LIGO/Virgo/KAGRA S250207bg: Updated Sky localization
  39. GRB250101A: Radio upper limits from VLA observations
  40. LIGO/Virgo/KAGRA S250306ej: Retraction of GW compact binary merger candidate
  41. GRB 250305A: SVOM/GRM observation of a burst
  42. The EP-WXT trigger 01709132323 is likely a flaring star
  43. EP250304A: Upper limits from Fermi-GBM Observations
  44. Fermi GRB 250305A: Global MASTER-Net observations report
  45. Fermi-LAT Gamma-ray Observations of IceCube-250302A
  46. GRB 250305A: Fermi GBM Final Real-time Localization
  47. EP250302a: Optical Observations at CrAO and SAO RAS
  48. GRB 250219A: SVOM/C-GFT optical upper limit at early phase
  49. EP 250304A: Optical counterpart detection by LCO
  50. EP250302A: 1.3m DFOT optical afterglow detection
  51. IceCube-250302A: Upper limits from a search for additional neutrino events in IceCube
  52. EP250304a: refined analysis of the EP-WXT and EP-FXT observations
  53. Konus-Wind detection of GRB 250222A
  54. EP250304a: REM NIR upper limits
  55. IPN triangulation of GRB 250222A
  56. EP250304a: Swift/UVOT detection of an optical counterpart with a rising light curve
  57. EP250302a: Mondy Continued Optical Observations
  58. EP250304a: VLT/X-shooter redshift z = 0.200
  59. EP250304a: Swift-XRT detection of a fading X-ray source
  60. EP250304a: TRT optical counterpart detection
  61. LIGO/Virgo/KAGRA S250304cb: Identification of a GW compact binary merger candidate
  62. EP250304a: Global MASTER-Net observations report
  63. EP250304a: Einstein Probe detection of an X-ray transient
  64. The EP-WXT trigger 01709132212 is not a real source
  65. EP250302a: SVOM/VT optical observation
  66. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: Swift/UVOT Upper Limits
  67. EP250302a: SAO RAS optical observations
  68. EP250302a : GIT optical follow-up
  69. EP250302a: VLT/X-shooter redshift confirmation
  70. EP250225a: the candidate optical counterpart is an AGN
  71. EP250302a: Kinder optical follow-up observations
  72. LIGO/Virgo/KAGRA S250302av: 2 counterpart neutrino candidate events from an IceCube neutrino search
  73. EP250302a: Swift/UVOT detection
  74. EP250302a: NUTTelA-TAO Early Measurments
  75. EP250302a: optical observation from the INAF Asiago Observatory
  76. EP250302a: REM NIR upper limits
  77. IceCube-241113A: MASTER flaring blazar 5BZB J1311+0853 with Zhirkov effect
  78. EP250302a: Mondy Observations and Optical Light Curve
  79. EP250302a: VLT/MUSE optical redshift z = 1.131
  80. INTEGRAL: end of scientific operations
  81. EP250302A: VLT near-infrared observations
  82. EP250302A: VLT/X-shooter tentative redshift
  83. EP250302a: OHP/T193 optical and spectroscopic observations
  84. EP250302a: Global MASTER-Net observations report
  85. EP250302a: Xinglong F60B optical observation
  86. EP250302a: Swift-XRT observations of a fading X-ray source
  87. EP250302a: Einstein Probe detection of an X-ray transient
  88. EP250302a: SVOM/C-GFT optical observations
  89. GRB 250226A: GRANDMA Optical Observations
  90. EP250302a: Montarrenti Observatory optical detection
  91. Fermi GRB 250302A: Global MASTER-Net observations report
  92. EP250302a: FTW optical and NIR detection
  93. EP250302a: Nanshan/HMT optical counterpart detection
  94. IceCube-250302A - IceCube observation of a high-energy neutrino candidate track-like event
  95. GRB 250302A: Fermi GBM Final Real-time Localization
  96. GRB 250228A: Fermi GBM Final Localization
  97. The EP-WXT trigger 01709132140 is likely a flaring star
  98. LIGO/Virgo/KAGRA S250206dm: early X-ray upper limits from Einstein Probe WXT and preliminary results of FXT observations
  99. GRB 250225B: VLT near-infrared afterglow confirmation
  100. EP250228a: Optical observations with Kinder and Swift/UVOT

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